Adhesion G Protein-coupled Receptor Research Articles

Essential Role of Latrophilin-1 Adhesion GPCR Nanoclusters in Inhibitory Synapses.

Latrophilin-1 (Lphn1, a.k.a. CIRL1 and CL1; gene symbol Adgrl1) is an Adhesion GPCR that has been implicated in excitatory synaptic transmission as a candidate receptor for α-latrotoxin. Here we analyzed conditional knockin/knockout mice for Lphn1 that contain an extracellular myc-epitope tag. Mice of both sexes were used in all experiments. Surprisingly, we found that Lphn1 is localized in cultured neurons to synaptic nanoclusters that are present in both excitatory and inhibitory synapses. Conditional deletion of Lphn1 in cultured neurons failed to elicit a detectable impairment in excitatory synapses but produced a decrease in inhibitory synapse numbers and synaptic transmission that was most pronounced for synapses close to the neuronal soma. No changes in axonal or dendritic outgrowth or branching were observed. Our data indicate that Lphn1 is among the few postsynaptic adhesion molecules that are present in both excitatory and inhibitory synapses and that Lphn1 by itself is not essential for excitatory synaptic transmission but contributes to inhibitory synaptic connections.Significance Statement Previously, the Adhesion-GPCRs Latrophilin-2/Latrophilin-3 have been shown to mediate excitatory, but not inhibitory, synapse assembly onto discreet dendritic compartments of hippocampal pyramidal neurons. Here we now show that Latrophilin-1 is targeted to both excitatory and inhibitory hippocampal synapses. Unexpectedly, we find that Latrophilin-1 is selectively essential for directing inhibitory synaptic connections to the neuronal soma. Our work supports a model by which Latrophilins are widely used as organizers of synaptic connectivity that act on a subcellular level. In the light of recent findings connecting haploinsufficiency of Latrophilin-1 to a plethora of neurodevelopmental and neuropsychiatric disorders, our study contributes to our understanding of the molecular mechanisms of Latrophilins that need to be targeted in order to address various pathologies.

Dysfunction of the adhesion G protein-coupled receptor latrophilin 1 (ADGRL1/LPHN1) increases the risk of obesity

Obesity is one of the diseases with severe health consequences and rapidly increasing worldwide prevalence. Understanding the complex network of food intake and energy balance regulation is an essential prerequisite for pharmacological intervention with obesity. G protein-coupled receptors (GPCRs) are among the main modulators of metabolism and energy balance. They, for instance, regulate appetite and satiety in certain hypothalamic neurons, as well as glucose and lipid metabolism and hormone secretion from adipocytes. Mutations in some GPCRs, such as the melanocortin receptor type 4 (MC4R), have been associated with early-onset obesity. Here, we identified the adhesion GPCR latrophilin 1 (ADGRL1/LPHN1) as a member of the regulating network governing food intake and the maintenance of energy balance. Deficiency of the highly conserved receptor in mice results in increased food consumption and severe obesity, accompanied by dysregulation of glucose homeostasis. Consistently, we identified a partially inactivating mutation in human ADGRL1/LPHN1 in a patient suffering from obesity. Therefore, we propose that LPHN1 dysfunction is a risk factor for obesity development.

G protein-coupled receptor-mediated autophagy in health and disease.

G protein-coupled receptors (GPCRs) constitute the largest and most diverse superfamily of mammalian transmembrane proteins. These receptors are involved in a wide range of physiological functions and are targets for more than a third of available drugs in the market. Autophagy is a cellular process involved in degrading damaged proteins and organelles and in recycling cellular components. Deficiencies in autophagy are involved in a variety of pathological conditions. Both GPCRs and autophagy are essential in preserving homeostasis and cell survival. There is emerging evidence suggesting that GPCRs are direct regulators of autophagy. Additionally, autophagic machinery is involved in the regulation of GPCR signalling. The interplay between GPCR and autophagic signalling mechanisms significantly impacts on health and disease; however, there is still an incomplete understanding of the underlying mechanisms and therapeutic implications in different tissues and disease contexts. This review aims to discuss the interactions between GPCR and autophagy signalling. Studies on muscarinic receptors, beta-adrenoceptors, taste receptors, purinergic receptors and adhesion GPCRs are summarized, in relation to autophagy.

ADGRG1, an adhesion G protein-coupled receptor, forms oligomers.

