The role of ERK 1/2 and p38 MAP-kinase pathways in Taxol-induced apoptosisin human ovarian carcinoma cells

Taxol is an anticancer agent of natural origin with significant activity ag ainst a number of human cancers including ovarian and breast carcinomas. It s cytotoxic activity has been attributed to its ability to stabilize microt ubules and to promote microtubule assembly. Recently it has become clearer that Taxol has additional activities including effects in cell signaling an d gene expression. We have shown previously that Taxol activates ERK 1/2 MA P-kinases and results in the formation of GRB2/SHC complexes in murine macr ophage-like RAW 267.4 cells. Here we demonstrate that Taxol activates ERK 1 /2 and p38 MAP-kinases in human ovarian carcinoma cells with distinct kinet ics. Activation of ERK1/2 has been observed at low concentrations of Taxol (1-100 nM) within 0.5-6 h, whereas longer exposure (24 h) to nanomolar conc entrations of Taxol resulted in an abrogation of the ERK1/2 phosphorylation /activation. Higher concentrations (1-10 tcm) resulted in a sharp inhibitio n of ERK1/2 activity. p38 kinase was activated by high concentrations (1-10 muM) of Taxol within 2 h and remained active for more than 24 h. The kinet ic studies showed that these effects of Taxol coincided with an inhibition of proliferation, and the onset of apoptosis. The appearance of the fragmen ted chromatin visualized by DA-PI staining, and DNA fragments seen on an ag arose gel, coincided with the decrease in ERK1/2 activation and concomitant increase of the level of active p38 MAPK. The inhibitor PD98059 abrogated ERK 1/2 activation and increased the cytotoxic effect of Taxol. An inhibito r of p38 kinase, SB203580, protected the cells partially from Taxol and, un expectedly, activated ERK 1/2 kinases. We conclude that the alternative use of ERK1/2 and p38 MAP-kinase pathways may be necessary for the transition from proliferation state to Taxol-induced apoptosis in human ovarian carcin oma cells. (C) 2001 Academic Press.