Clustering of GLUT4, TUG, and RUVBL2 protein levels correlate with myosin heavy chain isoform pattern in skeletal muscles, but AS160 and TBC1D1 levels do not

Skeletal muscle is a heterogeneous tissue. To further elucidate this heterogeneity, we probed relationships between myosin heavy chain (MHC) isoform composition and abundance of GLUT4 and four other proteins that are established or putative GLUT4 regulators Akt substrate of 160 kDa (AS160), Tre-2/Bub2/Cdc 16-domain member 1 (TBC1D1), Tethering protein containing an UBX-domain for GLUT4 (TUG), and RuvB-like protein two (RUVBL2) in 12 skeletal muscles or muscle regions from Wistar rats adductor longus, extensor digitorum longus, epitrochlearis, gastrocnemius (mixed, red, and white), plantaris, soleus, tibialis anterior (red and white), tensor fasciae latae, and white vastus lateralis. Key results were 1) significant differences found among the muscles (range of muscle expression values) for GLUT4 (2.5-fold), TUG (1.7-fold), RUVBL2 (2.0-fold), and TBC1D1 (2.7-fold), but not AS160; 2) significant positive correlations for pairs of proteins: GLUT4 vs. TUG (R = 0.699), GLUT4 vs. RUVBL2 (R = 0.613), TUG vs. RUVBL2 (R = 0.564), AS160 vs. TBC1D1 (R = 0.293), and AS160 vs. TUG (R = 0.246); 3) significant positive correlations for %MHC-I: GLUT4 (R = 0.460), TUG (R = 0.538), and RUVBL2 (R = 0.511); 4) significant positive correlations for %MHC-IIa: GLUT4 (R = 0.293) and RUVBL2 (R = 0.204); 5) significant negative correlations for %MHC-IIb vs. GLUT4 (R = -0.642), TUG (R = -0.626), and RUVBL2 (R = -0.692); and 6) neither AS160 nor TBC1D1 significantly correlated with MHC isoforms. In 12 rat muscles, GLUT4 abundance tracked with TUG and RUVBL2 and correlated with MHC isoform expression, but was unrelated to AS160 or TBC1D1. Our working hypothesis is that some of the mechanisms that regulate GLUT4 abundance in rat skeletal muscle also influence TUG and RUVBL2 abundance.