Regulation of MDR-1 (P-glycoprotein) by Cyclooxygenase-2

Vimal A Patel,Michael J Dunn,Andrey Sorokin

doi:10.1074/jbc.m206855200

Vimal A Patel, Michael J Dunn + Show 1 more

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https://doi.org/10.1074/jbc.m206855200

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Abstract

Cyclooxygenase-2 (Cox-2), an inducible form of the enzyme that catalyzes the first step in the synthesis of prostanoids, has been shown to be overexpressed in a wide range of tumors and possesses proangiogenic and antiapoptotic properties. To understand the molecular mechanism of Cox-2 action we used adenovirus-mediated transfer of rat Cox-2 cDNA into renal rat mesangial cells and determined the differential gene expression using cDNA microarrays. One of the several genes that were highly up-regulated by over expressed Cox-2 was MDR1. MDR1 or P-glycoprotein (P-gp), the product of the MDR1 gene, is implicated as the primary cause of multidrug resistance (MDR) in tumors where it acts as an efflux pump for chemotherapeutic agents. It is also expressed in normal tissues of the liver and kidney where it functions to actively transport lipophilic xenobiotics. Reverse transcriptase-PCR analysis confirmed the results of the microarray, showing increased mRNA levels for MDR1 in Cox-2 overexpressing cells. This increase in mRNA translated to an increase in MDR1 protein expression, which was dose-dependent on Cox-2 expression. Furthermore, using rhodamine 123 efflux assay we observed a significant increase in P-gp activity in Cox-2 overexpressing renal mesangial cells. The specific Cox-2 inhibitor NS398 was able to block the Cox-2-mediated increase in MDR1 expression and activity, suggesting that Cox-2 products may be implicated in this response. These results prove the existence of a causal link between Cox-2 and P-gp activity, which would have implications for kidney function and multidrug resistance in tumors where Cox-2 is overexpressed.

Highlights

Cyclooxygenase (Cox),1 known as prostaglandin endoperoxide synthase, is the key enzyme required for the conversion of arachidonic acid to prostaglandins [1]
To identify the differential gene expression as a result of Cox-2 overexpression, AtlasTM rat stress cDNA expression arrays (Clontech) were screened with 32P-labeled cDNA generated from mRNA from RMC infected with AdCox-2 or Ad5-based green fluorescent protein expression vector (AdGFP)
Of genes that were up-regulated in RMC MDR1 or P-gp showed the most significant increase, and because of the roles of Cox-2 and P-gp in cancer we investigated this correlation further

Summary

Introduction

Cyclooxygenase (Cox), known as prostaglandin endoperoxide synthase, is the key enzyme required for the conversion of arachidonic acid to prostaglandins [1]. A new class of Cox-2 selective inhibitors (COXIBs) preferentially inhibit the Cox-2 enzyme thereby reducing side effects such as gastrointestinal ulceration and bleeding and platelet dysfunction caused by inhibiting Cox-1. These specific Cox-2 inhibitors have emerged as important therapeutic tools for treatment of pain and arthritis [3]. P-gp is present in the brush border membrane of the proximal tubule [9, 11], a site compatible with a role in xenobiotic secretion It is expressed in the mesangium, the thick ascending limb of Henle’s loop, and the collecting duct [11], locations that are not traditionally associated with drug excretion.

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