MFGE8 encodes lactadherin (milk fat globule-EGF factor 8, MFG-E8), a secreted peripheral-membrane glycoprotein made by macrophages, microglia, astrocytes, mammary epithelium, vascular smooth muscle and other cells. It consists of an N-terminal EGF-like domain carrying an RGD motif followed by two discoidin (F5/8 type C) domains. The discoidin domains, chiefly C2, bind phosphatidylserine exposed on apoptotic cells, extracellular vesicles, milk fat globules and stressed neurons or synapses, while the RGD motif binds alphav-beta3 and alphav-beta5 integrins on phagocytes. MFG-E8 thereby acts as a bridging opsonin that tethers phosphatidylserine-exposing targets to engulfing cells and promotes their phagocytic clearance; loss of this clearance in mice leads to accumulation of unengulfed apoptotic cells and lupus-like autoimmunity. The same opsonophagocytic mechanism can drive microglial and astrocytic engulfment of viable neurons and synapses under inflammatory or amyloid-beta stress. Additional reported roles, mostly from mouse studies, include intestinal epithelial repair, VEGF-dependent neovascularization, macrophage uptake of collagen, and sperm-zona pellucida adhesion. A 50-residue internal fragment of the C2 domain, medin, forms aortic medial amyloid, the most common human amyloid, and co-aggregates with vascular amyloid-beta in cerebral amyloid angiopathy.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0001786 phosphatidylserine binding | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (PAINT) inference of phosphatidylserine binding for the MFG-E8/discoidin family node; consistent with direct experimental evidence for human, mouse and bovine lactadherin. Reason: PS binding via the C-terminal discoidin (F5/8 type C) domains, principally C2, is the defining membrane-recognition activity of lactadherin and one half of its bridging function. The target appearing in WITH/FROM reflects its own experimental grounding. Supporting Evidence: PMID:19204935 the human homolog of SED1/MFG-E8 (hMFG-E8) also binds phosphatidylserine and engages Ξ±vΞ²3 integrins PMID:18160406 Lactadherin is a phosphatidyl-L-serine (Ptd-L-Ser)-binding protein that decorates membranes of milk fat globules PMID:12000961 MFG-E8 specifically bound to apoptotic cells by recognizing aminophospholipids such as phosphatidylserine |
| GO:0001786 phosphatidylserine binding | IPI PMID:21196491 The Na/K-ATPase is obligatory for membrane anchorage of reti... | ACCEPT | Summary: IPI with phosphatidylserine (CHEBI:18303) from a retinoschisin study in which MFG-E8 serves as a PS-binding comparator; full text not cached (abstract only), but the activity is well established for human MFG-E8. Reason: Abstract of PMID:21196491 concerns retinoschisin, but the curator read the full text and MFG-E8 phosphatidylserine binding is independently established for the human protein (wild type and an SLE-associated truncation mutant) and structurally for the homologous bovine C2 domain. Deferring to the curator. Supporting Evidence: PMID:20213738 bound to phosphatidylserine and enhanced the phagocytosis of apoptotic cells PMID:19204935 the human homolog of SED1/MFG-E8 (hMFG-E8) also binds phosphatidylserine and engages Ξ±vΞ²3 integrins PMID:17123296 Macrophages secrete lactadherin, a PS-binding protein, which tethers apoptotic cells to macrophage integrins |
| GO:0002080 acrosomal membrane | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: IEA from UniProt subcellular location (acrosome membrane), itself inferred from porcine P47/SED1. Reason: Pig/mouse SED1/MFG-E8 is acquired by sperm (largely from epididymal secretion) and sits on the plasma membrane overlying the acrosome, where it mediates zona pellucida adhesion. Human-specific data are lacking and the precise compartment (plasma membrane over the acrosome vs acrosomal membrane) is loosely mapped; retain as non-core. Supporting Evidence: PMID:19204935 where it binds to the anterior dorsal aspect of the sperm plasma membrane, the area known to be responsible for mediating initial adhesion to the egg coat |
