title: Regulation of the Mdr1 isoforms in a p53-deficient mouse model.
abstract: Both p53 and multidrug transporters play important roles in chemoresistance. A transcriptional dependence of the Mdr1 gene promoter by p53 was first established a decade ago, and despite intense study, the p53-Mdr1 relationship still remains vague in vivo. The general model proposes that wild-type p53 down regulates, while mutant p53 up regulates, the Mdr1 promoter. Given that many studies have utilized cancer cell lines, minimal promoters and non-specific cDNA expression for in vitro experiments, we first sought to confirm the model using dermal fibroblasts isolated from the p53-knockout mice. We show that the gene products of the mouse Mdr1 homologue (Mdr1a and Mdr1b), namely P-glycoprotein (P-gp), appear upregulated at both the protein and mRNA levels in p53(-/-) mFbs compared with p53(+/+) cells. We demonstrate that transient transfection of a mouse p53(WT) expression plasmid into short-term primary p53(-/-) fibroblasts can revert P-gp overexpression. The difference in P-gp levels has functional significance in that p53(-/-) fibroblasts are more resistant to doxorubicin and vincristine treatment and this resistance can be attenuated in the presence of the P-gp inhibitor, verapamil. Furthermore, we demonstrate that in kidney, spleen and testis, P-gp expression is elevated in the absence of p53. In contrast, other organs such as heart, liver, lung, brain, thymus and skeletal muscle, show no difference in expression between p53(+/+) and p53(-/-) mice. Thus, our data shows a tissue-specific regulation of P-gp isoforms by p53 in the context of a p53-null mouse model.
authors.affiliation: Division of Dermatology, Department of Medicine, Vancouver Hospital and Health Sciences Centre, University of British Columbia, Vancouver, British Columbia V6H 3Z6, Canada.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Bush
authors.forename: Gang
authors.initials: G
authors.lastname: Li
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D005786:Gene Expression Regulation; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D017931:DNA Primers; D020033:Protein Isoforms; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53