Hsi-Hsien Lin

The macrophage F4/80 receptor is required for the induction of antigen-specific efferent regulatory T cells in peripheral tolerance

We show that the mouse macrophage-restricted F4/80 protein is not required for the development and distribution of tissue macrophages but is involved in the generation of antigen-specific efferent regulatory T (T reg) cells that suppress antigen-specific immunity. In the in vivo anterior chamber (a.c.)–associated immune deviation (ACAID) model of peripheral tolerance, a.c. inoculation of antigen into F4/80−/− mice was unable to induce efferent T reg cells and suppress delayed-type hypersensitivity (DTH) responses. Moreover, the use of anti-F4/80 mAb and F4/80−/− APCs in an in vitro ACAID model showed that all APC cells in the culture must be able to express F4/80 protein if efferent T reg cells were to be generated. In a low-dose oral tolerance model, WT but not F4/80−/− mice generated an efferent CD8+ T reg cell population that suppressed an antigen-specific DTH response. Peripheral tolerance was restored in F4/80−/− mice by adoptive transfer of F4/80+ APCs in both peripheral tolerance models, indicating a central role for the F4/80 molecule in the generation of efferent CD8+ T reg cells.

Adhesion-GPCRs: emerging roles for novel receptors

The G protein-coupled receptor (GPCR) family comprises the largest class of cell surface receptors found in metazoan proteomes. Within the novel GPCR subfamily of adhesion-GPCRs, approximately 150 distinct orthologues, from invertebrates to mammals, have been identified to date. All members of this family contain a large extracellular region, often containing common protein modules, coupled to a seven-transmembrane domain via a stalk region that seems to be crucial for functionality. Owing to their unique structure, restricted expression profile and involvement in several human diseases, adhesion-GPCRs have long been proposed to have vital dual roles in cellular adhesion and signalling. More recent studies have provided structural, evolutionary, developmental and immunological insights in relation to the adhesion-GPCR family.

International Union of Basic and Clinical Pharmacology. XCIV. Adhesion G Protein–Coupled Receptors

The Adhesion family forms a large branch of the pharmacologically important superfamily of G protein–coupled receptors (GPCRs). As Adhesion GPCRs increasingly receive attention from a wide spectrum of biomedical fields, the Adhesion GPCR Consortium, together with the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification, proposes a unified nomenclature for Adhesion GPCRs. The new names have ADGR as common dominator followed by a letter and a number to denote each subfamily and subtype, respectively. The new names, with old and alternative names within parentheses, are: ADGRA1 (GPR123), ADGRA2 (GPR124), ADGRA3 (GPR125), ADGRB1 (BAI1), ADGRB2 (BAI2), ADGRB3 (BAI3), ADGRC1 (CELSR1), ADGRC2 (CELSR2), ADGRC3 (CELSR3), ADGRD1 (GPR133), ADGRD2 (GPR144), ADGRE1 (EMR1, F4/80), ADGRE2 (EMR2), ADGRE3 (EMR3), ADGRE4 (EMR4), ADGRE5 (CD97), ADGRF1 (GPR110), ADGRF2 (GPR111), ADGRF3 (GPR113), ADGRF4 (GPR115), ADGRF5 (GPR116, Ig-Hepta), ADGRG1 (GPR56), ADGRG2 (GPR64, HE6), ADGRG3 (GPR97), ADGRG4 (GPR112), ADGRG5 (GPR114), ADGRG6 (GPR126), ADGRG7 (GPR128), ADGRL1 (latrophilin-1, CIRL-1, CL1), ADGRL2 (latrophilin-2, CIRL-2, CL2), ADGRL3 (latrophilin-3, CIRL-3, CL3), ADGRL4 (ELTD1, ETL), and ADGRV1 (VLGR1, GPR98). This review covers all major biologic aspects of Adhesion GPCRs, including evolutionary origins, interaction partners, signaling, expression, physiologic functions, and therapeutic potential.

