EFFECT OF THE 3'-UNTRANSLATED REGION ON THE EXPRESSION LEVELS AND MESSENGER-RNA STABILITY OF ALPHA-1(I) COLLAGEN GENE

Changes in the synthesis of type I collagen, a major extracellular mat rix component in skin and bones, are associated with both normal growt h or repair processes and with several pathological conditions such as lung fibrosis and liver cirrhosis. The expression of the alpha 1(I) c ollagen 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 t he hGH gene. In transient transfections into Rat-1 fibroblasts, no sig nificant differences between plasmids were found, which suggests that although 3'-end of the gene has been shown in previous studies to cont ain 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 indu ced a 2.5-fold expression of hGH mRNA from plasmids containing collage n promoter and either hGH or alpha 1(I) collagen 3'-UTR. In stable tra nsfections, mRNAs using the first polyadenylation site were not as sta ble as those transcibed from the endogenous alpha 1(I) collagen gene. We suggest that the 3'-UTR alone may not be sufficient to determine th e stability of the shorter alpha 1(I) collagen mRNA species.