Relation ship between the emergence of drug-resistant tumor cells and transformation of β-tubulin isotype mRNA expression

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The exposure of anti-microtubule drugs to tumor cells often results in the emergence of drug-resistance tumor cells. Vinca alkaloid enhanced expression of class II β-tubulin isotype in mouse B16F10 melanoma cells through the regulation of binding of p53 tumor suppressor gene in the region of the first intron. Vincristine-resistant melanoma cells elevated the mRNA level of class II isotype of β-tubulin, while suppressed class III and IVa isotype. As transient exposure of vincristine also increased mRNA level of class II isotype indicating direct effect of the drug, we tried to find the response element to vinca alkaloid in mouse class II β-tubulin gene. Deletion analyses and site-directed mutagenesis identified Sp1, CREB and p53 binding site as the important regions for class II isotype expression. Electrophoretic mobility shift assay and supershift assay showed release of p53 from the binding site was the critical role in vinka alkaloid-mediated upregulation of class II □-tubulin isotype. Furthermore, co-transfection of expression vector for wild-type p53 canceled the effect of vinka alkaloid. These results indicated that expression of class II isotype negatively regulated by p53 and vinka alkaoid induced loss of function of p53 during the emergence of drug-resitant tumor cells.