Glucocorticoids inhibit transcription and expression of the UT-A urea transporter gene.
Dexamethasone treatment increases urea excretion and decreases urea permeability and urea transporter UT-A1 protein abundance in the inner medullary collecting duct (IMCD) of adrenalectomized rats. We examined the effect of dexamethasone treatment for 3 days on the abundance of several UT-A mRNA transcripts in rat renal medulla. By Northern blot analysis, a significant decrease in mRNA expression was observed in the inner medulla of dexamethasone-treated rats compared with controls for UT-A1 (71%), UT-A3 (75%), and UT-A3b (75%), but not for UT-A2. We then tested the effect of 100 nM dexamethasone on the activity of promoter I in the UT-A gene, using LLC-PK(1)-GR101 cells that express the glucocorticoid receptor. Dexamethasone significantly decreased the activity of rat UT-A promoter I (72%) but did not affect UT-A promoter II. Deletion analysis and site-directed mutagenesis demonstrated that sequences between -423 and -244 are important for this inhibition and that a 10-bp sequence at -363, which binds a nuclear protein in a gel shift assay, is necessary for basal promoter activity. The specific factors involved in repression of UT-A promoter I activity by glucocorticoids remain to be determined.
Peng
Tao
T
Department of Pathology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Sands
Jeff M
JM
Bagnasco
Serena M
SM
D000818:Animals; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics*; D003907:Dexamethasone / Q000494:pharmacology; D017353:Gene Deletion; D015870:Gene Expression / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology*; D007679:Kidney Medulla / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000235:genetics*; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic / Q000187:drug effects; D000096982:Urea Transporters
D002352:Carrier Proteins; D003907:Dexamethasone; D005938:Glucocorticoids; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; D000096982:Urea Transporters