Regulation of type I collagen mRNA by amino acid deprivation in human lung fibroblasts

Abstract

The steady state levels of α1(I) collagen mRNA are decreased by retinoic acid and prostaglandin E2. These effector substances decrease the uptake of A system amino acids. We examined the effect of amino acid deprivation on the steady state levels of α1(I) collagen in human lung fibroblasts. Maintenance of fibroblasts in amino acid-free medium decreased α1(I) collagen mRNA levels by 29% at 24 h and 78% at 72 h. Frequent refeeding of cultures with amino acid-free medium resulted in more rapid decreases in intracellular amino acids and in α1(I) collagen mRNA levels. The decrease in α1(I) collagen mRNA levels was mediated by decreases in mRNA stability as assessed by a half-life determination using actinomycin D and by decreases in the rate of transcription as assessed by nuclear run-on assay. Treatment of fibroblasts with medium containing amino acids resulted in rapid restoration of α1(I) collagen mRNA levels. This increase in α1(I) collagen mRNA expression required protein synthesis as determined by cycloheximide sensitivity and was inhibited by prostaglandin E2. These data indicate that α1(I) collagen mRNA levels are sensitive to alterations in the amount of intracellular amino acids and suggest a potential mechanism whereby α1(I) collagen accumulation may be regulated independent of inflammatory mediators following lung injury.