REGULATION OF COLLAGEN-I GENE-EXPRESSION BY RAS

Although transformation of rodent fibroblasts can lead to dramatic changes in expression of extracellular matrix genes, the molecular basis and physiological significance of these changes remain Poorly understood. In this study, we have investigated the mechanism(s) by which ras affects expression of the genes encoding type I collagen. Levels of both alpha1(I) and alpha2(I) collagen mRNAs were markedly reduced in Rat 1 fibroblasts overexpressing either the N-ras(Lys-61) or the Ha-ras(Val-12) oncogene. In fibroblasts conditionally transformed with N-ras(Lys-61), alpha1(I) transcript levels began to decline within 8 h of ras induction and reached 1 to 5% of control levels after 96 h. In contrast, overexpression of normal ras p21 had no effect on alpha1(I) or alpha2(I) mRNA levels. Nuclear run-on experiments demonstrated that the transcription rates of both the alpha1(I) and alpha2(I) genes were significantly reduced in ras-transformed cells compared with those in parental cells. In addition, the alpha1(I) transcript was less stable in transformed cells. Chimeric plasmids containing up to 3.6 kb of alpha1(I) 5'-flanking DNA and up to 2.3 kb of the 3'-flanking region were expressed at equivalent levels in both normal and ras-transformed fibroblasts. However, a cosmid clone containing the entire mouse alpha1(I) gene, including 3.7 kb of 5'- and 4 kb of 3'-flanking DNA, was expressed at reduced levels in fibroblasts overexpressing oncogenic ras. We conclude that oncogenic ras regulates the type I collagen genes at both transcriptional and posttranscriptional levels and that this effect, at least for the alpha1 (I) gene, may be mediated by sequences located either within the body of the gene itself or in the distal 3'-flanking region.