Translocation of PDK-1 to the plasma membrane is important in allowing PDK-1 to activate protein kinase B.
BACKGROUND
Protein kinase B (PKB) is involved in the regulation of apoptosis, protein synthesis and glycogen metabolism in mammalian cells. Phosphoinositide-dependent protein kinase (PDK-1) activates PKB in a manner dependent on phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3), which is also needed for the translocation of PKB to the plasma membrane. It has been proposed that the amount of PKB activated is determined exclusively as a result of its translocation, and that a constitutively active pool of membrane-associated PDK-1 simply phosphorylates all the PKB made available. Here, we have investigated the effects of membrane localisation of PDK-1 on PKB activation.


RESULTS
Ectopically expressed PDK-1 translocated to the plasma membrane in response to platelet-derived growth factor (PDGF) and translocation was sensitive to wortmannin, an inhibitor of phosphoinositide 3-kinase. Translocation of PDK-1 also occurred upon its co-expression with constitutively active phosphoinositide 3-kinase, but not with an inactive form. Overexpression of PDK-1 enhanced the ability of PDGF to activate PKB. PDK-1 disrupted in the pleckstrin homology (PH) domain which did not translocate to the membrane did not increase PKB activity in response to PDGF, whereas membrane-targeted PDK-1 activated PKB to the extent that it could not be activated further by PDGF.


CONCLUSIONS
In response to PDGF, binding of Ptdlns (3,4,5)P3 and/or Ptdlns(3,4)P2 to the PH domain of PDK-1 causes its translocation to the plasma membrane where it co-localises with PKB, significantly contributing to the scale of PKB activation.
Anderson
K E
KE
Department of Signalling, Babraham Institute, Cambridge, UK. karen.anderson@bbsrc.ac.uk
Coadwell
J
J
Stephens
L R
LR
Hawkins
P T
PT
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004789:Enzyme Activation; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt
D064413:3-Phosphoinositide-Dependent Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D010982:Platelet-Derived Growth Factor; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt