The mammalian Chk2 kinase is thought to mediate ATM‐dependent signaling in response to DNA damage. The physiological role of mammalian Chk2 has now been investigated by the generation of Chk2‐deficient mice. Although Chk2−/− mice appeared normal, they were resistant to ionizing radiation (IR) as a result of the preservation of splenic lymphocytes. Thymocytes and neurons of the developing brain were also resistant to IR‐induced apoptosis. The IR‐induced G1/S cell cycle checkpoint, but not the G2/M or S phase checkpoints, was impaired in embryonic fibroblasts derived from Chk2−/− mice. IR‐induced stabilization of p53 in Chk2−/− cells was 50–70% of that in wild‐type cells. Caffeine further reduced p53 accumulation, suggesting the existence of an ATM/ATR‐dependent but Chk2‐independent pathway for p53 stabilization. In spite of p53 protein stabilization and phosphorylation of Ser23, p53‐dependent transcriptional induction of target genes, such as p21 and Noxa, was not observed in Chk2−/− cells. Our results show that Chk2 plays a critical role in p53 function in response to IR by regulating its transcriptional activity as well as its stability.

Late-onset hypogonadism (i.e. androgen deficiency) raises the risk for abdominal obesity in men. The mechanism for this obesity is unclear. Here, we demonstrated that hypogonadism after castration caused abdominal obesity in high-fat diet (HFD)-fed, but not in standard diet (SD)-fed, C57BL/6J mice. Furthermore, the phenotype was not induced in mice treated with antibiotics that disrupt the intestinal microflora. In HFD-fed mice, castration increased feed efficiency and decreased fecal weight per food intake. Castration also induced in an increase of visceral fat mass only in the absence of antibiotics in HFD-fed mice, whereas subcutaneous fat mass was increased by castration irrespective of antibiotics. Castration reduced the expression in the mesenteric fat of both adipose triglyceride lipase and hormonesensitive lipase in HFD-fed mice, which was not observed in the presence of antibiotics. Castration decreased thigh muscle (i.e. quadriceps and hamstrings) mass, elevated fasting blood glucose levels, and increased liver triglyceride levels in a HFD-dependent manner, whereas these changes were not observed in castrated mice treated with antibiotics. The Firmicutes/Bacteroidetes ratio and Lactobacillus species increased in the feces of HFD-fed castrated mice. These results show that androgen (e.g. testosterone) deficiency can alter the intestinal microbiome and induce abdominal obesity in a dietdependent manner.Obesity is a global epidemic problem due to its strong association with an increased risk of cardiovascular diseases 1,2 . The excess accumulation of abdominal visceral fat, a diagnostic criterion of the metabolic syndrome 2 , increases the disorder in lipid metabolism, including an elevation of hepatic triglyceride levels 3 . In contrast, subcutaneous fat reduces the incidence of cardiovascular diseases, indicating the importance of body fat distribution 1,2 . Recent results show that the changes in intestinal microbiota are related to the development of obesity and to the increase of visceral fat mass [4][5][6][7] . Testosterone is a male sexual hormone (viz. androgen) that exerts a broad range of male physiological functions, such as the development of reproductive organs and the emergence of sexual behaviors 8,9 . Hypogonadism (i.e. low testosterone level) increases in men the risk of obesity, cardiovascular diseases, and even mortality [10][11][12][13] through the increase of body fat, in particular visceral fat 14,15 ; and testosterone treatment reduces the amount of visceral fat 16 . Androgen deprivation therapies, such as either castration or an leteinizing hormone-releasing hormone analog for prostate cancer patients, also promote the development of obesity [17][18][19] . Because the blood bioactive testosterone level steadily drops approximately 2% per year after around the age of 20 to 30 in men 20 , the age-dependent decline of testosterone is a risk factor for the age-related prevalence of abdominal obesity and its related diseases in men 14,20 . Despite increasing evidence in both clinical an...

Androgen receptor (AR) functions as a transcriptional factor for genes involved in proliferation and differentiation of normal and cancerous prostate cells. Coactivators that bind to AR are required for maximal androgen action. Here we report that increasing the expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in a prostate cancer cell line by as little as 1.8-fold enhances transcriptional activity of AR (but not the transcriptional activity of glucocorticoid receptor or estrogen receptor ␣) in a ligand-dependent manner and results in an increased expression of prostate-specific antigen. Small interference RNA-mediated knockdown of GAPDH significantly attenuated ligand-activated AR transactivation. Immunoprecipitation analysis revealed the presence of an endogenous protein complex containing GAPDH and AR in both the cytoplasm and nucleus. Addition of a nuclear localization signal (NLS) to GAPDH (GAPDH-NLS) completely abolished the ability of GAPDH to transactivate AR. Neither wild-type GAPDH nor GAPDH-NLS enhanced transcriptional activity of mutant AR (AR⌬C-Nuc) that is a constitutively active form of AR in the nucleus, even though GAPDH-NLS formed a complex with wild-type AR or AR⌬C-Nuc. AR transactivation was enhanced by a mutant GAPDH lacking dehydrogenase activity. GAPDH enhanced the transcriptional activity of AR(T875A) activated by an antagonist such as hydroxyflutamide or cyproterone acetate. These results indicate that GAPDH functions as a coactivator with high selectivity for AR and enhances AR transactivation independent of its glycolytic activity. Further, these data suggest that formation of a GAPDH⅐AR complex in the cytoplasm rather than nucleus is essential for GAPDH to enhance AR transactivation.Androgens are steroid hormones that are required for the expression of the male phenotype such as male sexual differentiation, the development and maintenance of secondary male characteristics, the initiation and maintenance of spermatogenesis, the maturation of normal prostate, and the development and progression of prostate cancer (1). In mammals, virilization is mediated through two types of steroidal hormones, testosterone and 5␣-dihydrotestosterone (DHT).2 DHT is a more potent androgen whose action is mediated through binding to the androgen receptor (AR). The AR is a member of the nuclear receptor superfamily, which includes estrogen (ER), glucocorticoid (GR), mineralocorticoid, retinoic acid, and vitamin D receptors (2). The nuclear receptors share a common modular structure that is composed of three functional domains: the N-terminal domain (NTD), central DNA-binding domain (DBD) and C-terminal ligand-binding domain (LBD). Among the nuclear receptors, the primary sequence of the NTD is variable, whereas the structures of the DBD and LBD are more conserved. The ligand-independent activation function-1 and the ligand-dependent activation function-2 are located in the NTD and the LBD, respectively (3, 4). AR, when not bound to a ligand, exists in the cytosol in an inactive state in assoc...

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