Tenotomy decreases reporter protein synthesis via the 39-untranslated region of the b-myosin heavy chain mRNA

Ashley, William W., Jr. and Brenda Russell. Tenotomy decreases reporter protein synthesis via the 39-untranslated region of the b-myosin heavy chain mRNA. Am J Physiol Cell Physiol 279: C257–C265, 2000.—We tested the hypothesis that the b-myosin heavy chain (b-MHC) 39-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 39-UTR. b-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 b-MHC or SV40 39-UTR. After 48 h of tenotomy, there was no significant effect on LUC expression in the SV40 39-UTR group. In the b-MHC 39-UTR group, LUC expression was 37.3 6 4% (n 5 5, P 5 0.03) of that in sham controls. Gel mobility shift assays showed that a protein factor specifically interacts with the b-MHC 39-UTR and that tenotomy significantly increases the level of this interaction (25 6 7%, n 5 5, P 5 0.02). Thus the b-MHC 39-UTR is directly involved in decreased protein expression that is probably due to increased RNA-protein binding within the UTR.