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p53-dependent regulation of MDR1 gene expression causes selective resistance to chemotherapeutic agents
J V Thottassery1, G P Zambetti, K Arimori
1Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, 332 North Lauderdale Avenue, Memphis, TN 38105, USA.
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.
Insights
Loss of p53 function paradoxically alters cancer drug resistance by upregulating the multidrug resistance gene (MDR1). This explains why p53 inactivation can lead to selective resistance to chemotherapy agents.
Area of Science:
- Molecular Biology
- Cancer Biology
- Pharmacology
Background:
- The tumor suppressor protein p53 plays a critical role in cellular responses to DNA damage and stress.
- The relationship between p53 status and sensitivity to chemotherapeutic drugs is complex and often contradictory.
- Multidrug resistance (MDR) mediated by P-glycoprotein (Pgp) is a major challenge in cancer chemotherapy.
Purpose of the Study:
- To investigate the hypothesis that wild-type p53 regulates the expression of the multidrug resistance gene (MDR1).
- To elucidate the mechanism by which p53 inactivation influences drug sensitivity in cancer cells.
- To determine if p53-dependent regulation of MDR1 contributes to chemotherapeutic resistance.
Main Methods:
- Stable introduction of a trans-dominant negative (TDN) p53 into rodent H35 hepatoma cells and human LS180 colon carcinoma cells.
- Analysis of P-glycoprotein (Pgp) and mdr1a mRNA levels.
- Functional assessment of Pgp activity using vinblastine uptake assays.
- Cytotoxicity assays with Pgp substrate drugs and Pgp inhibitor reserpine.
Main Results:
- Expression of TDN p53 led to significantly elevated levels of Pgp and mdr1a mRNA in both rodent and human cell lines.
- Impaired p53 function (transactivation and transrepression) was associated with increased mdr1a gene expression.
- TDN p53 cell lines exhibited reduced sensitivity to Pgp substrates, which was reversed by reserpine, indicating drug retention as the cause.
- MDR1 gene amplification was ruled out as the cause of increased mdr1a expression.
Conclusions:
- Inactivation of p53 function leads to the upregulation of the multidrug resistance gene (MDR1) and P-glycoprotein (Pgp) expression.
- This p53-dependent upregulation of MDR1 confers selective resistance to chemotherapeutic agents that are substrates for Pgp.
- Understanding this mechanism provides insights into therapeutic resistance in cancers with p53 mutations and suggests potential strategies to overcome it.