Regulation of type I collagen mRNA in lung fibroblasts by cystine availability

The steady-state level of alpha 1(I) collagen mRNA is regulated by amino acid availability in human lung fibroblasts. Depletion of amino acids decreases alpha 1(I) collagen mRNA levels and repletion of amino acids induces rapid re-expression of alpha 1(I) mRNA. In these studies, we examined the requirements for individual amino acids on the regulation of alpha 1(I) collagen mRNA. We found that re-expression of alpha 1(I) collagen mRNA was critically dependent on cystine but not on other amino acids. However, the addition of cystine alone did not result in re-expression df alpha 1(I) collagen mRNA. Following amino acid depletion, the addition of cystine with selective amino acids increased alpha 1(I) collagen mRNA levels. The combination of glutamine and cystine increased alpha 1(I) collagen mRNA levels 6.3-fold. Methionine or a branch-chain amino acid (leucine, isoleucine or valine) also acted in combination with cystine to increase alpha 1(I) collagen mRNA expression, whereas other amino acids were not effective. The prolonged absence of cystine lowered steady-state levels of alpha 1(I) collagen mRNA through a mechanism involving decreases in both the rate of gene transcription as assessed by nuclear run-on experiments and mRNA stability as assessed by half-life determination in the presence of actinomycin D. The effect of cystine was not mediated via alterations in the level of glutathione, the major redox buffer in cells, as determined by the addition of buthionine sulphoximine, an inhibitor of gamma-glutamylcysteine synthetase. These data suggest that cystine directly affects the regulation of alpha 1(I) collagen mRNA.