The molecular mechanisms regulating expression of
utrophin A are of therapeutic interest since upregulating its expression at the sarcolemma can compensate for the lack of
dystrophin in animal models of
Duchenne Muscular Dystrophy (DMD). The 5'-UTR of
utrophin A has been previously shown to drive cap-independent
internal ribosome entry site (IRES)-mediated translation in response to muscle regeneration and
glucocorticoid treatment. To determine whether the
utrophin A IRES displays tissue specific activity, we generated transgenic mice harboring control (CMV/betaGAL/CAT) or
utrophin A 5'-UTR (CMV/betaGAL/UtrA/CAT) bicistronic reporter transgenes. Examination of multiple tissues from two CMV/betaGAL/UtrA/CAT lines revealed that the
utrophin A 5'-UTR drives cap-independent translation of the reporter gene exclusively in skeletal muscles and no other examined tissues. This expression pattern suggested that skeletal muscle-specific factors are involved in IRES-mediated translation of
utrophin A. We performed
RNA-affinity chromatography experiments combined with mass spectrometry to identify trans-factors that bind the
utrophin A 5'-UTR and identified eukaryotic
elongation factor 1A2 (eEF1A2). UV-crosslinking experiments confirmed the specificity of this interaction. Regions of the
utrophin A 5'-UTR that bound eEF1A2 also mediated cap-independent translation in C2C12 muscle cells. Cultured cells lacking eEF1A2 had reduced IRES activity compared with cells overexpressing eEF1A2. Together, these results suggest an important role for eEF1A2 in driving cap-independent translation of
utrophin A in skeletal muscle. The trans-factors and signaling pathways driving skeletal-muscle specific IRES-mediated translation of
utrophin A could provide unique targets for developing pharmacological-based DMD
therapies.