Abstract #3459: Reexpression of hSNF5 in malignant rhabdoid tumor cell lines causes cell cycle arrest through a p21^WAF1/CIP1 dependent mechanism

Malignant rhabdoid tumor (MRT), a highly aggressive neoplasm of young children, displays inactivation of the hSNF5 gene in almost 100% of primary tumors and cell lines. Reexpression of hSNF5 in MRT cell lines causes a G1 arrest, up-regulation of p16^INK4A (p16 )and p21^WAF1/CIP1 (p21) and down-regulation of cyclin D1, suggesting a key role for these genes in MRT cell cycle control. However, our previous study showed that reexpression of hSNF5 induced cell cycle arrest even in the absence of p16expression. Therefore, we examined the relationship between p21and hSNF5 in the regulation of growth of MRT cells. We reexpressed hSNF5 in the A204 and TTC642 MRT cell lines using adenoviral vectors expressing either hSNF5 and GFP (Ad-hSNF5) or GFP (Ad-GFP). Reexpression of hSNF5 induced G1 arrest at 24 hours with concomitant down-regulation of pRb and cyclin A in both MRT cell lines. The p21mRNA levels increased at 12 hours while the p16mRNA increased after 24 hours in both cell lines. We also observed a similar pattern in the increase of the respective protein levels in both cell lines. However, p16protein levels did not increase significantly until 48 hours in TTC642 cell line. Chromatin immnoprecipitation data confirmed that hSNF5 appeared at both the p21and p16promoters after reexpression. To determine the role of p21in hSNF5-induced growth arrest, we stably knocked down p21expression in both cell lines using lentiviral vectors encoding shRNA. Loss of p21expression significantly inhibited hSNF5-induced G1 arrest in both cell lines at 24 hours, accompanied by activation of cyclin A and phosphorylation of pRb (Table). Our results demonstrate that induction of p21precedes p16 expression during hSNF5-induced growth in MRT cell lines. Furthermore, our results suggest that hSNF5 loss may alter p21transcription by a different mechanism than that reported for the p16promoter in these cells. $$table_{22BF1C80-CDF7-413E-9AEE-9D0F3620ED0A}$$

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 3459.