Substitution of the autophosphorylation site Thr516 with a negatively charged residue confers constitutive activity to mouse 3-phosphoinositide-dependent protein kinase-1 in cells.
3-Phosphoinositide-dependent protein kinase-1 (PDK-1)is a serine/threonine kinase that has been found to phosphorylate and activate several members of the AGC protein kinase family including protein kinase B (Akt), p70 S6 kinase, and protein kinase Czeta. However, the mechanism(s) by which PDK-1 is regulated remains unclear. Here we show that mouse PDK-1 (mPDK-1) undergoes autophosphorylation in vitro on both serine and threonine residues. In addition, we have identified Ser(399) and Thr(516) as the major mPDK-1 autophosphorylation sites in vitro. Furthermore, we have found that these two residues, as well as Ser(244) in the activation loop, are phosphorylated in cells and demonstrated that Ser(244) is a major in vivo phosphorylation site. Abolishment of phosphorylation at Ser(244), but not at Ser(399) or Thr(516), led to a significant decrease of mPDK-1 autophosphorylation and kinase activity in vitro, indicating that autophosphorylation at Ser(399) or Thr(516) is not essential for mPDK-1 autokinase activity. However, overexpression of mPDK-1(T516E), but not of mPDK-1(S244E) or mPDK-1(S399D), in Chinese hamster ovary and HEK293 cells was sufficient to induce Akt phosphorylation at Thr(308) to a level similar to that of insulin stimulation. Furthermore, this increase in phosphorylation was independent of the Pleckstrin homology domain of Akt. Taken together, our results suggest that mPDK-1 undergoes autophosphorylation at multiple sites and that this phosphorylation may be essential for PDK-1 to interact with and phosphorylate its downstream substrates in vivo.
Wick
Michael J
MJ
Department of Pharmacology, The University of Texas Health Science Center, San Antonio, Texas 78229, USA.
Wick
KeriLyn R
KR
Chen
Hui
H
He
Huili
H
Dong
Lily Q
LQ
Quon
Michael J
MJ
Liu
Feng
F
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D018076:DNA, Complementary / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012694:Serine / Q000737:chemistry / Q000378:metabolism; D013912:Threonine / Q000737:chemistry*; D014162:Transfection
D018076:DNA, Complementary; D007328:Insulin; D013912:Threonine; D018698:Glutamic Acid; D012694:Serine; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578562:PDPK1 protein, human; D017346:Protein Serine-Threonine Kinases