title: Regulation of drug resistance by human pregnane X receptor in breast cancer.
abstract: Drug resistance is a significant barrier to an effective treatment of breast cancer. Human pregnane X receptor (hPXR), an orphan nuclear receptor known for its activation by many important clinical drugs, is a major transcription factor of drug metabolism enzymes (DMEs), such as cytochrome P450 3A4 (CYP3A4), and efflux transporters such as multi-drug resistance gene (MDR1). hPXR has been detected in human breast cancers but its role in responses of cancers toward drugs remains unknown. In this study, hPXR expression was confirmed in breast cancer cell lines and in normal and cancerous human breast specimens. Preactivation of hPXR by SR12813 in MDA-MB-231 cells led to an increased resistance to Taxol at concentrations of 20 and 50 nmol/L. A significant increase in resistance toward tamoxifen was also observed in MCF-7 with hPXR preactivation. Activation of hPXR led to an increased expression of CYP3A4 and MDR1, two possible mediators for hPXR-mediated drug resistance in breast cancers. Furthermore, knockdown of hPXR via small hairpin RNA (shRNA) sensitized MDA-MB-231 and MCF-7 cells to the treatment of Taxol, vinblastine or tamoxifen. The reduction in resistance of hPXR knockdown cells was further confirmed by reduced colony formation under the pressure of cancer treatment drugs. Taken together, our data suggest a potential role of hPXR in breast cancer resistance to drug treatments.
authors.affiliation: Department of Medical Microbiology, Immunology and Cell Biology, Southern Illinois University, School of Medicine and Simmons Cooper Cancer Institute, Springfield, IL 62794-9626, USA.
authors.forename: Yakun
authors.initials: Y
authors.lastname: Chen
authors.forename: Yong
authors.initials: Y
authors.lastname: Tang
authors.forename: Shuqing
authors.initials: S
authors.lastname: Chen
authors.forename: Daotai
authors.initials: D
authors.lastname: Nie
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D051544:Cytochrome P-450 CYP3A / Q000235:genetics / Q000378:metabolism; D004164:Diphosphonates / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D017239:Paclitaxel / Q000494:pharmacology; D000077297:Pregnane X Receptor; D034622:RNA Interference; D011987:Receptors, Steroid / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004164:Diphosphonates; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid; C100355:SR 12813; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D017239:Paclitaxel