3-Phosphoinositide-dependent protein kinase-1 (PDK1): structural and functional homology with the Drosophila DSTPK61 kinase.
BACKGROUND
The activation of protein kinase B (PKB, also known as c-Akt) is stimulated by insulin or growth factors and results from its phosphorylation at Thr308 and Ser473. We recently identified a protein kinase, termed PDK1, that phosphorylates PKB at Thr308 only in the presence of lipid vesicles containing phosphatidylinositol 3,4,5-trisphosphate (Ptdlns(3,4,5)P3) or phosphatidylinositol 3,4-bisphosphate (Ptdlns(3,4)P2).


RESULTS
We have cloned and sequenced human PDK1. The 556-residue monomeric enzyme comprises a catalytic domain that is most similar to the PKA, PKB and PKC subfamily of protein kinases and a carboxy-terminal pleckstrin homology (PH) domain. The PDK1 gene is located on human chromosome 16p13.3 and is expressed ubiquitously in human tissues. Human PDK1 is homologous to the Drosophila protein kinase DSTPK61, which has been implicated in the regulation of sex differentiation, oogenesis and spermatogenesis. Expressed PDK1 and DSTPK61 phosphorylated Thr308 of PKB alpha only in the presence of Ptdlns(3,4,5)P3 or Ptdlns(3,4)P2. Overexpression of PDK1 in 293 cells activated PKB alpha and potentiated the IGF1-induced phosphorylation of PKB alpha at Thr308. Experiments in which the PH domains of either PDK1 or PKB alpha were deleted indicated that the binding of Ptdlns(3,4,5)P3 or Ptdlns(3,4)P2 to PKB alpha is required for phosphorylation and activation by PDK1. IGF1 stimulation of 293 cells did not affect the activity or phosphorylation of PDK1.


CONCLUSIONS
PDK1 is likely to mediate the activation of PKB by insulin or growth factors. DSTPK61 is a Drosophila homologue of PDK1. The effect of Ptdlns(3,4,5)P3/Ptdlns(3,4)P2 in the activation of PKB alpha is at least partly substrate directed.
Alessi
D R
DR
Department of Biochemistry, University of Dundee, UK. dralessi@bad.dundee.ac.uk
Deak
M
M
Casamayor
A
A
Caudwell
F B
FB
Morrice
N
N
Norman
D G
DG
Gaffney
P
P
Reese
C B
CB
MacDougall
C N
CN
Harbison
D
D
Ashworth
A
A
Bownes
M
M
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000595:Amino Acid Sequence; D000818:Animals; D001798:Blood Proteins / Q000737:chemistry; D002461:Cell Line, Transformed; D004330:Drosophila / Q000201:enzymology*; D029721:Drosophila Proteins; D004789:Enzyme Activation; D005982:Glutathione Transferase / Q000235:genetics; D006801:Humans; D019476:Insect Proteins / Q000737:chemistry / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000201:enzymology; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010750:Phosphoproteins; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013912:Threonine / Q000378:metabolism; D014162:Transfection
D001798:Blood Proteins; D029721:Drosophila Proteins; D019476:Insect Proteins; D018129:Phosphatidylinositol Phosphates; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; C060974:phosphatidylinositol 3,4,5-triphosphate; C060980:phosphatidylinositol 3,4-diphosphate; C039077:platelet protein P47; D013912:Threonine; D007334:Insulin-Like Growth Factor I; D005982:Glutathione Transferase; D064413:3-Phosphoinositide-Dependent Protein Kinases; C494918:AKT1 protein, human; C494917:Akt1 protein, Drosophila; C578562:PDPK1 protein, human; C578560:Pdk1 protein, Drosophila; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt