Differential effects of low and high doses of taxol in anaplastic thyroid cancer cells: possible implication of the Pin1 prolyl isomerase
To study the molecular mechanisms of dose-dependent effects of an anticancer drug, Taxol, on the cell cycle machinery and apoptosis-related proteins in thyroid anaplastic cancer cell lines ARO and KTC-2. Materials and Methods: Western blot analysis was used for the detection of various proteins and of their phosphorylated forms. Results: Low dose of Taxol that cause apoptosis (25 nM) enhanced Rb protein phosphorylation, decreased the expression of cyclin-dependent kinase inhibitors р27KIP1 and p21WAF1, and potentiated the accumulation of phosphorylated p53 and of the prolyl isomerase Pin1. High Taxol doses (100 and 1000 nM) that cause necrosis-like cell death drastically decreased Pin1 level in both cell lines. Conclusion: Low doses of Taxol promoted G1/S transition, thus exhibiting mitogen-like effect. Drug-induced Pin1 accumulation could probably facilitate this transition and in parallel contribute to apoptosis via the p53/p73-dependent mechanism. At higher doses of Taxol, there was a dramatic decrease of Pin1 levels which may be a reason for G2/M cell cycle arrest.
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