Involvement Of CUL4A In Regulation Of Multidrug Resistance To P-gp Substrate Drugs In Breast Cancer Cells

CUL4A encodes a core component of a cullin-based E3ubiquitin ligase complex that regulates many critical processes such as cell cycle progression, DNA replication, DNA repair and chromatin remodeling by targeting a variety of proteins for ubiquitination and degradation. In the research described in this report, we aimed to clarify whether CUL4A participates in multiple drug resistance (MDR) in breast cancer cells. We first transfected vectors expressing CUL4A and specific shRNA to CUL4A into breast cancer cells and corresponding Adr cells respectively. Using reverse transcription polymerase chain reactions and western blots, we found that overexpression of CUL4A in MCF7and MDA-MB-468cells up-regulated MDRl/P-gp expression on both the transcription and protein levels, which conferred multidrug resistance to P-gp substrate drugs, as determined by3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. On the other hand, silencing CUL4A in MCF7/Adr and MDA-MB-468/Adr cells led to the opposite effect. Moreover, ERK1/2in CUL4A-overexpressing cells was highly activated and after treatment with PD98059, an ERK1/2-specific inhibitor, CUL4A-induced expression of MDR1/P-gp was decreased significantly. Lastly, immunohistochemistry in breast cancer tissues showed that P-gp expression had a positive correlation with the expression of CUL4A and ERK1/2. Thus, these results implied that CUL4A and ERK1/2participated in multi-drug resistance in breast cancer through regulation of MDR1/P-gp expression.