Two forms of the low-affinity Fc receptor for IgE differentially mediate endocytosis and phagocytosis: identification of the critical cytoplasmic domains.
We have previously identified two species of the low-affinity human Fc receptor for IgE, Fc epsilon RIIa and Fc epsilon RIIb, which differ only in a short stretch of amino acids at the N-terminal cytoplasmic end. Their differential expressions on B cells and monocytes suggest that Fc epsilon RIIa and Fc epsilon RIIb are involved in B-cell function and IgE-mediated immunity, respectively. Here we show that Fc epsilon RII-mediated endocytosis is observed only in Fc epsilon RIIa-expressing cells, whereas IgE-dependent phagocytosis is observed only in Fc epsilon RIIb-expressing cells, demonstrating the functional difference between Fc epsilon RIIa and Fc epsilon RIIb. Furthermore, site-directed mutagenesis revealed that the tyrosine residue in the Fc epsilon RIIa-specific region is important for endocytosis, and the Asn-Pro residues in the Fc epsilon RIIb-specific region are required for phagocytosis. These findings suggest that endocytosis and phagocytosis are functionally separable phenomena involving distinct amino acid residues.
Yokota
A
A
Institute for Molecular and Cellular Biology, Osaka University, Japan.
Yukawa
K
K
Yamamoto
A
A
Sugiyama
K
K
Suemura
M
M
Tashiro
Y
Y
Kishimoto
T
T
Kikutani
H
H
D000595:Amino Acid Sequence; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry / Q000502:physiology*; D001120:Arginine / Q000737:chemistry; D002478:Cells, Cultured; D004252:DNA Mutational Analysis; D004705:Endocytosis; D007073:Immunoglobulin E / Q000276:immunology; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D010587:Phagocytosis; D011392:Proline / Q000737:chemistry; D011961:Receptors, Fc / Q000737:chemistry / Q000502:physiology*; D017455:Receptors, IgE; D013329:Structure-Activity Relationship; D014162:Transfection
D000944:Antigens, Differentiation, B-Lymphocyte; D011961:Receptors, Fc; D017455:Receptors, IgE; D007073:Immunoglobulin E; D001120:Arginine; D011392:Proline