RESUMEN
Fcα/µR (CD351) is an Fc receptor for both IgA and IgM and forms an atypical dimer that is resistant to reduction by 2-mercaptoethanol or boiling. We previously demonstrated that the cytoplasmic portion of Fcα/µR is required for dimer formation and for its efficient cell-surface expression. However, the biochemical nature of these phenomena has not been determined. By using a BW5147 mouse cell line expressing deletion mutants of the cytoplasmic region of Fcα/µR, we found that the region spanning amino acids 504-523 was required for efficient cell-surface expression, whereas the region spanning amino acids 481-490 was required for dimmer formation. Immunoblotting analyses of transfectants simultaneously expressing Flag-tagged Fcα/µR and hemagglutinin-tagged Fcα/µR suggested that Fcα/µR does not form homodimers. Instead, our data suggest that Fcα/µR forms heterodimers with an as-yet-unknown molecule with a molecular weight of 60-70 kDa.
Asunto(s)
Multimerización de Proteína , Receptores Fc/química , Receptores Fc/metabolismo , Secuencia de Aminoácidos , Animales , Western Blotting , Línea Celular Tumoral , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Ratones , Datos de Secuencia Molecular , Mutación , Unión Proteica , Receptores Fc/genética , Homología de Secuencia de Aminoácido , TransfecciónRESUMEN
Fcalpha/mu receptor (Fcalpha/muR), an Fc receptor for IgA and IgM, is the only Fc receptor for IgM identified on hematopoietic cells in human and rodents and for IgA in rodents. Fcalpha/microR is a type 1 transmembrane protein containing one immunoglobulin-like domain in the extracellular portion. Both human and mouse Fcalpha/microR mediate endocytosis of the ligands IgA and IgM, for which the cytoplasmic portion of Fcalpha/microR is responsible. However, molecular characteristics of Fcalpha/muR involved in the function have been incompletely understood. Here, we show that both monomeric and dimeric Fcalpha/microR are expressed in a mouse B cell line BCL1-B20 and BW5147 or Ba/F3 transfectants stably expressing Fcalpha/microR. We also show that the dimeric, but not monomeric, Fcalpha/microR is preferentially localized to the cell surface of the transfectants. BW5147 transfectant expressing mutant Fcalpha/microR lacking the cytoplasmic portion expressed only the monomeric Fcalpha/microR. These results suggest that the cytoplasmic portion is required for the dimer formation and thus for efficient cell surface expression of Fcalpha/microR.