Effect of the 3'-untranslated region on the expression levels and mRNA stability of alpha 1(I) collagen gene.

Changes in the synthesis of type I collagen, a major extracellular matrix component in skin and bones, are associated with both normal growth or repair processes and with several pathological conditions such as lung fibrosis and liver cirrhosis. The expression of the alpha 1(I) collagen gene is regulated by transcriptional and post-transcriptional mechanisms. Regulation at both these levels are usually utilised when extensive changes occur in collagen synthesis. We constructed plasmids carrying the whole or partially deleted 3'-UTR sequences of the alpha 1(I) collagen gene, fused to two hGH exons and to the promoter of the alpha 1(I) collagen gene. A control plasmid contained the 3'-UTR of the hGH gene. In transient transfections into Rat-1 fibroblasts, no significant differences between plasmids were found, which suggests that although 3'-end of the gene has been shown in previous studies to contain DNaseI hypersensitive sites and to bind sequence-specific nuclear proteins it does not seem to function as a transcriptional regulator. This was further supported by the finding that TGF-beta treatment induced a 2.5-fold expression of hGH mRNA from plasmids containing collagen promoter and either hGH or alpha 1(I) collagen 3'-UTR. In stable transfections, mRNAs using the first polyadenylation site were not as stable as those transcribed from the endogenous alpha 1(I) collagen gene. We suggest that the 3'-UTR alone may not be sufficient to determine the stability of the shorter alpha 1(I) collagen mRNA species.