Tenotomy decreases reporter protein synthesis via the 3'-untranslated region of the beta-myosin heavy chain mRNA.

We tested the hypothesis that the beta-myosin heavy chain (beta-MHC) 3'-untranslated region (UTR) mediates decreased protein expression after tenotomy of the rat soleus. We also tested the hypothesis that decreased protein expression is the result of RNA-protein interactions within the 3'-UTR. beta-MHC was chosen for study because of its critical role in the function of postural muscles such as soleus. Adult rat soleus muscles were directly injected with luciferase (LUC) reporter constructs containing either the beta-MHC or SV40 3'-UTR. After 48 h of tenotomy, there was no significant effect on LUC expression in the SV40 3'-UTR group. In the beta-MHC 3'-UTR group, LUC expression was 37.3 +/- 4% (n = 5, P = 0.03) of that in sham controls. Gel mobility shift assays showed that a protein factor specifically interacts with the beta-MHC 3'-UTR and that tenotomy significantly increases the level of this interaction (25 +/- 7%, n = 5, P = 0.02). Thus the beta-MHC 3'-UTR is directly involved in decreased protein expression that is probably due to increased RNA-protein binding within the UTR.