Regulation of protein kinase C zeta by PI 3-kinase and PDK-1.
BACKGROUND
Protein kinase C zeta (PKC zeta) is a member of the PKC family of enzymes and is involved in a wide range of physiological processes including mitogenesis, protein synthesis, cell survival and transcriptional regulation. PKC zeta has received considerable attention recently as a target of phosphoinositide 3-kinase (PI 3-kinase), although the mechanism of PKC zeta activation is, as yet, unknown. Recent reports have also shown that the phosphoinositide-dependent protein kinase-1 (PDK-1), which binds with high affinity to the PI 3-kinase lipid product phosphatidylinositol-3,4,5-trisphosphate (Ptdins-3,4,5-P3), phosphorylates and potently activates two other PI 3-kinase targets, the protein kinases Akt/PKB and p70S6K. We therefore investigated whether PDK-1 is the kinase that activates PKC zeta.


RESULTS
In vivo, PI 3-kinase is both necessary and sufficient to activate PKC zeta. PDK-1 phosphorylates and activates PKC zeta in vivo, and we have shown that this is due to phosphorylation of threonine 410 in the PKC zeta activation loop. In vitro, PDK-1 phosphorylates and activates PKC zeta in a Ptdins-3,4,5-P3-enhanced manner. PKC zeta and PDK-1 are associated in vivo, and membrane targeting of PKC zeta renders it constitutively active in cells.


CONCLUSIONS
Our results have identified PDK-1 as the kinase that phosphorylates and activates PKC zeta in the PI 3-kinase signaling pathway. This phosphorylation and activation of PKC zeta by PDK-1 is enhanced in the presence of Ptdins-3,4-5-P3. Consistent with the notion that PKCs are enzymes that are regulated at the plasma membrane, a membrane-targeted PKC zeta is constitutively active in the absence of agonist stimulation. The association between PKC zeta and PDK-1 reveals extensive cross-talk between enzymes in the PI 3-kinase signaling pathway.
University of Pennsylvania School of Medicine, Department of Cell and Developmental Biology, Philadelphia 19104, USA.
M M
MM
Chou
W
W
Hou
J
J
Johnson
L K
LK
Graham
M H
MH
Lee
C S
CS
Chen
A C
AC
Newton
B S
BS
Schaffhausen
A
A
Toker
D064413:3-Phosphoinositide-Dependent Protein Kinases; D016475:3T3 Cells; D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection; D000099221:Protein Kinase C zeta
D064413:3-Phosphoinositide-Dependent Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D010769:Phosphothreonine; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011993:Recombinant Fusion Proteins; D000099221:Protein Kinase C zeta