Repulsive guidance molecule B (RGMB) plays negative roles in breast cancer by coordinating BMP signaling

Repulsive guidance molecules b (RGMb): molecular mechanism, function and role in diseases

Repulsive guidance molecule b (RGMb), a glycosylphosphatidylinositol-anchored member of the RGM family, is initially identified as a co-receptor of bone morphogenetic protein (BMP) in the nervous system. The expression of RGMb is transcriptionally regulated by dorsal root ganglion 11 (DRG11), which is a transcription factor expressed in embryonic DRG and dorsal horn neurons and plays an important role in the development of sensory circuits. RGMb is involved in important physiological processes such as embryonic development, immune response, intercellular adhesion and tumorigenesis. Furthermore, RGMb is mainly involved in the regulation of RGMb-neogenin-Rho and BMP signalling pathways. The recent discovery of programmed death-ligand 2 (PD-L2)-RGMb binding reveals that the cell signalling network and functional regulation centred on RGMb are extremely complex. The latest report suggests that down-regulation of the PD-L2-RGMb pathway in the gut microbiota promotes an anti-tumour immune response, which defines a potentially effective immune strategy. However, the biological function of RGMb in a variety of human diseases has not been fully determined, and will remain an active research field. This article reviews the properties and functions of RGMb, focusing on its role under various physiological and pathological conditions.

PD-L2 mediates tobacco smoking-induced recruitment of regulatory T cells via the RGMB/NFκB/CCL20 cascade

Programmed cell death ligand 2 (PD-L2), a ligand for the receptor programmed cell death 1 (PD-1), has an identity of 34% with its twin ligand PD-L1 and exhibits higher binding affinity with PD-1 than PD-L1. However, the role of PD-L2 in non-small cell lung cancer (NSCLC) progression, especially tobacco-induced cancer progression, has not been fully understood. Here, we found that PD-L2 promoted tumor growth in murine models with recruitment of regulatory T cells (Tregs). In patients with NSCLC, PD-L2 expression level in tumor samples was higher than in counterpart normal controls and was positively associated with patients' response to anti-PD-1 treatment. Mechanismly, PD-L2 bound its receptor Repulsive guidance molecule B (RGMB) on cancer cells and activated extracellular signal-regulated kinase (Erk) and nuclear factor κB (NFκB), leading to increased production of chemokine CCL20, which recruited Tregs and contributed to NSCLC progression. Consistently, knockdown of RGMB or NFκB p65 inhibited PD-L2-induced CCL20 production, and silencing of PD-L2 repressed Treg recruitment by NSCLC cells. Furthermore, cigarette smoke and carcinogen benzo(a)pyrene (BaP) upregulated PD-L2 in lung epithelial cells via aryl hydrocarbon receptor (AhR)-mediated transcription activation, whose deficiency markedly suppressed BaP-induced PD-L2 upregulation. These results suggest that PD-L2 mediates tobacco-induced recruitment of Tregs via the RGMB/NFκB/CCL20 cascade, and targeting this pathway might have therapeutic potentials in NSCLC.

Organ Boundary Circuits Regulate Sox9+ Alveolar Tuft Cells During Post-Pneumonectomy Lung Regeneration

Tissue homeostasis is controlled by cellular circuits governing cell growth, organization, and differentation. In this study we identify previously undescribed cell-to-cell communication that mediates information flow from mechanosensitive pleural mesothelial cells to alveolar-resident stem-like tuft cells in the lung. We find mesothelial cells to express a combination of mechanotransduction genes and lineage-restricted ligands which makes them uniquely capable of responding to tissue tension and producing paracrine cues acting on parenchymal populations. In parallel, we describe a large population of stem-like alveolar tuft cells that express the endodermal stem cell markers Sox9 and Lgr5 and a receptor profile making them uniquely sensitive to cues produced by pleural Mesothelium. We hypothesized that crosstalk from mesothelial cells to alveolar tuft cells might be central to the regulation of post-penumonectomy lung regeneration. Following pneumonectomy, we find that mesothelial cells display radically altered phenotype and ligand expression, in a pattern that closely tracks with parenchymal epithelial proliferation and alveolar tissue growth. During an initial pro-inflammatory stage of tissue regeneration, Mesothelium promotes epithelial proliferation via WNT ligand secretion, orchestrates an increase in microvascular permeability, and encourages immune extravasation via chemokine secretion. This stage is followed first by a tissue remodeling period, characterized by angiogenesis and BMP pathway sensitization, and then a stable return to homeostasis. Coupled with key changes in parenchymal structure and matrix production, the cumulative effect is a now larger organ including newly-grown, fully-functional tissue parenchyma. This study paints Mesothelial cells as a key orchestrating cell type that defines the boundary of the lung and exerts critical influence over the tissue-level signaling state regulating resident stem cell populations. The cellular circuits unearthed here suggest that human lung regeneration might be inducible through well-engineered approaches targeting the induction of tissue regeneration and safe return to homeostasis.

