title: Expression of alpha-ENaC2 is dependent on an upstream Sp1 binding motif and is modulated by protein phosphatase 1 in lung epithelial cells.
abstract: The amiloride-sensitive Na(+) channel ENaC is expressed in lung epithelium and plays a pivotal role in lung fluid clearance in the newborn. Multiple splice variants of the ENaC alpha-subunit have been reported. Among them, alpha-ENaC2 accounts for a considerable portion of alpha-ENaC transcripts in human lung and kidney, possesses channel functions similar to alpha-ENaC1, and is driven by a downstream promoter. In the current study, we examine the regulation of alpha-ENaC2 transcription in lung epithelial cells. We found that transcription factors Sp1 and Sp3 activate alpha-ENaC2 transcription through a GC-rich element (Sp1-binding site) in the promoter. Because alpha-ENaC expression and Sp1 phosphorylation are both significantly up-regulated in the perinatal lung, we then examined the possible connection between Sp1/Sp3 phosphorylation and alpha-ENaC2 expression. We found that protein phosphatase 1 (PP1) dephosphorylates Sp1 and Sp3 in lung epithelial cells, reduces their binding to the alpha-ENaC2 promoter, and decreases Sp1/Sp3-mediated promoter activity. Our results suggest that Sp1 and Sp3 are essential for alpha-ENaC2 transcription in lung epithelial cells and that dephosphorylation of the Sp transcription factors by PP1 suppresses alpha-ENaC2 expression. The significance of these findings in the regulation of gene expression in perinatal lung is discussed.
authors.affiliation: Department of Veterans Affairs Medical Center, McGuire Research Institute, Richmond, VA 23249, USA. schu@hsc.vcu.edu
authors.forename: Shijian
authors.initials: S
authors.lastname: Chu
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Cockrell
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Ferro
mesh_terms: D000328:Adult; D001483:Base Sequence; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D053503:Epithelial Sodium Channels; D005260:Female; D006801:Humans; D008168:Lung / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000502:physiology*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D054645:Protein Phosphatase 1; D020218:Response Elements; D015222:Sodium Channels / Q000235:genetics*; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D051705:Sp3 Transcription Factor; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; D053503:Epithelial Sodium Channels; C497121:SP3 protein, human; D015222:Sodium Channels; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D051705:Sp3 Transcription Factor; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1