The NAD-dependent histone deacetylase Sir2 plays a key role in connecting cellular metabolism with gene silencing and aging. The androgen receptor (AR) is a ligand-regulated modular nuclear receptor governing prostate cancer cellular proliferation, differentiation, and apoptosis in response to androgens, including dihydrotestosterone (DHT). Here, SIRT1 antagonists induce endogenous AR expression and enhance DHTmediated AR expression. SIRT1 binds and deacetylates the AR at a conserved lysine motif. Human SIRT1 (hSIRT1) repression of DHT-induced AR signaling requires the NAD-dependent catalytic function of hSIRT1 and the AR lysine residues deacetylated by SIRT1. SIRT1 inhibited coactivator-induced interactions between the AR amino and carboxyl termini. DHT-induced prostate cancer cellular contact-independent growth is also blocked by SIRT1, providing a direct functional link between the AR, which is a critical determinant of progression of human prostate cancer, and the sirtuins.

The cyclin D1 gene is overexpressed in human breast cancers and is required for oncogene-induced tumorigenesis. Peroxisome proliferator-activated receptor ␥ (PPAR␥) is a nuclear receptor selectively activated by ligands of the thiazolidinedione class. PPAR␥ induces hepatic steatosis, and liganded PPAR␥ promotes adipocyte differentiation. Herein, cyclin D1 inhibited ligand-induced PPAR␥ function, transactivation, expression, and promoter activity. PPAR␥ transactivation induced by the ligand BRL49653 was inhibited by cyclin D1 through a pRB-and cdk-independent mechanism, requiring a region predicted to form an helix-loop-helix ( The cyclin-dependent kinase holoenzymes are a family of serine/threonine kinases that play a pivotal role in controlling progression through the cell cycle (38,47). Dysregulation of the cell cycle control apparatus is an almost uniform aberration in tumorigenesis (48). The cyclins encode regulatory subunits of the kinases which phosphorylate specific proteins, including the retinoblastoma (pRB) protein, to promote transition through specific cell cycle checkpoints (47, 57). Cyclin D1 plays a pivotal role in G 1 /S phase cell cycle progression in fibroblasts and is rate limiting in growth factor-or estrogen-induced mammary epithelial cell proliferation (29, 67). Cyclin D1 overexpression is found in Ͼ30% of human breast cancers, correlating with poor prognosis (23). Several different oncogenic signals induce cyclin D1 expression, including mutations of the Ras and Wnt/APC/␤-catenin pathway (2, 49). Mammary-targeted expression of cyclin D1 is sufficient for the induction of mammary adenocarcinoma, and cyclin D1 Ϫ/Ϫ mice are resistant to ErbB2-induced tumorigenesis (53,64).In addition to binding cyclin-dependent kinases 4 and 6 (cdk4 and cdk6) and pRB, cyclin D1 forms physical associations with P/CAF (p300/CBP-associated factor), Myb, MyoD, and the cyclin D1 myb-like binding protein (DMP1) (16,20,31,39). Binding of cyclin D1 to the estrogen receptor alpha (ER␣) enhances ligand-independent reporter gene activity, and liganded androgen receptor reporter gene activity is inhibited by cyclin D1 (33, 39, 68). The in vivo or genetic evidence indicating a requirement for cyclin D1 in nuclear receptor function remained to be determined. The peroxisome proliferator-activator receptors, including PPAR␣, PPAR␥, and PPAR␦, are ligand-activated nuclear receptors (42). Their modular structure resembles those of other nuclear hormone receptors with N-terminal AF-1, a DNA binding domain, and a carboxyl-terminal ligand-binding domain (LBD). PPAR␥ was cloned as a transcription factor involved in fat cell differentiation and is required for the induction of adipocyte differentiation (41, 51). Adenoviral delivery of PPAR␥ to the livers of mice induces hepatic steatosis, consistent with an important role for PPAR␥ in hepatocellular lipid biosynthesis (65). The PPAR␥ ligands include eicosanoids, such as 15-deoxy-⌬12,14-prostaglandin J2 (15d-PGJ 2 ), and synthetic ligands of the thiazolidinedione (TZD) class. PPAR␥ ...

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The cellular mechanisms that modulate the redox state of p53 tumor suppressor remain unclear, although its DNA binding function is known to be strongly inhibited by oxidative and nitrosative stresses. We show that human p53 is subjected to a new and reversible posttranslational modification, namely, S-glutathionylation in stressed states, including DNA damage. First, a rapid and direct incorporation of biotinylated GSH or GSSG into the purified recombinant p53 protein was observed. The modified p53 had a significantly weakened ability to bind its consensus DNA sequence. Reciprocal immunoprecipitations and a GST overlay assay showed that p53 in tumor cells was marginally glutathionylated; however, the level of modification increased greatly after oxidant and DNA-damaging treatments. GSH modification coexisted with the serine phophorylations in activated p53, and the thiol-conjugated protein was present in nuclei. When tumor cells treated with camptothecin or cisplatin were subsequently exposed to glutathione-enhancing agents, p53 underwent dethiolation accompanied by detectable increases in the level of p21waf1 expression, relative to the DNA-damaging drugs alone. Mass spectrometry of GSH-modified p53 protein identified cysteines 124, 141, and 182, all present in the proximal DNA-binding domain, as the sites of glutathionylation. Biotinylated maleimide also reacted rapidly with Cys141, implying that this is the most reactive cysteine on the p53 surface. The glutathionylatable cysteines were found to exist in a negatively charged microenvironment in cellular p53. Molecular modeling studies located Cys124 and -141 at the dimer interface of p53 and showed glutathionylation of either residue would inhibit p53-DNA association and also interfere with protein dimerization. These results show for the first time that shielding of reactive cysteines contributes to a negative regulation for human p53 and imply that such an inactivation of the transcription factor may represent an acute defensive response with significant consequences for oncogenesis.