RGMb expression in goat uterine tissues: possible role of RGMb in the proliferation and apoptosis of endometrial epithelial cells

Context Bone morphogenetic proteins (BMPs) play an important role in the uteri. Repulsive guidance molecule b (RGMb; a.k.a. Dragon) has been confirmed as the coreceptor of BMPs to function through drosophila mothers against decapentaplegic protein (Smads) and mitogen-activated protein kinases (MAPK) pathways. We hypothesise that RGMb regulates the uterine function through the Smads and MAPK pathways. Aims This study aimed to investigate the expression of RGMb in goat uteri and the potential role of RGMb in the endometrial epithelial cells (EECs). Methods The localisation of RGMb in goat uterine tissues was detected by immunohistochemistry (IHC), EECs were isolated and transfected with siRNA to investigate the role of RGMb in proliferation, and apoptosis. The expression levels of Smads and MAPK members was measured by western blot (WB) and real-time PCR (RT-PCR). Key results IHC showed that RGMb was localised in goat endometrial luminal cells, glandular epithelial cells, and circular muscle fibres, but not in stromal cells. RT-PCR results showed that treatment with RGMb siRNA suppressed the expressions of proliferation-related genes cyclin D1 (CCND1 , P =0.0291), cyclin-dependent kinase 2 (CDK2 P =0.0107), and proliferating cell nuclear antigen (PCNA, P =0.0508), leading to the reduced viability of EECs (P =0.0010). WB results showed that the expression ratio of cleaved-caspase 3/caspase 3 (P =0.0013) was markedly increased after RGMb siRNA transfection. Likewise, the level of phospho-extracellular signal-regulated kinase 1/2 (p-ERK1/2, P =0.0068) and p-Smad1/5/8 (P =0.0011) decreased significantly, while there were no appreciable differences in the level of p-P38 MAPK expression (P >0.05). Conclusions RGMb might participate in the regulation of cell proliferation and apoptosis through Smads and ERK signalling pathways in goat EECs. Implications RGMb is involved in regulating the proliferation and apoptosis in goat endometrial epithelial cells.

RGMb impacts partial epithelial-mesenchymal transition and BMP2-Induced ID mRNA expression independent of PD-L2 in nonsmall cell lung cancer cells

PD-1/PD-ligand-axis immunotherapy-mediated activation of T-cells for cancer cell elimination is a promising treatment of nonsmall cell lung cancer (NSCLC). However, the effect of immunotherapy on intracellular signaling pathways in cancer cells still needs further delineation. Repulsive Guidance Molecule b (RGMb), a regulator of Bone Morphogenetic Proteins (BMPs) signaling, interacts with the PD-ligand, PD-L2, at cancer cell membranes. Accordingly, a clarification of the functions of RGMb and its relation to PD-L2 might provide insight into NSCLC cell signaling responses to PD-1/PD-ligand-axis immunotherapy. In this study, the functions of RGMb and PD-L2 were examined using the two NSCLC cell lines HCC827 and A549. CRISPR/Cas9 was used to decrease the expression of RGMb and PD-L2, while lentiviral vectors were used to increase their expression. Downstream effects were examined by RT-qPCR and immunoassays. Ectopic expression of RGMb impacted BMP2-induced expression of ID1 and ID2 messenger RNA (mRNA) independently of PD-L2, while RGMb depletion by CRISPR/Cas9 did not affect the BMP2-mediated induction of ID1, ID2, and ID3 mRNA. However, depletion of RGMb resulted in a partial epithelial-mesenchymal transition (EMT) gene expression profile in HCC827 cells, which was not mimicked by PD-L2 depletion. The results show that RGMb is a coregulator of BMP signaling and hence, ID mRNA expression and that RGMb can control the EMT balance in NSCLC cells. However, RGMb appears to exert these functions independently of PD-L2, and accordingly, the PD-1/PD-ligand axis for immune surveillance in NSCLC cells.

