REGULATION OF TYPE-I COLLAGEN MESSENGER-RNA IN LUNG FIBROBLASTS BY CYSTINE AVAILABILITY

The steady-state level of alpha 1(I) collagen mRNA is regulated by ami no acid availability in human lung fibroblasts. Depletion of amino aci ds decreases alpha 1(I) collagen mRNA levels and repletion of amino ac ids induces rapid re-expression of alpha 1(I) mRNA. In these studies, we examined the requirements for individual amino acids on the regulat ion 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 othe r amino acids. However, the addition of cystine alone did not result i n re-expression df alpha 1(I) collagen mRNA. Following amino acid depl etion, the addition of cystine with selective amino acids increased al pha 1(I) collagen mRNA levels. The combination of glutamine and cystin e 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 expressi on, whereas other amino acids were not effective. The prolonged absenc e of cystine lowered steady-state levels of alpha 1(I) collagen mRNA t hrough a mechanism involving decreases in both the rate of gene transc ription as assessed by nuclear run-on experiments and mRNA stability a s 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-glutamylcys teine synthetase. These data suggest that cystine directly affects the regulation of alpha 1(I) collagen mRNA.