Increased collagen gene expression in vascular smooth muscle cells cultured in serum or isoleucine deprived medium

The relationship between type I and type III collagen gene expression and the growth state of cultured bovine vascular smooth muscle cells has been investigated. Growth was modulated by incubation of subconfluent cultures of smooth muscle cells in media containing concentrations of fetal calf serum ranging from 10% to 0.5%. As the serum concentration was lowered, the doubling time increased from 17 hours to 70 hours, and collagen mRNA levels increased as judged by Northern blot analysis. The levels of induction were 5- to 15-fold for alpha 1(I), 2- to 3-fold for alpha 2(I), and 4- to 7-fold for alpha 1(III). Metabolic cell labelling with precursor amino acids indicated that type I and type III procollagen synthesis was elevated approximately 2-fold as growth slowed. A similar 2-fold increase occurred upon translation of isolated RNAs in a rabbit reticulocyte cell-free system. Nuclear run-on analysis indicated that increased collagen transcription can account for part of the increase in mRNA levels following incubation in lowered fetal calf serum. To further examine the influence of proliferation on collagen gene expression, smooth muscle cells were cultured in isoleucine-free medium, which resulted in quiescence within 36 hours. Induction of collagen mRNA levels was observed within 24 hours of incubation in isoleucine-free medium. Thus, collagen gene expression increases as the growth of vascular smooth muscle cells is slowed by either deprivation of growth factors or essential amino acids. Regulation is mediated at several sites, including gene transcription and mRNA translation, and possibly post-transcriptional steps.