Circ_0000419 acts as a tumor suppressor in gastric cancer development via regulating miR-300/RGMB axis

OBJECTIVE

Dysregulated circular RNAs (circRNAs) have been verified to function in the development of gastric cancer (GC). The current study was designed to investigate the role of circ_0000419 in GC progression, and the potential mechanistic pathway.

METHODS

Relative expression of circ_0000419, microRNA-300 (miR-300) and Repulsive Guidance Molecule B (RGMB) was analyzed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assay. Cell metastasis, including migration and invasion, was assessed by wound healing and Transwell assays. Glucose consumption and lactate production were examined using kits. The association between miR-300 and circ_0000419 or RGMB was validated by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assays. Role of circ_0000419 in vivo was determined by xenograft experiment.

RESULTS

Circ_0000419 and RGMB were downregulated, while miR-300 was upregulated in GC tissues and cells. Gain of circ_0000419 inhibited migration, invasion and glycolysis in GC cells, which was attenuated by introduction of miR-300 or silencing of RGMB. Circ_0000419 sponged miR-300, and RGMB was direct target of miR-300. Circ_0000419 overexpression could block GC tumor growth in vivo.

CONCLUSION

Circ_0000419 inhibited GC cell migration, invasion and glycolysis through regulation of miR-300/RGMB axis, at least in part, affording a molecular target for GC treatment.

Pan-cancer analysis identifies PD-L2 as a tumor promotor in the tumor microenvironment

BACKGROUND

Programmed cell death protein 1 (PD-1) receptor has two ligands,programmed death-ligand 1 (PD-L1) and PD-L2. When compared with PD-L1, PD-L2 has not received much attention, and its role remains unclear.

METHODS

The expression profiles of pdcd1lg2 (PD-L2-encoding gene) mRNA and PD-L2 protein were analyzed using TCGA, ICGC, and HPA databases. Kaplan-Meier and Cox regression analyses were used to assess the prognostic significance of PD-L2. We used GSEA, Spearman's correlation analysis and PPI network to explore the biological functions of PD-L2. PD-L2-associated immune cell infiltration was evaluated using the ESTIMATE algorithm and TIMER 2.0. The expressions of PD-L2 in tumor-associated macrophages (TAMs) in human colon cancer samples, and in mice in an immunocompetent syngeneic setting were verified using scRNA-seq datasets, multiplex immunofluorescence staining, and flow cytometry. After fluorescence-activated cell sorting, flow cytometry and qRT-PCR and transwell and colony formation assays were used to evaluate the phenotype and functions of PD-L2+TAMs. Immune checkpoint inhibitors (ICIs) therapy prediction analysis was performed using TIDE and TISMO. Last, a series of targeted small-molecule drugs with promising therapeutic effects were predicted using the GSCA platform.

RESULTS

PD-L2 was expressed in all the common human cancer types and deteriorated outcomes in multiple cancers. PPI network and Spearman's correlation analysis revealed that PD-L2 was closely associated with many immune molecules. Moreover, both GSEA results of KEGG pathways and GSEA results for Reactome analysis indicated that PD-L2 expression played an important role in cancer immune response. Further analysis showed that PD-L2 expression was strongly associated with the infiltration of immune cells in tumor tissue in almost all cancer types, among which macrophages were the most positively associated with PD-L2 in colon cancer. According to the results mentioned above, we verified the expression of PD-L2 in TAMs in colon cancer and found that PD-L2+TAMs population was not static. Additionally, PD-L2+TAMs exhibited protumor M2 phenotype and increased the migration, invasion, and proliferative capacity of colon cancer cells. Furthermore, PD-L2 had a substantial predictive value for ICIs therapy cohorts.

CONCLUSION

PD-L2 in the TME, especially expressed on TAMs, could be applied as a potential therapeutic target.