| GO:0005178 integrin binding | IEA GO_REF:0000107 | ACCEPT | Summary: Integrin binding transferred from mouse Mfge8 by Ensembl Compara orthology. Human MFG-E8 carries the RGD motif (residues 46-48) in its EGF-like domain and engages alphav-beta3/alphav-beta5 integrins. Reason: The RGD-integrin interaction is the phagocyte-facing half of the MFG-E8 bridge and is supported for the human protein; RGE mutants bind PS but fail to promote engulfment. Integrin binding is an informative, specific binding term here. Supporting Evidence: PMID:12000961 MFG-E8, when engaged by phospholipids, bound to cells via its RGD (arginine-glycine-aspartate) motif--it bound particularly strongly to cells expressing alpha(v)beta(3) integrin PMID:19204935 the human homolog of SED1/MFG-E8 (hMFG-E8) also binds phosphatidylserine and engages Ξ±vΞ²3 integrins PMID:15834428 lactadherin interacts with alphavbeta3 and alphavbeta5 integrins and alters both VEGF-dependent Akt phosphorylation and neovascularization PMID:37652017 AD promotes increased synapse ingestion by human glial cells at least in part via an MFG-E8 opsonophagocytic mechanism |
| GO:0005201 extracellular matrix structural constituent | RCA PMID:20551380 Proteomics characterization of extracellular space component... | MARK AS OVER ANNOTATED | Summary: RCA annotation derived from matrisome classification of ECM proteomics datasets. Reason: MFG-E8 is detected in ECM-rich tissue fractions (e.g. aortic media, the site of medin amyloid), but it is a soluble bridging opsonin acting through PS and integrin binding; there is no evidence it confers structural integrity on the matrix. Presence in an ECM proteome supports a location annotation, not a structural-constituent activity. Supporting Evidence: PMID:10411933 By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. PMID:19204935 The C-terminal domains mediate attachment to phosphatidylserine and phosphatidylethanolamine residues exposed on the surface of the apoptotic lymphocyte, whereas the RGD motif binds to Ξ±v integrins expressed on the advancing phagocyte |
| GO:0005201 extracellular matrix structural constituent | RCA PMID:27068509 Extracellular matrix remodelling in response to venous hyper... | MARK AS OVER ANNOTATED | Summary: RCA annotation derived from matrisome classification of ECM proteomics datasets. Reason: MFG-E8 is detected in ECM-rich tissue fractions (e.g. aortic media, the site of medin amyloid), but it is a soluble bridging opsonin acting through PS and integrin binding; there is no evidence it confers structural integrity on the matrix. Presence in an ECM proteome supports a location annotation, not a structural-constituent activity. Supporting Evidence: PMID:10411933 By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. PMID:19204935 The C-terminal domains mediate attachment to phosphatidylserine and phosphatidylethanolamine residues exposed on the surface of the apoptotic lymphocyte, whereas the RGD motif binds to Ξ±v integrins expressed on the advancing phagocyte |
| GO:0005201 extracellular matrix structural constituent | RCA PMID:27559042 Glycoproteomics Reveals Decorin Peptides With Anti-Myostatin... | MARK AS OVER ANNOTATED | Summary: RCA annotation derived from matrisome classification of ECM proteomics datasets. Reason: MFG-E8 is detected in ECM-rich tissue fractions (e.g. aortic media, the site of medin amyloid), but it is a soluble bridging opsonin acting through PS and integrin binding; there is no evidence it confers structural integrity on the matrix. Presence in an ECM proteome supports a location annotation, not a structural-constituent activity. Supporting Evidence: PMID:10411933 By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. PMID:19204935 The C-terminal domains mediate attachment to phosphatidylserine and phosphatidylethanolamine residues exposed on the surface of the apoptotic lymphocyte, whereas the RGD motif binds to Ξ±v integrins expressed on the advancing phagocyte |
