Recent investigations discovered that CIAPIN1 might be another drug resistance-associated molecule in cancer cells. However, the underlying mechanisms of CIAPIN1-related multidrug resistance (MDR) remain elusive. In the present study, we investigated the role and possible mechanisms of CIAPIN1 in MDR of human colon carcinoma LoVo/Adr cells which express the wild-type p53 gene. By using small interference RNA and gene transfection techniques, we found that knockdown of CIAPIN1 expression re-sensitized LoVo/Adr cells to anti-cancer drugs and up-regulation of CIAPIN1 in sensitive LoVo cells resulted in a distinct MDR phenotype. We further revealed that CIAPIN1 conferred the MDR phenotype in LoVo/Adr cells through up-regulating expression of MDR-1 (P-gp) and Bcl-xL. Finally, by analyzing the effect of inactivation of wild-type p53 on CIAPIN1-induced up-regulation of P-gp and Bcl-xL, we determined that CIAPIN1 could exhibit its MDR-related function independently of the p53 signaling pathway. Overall, the results presented here further suggest that over-expression of CIAPIN1 is an important mechanism of drug resistance in human cancers, even if not the sole one.

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