title: Activation of the Akt-related cytokine-independent survival kinase requires interaction of its phox domain with endosomal phosphatidylinositol 3-phosphate.
abstract: Protein kinases of the Akt and related serum- and glucocorticoid-regulated kinase (SGK) families are major downstream mediators of phosphatidylinositol (PI) 3-kinase signaling to many cellular processes including metabolic flux, membrane trafficking, and apoptosis. Activation of these kinases is thought to occur at the plasma membrane through their serine and threonine phosphorylation by the phosphoinositide-dependent kinase 1 (PDK1) protein kinase, which interacts with membrane 3'-polyphosphoinositides through its pleckstrin homology (PH) domain. Here, we demonstrate that the SGK family member cytokine-independent survival kinase (CISK) binds strongly and selectively to the monophosphoinositide PI(3)P through its phox homology (PX) domain. Comparing native green fluorescent protein-CISK (EGFP-CISK) to a mutant EGFP-CISK (Y51A) that displays attenuated binding to PI(3)P reveals that this interaction is both necessary and sufficient for its localization to early endosome antigen (EEA1)-positive endosomes. Furthermore, early endosome association of expressed epitope-tagged CISK in COS cells directed by binding of its PX domain to PI(3)P is required for activation of the CISK protein kinase by both insulin-like growth factor-1 and epidermal growth factor. Taken together, these results reveal a critical role of endosomal PI(3)P in the signal transmission mechanism whereby this survival kinase is activated in response to PI3-kinase stimulation by growth factors.
authors.affiliation: Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01605, USA.
authors.forename: J V
authors.initials: JV
authors.lastname: Virbasius
authors.forename: X
authors.initials: X
authors.lastname: Song
authors.forename: D P
authors.initials: DP
authors.lastname: Pomerleau
authors.forename: Y
authors.initials: Y
authors.lastname: Zhan
authors.forename: G W
authors.initials: GW
authors.lastname: Zhou
authors.forename: M P
authors.initials: MP
authors.lastname: Czech
mesh_terms: D000818:Animals; D019556:COS Cells; D016207:Cytokines / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism*; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066298:In Vitro Techniques; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt
chemical_list: D016207:Cytokines; D011518:Proto-Oncogene Proteins; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D010744:Phosphoric Monoester Hydrolases; C061816:phosphatidylinositol-3-phosphatase