G protein-coupled receptor (GPCR) oligomerization is a highly debated topic in the field. While initially believed to function as monomers, current literature increasingly suggests that these cell surface receptors, spanning almost all GPCR families, function as homo- or hetero-oligomers. Yet, the functional consequences of these oligomeric complexes remain largely unknown. Adhesion GPCRs (aGPCRs) present an intriguing family of receptors characterized by their large and multi-domain N-terminal fragments (NTFs), intricate activation mechanisms, and the prevalence of numerous splice variants in almost all family members. In the present study, bioluminescence energy transfer (BRET) and Förster resonance energy transfer (FRET) were used to study the homo-oligomerization of adhesion G protein-coupled receptor G1 (ADGRG1; also known as GPR56) and to assess the involvement of NTFs in these receptor complexes. Based on the results presented herein, we propose that ADGRG1 forms 7-transmembrane-driven homo-oligomers on the plasma membrane. Additionally, Stachel motif interactions appear to influence the conformation of these receptor complexes.

The repertoire and structure of adhesion GPCR transcript variants assembled from publicly available deep-sequenced human samples.

Alternative splicing and multiple transcription start and termination sites can produce a diverse repertoire of mRNA transcript variants from a given gene. While the full picture of the human transcriptome is still incomplete, publicly available RNA datasets have enabled the assembly of transcripts. Using publicly available deep sequencing data from 927 human samples across 48 tissues, we quantified known and new transcript variants, provide an interactive, browser-based application Splice-O-Mat and demonstrate its relevance using adhesion G protein-coupled receptors (aGPCRs) as an example. On average, 24 different transcript variants were detected for each of the 33 human aGPCR genes, and several dominant transcript variants were not yet annotated. Variable transcription starts and complex exon-intron structures encode a flexible protein domain architecture of the N- and Ctermini and the seven-transmembrane helix domain (7TMD). Notably, we discovered the first GPCR (ADGRG7/GPR128) with eight transmembrane helices. Both the N- and C terminus of this aGPCR were intracellularly oriented, anchoring the N terminus in the plasma membrane. Moreover, the assessment of tissue-specific transcript variants, also for other gene classes, in our application may change the evaluation of disease-causing mutations, as their position in different transcript variants may explain tissue-specific phenotypes.

The adhesion GPCR and PCP component flamingo (FMI-1) alters body size and regulates the composition of the extracellular matrix

The extracellular matrix (ECM) is a network of macromolecules that presents a vital scaffold for cells and enables multiple ways of cellular communication. Thus, it is essential for many physiological processes such as development, tissue morphogenesis, homeostasis, the shape and partially the size of the body and its organs. To ensure these, the composition of the ECM is tissue-specific and highly dynamic. ECM homeostasis is therefore tightly controlled by several mechanisms.Here, we show that FMI-1, the homolog of the Adhesion GPCR Flamingo/CELSR/ADGRC in the nematode Caenorhabditis elegans, modulates the composition of the ECM by controlling the production both of ECM molecules such as collagens and also of ECM modifying enzymes. Thereby, FMI-1 affects the morphology and functionality of the nematode´s cuticle, which is mainly composed of ECM, and also modulates the body size. Mechanistic analyses highlight the fact that FMI-1 exerts its function from neurons non-cell autonomously (trans) solely via its extracellular N terminus. Our data support a model, by which the activity of the receptor, which has a well-described role in the planar cell polarity (PCP) pathway, involves the PCP molecule VANG-1, but seems to be independent of the DBL-1/BMP pathway.

The dark sides of the GPCR tree ‐ research progress on understudied GPCRs

AbstractA large portion of the human GPCRome is still in the dark and understudied, consisting even of entire subfamilies of GPCRs such as odorant receptors, class A and C orphans, adhesion GPCRs, Frizzleds and taste receptors. However, it is undeniable that these GPCRs bring an untapped therapeutic potential that should be explored further. Open questions on these GPCRs span diverse topics such as deorphanisation, the development of tool compounds and tools for studying these GPCRs, as well as understanding basic signalling mechanisms. This review gives an overview of the current state of knowledge for each of the diverse subfamilies of understudied receptors regarding their physiological relevance, molecular mechanisms, endogenous ligands and pharmacological tools. Furthermore, it identifies some of the largest knowledge gaps that should be addressed in the foreseeable future and lists some general strategies that might be helpful in this process.

