GPR56 contributes to the development of acute myeloid leukemia in mice

Immunophenotypic features of early haematopoietic and leukaemia stem cells

Many tumours are organised in a hierarchical structure with at its apex a cell that can maintain, establish, and repopulate the tumour-the cancer stem cell. The haematopoietic stem cell (HSC) is the founder cell for all functional blood cells. Like HSCs, the leukaemia stem cells (LSC) are hypothesised to be the leukaemia-initiating cells, which have features of stemness such as self-renewal, quiescence, and resistance to cytotoxic drugs. Immunophenotypically, CD34+CD38- defines HSCs by adding lineage negativity and CD90+CD45RA-. At which stage of maturation the further differentiation is blocked, determines the type of leukaemia, and determines the immunophenotype of the LSC specific to the leukaemia type. No apparent LSC phenotype has been described in lymphoid leukaemia, and it is debated if a specific acute lymphocytic leukaemia-initiating cell is present, as all cells are capable of engraftment in a secondary mouse model. In chronic lymphocytic leukaemia, a B-cell clone is responsible for uncontrolled proliferation, not a specific LSC. In chronic and acute myeloid leukaemia, LSC is described as CD34+CD38- with the expression of a marker that is aberrantly expressed (LSC marker), such as CD45RA, CD123 or in the case of chronic myeloid leukaemia CD26. In acute myeloid leukaemia, the LSC load had prognostic relevance and might be a biomarker that can be used for monitoring and as an addition to measurable residual disease. However, challenges such as the CD34-negative immunophenotype need to be explored.

An antibody-drug conjugate targeting GPR56 demonstrates efficacy in preclinical models of colorectal cancer

BACKGROUND

Long-term prognosis remains poor for colorectal cancer (CRC) patients with advanced disease due to treatment resistance. The identification of novel targets is essential for the development of new therapeutic approaches. GPR56, an adhesion GPCR, is highly expressed in CRC tumours and correlates with poor survival. Here, we describe the generation and preclinical evaluation of a novel ADC consisting of an anti-GPR56 antibody (10C7) conjugated with the DNA-damaging payload duocarmycin.

METHODS

RNA-seq dataset analysis was performed to determine GPR56 expression in CRC subtypes. The specificity of binding, epitope mapping, and internalisation of 10C7 was examined. 10C7 was conjugated to payload and ADC cytotoxicity was assessed against a panel of CRC cell lines and tumour organoids. Antitumour efficacy was evaluated in xenograft models of CRC cell lines and patient-derived tumours.

RESULTS

High GPR56 was shown to be associated with the microsatellite stable (MSS) subtype that accounts for 80-85% of CRC. GPR56 ADC selectively induced cytotoxicity in CRC cells and tumour organoids at low nanomolar potency in a GPR56-dependent manner and showed significant antitumour efficacy against GPR56-expressing xenograft models.

CONCLUSIONS

This study provides the rationale for the future development of a GPR56-targeted ADC approach to potentially treat a large fraction of MSS CRC patients.

Role of Adhesion G Protein-Coupled Receptors in Immune Dysfunction and Disorder

Disorders of the immune system, including immunodeficiency, immuno-malignancy, and (auto)inflammatory, autoimmune, and allergic diseases, have a great impact on a host’s health. Cellular communication mediated through cell surface receptors, among different cell types and between cell and microenvironment, plays a critical role in immune responses. Selective members of the adhesion G protein-coupled receptor (aGPCR) family are expressed differentially in diverse immune cell types and have been implicated recently in unique immune dysfunctions and disorders in part due to their dual cell adhesion and signaling roles. Here, we discuss the molecular and functional characteristics of distinctive immune aGPCRs and their physiopathological roles in the immune system.