Molecular Analysis of the Epidermal Growth Factor-like Short Consensus Repeat Domain-mediated Protein-Protein Interactions DISSECTION OF THE CD97-CD55 COMPLEX

Epidermal growth factor-like (EGF) and short consensus repeat (SCR) domains are commonly found in cell surface and soluble proteins that mediate specific protein-protein recognition events. Unlike the immunoglobulin (Ig) superfamily, very little is known about the general properties of intermolecular interactions encoded by these common modules, and in particular, how specificity of binding is achieved. We have dissected the binding of CD97 (a member of the EGF-TM7 family) to the complement regulator CD55, two cell surface modular proteins that contain EGF and SCR domains, respectively. We demonstrate that the interaction is mediated solely by these domains and is characterized by a low affinity (86 μm) and rapid off-rate (at least 0.6 s−1). The interaction is Ca2+ -dependent but is unaffected by glycosylation of the EGF domains. Using biotinylated multimerized peptides in cell binding assays and surface plasmon resonance, we show that a CD97-related EGF-TM7 molecule (termed EMR2), differing by only three amino acids within the EGF domains, binds CD55 with aK D at least an order of magnitude weaker than that of CD97. These results suggest that low affinity cell-cell interactions may be a general feature of highly expressed cell surface proteins and that specificity of SCR-EGF binding can be finely tuned by a small number of amino acid changes on the EGF module surface.

F4/80 and the related adhesion-GPCRs.

The F4/80 monoclonal antibody was first reported in this journal 30 years ago (Eur. J. Immunol. 1981. 11: 805–815). F4/80 has become a widely used marker for monocytes and many, but not all, tissue macrophages in the mouse. F4/80 is a member of the EGF‐TM7 family of leukocyte plasma membrane heptahelical molecules, which includes CD97 and EMR2. This Viewpoint summarises current knowledge of the expression, structure and functions of the EGF‐TM7 family, as part of a larger family of tissue adhesion‐GPCRs.

Ligation of the adhesion-GPCR EMR2 regulates human neutrophil function

At present, ~150 different members of the adhesion‐G protein‐coupled receptor (GPCR) family have been identified in metazoans. Surprisingly, very little is known about their function, although they all possess large extracellular domains coupled to a seven‐transmembrane domain, suggesting a potential role in cell adhesion and signaling. Here, we demonstrate how the human‐restricted adhesion‐GPCR, EMR2 (epidermal growth factor‐like module‐containing mucin‐like hormone receptor), regulates neutrophil responses by potentiating the effects of a number of proinflamma‐tory mediators and show that the transmembrane region is critical for adhesion‐GPCR function. Using an anti‐EMR2 antibody, ligation of EMR2 increases neu‐trophil adhesion and migration, and augments superoxide production and proteolytic enzyme degranulation. On neutrophil activation, EMR2 is rapidly translocated to membrane ruffles and the leading edge of the cell. Further supporting the role in neutrophil activation, EMR2 expression on circulating neutrophils is significantly increased in patients with systemic inflammation. These data illustrate a definitive function for a human adhesion‐GPCR within the innate immune system and suggest an important role in potentiating the inflammatory response. Ligation of the adhesion‐GPCR EMR2 regulates human neutrophil function.—Yona S., Lin, H.‐H., Dri, P., Davies, J. Q., Hayhoe, R. P. G., Lewis, S. M., Heinsbroek, S. E. M., Brown, K. A., Perretti, M., Hamann, J., Treacher, D. F., Gordon S., Stacey M. Ligation of the adhesion‐GPCR EMR2 regulates human neutrophil function. FASEB J. 22, 741–751 (2008)

Foxp3-positive macrophages display immunosuppressive properties and promote tumor growth

Identification of a population of Foxp3-expressing suppressive macrophages.