CELSR1, a core planar cell polarity protein, features a weakly adhesive and flexible cadherin ectodomain

Planar cell polarity (PCP), essential to multicellular developmental processes, arises when cells polarize and align across tissues. Central to PCP is CELSR1, an atypical cadherin featuring a long ectodomain with nine extracellular cadherin (EC) repeats, a membrane adjacent domain (MAD10), and several characteristic adhesion GPCR domains. Cell-based aggregation assays have demonstrated CELSR1's homophilic adhesive nature, but mechanistic details are missing. Here, we investigate the possible adhesive properties and structures of CELSR1 EC repeats. Our bead aggregation assays do not support strong adhesion by EC repeats alone. Consistently, EC1-4 only dimerizes at high concentration in solution. Crystal structures of human CELSR1 EC1-4 and EC4-7 reveal typical folds and a non-canonical linker between EC5 and EC6. Simulations and experiments using EC4-7 indicate flexibility at EC5-6, and solution experiments show EC7-MAD10-mediated dimerization. Our results suggest weak homophilic adhesion by CELSR1 cadherin repeats and provide mechanistic insights into the structural determinants of CELSR1 function.

The adhesion GPCR GPR116/ADGRF5 has a dual function in pancreatic islets regulating somatostatin release and islet development

Glucose homeostasis is maintained by hormones secreted from different cell types of the pancreatic islets and controlled by manifold input including signals mediated through G protein-coupled receptors (GPCRs). RNA-seq analyses revealed expression of numerous GPCRs in mouse and human pancreatic islets, among them Gpr116/Adgrf5. GPR116 is an adhesion GPCR mainly found in lung and required for surfactant secretion. Here, we demonstrate that GPR116 is involved in the somatostatin release from pancreatic delta cells using a whole-body as well as a cell-specific knock-out mouse model. Interestingly, the whole-body GPR116 deficiency causes further changes such as decreased beta-cell mass, lower number of small islets, and reduced pancreatic insulin content. Glucose homeostasis in global GPR116-deficient mice is maintained by counter-acting mechanisms modulating insulin degradation. Our data highlight an important function of GPR116 in controlling glucose homeostasis.

Isoform Specific Roles for the Acute Myeloid Leukemia Stem Cell Antigen CD97

CD97 is an adhesion GPCR protein frequently upregulated in AML and required for LSC self-renewal that is alternatively spliced to form three isoforms that are distinct with respect to their extracellular domain. Our analysis of HSCs from MDS patients with low-risk disease revealed overexpression of CD97 isoform 1 (CD97iso1), while analysis of AML samples from the TCGA dataset revealed preferential expression of CD97iso2 (p<0.0001) (Figure1A). As these data suggested potential isoform specific roles of CD97 in myeloid leukemogenesis, we investigated if the different CD97 isoforms support different functional roles by testing the effect of each isoform on growth, differentiation, and clonogenicity of AML blasts. Consistent with our prior studies demonstrating CD97iso1 promotion of self-renewal in normal CD34+ hematopoietic stem/progenitor cells, over expression of CD97iso1 in AML cell lines increased their serial replating ability, while knockout abrogated their clonogenicity. In stark contrast, overexpression of CD97iso2 or CD97iso3 resulted in decreased clonogenicity upon replating. Overexpression of CD97iso2 conferred the greatest growth advantage to AML cells among the CD97 isoforms. Importantly, knockout of CD97iso2 increased cell differentiation and primed the cells towards apoptosis. Supporting CD97iso2's role in cell growth/survival, daunorubicin treatment increased the expression of CD97iso2. Consistent with CD97's role in increasing migration and invasiveness in solid tumors, we performed trans well migration assays using AML cell lines and observed the highest increase in migration in blasts over expressing CD97iso3 (p<0.01). While CD97 is thought to activate several downstream signaling pathways including the MEK-ERK pathway and PI3K/AKT pathway, it is unknown whether the different CD97 isoforms activate unique downstream signaling pathways, and thus we used an unbiased Bio-ID screen to identify the C-terminal interacting partners of the different CD97 isoforms. We observed preferential enrichment of NLRX1 interactions in CD97iso1 expressing cells, while PI4KA was enriched in CD97iso2 expressing cells. Consistent with NLRX1's role in increasing autophagy, we observed an increase in autophagy upon overexpressing CD97iso1, and consistent with CD97iso2's association with PI4KA, CD97iso2 overexpressing cells showed increased PI4KA and phosphoERK1/2. Finally, confirming non-redundant functional roles of CD97 isoforms in vivo, xenograft studies in NSG mice using AML cell lines revealed that CD97iso2 promoted the most rapid engraftment and shortest survival in recipients (p=0.0001). Given the importance of all the CD97 isoforms in regulating different blast function, we developed antibody-drug conjugates (ADCs) based on human synthetic antibodies that target all isoforms of CD97. ADC against CD97 specifically kills AML cells overexpressing CD97, suggesting the potential use of anti-CD97 ADC for AML therapy. Collectively, these studies demonstrate that CD97 isoforms mediate unique biological roles in vitro and in vivo, and that they likely mediate these functions through differential activation of downstream signaling pathways. We speculate that differential expression of the CD97 isoforms in MDS and AML likely reflects the unique features of MDS HSCs (high levels of CD97iso1 enhancing self-renewal in MDS) versus AML LSCs (CD97iso2 promoting proliferation in AML) (Figure 1B). These studies also highlight the importance of isoform-specific gene expression during myeloid leukemogenesis and suggest that explorations of altered isoform expression in MDS/AML will yield novel insights into the molecular mechanisms that promote disease development and progression.

