CD47, a Ligand for the Macrophage Fusion Receptor, Participates in Macrophage Multinucleation

Abstract

The macrophage fusion receptor (MFR), also called P84/BIT/SIRP␣/SHPS-1, is a transmembrane glycoprotein that belongs to the superfamily of immunoglobulins. Previously, we showed that MFR expression is highly induced at the onset of fusion in macrophages, and that MFR appears to play a role in macrophagemacrophage adhesion/fusion leading to multinucleation. The recent finding that IAP/CD47 acts as a ligand for MFR led us to hypothesize that it interacts with CD47 at the onset of cell-cell fusion. CD47 is a transmembrane glycoprotein, which, like MFR, belongs to the superfamily of immunoglobulins. We show that macrophages express the hemopoietic form of CD47, the expression of which is induced at the onset of fusion, but to a lower level than MFR. A glutathione S-transferase CD47 fusion protein engineered to contain the extracellular domain of CD47, binds macrophages, associates with MFR, and prevents multinucleation. CD47 and MFR associate via their amino-terminal immunoglobulin variable domain. Of the nine monoclonal antibodies raised against the extracellular domain of CD47, three block fusion, as well as MFR-CD47 interaction, whereas the others have no effect. Together, these data suggest that CD47 is involved in macrophage multinucleation by virtue of interacting with MFR during adhesion/fusion.Osteoclasts and giant cells are characterized by multinucleation and a powerful ability to resorb the substrate onto which they adhere. Although osteoclasts and giant cells play an important role in bone remodeling and immune defense, respectively, they are also associated with osteoporosis, granulomatous diseases, and tumors.Multinucleation appears to endow macrophages with the capacity to digest and resorb extracellular infectious agents, foreign material, and other components that are too large to be internalized, such as bone. This resorption occurs in an "extracellular lysosomal compartment" sealed off between the multinucleated cell and its target substrate (reviewed in Ref.1). The plasma membrane that faces that extracellular domain is highly ruffled and specialized. Multinucleation gives macrophages added resorptive capacity, in part by making available a large excess of plasma membrane.Understanding the mechanism by which macrophages differentiate into osteoclasts and multinucleated giant cells is of extreme importance. One of the key steps in the differentiation of osteoclasts and giant cells is the fusion mechanism of their mononucleated precursor cells. It is assumed that both osteoclasts and giant cells originate from the fusion of mononuclear phagocytes. Despite the pathophysiological importance of these cells, the mechanism by which their mononucleated precursors fuse remains poorly understood. Indeed, cell-cell fusion itself, whether it concerns that of sperm cells with oocytes in fertilization or myoblasts with myoblasts in muscle development, has not been investigated thoroughly. It is proposed that cell-cell fusion involves a set of proteins similar to those used by viruses to fuse with host cells be...

Reply to Soto-Pantoja et al. and Zhao et al.: Targeting CD47 on human solid tumors

“…MIAP410 was previously reported to not block mCD47-mSIRPα interactions (2). In contrast, we have determined that MIAP410 does block mCD47-mSIRPα interactions (Fig.…”

“…1). This discrepancy may be attributable to the N-terminal GST-CD47 fusion protein used in the prior blocking assays (2). Polypeptide additions at the N terminus of CD47 prevent the N-terminal glutamine residue of CD47 from forming pyroglutamic acid.…”

Osteoclast stimulatory transmembrane protein and dendritic cell–specific transmembrane protein cooperatively modulate cell–cell fusion to form osteoclasts and foreign body giant cells

“…(13) Therefore, although the functions of osteoclasts and FBGCs differ, they express common molecules, such as DC-STAMP, that function in cell-cell fusion. (3) To date, various molecules have been identified that regulate fusion of osteoclasts or macrophages, including DC-STAMP, ATP6v0d2, CD47, CD44, CD9, CD81, MFR, E-cadherin, and meltrin-a (3,(14)(15)(16)(17)(18)(19)(20)(21) ATP6v0d2-deficient mice show significant reductions in fusion of either cell type. (21) DC-STAMP-deficient osteoclasts or FBGCs show a complete lack of cell-cell fusion, a function specific for macrophage lineage fusion, since fertilization and myotube formation is normal in DC-STAMP-deficient mice.…”

CD200 and its receptor, CD200R, modulate bone mass via the differentiation of osteoclasts

“…In 1998, we reported that the expression of macrophage fusion receptor/signal regulatory protein ␣ (MFR/ SIRP␣) is induced transiently in macrophages at the onset of fusion (9). MFR/SIRP␣ and its receptor, CD47, belong to the superfamily of immunoglobulins (IgSF), as does CD4, and their interaction plays a role in the recognition of self and in the fusion of macrophages (10). To gain further insight into the mechanism of macrophage fusion, we subjected fusing alveolar macrophages from rats to genome-wide oligonucleotide microarray analysis, and we discovered the expression of CD200 de novo at the onset of fusion.…”