Protein Kinase C (PKC)-α Activation Inhibits PKC-ζ and Mediates the Action of PED/PEA-15 on Glucose Transport in the L6 Skeletal Muscle Cells

Protein Kinase C (PKC)-α Activation Inhibits PKC-ζ and Mediates the Action of PED/PEA-15 on Glucose Transport in the L6 Skeletal Muscle Cells Gerolama Condorelli , Giovanni Vigliotta , Alessandra Trencia , Maria Alessandra Maitan , Matilde Caruso , Claudia Miele , Francesco Oriente , Stefania Santopietro , Pietro Formisano and Francesco Beguinot Dipartimento di Biologia e Patologia Cellulare e Molecolare and the Centro di Endocrinologia ed Oncologia Sperimentale del C.N.R., Federico II University of Naples, Naples, Italy Abstract Overexpression of the PED/PEA-15 protein in muscle and adipose cells increases glucose transport and impairs further insulin induction. Like glucose transport, protein kinase C (PKC)-α and -β are also constitutively activated and are not further stimulatable by insulin in L6 skeletal muscle cells overexpressing PED (L6 PED ). PKC-ζ features no basal change but completely loses insulin sensitivity in L6 PED . In these cells, blockage of PKC-α and -β additively returns 2-deoxy- d -glucose (2-DG) uptake to the levels of cells expressing only endogenous PED (L6 WT ). Blockage of PKC-α and -β also restores insulin activation of PKC-ζ in L6 PED cells, with that of PKC-α sixfold more effective than PKC-β. Similar effects on 2-DG uptake and PKC-ζ were also achieved by 50-fold overexpression of PKC-ζ in L6 PED . In L6 WT , fivefold overexpression of PKC-α or -β increases basal 2-DG uptake and impairs further insulin induction with no effect on insulin receptor or insulin receptor substrate phosphorylation. In these cells, overexpression of PKC-α blocks insulin induction of PKC-ζ activity. PKC-β is 10-fold less effective than PKC-α in inhibiting PKC-ζ stimulation. Expression of the dominant-negative K 281 →W PKC-ζ mutant simultaneously inhibits insulin activation of PKC-ζ and 2-DG uptake in the L6 WT cells. We conclude that activation of classic PKCs, mainly PKC-α, inhibits PKC-ζ and may mediate the action of PED on glucose uptake in L6 skeletal muscle cells. Footnotes Address correspondence and reprint requests to Francesco Beguinot, MD, PhD, Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università di Napoli Federico II, Via S. Pansini 5, 80131 Naples, Italy. E-mail: beguino{at}unina.it . Received for publication 15 August 2000 and accepted in revised form 22 February 2001. G.C. and G.V. contributed equally to this article. 2-DG, 2-deoxy- d -glucose; DAG, diacylglycerol; DMEM, Dulbecco’s modified Eagle’s medium; ECL, enhance