Fcγ receptor transmembrane domains: Role in cell surface expression, γ chain interaction, and phagocytosis

Abstract

We constructed chimeric receptors to dissect the role of the transmembrane (TM) domain in cell surface expression of and phagocytosis by the γ chain-dependent Fcγ receptors FcγRIIIA and Fc-γRI. FcγR chimeras containing the TM and cytoplasmic (CY) domains of the γ chain were expressed on the cell surface and mediated an efficient phagocytic signal. In contrast, chimeras containing the FcγRIIIA TM were poorly expressed. Receptors containing the FcγRI TM and the γ chain CY but lacking the γ chain TM also were expressed efficiently and mediated phagocytosis, suggesting that a γ chain dimer induced by the γ chain TM is not required for efficient phagocytosis. Cotransfection of FcγRI or FcγRIIIA with the chimera CD8-γ-γ (EC-TM-CY) resulted in FcγR cell surface expression and phagocytosis, whereas CD8-CD8-γ, whose TM does not associate with FcγR, allowed cell surface expression of (but not phagocytosis by) FcγRI. CD8-CD8-γ also did not allow surface expression of FcγRIIIA. Exchanging FcγRI and CD8 TMs indicated that the C-terminal 11 amino acids of the FcγRI TM are essential for association of FcγRI with the γ chain and phagocytosis. The data indicate that specific sequences in the FcγRIIIA and FcγRI TMs govern their different interactions with the γ chain in cell surface expression and phagocytosis and that γ chain TM sequences are not required for γ chain-mediated phagocytosis. The data identify a specific region of the FcγRI TM and its asparagine as important for FcγRI cell surface expression in the absence of the γ chain and for distinguishing the FcγRI and FcγRIIIA phenotypes. © 2003 by The American Society of Hematology.