Tyrosine-protein phosphatase non-receptor type substrate 1 （SHPS1）, also known as CD172 antigen-like family member A （CD172a）, Macrophage fusion receptor, MyD-1 antigen, Signal-regulatory protein alpha （SIRPA or SIRP alpha）, or p84, is a member of the SIRP family and belongs to the immunoglobulin superfamily. SIRP alpha is ubiquitously expressed, with particularly high levels in the brain. SIRPA/CD172a is an immunoglobulin-like cell surface receptor for CD47 and acts as a docking protein, inducing the translocation of PTPN6, PTPN11, and other binding partners from the cytosol to the plasma membrane.
SIRPA/SHPS-1 supports the adhesion of cerebellar neurons, neurite outgrowth, and glial cell attachment, and may play a key role in intracellular signaling during synaptogenesis and synaptic function. By similarity, SIRPA/MyD1 is involved in the negative regulation of receptor tyrosine kinase-coupled cellular responses induced by cell adhesion, growth factors, or insulin, and mediates negative regulation of phagocytosis, mast cell activation, and dendritic cell activation. CD47 binding prevents the maturation of immature dendritic cells and inhibits cytokine production by mature dendritic cells.