p21 regulates the cell cycle...or the other way around?

Abstract

For many years, the upregulation of the p53- p21 pathway was supposed to represent the universal response to genotoxic stress. i n triguingly, many genotoxic agents (hydroxy - urea, aphidicolin, hypoxia, cisplatinun and U v irradiation) do not upregulate p21 despite p53 activation. 1 Remarkably, in the August 15th issue of Cell Cycle , Ciznadija and colleagues 2 showed that g i R (gamma ionizing radiation), a D n A damaging agent which was previously characterized as a bona fide inducer of p21, fails to promote such accumulation in s phase. Remarkably, this happens in the context of high p53 levels demonstrating that also in the context of g i R, as well as signals downstream of p53 specifically prevent p21 accumulation during s phase.