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(Bio) Cell Division: A Switch between Life and Death

 
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adedios
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PostPosted: Mon Aug 28, 2006 10:00 am    Post subject: (Bio) Cell Division: A Switch between Life and Death Reply with quote






Heidelberg, 25 August 2006

A switch between life and death

European Molecular Biology Laboratory

Researchers discover how a signal tells cells whether to grow or die

Cells in an embryo divide at an amazing rate to build a whole body, but this growth needs to be controlled. Otherwise the result may be defects in embryonic development or cancer in adults. Controlling growth requires that some cells divide while others die; their fates are determined by signals that are passed from molecule to molecule within the cell. Researchers at the European Molecular Biology Laboratory [EMBL] in Heidelberg have now discovered how one of these signaling pathways controls the life and death of cells in the fruit fly. The study will be published in this week's issue of the journal Cell.

The breakthrough came as Barry Thompson from Stephen Cohen's group at EMBL looked at a recently discovered signaling pathway called Hippo.

"Hippo acts as a switch between cell division and death," says Barry Thompson, "if the pathway is too active, tissues overgrow because too many cells divide and too few die. But until now, we hadn't found a connection between the signals and the cellular machinery that drives growth."

Using sophisticated genetic techniques, Thompson and Cohen established that a small molecule, a microRNA called bantam, makes this link. Without bantam, tissues grow too slowly and remain smaller than normal. The amount of bantam produced by the cell directly depends on the amount of traffic on the Hippo signaling pathway, and higher levels of bantam prompt more cell division.

"bantam is an unusual type of RNA molecule," Thompson says. "Normally, RNAs go on to make protein, but bantam is different. Its job is to regulate other RNAs by attaching itself to them; the result is that they block their expression into proteins. In this case, those proteins would go on to shut down cell division. With bantam around, the brake is off, and they continue to divide."

Cohen and his lab have been studying microRNAs like bantam for some time because of their important role in the regulation of many vital processes across species. The next step will be to identify the RNAs that bantam docks onto to control. This will provide a more complete view of the Hippo pathway and may provide insights into the central role it plays in tissue growth and cancers in humans and other organisms.

Source Article
--------------------------------------------------------------------------------
B.J. Thompson & S.M. Cohen. The Hippo pathway regulates the bantam microRNA to control cell proliferation and apoptosis in Drosophila, Cell, 25 August 2006

*************************************************************

Questions to explore further this topic:

What are cells?

http://www.paete.org/forums/viewtopic.php?t=1296

What is cell division (mitosis and meiosis)?

http://www.cellsalive.com/cell_cycle.htm
http://www.bbc.co.uk/schools/g.....rev1.shtml
http://www.pbs.org/wgbh/nova/miracle/divide.html
http://biog-101-104.bio.cornel.....ision.html
http://cancerquest.org/index.cfm?page=51
http://www.explorelearning.com.....urceID=443
http://www.newi.ac.uk/buckleyc.....vision.htm


Meiosis
http://www.cellsalive.com/meiosis.htm
http://www.accessexcellence.or.....iosis.html
http://www.biology.arizona.edu...../main.html
http://www.emc.maricopa.edu/fa.....iosis.html

Mitosis
http://www.cellsalive.com/mitosis.htm
http://www.accessexcellence.or.....osis2.html
http://www.biology.arizona.edu...../main.html
http://www.emc.maricopa.edu/fa.....kmito.html

Plant and Animal Cell Division Movies

http://www.iknow.net/CDROMs/ce.....vies.shtml
http://www.loci.wisc.edu/outre.....CDBio.html

What is cell death?

http://users.rcn.com/jkimball......tosis.html

What is programmed cell death?

http://www.cellsalive.com/apop.htm
http://www.dnalc.org/nobel2002.html
http://en.wikipedia.org/wiki/Programmed_cell_death
http://www.acs.ucalgary.ca/~browder/apoptosis.html
http://www.ncbi.nlm.nih.gov/bo.....ction.6889
http://www.sgul.ac.uk/depts/im.....apoptosis/

What is the relationship between cell division and cancer?

http://www.insidecancer.org/
http://www.schoolscience.co.uk.....index.html
http://www-saps.plantsci.cam.a.....cancer.htm
http://www.ndsu.nodak.edu/inst...../index.htm

GAMES

http://nobelprize.org/educatio.....cine/2001/
http://www.biologyinmotion.com/cell_division/
http://projects.coe.uga.edu/lr.....asp?ID=947


Last edited by adedios on Sat Jan 27, 2007 3:35 pm; edited 2 times in total
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PostPosted: Wed Dec 06, 2006 7:13 am    Post subject: Blame Our Evolutionary Risk of Cancer on Our Body Mass Reply with quote

December 6, 2006
University of Rochester

Blame Our Evolutionary Risk of Cancer on Our Body Mass

A key enzyme that cuts short our cellular lifespan in an effort to thwart cancer has now been linked to body mass.

Until now, scientists believed that our relatively long lifespans controlled the expression of telomerase—an enzyme that can lengthen the lives of cells, but can also increase the rate of cancer.

Vera Gorbunova, assistant professor of biology at the University of Rochester, conducted a first-of-its-kind study to discover why some animals express telomerase while others, like humans, don't. The findings are reported in today's issue of Aging Cell.

"Mice express telomerase in all their cells, which helps them heal dramatically fast," says Gorbunova. "Skin lesions heal much faster in mice, and after surgery a mouse's recovery time is far shorter than a human's. It would be nice to have that healing power, but the flip side of it is runaway cell reproduction—cancer."

Up until now, scientists assumed that mice could afford to express telomerase, and thereby benefit from its curative powers, because their natural risk of developing cancer is low—they simply die before there's much likelihood of one of their cells becoming cancerous.

"Most people don't know that if you put mice in a cage so the cat can't eat them, 90 percent of them will die of cancer," says Gorbunova.

Evolution, it seems, has determined which species are allowed to express telomerase in their somatic cells in order to maintain a delicate balance between cells that live long, and cells that become cancerous. But while most scientists believed an organism's lifespan determined whether it was at a higher risk of cancer, Gorbunova has revealed evidence that it is not our long lifespan that puts us at risk, but our much-heavier-than-a-mouse body mass.

