title: Ras is an indispensable coregulator of the class IB phosphoinositide 3-kinase p87/p110gamma.
abstract: Class I(B) phosphoinositide 3-kinase gamma (PI3Kgamma) elicits various immunologic and cardiovascular responses; however, the molecular basis for this signal heterogeneity is unclear. PI3Kgamma consists of a catalytic p110gamma and a regulatory p87(PIKAP) (p87, also p84) or p101 subunit. Hitherto p87 and p101 are generally assumed to exhibit redundant functions in receptor-induced and G protein betagamma (Gbetagamma)-mediated PI3Kgamma regulation. Here we investigated the molecular mechanism for receptor-dependent p87/p110gamma activation. By analyzing GFP-tagged proteins expressed in HEK293 cells, PI3Kgamma-complemented bone marrow-derived mast cells (BMMCs) from p110gamma(-/-) mice, and purified recombinant proteins reconstituted to lipid vesicles, we elucidated a novel pathway of p87-dependent, G protein-coupled receptor (GPCR)-induced PI3Kgamma activation. Although p101 strongly interacted with Gbetagamma, thereby mediating PI3Kgamma membrane recruitment and stimulation, p87 exhibited only a weak interaction, resulting in modest kinase activation and lack of membrane recruitment. Surprisingly, Ras-GTP substituted the missing Gbetagamma-dependent membrane recruitment of p87/p110gamma by direct interaction with p110gamma, suggesting the indispensability of Ras for activation of p87/p110gamma. Consequently, interference with Ras signaling indeed selectively blocked p87/p110gamma, but not p101/p110gamma, kinase activity in HEK293 and BMMC cells, revealing an important crosstalk between monomeric and trimeric G proteins for p87/p110gamma activation. Our data display distinct signaling requirements of p87 and p101, conferring signaling specificity to PI3Kgamma that could open up new possibilities for therapeutic intervention.
authors.affiliation: Department of Pharmacology and Experimental Therapy, Institute of Experimental and Clinical Pharmacology and Toxicology, Eberhard Karls University Hospitals and Clinics, and Interfaculty Center of Pharmacogenomics and Pharmaceutical Research, University of Tübingen, 72074 Tübingen, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Kurig
authors.forename: Aliaksei
authors.initials: A
authors.lastname: Shymanets
authors.forename: Thomas
authors.initials: T
authors.lastname: Bohnacker
authors.lastname: Prajwal
authors.forename: Carsten
authors.initials: C
authors.lastname: Brock
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Ahmadian
authors.forename: Michael
authors.initials: M
authors.lastname: Schaefer
authors.forename: Antje
authors.initials: A
authors.lastname: Gohla
authors.forename: Christian
authors.initials: C
authors.lastname: Harteneck
authors.forename: Matthias P
authors.initials: MP
authors.lastname: Wymann
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Jeanclos
authors.forename: Bernd
authors.initials: B
authors.lastname: Nürnberg
mesh_terms: D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D049452:Green Fluorescent Proteins; D006801:Humans; D008407:Mast Cells / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D008958:Models, Molecular; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D043562:Receptors, G-Protein-Coupled; D049452:Green Fluorescent Proteins; D019869:Phosphatidylinositol 3-Kinases; D018631:ras Proteins