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Fc fragment of IgM receptor

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Immunopharmacology Ligand target has curated data in GtoImmuPdb

Target id: 2992

Nomenclature: Fc fragment of IgM receptor

Abbreviated Name: FcμRI

Family: Immunoglobulin like domain containing proteins

Gene and Protein Information Click here for help
Species TM AA Chromosomal Location Gene Symbol Gene Name Reference
Human 1 390 1q32.1 FCMR Fc mu receptor 3
Mouse 1 422 1 E4 Fcmr Fc fragment of IgM receptor
Rat 1 426 13q13 Fcmr Fc mu receptor
Gene and Protein Information Comments
Three alternate transcripts translating to two protein variants are reported for human FCMR.
Previous and Unofficial Names Click here for help
FAIM3 | Fas apoptotic inhibitory molecule 3 | TOSO
Database Links Click here for help
Ensembl Gene
Entrez Gene
Human Protein Atlas
RefSeq Nucleotide
RefSeq Protein
Immunopharmacology Comments
FcμRI is the cognate Fc receptor for immunoglobulin M (IgM) [3-4,8]. FcμRI was previously known as Toso, and had been reported as an inhibitor of Fas-mediated apoptosis [2]. Experimental confirmation of this functional activity lead to naming of the human and mouse genes as FAIM3 (Fas apoptosis inhibitory molecule 3) [7,9]. FcμRI and IgM play functional roles in regulation of the immune system, clearance of pathogens, dead cells and damaged tissues, and the maintainance of immune homeostasis under physiological and pathological conditions [10]. Unlike IgG-Fcβ receptor interactions that are modulated by the glycosylation state of the antibody, IgM-FcμRI binding and subsequent internalisation are glycan independent [4].

FcμRI overexpression has been reported as a potential prognostic marker for chronic lymphocytic leukemia (CLL) progression [1], as its expression is significantly upregulated in leukemic lymphocytes derived from patients with CLL compared to healthy controls [1,5-6].
Cell Type Associations
Immuno Cell Type:  B cells
Cell Ontology Term:   B cell (CL:0000236)
Comment:  Upregulated expression of FcμRI renders malignant B cells in chronic lymphocytic leukemia (CLL) resistant to apoptosis, and leads to their accumulation.
References:  5


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1. Hancer VS, Diz-Kucukkaya R, Aktan M. (2012) Overexpression of Fc mu receptor (FCMR, TOSO) gene in chronic lymphocytic leukemia patients. Med Oncol, 29 (2): 1068-72. [PMID:21264533]

2. Hitoshi Y, Lorens J, Kitada SI, Fisher J, LaBarge M, Ring HZ, Francke U, Reed JC, Kinoshita S, Nolan GP. (1998) Toso, a cell surface, specific regulator of Fas-induced apoptosis in T cells. Immunity, 8 (4): 461-71. [PMID:9586636]

3. Kubagawa H, Carroll MC, Jacob CO, Lang KS, Lee KH, Mak T, McAndrews M, Morse 3rd HC, Nolan GP, Ohno H et al.. (2015) Nomenclature of Toso, Fas apoptosis inhibitory molecule 3, and IgM FcR. J Immunol, 194 (9): 4055-7. [PMID:25888699]

4. Lloyd KA, Wang J, Urban BC, Czajkowsky DM, Pleass RJ. (2017) Glycan-independent binding and internalization of human IgM to FCMR, its cognate cellular receptor. Sci Rep, 7: 42989. [PMID:28230186]

5. Pallasch CP, Schulz A, Kutsch N, Schwamb J, Hagist S, Kashkar H, Ultsch A, Wickenhauser C, Hallek M, Wendtner CM. (2008) Overexpression of TOSO in CLL is triggered by B-cell receptor signaling and associated with progressive disease. Blood, 112 (10): 4213-9. [PMID:18708628]

6. Proto-Siqueira R, Panepucci RA, Careta FP, Lee A, Clear A, Morris K, Owen C, Rizzatti EG, Silva Jr WA, Falcão RP et al.. (2008) SAGE analysis demonstrates increased expression of TOSO contributing to Fas-mediated resistance in CLL. Blood, 112 (2): 394-7. [PMID:18434611]

7. Richter GH, Mollweide A, Hanewinkel K, Zobywalski C, Burdach S. (2009) CD25 blockade protects T cells from activation-induced cell death (AICD) via maintenance of TOSO expression. Scand J Immunol, 70 (3): 206-15. [PMID:19703010]

8. Shima H, Takatsu H, Fukuda S, Ohmae M, Hase K, Kubagawa H, Wang JY, Ohno H. (2010) Identification of TOSO/FAIM3 as an Fc receptor for IgM. Int Immunol, 22 (3): 149-56. [PMID:20042454]

9. Song Y, Jacob CO. (2005) The mouse cell surface protein TOSO regulates Fas/Fas ligand-induced apoptosis through its binding to Fas-associated death domain. J Biol Chem, 280 (10): 9618-26. [PMID:15632112]

10. Wang H, Coligan JE, Morse 3rd HC. (2016) Emerging Functions of Natural IgM and Its Fc Receptor FCMR in Immune Homeostasis. Front Immunol, 7: 99. [PMID:27014278]

How to cite this page

Immunoglobulin like domain containing proteins: Fc fragment of IgM receptor. Last modified on 06/03/2018. Accessed on 14/06/2024. IUPHAR/BPS Guide to PHARMACOLOGY,