Signal Regulatory Proteins Negatively Regulate Immunoreceptor-dependent Cell Activation

doi:10.1074/jbc.274.45.32493

Signal Regulatory Proteins Negatively Regulate Immunoreceptor-dependent Cell Activation*

From the Laboratoire d'Immunologie Cellulaire et Clinique, INSERM U.255, Institut Curie, 75005 Paris, France

Abstract

Signal regulatory proteins of the α subtype (SIRPα) are ubiquitous molecules of the immunoglobulin superfamily that negatively regulate protein tyrosine kinase receptor-dependent cell proliferation. Their intracytoplasmic domain contains four motifs that resemble immunoreceptor tyrosine-based inhibition motifs (ITIMs) and that, when tyrosyl-phosphorylated, recruit cytoplasmic SH2 domain-bearing protein tyrosine phosphatases (SHPs). ITIMs are borne by molecules that negatively regulate cell activation induced by receptors bearing immunoreceptor tyrosine-based activation motifs (ITAMs). Because SIRPα are coexpressed with ITAM-bearing receptors in hematopoietic cells, we investigated whether SIRPα could negatively regulate ITAM-dependent cell activation. We found SIRPα transcripts in human mast cells, and we show that a chimeric molecule having the transmembrane and intracytoplasmic domains of SIRPα could inhibit IgE-induced mediator secretion and cytokine synthesis by mast cells. Inhibition required that the SIRPα chimera was coaggregated with ITAM-bearing high affinity IgE receptors (FcεRI). It was correlated with the tyrosyl phosphorylation of the SIRPα chimera and the recruitment of SHP-1 and SHP-2. The phosphorylation of FcεRI ITAMs was decreased; the mobilization of intracellular Ca²⁺and the influx of extracellular Ca²⁺ were reduced, and the activation of the mitogen-activated protein kinases Erk1 and Erk2 was abolished. SIRPα can therefore negatively regulate not only receptor tyrosine kinase-dependent cell proliferation but also ITAM-dependent cell activation.

Footnotes

↵* This work was supported by the INSERM, the Association pour la Recherche sur le Cancer, and the Institut Curie.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‡ Recipient of a Rhône-Poulenc Rorer CIFRE contract.
↵§ Recipient of a fellowship from the Ministère de l'Enseignement Supérieur et de la Recherche.
↵¶ To whom correspondence should be addressed: Laboratoire d'Immunologie Cellulaire et Clinique, INSERM U.255, Institut Curie, 26 rue d'Ulm, 75005 Paris, France. Tel.: 33-1-4432-4223; Fax: 33-1-4051-0420; E-mail: Marc.Daeron@curie.fr.
Abbreviations:

BIT

brain immunoglobulin-like molecule with tyrosine-based activation motifs

FcεRI

high affinity IgE receptors

FcγRIIB and FcγRIIIA

low affinity IgG Receptors

GAM

goat anti-mouse Ig

GAR

goat anti-rabbit Ig

HRP

horseradish peroxidase

IC

intracytoplasmic

ITAM

immunoreceptor tyrosine-based activation motif

ITIM

immunoreceptor tyrosine-based inhibition motif

KIRs

killer cell inhibitory receptors

MAR

mouse anti-rat Ig

RTK

receptor tyrosine kinase

SH2

Src homology domain 2

SHIP

SH2 domain-bearing inositol-phosphate phosphatase

SHP

SH2 domain-bearing protein tyrosine phosphatase

SHPS-1

SH2 domain-bearing phosphatase substrate 1

SIRPs

signal regulatory proteins

TNP

trinitrophenyl

MAP

mitogen-activated protein

DNP

2,4-dinitrophenol

BSA

bovine serum albumin

mAb

monoclonal antibody

FITC

fluorescein isothiocyanate

PAGE

polyacrylamide gel electrophoresis

RT-PCR

reverse transcriptase-polymerase chain reaction

TNF

tumor necrosis factor

TM

transmembrane
- Received May 18, 1999.
- Revision received September 3, 1999.
The American Society for Biochemistry and Molecular Biology, Inc.