SIRT1 takes down tumors

New study identifies another anti-cancer effect of the 'longevity' protein SIRT1

14 april 2009--Yuan et al. have identified another anti-cancer effect of the "longevity" protein SIRT1. By speeding the destruction of the tumor promoter c-Myc, SIRT1 curbs cell division. The study will be published online April 13 (www.jcb.org) and will appear in the April 20 print issue of the Journal of Cell Biology.

The yeast and nematode equivalents of SIRT1 are fountains of youth that stretch lifespan. Whether SIRT1 slows aging in mammals isn't certain, but it's beneficial in other ways. The protein tunes up metabolism, reducing blood levels of glucose and insulin, and might forestall neurodegenerative illnesses such as Alzheimer's disease and ALS. Given its pro-life credentials, you might expect SIRT1 to inhibit cancer. And several studies suggest that it does. But other work indicates that the protein aids tumors. For example, SIRT1 chops off acetyl groups, which can inactivate the tumor suppressor p53.

Yuan et al. determined SIRT1's effect on the transcription factor c-Myc, whose expression surges in many breast, colon, and liver cancers. The two proteins are tangled in a regulatory loop, the team found. c-Myc latched onto SIRT1's promoter, spurring cells to manufacture more SIRT1. In turn, SIRT1 detached acetyl groups from c-Myc, hastening its breakdown. To test SIRT1's effects on tumor growth, the researchers implanted cancerous cells expressing c-Myc into nude mice that lack immune defenses. Boosting production of SIRT1 blocked tumor formation.

How deacetylation of c-Myc sparks its destruction is still a mystery. The researchers say that the results don't necessarily conflict with studies suggesting that SIRT1 is pro-tumor. Whether SIRT1 promotes or prevents cancer probably depends on the situation.

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About the Journal of Cell Biology

Founded in 1955, the Journal of Cell Biology (JCB) is published by the Rockefeller University Press. All editorial decisions on manuscripts submitted are made by active scientists in conjunction with our in-house scientific editors. JCB content is posted to PubMed Central, where it is available to the public for free six months after publication. Authors retain copyright of their published works and third parties may reuse the content for non-commercial purposes under a creative commons license. For more information, please visit www.jcb.org or visit the JCB press release archive at http://www.eurekalert.org/jrnls/rupress.

Yuan, J., et al. 2009. J. Cell Biol. doi:10.1083/jcb.200809167.

Anti-aging pathway enhances cell stress response

People everywhere are feeling the stress of a worldwide recession. Our cells, too, are under continual assault from stress.

20 feb 2009--Hidden from sight, our cells battle challenges such as their environment, bacteria, viruses, too much or too little oxygen, and physiological stressors. Molecular systems protect cells under assault, but those systems can break down, especially with age.

To better understand how cells are protected from stress and damage, a team led by Northwestern University researchers studied the effect of resveratrol, a beneficial chemical found in red wine, on human cells in tissue culture.

The findings may help explain what happens in neurodegenerative diseases, which are age-related, when cell protection fails, proteins misfold, lots of damage accumulates and the system falls apart.

The researchers discovered a new molecular relationship critical to keeping cells healthy across a long span of time: a protein called SIRT1, important for caloric restriction and lifespan and activated by resveratrol, regulates heat shock factor 1 (HSF1), keeping it active. HSF1 in turn senses the presence of damaged proteins in the cell and elevates the expression of molecular chaperones to keep a cell's proteins in a folded, functional state. Regulation of this pathway has a direct beneficial effect to cells, the research shows.

This role of SIRT1 -- a protein already of great interest to pharmaceutical companies -- was not previously known. The results will be published in the Feb. 20 issue of the journal Science.

"When SIRT1 levels are high, you are in a high-protection mode," said Richard I. Morimoto, Bill and Gayle Cook Professor of Biochemistry, Molecular Biology and Cell Biology in Northwestern's Weinberg College of Arts and Sciences. He led the research team.

"Ironically, triggering the stress response and perhaps maintaining the cell in a protective state over a long period of time can keep cells healthy," said Morimoto. "The cell is protected against an accumulation of damage when HSF1 is more active."

SIRT1 levels decrease as humans age, Morimoto explains. Cells can't respond to stress as well. This decrease in SIRT1 may help explain why protein misfolding diseases, such as Alzheimer's, Parkinson's, Huntington's and adult-onset diabetes, are diseases of aging.

"We now have a powerful way to think about addressing neurodegenerative diseases," said Morimoto. "We have identified a pathway that can be manipulated to alter lifespan. Discovering this new basis for therapeutics is very exciting."

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In addition to Morimoto, other authors of the Science paper, titled "Stress-Inducible Regulation of Heat Shock Factor 1 by the Deacetylase SIRT1," are Sandy D. Westerheide, from Northwestern; Julius Anckar and Lea Sistonen, from Åbo Akademi University in Turku, Finland; and Stanley M. Stevens Jr., from the University of Florida.