The core promoter region of the P-glycoprotein gene is sufficient to confer differential responsiveness to wild-type and mutant p53.
The overexpression of P-glycoprotein is thought to be responsible for resistance to chemotherapy in some non-responsive cancers. The mechanism by which P-glycoprotein is overexpressed in human tumors is poorly understood. However, several lines of evidence suggest that the major regulatory mechanism of P-glycoprotein overexpression in human tumors is at the transcriptional level. During tumor progression one of the most commonly observed alterations is mutation of the p53 tumor-suppressor gene. It has been shown that the p53 protein plays a role in transcriptional regulation. To gain insight into the effect p53 protein may have on P-glycoprotein promoter activity, we transiently co-transfected plasmids containing the hamster pgp1 or human mdr1 promoter linked to the chloramphenicol acetyltransferase (CAT) reporter gene with plasmids encoding either wild-type or mutant p53 protein into Chinese hamster ovary (CHO) cells. In this report, we show that wild-type p53 protein represses P-glycoprotein promoter activity, while mutant forms of p53 protein enhance P-glycoprotein promoter activity. Furthermore, we present data which indicate that the transcriptional regulatory effects of p53 are mediated through interactions with pgp1/mdr1 core promoter sequences. These findings have implications for our understanding of the molecular mechanism(s) by which p53 protein functions as a transcriptional regulator of gene expression. In addition, our results suggest a mechanism by which P-glycoprotein may be overexpressed in human cancers that also express mutant forms of p53 protein.
Ontario Cancer Institute, University of Toronto, Canada.
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Zastawny
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Salvino
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Chen
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Benchimol
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Ling
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D006224:Cricetinae; D004351:Drug Resistance / Q000235:genetics*; D016158:Genes, p53; D006023:Glycoproteins / Q000235:genetics*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D010957:Plasmids; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D015183:Restriction Mapping; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
D006023:Glycoproteins; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D016159:Tumor Suppressor Protein p53; D015500:Chloramphenicol O-Acetyltransferase