PI3K
Adaptor Subunits Define Coupling to Degranulation and Cell Motility by Distinct PtdIns(3,4,5)P3 Pools in Mast Cells
Thomas Bohnacker1,
Romina Marone1*,
Emilie Collmann1*,
Ronan Calvez1
,
Emilio Hirsch2, and
Matthias P. Wymann1
1 Institute of Biochemistry and Genetics, Department of Biomedicine, University of Basel, Mattenstrasse 28, CH-4058 Basel, Switzerland.
2 Dipartimento di Genetica, Biologia e Biochimica, Università di Torino, Via Nizza 52, I-10126 Turin, Italy.
* These authors contributed equally to this work.
Present address: Marie Curie Excellence Team, INSERM U563, CHU Purpan, BP 3028, 31024 Toulouse Cedex 3, France.
Abstract:
Phosphoinositide 3-kinase 
(PI3K) plays a major role in chronic inflammation and allergy. It is a heterodimer of a catalytic p110 subunit and an adaptor protein, either p101 or the p101 homolog p84 (p87PIKAP). It is unclear whether both PI3K complexes specifically modulate responses such as chemotaxis and degranulation. In mast cells, the p84:p110 complex synergizes with immunoglobulin E (IgE)– and antigen-clustered Fc
RI receptor signaling and is required to achieve maximal degranulation. During this process, PI3K is activated by ligands of heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (GPCRs), in particular adenosine receptors, through autocrine and paracrine pathways. Here, we show that p110 needs p84 to relay signals from GPCRs to formation of phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3], phosphorylation of Akt, migration of cells, and synergistic adenosine-enforced degranulation. Furthermore, the absence of adaptor subunits could not be compensated for by increased p110 abundance. Differentiated, p110 null cells also lost adaptor proteins. Complementation of p110 null mast cells with p101 and p110 restored the activation of Akt and cell migration, but failed to support degranulation. Lack of degranulation was attributed to a change in the spatiotemporal localization of PI3K-derived PtdIns(3,4,5)P3; although both p84:p110 and p101:p110 complexes initially deposited PtdIns(3,4,5)P3 at the plasma membrane, p101:p110–derived PtdIns(3,4,5)P3 was rapidly endocytosed to motile, microtubule-associated vesicles. In addition, p84:p110, but not p101:p110 signaling was sensitive to disruption of lipid rafts. Our results demonstrate a nonredundant function for the p101 and p84 PI3K adaptor proteins and show that distinct pools of PtdIns(3,4,5)P3 at the plasma membrane can elicit specific cell responses.
To whom correspondence should be addressed. E-mail: Matthias.Wymann{at}UniBas.ch