Overexpressed transient receptor potential vanilloid 1 (TRPV1) in lung adenocarcinoma harbours a new opportunity for therapeutic targeting

The specific biological function of transient receptor potential vanilloid 1 (TRPV1) in pathogenesis of lung adenocarcinoma (LUAD) remains unclear. In this study, TRPV1 expression in tumor tissues, primary cells and cell lines of LUAD, as well as the mechanism mediating its hyperexpression were systematically studied. Multiple models and techniques were adopted to elucidate the relationship between TRPV1 hyperexpression and tumor recurrence and metastasis. Results showed that TRPV1 expression was increased in tumor tissues and primary tumor cells of LUAD patients. The increased expression was associated with worse overall survival outcome and raised HIF1α levels. TRPV1 expression in A549 and NCI-H292 cells was increased after pretreatment with cigarette smoke extract or spermine NONOate. Moreover, A549 cells with TRPV1 overexpression has enhanced tumor growth rates in subcutaneous grafted tumor models, and increased intrapulmonary metastasis after tail vein infusion in nude BALB/c nude mice. Mechanistically, TRPV1 overexpression in A549 cells promoted HIF1α expression and nuclear translocation by promoting CREB phosphorylation and activation of NOS1-NO pathway, ultimately leading to accelerated cell proliferation and stronger invasiveness. In addition, based on photothermal effects, CuS-TRPV1 mAb effectively targeted and induced apoptosis of TRPV1-A549 cells both in vivo and in vitro, thereby mitigating tumor growth and metastasis induced by xenotransplantation of TRPV1-A549 cells. In conclusion, TRPV1 hyperexpression in LUAD is a risk factor for tumor progression and is involved in proliferation and migration of tumor cells through activation of HIF1α. Our study also attempted a new strategy inhibiting the recurrence and metastasis of LUAD: by CuS-TRPV1 mAb precisely kill TRPV1 hyperexpression cells through photothermal effects.

RNF4~RGMb~BMP6 axis required for osteogenic differentiation and cancer cell survival

Molecular understanding of osteogenic differentiation (OD) of human bone marrow-derived mesenchymal stem cells (hBMSCs) is important for regenerative medicine and has direct implications for cancer. We report that the RNF4 ubiquitin ligase is essential for OD of hBMSCs, and that RNF4-deficient hBMSCs remain as stalled progenitors. Remarkably, incubation of RNF4-deficient hBMSCs in conditioned media of differentiating hBMSCs restored OD. Transcriptional analysis of RNF4-dependent gene signatures identified two secreted factors that act downstream of RNF4 promoting OD: (1) BMP6 and (2) the BMP6 co-receptor, RGMb (Dragon). Indeed, knockdown of either RGMb or BMP6 in hBMSCs halted OD, while only the combined co-addition of purified RGMb and BMP6 proteins to RNF4-deficient hBMSCs fully restored OD. Moreover, we found that the RNF4-RGMb-BMP6 axis is essential for survival and tumorigenicity of osteosarcoma and therapy-resistant melanoma cells. Importantly, patient-derived sarcomas such as osteosarcoma, Ewing sarcoma, liposarcomas, and leiomyosarcomas exhibit high levels of RNF4 and BMP6, which are associated with reduced patient survival. Overall, we discovered that the RNF4~BMP6~RGMb axis is required for both OD and tumorigenesis.

Loss of Vlk in Prx1+ Cells Delays the Initial Steps of Endochondral Bone Formation and Fracture Repair in the Limb

Vertebrate lonesome kinase (Vlk) is a secreted tyrosine kinase important for normal skeletogenesis during embryonic development. Vlk null mice (Vlk^-/- ) are born with severe craniofacial and limb skeletal defects and die shortly after birth. We used a conditional deletion model to remove Vlk in limb bud mesenchyme (Vlk-Prx1 cKO) to assess the specific requirement for Vlk expression by skeletal progenitor cells during endochondral ossification, and an inducible global deletion model (Vlk-Ubq iKO) to address the role of Vlk during fracture repair. Deletion of Vlk with Prx1-Cre recapitulated the limb skeletal phenotype of the Vlk^-/- mice and enabled us to study the postnatal skeleton as Vlk-Prx1 cKO mice survived to adulthood. In Vlk-Prx1 cKO adult mice, limbs remained shorter with decreased trabecular and cortical bone volumes. Both Vlk-Prx1 cKO and Vlk-Ubq iKO mice had a delayed fracture repair response but eventually formed bridging calluses. Furthermore, levels of phosphorylated osteopontin (OPN) were decreased in tibias of Vlk-Ubq iKO, establishing OPN as a Vlk substrate in bone. In summary, our data indicate that Vlk produced by skeletal progenitor cells influences the timing and extent of chondrogenesis during endochondral bone formation and fracture repair. © 2022 American Society for Bone and Mineral Research (ASBMR).

