Taxol induced Bcl-2 protein phosphorylation in human hepatocellular carcinoma QGY-7703 cell line.

Bcl-2 family proteins play a critical role in the regulation of apoptosis. Treatment of a human hepatocellular carcinoma cell line, QGY-7703, with Taxol induced apoptosis and Bcl-2 protein phosphorylation. Microscopic observation indicated that apoptotic bodies (0-15%) of Taxol-treated QGY cells appeared after 12 h of treatment, and apoptotic QGY cells gradually increased to 40% after 24 h and 70% after 48 h. A DNA fragmentation assay showed that Taxol induced genomic DNA cleavage into 200 bp DNA fragments. Bcl-2 protein was phosphorylated in Taxol-treated QGY cells within 3 h of treatment, and continued gradually up to 24 h. By 48 h, the protein was unphosphorylated. Other Bcl-2 family proteins, including Bax (a heterodimerization partner of Bcl-2), Bcl-XL, Bak and Bad, were expressed, but at constant levels. The results show a close correlation between Bcl-2 phosphorylation and apoptosis in QGY cells. The inactivation of Bcl-2 protein phosphorylation could be one of the key mechanisms needed for the induction of apoptosis in Taxol-treated QGY cells.