UC Irvine

Chicken embryo fibroblasts infected with a strain of Rous sarcoma virus containing a temperature-sensitive mutation in the gene coding for pp60src, a protein kinase, undergo changes in collagen synthesis within 4 h after a temperature shift. Cells shifted from the restrictive to the permissive temperature for transformation show decreasing levels of collagen synthesis and increasing levels of kinase activity; the reverse occurs when infected cells are shifted from the permissive to the restrictive temperature. Levels of type I procollagen mRNAs coding for pro alpha 1 and pro alpha 2 chains, measured by hybridization to nick-translated cloned alpha 1 and alpha 2 cDNA, decreased simultaneously soon after a reduction in temperature and reached a new steady state at about 50 h after the shift. In order to test for regulation at the transcriptional level, nuclei were isolated from normal and Rous sarcoma virus-transformed chicken embryo fibroblasts and allowed to transcribe in the presence of [alpha-32P]UTP. Procollagen mRNA sequences in newly synthesized and in total RNA from transformed cell preparations were both about 5-fold lower than the levels in normal cell preparations. We conclude that the coordinate decrease in procollagen mRNAs observed in Rous sarcoma virus-transformed chicken embryo fibroblasts is caused primarily by a decrease in the transcription of the type I procollagen genes, a decrease which is directly or indirectly mediated by the pp60src protein kinase.