Glucocorticoid coordinate regulation of type I procollagen gene expression and procollagen DNA-binding proteins in chick skin fibroblasts

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Abstract
Nuclei were isolated from control and dexamethasone-treated (2 h) embryonic chick skin fibroblasts and transcribed in vitro. Nuclei isolated from dexamethasone-treated fibroblasts transcribed less pro.alpha.1(I) and pro.alpha.2(I) mRNAs but not .beta.-actin mRNA. Fibroblasts receiving dexamethasone and [5,6-3H]uridine also demonstrated decreased synthesis of nuclear type I procollagen mRNAs but not .beta.-actin mRNA. In fibroblasts treated with cycloheximide the newly synthesized nuclear type I procollagen mRNA species were markedly decreased. An enhanced inhibitory effect was observed when fibroblasts were treated with cycloheximide plus dexamethasone. Since the studies above demonstrate that active protein synthesis is required to maintain the constitutive expression of the type I procollagen genes, we determined if glucocorticoids regulate DNA-binding proteins with sequence specificity for the .alpha.2(I) procollagen gene. Nuclear protein blots were probed with the 32P-end-labeled pBR322 vector DNA and 32P-end-labeled .alpha.2)I) procollagen promoter containing DNA. Nonhistone proteins remained bound to labeled DNA at stringency washes of 0.05 and 0.1 M NaCl. As the ionic strength was increased to 0.2 and 0.3 M NaCl, the nonhistone-protein DNA binding was preferentially lost. Only the low molecular weight proteins remained bound to labeled DNA at the highest ionic strengtrh, indicating nonspecific binding of these nuclear proteins. Dexamethasone treatment resulted in an increase of binding of nonhistone proteins to vector- and promoter-labeled DNAs over that observed in control fibroblasts at stringency washes of 0.05 and 0.1 M NaCl and to a lesser extent at 0.2 M NaCl. The binding specificities of nonhistone proteins for the .alpha.2(I) procollagen promoter containing DNA were calculated. Three nonhistone DNA-binding proteins of Mr 90,000, 50,000 and 30,000 had altered specificities following dexamethasone treatment.