AH PH DOMAIN-MEDIATED INTERACTION BETWEEN AKT MOLECULES AND ITS POTENTIAL ROLE IN AKT REGULATION/

The cytoplasmic serine-threonine protein kinase coded for by the e-akr proto-oncogene features a protein kinase C-like catalytic domain and a unique NH2-terminal domain (AH domain). The AH domain is a member of a domain superfamily whose prototype was observed in pleckstrin (plec kstrin homology, or PH, domain). In this communication, we present evi dence that the AH/PH domain is a domain of protein-protein interaction which mediates the formation of Akt protein complexes. The interactio n between c-akt AH/PH domains is highly specific, as determined by the failure of this domain to bind AKT2. The AH/PH domain-mediated intera ctions depend on the integrity of the entire domain. Akt molecules wit h deletions of the NH2-terminal portion (amino acids 11 to 60) and AH/ PH constructs with deletions of the C-terminal portion of this domain (amino acids 107 to 147) fail to interact with c-akt. To determine the significance of these findings, we carried out in vitro kinase assays using Akt immunoprecipitates from serum-starved and serum-starved, pl atelet-derived growth factor-stimulated NIH 3T3 cells. Addition of mal tose-binding protein-AH/PH fusion recombinant protein, which is expect ed to bind Akt, to the immunoprecipitates from serum-starved cells ind uced the activation of the Akt kinase.