Human type III collagen gene expression is coordinately modulated with the type I collagen genes during fibroblast growth
Type III collagen is one of the major interstitial collagens and, as such, plays an important role in modulating the structure and function of most tissues. To compare the expression of the type III collagen gene to that of the type I collagen alpha 1(I) and alpha 2(I) genes, cDNAs encoding the 3' one-third of the human alpha 1(III) collagen mRNA were obtained by screening a human fetal lung fibroblast cDNA library with a cloned segment of the chicken alpha 1(III) gene. Northern blot analysis of human fetal lung fibroblast RNA demonstrated two alpha 1(III)-specific mRNAs of sizes 6.6 and 5.8 kilobases, sizes clearly different from those of the type I collagen mRNAs. Analyses of populations of dividing and nondividing human lung fibroblasts revealed that, on a per cell basis, the nondividing population contained twice as much alpha 1(III) mRNA than did the dividing population. The same was true for the type I collagen alpha 1(I) and alpha 2(I) mRNA transcripts. Similar results were obtained when alpha 1(III), alpha 1(I), and alpha 2(I) mRNA transcripts were quantified by using dot blot evaluation of total RNA, Northern analysis of total RNA, and dot blot evaluation of cytoplasmic RNA. Thus, despite the fact that the alpha 1(III) collagen gene is located on a chromosome different from the alpha 1(I) and alpha 2(I) genes, the expression of these three collagen chains appears to be coordinately controlled during periods of rapid and slow fibroblast growth.