The tips of chromosomes, called telomeres, shorten every time a cell divides. After about 60 divisions, the telomeres are eroded away to the point that the cell stops dividing. Telomerase rebuilds those tips, so animals that express it, like mice, have cells that can reproduce more extensively and thus heal better.

Cancer cells, however, are those cells that constantly reproduce unchecked, and so evolution has shut off the expression of telomerase in human somatic cells, presumably because the threat of cancer outweighs the benefits of quick-healing.

But no one has looked into why mice express telomerase and humans don't. In fact, telomerase activity has been barely catalogued in the animal kingdom.

Gorbunova decided to take on the question by creating a unique test. She investigated 15 rodents from across the globe to determine what level of telomerase activity each species expressed, to see if there were some correlation she could find.

The species ranged from tiny field mice to the 100-pound capybara from Brazil. Lifespans ranged from three years for the mice, to 23 or more for common backyard squirrels.

Acquiring specimens of these animals from around the world proved to be an unusual task.

"At one point I was woken up at two in the morning by a guy on a cell phone hunting pest beavers in Montezuma," says Gorbunova. "I'm still trying to wake up and this voice says, 'I hear you're looking for beavers.' "

For over a year, Gorbunova collected deceased rodents from around the world and had them shipped to her lab in chilled containers. She analyzed their tissues to determine if the telomerase was fully active in them, as it was in mice, or suppressed, as it is in humans. Rodents are close to each other on the evolutionary tree and so if there were a pattern to the telomerase expression, she should be able to spot it there.

To her surprise, she found no correlation between telomerase and longevity. The great monkey wrench in that theory was the common gray squirrel, which lives an amazing two decades, yet also expresses telomerase in great quantity. Evolution clearly didn't see long life in a squirrel to be an increased risk for cancer.

Body mass, however, showed a clear correlation across the 15 species. The capybara, nearly the size of a grown human, was not expressing telomerase, suggesting evolution was willing to forgo the benefits in order to reign in cancer.

The results cannot be directly related to humans, but Gorbunova set up the study to produce very strong across-the-board indicators. It's clear that evolution has found that the length of time an organism is alive has little effect on how likely some of its cells might mutate into cancer. Instead, simply having more cells in your body does raise the specter of cancer—and does so enough that the benefits of telomerase expression, such as fast healing, weren't worth the cancer risk.

Gorbunova points out that these findings raise another, perhaps far more important question: What, then, does this mean for animals that are far larger than humans? If a 160-pound human must give up telomerase to thwart cancer, then what does a 250,000-pound whale have to do to keep its risk of cancer at bay?

"It may be that whales have a cancer suppressant that we've never considered," says Gorbunova. "I'd like to find out what kind of telomerase expression they have, and find out what else they use to combat cancer."

As for the tiny mice: "They don't have to worry about cancer," she says. "They're probably all praying for an anti-cat gene."

About the University of Rochester
The University of Rochester (www.rochester.edu) is one of the nation's leading private universities. Located in Rochester, N.Y., the University gives students exceptional opportunities for interdisciplinary study and close collaboration with faculty through its unique cluster-based curriculum. Its College of Arts, Sciences, and Engineering is complemented by the Eastman School of Music, Simon School of Business, Warner School of Education, Laboratory for Laser Energetics, and Schools of Medicine and Nursing.
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PostPosted: Wed Feb 28, 2007 8:30 am    Post subject: Cancer cells forming blood vessels send their copper to the Reply with quote

Cancer cells forming blood vessels send their copper to the edge
27 February 2007
Argonne National Laboratory

ARGONNE, Ill. (Feb. 26, 2007) — New information about a link between the growth of blood vessels critical to the spread of cancer and the copper in our bodies has been discovered by researchers from the U.S. Department of Energy's Argonne National Laboratory and the University of Chicago, using a beamline at the Advanced Photon Source.

Growing new blood vessels from existing ones — a process called angiogenesis — is important in growth, development and wound healing. But it also enables the spread of tumors throughout the body, so researchers have been scrambling for ways to stop angiogenesis in the fight against cancer.

One element critical to blood vessel growth is copper, a vital nutrient that plays important roles in many life processes. Compounds that reduce copper in the body without disrupting the body's normal functions can inhibit the growth of blood vessels — and some of these compounds are even in clinical trials for use in cancer therapy. Yet, the biological basis for this sensitivity of angiogenesis to copper has been an enigma.

In search of an answer, researchers from the Biosciences and X-ray Science divisions at Argonne and the Department of Medicine, Section of Hematology/Oncology, at the University of Chicago, have used X-ray fluorescence microprobe imaging at the Advanced Photon Source at Argonne, the Western Hemisphere's most brilliant source of X-rays for research. The X-rays allowed the researchers to look at the distribution of copper in both a cell model of angiogenesis and sections of breast tumor tissue rich in blood vessels.

“We found that cells undergoing angiogenesis exhibit a distribution of their cellular copper that is distinctly different from other cells,” said Argonne biologist and lead author Lydia Finney. “This discovery may help explain how copper-reducing cancer therapy works.” The findings are reported in the current issue of the Proceedings of the National Academy of Sciences, or PNAS.

“We began our study,” Finney explained, “ by examining a model of angiogenesis that uses human microvascular endothelial cells to form capillary-like structures within about eight hours of being stimulated with specific growth factors. We then examined the distribution of elements in these structures by using imaging resources.”

The APS played a key role in the research. The particular APS beamline Finney and her colleagues used employs specialized optics to focus coherent X-rays to sub-micrometer spot sizes, through which the sample is raster scanned (scanning from side to side, top to bottom). By collecting emitted fluorescence spectra at each point using an energy-dispersive detector, the researchers obtained images displaying the concentration and spatial distribution of many elements, including phosphorous, sulfur, iron, copper and zinc. Overlaying these elemental maps onto optical images of the cells, Finney and her colleagues then correlated elemental content with cellular structures.

