Differential effects of low and high doses of Taxol in anaplastic thyroid cancer cells: possible implication of the Pin1 prolyl isomerase.

AIM: 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 p27(KIP1) and p21(WAF1) , 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 G(1)/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 G(2)/M cell cycle arrest.