Permissive action of protein kinase C-ζ in insulin-induced CD36- and GLUT4 translocation in cardiac myocytes

Abstract

Insulin stimulates cardiac long-chain fatty acid (LCFA) and glucose uptake via translocation of human homolog of rat fatty acid translocase (CD36) and GLUT4 respectively, from intracellular membrane compartments to the sarcolemma, a process dependent on the activation of phosphatidylinositol-3 kinase. To identify downstream kinases of insulin signaling involved in translocation of CD36 and GLUT4 in the heart, we tested i) which cardiac protein kinase C (PKC) isoforms (a, d, 3 or z) are activated by insulin, and ii) whether PKC isoform-specific inhibition affects insulin-stimulated substrate uptake in the heart. Insulin-stimulated LCFA and glucose uptake were completely blunted by inhibition of PKC-z, but not by inhibition of conventional or novel PKCs. Concomitantly, translocation of CD36 and GLUT4 to the sarcolemma was completely blunted upon inhibition of PKC-z. However, insulin, in contrast to the diacylglycerol-analog phorbol-12-myristate-13-acetate (PMA), did not induce membrane-attachment of the conventional and novel PKCs-a, -d, and -3. PKC-z was already entirely membranebound in non-stimulated cells, and neither insulin nor PMA treatment had any effect on the subcellular localization of PKC-z. Furthermore, insulin treatment did not change phosphorylation of PKC-a, -d, and -z or enzymatic activity of PKC-z towards a PKC-z substrate peptide. It is concluded that PKC-z, but not any other PKC isoform, is necessary for insulin-induced translocation of GLUT4 and CD36. However, PKC-z is already fully active under basal conditions and not further activated by insulin, indicating that its role in insulin-stimulated uptake of both glucose and LCFA is permissive rather than regulatory.

Targeted Induction of Ceramide Degradation Leads to Improved Systemic Metabolism and Reduced Hepatic Steatosis

“…In addition to their roles as mediators of ceramide-induced insulin resistance, atypical PKCs have been noted to relay critical signals for lipogenesis and lipid uptake (Luiken et al, 2009; Sajan et al, 2004; Sajan et al, 2009; Taniguchi et al, 2006). Consistent with this, aPKC expression (Fig.…”

“…PKCζ has also attracted attention for its role in lipid homeostasis, particularly as a mediator of SREBP-1c driven lipogenesis (Sajan et al, 2004; Sajan et al, 2009; Taniguchi et al, 2006). Moreover, PKCζ has also been previously noted to play a facilitative role in CD36 activation to promote lipid uptake into cardiomyocytes (Luiken et al, 2009). We show here that targeted manipulation of ceramide alters atypical PKC activation in the liver.…”

Membrane Fatty Acid Transporters as Regulators of Lipid Metabolism: Implications for Metabolic Disease

“…Likely, class II PI3Ks can be excluded because isoforms within this class are relatively resistant towards both inhibitors (108). Recent studies in L6 muscle cells and in primary cardiac myocytes using pharmacological inhibitors have found that downstream of PI3K, atypical PKC-, but not PKB/Akt, mediates the effects of insulin on fatty acid uptake (239) via translocation of CD36 (284). In contrast to L6 muscle cells, it does appear, however, that Akt-2 is required in mammalian muscle for insulin-induced fatty acid transport and for the translocation of selected fatty acid transporters.…”

Glucose Transporters in Cardiac Metabolism and Hypertrophy

“…In PKCλ-knockout heart, insulin-stimulated glucose uptake is markedly reduced (54). The activity of PKCζ is required for insulin mediated GLUT4 translocation, although insulin does not further increase its activity in the heart (132). Therefore, PKCζ seems to play a permissive rather than a stimulatory role in insulin-mediated glucose uptake in cardiomyocytes (132).…”