Genomic organization of the 5′ end of human β-ENaC and preliminary characterization of its promoter

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Abstract
The mRNA for the β-subunit of the epithelial Na+channel (β-ENaC) is regulated developmentally and, in some tissues, in response to corticosteroids. To understand the mechanisms of transcriptional regulation of the human β-ENaC gene, we characterized the 5′ end of the gene and its 5′-flanking regions. Adaptor-ligated human kidney and lung cDNA were amplified by 5′ rapid amplification of cDNA ends, and transcription start sites of two 5′ variant transcripts were determined by nuclease protection or primer extension assays. Cosmid clones that contain the 5′ end of the gene were isolated, and analysis of these clones indicated that alternate first exons ∼1.5 kb apart and ∼ 45 kb upstream of a common second exon formed the basis of these transcripts. Genomic fragments that included the proximal 5′-flanking region of either transcript were able to direct expression of a reporter gene in lung epithelia and to bind Sp1 in nuclear extracts, confirming the presence of separate promoters that regulate β-ENaC expression.