Promoter activity of the rat connexin 43 gene in NRK cells

Cellular communication mediated by gap junctions plays a major role in organ function. Gap junction channels are formed by the organization of polypeptide subunits, termed connexins (Cx), on the cell surface of adjacent cells. One mechanism to regulate gap-junctional communication is by change in Cx expression. In the present study, the promoter region of the rat Cx43 gene was characterized. Nested deletions of the 5' flanking region of the first Cx43 exon were coupled to the human growth hormone gene and transfected into normal rat kidney (NRK) cells, that express this gene constitutively. The minimal region of the Cx43 gene that showed maximal promoter activity was localized within 110 bp upstream of the transcriptional initiation site. One particular subregion that contains a Sp-1 binding site (located within 98--93 bp from the transcriptional initiation site) was found to sustain Cx43 promoter activity to the same extent as that of the 110 bp promoter region. Mutations of this Sp-1 binding site abolished transcriptional activity and DNA-protein interactions. These observations suggest that the Sp-1 binding site plays a major role in the basal transcriptional activity of Cx43 gene in NRK cells.