Paclitaxel selects for mutant or pseudo-null p53 in drug resistance associated with tubulin mutations in human cancer

Abstract

The efficacy of anticancer therapy is limited by the development of drug resistance. While the role of p53 in the intrinsic sensitivity of human cancer cells to paclitaxel (PTX) remains controversial, its role in acquired paclitaxel resistance has never been addressed. In this study we examined the p53 status of three paclitaxel selected human ovarian carcinoma sublines, resistant to paclitaxel due to acquired β-tubulin mutations which impair paclitaxel's interaction with tubulin. In contrast to parental cells which have wt p53, in all PTX-resistant sublines p53 was functionally inactive. Two of the resistant sublines expressed high levels of transcriptionally inactive p53 protein, each with a distinct point mutation in codons 236 and 239 of the DNA binding domain. The third subline presented a novel p53 pseudo-null phenotype as a result of markedly decreased wt p53 mRNA expression. Introduction of ectopic wt p53 had no effect on PTX sensitivity in both parental and resistant cells, while it induced p21^WAF1/CIP1, demonstrating an intact p53 pathway. While PTX resistance is primarily conferred by the tubulin mutations, the loss of functional p53 observed in all clones, suggests that this loss may facilitate the development of resistance potentially by providing a clonal advantage which promotes the isolation of paclitaxel resistant cells.