Early phosphoinositide 3-kinase activity is required for late activation of protein kinase Cepsilon in platelet-derived-growth-factor-stimulated cells: evidence for signalling across a large temporal gap.
At least two signalling systems have the potential to contribute to the activation of protein kinase C (PKC) family members such as PKCepsilon. One of these is phosphoinositide 3-kinase (PI 3-kinase), whose lipid products activate PKCepsilon in vitro and in living cells. The recent observation that there are multiple waves of PI 3-kinase and PKCepsilon activity within the G(0)-to-S phase interval provides a new opportunity to investigate the relationship between these two signalling enzymes in vivo. We have assessed the relative importance of the early and late waves of PI 3-kinase activity for the corresponding waves of PKCepsilon activity. Blocking the first phase of PI 3-kinase activity inhibited both early and late activation of PKCepsilon. In contrast, the second wave of PI 3-kinase activity was dispensable for late activation of PKCepsilon. These findings suggested that early PI 3-kinase activation induced a stable change in PKCepsilon, which predisposed it to subsequent activation by lipid cofactors. Indeed, partial proteolysis of PKCepsilon indicated that early activation of PI 3-kinase led to a conformation change in PKCepsilon that persisted as the activity of PKCepsilon cycled. We propose a two-step hypothesis for the activation of PKCepsilon in vivo. One step is stable and depends on PI 3-kinase, whereas the other is transient and may depend on the availability of lipid cofactors. Finally, these studies reveal that PI 3-kinase and PKCepsilon are capable of communicating over a relatively long time interval and begin to elucidate the mechanism.
Balciunaite
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E
Institute of Biotechnology, Graiciuno 8, 2028 Vilnius, Lithuania.
Kazlauskas
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A
D002460:Cell Line; D004789:Enzyme Activation; D004795:Enzyme Stability; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011487:Protein Conformation; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism*; D051744:Protein Kinase C-epsilon; D015398:Signal Transduction
D007527:Isoenzymes; D010982:Platelet-Derived Growth Factor; D019869:Phosphatidylinositol 3-Kinases; C497255:PRKCE protein, human; D011493:Protein Kinase C; D051744:Protein Kinase C-epsilon