Identification of a chromosome 3p14.3-21.1 gene, APPL, encoding an adaptormolecule that interacts with the oncoprotein-serine/threonine kinase AKT2

AKT2 is a serine/threonine kinase implicated in human ovarian and pancreati c cancers, AKT2 is activated by a variety of growth factors and insulin via phosphatidylinositol 3-kinase (PI3K), However, its normal cellular role is not well understood, To gain insight into the function of AKT2, we perform ed yeast two-hybrid system to screen for interacting proteins. Using this t echnique, we identified a novel interactor, designated APPL, which contains a pleckstrin homology (PH) domain, a phosphotyrosine binding (PTB) domain and a leucine zipper, classes of motifs defined in signaling molecules as f unctional interaction domains with specific targets. The PH domain of APPL shows similarity to those found in GTPase-activating proteins such as oligo phrenin-1 and Craf, whereas its PTB domain exhibits homology with CED-6, an adaptor protein that promotes engulfment of apoptotic cells, and IB1, a tr ansactivator of the GLUT2 gene. APPL is highly expressed in skeletal muscle , heart, ovary and pancreas, tissues in which AKT2 mRNA is abundant. APPL i nteracts with the inactive form of AKT2; moreover, APPL binds to the PI3K c atalytic subunit, p110 alpha. These data suggest that APPL is an adaptor th at may tether inactive AKT2 to p110 alpha in the cytoplasm and thereby may expedite recruitment of AKT2 and p110 alpha to the cell membrane upon mitog enic stimulation. Furthermore, the APPL gene was mapped to human chromosome 3p14.3-p21.1, where deletions and other rearrangements have often been rep orted in a variety of tumor types, The identification of APPL may facilitat e further analysis of the physiological and oncogenic activities of AKT2.