Disease-associated GPR56 Mutations Cause Bilateral Frontoparietal Polymicrogyria via Multiple Mechanisms

Loss-of-function mutations in the gene encoding G protein-coupled receptor 56 (GPR56) lead to bilateral frontoparietal polymicrogyria (BFPP), an autosomal recessive disorder affecting brain development. The GPR56 receptor is a member of the adhesion-GPCR family characterized by the chimeric composition of a long ectodomain (ECD), a GPCR proteolysis site (GPS), and a seven-pass transmembrane (7TM) moiety. Interestingly, all identified BFPP-associated missense mutations are located within the extracellular region of GPR56 including the ECD, GPS, and the extracellular loops of 7TM. In the present study, a detailed molecular and functional analysis of the wild-type GPR56 and BFPP-associated point mutants shows that individual GPR56 mutants most likely cause BFPP via different combination of multiple mechanisms. These include reduced surface receptor expression, loss of GPS proteolysis, reduced receptor shedding, inability to interact with a novel protein ligand, and differential distribution of the 7TM moiety in lipid rafts. These results provide novel insights into the cellular functions of GPR56 receptor and reveal molecular mechanisms whereby GPR56 mutations induce BFPP.

Activation of Myeloid Cell-Specific Adhesion Class G Protein-Coupled Receptor EMR2 via Ligation-Induced Translocation and Interaction of Receptor Subunits in Lipid Raft Microdomains

ABSTRACT The adhesion class G protein-coupled receptors (adhesion-GPCRs) play important roles in diverse biological processes ranging from immunoregulation to tissue polarity, angiogenesis, and brain development. These receptors are uniquely modified by self-catalytic cleavage at a highly conserved GPCR proteolysis site (GPS) dissecting the receptor into an extracellular subunit (α) and a seven-pass transmembrane subunit (β) with cellular adhesion and signaling functions, respectively. Using the myeloid cell-restricted EMR2 receptor as a paradigm, we exam the mechanistic relevance of the subunit interaction and demonstrate a critical role for GPS autoproteolysis in mediating receptor signaling and cell activation. Interestingly, two distinct receptor complexes are identified as a result of GPS proteolysis: one consisting of a noncovalent α-β heterodimer and the other comprising two completely independent receptor subunits which distribute differentially in membrane raft microdomains. Finally, we show that receptor ligation induces subunit translocation and colocalization within lipid rafts, leading to receptor signaling and inflammatory cytokine production by macrophages. Our present data resolve earlier conflicting results and provide a new mechanism of receptor signaling, as well as providing a paradigm for signal transduction within the adhesion-GPCR family.

Leukocyte adhesion-GPCR EMR2 is aberrantly expressed in human breast carcinomas and is associated with patient survival

EGF-like module containing mucin-like hormone receptor 2 (EMR2) is a leukocyte-restricted adhesion G protein-coupled receptor. Aberrant expression of EMR2 and its highly homologous molecule CD97 have been reported in various human cancers. Herein, we investigate the expression of EMR2 in neoplastic breast human tissue and its relationship with patient survival. EMR2 expression in normal and neoplastic breast tissue was assessed by immunohistochemistry in sections from 10 normal controls and micro-arrayed tissue cores from 69 cases of ductal carcinoma in situ (DCIS) and 272 invasive carcinomas. The pattern and intensity of staining was correlated with the clinicopathological characteristics of each case and the disease outcome. While absent in normal breast epithelium, EMR2 was significantly up-regulated in the cytoplasmic and nuclear compartments of both DCIS and invasive carcinoma, with invasive samples displaying significantly higher expression levels compared with in situ disease. In invasive disease, EMR2 cytoplasmic expression was significantly associated with higher tumour grade but not with patient age, nodal status, tumour size, estrogen receptor expression, relapse-free or overall survival. In contrast, EMR2 nuclear expression correlated negatively with higher tumour grade. Of note, EMR2 nuclear expression was associated with longer relapse-free survival as well as overall survival. This study indicates that EMR2 is expressed in neoplastic breast epithelium and suggests that expression patterns of EMR2 are relevant in breast cancer progression. The association of improved patient survival with higher nuclear expression levels identifies EMR2 as a potential biomarker in patients with invasive breast cancer.