Reexpression of hSNF5 in malignant rhabdoid tumor cell lines causes cell cycle arrest through a p21CIP1/WAF1-dependent mechanism

摘要

Loss of hSNF5 function is usually observed in malignant rhabdoid tumor (MRT), a highly aggressive pediatric neoplasm. Previous studies have shown that reexpression of hSNF5 in MRT cell lines causes G1 cell cycle arrest with p16^INK4A, p21^CIP1/WAF1 and cyclin D1 playing key roles in MRT cell growth control. However, we have shown that reexpression of hSNF5 induced cell cycle arrest in the absence of p16^INK4A expression. These results indicate that the mechanism of hSNF5-induced cell cycle arrest is context dependent. Here, we investigated the relationship between p21^CIP1/WAF1 and hSNF5 in the regulation of growth using several MRT cell lines. We found that G1 cell cycle arrest occurred concomitant with an increase in p21^CIP1/WAF1 mRNA and protein levels and preceeded p16^INK4A mRNA and protein up-regulation. Chromatin immunoprecipitation data confirmed that hSNF5 appeared at both p21^CIP1/WAF1 and p16^INK4A promoters after reexpression. We further showed that p21^CIP1/WAF1 induction showed both p53 dependent and independent mechanisms. We also demonstrated that reduction of p21^CIP1/WAF1 expression by RNAi significantly inhibited hSNF5-induced G1 arrest. Our results demonstrate that both p21^CIP1/WAF1 and p16^INK4A are targets for hSNF5, and that p21^CIP1/WAF1 up-regulation during hSNF5-induced G1 arrest precedes p16^INK4A up-regulation. These findings indicate that SNF5 mediates a temporally controlled program of CDK inhibition to restrict aberrant proliferation in MRT cells.