Adhesion G protein-coupled receptors: structure, signaling, physiology, and pathophysiology

Adhesion G protein-coupled receptors (AGPCRs) are a family of 33 receptors in humans exhibiting a conserved general structure but diverse expression patterns and physiological functions. The large NH2 termini characteristic of AGPCRs confer unique properties to each receptor and possess a variety of distinct domains that can bind to a diverse array of extracellular proteins and components of the extracellular matrix. The traditional view of AGPCRs, as implied by their name, is that their core function is the mediation of adhesion. In recent years, though, many surprising advances have been made regarding AGPCR signaling mechanisms, activation by mechanosensory forces, and stimulation by small-molecule ligands such as steroid hormones and bioactive lipids. Thus, a new view of AGPCRs has begun to emerge in which these receptors are seen as massive signaling platforms that are crucial for the integration of adhesive, mechanosensory, and chemical stimuli. This review article describes the recent advances that have led to this new understanding of AGPCR function and also discusses new insights into the physiological actions of these receptors as well as their roles in human disease.

Functions of G protein-coupled receptor 56 in health and disease

Human G protein-coupled receptor 56 (GPR56) is encoded by gene ADGRG1 from chromosome 16q21 and is homologously encoded in mice, at chromosome 8. Both 687 and 693 splice forms are present in humans and mice. GPR56 has a 381 amino acid-long N-terminal extracellular segment and a GPCR proteolysis site upstream from the first transmembrane domain. GPR56 is mainly expressed in the heart, brain, thyroid, platelets, and peripheral blood mononuclear cells. Accumulating evidence indicates that GPR56 promotes the formation of myelin sheaths and the development of oligodendrocytes in the cerebral cortex of the central nervous system. Moreover, GPR56 contributes to the development and differentiation of hematopoietic stem cells, induces adipogenesis, and regulates the function of immune cells. The lack of GPR56 leads to nervous system dysfunction, platelet disorders, and infertility. Abnormal expression of GPR56 is related to the malignant transformation and tumor metastasis of several cancers including melanoma, neuroglioma, and gastrointestinal cancer. Metabolic disorders and cardiovascular diseases are also associated with dysregulation of GPR56 expression, and GPR56 is involved in the pharmacological resistance to some antidepressant and cancer drug treatments. In this review, the molecular structure, expression profile, and signal transduction of GPR56 are introduced, and physiological and pathological functions of GRP56 are comprehensively summarized. Attributing to its significant biological functions and its long N-terminal extracellular region that interacts with multiple ligands, GPR56 is becoming an attractive therapeutic target in treating neurological and hematopoietic diseases.

Role of ADGRG1/GPR56 in Tumor Progression

Cellular communication plays a critical role in diverse aspects of tumorigenesis including tumor cell growth/death, adhesion/detachment, migration/invasion, angiogenesis, and metastasis. G protein-coupled receptors (GPCRs) which constitute the largest group of cell surface receptors are known to play fundamental roles in all these processes. When considering the importance of GPCRs in tumorigenesis, the adhesion GPCRs (aGPCRs) are unique due to their hybrid structural organization of a long extracellular cell-adhesive domain and a seven-transmembrane signaling domain. Indeed, aGPCRs have been increasingly shown to be associated with tumor development by participating in tumor cell interaction and signaling. ADGRG1/GPR56, a representative tumor-associated aGPCR, is recognized as a potential biomarker/prognostic factor of specific cancer types with both tumor-suppressive and tumor-promoting functions. We summarize herein the latest findings of the role of ADGRG1/GPR56 in tumor progression.

ADGRG1 Is a Predictor of Chemoresistance and Poor Survival in Cervical Squamous Carcinoma

Background

Cisplatin is the first-line chemotherapy for cervical cancer. Cisplatin resistance has always been one of the most significant barriers to acquiring better outcomes. However, the complex molecular mechanisms accounting for the phenomenon are not completely clear.