“Our findings were very clear,” said Finney. “We observed a dramatic relocalization of between 80 and 90 percent of cellular copper to the tips of the tendril-like projections angiogenic cells send out between one another and across the cellular membrane within the first two hours.” Copper did, indeed, appear to play a special role in angiogenesis, at least on the basis of this observation.

To extend these studies to a living organism, Finney and her colleagues then examined sections of breast tumor tissue that were rich in newly formed blood vessels. “Once again,” said Finney, “we found that in contrast to both non-vascularized areas and areas of mature blood vessels, in areas of tissue where blood vessels were newly invading surrounding tissue, the cells showed copper localized at the periphery of the cells and in areas immediately outside of any apparent cellular structures.”

What are the implications of this discovery?

According to Finney, “These findings improve our understanding of how removing copper from the body can help stop angiogenesis. If a drug can be used to intercept vital copper being translocated outside of the cell during angiogenesis, the process stops, preventing growth of the tumor.”

The implications of the research do not end with the effect on angiogenesis. The dynamics of cellular copper this study revealed also have broad implications on the regulation of the metal ion content in metal-binding proteins. If such dramatic changes in where cellular copper is stored and used can happen so rapidly during angiogenesis, then the interactions of metal ions, such as copper, with the proteins and macromolecules that bind them in the cell must have very fluid dynamics themselves.

Other authors on the study are Suneeta Mandava, Lyann Ursos, Wen Zhang, Diane Rodi, Stefan Vogt, Daniel Legnini, Jörg Maser and David Glesne of Argonne and Francis Ikpatt and Olufunmilayo I. Olopade of the University of Chicago.

The research, and use of the Advanced Photon Source, were supported by the U. S. Department of Energy, Office of Science. — Kevin Brown

The nation's first national laboratory, Argonne National Laboratory conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. Since 1990, Argonne has worked with more than 600 companies and numerous federal agencies and other organizations to help advance America's scientific leadership and prepare the nation for the future. Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.
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PostPosted: Mon May 21, 2007 8:34 pm    Post subject: K-State biologist hopes mosquito can break viral chain Reply with quote

Kansas State University
21 May 2007

K-State biologist hopes mosquito can break viral chain

MANHATTAN, KAN. -- Most people do their best to avoid mosquitoes. But this summer Rollie Clem will play the wary host to his own homegrown swarm of Aedes aegypti, the yellow fever mosquito. He's made a room ready for them, and even a menu.

"Sheep's blood or cow's blood," said Clem, an associate professor of biology at Kansas State University. "This particular species is less finicky than others," so Clem won't need to stock their cages with sweaty socks. (Some mosquitoes won't feed without the persuasive scent of humans in the air.)

Clem, who studies molecular virology, is going out of his way to accommodate A. aegypti in hopes of learning more about how viruses disrupt the programmed death of cells, or apoptosis.

"Millions of cells are dying at any given moment in our body," Clem said. "And that's a good thing."

Programmed cell death is tidier than necrosis, in which injury prompts inflammatory cells to rush in and clean up. In contrast, apoptosis relies on a cell's genes to trigger an orderly disassembly.

It's the body's way of removing tissue that has done its job, such as the webbing between the developing fingers of an embryo, or cells whose DNA is damaged. Malfunctions in apoptosis are associated with cancer, neurological diseases such as Alzheimer's and immune disorders such as AIDS and rheumatoid arthritis.

Though scientists knew of apoptosis as long ago as the late 1800s, interest in the field has intensified only in the last 15 years, Clem said.

"It was very obscure" when he was a graduate student at the University of Georgia in the early 1990s, he said. "Now it's taught to undergraduates."

Clem's current experiment, helped by a grant from the National Institutes of Health, grew from his work with moths that were naturally immune to fatal viruses. Clem chose A. aegypti for this round because it spreads such diseases as dengue fever, the most important of the world's mosquito-borne viruses. The Centers for Disease Control estimate that 100 million cases occur annually.

But the mosquito's effectiveness in spreading the disease varies from place to place. Clem wants to find out whether apoptosis plays a role in that variability.

Once his mosquitoes are safely housed in their lab, Clem plans to infect them with genetically altered strains of Sindbis, a virus related to those that cause equine encephalitis. Some strains will contain genes that block apoptosis, Clem said, and others will encourage the process.

He will go on to test other mosquitoes with unaltered strains of Sindbis. The results should suggest whether A. aegypti can be made immune to viruses.

Clem stresses that A. aegypti's living arrangements will be anything but casual. His lab's insectary is approved by the CDC to conform to "arthropod containment level 2," which specifies such things as screened drainage, extensive caulking, and heat-sterilization of equipment and waste. So whatever you're swatting this summer, it won't be one of Clem's mosquitoes.

"Our work will be taking place in a very secure environment," he said.

In the Western Hemisphere, A. aegypti is widespread in Latin America but occupies only bits of the southern United States, particularly south Florida. The species has made a comeback since eradication programs ended in the 1970s, and dengue fever has expanded along with it.

In Kansas, Culex tarsalis and other members of the Culex group do most of the biting. They don't transmit dengue, but C. tarsalis is known to spread West Nile and western equine encephalitis. The world's most troublesome mosquito-borne disease, malaria, is spread by Anopheles gambiae.

One of Clem's students is investigating a dozen or so genes in A. aegypti because of their similarity to genes that control apoptosis in the fruit fly. "But even in humans, the genes are similar in their sequence," Clem said. This phenomenon of "gene homology" means that insects have a lot to tell the species on the other end of the microscope about its own genetic workings.
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PostPosted: Sat Jun 02, 2007 7:59 am    Post subject: Cells re-energize to come back from the brink of death Reply with quote

St. Jude Children's Research Hospital
1 June 2007

Cells re-energize to come back from the brink of death

St. Jude researchers discover that cancer cells can evade not only the main self-destruct program -- apoptosis -- but also the backup program CICD, by increasing production of the enzyme GAPDH
The discovery of how some abnormal cells can avoid a biochemical program of self-destruction by increasing their energy level and repairing the damage, is giving investigators at St. Jude Children's Research Hospital insights into a key strategy cancer cells use to survive and thrive.

The finding offers an explanation of how abnormal cells that have cheated death once by disabling the main suicide pathway called apoptosis can also foil a backup self-destruct program, which allows them to survive and become cancerous.

