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-l phosphorylate threonine-308, Integrin-linked kinase reportedly phophorylates serine-473, Consistent,vith 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 C-2-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, 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.