title: Expression and activity of p-glycoprotein elevated by dexamethasone in cultured retinal pigment epithelium involve glucocorticoid receptor and pregnane X receptor.
abstract: OBJECTIVE
  To investigate whether dexamethasone has an effect on functional expression of p-glycoprotein in cultured human RPE and, if so, whether this occurs through interaction with glucocorticoid receptor (GR) and pregnane X receptor (PXR).
  
  
  METHODS
  The human RPE D407 was treated with increasing concentrations of dexamethasone and/or RU486 for various time periods up to 24 hours. Treated cells were collected for cell viability, expressions of p-glycoprotein and PXR, and rhodamine 123 accumulation assays. GR expression plasmid and rifampicin were chosen to investigate the relationship of GR/PXR activation and p-glycoprotein expression.
  
  
  RESULTS
  Significant increases in p-glycoprotein, as indicated by mRNA and protein levels, as well as by functional activity, were induced within 12 hours of dexamethasone treatment, persisted as long as 24 hours, and were dose-dependent and attenuable with coculture of RU486. In parallel, a dose-dependent upregulation of PXR was notable at both mRNA and protein levels by 24 hours of dexamethasone treatment, and was partially reversible with RU486 coculture. Additionally, transfection of GR expression plasmid increased the transitional expressions of PXR and p-glycoprotein in untreated cells, and enhanced PXR transcriptional expression in dexamethasone-treated cells. Further, PXR silencing inhibited the dexamethasone-induced p-glycoprotein alterations; however, rifampicin had no apparent effects on the dexamethasone-induced p-glycoprotein alterations.
  
  
  CONCLUSIONS
  Our results suggest for the first time that expression and activation of p-glycoprotein involve GR and PXR in human RPE.
authors.affiliation: Department of Ophthalmology and Anesthesiology, First Municipal People's Hospital of Guangzhou, Affiliated Hospital of Guangzhou Medical College, Guangzhou, China.
authors.forename: Yuehong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Min
authors.initials: M
authors.lastname: Lu
authors.forename: Xuerong
authors.initials: X
authors.lastname: Sun
authors.forename: Chunmei
authors.initials: C
authors.lastname: Li
authors.forename: Xielan
authors.initials: X
authors.lastname: Kuang
authors.forename: Xiangcai
authors.initials: X
authors.lastname: Ruan
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002470:Cell Survival; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005938:Glucocorticoids / Q000494:pharmacology*; D006727:Hormone Antagonists / Q000494:pharmacology; D006801:Humans; D008858:Microscopy, Phase-Contrast; D015735:Mifepristone / Q000494:pharmacology; D010957:Plasmids / Q000235:genetics; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism*; D011987:Receptors, Steroid / Q000235:genetics / Q000378:metabolism*; D055213:Retinal Pigment Epithelium / Q000187:drug effects* / Q000378:metabolism; D020112:Rhodamine 123 / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D005938:Glucocorticoids; D006727:Hormone Antagonists; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D011987:Receptors, Steroid; D020112:Rhodamine 123; D015735:Mifepristone; D003907:Dexamethasone