The St. Jude study also suggests that a drug that disrupts a cancer cell’s ability to block this backup program would allow that program to kill the cell. Such a specifically targeted drug might be more effective and less toxic than standard chemotherapy. A report on this work is in the June 1 issue of “Cell.”

Apoptosis is triggered by a variety of factors, including gene mutations that can make the cell become cancerous. During apoptosis, the membrane covering the cell’s mitochondria develop holes and leak a molecule called cytochrome c, which triggers the activity of enzymes called caspases. In turn, caspases trigger a series of events that kills the cell. Mitochondria are tiny structures that act as power plants to supply the cell with energy, but also hold the keys to the cells’ life and death.

The process by which the membranes develop holes—mitochondrial outer membrane permeability (MOMP)—is often the “point of no return” for self-destruction, said Douglas Green, Ph.D., chair of the St. Jude Immunology department and the study’s senior author. MOMP triggers apoptosis, but if apoptosis fails because there is no caspase available, the backup program called caspase-independent cell death (CICD) takes over the process.

Previous research has shown that cells that become cancerous lack caspase and other proteins needed to support apoptosis after MOMP releases cytochrome c. But this victory over death is short-lived if CICD is activated. However, some cancerous cells not only dodge death from apoptosis by eliminating caspase activation, but they also foil CIDC. “Our study sought to understand how a cancer cell without caspase activation bypasses CICD as well,” Green said.

The St. Jude team discovered that a cell that lacks caspase activation and cannot undergo apoptosis increases the levels of an enzyme called GAPDH in order to counteract CICD. GAPDH appears to prevent CICD by supporting the functioning of the mitochondria and triggering the activity of certain genes that prevent or repair cell damage. The findings also suggest that the increase in GAPDH provides energy to increase autophagy—the process by which a cell “chews up” debris and broken components, such as damaged mitochondria. After disposing of damaged mitochondria the cell can replace these vital components.

“We found that in the absence of caspase activation, cells that avoided CICD took about a week or so to begin multiplying again,” Green said. “This might represent the time it takes for the cell to restore enough mitochondria to allow the cell to function normally.”

The discovery that GAPDH appears to save cells from CICD suggests that blocking this enzyme would kill abnormal cells that lack caspase activation and cannot undergo apoptosis. That strategy would be the basis of novel anti-cancer drugs.

The St. Jude study was conducted in culture dishes in which normal cells were exposed to cancer drugs or other agents that triggered apoptosis. The researchers then blocked apoptosis in order to study CICD. “The GAPDH response appears to represent a basic, reproducible event. But in order to verify that hypothesis, we’ll need to study it in the body, especially as we try to develop ways to force cancer cells without caspase to undergo CICD,” Green said. “Our goal is to find better ways to treat these diseases.”

###
Other authors of this study include Anna Colell (Institut d’Investigacions Biomediques de Barcelona, Spain); Jean-Ehrland Ricci (Universite de Nice Sophia, Antipolis, France); Stephen Tait, Sandra Milasta, Lisa Bouchier-Hayes, Patrick Fitzgerald and Helen M. Beere (St. Jude); Ana Guio-Carrion, Cindy Wei Li and Donald D. Newmeyer (La Jolla Institute for Allergy and Immunology, San Diego); Nigel J. Waterhouse (Peter MacCallum Cancer Centre, Melbourne, Australia); and Bernard Mari and Pascal Barbry (Institute de Pharmacologie Moléculaire et Cellulaire, Sophia Antipolis, France).

This work was supported in part by the National Institutes of Health (DRG); Association pour la Recherche Contre le Cancer; Fondation pour la Recherche Médicale grants (JER); and Plan Nacional I+D+I grant (AC). AC received a fellowship from the Secretaria de Estado de Universidades e Investigacion of Spain.

St. Jude Children's Research Hospital:

St. Jude Children's Research Hospital is internationally recognized for its pioneering work in finding cures and saving children with cancer and other catastrophic diseases. Founded by late entertainer Danny Thomas and based in Memphis, Tenn., St. Jude freely shares its discoveries with scientific and medical communities around the world. No family ever pays for treatments not covered by insurance, and families without insurance are never asked to pay. St. Jude is financially supported by ALSAC, its fundraising organization.

For more information, please visit: http://www.stjude.org
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PostPosted: Mon Jul 30, 2007 2:19 pm    Post subject: Researchers discover pathway to cell size, division Reply with quote

Researchers discover pathway to cell size, division

Cut and run

By Erin Fults


July 30, 2007 -- Organisms precisely regulate cell size to ensure that daughter cells have sufficient cellular material to thrive or to create specific cell types: a tiny sperm versus a gargantuan egg for example. In single-celled organisms such as yeast and bacteria, nutrient availability is the primary determinant of cell size. In animal cells, size is controlled in large part by a molecule that senses the blood sugar-dependent hormone insulin.

Petra Levin, Ph.D., Assistant Professor of Biology at Washington University in St. Louis, and her laboratory have recently identified a trio of enzymes that act in concert to link nutrient availability to cell size in the soil bacterium Bacillus subtilis.

Levin and her lab are looking into the factors that control the timing and position of cell division in B. subtilis. B. subtilis serves as the model system for a large family of bacteria that includes the causative agents of several important diseases, including anthrax and botulism. By learning how these simple organisms regulate division, she hopes to better understand why this process goes awry in cancer cells resulting in uncontrolled growth and aberrant division.

A primary focus of the Levin lab's research is a protein called FtsZ. FtsZ is an ancestor of tubulin, the protein that is responsible for distributing duplicated chromosomes between dividing human cells. In bacteria, FtsZ forms a ring at the future division site. The FtsZ ring then recruits all other components necessary for cell division and serves as the scaffolding for the entire division process.

The factors that regulate FtsZ ring formation determine when and where the cell is going to divide. "Theoretically a cell could divide anywhere and at anytime," said Brad Weart, a graduate student in Levin's lab. "The cell has to very precisely restrain that process so that it only happens when and where the cell wants it to happen."

