The Low Affinity IgE Receptor (CD23) Is Cleaved by the Metalloproteinase ADAM10

Abstract

The low affinity IgE receptor, Fc⑀RII (CD23), is both a positive and negative regulator of IgE synthesis. The proteinase activity that converts the membrane-bound form of CD23 into a soluble species (sCD23) is an important regulator of the function of CD23 and may be an important therapeutic target for the control of allergy and inflammation. We have characterized the catalytic activity of ADAM (a disintegrin and metalloproteinase) 10 toward human CD23. We found that ADAM10 efficiently catalyzes the cleavage of peptides derived from two distinct cleavage sites in the CD23 backbone. Tissue inhibitors of metalloproteinases and a specific prodomain-based inhibitor of ADAM10 perturb the release of endogenously produced CD23 from human leukemia cell lines as well as primary cultures of human B-cells. Expression of a mutant metalloproteinase-deficient construct of ADAM10 partially inhibited the production of sCD23. Similarly, small inhibitory RNA knockdown of ADAM10 partially inhibited CD23 release and resulted in the accumulation of the membrane-bound form of CD23 on the cells. ADAM10 contributes to CD23 shedding and thus could be considered a potential therapeutic target for the treatment of allergic disease.The low affinity IgE receptor Fc⑀RII (CD23) is a 46-kDa type II membrane protein that is expressed on B-cells and cells of the myeloid lineage (1). CD23 has multiple functions. It is both a positive and negative regulator of IgE synthesis (2). It facilitates IgE-dependent antigen presentation through its binding of IgEantigen complexes (3,4). Moreover, the release of proinflammmatory cytokines from macrophages is stimulated by CD23 binding to CD18/11b and /11c (complement receptors 3 and 4) (5-7).In humans, two isoforms of CD23 that differ by only seven amino acids in the short N-terminal cytoplasmic domain are observed (8). CD23a is expressed only on B-cells. Stimulation of B-cells and cells of the myeloid lineage with interleukin-4 (IL-4) 3 induces the expression of CD23b. The C-terminal extracellular domain consists of a globular fold that has homology to the C-type lectin family (9). This globular domain has been shown to contain two distinct binding sites, one for IgE and a second that recognizes CD21 (complement receptor 2) (10, 11). At the cell surface CD23 self-assembles to form homotrimers that have a higher affinity for IgE than the CD23 monomer (12, 13). The self-association is driven by a leucine zipper-like domain (14) that connects the N-terminal cytoplasmic and transmembrane domains to the C-terminal globular domain.Homotrimeric CD23 molecules exhibit a 15-nm ␣-helical coiled coil stalk that extends the globular C-terminal domains from the plasma membrane (15). Cleavage in the stalk region by a membrane-associated endoproteolytic activity generates soluble fragments of CD23 (sCD23) that possess apparent molecular masses of 37, 33, and 29 kDa (16). All three of these sCD23 fragments exist as homotrimers (15). Smaller fragments of CD23 (25 and 16 kDa) are known. However, these are thought to be form...

Crystal structure of IgE bound to its B-cell receptor CD23 reveals a mechanism of reciprocal allosteric inhibition with high affinity receptor FcεRI

“…A single head domain binds to IgE-Fc with lower affinity (K A = 10 5 -10 6 M −1 ) than FcεRI (4)(5)(6)(7)(8), although avidity of the trimer can substantially enhance this interaction (7,(9)(10)(11). Membrane CD23 (mCD23) is cleaved from the cell surface by endogenous proteases such as ADAM10 (12,13) to yield soluble trimeric and monomeric forms (sCD23), which have been implicated in both positive and negative feedback mechanisms for the regulation of IgE synthesis by B cells that have switched to IgE production (1,7,8,(14)(15)(16). Both FcεRI and CD23 are also expressed on a range of antigenpresenting cells (APCs), where they play similar roles in trapping IgE-allergen complexes and promoting the allergic response (1,14,15), but the functional interplay-cooperation or competitionbetween these two receptors in the context of APCs is not well understood.…”

CD23-Dependent Transcytosis of IgE and Immune Complex across the Polarized Human Respiratory Epithelial Cells

“…Although CD23 monomers display lower-affinity binding for IgE, the membrane-bound CD23 can also form trimers, which enables CD23 to bind IgE with higher affinity (4,17,19). More interestingly, the stalk region of CD23 is susceptible to proteolysis by enzymes, such as the metalloproteinase ADAM10, to release various soluble CD23 (sCD23) fragments (20)(21)(22). sCD23 also has IgE-binding activity (23), and its level is increased in allergies (24).…”

Soluble CD23 Monomers Inhibit and Oligomers Stimulate IGE Synthesis in Human B Cells

“…The enzyme responsible for this cleavage appears to be the metalloproteinase ADAM10 (19,20). Other enzymes cleave the 37-kDa fragments further up the stalk and at a site within the tail to produce progressively smaller fragments containing the head and a portion of the tail (18).…”