SIRT1 and Cancer
This research suggests a way in which calorie restriction (which upregulates sirtuins) might be effective in resisting cancer: "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. [Researchers] 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."
Link: http://www.sciencedaily.com/releases/2009/04/090413083311.htm