Regulation of Class II β-Tubulin Expression by Tumor Suppressor p53 Protein in Mouse Melanoma Cells in Response toVincaAlkaloid

Abstract

The continuous exposure of antimicrotubule drugs to tumors often results in the emergence of drug-resistant tumor cells with altered expression of several beta-tubulin isotypes. We found that Vinca alkaloid enhanced expression of class II beta-tubulin isotype (mTUBB2) in mouse B16F10 melanoma cells via alteration of the tumor suppressor p53 protein. Vincristine treatment stimulated an increase in mTUBB2 mRNA expression and promoted accumulation of this isotype around the nuclei. Transient transfection assays employing a reporter construct, together with site-directed mutagenesis studies, suggested that the p53-binding site found in the first intron was a critical region for mTUBB2 expression. Electrophoretic mobility shift assay and associated antibody supershift experiments showed that vincristine promoted release of p53 protein from the binding site. In addition, exogenous induction of TAp63gamma (p51A), a homologue of p53, canceled the effect of vincristine on mTUBB2 expression. These results suggest that p53 protein may function as a suppressor of mTUBB2 expression and vincristine-mediated inhibition of p53 binding results in enhanced mTUBB2 expression. This phenomenon could be related with the emergence of drug-resistant tumor cells induced by Vinca alkaloid and may participate in determining the fate of these cells.