Regulation of Na+/H+ exchanger-NHE3 by angiotensin-II in OKP cells.
Previous studies have shown that circulating Angiotensin II (A-II) increases renal Na+ reabsorption via elevated Na+/H+ exchanger isoform 3 (NHE3) activity. We hypothesized that prolonged exposure to A-II leads to an increased expression of renal NHE3 by a transcriptionally mediated mechanism. To test this hypothesis, we utilized the proximal tubule-like OKP cell line to evaluate the effects of 16-h treatment with A-II on NHE3 activity and gene expression. A-II significantly stimulated NHE3-mediated, S-3226-sensitive Na+/H+ exchange. Inhibition of transcription with actinomycin D abolished the stimulatory effect of A-II on NHE3-mediated pH recovery in acid-loaded OKP cells. This prolonged exposure to A-II was also found to elevate endogenous NHE3 mRNA (by 40%)-an effect also abolished by inhibition of gene transcription. To evaluate the molecular mechanism by which A-II regulates NHE3 expression, the activity of NHE3 promoter driven reporter gene was analyzed in transient transfection assays. In transfected OKP cells, rat NHE3 promoter activity was significantly stimulated by A-II treatment, and preliminary mapping indicated that the A-II responsive element(s) is present between 149 and 548 bp upstream of the transcription initiation site in the NHE3 gene promoter. We conclude that a transcriptional mechanism is at least partially responsible for the chronic effects of A-II treatment on renal NHE3 activity.
Xu
Liping
L
Department of Pediatrics and Physiology, Steele Children's Research Center, University of Arizona Health Sciences Center, 1501 N. Campbell Avenue, Tucson, AZ 85724, USA.
Dixit
Mehul P
MP
Nullmeyer
Kevin D
KD
Xu
Hua
H
Kiela
Pawel R
PR
Lynch
Ronald M
RM
Ghishan
Fayez K
FK
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007668:Kidney; D007700:Kinetics; D009893:Opossums; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology
D017931:DNA Primers; D004791:Enzyme Inhibitors; D006146:Guanidines; D012333:RNA, Messenger; D011994:Recombinant Proteins; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; D000804:Angiotensin II; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine