Regulation of protein kinase B/Akt-serine 473 phosphorylation by integrin-linked kinase: critical roles for kinase activity and amino acids arginine 211 and serine 343.
Protein kinase B (PKB/Akt) is a regulator of cell survival and apoptosis. To become fully activated, PKB/Akt requires phosphorylation at two sites, threonine 308 and serine 473, in a phosphatidylinositol (PI) 3-kinase-dependent manner. The kinase responsible for phosphorylation of threonine 308 is the PI 3-kinase-dependent kinase-1 (PDK-1), whereas phosphorylation of serine 473 has been suggested to be regulated by PKB/Akt autophosphorylation in a PDK-1-dependent manner. However, the integrin-linked kinase (ILK) has also been shown to regulate phosphorylation of serine 473 in a PI 3-kinase-dependent manner. Whether ILK phosphorylates this site directly or functions as an adapter molecule has been debated. We now show by in-gel kinase assay and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry that biochemically purified ILK can phosphorylate PKB/Akt directly. Co-immunoprecipitation analysis of cell extracts demonstrates that ILK can complex with PKB/Akt as well as PDK-1 and that ILK can disrupt PDK-1/PKB association. The amino acid residue serine 343 of ILK within the activation loop is required for kinase activity as well as for its interaction with PKB/Akt. Mutational analysis of ILK further shows a crucial role for arginine 211 of ILK within the phosphoinositide phospholipid binding domain in the regulation of PKB- serine 473 phosphorylation. A highly selective small molecule inhibitor of ILK activity also inhibits the ability of ILK to phosphorylate PKB/Akt in vitro and in intact cells. These data demonstrate that ILK is an important upstream kinase for the regulation of PKB/Akt.
Persad
S
S
British Columbia Cancer Agency, Vancouver Hospital Health Sciences Centre, Jack Bell Research Centre, Vancouver, British Columbia V6H 3Z6, Canada.
Attwell
S
S
Gray
V
V
Mawji
N
N
Deng
J T
JT
Leung
D
D
Yan
J
J
Sanghera
J
J
Walsh
M P
MP
Dedhar
S
S
D000595:Amino Acid Sequence; D001483:Base Sequence; D017931:DNA Primers; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012694:Serine / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014407:Tumor Cells, Cultured; D000099200:Scaffold Protein ILK
D017931:DNA Primers; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012694:Serine; D000099200:Scaffold Protein ILK; C494918:AKT1 protein, human