In their most recent paper, published in the July 27, 2007 issue of Cell, Weart et al. identified a metabolic sensor that links cell division and cell size in B. subtilis with nutritional availability. This sensor is comprised of a three enzyme pathway that was previously shown to be involved in synthesizing a modified component of the cell membrane. The Levin lab's data indicates the pathway also has a major role in cell division. "So far this has been the only pathway that's been identified in bacteria that directly regulates cell size," says Levin.

Typically, cells in nutrient-rich environments grow bigger than cells in nutrient-poor environments. The Levin lab determined that mutations in genes encoding the three enzymes resulted in cells that were small even when they were in a nutrient-rich environment. "Basically, the cells had no way to tell the division apparatus to wait until they've reached the size they should be. The cells would divide when they were still very short," said Levin. "It was almost as if they were growing in really great media but they didn't know it."

Knowing when to divide

Further work indicated that the mutation perturbed FtsZ ring formation. In the cell, FtsZ exists in a balance between its unassembled and assembled state. The enzyme trio regulated FtsZ ring formation by changing this balance — pushing FtsZ towards its unassembled state when the cells were growing in nutrient-rich conditions, thereby delaying cell division and increasing cell size.

All three enzymes in the pathway are sensitive to glucose levels, and the pathway is therefore well suited to communicating nutritional information directly to the cell's division apparatus. In nutrient-poor conditions the enzymes no longer inhibit FtsZ assembly, allowing the FtsZ ring to form when the cells are still small, resulting in the formation of smaller daughter cells. The third enzyme in the pathway, UgtP, physically interacts with FtsZ to prevent ring formation. UgtP responds to low levels of glucose (nutrient-poor conditions) by becoming unstable and forming what appear to be inactive aggregates.

Disrupting this pathway leads to defects in chromosome segregation. A cell that is too small is unable to effectively move its DNA away from the division site and the resultant daughter cells frequently do not contain all the genetic material that they should. By coordinating cell size with growth rate, cells are able to maintain proper distribution of DNA.

This work is also something of a cautionary tale about the limitations of genome sequencing. "More and more often we are finding that metabolic enzymes have more than one function," said Levin, "There is no hint from their sequence that they have other activities so you really need to delve deeper and apply different methods to identify them."

Levin notes that her research is uncovering just the "tip of the iceberg" in the field of cell size control, but identifying genes such as ugtP helps Levin and other researchers get a better handle on precisely what determine how big a cell will be.
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PostPosted: Thu Sep 20, 2007 12:43 pm    Post subject: Pathway to cell death redefined in landmark study Reply with quote

University of Pittsburgh Schools of the Health Sciences
20 September 2007

Pathway to cell death redefined in landmark study

University of Pittsburgh School of Medicine findings hold promise in fight against cancer, stroke, heart disease and other life-threatening illnesses
PITTSBURGH, Sept. 20 -- A new study led by investigators from the University of Pittsburgh School of Medicine demonstrates that the process of necrosis, long thought to be a chaotic, irreversible pathway to cell death, may actually be triggered as part of a regulated response to stress by a powerful protein, SRP-6, that can potentially halt necrosis in its path. Further, the research team realized that this protein might be harnessed to direct some cells -- those in cancerous tumors, for instance -- to die, while saving others, such as degenerating neural cells responsible for Alzheimer’s and Parkinson’s diseases. The work appears on the Sept. 21 cover of the journal Cell.

This remarkable molecular trigger, SRP-6, is a serine protease inhibitor or serpin, and targets the cell’s digestive center, the lysosome. The authors report that the family of intracellular serpins may help cells survive in the face of stressors by protecting against lysosomal injury and its cellular consequences.

“For years, we believed that cell death related to a catastrophic insult such as a stroke or heart attack that deprives tissue of oxygen couldn’t really be treated, so we focused on strategies to prevent further damage by restoring blood flow as quickly as possible with clot busters and surgery,” said Gary A. Silverman, M.D., Ph.D., chief of newborn medicine in the department of pediatrics at the Pitt School of Medicine and the study’s senior author. “But our research indicates that necrosis can be interrupted and possibly repaired, even after the injury process is well underway. This insight has exciting implications for the management of heart disease, stroke and neurological illnesses.”

Representing more than five years of study, the Cell publication is the result of a chance observation made by primary author Cliff J. Luke, Ph.D., assistant professor of pediatrics at Pitt and an investigator at the university-affiliated Magee-Womens Research Institute. Drs. Luke, Silverman and colleagues have been studying how a certain class of proteins called proteases, when uncontrolled, can kill cells. In the process, they discovered that another group of proteins, the serpins, might block, or inhibit, these destructive proteases and protect cells from injury. SRP-6 is among a vast family of pro-survival serpins, which are key regulatory molecules in many complex biologic processes, including blood cell coagulation, inflammation, tumor growth and cell death. Although previous research has shown that bloodstream serpins, including antithrombin and alpha-1 antitrypsin, control protein degradation, little is known about the role of serpins that function within cells, especially in a living organism.

Enter serendipity. When collecting specimens of a microscopic worm called Caenorhabditis elegans in water, rather than in a saline solution as is more common, Dr. Luke noticed that an extraordinarily large number of the animals were dying. “My worm yield was way down,” he said. When he examined the dying worms, he determined that they were genetic “knock-outs” that had been modified to be deficient in SRP-6. The normal worms were just fine.

A frequently studied animal model because of its 1,000-cell structure, transparency and easily visible development, C. elegans is a primitive organism whose complete genetic code has been sequenced and is well known to scientists. The worm typically lives in soil, flourishes in water and exists to eat bacteria and reproduce. The investigators were using a “reverse genetic” approach in which they hoped, by studying the relatively limited intracellular serpin repertoire of C. elegans, they could gain insights that might be applicable to serpin function in higher organisms, including humans.

“Serpin proteins are critical,” said Dr. Silverman, a neonatologist and a senior investigator at the Magee-Womens Research Institute. “For example, we know that in patients who have a certain type of skin cancer, those whose tumors express a lot of intracellular serpins don’t do as well. Now we know that SRP-6 is a crucial pro-survival mechanism that can protect cells from injury, initiate repair after injury, or, if absent, lead to a cascade of cell death.”

