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'-unt ranslated region (UTR) mediates decreased protein expression after tenotomy of the rat soleus. We also tested the hypothesis that decreased protein ex pression 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 po stural muscles such as soleus. Adult rat soleus muscles were directly injec ted with luciferase (LUC) reporter constructs containing either the beta-MH C or SV40 3'-UTR. After 48 h of tenotomy, there was no significant effect o n LUC expression in the SV40 3'-UTR group. In the beta-MHC 3'-UTR group, LU C expression was 37.3 +/- 4% (n = 5, P = 0.03) of that in sham controls. Ge l mobility shift assays showed that a protein factor specifically interacts with the beta-MHC 3'-UTR and that tenotomy significantly increases the lev el of this interaction (25 +/- 7%, n = 5, P = 0.02). Thus the beta-MHC 3'-U TR is directly involved in decreased protein expression that is probably du e to increased RNA-protein binding within the UTR.