Background: Sirtuin1 (SIRT1) is one of the NAD-dependent histone deacetylases, known as a longevity gene induced by caloric restriction or various stresses. SIRT1 also contributes to cell survival under stress conditions through deacetylation of apoptosis or cell cycle-related proteins. The overexpression of SIRT1 in several cancers was reported, however, the expression and function of SIRT1 in endometrial cancer remained undetermined. In this study, we examined the role of SIRT1 on the carcinogenesis and survival of endometrial carcinoma cells.

Methods: The expressions of SIRT1 protein was examined by immunostaining using formalin-fixed tissue specimens of 110 endometrial carcinomas, 72 normal endometria and 24 endometrial hyperplasias. Immunoreactivity was evaluated according to the ratio of positive cells in 500 cells and described as a positivity index (PI, full score 100). All of surgical specimens were used after obtaining the consents. The mRNA and protein levels of SIRT1 in endometrial carcinoma cell lines, Ishikawa and HEC1B, were examined using real-time RT-PCR and Western blotting under stresses such as ultraviolet, hypoxia and cisplatin (CDDP) treatment. The viability of those cells under CDDP treatment was examined using WST-1 assay with/without suppression of SIRT1 by SIRT1 inhibitor (EX527) or siRNA. The effect of SIRT1 inhibition on the acetylation of p53 and the p53-related protein expression was in Ishikawa and HEC1B cells were examined using Western blotting under CDDP treatment.

Results: Imunoreactivity of SIRT1 protein of carcinoma (PI=37.0±25.6) was significantly higher than that of normal endometrium (PI=25.3±26.5, P= 0.006). The expression of SIRT1 was significantly higher in grade 3 tumors (P= 0.006) and those with lympho-vascular space invasion (P= 0.044). There is a weak correlation between the expression of SIRT1 and growth potential indicated by Ki67 (P=0.051). The expression of SIRT1 protein was inversely correlated with that of p53 in carcinoma tissues and cell lines. In addition, the suppression of SIRT1 significantly reduced cell proliferation activity (P=0.01) and resistance against CDDP (P=0.004) in Ishikawa and HEC1B cells. The suppression of SIRT1 enhanced the acetylation of p53 protein and its downstream proteins.

Conclusions: SIRT1 is over-expressed in endometrial carcinoma and may be involved in the carcinogenesis and development. SIRT1 may enhance the survival of endometrial carcinoma cells against various stresses, especially CDDP exposure, via inhibition of p53 by deacetylation. These findings suggest that SIRT1 can be a potent therapeutic target of endometrial carcinoma.

Citation Format: Ryoichi Asaka, Tsutomu Miyamoto, Kaori Ishikawa, Yasushi Yamada, Hisanori Kobara, Akihisa Suzuki, Shun'ichiro Taniguchi, Tanri Shiozawa. Sirtuin1, a longevity gene, is over-expressed and enhances proliferation and survival of endometrial carcinoma cells via deacetylation of p53. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 845. doi:10.1158/1538-7445.AM2013-845