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

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 ref lect 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.

Effects of Multidrug Resistance Gene Expression in Acute Erythroleukemia

“…Besides its role in unregulated proliferation and clonal expansion, mutated p53 has been shown specifically to stimulate the MDR-1 promoter, whereas wild-type p53 represses it (13,14). P53 mutation does not lead to generalized drug resistance but rather causes selective resistance to P-glycoprotein substrates and increases sensitivity of the tumor cells to other drugs, such as methotrexate (13).…”

“…P53 mutation does not lead to generalized drug resistance but rather causes selective resistance to P-glycoprotein substrates and increases sensitivity of the tumor cells to other drugs, such as methotrexate (13). An extensive study demonstrating this decreased growth inhibition by chemotherapeutic agents (drug resistance) in the presence of p53 mutations was recently reported (15).…”

“…An extensive study demonstrating this decreased growth inhibition by chemotherapeutic agents (drug resistance) in the presence of p53 mutations was recently reported (15). P-glycoprotein is a transmembrane protein that functions as an energy-dependent drug efflux pump for selective resistance to anthracyclines (daunorubicin and doxorubicin), vinca alkaloids, podophyllotoxins (etoposide), antimicrotubule agents (paclitaxel and colchicine), and actinomycin D (1,13,16,17). This multidrug resistance may be reversed or overcome by such agents as calciumchannel blockers, analogs of anthracyclines and vinca alkaloids, steroids and hormonal analogs, cyclosporine analogs, and miscellaneous hydrophobic cationic compounds (3, 18 -20).…”

Cell type dependent regulation of multidrug resistance-1 gene expression by AML1-ETO

“…Scott Hiebert (Nashville, TN) and John Schuetz (Memphis, TN) [29]. The AML1 point mutation within the MDR1 promoter-luciferase construct was made using the Stratagene Quickchange kit following the manufacturer's protocol with the following oligonucleotides to mutate the consensus AML1 binding site within the MDR1 promoter from 5′-TGTGGT-3′ to 5′-TGTTAG-3′ [30]: 5′-CGGGAGCAGTCATCTAGGAGGCAGATTGGCTGGG-3′ and 5′-CCCAGCCAATCAGCCTCCTAACAGATGACTGCTCCCG-3′.…”

Transcriptional regulation of MDR genes

“…Recently, the effect of p53 on endogenous MDR1 activity has been evaluated. In one study, a dominant negative p53 expression vector was stably transfected into rodent H35 hepatoma cells that express Pgp and wild-type p53 (Thottassery, 1997). The levels of Pgp mRNA and protein were markedly elevated in these stable transfectants, and this increase was accompanied by an increase in resistance to MDR drugs.…”