TAXANES PROPAGATE APOPTOSIS VIA 2 CELL-POPULATIONS WITH DISTINCTIVE CYTOLOGICAL AND MOLECULAR TRAITS

Taxol and Taxotere propagate apoptosis in Jurkat T cells via molecular signals that coincide with the appearance of two distinct cell popula tions. Cell cycle arrest in G(2)-M phase and activation of cell cycle- dependent kinases begin within 2 h and extend to most cells by 16 h. P hosphorylation of Bcl-2 also begins within 2 h and intensifies from 2- 16 h. Cell cycle arrest, activation of mitotic kinases, and phosphoryl ation of Bcl-2 coincided with the appearance of a population of metast able cells that accumulate YO-PRO-1 dye, are resistant to the caspase inhibitor -aspartyl-alpha-[(2,6-dichlorobenzoyl)oxy]methane, and have and have intact genomic DNA. Phosphorylation and deactivation of kinas es that relay survival/mitogenesis signals in T cells begin after 8 h and are prominent by 12-16 h. Deactivated kinases include c-Raf-1, p44 extracellular receptor kinase, and the tyrosine kinases c-Lck and ZAP -70. Activation of M-r 40,000 and M-r 52,000 kinases is also prominent by 12-16 h. The modulation of all these kinases coincided with the ac tivation of caspase-3 at 12 h and the appearance of a population of ap optotic cells that accumulate YO-PRO-1, are susceptible to the caspase inhibitor aspartyl-alpha-[(2,6-dichloro-benzoyl)oxy]methane, and and contain fragmented genomic DNA. This distinctive apoptosis signaling p athway may help account for the superior cytotoxic efficacy of taxanes in certain types of cancer.