Activation of the Akt-related cytokine-independent survival kinase requires interaction of its phox domain with endosomal phosphatidylinositol 3-phosphate

UMMS Affiliation

Program in Molecular Medicine

Publication Date


Document Type



Animals; COS Cells; Cytokines; Endosomes; Enzyme Activation; Epidermal Growth Factor; Insulin-Like Growth Factor I; Microscopy, Fluorescence; Phosphoric Monoester Hydrolases; Protein Binding; Protein Kinases; *Protein-Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt


Life Sciences | Medicine and Health Sciences


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.

DOI of Published Version



Proc Natl Acad Sci U S A. 2001 Nov 6;98(23):12908-13. Epub 2001 Oct 23. Link to article on publisher's site

Journal/Book/Conference Title

Proceedings of the National Academy of Sciences of the United States of America

Related Resources

Link to Article in PubMed

PubMed ID