PKC and Rab13 mediate Ca2+ signal-regulated GLUT4 traffic

Abstract Exercise/muscle contraction increases cell surface glucose transporter 4 (GLUT4), leading to glucose uptake to regulate blood glucose level. Elevating cytosolic Ca 2+ mediates this effect, but the detailed mechanism is not clear yet. We used calcium ionophore ionomycin to raise intracellular cytosolic Ca 2+ level to explore the underlying mechanism. We showed that in L6 myoblast muscle cells stably expressing GLUT4 myc , ionomycin increased cell surface GLUT4 myc levels and the phosphorylation of AS160, TBC1D1. siPKCα and siPKCθ but not siPKCδ and siPKCe inhibited the ionomycin-increased cell surface GLUT4 myc level. siPKCα, siPKCθ inhibited the phosphorylation of AS160 and TBC1D1 induced by ionomycin. siPKCα and siPKCθ prevented ionomycin-inhibited endocytosis of GLUT4 myc . siPKCθ, but not siPKCα inhibited ionomycin-stimulated exocytosis of GLUT4 myc . siRab13 but not siRab8a, siRab10 and siRab14 inhibited the exocytosis of GLUT4 myc promoted by ionomycin. In summary, ionomycin-promoted exocytosis of GLUT4 is partly reversed by siPKCθ, whereas ionomycin-inhibited endocytosis of GLUT4 requires both siPKCα and siPKCθ. PKCα and PKCθ contribute to ionomycin-induced phosphorylation of AS160 and TBC1D1. Rab13 is required for ionomycin-regulated GLUT4 exocytosis.