AH/PH Domain-Mediated Interaction between Akt Molecules and Its Potential Role in Akt Regulation

Abstract

The cytoplasmic serine-threonine protein kinase coded for by the c-akt proto-oncogene features a protein kinase C-like catalytic domain and a unique NH 2 -terminal domain (AH domain). The AH domain is a member of a domain superfamily whose prototype was observed in pleckstrin (pleckstrin homology, or PH, domain). In this communication, we present evidence that the AH/PH domain is a domain of protein-protein interaction which mediates the formation of Akt protein complexes. The interaction 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 interactions depend on the integrity of the entire domain. Akt molecules with deletions of the NH 2 -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, plateletderived growth factor-stimulated NIH 3T3 cells. Addition of maltose-binding protein-AH/PH fusion recombinant protein, which is expected to bind Akt, to the immunoprecipitates from serum-starved cells induced the activation of the Akt kinase.

Protein kinase B (c-Akt): a multifunctional mediator of phosphatidylinositol 3-kinase activation

“…It has been demonstrated that the PH domain of PKB mediates interaction between PKB molecules, playing a role in regulation [51]. Transfection of COS-1 cells with an epitope-tagged C-terminally truncated PKB allows co-immunoprecipitation of full-length PKB.…”

“…In Madin-Darby canine kidney (MDCK) cells it has been demonstrated that detachment from the matrix leads to a rapid decrease in the levels of PI-3K products and PKB activity, and vice versa for attachment [120]. Introduction of active mutants of p21ras, PI-3K or PKB protects MDCK cells from apoptosis in suspension, while inhibition of PI-3K with LY294002, or PKB by transient expression of the PH domain alone [51], resulted in enhanced apoptosis of adhered cells [120]. These data suggest a model whereby through engagement of integrins by extracellular-matrix interactions, PI-3K becomes activated and provides a protective signal through activation of PKB.…”

Targeting the translational apparatus to improve leukemia therapy: roles of the PI3K/PTEN/Akt/mTOR pathway

“…Akt can directly phosphorylate BAD on S136 (ref. 94,95), causing its inactivation and inability to interact with antiapoptotic members of the Bcl-2 family of proteins (Bcl-2, Bcl-X L ). 96,97 Activated Akt can inhibit the release of cytochrome c from the mitochondria, which is a potent activator of the apoptotic caspase cascade.…”

Immunohistochemical heterogeneity of breast carcinomas negative for estrogen receptors, progesterone receptors and Her2/neu (basal-like breast carcinomas)

“…[51][52][53][54][55][56] Generally, PTEN absence in breast carcinomas is due to gene promoter hypermethylation [51][52][53][54][55] or loss of heterozygosity, 53 whereas PTEN mutations are exceptional in sporadic neoplasms. 57 Loss of 51,56 as in our series where Akt, present in 28% of tumors, was more frequently associated with growth factor receptors than with the PTEN pathway. 52,57 Recently, pAkt overexpression was described in 33% of in situ and 38% of ductal invasive breast carcinomas, although without any significant clinicopathological relationship, 56 as in our cases.…”