PKC epsilon Regulates Contraction-Stimulated GLUT4 Traffic in Skeletal Muscle Cells

The signaling pathways that stimulate glucose uptake in response to muscle contraction are not well defined. Recently, we showed that carbachol, an acetylcholine analog, stimulates contraction of C2C12 myotube cultures and the rapid arrival of myc-epitope tagged GLUT4 glucose transporters at the cell surface. Here, we explore a role for protein kinase C (PKC) in regulating GLUT4 traffic. Cell surface carbachol-induced GLUT4myc levels were partly inhibited by the conventional/novel PKC inhibitors GF-109203X, Go6983, and Ro-31-8425 but not by the conventional PKC inhibitor Go6976. C2C12 myotubes expressed several novel isoforms of PKC mRNA with PKC delta and PKC epsilon in greater abundance. Carbachol stimulated phosphorylation of PKC isoforms and translocation of PKC delta and PKC epsilon to membranes within 5 min. However, only a peptidic inhibitor of PKC epsilon translocation (myristoylated-EAVSLKPT), but not one of PKC delta (myristoylated-SFNSYELGSL), prevented the GLUT4myc response to carbachol. Significant participation of PKC epsilon in the carbachol-induced gain of GLUT4myc at the surface of C2C12 myotubes was further supported through siRNA-mediated PKC epsilon protein knockdown. These findings support a role for novel PKC isoforms, especially PKC epsilon, in contraction-stimulated GLUT4 traffic in muscle cells. J. Cell. Physiol. 226: 173-180, 2010. (C) 2010 Wiley-Liss, Inc.