Methods

Construction of the cisplatin-resistant cell model of cervical cancer, then performing RNA sequencing and bioinformatic analysis of the differential expression genes. Then Adhesion G protein-coupled receptor G1 (ADGRG1) was screened out as our target gene. Gene Expression Profiling Interactive Analysis (GEPIA) was searched to show the expression level of ADGRG1 in cervical cancer and normal tissue. Kaplan-Meier Plotter (Kmplot) was used to explore the relationship of its expression with survival data. Tissue specimens were used to verify the relationship between the clinicopathological characteristics and ADGRG1 expression. Then we explored the roles of ADGRG1 in tumorigenesis through in vitro and in vivo assays.

Results

We found the ADGRG1 was significantly overexpressed in cervical cancer tissues compared to corresponding normal tissues. Higher ADGRG1 expression was correlated with poor progress-free survival. Knockdown of ADGRG1 markedly suppressed cell proliferation, migration, and invasion and increased cell sensitivity to cisplatin in vitro. Similarly, the role of ADGRG1 knockdown on tumorigenicity and sensitivity to cisplatin treatment was verified in vivo. The underlying mechanism was explored by western blotting that ADGRG1 knockdown inhibited tumorigenesis by PI3K/Akt/mTOR signaling pathway.

Conclusion

ADGRG1 acts as an oncogene to maintain tumorigenicity, migration, and invasion, and its depressed expression prompts sensitivity to cisplatin. Thus, ADGRG1 may represent a potential prognostic marker and possible therapeutic target for cervical cancer.

Unexpected redundancy of Gpr56 and Gpr97 during hematopoietic cell development and differentiation

Integrated molecular signals regulate cell fate decisions in the embryonic aortic endothelium to drive hematopoietic stem cell (HSC) generation during development. The G-protein-coupled receptor 56 (Gpr56, also called Adgrg1) is the most highly upregulated receptor gene in cells that take on hematopoietic fate and is expressed by adult bone marrow HSCs. Despite the requirement for Gpr56 in hematopoietic stem/progenitor cell (HS/PC) generation in zebrafish embryos and the highly upregulated expression of GPR56 in treatment-resistant leukemic patients, its function in normal mammalian hematopoiesis remains unclear. Here, we examine the role of Gpr56 in HS/PC development in Gpr56 conditional knockout (cKO) mouse embryos and Gpr knockout (KO) embryonic stem cell (ESC) hematopoietic differentiation cultures. Our results show a bias toward myeloid differentiation of Gpr56 cKO fetal liver HSCs and an increased definitive myeloid progenitor cell frequency in Gpr56KO ESC differentiation cultures. Surprisingly, we find that mouse Gpr97 can rescue Gpr56 morphant zebrafish hematopoietic generation, and that Gpr97 expression is upregulated in mouse Gpr56 deletion models. When both Gpr56 and Gpr97 are deleted in ESCs, no or few hematopoietic PCs (HPCs) are generated upon ESC differentiation. Together, our results reveal novel and redundant functions for these 2 G-protein coupled receptors in normal mammalian hematopoietic cell development and differentiation.

The role of GPR56/ADGRG1 in health and disease

GPR56/ADGRG1 is a versatile adhesion G protein-coupled receptor important in the physiological functions of the central and peripheral nervous systems, reproductive system, muscle hypertrophy, immune regulation, and hematopoietic stem cell generation. By contrast, aberrant expression or deregulated functions of GPR56 have been implicated in diverse pathological processes, including bilateral frontoparietal polymicrogyria, depression, and tumorigenesis. In this review article, we summarize and discuss the current understandings of the role of GPR56 in health and disease.

