title: Inhibition of PI3K binding to activators by serine phosphorylation of PI3K regulatory subunit p85alpha Src homology-2 domains.
abstract: Class IA PI3Ks are activated by growth factor receptors and generate lipid second messengers that mediate downstream responses including cell growth, cell migration, and cell survival. The p85 regulatory subunit of PI3K contains Src homology-2 (SH2) domains that mediate binding to tyrosine-phosphorylated receptors or adaptor proteins to facilitate localization and activation of PI3K at the plasma membrane. We report here that persistent activation of PKC family members by phorbol ester stimulation in cells leads to phosphorylation of two serine residues at analogous sites on both SH2 domains of p85α (S361 and S652). The modified serine residues are located in the phospho-tyrosine binding pockets of the two SH2 domains, and in the crystal structures the phosphate moieties are predicted to occupy the same space as the phosphate moieties of bound phospho-tyrosine peptides. Consistent with this prediction, phosphorylation at these serine residues or mutation to aspartate inhibits binding of p85α to tyrosine-phosphorylated peptides. We provide evidence that protein kinase D, which is phosphorylated and activated by PKCs, mediates phosphorylation of S652 in the C-terminal SH2 domain. These results reveal cross talk between PKC signaling and PI3K signaling that impairs PI3K pathway activation under conditions of persistent PKC (and protein kinase D) activity.
authors.affiliation: Division of Signal Transduction, Cancer Center, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
authors.forename: Jennifer Y
authors.initials: JY
authors.lastname: Lee
authors.forename: Yu-Hsin
authors.initials: YH
authors.lastname: Chiu
authors.forename: John
authors.initials: J
authors.lastname: Asara
authors.forename: Lewis C
authors.initials: LC
authors.lastname: Cantley
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D058543:Class Ia Phosphatidylinositol 3-Kinase / Q000737:chemistry* / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D020536:Enzyme Activators / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010455:Peptides / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D055503:Protein Multimerization / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D018909:src Homology Domains
chemical_list: D020536:Enzyme Activators; D010455:Peptides; D010768:Phosphoserine; D019000:Phosphotyrosine; D058543:Class Ia Phosphatidylinositol 3-Kinase; C089212:protein kinase D; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate