Signal-regulatory protein alpha

SIRPA
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 2JJS, 2JJT, 2UV3, 2WNG, 4CMM
Identifiers
Aliases	SIRPA, BIT, CD172A, MFR, MYD-1, P84, PTPNS1, SHPS1, SIRP, Signal-regulatory protein alpha, signal regulatory protein alpha
External IDs	OMIM: 602461; MGI: 108563; HomoloGene: 7246; GeneCards: SIRPA; OMA:SIRPA - orthologs
Gene location (Human) Chr. Chromosome 20 (human)[1] Band 20p13 Start 1,894,167 bp[1] End 1,940,592 bp[1]
Gene location (Mouse) Chr. Chromosome 2 (mouse)[2] Band 2 F1|2 63.19 cM Start 129,434,755 bp[2] End 129,474,148 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in right frontal lobe Brodmann area 9 right hemisphere of cerebellum postcentral gyrus lateral nuclear group of thalamus prefrontal cortex superior frontal gyrus amygdala middle temporal gyrus nucleus accumbens Top expressed in stroma of bone marrow granulocyte prefrontal cortex superior frontal gyrus primary visual cortex dentate gyrus of hippocampal formation granule cell cerebellar cortex tibiofemoral joint perirhinal cortex entorhinal cortex More reference expression data BioGPS More reference expression data
Gene ontology Molecular function SH3 domain binding protein phosphatase binding GTPase regulator activity protein binding involved in heterotypic cell-cell adhesion cell-cell adhesion mediator activity protein antigen binding protein tyrosine kinase binding Cellular component integral component of membrane plasma membrane extracellular exosome membrane tertiary granule membrane ficolin-1-rich granule membrane integral component of plasma membrane cell surface Biological process cell adhesion leukocyte migration neutrophil degranulation negative regulation of protein phosphorylation regulation of gene expression cell migration positive regulation of cell-cell adhesion regulation of interferon-gamma production regulation of interleukin-1 beta production regulation of interleukin-6 production regulation of tumor necrosis factor production negative regulation of interferon-beta production negative regulation of interleukin-6 production negative regulation of tumor necrosis factor production heterotypic cell-cell adhesion monocyte extravasation negative regulation of nitric oxide biosynthetic process regulation of nitric oxide biosynthetic process negative regulation of JNK cascade negative regulation of inflammatory response negative regulation of phagocytosis positive regulation of phagocytosis regulation of catalytic activity positive regulation of T cell activation cellular response to hydrogen peroxide negative regulation of ERK1 and ERK2 cascade cellular response to lipopolysaccharide cellular response to interferon-gamma cellular response to interleukin-1 cellular response to interleukin-12 negative regulation of macrophage inflammatory protein 1 alpha production negative regulation of chemokine (C-C motif) ligand 5 production cell-cell adhesion negative regulation of cytokine production involved in inflammatory response negative regulation of I-kappaB phosphorylation Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 140885 19261 Ensembl ENSG00000198053 ENSMUSG00000037902 UniProt P78324 P97797 RefSeq (mRNA) NM_001040022 NM_001040023 NM_080792 NM_001330728 NM_001177646 NM_001177647 NM_001291019 NM_001291020 NM_001291021 NM_001291022 NM_007547 NM_001355158 NM_001355160 RefSeq (protein) NP_001035111 NP_001035112 NP_001317657 NP_542970 NP_001171118 NP_001277948 NP_001277949 NP_001277950 NP_001277951 NP_031573 NP_001342087 NP_001342089 Location (UCSC) Chr 20: 1.89 – 1.94 Mb Chr 2: 129.43 – 129.47 Mb PubMed search [3] [4]
Wikidata
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Signal regulatory protein α (SIRPα) is a regulatory membrane glycoprotein from SIRP family expressed mainly by myeloid cells and also by stem cells^{[citation needed]} or neurons.

SIRPα acts as inhibitory receptor and interacts with a broadly expressed transmembrane protein CD47 also called the "don't eat me" signal. This interaction negatively controls effector function of innate immune cells such as host cell phagocytosis. SIRPα diffuses laterally on the macrophage membrane and accumulates at a phagocytic synapse to bind CD47 and signal 'self', which inhibits the cytoskeleton-intensive process of phagocytosis by the macrophage.^[5] This is analogous to the self signals provided by MHC class I molecules to NK cells via Ig-like or Ly49 receptors.^[6][7] NB. Protein shown to the right is CD47 not SIRP α.

Structure

The cytoplasmic region of SIRPα is highly conserved between rats, mice and humans. Cytoplasmic region contains a number of tyrosine residues, which likely act as ITIMs. Upon CD47 ligation, SIRPα is phosphorylated and recruits phosphatases like SHP1 and SHP2.^[8] The extracellular region contains three Immunoglobulin superfamily domains – single V-set and two C1-set IgSF domains. SIRP β and γ have the similar extracellular structure but different cytoplasmic regions giving contrasting types of signals. SIRP α polymorphisms are found in ligand-binding IgSF V-set domain but it does not affect ligand binding. One idea is that the polymorphism is important to protect the receptor of pathogens binding.^[6][9]

Ligands

SIRPα recognizes CD47, an anti-phagocytic signal that distinguishes live cells from dying cells. CD47 has a single Ig-like extracellular domain and five membrane spanning regions. The interaction between SIRPα and CD47 can be modified by endocytosis or cleavage of the receptor, or interaction with surfactant proteins. Surfactant protein A and D are soluble ligands, highly expressed in the lungs, that bind to the same region of SIRPα as CD47 and can therefore competitively block binding.^[9][10]

Signalling

The extracellular domain of SIRP α binds to CD47 and transmits intracellular signals through its cytoplasmic domain. CD47-binding is mediated through the NH2-terminal V-like domain of SIRP α. The cytoplasmic region contains four ITIMs that become phosphorylated after binding of ligand. The phosphorylation mediates activation of tyrosine kinase SHP2. SIRP α has been shown to bind also phosphatase SHP1, adaptor protein SCAP2 and FYN-binding protein. Recruitment of SHP phosphatases to the membrane leads to the inhibition of myosin accumulation at the cell surface and results in the inhibition of phagocytosis.^[9][10]

Cancer

Cancer cells highly expressed CD47 that activate SIRP α and inhibit macrophage-mediated destruction. In one study, they engineered high-affinity variants of SIRP α that antagonized CD47 on cancer cells and caused increase phagocytosis of cancer cells.^[11] Another study (in mice) found anti-SIRPα antibodies helped macrophages to reduce cancer growth and metastasis, alone and in synergy with other cancer treatments.^[12][13]

References

Further reading

This article incorporates text from the United States National Library of Medicine, which is in the public domain.