| GO:0005201 extracellular matrix structural constituent | RCA PMID:28327460 Comprehensive proteomic characterization of stem cell-derive... | MARK AS OVER ANNOTATED | Summary: RCA annotation derived from matrisome classification of ECM proteomics datasets. Reason: MFG-E8 is detected in ECM-rich tissue fractions (e.g. aortic media, the site of medin amyloid), but it is a soluble bridging opsonin acting through PS and integrin binding; there is no evidence it confers structural integrity on the matrix. Presence in an ECM proteome supports a location annotation, not a structural-constituent activity. Supporting Evidence: PMID:10411933 By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. PMID:19204935 The C-terminal domains mediate attachment to phosphatidylserine and phosphatidylethanolamine residues exposed on the surface of the apoptotic lymphocyte, whereas the RGD motif binds to Ξ±v integrins expressed on the advancing phagocyte |
| GO:0005576 extracellular region | HDA PMID:16502470 Human colostrum: identification of minor proteins in the aqu... | ACCEPT | Summary: Detected in the aqueous phase of human colostrum by proteomics. Reason: Consistent with secretion of lactadherin into milk, where it decorates milk fat globule membranes. Supporting Evidence: PMID:10411933 previously known to be expressed by mammary epithelial cells as a cell surface protein and secreted as part of the milk fat globule membrane |
| GO:0005576 extracellular region | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference that family members are active in the extracellular region. Reason: MFG-E8 is a secreted glycoprotein acting extracellularly to tether PS-exposing cells/vesicles to phagocyte integrins. Supporting Evidence: PMID:17123296 Macrophages secrete lactadherin, a PS-binding protein, which tethers apoptotic cells to macrophage integrins PMID:10411933 previously known to be expressed by mammary epithelial cells as a cell surface protein and secreted as part of the milk fat globule membrane |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | ACCEPT | Summary: Combined automated annotation (orthology and UniProt subcellular location "Secreted"). Reason: MFG-E8 is secreted. Supporting Evidence: PMID:17123296 Macrophages secrete lactadherin, a PS-binding protein, which tethers apoptotic cells to macrophage integrins |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-976734 | ACCEPT | Summary: Reactome amyloid reaction (Reactome:R-HSA-976734) placing medin (aortic medial amyloid derived from MFG-E8) in the extracellular region. Reason: Medin is an extracellular amyloid deposit derived from lactadherin; extracellular localization of the parent protein is correct, although the amyloid context is pathological rather than a physiological function. Supporting Evidence: PMID:10411933 We found that the main constituent of aortic medial amyloid is a 50-aa-long peptide, here called medin, that is positioned within the coagulation factor-like domain of lactadherin. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-977136 | ACCEPT | Summary: Reactome amyloid reaction (Reactome:R-HSA-977136) placing medin (aortic medial amyloid derived from MFG-E8) in the extracellular region. Reason: Medin is an extracellular amyloid deposit derived from lactadherin; extracellular localization of the parent protein is correct, although the amyloid context is pathological rather than a physiological function. Supporting Evidence: PMID:10411933 We found that the main constituent of aortic medial amyloid is a 50-aa-long peptide, here called medin, that is positioned within the coagulation factor-like domain of lactadherin. |
| GO:0005788 endoplasmic reticulum lumen | TAS Reactome:R-HSA-8952289 | KEEP AS NON CORE | Summary: Reactome TAS from the FAM20C reaction (FAM20C phosphorylates secreted substrates; MFG-E8 is among the substrates of the secretory-pathway kinase). Reason: Transit location during biosynthesis/processing in the secretory pathway; correct but not where MFG-E8 executes its function. |
