Role of MicroRNA miR-27a and miR-451 in the regulation of MDR1/P-glycoprotein expression in human cancer cells

Abstract

MicroRNAs are short non-coding RNA molecules able to affect stability and/or translation of mRNA, thereby regulating the expression of genes involved in many biological processes. We report here that microRNAs miR-27a and miR-451 are involved in activating the expression of P-glycoprotein, the MDR1 gene product that confers cancer cell resistance to a broad range of chemotherapeutics. We showed that expressions of miR-27a and miR-451 were up-regulated in multidrug resistant (MDR) cancer cell lines A2780DX5 and KB-V1, as compared with their parental lines A2780 and KB-3-1. Treatment of A2780DX5 cells with the antagomirs of miR-27a or miR-451 decreased the expression of P-glycoprotein and MDR1 mRNA. In contrast, the mimics of miR-27a and miR-451 increased MDR1 expression in the parental cells A2780. The sensitivity to and intracellular accumulation of cytotoxic drugs that are transported by P-glycoprotein were enhanced by the treatment with the antagomirs of miR-27a or miR-451. Our results demonstrate for the first time the roles of microRNAs in the regulation of drug resistance mediated by MDR1/P-glycoprotein, and suggest the potential for targeting miR-27a and miR-451 as a therapeutic strategy for modulating MDR in cancer cells.

Introduction

Drug resistance constitutes a major obstacle to successful chemotherapy in cancer patients. One of the common forms of resistance to chemotherapy is caused by activation of the MDR1 (ABCB1) gene, resulting in overexpression of P-glycoprotein (P-gp), a 170–190 kDa transmembrane glycoprotein that belongs to the ATP-binding cassette superfamily and acts as a multidrug transporter [1]. Overexpression of P-gp confers cancer cell resistance to a broad range of structurally and functionally diverse chemotherapeutic drugs [2]. Multidrug resistance (MDR) mediated by the overexpression of MDR1/P-gp can be intrinsic, or induced by a variety of chemical and physical insults such as cytotoxic agents, arsenite, heat shock, and UV irradiation [3], [4], [5], [6], [7], [8], and the transcriptional activation of the MDR1 gene is a highly regulated complex event and is associated with several signaling pathways. For example, our laboratory demonstrated that activation of the phospholipase C/Raf/mitogen-activated protein kinase pathway stimulates the transcription of the MDR1 gene and expression of P-gp, and this pathway can be activated by heat shock, platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) [9]. We also showed that the activation of the MDR1 gene transcription requires involvement of a number of transcriptional factors such as C-terminal-binding protein 1 (CtBP1) [10]. Nevertheless, the precise mechanism(s) underlying the activation of MDR1 gene expression is still not fully understood. We previously reported the inhibitory effect of small interfering RNA (siRNA) on MDR1/P-gp expression and the feasibility of using RNA interference (RNAi) approach to modulate MDR phenotype [11]. These studies have led to a better understanding of the regulation of the expression of MDR1 gene, and have helped to develop new strategies to inhibit or prevent the induction of MDR1/P-gp expression. To further understand the roles of small RNA molecules in the regulation of drug resistance genes, we investigated the involvement of microRNAs (miRNA) in controlling MDR phenotype mediated by MDR1/P-gp. MiRNAs are a class of endogenous, 19–25 nucleotides RNA molecules that are able to induce mRNA degradation, translational repression, or both, via pairing with partially complementary sites in the 3′ UTR of the targeted genes [12]. It is estimated that there are over 600 miRNAs in mammalian cells, and that 30% of all genes are regulated by miRNAs. Because miRNAs have the ability to target numerous mRNAs, these small RNA molecules can operate highly complex regulatory networks and regulate the expression of genes in many pathways that are associated with tumor initiation, development and progression. Through regulating gene expression, miRNAs can have a profound impact on many patho-physiologic processes, including proliferation, apoptosis, and stress response [13], [14]. In the current study, we observed that miRNAs were differentially expressed in MDR cancer cells, and demonstrated that expressions of miRNA 27a and 451 are associated with the activation of MDR1/P-gp expression and contribute to drug resistance in cancer cells.