Adhesion GPCRs in glioblastoma revisited

Glioblastoma is a devastating brain malignancy that has remained intractable to modern cancer treatments. Ravn-Boess etal.1 have discovered that the adhesion G protein-coupled receptor CD97/ADGRE5 contributes to glioblastogenesis and makes for an excellent molecular surface marker flagging the tumor cells.

Correction for Chen et al., mthl1, a potential Drosophila homologue of mammalian adhesion GPCRs, is involved in antitumor reactions to injected oncogenic cells in flies.

Correction for Chen et al., mthl1, a potential Drosophila homologue of mammalian adhesion GPCRs, is involved in antitumor reactions to injected oncogenic cells in flies.

CryoEM structures of adhesion in GPCR CD97: Filling in some of the gaps

CD97 (ADGRE5) is an adhesion GPCR (aGPCR) that plays crucial roles in the immune system and cancer. In this issue of Cell Chemical Biology, Wang etal.1 present the cryoEM structures of CD97 in complex with G13, Gq, and Gs G protein subtypes, revealing in-depth insight into aGPCR activation and G protein selectivity.

Unveiling Mechanical Activation: GAIN Domain Unfolding and Dissociation in Adhesion GPCRs.

Adhesion G protein-coupled receptors (aGPCRs) have extracellular regions (ECRs) containing GPCR autoproteolysis-inducing (GAIN) domains. The GAIN domain enables the ECR to self-cleave into N- and C-terminal fragments. However, the impact of force on the GAIN domain's conformation, critical for mechanosensitive aGPCR activation, remains unclear. Our study investigated the mechanical stability of GAIN domains in three aGPCRs (B, G, and L subfamilies) at a loading rate of 1 pN/s. We discovered that forces of a few piconewtons can destabilize the GAIN domains. In autocleaved aGPCRs ADGRG1/GPR56 and ADGRL1/LPHN1, these forces cause the GAIN domain detachment from the membrane-proximal Stachel sequence, preceded by partial unfolding. In noncleavable aGPCR ADGRB3/BAI3 and cleavage-deficient mutant ADGRG1/GPR56-T383G, complex mechanical unfolding of the GAIN domain occurs. Additionally, GAIN domain detachment happens during cell migration. Our findings support the mechanical activation hypothesis of aGPCRs, emphasizing the sensitivity of the GAIN domain structure and detachment to physiological force ranges.

OR12-06 Hypothalamic Adgrl1 Is A Potential Glucoreceptor Involved In Regulating Energy Balance, Glucose Homeostasis, And Leptin Sensitivity In Mice