Anti-GPR56 monoclonal antibody potentiates GPR56-mediated Src-Fak signaling to modulate cell adhesion

GPR56 is a member of the adhesion G-protein-coupled receptor family shown to play important roles in cell adhesion, brain development, immune function, and tumorigenesis. GPR56 is highly upregulated in colorectal cancer and correlates with poor prognosis. Several studies have shown GPR56 couples to the Gα_12/13 class of heterotrimeric G-proteins to promote RhoA activation. However, due to its structural complexity and lack of a high-affinity receptor-specific ligand, the complete GPR56 signaling mechanism remains largely unknown. To delineate the activation mechanism and intracellular signaling functions of GPR56, we generated a monoclonal antibody (mAb) that binds with high affinity and specificity to the extracellular domain (ECD). Using deletion mutants, we mapped the mAb binding site to the GAIN domain, which mediates membrane-proximal autoproteolytic cleavage of the ECD. We showed that GPR56 overexpression in 293T cells leads to increased phosphorylation of Src, Fak, and paxillin adhesion proteins and activation of the Gα_12/13-RhoA-mediated serum response factor (SRF) pathway. Treatment with the mAb potentiated Src-Fak phosphorylation, RhoA–SRF signaling, and cell adhesion. Consistently, GPR56 knockdown in colorectal cancer cells decreased Src–Fak pathway phosphorylation and cell adhesion. Interestingly, GPR56-mediated activation of Src–Fak phosphorylation occurred independent of RhoA, yet mAb-induced potentiation of RhoA–SRF signaling was Src-dependent. Furthermore, we show that the C-terminal portion of the Serine–Threonine–Proline-rich (STP) region, adjacent to the GAIN domain, was required for Src–Fak activation. However, autoproteolytic cleavage of the ECD was dispensable. These data support a new ECD-dependent mechanism by which GPR56 functions to regulate adhesion through activation of Src–Fak signaling.

Acute Myeloid Leukemia Stem Cells: The Challenges of Phenotypic Heterogeneity

Patients suffering from acute myeloid leukemia (AML) show highly heterogeneous clinical outcomes. Next to variabilities in patient-specific parameters influencing treatment decisions and outcome, this is due to differences in AML biology. In fact, different genetic drivers may transform variable cells of origin and co-exist with additional genetic lesions (e.g., as observed in clonal hematopoiesis) in a variety of leukemic (sub)clones. Moreover, AML cells are hierarchically organized and contain subpopulations of more immature cells called leukemic stem cells (LSC), which on the cellular level constitute the driver of the disease and may evolve during therapy. This genetic and hierarchical complexity results in a pronounced phenotypic variability, which is observed among AML cells of different patients as well as among the leukemic blasts of individual patients, at diagnosis and during the course of the disease. Here, we review the current knowledge on the heterogeneous landscape of AML surface markers with particular focus on those identifying LSC, and discuss why identification and targeting of this important cellular subpopulation in AML remains challenging.

Weighted gene co-expression network analysis identified underlying hub genes and mechanisms in the occurrence and development of viral myocarditis

Background

Myocarditis is an inflammatory myocardial disease, which may lead to heart failure and sudden death. Despite extensive research into the pathogenesis of myocarditis, effective treatments for this condition remain elusive. This study aimed to explore the potential pathogenesis and hub genes for viral myocarditis.

Methods

A weighted gene co-expression network analysis (WGCNA) was performed based on the gene expression profiles derived from mouse models at different stages of viral myocarditis (GSE35182). Functional annotation was executed within the key modules. Potential hub genes were predicted based on the intramodular connectivity (IC). Finally, potential microRNAs that regulate gene expression were predicted by miRNet analysis.

Results

Three gene co-expression modules showed the strongest correlation with the acute or chronic disease stage. A significant positive correlation was detected between the acute disease stage and the turquoise module, the genes of which were mainly enriched in antiviral response and immune-inflammatory activation. Furthermore, a significant positive correlation and a negative correlation were identified between the chronic disease stage and the brown and yellow modules, respectively. These modules were mainly associated with the cytoskeleton, phosphorylation, cellular catabolic process, and autophagy. Subsequently, we predicted the underlying hub genes and microRNAs in the three modules.

Conclusions

This study revealed the main biological processes in different stages of viral myocarditis and predicted hub genes in both the acute and chronic disease stages. Our results may be helpful for developing new therapeutic targets for viral myocarditis in future research.