| GO:0009897 external side of plasma membrane | IEA GO_REF:0000107 | ACCEPT | Summary: Orthology transfer from mouse: on the external side of the plasma membrane. Reason: MFG-E8 binds the outer leaflet of PS-exposing plasma membranes (apoptotic cells, activated platelets, milk fat globule membrane) as a peripheral protein; this is the location where its bridging activity is executed. Supporting Evidence: PMID:17123296 Macrophages secrete lactadherin, a PS-binding protein, which tethers apoptotic cells to macrophage integrins PMID:10411933 previously known to be expressed by mammary epithelial cells as a cell surface protein and secreted as part of the milk fat globule membrane |
| GO:0016020 membrane | HDA PMID:19946888 Defining the membrane proteome of NK cells. | KEEP AS NON CORE | Summary: Detected in an NK-cell membrane proteome (abstract only). Reason: Consistent with MFG-E8 being a peripheral membrane protein bound to PS-containing membranes; generic term, the more informative location is external side of plasma membrane. |
| GO:0016020 membrane | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: IEA from UniProt subcellular location (Membrane; peripheral membrane protein). Reason: Correct but general; MFG-E8 associates peripherally with PS-containing membranes via its C2 domain. The more informative location, external side of plasma membrane, is accepted separately. Supporting Evidence: PMID:18160406 Lactadherin is a phosphatidyl-L-serine (Ptd-L-Ser)-binding protein that decorates membranes of milk fat globules |
| GO:0031012 extracellular matrix | HDA PMID:20551380 Proteomics characterization of extracellular space component... | KEEP AS NON CORE | Summary: Identified in an extracellular matrix proteomics dataset (PMID:20551380). Reason: MFG-E8 is expressed by aortic medial smooth muscle cells and is found in ECM-rich vascular tissue, where its medin fragment forms amyloid. A genuine but non-core location. Supporting Evidence: PMID:10411933 By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. |
| GO:0031012 extracellular matrix | HDA PMID:27068509 Extracellular matrix remodelling in response to venous hyper... | KEEP AS NON CORE | Summary: Identified in an extracellular matrix proteomics dataset (PMID:27068509). Reason: MFG-E8 is expressed by aortic medial smooth muscle cells and is found in ECM-rich vascular tissue, where its medin fragment forms amyloid. A genuine but non-core location. Supporting Evidence: PMID:10411933 By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. |
| GO:0031012 extracellular matrix | HDA PMID:27559042 Glycoproteomics Reveals Decorin Peptides With Anti-Myostatin... | KEEP AS NON CORE | Summary: Identified in an extracellular matrix proteomics dataset (PMID:27559042). Reason: MFG-E8 is expressed by aortic medial smooth muscle cells and is found in ECM-rich vascular tissue, where its medin fragment forms amyloid. A genuine but non-core location. Supporting Evidence: PMID:10411933 By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. |
| GO:0031012 extracellular matrix | HDA PMID:28327460 Comprehensive proteomic characterization of stem cell-derive... | KEEP AS NON CORE | Summary: Identified in an extracellular matrix proteomics dataset (PMID:28327460). Reason: MFG-E8 is expressed by aortic medial smooth muscle cells and is found in ECM-rich vascular tissue, where its medin fragment forms amyloid. A genuine but non-core location. Supporting Evidence: PMID:10411933 By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. |
| GO:0043277 apoptotic cell clearance | IEA GO_REF:0000107 | ACCEPT | Summary: Orthology transfer from mouse Mfge8, the founding bridging factor for apoptotic cell clearance. Reason: MFG-E8 performs part of the work of apoptotic cell clearance: it binds PS on the dying cell and integrins on the phagocyte, physically linking them; RGE mutants are dominant-negative and knockouts accumulate unengulfed apoptotic cells. The human protein binds PS and enhances phagocytosis of apoptotic cells. Supporting Evidence: PMID:12000961 MFG-E8 specifically bound to apoptotic cells by recognizing aminophospholipids such as phosphatidylserine PMID:15155946 These data demonstrate that MFG-E8 has a critical role in removing apoptotic B cells in the germinal centers and that its failure can lead to autoimmune diseases PMID:20213738 bound to phosphatidylserine and enhanced the phagocytosis of apoptotic cells |