With further investigation, it may be possible to use this knowledge to deprive cancer cells of their serpin protectors and target them for death. Alternatively, physicians might be able to boost serpin activity to stop cells from dying – for example, intestinal cells affected by the bacterial infection necrotizing enterocolitis (NEC), a major cause of death and illness in fragile, premature infants.

“We still treat NEC the same way we did 30 years ago, with supportive care, antibiotics and surgery to remove dead portions of intestine,” said Dr. Silverman. “We can’t stop the mucosal lining from dying. But with these worms as models, we can do drug screens to search for compounds that can block necrosis.”

Drs. Silverman, Luke and colleagues have dramatically illustrated the devastating consequences of cellular stress in C. elegans when the crucial protector SRP-6 is missing. A cascade of cell necrosis begins in SRP-6-deficient animals exposed to a number of different stressors, including water, heat and lack of oxygen. In the case of water exposure, the SRP-6 knock-outs move a bit but soon become immobile. Finally, the worms’ organs are violently expelled through their bodily openings, resulting in what the authors refer to as a “grim fate.”

“Animals with normal genetic sequences are fine in water, but the knock-out animals usually die rapidly,” said Dr. Luke, explaining that this observation led him to realize the importance of SRP-6 in protecting the lysosome, an internal cell structure enclosed in its own protective membrane that acts as the cell’s garbage disposal. Powerful enzymes within the lysosome digest old, worn out proteins, carbohydrates, lipids, DNA, RNA, other damaged cell structures and even invading bacteria and viruses. But if the lysosome becomes damaged and leaky, these enzymes can turn against the cell and possibly overcome the serpin defense – useful if the cell is part of a cancerous tumor.

The investigators determined that SRP-6 staves off necrosis by protecting the lysosome membrane from damage caused by the calpain family of cysteine proteases and by neutralizing other cysteine proteases released from injured cellular structures called organelles as they are being digested by the lysosome. As part of their study, Drs. Silverman, Luke and colleagues labeled enzymes within the lysosomes of SRP-6-deficient animals with a fluorescent biomarker to observe how these enzymes reacted after an injury to the critical structure.

“The lysosomes popped, released their contents into the cell and these digestive enzymes began to activate, making the whole animal fluoresce,” said Dr. Silverman. “Again, this experiment showed the importance of SRP-6 in management of the necrosis pathway.”

“There are a lot of diseases associated with cell necrosis, such as stroke, neurodegenerative diseases and NEC, and now we know that the pathway to necrosis is much more systematic than we once thought it was,” said Dr. Luke. “With further study, we may be able to identify targets of intervention to halt the necrotic progression in some of these diseases and possibly even prevent them.”


###
The study was funded by the National Cancer Institute, the National Human Genome Research Institute, the Mario Lemieux Foundation and the Twenty-Five Club of Magee-Womens Hospital of the University of Pittsburgh Medical Center.

In addition to Drs. Silverman and Luke, other authors are Stephen C. Pak, Ph.D., Yuko S. Askew, M.D., Ph.D., Terra L. Naviglia, David J. Askew, Ph.D., Shila M. Nobar, Ph.D., Anne C. Vetica, Olivia S. Long, B.S., Simon C. Watkins, Ph.D., and Donna B. Stolz, Ph.D., all of the University of Pittsburgh School of Medicine; Robert J. Barstead, Ph.D., and Gary L. Moulder, B.S., of the Oklahoma Medical Research Foundation; and Deiter Bromme, Ph.D., of the University of British Columbia.
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PostPosted: Mon Nov 12, 2007 2:28 pm    Post subject: Synthetic compound promotes death of lung-cancer cells, tumo Reply with quote

UT Southwestern Medical Center

Synthetic compound promotes death of lung-cancer cells, tumors

DALLAS – Nov. 12, 2007 – Human lung-cancer tumors grown in mice have been shown to regress or disappear when treated with a synthetic compound that mimics the action of a naturally occurring “death-promoting” protein found in cells, researchers at UT Southwestern Medical Center report.

The findings, appearing in today’s issue of Cancer Cell, suggest that the compound might one day be used in targeted therapies for lung and possibly other cancers, the researchers said.

“We found that certain kinds of lung-cancer cells were sensitive to this compound, which sends a signal to cancer cells to self-destruct,” said Dr. Xiaodong Wang, professor of biochemistry at UT Southwestern and senior author of the study.

In 2000, Dr. Wang announced the discovery of a cellular protein called Smac, which plays a key role in the normal self-destruction apparatus present in every cell. This process, called apoptosis, is activated when a cell needs to be terminated, such as when a cell is defective or becomes unnecessary during normal growth and development. In cancer cells, the self-destruct mechanism is faulty.

In 2004, Dr. Wang and his colleagues developed a compound that mimics the action of Smac. They found that in cell cultures, the compound killed cancer cells but left healthy cells unaffected. In those studies, however, the Smac mimic only killed cancer cells when it was introduced along with another molecule often involved in the cell-death machinery, called tumor necrosis factor-a, or TNFa.

In the current study, Dr. Wang’s research group tested 50 human non-small-cell lung-cancer cell lines in culture and found that 22 percent of them were sensitive to the Smac mimic alone, without having to add TNFa. The researchers also found that the Smac mimic alone was effective against some types of breast cancer and melanoma cells in culture.

“The apparent ability of a Smac mimetic, as a single agent, to induce cell death in nearly one-quarter of lung-cancer cell lines tested was quite remarkable,” said Dr. Wang, who is a Howard Hughes Medical Institute investigator at UT Southwestern.

The researchers then introduced those sensitive cancer-cell lines into mice, where they grew into tumors. When the lung-tumor-bearing mice were injected with the Smac mimic, the tumors reduced significantly in size, and in some cases, the tumors disappeared completely.

Also tried was a similar experiment treating breast-cancer tumors in mice with the Smac mimic alone. That treatment, however, showed little effect.

The researchers then investigated what made those particular lung-cancer cell lines so sensitive to the Smac mimic alone.

“We found that these sensitive cell lines produce their own TNFa,” Dr. Wang said.

