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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2005.03.037 Byline: Delin Chen (1), Ning Kon (1), Muyang Li (1), Wenzhu Zhang (1), Jun Qin (2), Wei Gu Abstract: Although the importance of the ARF tumor suppressor in p53 regulation is well established, numerous studies indicate that ARF also suppresses cell growth in a p53/Mdm2-independent manner. To understand the mechanism of ARF-mediated tumor suppression, we identified a ubiquitin ligase, ARF-BP1, as a key factor associated with ARF in vivo. ARF-BP1 harbors a signature HECT motif, and its ubiquitin ligase activity is inhibited by ARF. Notably, inactivation of ARF-BP1, but not Mdm2, suppresses the growth of p53 null cells in a manner reminiscent of ARF induction. Surprisingly, in p53 wild-type cells, ARF-BP1 directly binds and ubiquitinates p53, and inactivation of endogenous ARF-BP1 is crucial for ARF-mediated p53 stabilization. Thus, our study modifies the current view of ARF-mediated p53 activation and reveals that ARF-BP1 is a critical mediator of both the p53-independent and p53-dependent tumor suppressor functions of ARF. As such, ARF-BP1 may serve as a potential target for therapeutic intervention in tumors regardless of p53 status. Author Affiliation: (1) Institute for Cancer Genetics, Department of Pathology, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, New York 10032 (2) Departments of Biochemistry and Cell Biology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030 Article History: Received 13 September 2004; Revised 24 February 2005; Accepted 30 March 2005 Article Note: (miscellaneous) Published: June 30, 2005

The deacetylation and repression of the activity of forkhead transcription factor - Foxo3a and other mammalian forkhead factors by the mammalian SIR2 ortholog SIRT1 is reported. The speculation over the down regulation of the two classes of damage - responsive mammalian factors, favoring longer life - span under specific environmental conditions is presented.