Cytoplasmic domain of human Fcalpha/mu receptor is required for ligand internalization.
The Fcalpha/mu receptor (Fcalpha/microR), a type I transmembrane protein, is an immunoglobulin Fc receptor for both IgA and IgM. Its functions in immune defense are not clear at present. In this work, human Fcalpha/microR was expressed in CHO, 293T, and COS-7 cells to study its biochemical functions. Fcalpha/microR expressed by CHO and 293T was only in monomer form in cytoplasma and the monomeric receptor could not bind IgA or IgM. In comparison, Fcalpha/microR expressed by COS-7 cells had both monomer and dimer forms. The binding assay showed that Fcalpha/microR expressed by COS-7 cells could bind IgM strongly and IgA weakly, implying that dimeric receptor could be expressed on cell membrane and functioned. The bound IgM could be internalized and the internalization was abolished when the cytoplasmic domain of Fcalpha/microR was truncated. Therefore, the cytoplasmic portion of human Fcalpha/microR is required in the internalization.
Yang
Lijun
L
Institute of Basic Medical Sciences Chinese Academy of Medical Sciences, School of Basic Medicine Peking Union Medical College, Beijing, China.
Shen
Lian
L
Shao
Yuehu
Y
Zhao
Qing
Q
Zhang
Wei
W
D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D004705:Endocytosis / Q000502:physiology*; D006801:Humans; D007070:Immunoglobulin A / Q000276:immunology / Q000378:metabolism*; D007075:Immunoglobulin M / Q000276:immunology / Q000378:metabolism*; D008024:Ligands; D055503:Protein Multimerization; D011961:Receptors, Fc / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D014162:Transfection
C526790:Fcalpha-mu receptor, human; D007070:Immunoglobulin A; D007075:Immunoglobulin M; D008024:Ligands; D011961:Receptors, Fc