In addition to aiding in cell death, TNFa also is known, paradoxically, to sometimes play a role in aiding cancer-cell survival and growth. In combination with the Smac mimic, however, the role of this molecule is clear: cell death.

“The Smac mimetic is able to exploit certain cancer cells that secrete TNFa and usurp this pro-survival signal to promote cell death,” Dr. Wang said.

“Not only is single-agent Smac mimetic treatment highly effective at inducing cell death in these cell lines, but it also offers the possibility of highly specific and relatively nontoxic future therapeutic treatments by exploiting certain cancer cells’ own production of TNFa.”

Additional research and tests will be needed before the Smac mimic is tested in humans, Dr. Wang said, adding that detecting the presence of TNFa in a patient could serve as a marker to indicate that the cancer might be sensitive to treatment with the Smac mimic alone.

“The challenge for cancer therapies now is that they also tend to kill normally growing cells as well as cancer cells, which results in undesirable side effects,” he said. “Because this compound affects cancer cells selectively, it could combat this problem.”


###
Other UT Southwestern researchers involved in the study were: lead author Sean Petersen, graduate student in biochemistry; Dr. Lai Wang, postdoctoral research fellow in biochemistry; Asligul Yalcin-Chin, graduate student in biochemistry; Dr. Patrick Harran, professor of biochemistry; Dr. Michael Peyton, research scientist in the Nancy B. and Jake L. Hamon Center for Therapeutic Oncology Research; and Dr. John Minna, director of the Hamon Center and of the W.A. “Tex” and Deborah Moncrief Jr. Center for Cancer Genetics.

Lin Li of Joyant Pharmaceuticals also participated. Drs. Wang and Harran are cofounders of Joyant Pharmaceuticals, a Dallas-based company and UT Southwestern spin-off that is developing medical applications of Smac-mimetic compounds.

The research was supported by the National Cancer Institute and HHMI.
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PostPosted: Thu Nov 29, 2007 6:16 pm    Post subject: Homeless cells find temporary lodging -- and their demise Reply with quote

Harvard Medical School

Homeless cells find temporary lodging -- and their demise

BOSTON, Mass. (Nov. 29, 2007)—Sometimes healthy cells commit suicide. In the 1970s, scientists showed that a type of programmed cell death called apoptosis plays a key role in development, and the 2002 Nobel Prize in Physiology or Medicine recognized their work. As apoptotic cells degrade, they display standard characteristics, including irregular bulges in the membrane and nuclear fragmentation.

Now, Harvard Medical School researchers have uncovered a new type of death devoid of these features. In the Nov. 30 issue of Cell, they report a bizarre cell-in-cell invasion and death process, which they name entosis, after the Greek word for “within.”

“We watched homeless cells, free of their normal attachments, bore into their neighbors and die inside compartments called vacuoles,” says Michael Overholtzer, a postdoctoral researcher in Joan Brugge’s lab.

“We’re not sure if entosis evolved to play a particular role or if it’s simply an aberration of a normal process,” adds Brugge, who is Chair of the Department of Cell Biology.

Overholtzer discovered entosis while working with human breast cells that normally form sheets of tissue. When these cells become detached from their protein-rich beds, they generally die through apoptosis. But Overholtzer noticed that they behave oddly long before displaying apoptotic features. In fact, many of these homeless cells actually nest inside their neighbors.

Further experimentation revealed that the cells actively invade neighboring cells. While some of the intruders—which initially appear healthy—later exit their hosts unharmed, most die inside vacuoles.

But Overholtzer didn’t realize the implications of his initial observation until he crossed paths with Brigham and Women’s Hospital pathologist Andrea Richardson. She informed him that the scientific literature is full of “cell-in-cell” references in the context of cancer.

“Although these structures have been described by pathologists for decades, nobody knew how they formed,” says Brugge.

Overholtzer conducted additional experiments with his non-cancerous cell line. In collaboration with Guillaume Normand of Associate Professor of Cell Biology Randall King’s lab, he tracked the cells over time and was shocked to see that some of them actively bored into their neighbors. Furthermore, the invaders appeared to be healthy.

The fate of the internalized cells was even more surprising. While most of them eventually died, some exited their hosts and swam off unharmed. Still others divided inside their vacuoles, producing daughter cells—and additional proof of the invaders’ viability. Overholtzer stained the suspended cells for a protein associated with apoptosis to confirm that it was not playing a role.

“Pathologists have speculated for years that some internalized cells are alive and our data suggests they were right,” says Overholtzer.

Next, he looked at other human cell lines. A variety of them displayed entosis when tested, including four of nine tumor lines. Cancerous MCF7 cells proved particularly prone to invasions with a whopping 30 percent of them housing “neighbors.” These hospitable hosts invited additional experiments.

After 24 hours, 12 percent of MCF7 cells displayed massive cellular and nuclear degradation lacking apoptotic hallmarks. All of these cells were nestled inside vacuoles, and stains implicated acidification in their death.

He still doesn’t know which cell orders the killing, but it appears the houseguest forces its way into the host. The initial contacts between MCF7 cells resemble the junctions established during a normal epithelial process that occurs when cells press against each other to form dense sheets. In suspension, epithelial cells may hijack this process to push into neighboring cells or to pull the membrane of a neighboring cell around them.

“The simplest explanation is that entosis is an aberration of normal epithelial processes,” Overholtzer says. “The invasion could occur when you get unequal contractile forces between two unanchored cells.”

But he and Brugge haven’t ruled out other possibilities. Perhaps entosis represents a new type of programmed cell death that evolved for a particular purpose.

“It’s very difficult to know whether this is a cellular program with a normal role in development,” says Brugge.

Regardless of its origins, entosis shows up in the clinic. Overholtzer collaborated with Edmund Cibas at Brigham and Women’s Hospital and Stuart Schnitt at Beth Israel Deaconess Medical Center to obtain fluid exudates (derived from the circulatory system) and primary tumor tissue from breast cancer patients. Seven of eight exudates and 11 of 20 primary breast carcinomas displayed some cell internalization.

The next step is to determine if entosis helps or hurts cancer cells.

