Intracellular Immunoreceptor Tyrosine-based Inhibitory Motifs Research Articles

Identification of a variant form of PZR lacking immunoreceptor tyrosine-based inhibitory motifs

PZR is an immunoglobulin superfamily protein that specifically binds tyrosine phosphatase SHP-2 through its intracellular immunoreceptor tyrosine-based inhibitory motifs (ITIMs). Here we report a novel isoform of the protein designated PZR1b. PZR1b shares the same extracellular region with PZR, but it lacks intracellular ITIMs and thus the ability to recruit SHP-2. Genomic sequence analysis revealed that PZR1b is resulted from alternative gene splicing of the PZR gene localized at chromosome 1q24. Like PZR, PZR1b is widely expressed. However, the relative ratio of two forms varies in different human tissues and cells. More importantly, overexpression of PZR1b in human HT-1080 cells had a dominant negative effect by blocking concanavalin A-induced tyrosine phosphorylation of full-length PZR and recruitment of tyrosine phosphatase SHP-2. Therefore, PZR1b may have an important role in cell signaling by counteracting with PZR.

CD47 is a ligand for rat macrophage membrane signal regulatory protein SIRP (OX41) and human SIRPalpha 1.

The rat OX41 antigen is a cell surface protein containing three immunoglobulin superfamily domains and intracellular immunoreceptor tyrosine-based inhibitory motifs (ITIM). It is a homologue of the human signal-regulatory protein (SIRP) also known as SHPS-1, BIT or MFR. Cell activation-induced phosphorylation of the intracellular ITIM motifs induces association with the tyrosine phosphatases SHP-1 and SHP-2. To identify the physiological OX41 ligand, recombinant OX41-CD4d3+4 fusion protein was coupled to fluorescent beads to produce a multivalent cell binding reagent. The OX41-CD4d3+4 beads bound to thymocytes and concanavalin A-stimulated splenocytes. This interaction was blocked by the monoclonal antibody (mAb) OX101. Affinity chromatography with OX101 mAb and peptide sequencing revealed the rat SIRP ligand to be CD47 (integrin-associated protein). A direct interaction between human SIRP and human CD47 was demonstrated using purified recombinant proteins and surface plasmon resonance ruling out the involvement of other proteins known to be associated with CD47. The affinity of the SIRP/CD47 interaction was K(d) approximately 8 microM at 37 degrees C with a k(off )>/=2.1 s(-1). The membrane-distal SIRP V-like domain was sufficient for binding to CD47.