p53-dependent regulation of MDR1 gene expression causes selective resistance to chemotherapeutic agents

p53-dependent regulation of MDR1 gene expression causes selective resistance to chemotherapeutic agents

Departments of ^*Pharmaceutical Sciences and ^†Biochemistry, St. Jude Children’s Research Hospital, 332 North Lauderdale Avenue, Memphis, TN 38105; and ^‡Department of Pharmacy, Kumamoto University Hospital, Honjo, Kumamoto 360, Japan

Edited by George R. Stark, Cleveland Clinic Foundation, Cleveland, OH, and approved July 24, 1997 (received for review May 7, 1997)

Abstract

Loss of functional p53 paradoxically results in either increased or decreased resistance to chemotherapeutic drugs. The inconsistent relationship between p53 status and drug sensitivity may reflect p53’s selective regulation of genes important to cytotoxic response of chemotherapeutic agents. We reasoned that the discrepant effects of p53 on chemotherapeutic cytotoxicity is due to p53-dependent regulation of the multidrug resistance gene (MDR1) expression in tumors that normally express MDR1. To test the hypothesis that wild-type p53 regulates the endogenous mdr1 gene we stably introduced a trans-dominant negative (TDN) p53 into rodent H35 hepatoma cells that express P-glycoprotein (Pgp) and have wild-type p53. Levels of Pgp and mdr1a mRNA were markedly elevated in cells expressing TDN p53 and were linked to impaired p53 function (both transactivation and transrepression) in these cells. Enhanced mdr1a gene expression in the TDN p53 cells was not secondary to mdr1 gene amplification and Pgp was functional as demonstrated by the decreased uptake of vinblastine. Cytotoxicity assays revealed that the TDN p53 cell lines were selectively insensitive to Pgp substrates. Sensitivity was restored by the Pgp inhibitor reserpine, demonstrating that only drug retention was the basis for loss of drug sensitivity. Similar findings were evident in human LS180 colon carcinoma cells engineered to overexpress TDN p53. Therefore, the p53 inactivation seen in cancers likely leads to selective resistance to chemotherapeutic agents because of up-regulation of MDR1 expression.

Footnotes

↵ § To whom reprint requests should be addressed. e-mail: john.schuetz{at}stjude.org.
This paper was submitted directly (Track II) to the Proceedings Office.
Abbreviations: PGP, human P-glycoprotein; Pgp, rodent P-glycoprotein; TDN, trans-dominant negative; CMV, cytomegalovirus; LDH, lactate dehydrogenase; MTX, methotrexate.
↵ ¶ MDR1 refers throughout to the human multidrug resistance gene or mRNA encoding the drug-transporting PGP protein, and mdr1a and mdr1b refer to the two drug-transporting rodent mdr1 genes or mRNA encoding Pgp.