Publication Date:
2011-12-21
Description:
Multidrug resistance (MDR) is a barrier to successful cancer chemotherapy. Although MDR is associated with overexpression of ATP-binding cassette (ABC) membrane transporters, mechanisms behind their up-regulation are not entirely understood. The cleaved form of the Notch1 protein, intracellular Notch1 (N1IC), is involved in transcriptional regulation of genes. To test whether Notch1 is involved in the expression of multidrug resistance-associated protein 1 (ABCC1/MRP1; herein referred to as ABCC1), we measured N1IC and presenilin 1 (PSEN1), the catalytic subunit of γ-secretase required for Notch activation. We observed higher levels of N1IC and PSEN1 proteins as well as higher activity of N1IC in ABCC1-expressing MDR MCF7/VP cells compared with parental MCF7/WT cells. Reducing N1IC levels in MCF7/VP cells with either a γ-secretase inhibitor or shRNA led to reduction of ABCC1. By contrast, ectopic expression of N1IC in MCF7/WT cells led to increased expression of ABCC1 and associated drug resistance, consistent with expression of this transporter. Inhibition of ABCC1 reversed drug resistance of N1IC-overexpressing stable cells. Using an ABCC1 promoter construct, we observed both its reduced transcriptional activity after blocking the generation of N1IC and its increased transcriptional activity in stable cells overexpressing N1IC. ChIP and gel-shift assays revealed an interaction between a specific promoter region of ABCC1 and the N1IC-activated transcription factor CBF1, suggesting that the regulation of ABCC1 expression by Notch1 is mediated by CBF1. Indeed, deletion or site-directed mutagenesis of these CBF1 binding sites within the ABCC1 promoter region attenuated promoter-reporter activity. Overall, our results reveal a unique regulatory mechanism of ABCC1 expression.
Print ISSN:
0027-8424
Electronic ISSN:
1091-6490
Topics:
Biology
,
Medicine
,
Natural Sciences in General
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