Phosphoinositide 3-Kinase and p72 Noncovalently Associate with the Low Affinity Fc Receptor on Human Platelets through an Immunoreceptor Tyrosine-based Activation Motif

doi:10.1074/jbc.271.18.10775

Phosphoinositide 3-Kinase and p72 Noncovalently Associate with the Low Affinity Fc Receptor on Human Platelets through an Immunoreceptor Tyrosine-based Activation Motif

RECONSTITUTION WITH SYNTHETIC PHOSPHOPEPTIDES (*)

From the (1)Departments of Internal Medicine,
(2)Pathology, and
(3)Microbiology, The Ohio State University, Columbus, Ohio 43210

^¶ To whom correspondence should be addressed:
S2054 Davis Medical Center, 480 W. 9th Ave., Columbus, OH 43210.
Tel.: 614-293-4819; Fax: 614-293-5631; anderson.48{at}osu.edu.

↵^§ Present address: Dept. of Microbiology, The Ohio State University, Columbus, OH 43210.

Abstract

Previously, we have demonstrated that the cytoplasmic tyrosine kinase p72 is coupled to the platelet Fc receptor for IgG (FcRIIA) (Chacko, G. W., Duchemin, A. M., Coggeshall, K. M., Osborne, J. M., Brandt, J. T., and Anderson, C. L. (1994) J. Biol. Chem. 269, 32435-32440). Further analysis of the platelet activation by FcRIIA demonstrated that FcRIIA is also inducibly coupled to the serine/threonine and lipid kinase, phosphoinositide 3-kinase (PI 3-K). Activation of platelets with anti-FcRIIA antibodies resulted in the noncovalent association of PI 3-K with FcRIIA as well as an increase in FcRIIA-associated PI 3-K activity. Binding of both p72 and PI 3-K to FcRIIA was reconstituted with synthetic phosphopeptides corresponding to the sequence of the atypical immunoreceptor tyrosine-based activation motif (ITAM) in the cytoplasmic domain of FcRIIA. Our findings demonstrate that coupling of both p72 and PI 3-K activities to FcRIIA is regulated by tyrosine phosphorylation of the ITAM, and we speculate that p72 might act as an adapter to recruit PI 3-K to activated FcRIIA.

Footnotes

↵* This work was supported by United States Public Health Service Award RO1-HL46652 (to C. L. A.) and CA64268 (to K. M. C.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

FcR

Fc receptor for IgG

ITAM

immunoreceptor tyrosine-based activation motif

PDGF

platelet-derived growth factor

SOS

Son of Sevenless

Grb2

growth factor receptor binding protein 2

PI 3-K

phosphoinositide 3-kinase

PtdIns

phosphatidylinositol

SH2

src homology region 2

SH3

src homology region 3.
↵²Immunoblotting experiments determined that the expression p72 from Raji cells was reactive with the anti-p72 antibody under our conditions of immunoprecipitation and immunoblotting. Therefore, Raji cells were used a source of p72 in some binding experiments.
↵³D. M. Maresco, A. C. Chan, and C. L. Anderson, manuscript in preparation.
- Received December 4, 1995.
- Revision received February 14, 1996.