Protein kinase Cξ mediates insulin-induced glucose transport through actin remodeling in L6 muscle cells

Protein kinase C (PKC) zeta has been implicated in insulin-induced glucose uptake in skeletal muscle cell, although the underlying mechanism remains unknown. In this study, we investigated the effect of PKC zeta on actin remodeling and glucose transport in differentiated rat L6 muscle cells expressing myc-tagged glucose transporter 4 (GLUT4). On insulin stimulation, PKC zeta translocated from low-density microsomes to plasma membrane accompanied by increase in GLUT4 translocation and glucose uptake. Z-scan confocal microscopy revealed a spatial colocalization of relocated PKC zeta with the small GTPase Rac-1, actin, and GLUT4 after insulin stimulation. The insulin-mediated colocalization, PKC zeta distribution, GLUT4 translocation, and glucose uptake were inhibited by wortmannin and cell-permeable PKC zeta pseudosubstrate peptide. In stable transfected cells, overexpression of PKC zeta caused an insulin-like effect on actin remodeling accompanied by a 2.1-fold increase in GLUT4 translocation and 1.7-fold increase in glucose uptake in the absence of insulin. The effects of PKC zeta overexpression were abolished by cell-permeable PKC zeta pseudosubstrate peptide, but not wortmannin. Transient transfection of constitutively active Rac-1 recruited PKC zeta to new structures resembling actin remodeling, whereas dominant negative Rac-1 prevented the insulin-mediated PKC zeta translocation. Together, these results suggest that PKC zeta mediates insulin effect on glucose transport through actin remodeling in muscle cells.