Targeting Immunophenotypic Markers on Leukemic Stem Cells: How Lessons from Current Approaches and Advances in the Leukemia Stem Cell (LSC) Model Can Inform Better Strategies for Treating Acute Myeloid Leukemia (AML)

Therapies targeting cell-surface antigens in acute myeloid leukemia (AML) have been tested over the past 20 years with limited improvement in overall survival. Recent advances in the understanding of AML pathogenesis support therapeutic targeting of leukemia stem cells as the most promising avenue toward a cure. In this review, we provide an overview of the evolving leukemia stem cell (LSC) model, including evidence of the cell of origin, cellular and molecular disease architecture, and source of relapse in AML. In addition, we explore limitations of current targeted strategies utilized in AML and describe the various immunophenotypic antigens that have been proposed as LSC-directed therapeutic targets. We draw lessons from current approaches as well as from the (pre)-LSC model to suggest criteria that immunophenotypic targets should meet for more specific and effective elimination of disease-initiating clones, highlighting in detail a few targets that we suggest fit these criteria most completely.

An Overview on G Protein-coupled Receptor-induced Signal Transduction in Acute Myeloid Leukemia

BACKGROUND

Acute Myeloid Leukemia (AML) is a genetically heterogeneous disease characterized by uncontrolled proliferation of precursor myeloid-lineage cells in the bone marrow. AML is also characterized by patients with poor long-term survival outcomes due to relapse. Many efforts have been made to understand the biological heterogeneity of AML and the challenges to develop new therapies are therefore enormous. G Protein-coupled Receptors (GPCRs) are a large attractive drug-targeted family of transmembrane proteins, and aberrant GPCR expression and GPCR-mediated signaling have been implicated in leukemogenesis of AML. This review aims to identify the molecular players of GPCR signaling, focusing on the hematopoietic system, which are involved in AML to help developing novel drug targets and therapeutic strategies.

METHODS

We undertook an exhaustive and structured search of bibliographic databases for research focusing on GPCR, GPCR signaling and expression in AML.

RESULTS AND CONCLUSION

Many scientific reports were found with compelling evidence for the involvement of aberrant GPCR expression and perturbed GPCR-mediated signaling in the development of AML. The comprehensive analysis of GPCR in AML provides potential clinical biomarkers for prognostication, disease monitoring and therapeutic guidance. It will also help to provide marker panels for monitoring in AML. We conclude that GPCR-mediated signaling is contributing to leukemogenesis of AML, and postulate that mass spectrometrybased protein profiling of primary AML cells will accelerate the discovery of potential GPCR related biomarkers for AML.

A six-gene leukemic stem cell score identifies high risk pediatric acute myeloid leukemia

Recently, mRNA-expression signature enriched in LSCs was used to create a 17-gene leukemic stem cell (LSC17) score predictive of prognosis in adult AML. By fitting a Cox-LASSO regression model to the clinical outcome and gene-expression levels of LSC enriched genes in 163 pediatric participants of the AML02 multi-center clinical trial (NCT00136084), we developed a 6-gene LSC score of prognostic value in pediatric AML (pLSC6). In the AML02 cohort, the 5-year event-free survival (EFS) of patients within low-pLSC6 group (n=97) was 78.3 (95% CI=70.5–86.9%) as compared to 34.5(95% CI=24.7–48.2 %) in patients within high-pLSC6 group (n=66 subjects), p<0.00001. pLSC6 remained significantly associated with EFS and overall survival (OS) after adjusting for induction 1-MRD status, risk-group, FLT3-status, WBC-count at diagnosis and age. pLSC6 formula developed in the AML02 cohort was validated in the pediatric AML-TARGET project data (n=205), confirming its prognostic value in both single-predictor and multiple-predictor Cox regression models. In both cohorts, pLSC6 predicted outcome of transplant patients, suggesting it as a useful criterion for transplant referrals. Our results suggest that pLSC6 score holds promise in redefining initial risk-stratification and identifying poor risk AML thereby providing guidance for developing novel treatment strategies.

