Gβγ Stimulates Phosphoinositide 3-Kinase-γ by Direct Interaction with Two Domains of the Catalytic p110 Subunit

• Published in: The Journal of biological chemistry Vol. 273; no. 12; p. 7024
• Main Authors: Daniela Leopoldt, Theodor Hanck, Torsten Exner, Udo Maier, Reinhard Wetzker, Bernd Nürnberg
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 20-03-1998
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.12.7024

Class I phosphoinositide 3-kinases (PI3Ks) regulate important cellular processes such as mitogenesis, apoptosis, and cytoskeletal
functions. They include PI3Kα, -β, and -δ isoforms coupled to receptor tyrosine kinases and a PI3Kγ isoform activated by receptor-stimulated
G proteins. This study examines the direct interaction of purified recombinant PI3Kγ catalytic subunit (p110γ) and Gβγ complexes.
When phosphatidylinositol was used as a substrate, Gβγ stimulated p110γ lipid kinase activity more than 60-fold (EC 50 , ∼20 n m ). Stimulation was inhibited by Gα o -GDP or wortmannin in a concentration-dependent fashion. Stoichiometric binding of a monoclonal antibody to the putative pleckstrin
homology domain of p110γ did not affect Gβγ-mediated enzymatic stimulation, whereas incubation of Gβγ with a synthetic peptide
resembling a predicted Gβγ effector domain of type 2 adenylyl cyclase selectively inhibited activation of p110γ. Gβγ complexes
bound to N- as well as C-terminal deletion mutants of p110γ. Correspondingly, these enzymatically inactive N- and C-terminal
mutants inhibited Gβγ-mediated activation of wild type p110γ. Our data suggest that (i) p110γ directly interacts with Gβγ,
(ii) the pleckstrin homology domain is not the only region important for Gβγ-mediated activation of the lipid kinase, and
(iii) Gβγ binds to at least two contact sites of p110γ, one of which is close to or within the catalytic core of the enzyme.