Reexpression of hSNF5 in Malignant Rhabdoid Tumor Cell Lines Causes Cell Cycle Arrest through a p21CIP1/WAF1-Dependent Mechanism

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 p16INK4A, p21CIP1/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 p16INK4A expression. These results indicate that the mechanism of hSNF5-induced cell cycle arrest is context dependent. Here, we investigated the relationship between p21CIP1/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 p21CIP1/WAF1 mRNA and protein levels and preceeded p16INK4A mRNA and protein up-regulation. Chromatin immunoprecipitation data confirmed that hSNF5 appeared at both p21CIP1/WAF1 and p16INK4A promoters after reexpression. We further showed that p21CIP1/WAF1 induction showed both p53 dependent and independent mechanisms. We also demonstrated that reduction of p21CIP1/WAF1 expression by RNAi significantly inhibited hSNF5-induced G1 arrest. Our results demonstrate that both p21CIP1/WAF1 and p16INK4A are targets for hSNF5, and that p21CIP1/WAF1 up-regulation during hSNF5-induced G1 arrest precedes p16INK4A up-regulation. These findings indicate that SNF5 mediates a temporally controlled program of CDK inhibition to restrict aberrant proliferation in MRT cells