A second messenger RNA species of transforming growth factor beta 1 in infarcted rat heart.

Transforming growth factor-beta 1 (TGF-beta 1) is encoded predominantly by a 2.4-kb mRNA in most tissues. However, an additional transcript of 1.9 kb can be detected in rat heart after experimental myocardial infarction caused by ligation of the left coronary artery. This transcript level is significantly higher in infarcted heart tissue than in normal heart tissue, suggesting an important role for this mRNA species in response to injury. Structural characterization of the 1.9-kb mRNA showed that it included the entire coding sequence present in the 2.4-kb TGF-beta 1 mRNA, but also contained an additional nonhomologous 3'-untranslated region (UTR). The junction between the shared and unique 3' sequence in the 1.9-kb mRNA occurred only two nucleotides before the proposed polyadenylation site of the rat TGF-beta 1 2.4-kb mRNA. The unique 3'-UTR and the deduced shortened 5'-UTR in the novel 1.9-kb TGF-beta 1 mRNA suggest different transcriptional and translational regulatory mechanisms under conditions of tissue injury.