title: Transcriptional stimulation of the human NHE3 promoter activity by PMA: PKC independence and involvement of the transcription factor EGR-1.
abstract: NHE3 (Na+/H+ exchanger 3) is essential for Na+ absorption in the ileum and is expressed in a cell-specific manner in the apical membrane of the intestinal epithelial cells. In the present study, we report the stimulatory effect of PMA on the hNHE3 (human NHE3) transcription. Pretreatment with actinomycin D or cycloheximide blocked the up-regulation of the NHE3 mRNA by PMA, indicating that the increased level of NHE3 mRNA expression is regulated by transcriptional activation and is dependent on de novo protein synthesis. 5'-Deletion of the promoter region and transfection analysis in C2BBe1 cells revealed that the PMA effect is mediated through a GC-rich DNA region between nt -88 and -69. Gel mobility-shift assays demonstrated that in nuclear extracts from C2BBe1 cells grown under the basal growth conditions, Sp1 (stimulating protein-1) and Sp3 interact with this GC-rich DNA region, while, in PMA-treated nuclear extracts, PMA-induced EGR-1 (early growth response gene product 1) transcription factor binds to the same site. Binding of EGR-1 diminished the Sp1 and Sp3 interactions with this promoter region significantly. Co-transfection of Sp1 or Sp3 into SL2 cells activated the NHE3-reporter constructs, suggesting that Sp1 and Sp3 act as positive regulators of the NHE3 expression. In addition, overexpression of EGR-1 was sufficient to transactivate the NHE3-reporter gene activity, and knockdown of EGR-1 with gene-specific small interfering RNA resulted in inhibition of the PMA-induced up-regulation of the endogenous NHE3 mRNA expression. Furthermore, the PKC (protein kinase C) inhibitor chelerythrine chloride did not affect PMA-induced NHE3 promoter activity, suggesting that PMA stimulation of the hNHE3 gene expression may be PKC-independent.
authors.affiliation: Section of Digestive and Liver Diseases, Department of Medicine, University of Illinois at Chicago, 840 South Wood Street, Chicago, IL 60612, USA. malakoot@uic.edu
authors.forename: Jaleh
authors.initials: J
authors.lastname: Malakooti
authors.forename: Ricardo
authors.initials: R
authors.lastname: Sandoval
authors.forename: Md Ruhul
authors.initials: MR
authors.lastname: Amin
authors.forename: Jeremy
authors.initials: J
authors.lastname: Clark
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Dudeja
authors.forename: Krishnamurthy
authors.initials: K
authors.lastname: Ramaswamy
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001483:Base Sequence; D018938:Caco-2 Cells; D002478:Cells, Cultured; D004330:Drosophila / Q000378:metabolism; D029721:Drosophila Proteins / Q000378:metabolism; D051766:Early Growth Response Protein 1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism*; D015398:Signal Transduction; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000378:metabolism; D051705:Sp3 Transcription Factor / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D029721:Drosophila Proteins; D051766:Early Growth Response Protein 1; D009687:Nuclear Proteins; C000613385:SLC9A3 protein, human; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D016329:Sp1 Transcription Factor; C403210:Sp1 protein, Drosophila; D051705:Sp3 Transcription Factor; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate