Role of p21^WAF1 in green tea polyphenol-induced growth arrest and apoptosis of oral carcinoma cells

The cyclin-dependent kinase inhibitor p21^WAF1 participates in cell growth, differentiation and apoptosis. p21^WAF1 can be induced by green tea polyphenol EGCG in several cancer cell types, but its role in the oral cancer cell response to EGCG is not known. We found that EGCG upregulates p21^WAF1 in an oral carcinoma cell line, OSC2, by cDNA microarray. The current study determined the impact of siRNA-suppressed p21^WAF1 and its response to EGCG on cell growth, DNA synthesis and apoptosis by RT-PCR, Western blot, BrdU incorporation, MTT and caspase 3 activity assays. Suppression of p21^WAF1 by siRNA resulted in an accelerated cell growth and DNA synthesis, and increased cell viability. However, caspase 3 activity was not significantly inhibited. The evidence showed that p21^WAF1 is involved in EGCG-induced growth arrest of OSC2 cells, which may facilitate caspase 3-mediated apoptosis. Thus, expression of functional p21^WAF1 may promote phytochemical-mediated growth arrest and apoptosis in oral carcinoma cells.