GAIN domain-mediated cleavage is required for activation of G protein-coupled receptor 56 (GPR56) by its natural ligands and a small-molecule agonist

Adhesion G protein-coupled receptors (aGPCRs) represent a distinct family of GPCRs that regulate several developmental and physiological processes. Most aGPCRs undergo GPCR autoproteolysis-inducing domain-mediated protein cleavage, which produces a cryptic tethered agonist (termed Stachel (stinger)), and cleavage-dependent and -independent aGPCR signaling mechanisms have been described. aGPCR G1 (ADGRG1 or G protein-coupled receptor 56 (GPR56)) has pleiotropic functions in the development of multiple organ systems, which has broad implications for human diseases. To date, two natural GPR56 ligands, collagen III and tissue transglutaminase (TG2), and one small-molecule agonist, 3-α-acetoxydihydrodeoxygedunin (3-α-DOG), have been identified, in addition to a synthetic peptide, P19, that contains seven amino acids of the native Stachel sequence. However, the mechanisms by which these natural and small-molecule agonists signal through GPR56 remain unknown. Here we engineered a noncleavable receptor variant that retains signaling competence via the P19 peptide. We demonstrate that both natural and small-molecule agonists can activate only cleaved GPR56. Interestingly, TG2 required both receptor cleavage and the presence of a matrix protein, laminin, to activate GPR56, whereas collagen III and 3-α-DOG signaled without any cofactors. On the other hand, both TG2/laminin and collagen III activate the receptor by dissociating the N-terminal fragment from its C-terminal fragment, enabling activation by the Stachel sequence, whereas P19 and 3-α-DOG initiate downstream signaling without disengaging the N-terminal fragment from its C-terminal fragment. These findings deepen our understanding of how GPR56 signals via natural ligands, and a small-molecule agonist may be broadly applicable to other aGPCR family members.

Characterization of upregulated adhesion GPCRs in acute myeloid leukemia

The role of adhesion G protein-coupled receptors (aGPCRs) in cancer has become increasingly evident in recent years. Yet, data supporting the contribution of this family of genes to hematological malignancies, particularly acute myeloid leukemia (AML) are limited. Here, we use publicly available genomic data to characterize the expression of the 33 aGPCRs in patients with AML and examine whether upregulation of these genes is associated with the clinical and molecular characteristics of patients. Upregulation in one or more of eight aGPCR genes (ADGRB1, ADGRC2, ADGRD1, ADGRE1, ADGRE2, ADGRE5, ADGRG1, and/or ADGRG3) was significantly associated with shorter overall survival (OS) (median OS: 11.8 vs 55.4 months; P < 0.0001). This was also significant in multivariate survival analysis (hazard ratio: 1.73; 95% confidence interval 1.11-2.69; P = 0.015) after adjusting for age, molecular risk status, and transplant status. High expression of the eight aGPCRs was significantly associated with older age (≥60; P = 0.011). Patients with high aGPCRs expression were more frequently classified in the poor molecular risk status group and less in the good risk status group compared with patients with low aGPCRs expression (31% vs 17% P = 0.049 and 14% vs 28% P = 0.027, respectively). Via Ingenuity Pathway Analysis, we identified the interleukin-8 signaling pathway among the most activated pathways in patients with high aGPCRs expression. Overall, our data suggest that particular aGPCRs are frequently upregulated in AML and associated with poor clinical outcome. Future functional and mechanistic analyses are needed to address the role of aGPCRs in AML.