Abstract Disclosure: D.J. Samuel: None. T.S. Faniyan: None. M.U. Raza: None. S. Bathina: None. K.H. Chhabra: None. The hypothalamus regulates energy and glucose homeostasis by influencing glucose-stimulated insulin secretion, insulin sensitivity, and activating the hypoglycemia counterregulatory response. Although hypothalamic glucose transporters coupled with glucose metabolism are involved in mediating some of these effects, it is unknown whether a plasma membrane receptor that directly binds to glucose can contribute to hypothalamic glucose signaling. We used affinity chromatography and biotin-labeled glucose to enrich glucose-binding plasma membrane proteins/receptors in the mouse hypothalamus and then performed proteomic analyses. Adhesion G-protein Coupled Receptor L1 (Adgrl1) was a top candidate as a potential glucoreceptor. Therefore, we generated Adgrl1loxp/loxp mice to knockout Adgrl1 in the ventromedial hypothalamus (VMH; a region known for glucose sensing) using the Cre-Lox system to determine the role of Adgrl1VMH in glucose homeostasis, energy balance, and leptin sensitivity. We measured body weight, food intake, 6h fasting blood glucose and plasma insulin levels. We also determined leptin sensitivity in the Adgrl1VMH deficient mice. We observed that 24 weeks old male Adgrl1VMH deficient mice had higher (p<0.05) body weight (49 ±3.6 vs 35 ±1.3 g), blood glucose (210 ±4 vs 180 ±5 mg/dl), plasma insulin levels (2.92 ±0.24 vs 1.63 ±0.09 ng/ml), and leptin levels (21.11 ±1.72 vs 8.38 ±0.80 ng/ml) compared to their control littermates. Hyperinsulinemia and hyperleptinemia persisted in the Adgrl1VMH knockout mice even when they were weight-matched to their littermate controls, indicating the direct role of Adgrl1VMH in regulating plasma insulin and leptin levels. Ovariectomy in female mice was necessary to unmask the effects of Adgrl1VMH deficiency on energy and glucose homeostasis. To assess acute leptin sensitivity, we injected Adgrl1VMH deficient mice and their littermate control mice with recombinant mouse leptin (5 mg/Kg, i.p., twice a day for two days), and monitored their body weight and food intake. Male Adgrl1VMH deficient mice were more susceptible (p<0.05) to leptin mediated decrease in food intake (-1 ±0.1 vs -0.5 ±0.005, g/day; these values are relative to each group’s corresponding baseline food intake) than their littermate controls. Decrease in body weight was similar in both groups with this acute leptin treatment. These findings suggest that Adgrl1VMH is essential in regulating energy and glucose homeostasis in a sex-specific manner. Moreover, Adgrl1VMH contributes to leptin’s acute effects on food intake. Therefore, hypothalamic Adgrl1 could be a target to enhance leptin sensitivity in future therapies for treating type 2 diabetes and obesity. Presentation: Friday, June 16, 2023

GPR114/ADGRG5 is activated by its tethered peptide agonist because it is a cleaved adhesion GPCR

Family B2 or adhesion G protein-coupled receptors (AGPCRs) are distinguished by variable extracellular regions that contain a modular protease, termed the GPCR autoproteolysis-inducing domain that self-cleaves the receptor into an N-terminal fragment (NTF) and a C-terminal fragment (CTF), or seven transmembrane domain (7TM). The NTF and CTF remain bound after cleavage through noncovalent interactions. NTF binding to a ligand(s) presented by nearby cells, or the extracellular matrix anchors the NTF, such that cell movement generates force to induce NTF/CTF dissociation and expose the AGPCR tethered peptide agonist. The released tethered agonist (TA) binds rapidly to the 7TM orthosteric site to activate signaling. The orphan AGPCR, GPR114 was reported to be uncleaved, yet paradoxically capable of activation by its TA. GPR114 has an identical cleavage site and TA to efficiently cleave GPR56. Here, we used immunoblotting and biochemical assays to demonstrate that GPR114 is a cleaved receptor, and the self-cleavage is required for GPR114 TA-activation of Gs and no other classes of G proteins. Mutagenesis studies defined features of the GPR114 and GPR56 GAINA subdomains that influenced self-cleavage efficiency. Thrombin treatment of protease-activated receptor 1 leader/AGPCR fusion proteins demonstrated that acute decryption of the GPR114/56TAs activated signaling. GPR114 was found to be expressed in an eosinophilic-like cancer cell line (EoL-1cells) and endogenous GPR114 was efficiently self-cleaved. Application of GPR114TA peptidomimetics to EoL-1cells stimulated cAMP production. Our findings may aid future delineation of GPR114 function in eosinophil cAMP signaling related to migration, chemotaxis, or degranulation.

A method for structure determination of GPCRs in various states.

