p21WAF1/Cip1 (Concentrate)

The protein p21^WAF1/Cip1 inhibits the activity of several cyclin/cyclin-dependent kinase complexes and blocks cell-cycle progression (1). In tumor cells that have lost the p53 protein, or contain an altered form of p53, p21^WAF1/Cip1 levels are dramatically reduced or totally absent (2). Because p21^WAF1/Cip1 appears to mediate several of the growth-regulatory functions of p53, its expression would be predicted to reflect the functional status of p53 more precisely than p53 accumulation.