Activation and mitochondrial translocation of protein kinase Cδ are necessary for insulin stimulation of pyruvate dehydrogenase complex activity in muscle and liver cells

In L6 skeletal muscle cells and immortalized hepatocytes, insulin induced a 2-fold increase in the activity of the pyruvate dehydrogenase (PDH) complex. This effect was almost completely blocked by the protein kinase C (PKC) delta inhibitor Rottlerin and by PKC delta antisense oligonucleotides. At variance, overexpression of wild-type PKC delta or of an active PKC delta mutant induced PDH complex activity in both L6 and liver cells. Insulin stimulation of the activity of the PDH complex was accompanied by a 2.5-fold increase in PDH phosphatases 1 and 2 (PDP1/2) activity with no change in the activity of PDH kinase. PKC delta antisense blocked insulin activation of PDP1/2, the same as with PDH. In insulin-exposed cells, PDP1/2 activation was paralleled by activation and mitochondrial translocation of PKC8 delta, as revealed by cell subfractionation and confocal microscopy studies. The mitochondrial translocation of PKC delta, like its activation, was prevented by Rottlerin. In extracts from insulin-stimulated cells, PKC delta co-precipitated with PDP1/2. PKC delta also bound to PDP1/2 in overlay blots, suggesting that direct PKC delta -PDP interaction may occur in vivo as well. In intact cells, insulin exposure determined PDP1/2 phosphorylation, which was specifically prevented by PKC delta antisense. PKC delta also phosphorylated PDP in vitro, followed by PDP1/2 activation. Thus, in muscle and liver cells, insulin causes activation and mitochondrial translocation of PKC delta, accompanied by PDP phosphorylation and activation. These events are necessary for insulin activation of the PDH complex in these cells.