Protein Kinase Cζ Mediates Insulin-induced Glucose Transport through Actin Remodeling in L6 Muscle Cells

Protein kinase C (PKC) ζ 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 PKCζ on actin remodeling and glucose transport in differentiated rat L6 muscle cells expressing myc-tagged glucose transporter 4 (GLUT4). On insulin stimulation, PKCζ 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 PKCζ with the small GTPase Rac-1, actin, and GLUT4 after insulin stimulation. The insulin-mediated colocalization, PKCζ distribution, GLUT4 translocation, and glucose uptake were inhibited by wortmannin and cell-permeable PKCζ pseudosubstrate peptide. In stable transfected cells, overexpression of PKCζ 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 PKCζ overexpression were abolished by cell-permeable PKCζ pseudosubstrate peptide, but not wortmannin. Transient transfection of constitutively active Rac-1 recruited PKCζ to new structures resembling actin remodeling, whereas dominant negative Rac-1 prevented the insulin-mediated PKCζ translocation. Together, these results suggest that PKCζ mediates insulin effect on glucose transport through actin remodeling in muscle cells.