Adhesion G protein-coupled receptors: opportunities for drug discovery

Adhesion G protein-coupled receptors (aGPCRs) - one of the five main families in the GPCR superfamily - have several atypical characteristics, including large, multi-domain N termini and a highly conserved region that can be autoproteolytically cleaved. Although GPCRs overall have well-established pharmacological tractability, currently no therapies that target any of the 33 members of the aGPCR family are either approved or in clinical trials. However, human genetics and preclinical research have strengthened the links between aGPCRs and disease in recent years. This, together with a greater understanding of their functional complexity, has led to growing interest in aGPCRs as drug targets. A framework for prioritizing aGPCR targets and supporting approaches to develop aGPCR modulators could therefore be valuable in harnessing the untapped therapeutic potential of this family. With this in mind, here we discuss the unique opportunities and challenges for drug discovery in modulating aGPCR functions, including target identification, target validation, assay development and safety considerations, using ADGRG1 as an illustrative example.

GPR56 Drives Colorectal Tumor Growth and Promotes Drug Resistance through Upregulation of MDR1 Expression via a RhoA-Mediated Mechanism

Drug resistance continues to be a major obstacle of effective therapy for colorectal cancer, leading to tumor relapse or treatment failure. Cancer stem cells (CSC) or tumor-initiating cells are a subpopulation of tumor cells which retain the capacity for self-renewal and are suggested to be implicated in drug resistance. LGR5 is highly expressed in colorectal cancer and marks CSCs that drive tumor growth and metastasis. LGR5(⁺) CSCs cells were shown to interconvert with more drug-resistant LGR5(^-) cancer cells, and treatment with LGR5-targeted antibody-drug conjugates (ADC) eliminated LGR5(⁺) tumors, yet a fraction of LGR5(^-) tumors eventually recurred. Therefore, it is important to identify mechanisms associated with CSC plasticity and drug resistance in order to develop curative therapies. Here, we show that loss of LGR5 in colon cancer cells enhanced resistance to irinotecan and 5-fluorouracil and increased expression of adhesion G-protein-coupled receptor, GPR56. GPR56 expression was significantly higher in primary colon tumors versus matched normal tissues and correlated with poor survival outcome. GPR56 enhanced drug resistance through upregulation of MDR1 levels via a RhoA-mediated signaling mechanism. Loss of GPR56 led to suppression of tumor growth and increased sensitivity of cancer cells to chemotherapy and monomethyl auristatin E-linked anti-LGR5 ADCs, by reducing MDR1 levels. These findings suggest that upregulation of GPR56 may be a mechanism associated with CSC plasticity by which LGR5(^-) cancer cells acquire a more drug-resistant phenotype. IMPLICATIONS: Our findings suggest that targeting GPR56 may provide a new strategy for the treatment of colorectal cancer and combatting drug resistance.

High GPR56 surface expression correlates with a leukemic stem cell gene signature in CD34-positive AML

Acute myeloid leukemia (AML) is driven by a minor fraction of leukemic stem cells (LSCs) whose persistence is considered being the primary cause of disease relapse. A detailed characterization of the surface immunophenotype of LSCs to discriminate them from bulk leukemic blasts may enable successful targeting of this population thereby improving patient outcomes in AML. To identify surface markers, which may reflect LSC activity at diagnosis, we performed a detailed analysis of 16 putative LSC markers in CD34/38 leukemic subcompartments of 150 diagnostic AML samples using multicolor flow cytometry. The most promising markers were then selected to determine a possible correlation of their expression with a recently published LSC gene signature. We found GPR56 and CLL-1 to be the most prominently differently expressed surface markers in AML subcompartments. While GPR56 was highest expressed within the LSC-enriched CD34⁺ 38^- subcompartment as compared to CD34⁺ 38⁺ and CD34^- leukemic bulk cells, CLL-1 expression was lowest in CD34⁺ 38^- leukemic cells and increased in CD34⁺ 38⁺ and CD34^- blasts. Furthermore, high GPR56 surface expression in CD34⁺ 38^- leukemic cells correlated with a recently published LSC gene expression signature and was associated with decreased overall survival in patients receiving intensive chemotherapy. In contrast, CLL-1 expression correlated inversely with the LSC gene signature and was not informative on outcome. Our data strongly support GPR56 as a promising clinically relevant marker for identifying leukemic cells with LSC activity at diagnosis in CD34-positive AML.