G-protein-coupled receptors (GPCRs) are a class of integral membrane proteins that detect environmental cues and trigger cellular responses. Deciphering the functional states of GPCRs induced by various ligands has been one of the primary goals in the field. Here we developed an effective universal method for GPCR cryo-electron microscopy structure determination without the need to prepare GPCR-signaling protein complexes. Using this method, we successfully solved the structures of the β2-adrenergic receptor (β2AR) bound to antagonistic and agonistic ligands and the adhesion GPCR ADGRL3 in the apo state. For β2AR, an intermediate state stabilized by the partial agonist was captured. For ADGRL3, the structure revealed that inactive ADGRL3 adopts a compact fold and that large unusual conformational changes on both the extracellular and intracellular sides are required for activation of adhesion GPCRs. We anticipate that this method will open a new avenue for understanding GPCR structure‒function relationships and drug development.

Adhesion GPCR Gpr126 (Adgrg6) Expression Profiling in Zebrafish, Mouse, and Human Kidney.

Adhesion G protein-coupled receptors (aGPCRs) comprise the second-largest class of GPCRs, the most common target for approved pharmacological therapies. aGPCRs play an important role in development and disease and have recently been associated with the kidney. Several aGPCRs are expressed in the kidney and some aGPCRs are either required for kidney development or their expression level is altered in diseased kidneys. Yet, general aGPCR function and their physiological role in the kidney are poorly understood. Here, we characterize in detail Gpr126 (Adgrg6) expression based on RNAscope® technology in zebrafish, mice, and humans during kidney development in adults. Gpr126 expression is enriched in the epithelial linage during nephrogenesis and persists in the adult kidney in parietal epithelial cells, collecting ducts, and urothelium. Single-cell RNAseq analysis shows that gpr126 expression is detected in zebrafish in a distinct ionocyte sub-population. It is co-detected selectively with slc9a3.2, slc4a4a, and trpv6, known to be involved in apical acid secretion, buffering blood or intracellular pH, and to maintain high cytoplasmic Ca2+ concentration, respectively. Furthermore, gpr126-expressing cells were enriched in the expression of potassium transporter kcnj1a.1 and gcm2, which regulate the expression of a calcium sensor receptor. Notably, the expression patterns of Trpv6, Kcnj1a.1, and Gpr126 in mouse kidneys are highly similar. Collectively, our approach permits a detailed insight into the spatio-temporal expression of Gpr126 and provides a basis to elucidate a possible role of Gpr126 in kidney physiology.

Functional partnerships between GPI-anchored proteins and adhesion GPCRs.

Specific extracellular interaction between glycophosphatidylinositol (GPI)-anchored proteins and adhesion G protein-coupled receptors (aGPCRs) plays an important role in unique biological functions. GPI-anchored proteins are derived from a novel post-translational modification of single-span membrane molecules, while aGPCRs are bona fide seven-span transmembrane proteins with a long extracellular domain. Although various members of the two structurally-distinct protein families are known to be involved in a wide range of biological processes, many remain as orphans. Interestingly, accumulating evidence has pointed to a complex interaction and functional synergy between these two protein families. I discuss herein current understanding of specific functional partnerships between GPI-anchored proteins and aGPCRs.

Mthl1, a potential Drosophila homologue of mammalian adhesion GPCRs, is involved in antitumor reactions to injected oncogenic cells in flies

Injection of OCs into adult male flies induces a strong transcriptomic response in the host flies featuring in particular genes encoding bona fide G coupled proteins, among which the gene for methuselah like 1 is prominent. The injection is followed after a 3-d lag period, by the proliferation of the oncogenic cells. We hypothesized that through the product of mthl1 the host might control, at least in part, this proliferation as a defense reaction. Through a combination of genetic manipulations of the mthl1 gene (loss of function and overexpression of mthl1), we document that indeed this gene has an antiproliferative effect. Parallel injections of primary embryonic Drosophila cells or of various microbes do not exhibit this effect. We further show that mthl1 controls the expression of a large number of genes coding for chemoreceptors and genes implicated in regulation of development. Of great potential interest is our observation that the expression of the mouse gene coding for the adhesion G-protein-coupled receptor E1 (Adgre1, also known as F4/80), a potential mammalian homologue of mthl1, is significantly induced by B16-F10 melanoma cell inoculation 3 d postinjection in both the bone marrow and spleen (nests of immature and mature myeloid-derived immune cells), respectively. This observation is compatible with a role of this GPCR in the early response to injected tumor cells in mice.