p53 activation in response to microtubule disruption is mediated by integrin-Erk signaling

The p53 tumor suppressor is activated in response to various stresses drivi ng the cells into growth arrest or apoptosis. We have addressed the questio n of how disintegration of microtubule system induces activation of p53. De polymerization of microtubules by colcemid in rat and human quiescent fibro blasts resulted in accumulation of transcriptionally active p53 that caused cell-cycle arrest at the G1/S boundary. The p53 activation correlated with prominent activation of Erk1/2 MAP kinases that resulted from colcemid-sti mulated development of focal adhesions. Inhibition of focal contacts develo pment hy plating of cells onto poly-L-lysine abrogated both Erk1/2 and p53 activations in colcemid-treated cells, while plating of cells onto fibronec tin caused transient up-regulation of p53 even in the absence of colcemid. Pre-treatment of cells with the specific MEK1 inhibitor PD098059 also atten uated colcemid-induced p53 activation and G1 cell cycle arrest. Cell types which either failed to develop focal adhesions in response to colcemid trea tment (human MCF-7 epithelial cells), or lacked colcemid-induced sustained Erk activation (primary mouse embryo fibroblasts and 12(1) cells) showed vi rtually no p53 up-regulation in response to disruption of microtubules duri ng G0/G1. Our results indicate that p53 activation is not triggered by disi ntegration of microtubule system by itself, but rather originates from some of the consequences of such disintegration, in particular, from the develo pment of focal adhesions leading to activation of Erk signaling pathway.