title: Bifunctional promoter of type IV collagen COL4A5 and COL4A6 genes regulates the expression of alpha5 and alpha6 chains in a distinct cell-specific fashion.
abstract: Type IV collagen is present ubiquitously in basement membranes. A bifunctional promoter regulates the expression of the alpha1/alpha2 genes, and the alpha3/alpha4 and the alpha5/alpha6 genes are also considered to be regulated by putative bifunctional promoters. Unlike the other type IV collagen chains, the alpha5(IV) and alpha6(IV) chains do not always co-localize and are present in distinct basement membranes. To address such dichotomy in the alpha5(IV) and alpha6(IV) gene regulation, we cloned a mouse genomic DNA fragment containing the promoter region between the two transcription start sites of these genes and we then placed this putative promoter sequence between the chloramphenicol acetyltransferase and Luciferase reporter genes, so that these genes would be transcribed in opposite directions in this unique construct. Glomerular endothelial cells and mesangial cells generate the kidney glomerular basement membrane, which always contains the alpha5(IV) chain but not the alpha6(IV) chain. In contrast, the basement membranes of Bowman's capsule and distal tubuli (produced by the tubular epithelial cells) contain the alpha6(IV) chain. We demonstrate that, in response to TGF-beta (transforming growth factor beta), epidermal growth factor, vascular endothelial growth factor and platelet-derived growth factor, expression from the alpha5(IV) gene is significantly enhanced in the glomerular endothelial cells and mesangial cells, but not expression from the alpha6(IV) gene. In contrast, the expression from the alpha6(IV) gene, and not that from the alpha5(IV) gene, was significantly enhanced in response to growth factors in the tubular epithelial cells. Our results demonstrate that the proximal bifunctional promoter regulates the expression of the alpha5(IV) and alpha6(IV) genes in a cell-specific manner and offers the first demonstration of the promoter plasticity in growth factor regulation of type IV collagen genes in different tissues of the body.
authors.affiliation: Center for Matrix Biology, Department of Medicine, DANA 514, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Malin
authors.initials: M
authors.lastname: Sund
authors.forename: Yohei
authors.initials: Y
authors.lastname: Maeshima
authors.forename: Raghu
authors.initials: R
authors.lastname: Kalluri
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D024141:Collagen Type IV / Q000096:biosynthesis* / Q000737:chemistry; D042783:Endothelial Cells / Q000378:metabolism*; D005091:Exons; D005786:Gene Expression Regulation / Q000502:physiology*; D007438:Introns; D007678:Kidney Glomerulus / Q000166:cytology; D007684:Kidney Tubules / Q000166:cytology; D051379:Mice; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000502:physiology*; D021122:Protein Subunits
chemical_list: D024141:Collagen Type IV; D021122:Protein Subunits