Dual role of cAMP in the transcriptional regulation of multidrug resistance-associated protein 4 (MRP4) in pancreatic adenocarcinoma cell lines.

Alejandro Carozzo,Carlos Davio,Maia Cabrera,Natalia Fernández,Natalia Gomez,Carina Shayo,Federico Diez,Rebecca Berdeaux

doi:10.1371/journal.pone.0120651

Abstract

Cyclic AMP represents one of the most studied signaling molecules and its role in proliferation and differentiation processes has been well established. Intracellular cAMP levels are tightly regulated where the MRP4 transporter plays a major role. In the present study, we sought to establish whether cAMP modulated MRP4 expression in pancreatic adenocarcinoma cell lines. Quantitative PCR and western blot studies showed that cAMP-increasing agents enhanced MRP4 transcripts and protein levels in PANC-1 cells. Reporter luciferase experiments carried out in pancreatic AR42J cells showed that intracellular cAMP up-regulates MRP4 through an Epac2- and Rap1- mediated mechanism whereas extracellular cAMP reduced MRP4 promoter activity by a MEK/ERK-mediated pathway. Present results show that cAMP regulates MRP4 promoter activity, and further indicate that the balance between intracellular and extracellular cAMP levels determines MRP4 expression.

Highlights

Cyclic AMP, the first second messenger discovered, is one of the most studied signaling molecules and plays a critical role in cellular responses to extracellular stimuli
In order to evaluate the role of Cyclic AMP (cAMP) in modulating Multidrug-Resistance Protein 4 (MRP4) expression in pancreatic cell lines, MRP4 mRNA transcripts were assessed by real-time PCR
In accordance, when MRP4 protein levels were analyzed by western blot, we observed a significant increase in MRP4 expression in cells exposed to forskolin, db-cAMP and IBMX (Fig. 1B)

Summary

Introduction

Cyclic AMP (cAMP), the first second messenger discovered, is one of the most studied signaling molecules and plays a critical role in cellular responses to extracellular stimuli It controls a wide spectrum of biological effects including cell proliferation, differentiation, and apoptosis. The intracellular regulation of cAMP depends on the balance between its production by adenylyl cyclase, an enzyme stimulated by diverse hormones and neurotransmitters, and its degradation by phosphodiesterases (PDEs) [1]. Recent studies support that the efflux of cAMP through members of the multidrug associated resistance protein family (MRPs) like MRP4, MRP5, and MRP8, constitutes an additional relevant mechanism involved in the regulation of cAMP signaling [2,3,4,5].

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