Functional requirements for inhibitory signal transmission by the immunomodulatory receptor CD300a

Karen E Debell,Francisco Borrego,Venkateswara R Simhadri,John L Mariano

doi:10.1186/1471-2172-13-23

Abstract

BackgroundActivation signals can be negatively regulated by cell surface receptors bearing immunoreceptor tyrosine-based inhibitory motifs (ITIMs). CD300a, an ITIM bearing type I transmembrane protein, is expressed on many hematopoietic cells, including subsets of lymphocytes.ResultsWe have taken two approaches to further define the mechanism by which CD300a acts as an inhibitor of immune cell receptor signaling. First, we have expressed in Jurkat T cells a chimeric receptor consisting of the extracellular domains of killer-cell immunoglobulin-like receptor (KIR)2DL2 fused to the transmembrane and cytoplasmic segments of CD300a (KIR-CD300a) to explore surrogate ligand-stimulated inhibition of superantigen stimulated T cell receptor (TCR) mediated cell signaling. We found that intact CD300a ITIMs were essential for inhibition and that the tyrosine phosphorylation of these ITIMs required the src tyrosine kinase Lck. Tyrosine phosphorylation of the CD300a ITIMs created docking sites for both src homology 2 domain containing protein tyrosine phosphatase (SHP)-1 and SHP-2. Suppression of SHP-1 and SHP-2 expression in KIR-CD300a Jurkat T cells with siRNA and the use of DT40 chicken B cell lines expressing CD300a and deficient in several phosphatases revealed that SHP-1, but not SHP-2 or the src homology 2 domain containing inositol 5’ phosphatase SHIP, was utilized by CD300a for its inhibitory activity.ConclusionThese studies provide new insights into the function of CD300a in tuning T and B cell responses.

Highlights

Activation signals can be negatively regulated by cell surface receptors bearing immunoreceptor tyrosine-based inhibitory motifs (ITIMs)
Intact ITIM motifs are required for CD300a mediated inhibitory signal Recently, we have demonstrated that the immunomodulatory receptor CD300a is expressed in certain subsets of human B and T cells and that it functions as a negative regulator of B and T cell signaling [25,33,38]
We examined the inhibitory effects of CD300a ligation on two B cell receptor (BCR) mediated events

Summary

Introduction

Activation signals can be negatively regulated by cell surface receptors bearing immunoreceptor tyrosine-based inhibitory motifs (ITIMs). A characteristic of many of these receptors is a consensus amino acid sequence in their cytoplasmic tail, i.e. the immunoreceptor tyrosine-based inhibitory motif (ITIM) [3,4,5,6,7,8]. Ligand interaction with these receptors results in ITIM tyrosine phosphorylation, usually by a src family kinase, providing sites for binding proteins via their src-homology 2 (SH2) domains [9,10,11,12,13,14]. Several targets of these phosphatases have been proposed, the specific pathways and mechanisms by which each phosphatase participates in the signaling cascade downstream from the inhibitory receptors remain incompletely understood [17,18,19]

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Conclusion