A Common Site of the Fc Receptor γ Subunit Interacts with the Unrelated Immunoreceptors FcαRI and FcϵRI

Abstract

The transmembrane (TM) region of the Fc receptor-␥ (FcR␥) chain is responsible for the association of this ubiquitous signal transduction subunit with many immunoreceptor ligand binding chains, making FcR␥ key to a number of leukocyte activities in immunity and disease. Some receptors contain a TM arginine residue that interacts with Asp-11 of the FcR␥ subunit, but otherwise the molecular basis for the FcR␥ subunit interactions is largely unknown. This study reports residues in the TM region of the FcR␥ subunit are important for association with the high affinity IgE receptor Fc⑀RI and a leukocyte receptor cluster member, the IgA receptor Fc␣RI. FcR␥ residue Leu-21 was essential for surface expression of Fc⑀RI␣/␥ 2 and Tyr-8, Leu-14, and Phe-15 contributed to expression. Likewise, detergent-stable FcR␥ association with Fc␣RI was also dependent on Leu-14 and Leu-21 and in addition required residues Tyr-17, Tyr-25, and Cys-26. Modeling the TM regions of the FcR␥ dimer indicated these residues interacting with both Fc␣RI and Fc⑀RI are near the interface between the two FcR␥ TM helices. Furthermore, the FcR␥ residues interacting with Fc␣RI form a leucine zipper-like interface with mutagenesis confirming a complementary interface comprising Fc␣RI residues Leu-217, Leu-220, and Leu-224. The dependence of these two nonhomologous receptor interactions on FcR␥ Leu-14 and Leu-21 suggests that all the associated Fc receptors and the activating leukocyte receptor cluster members interact with this one site. Taken together these data provide a molecular basis for understanding how disparate receptor families assemble with the FcR␥ subunit.The Fc receptor ␥ subunit (FcR␥) 2 is a ubiquitous signal transduction subunit widely found in hematopoietic cells and is present on macrophages, monocytes, dendritic cells, natural killer cells, platelets, eosinophils, mast cells, ␥␦ T cells, and CD4 ␣␤ effector T cells (1, 2). It is a promiscuous receptor subunit originally identified as a subunit of the high affinity IgE receptor Fc⑀RI (3) but is also associated with the ␥␦ TCR (4), the ␣␤ TCR (1, 2), DCAR (a novel C-type lectin immunoreceptor expressed on DC) (5, 6), mouse NKRP1A/C/F (7), NKp46 (8), the high affinity IgG receptor Fc␥RI (9), the low affinity IgG receptor Fc␥RIIIa (10), and the IgA receptor Fc␣RI (11,12). Fc␣RI, although a functional FcR, is a member of the leukocyte receptor cluster (LRC) whose genes are all encoded at 19q13.4 (13). A potentially charged TM residue in the Ig superfamily receptors is generally indicative of assembly with a small signal transduction molecule (14). The activating LRC receptors, Fc␣RI (11,12,15), the leukocyte Ig-like receptor A2 (LILR-A2, LIR7, ILT-1) (16), and the platelet collagen receptor glycoprotein VI (17, 18), NKp46 (8), and OSCAR (6), contain a TM arginine residue essential for interaction with FcR␥. Other than the TM arginine residue, it is not known if other TM residues of the activating LRC receptors are important in interacting with FcR␥. The TM regions of the FcRs, Fc⑀RI, Fc␥...

Fc receptor γ-chain, a constitutive component of the IL-3 receptor, is required for IL-3-induced IL-4 production in basophils

“…This same arginine is also absent in the transmembrane region of βc. In addition, we showed here that leucine-21 in the transmembrane region of FcRγ, a residue required for both arginine-dependent and independent associations 33 , is dispensable for physical and functional association of βc with FcRγ, suggesting that this association occurs via a mode distinct from those previously known for FcRγ.…”

“…In a group of FcRγ-associated receptors including FcαRI (also termed CD89), NKp46, the platelet collagen receptor glycoprotein VI and the paired Ig-like receptor A, an arginine residue in their transmembrane regions is required for interaction with the negatively charged aspartic acid residue in FcRγ 40 . In contrast, receptors such as FcεRI, FcγRI and FcγRIII lack the canonical transmembrane arginine but are nevertheless able to associate with FcRγ through mechanisms still not fully understood 33 . This same arginine is also absent in the transmembrane region of βc.…”

“…5a and Supplementary Fig. 10a online), a mutant known to be unable to bind to FcεRIα or FcαRI 33 . BM-derived basophils expressing FcRγ-L21A indeed failed to express FcεRI on the surface even though FcRγ-L21A and wild-type FcRγ proteins were expressed at comparable levels ( Fig.…”

Characterization of Leukocyte Mono-immunoglobulin-like Receptor 7 (LMIR7)/CLM-3 as an Activating Receptor

“…6A, LMIR7 differed from LMIR4 by only three amino acid residues in the transmembrane domain. As it is generally accepted that a transmembrane structure plays a critical role in receptor interaction (15,24,25), we generated a chimera receptor composed of an extracellular domain, LMIR7, a transmembrane domain, LMIR4, and an intracellular domain, LMIR7, designated LMIR7-M1. When Ba/F3 cells were transduced with Myctagged LMIR-M1 as well as Myc-tagged LMIR4, LMIR7, or mock, flow cytometric analysis using anti-Myc mAb showed that surface expression levels of LMIR7-M1 were equivalent to those of LMIR4 and lower than those of LMIR7 (Fig.…”

“…In addition, FcR␥ interacts with various activating receptors such as paired Ig-like receptor A (PIR-A) (22) or platelet collagen receptor glycoprotein VI (23). Although the Arg/Asp charge interaction between transmembrane domains is well characterized, recent studies have also implicated a transmembrane leucine zipper-like interaction between activating receptors and FcR␥ (24,25). However, the relevant molecular mechanism remains incompletely understood.…”