| GO:0070062 extracellular exosome | HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos... | KEEP AS NON CORE | Summary: High-throughput exosome proteomics (PMID:19056867). Reason: Lactadherin is a well-known exosome surface marker, consistent with its binding to PS exposed on extracellular vesicles; correct but not the core location of function. |
| GO:0070062 extracellular exosome | HDA PMID:19199708 Proteomic analysis of human parotid gland exosomes by multid... | KEEP AS NON CORE | Summary: High-throughput exosome proteomics (PMID:19199708). Reason: Lactadherin is a well-known exosome surface marker, consistent with its binding to PS exposed on extracellular vesicles; correct but not the core location of function. Supporting Evidence: PMID:19199708 proteins exposed on the exosomal surface involved in cell-adhesion (Von Willebrand factor A domain-related protein isoform 1, MFGE8, LAMB2, LAMC1) |
| GO:0070062 extracellular exosome | HDA PMID:20458337 MHC class II-associated proteins in B-cell exosomes and pote... | KEEP AS NON CORE | Summary: High-throughput exosome proteomics (PMID:20458337). Reason: Lactadherin is a well-known exosome surface marker, consistent with its binding to PS exposed on extracellular vesicles; correct but not the core location of function. |
| GO:0070062 extracellular exosome | HDA PMID:21362503 Protein profile of exosomes from trabecular meshwork cells. | KEEP AS NON CORE | Summary: High-throughput exosome proteomics (PMID:21362503). Reason: Lactadherin is a well-known exosome surface marker, consistent with its binding to PS exposed on extracellular vesicles; correct but not the core location of function. Supporting Evidence: PMID:21362503 Included in this list are additional common exosome markers including; CD-9, CD-63, CD81, cofilin-1, 14-3-3 proteins epsilon and zeta, phosphoglycerate kinase, lactadherin |
| GO:0140149 non-collagenous component of interstitial matrix | TAS PMID:36399478 MatrisomeDB 2.0: 2023 updates to the ECM-protein knowledge d... | KEEP AS NON CORE | Summary: MatrisomeDB-based TAS placing MFG-E8 in the non-collagenous interstitial matrix. Reason: Consistent with vascular/interstitial ECM detection (aortic media); non-core location. Supporting Evidence: PMID:10411933 By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. |
| GO:1903561 extracellular vesicle | HDA PMID:24769233 Proteomic analysis of cerebrospinal fluid extracellular vesi... | KEEP AS NON CORE | Summary: Detected in human CSF extracellular vesicles by proteomics (abstract only). Reason: Consistent with lactadherin binding PS on extracellular vesicles; non-core. |
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Download this section (compressed HTML)Q: Does MFG-E8 opsonization of synapses in human Alzheimer disease depend on phosphatidylserine exposure on those synapses, and is it independent of, additive to, or redundant with C1q/C3-dependent synapse tagging?
Q: Should GO capture phosphatidylserine-bridging opsonins (MFG-E8, GAS6, PROS1) with a dedicated molecular function term for apoptotic-cell/phagocyte bridging rather than only paired lipid- and receptor-binding terms?
Q: Which protease(s) liberate medin from the lactadherin C2 domain in the vessel wall, and does medin generation reduce the phosphatidylserine-binding/opsonin capacity of vascular MFG-E8?
Experiment: Treat human iPSC-derived microglia and astrocytes with AD-derived synaptoneurosomes pre-incubated with wild-type MFG-E8, an RGE (integrin-dead) mutant, or a C2-domain PS-binding mutant, combined with annexin V masking of PS, to test whether synapse engulfment requires both halves of the bridge.
Experiment: Compare synapse loss in amyloid mouse models crossed onto Mfge8-null, C3-null and double-null backgrounds to determine whether MFG-E8 and complement act in the same or parallel synapse-elimination pathways.
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