We analyzed taxol-induced apoptosis in human colon carcinoma cell lines. Cells expressing Bcl-2 (COLO320) and those that did not (DLD-1), underwent apoptosis after 24 h exposure to 1 mu M taxol. Flow cytometry showed that the numbers of cells arrested in G(2)/M decreased and that of apoptotic cells increased time-dependently. The molecular weight of Bcl-2 was increased to above 26 kDa in COLO320 and LoVo cells after a 4 h exposure to taxol. Incubating the cells with genistein, a protein tyrosine kinase inhibitor, inhibited the taxol-induced modified Bcl-2 expression and apoptosis. These results suggest that taxol induces apoptosis in cells arrested in G(2)/M phase which might be partly explained by Bcl-2 inactivation by phosphorylation in human colon carcinoma cell lines.

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