Genome-wide association analysis identifies SNPs predictive of in vitro leukemic cell sensitivity to cytarabine in pediatric AML

Cytarabine has been an integral part of acute myeloid leukemia (AML) chemotherapy for over four decades. However, development of resistance and high rates of relapse is a significant impediment in successfully treating AML. We performed a genome-wide association analysis (GWAS) and identified 113 (83 after adjusting for Linkage Disequilibrium) SNPs associated with in vitro cytarabine chemosensitivity of diagnostic leukemic cells from a cohort of 50 pediatric AML patients (p<10^-4). Further evaluation of diagnostic leukemic cell gene-expression identified 19 SNP-gene pairs with a concordant triad of associations: i)SNP genotype with cytarabine sensitivity (p<0.0001), ii) gene-expression with cytarabine sensitivity (p<0.05), and iii) genotype with gene-expression (p<0.1). Two genes from SNP-gene pairs, rs1376041-GPR56 and rs75400242-IGF1R, were functionally validated by siRNA knockdown in AML cell lines. Consistent with association of rs1376041 and gene-expression in AML patients siRNA mediated knock-down of GPR56 increased cytarabine sensitivity of AML cell lines. Similarly for IGF1R, knockdown increased the cytarabine sensitivity of AML cell lines consistent with results in AML patients. Given both IGF1R and GPR56 are promising drug-targets in AML, our results on SNPs driving the expression/function of these genes will not only enhance our understanding of cytarabine resistance but also hold promise in personalizing AML for targeted therapies.

The Activation and Signaling Mechanisms of GPR56/ADGRG1 in Melanoma Cell

Adhesion G protein-coupled receptors (aGPCRs) constitute the second largest GPCR subfamily. GPR56/ADGRG1 is a member of the ADGRG subgroup of aGPCRs. Although GPR56 is best known for its pivotal role in the cerebral cortical development, it is also important for tumor progression. Numerous studies have revealed that GPR56 is expressed in various cancer types with a role in cancer cell adhesion, migration and metastasis. In a recent study, we found that the immobilized GPR56-specific CG4 antibody enhanced IL-6 production and migration ability of melanoma cells. In this review, we will summarize the current understanding of GPR56 function and discuss the activation and signaling mechanisms of GPR56 in melanoma cells.

Integrated epigenetic and genetic analysis identifies markers of prognostic significance in pediatric acute myeloid leukemia

Acute myeloid leukemia (AML) may be an epigenetically-driven malignancy because it harbors fewer genomic mutations than other cancers. In recent studies of AML in adults, DNA methylation patterns associate with clinical risk groups and prognosis. However, thorough evaluations of methylation in pediatric AML have not been done. Therefore, we performed an integrated analysis (IA) of the methylome and transcriptome with clinical outcome in 151 pediatric patients from the multi-center AML02 clinical trial discovery cohort. Intriguingly, reduced methylation and increased expression of DNMT3B was associated with worse clinical outcomes (IA p ≤ 10⁻⁵; q ≤ 0.002). In particular, greater DNMT3B expression associated with worse minimal residual disease (MRD; p < 10⁻⁵; q = 0.01), a greater rate of relapse or resistant disease (RR) (p = 0.00006; q = 0.06), and event-free survival (EFS; p = 0.00003; q = 0.04). Also, greater DNMT3B expression associated with greater genome-wide methylation burden (GWMB; R = 0.39; p = 10⁻⁶) and greater GWMB associated with worse clinical outcomes (IA p < 10⁻⁵). In an independent validation cohort of 132 similarly treated AAML0531 clinical trial patients, greater DNMT3B expression associated with greater GWMB, worse MRD, worse RR, and worse EFS (all p < 0.03); also, greater GWMB associated with worse MRD (p = 0.004) and EFS (p = 0.037). These results indicate that DNMT3B and GWMB may have a central role in the development and prognosis of pediatric AML.