IL-1-induced ERK1/2 activation up-regulates p21(Waf1/Cip1) protein by inhibition of degradation via ubiquitin-independent pathway in human melanoma cells A375.

IL-1 inhibits the proliferation of human melanoma cells A375 by arresting the cell cycle at G0/G1 phase, which accompanies the increase of p21(Waf1/Cip1) (p21) protein. Here, we demonstrate that IL-1 induces the stabilization of p21 protein via ERK1/2 pathway. The degradation of p21 was inhibited by IL-1, however the ubiquitination level of p21 was not affected. In addition, the degradation of non-ubiquitinated form of lysine less mutant p21-K6R was also inhibited by IL-1, suggesting that IL-1 stabilized p21 protein via ubiquitin-independent pathway. Furthermore, the inhibition of p21 protein degradation was prevented by a selective inhibitor of ERK1/2 pathway, PD98059. These results suggest that IL-1-induced ERK1/2 activation leads to the up-regulation of p21 by inhibiting degradation via ubiquitin-independent pathway in human melanoma cells A375.