“Our first instinct is that entosis inhibits tumor progression by killing ‘homeless’ cancer cells before they colonize distant sites, and we’re working on ways to model this,” says Overholtzer. “One could also imagine that entosis promotes tumor progression by providing nutrients for some cells from their neighbors, but we do not yet have evidence for this.”


###
The National Cancer Institute and the Breast Cancer Research Foundation supported this research.
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PostPosted: Sat Dec 15, 2007 1:27 pm    Post subject: How molecular muscles help cells divide Reply with quote

Yale University
14 December 2007

How molecular muscles help cells divide

New Haven, Conn. — Time-lapse videos and computer simulations provide the first concrete molecular explanation of how a cell flexes tiny muscle-like structures to pinch itself into two daughter cells at the end of each cell division, according to a report in Science Express.

Cell biologists at Yale and physicists at Columbia teamed up to model and then observe the way a cell assembles the “contractile ring,” the short-lived force-producing structure that physically divides cells and is always located precisely between the two daughter cell nuclei.

“This contractile ring is thought to operate like an old-fashioned purse string,” said senior author Thomas D. Pollard, Sterling Professor and Chair of the Department of Molecular, Cellular & Developmental Biology at Yale. “It constricts the cell membrane into a cleavage furrow that eventually pinches the cell in two.”

Living cells divide into two daughter cells to reproduce themselves. In one-celled organisms like yeast, each cell division yields a new creature. In humans and other multicellular species, cell division creates an adult from an embryo. In fully developed adults, it provides necessary replacements for cells that are continuously dying in the course of natural wear and tear.

Scientists have long studied aspects of how cells actually make this division — the structure of the cellular machinery, how it assembles and how the machine works. Since the 1970s, it has been known that the contractile ring is made up of muscle-like actin and myosin — contractile proteins that are involved a process in some ways similar to the muscle contraction used to move arms or legs. However, there was no plausible mechanism to explain how it worked.

“We found that fission yeast cells assemble their contractile ring using a ‘search, capture, pull and release’ mechanism,” said Pollard. “This is important because it shows for the first time how the contractile machinery assembles and how all the pieces get to the right place to get the job done.”

Time-lapse imaging and computer modeling demonstrated that cells undergoing mitosis set up small clusters of proteins, or nodes, on the inside of the cell membrane around the equator of the cell. Proteins in these nodes begin to put out a small number of filaments composed of the protein actin. The filaments grow in random directions until they encounter another node, where myosin motors in the contacted node pull on the actin filament, bringing the two nodes together.

However, the researchers found that each connection is broken in about 20 seconds. Releasing the connections and initiating subsequent rounds of “search and capture” appears essential to the assembly process, say the scientists. The assembly involves many episodes of attractions between pairs of nodes proceeding in parallel. Eventually the nodes form into a condensed contractile ring around the equator, ready to pinch the mother into two daughters at a later stage.

“A novel and important aspect of this work was that we used computer simulations at every step to test what is feasible physically and to guide our experiments,” said author Ben O’Shaughnessy, professor of chemical engineering at Columbia. “The simulations show that cells use reaction rates that are nearly ideal to make this mechanism work on the time scale of the events in the cells.”

“Future work will involve testing the concepts learned from fission yeast in other cells to learn if the mechanism is universal,” said Pollard. “Since other cells, including human cells, depend on similar proteins for cytokinesis [cell division], it is entirely possible that they use the same strategy.”


###
Other authors on the paper were Dimitrios Vavylonis at Columbia, Yale and Lehigh University; Jian-Qui Wu and Steven Hao at Yale. The work was supported by research grants from the National Institutes of Health.

Citation: Science Express: (December 13, 2007).
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PostPosted: Wed Dec 19, 2007 6:49 pm    Post subject: Why don't we get cancer all the time? Reply with quote

University of Arizona
19 December 2007

Why don't we get cancer all the time?

The seemingly inefficient way our bodies replace worn-out cells is a defense against cancer, according to new research.

Having the neighboring cell just split into two identical daughter cells would seem to be the simplest way to keep bodies from falling apart.

However that would be a recipe for uncontrolled growth, said John W. Pepper of The University of Arizona in Tucson.

"If there were only one cell type in the group, it would act like an evolving population of cells. Individual cells would get better and better at surviving and reproducing," said Pepper, a UA assistant professor of ecology and evolutionary biology and a member of UA's BIO5 Institute.

"When cells reach the point where they divide constantly, instead of only when needed, they are cancer cells."

Instead, multicellular organisms use a seemingly inefficient process to replace lost cells, Pepper said. An organ such as the skin calls upon skin-specific stem cells to produce intermediate cells that in turn produce skin cells.

Although great at their job, the new skin cells are evolutionary dead ends. The cells cannot reproduce.

Losing the ability to reproduce was part of the evolutionary path single-celled organisms had to take to become multicellular, Pepper said.

What was in it for the single cells?

"Probably they got to be part of something more powerful," Pepper said. "Something that was hard to eat and good at eating other things."

Pepper and his colleagues published their paper, "Animal Cell Differentiation Patterns Suppress Somatic Evolution," in the current issue of PLoS Computational Biology. Pepper's co-authors are Kathleen Sprouffske of the University of Pennsylvania in Philadelphia and the Wistar Institute in Philadelphia and Carlo C. Maley of the Wistar Institute.

The National Institutes of Health, the Pennsylvania Department of Health, the Pew Charitable Trust and the Santa Fe Institute funded the research.

Pepper became curious about the origins of cooperation between cells while he was a postdoctoral fellow at the Santa Fe Institute in New Mexico.

"Organisms are just a bunch of cells," he said.

"If you understand the conditions under which they cooperate, you can understand the conditions under which cooperation breaks down. Cancer is a breakdown of cooperation."

Pepper and his colleagues used a kind of computer model called an agent-based model to compare different modes of cellular reproduction.

The results indicate that if cells reproduce by simply making carbon-copies of themselves, the cells' descendants are more likely to accumulate mutations.

In contrast, if cellular reproduction was much more complicated, the cells' descendants had fewer mutations.

Suppressing mutations that might fuel uncontrolled growth of cells would be particularly important for larger organisms that had long lives, the team wrote in their research report.
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