BioProject

Sirtuins (SIRT) are NAD-dependent protein deacteylases and function in cellular metabolism, stress resistance, proliferation and disease. More...

Sirtuins (SIRT) are NAD-dependent protein deacteylases and function in cellular metabolism, stress resistance, proliferation and disease. For SIRT7, a role in ribosomal gene transcription is proposed, but its function in cancer is currently unknown. In this study, we showed that SIRT7 expression was up-regulated in a large cohort of human hepatocellular carcinoma (HCC) patients, and that high expression of SIRT7 was associated with poor prognosis of HCC patients. Notably, inactivation of SIRT7 by siRNA suppressed tumor cell growth and caused G1/S cell cycle arrest in liver cancer cells. This treatment restored p21WAF1/Cip1 activity, induced Beclin-1 and autophagic gene expression and repressed cyclin D1. To explore mechanisms in SIRT7 regulation, microRNA (miRNA) profiling was carried out. This identified five significantly down-regulated miRNAs in HCC. Bioinformatic analysis of target sites and ectopic expression in HCC cells evidenced miR-125a-5p and miR-125b to suppress SIRT7 and cyclin D1 expression and to induce p21WAF1/Cip1-dependent G1 cell cycle arrest. Furthermore, treatment of HCC cells with 5-aza-2’-deoxycytidine or ectopic expression of wild-type but not mutated p53 restored miR-125a-5p and miR-125b expression and inhibited tumor cell growth to suggest their regulation by promoter methylation and p53 activity. To evidence clinical significance of these findings, mutations in the DNA binding domain of p53 and promoter methylation of miR-125b were investigated. Four out of nine patients with induced SIRT7 carried mutations in p53 gene and one patient showed hypermethylation of miR-125b promoter region. Conclusion: Our findings suggest that oncogenic potential of SIRT in hepatocarcinogenesis and that a regulatory loop is proposed whereby SIRT7 inhibits transcriptional activation of p21WAF1/Cip1 via repression of miR-125a-5p and miR-125b. This makes SIRT7 a promising target in cancer therapy. Overall design: miRNA expression profiling of 8 normal liver and 16 HCC tissues was performed using GenoExplorer Microarray platform. 10 µg of total RNA was isolated from normal liver and HCC tissues and then labeled and hybridized to a to microRNA chip for analysis under optimized conditions. The arrays with hybridized targets were scanned using an Axon scanner and the scanned images were analyzed using GenePix® Pro 5.0 software (Axon Instruments) and spots of poor quality determined by visual inspection were also removed from further analysis. The resulting data, the average of 3 mean fluorescence signal intensities for each probe, collected from each array was submitted to the GenePlex 3.0 (Istech Inc. Seoul, Korea) database. Data were normalized using the method of quantile normalization and class-specific filtering. Less...