Integrin-linked kinase regulates phosphorylation of serine 473 of protein kinase B by an indirect mechanism.
The serine threonine kinase protein kinase B regulates cellular activities as diverse as glycogen metabolism and apoptosis. Full activation of protein kinase B requires 3-phosphoinositides and dual phosphorylation on threonine-308 and serine-473. CaM-K kinase and 3-phosphoinositide dependent-kinase-1 phosphorylate threonine-308. Integrin-linked kinase reportedly phophorylates serine-473. Consistent with this, in a model COS cell system we show that expression of wild-type integrin-linked kinase promotes the wortmannin sensitive phosphorylation of serine-473 of protein kinase B and its downstream substrates, and inhibits C2-ceramide induced apoptosis. In contrast, integrin-linked kinase mutated in a lysine residue critical for function in protein kinases is inactive in these experiments, and furthermore, acts dominantly to block serine-473 phosphorylation induced by ErbB4. However, alignment of analogous sequences from different species demonstrates that integrin-linked kinase is not a typical protein kinase and identifies a conserved serine residue which potentially regulates kinase activity in a phosphorylation dependent manner. Mutation of this serine to aspartate or glutamate, but not alanine, in combination with the inactivating lysine mutation restores integrin-linked kinase dependent phosphorylation of serine-473 of protein kinase B. These data strongly suggest that integrin-linked kinase does not possess serine-473 kinase activity but functions as an adaptor to recruit a serine-473 kinase or phosphatase.
Lynch
D K
DK
Department of Pathology, Cambridge Unversity, Tennis Court Road, Cambridge CB2 1QP, UK.
Ellis
C A
CA
Edwards
P A
PA
Hiles
I D
ID
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins; D020134:Catalytic Domain; D029721:Drosophila Proteins; D004331:Drosophila melanogaster; D006801:Humans; D008969:Molecular Sequence Data; D010716:Phosphatidylinositols / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D000099200:Scaffold Protein ILK
D029742:Caenorhabditis elegans Proteins; D029721:Drosophila Proteins; D010716:Phosphatidylinositols; D010768:Phosphoserine; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D011994:Recombinant Proteins; D000099200:Scaffold Protein ILK; C494917:Akt1 protein, Drosophila; C494915:akt-1 protein, C elegans