Role of the 5'-untranslated region in regulating translational efficiency of specific mRNAs in adult cardiocytes.
It has been hypothesized that translational efficiency is determined by the amount of secondary structure in the 5'-untranslated region (5'-UTR) of mRNA. Here, we examined whether specific 5'-UTRs with excessive secondary structure selectively regulate translational efficiency in adult cardiocytes. Recombinant adenoviruses were generated to express reporter mRNAs consisting of the 5'-UTR derived from c-jun or ornithine decarboxylase (ODC) fused to beta-galactosidase (betaGal) coding sequence. Each adenovirus expressed GFP mRNA as a control for 5'-UTRs with minimal secondary structure. Subsequently, cardiocytes were electrically stimulated to contract at 1 Hz to accelerate protein synthesis as compared to quiescent controls. Translational efficiency was calculated by measuring protein expression as a function of mRNA levels. Translational efficiency of c-jun/betaGal mRNA increased significantly by 3.7-fold in contracting vs. quiescent cardiocytes, but ODC/betaGal mRNA was unchanged. Contraction increased c-jun/betaGal mRNA levels in polyribosomes by 2.3-fold, which indicates that translational efficiency was enhanced by mobilization. A short, unstructured 5'-UTR was sufficient for efficient translation of betaGal mRNA in quiescent and contracting cardiocytes. GFP mRNA produced similar results. These studies demonstrate that the 5'-UTR functions as a determinant of translational efficiency of specific mRNAs, such as c-jun, that regulate growth of the adult cardiocyte.
Gazes Cardiac Research Institute, Department of Medicine, Medical University of South Carolina, Charleston, SC 29403, USA.
Laura S
LS
Spruill
Paul J
PJ
McDermott
D020121:5' Untranslated Regions / Q000235:genetics*; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002415:Cats; D049109:Cell Proliferation; D032383:Myocytes, Cardiac / Q000166:cytology; D014176:Protein Biosynthesis; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis*; D014161:Transduction, Genetic
D020121:5' Untranslated Regions; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger