Transcription factors that mediate epithelial–mesenchymal transition lead to multidrug resistance by upregulating ABC transporters

M Saxena,M A Stephens,A Rangarajan,H Pathak

doi:10.1038/cddis.2011.61

Abstract

Development of multidrug resistance (MDR) is a major deterrent in the effective treatment of metastatic cancers by chemotherapy. Even though MDR and cancer invasiveness have been correlated, the molecular basis of this link remains obscure. We show here that treatment with chemotherapeutic drugs increases the expression of several ATP binding cassette transporters (ABC transporters) associated with MDR, as well as epithelial–mesenchymal transition (EMT) markers, selectively in invasive breast cancer cells, but not in immortalized or non-invasive cells. Interestingly, the mere induction of an EMT in immortalized and non-invasive cell lines increased their expression of ABC transporters, migration, invasion, and drug resistance. Conversely, reversal of EMT in invasive cells by downregulating EMT-inducing transcription factors reduced their expression of ABC transporters, invasion, and rendered them more chemosensitive. Mechanistically, we demonstrate that the promoters of ABC transporters carry several binding sites for EMT-inducing transcription factors, and overexpression of Twist, Snail, and FOXC2 increases the promoter activity of ABC transporters. Furthermore, chromatin immunoprecipitation studies revealed that Twist binds directly to the E-box elements of ABC transporters. Thus, our study identifies EMT inducers as novel regulators of ABC transporters, thereby providing molecular insights into the long-standing association between invasiveness and MDR. Targeting EMT transcription factors could hence serve as novel strategies to curb both metastasis and the associated drug resistance.

Highlights

Cancers can either be inherently drug resistant before drug exposure or can acquire drug resistance after the administration of drugs.[2]
We have investigated the role of epithelial–mesenchymal transition (EMT)-inducing transcription factors in drug resistance mediated by ABC transporters in breast cancer cells
To assess the basal level of expression of the 16 ABC transporters implicated in drug resistance,[5] we undertook a detailed reverse transcriptase polymerase chain reaction (RT-PCR)-based analysis in nine breast epithelial cell lines comprising of immortalized, non-invasive and invasive cell types for our study

Summary

Introduction

Cancers can either be inherently drug resistant before drug exposure or can acquire drug resistance after the administration of drugs.[2]. ABC transporters form the largest transportome in the human genome.[4] They are ubiquitously and heterogeneously expressed in various body tissues and important pharmacological barriers where they have a pivotal role in host cell detoxification and protection of the body against xenobiotics.[1,2] ABC transporters are overexpressed in several cancers.[1,2] These transporters actively efflux a wide spectrum of commonly employed chemotherapeutic drugs like estramustine, mitoxantrone, anthracyclines, vinca alkaloids, taxanes, thiopurines, and so on.[5] Recently, as many as 16 ABC transporters have been implicated in MDR.[5] understanding the mechanisms that regulate ABC transporter expression becomes imperative in addressing the problem of MDR. We have investigated the role of EMT-inducing transcription factors in drug resistance mediated by ABC transporters in breast cancer cells. We demonstrate that the very transcription factors that lead to EMT and invasion orchestrate the overexpression of drug transporters by directly modulating their promoter activity, providing a novel molecular mechanism for the long-standing association between invasiveness and drug resistance

Methods

Results

Conclusion