title: Parathyroid hormone inhibition of Na(+)/H(+) exchanger 3 transcription: Intracellular signaling pathways and transcription factor expression.
abstract: The main transport mechanism of reabsorption of sodium bicarbonate and fluid in the renal proximal tubules involves Na(+)/H(+) exchanger 3 (NHE3), which is acutely and chronically downregulated by parathyroid hormone (PTH). Although PTH is known to exert an inhibitory effect on NHE3 expression and transcription, the molecular mechanisms involved remain unclear. Here, we demonstrated that, in opossum kidney proximal tubule (OKP) cells, PTH-induced inhibition of Nhe3 gene promoter occurs even in the core promoter that controls expression of the reporter gene. We found that inhibition of the protein kinase A (PKA) and Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways transformed PTH from an inhibitor of promoter activity into an activator of that same activity, as did point mutations in the EGR1, Sp1, and Sp3 binding consensus elements in the promoter. In nuclear extracts of PTH-treated OKP cells, we also observed increased expression of EGR1 mRNA and of some Sp3 isoforms. Electrophoretic mobility shift assay showed a supershift of the -61 to -42-bp probe with an anti-EGR1 antibody in PTH-treated cells, suggesting that EGR1 binding is relevant for the inhibitory activity of PTH. We conclude that PTH-induced inhibition of NHE3 transcription is related to higher EGR1 expression; to EGR1 binding to the proximal and core promoters; and to PKA and JAK/STAT pathway activation. This mechanism might be responsible, at least in part, for lower NHE3 expression and sodium reabsorption in renal proximal tubules in the presence of high PTH levels.
authors.affiliation: Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Elida Adalgisa
authors.initials: EA
authors.lastname: Neri
authors.affiliation: Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil. Electronic address: camilab@icb.usp.br.
authors.forename: Camila Nogueira Alves
authors.initials: CN
authors.lastname: Bezerra
authors.affiliation: Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Gabriella Duarte
authors.initials: GD
authors.lastname: Queiroz-Leite
authors.affiliation: Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Juliano Zequini
authors.initials: JZ
authors.lastname: Polidoro
authors.affiliation: Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Nancy Amaral
authors.initials: NA
authors.lastname: Rebouças
mesh_terms: D000818:Animals; D002460:Cell Line; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009893:Opossums; D010281:Parathyroid Hormone / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects / Q000235:genetics*
chemical_list: D010281:Parathyroid Hormone; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D014157:Transcription Factors
keywords: OKP cells; Proximal tubule; Sodium hydrogen exchanger; Transcriptional regulation