TGF-β superfamily co-receptors in cancer

Transforming growth factor-β (TGF-β) superfamily signaling via their cognate receptors is frequently modified by TGF-β superfamily co-receptors. Signaling through SMAD-mediated pathways may be enhanced or depressed depending on the specific co-receptor and cell context. This dynamic effect on signaling is further modified by the release of many of the co-receptors from the membrane to generate soluble forms that are often antagonistic to the membrane-bound receptors. The co-receptors discussed here include TβRIII (betaglycan), endoglin, BAMBI, CD109, SCUBE proteins, neuropilins, Cripto-1, MuSK, and RGMs. Dysregulation of these co-receptors can lead to altered TGF-β superfamily signaling that contributes to the pathophysiology of many cancers through regulation of growth, metastatic potential, and the tumor microenvironment. Here we describe the role of several TGF-β superfamily co-receptors on TGF-β superfamily signaling and the impact on cellular and physiological functions with a particular focus on cancer, including a discussion on recent pharmacological advances and potential clinical applications targeting these co-receptors.

Curcumin mediates repulsive guidance molecule B (RGMb) in the treatment mechanism of renal fibrosis induced by unilateral ureteral obstruction

In this study, we explored the role and mechanism of repulsive guidance molecule B (RGMb, also known as Dragon) in the protective effects of curcumin against renal fibrosis and verified Dragon's effect on renal tubular epithelial cell apoptosis and cell programmability. Unilateral ureteral obstruction (UUO) was surgically induced in rats to establish a model of renal interstitial fibrosis (RIF). The rats were then treated with curcumin. Curcumin prominently decreased the serum creatinine (SCr) and blood urea nitrogen (BUN) levels, and also improved the tubular injury in the UUO-induced rats. Curcumin significantly downregulated the TGF-β1, P-Smad2/3, cleaved caspase-3, cleaved caspase-8 and Dragon levels. Dragon knockdown also markedly reduced the TGF-β1, P-Smad2/3, Smad2/3, cleaved caspase-3, cleaved caspase-8, fibronectin, collagen I, collagen IV, vimentin, and α-SMA expression levels. Conversely, Dragon overexpression caused higher expression levels of these proteins, and curcumin reversed this effect. Furthermore, Dragon knockdown increased the E-cadherin levels, whereas Dragon overexpression decreased these levels. Overexpressing Dragon significantly decreased the cell viability, and curcumin reversed this effect. In conclusion, curcumin acted on Dragon and attenuated RIF in UUO rat models. Curcumin downregulated the TGF-β1/Smad signaling pathway and inhibited Dragon and fibrogenic molecules in both rats and HK-2 cells.

Exploring the therapeutic promise of targeting Rho kinase in rheumatoid arthritis

Rheumatoid arthritis (RA) is a prevalent systemic autoimmune disease caused by dysregulated inflammatory reactions, T lymphocyte invasion into the joints, and articular thickening. Immune cells, primarily tumor necrosis factor-alpha (TNF-α) and chemokines (interleukin or IL-1), which are predominantly generated by activated macrophages cells, have also been involved with the pathogenesis of rheumatoid arthritis. Rho GTPases are integral factors of biochemical cascades utilized by antigens, and also by cellular receptors, cytokines, and chemokines, to modulate inflammatory reactions, according to growing data. The Rho family is a group of G proteins that govern a variety of biological and physiological activities such as mobility, actin stress fiber production, growth, and polarity. Research suggests that the Rho A and Rho-associated coiled-coil kinase (ROCK) regulatory cascade could be essential in several autoimmune conditions, including RA. ROCK is activated in the synovial of rheumatoid arthritis patients, while the blocking of ROCK with fasudil could also decrease IL-6, TNF-α, and IL-1. This review covers current developments in understanding the overactivation of Rho enzyme activity in RA suppressed by ROCK inhibitors which can be utilized for the treatment of autoimmune disease. We offer an outline of the function of ROCK inhibitors in immune cells and discuss findings which emphasize the rising participation of this category of kinases within the pathological process of autoimmune disorders. Assuming the potential ability of ROCK as a therapeutic, we define approaches that might be used to inhibit Rho kinase activity in rheumatoid disorders.

Expression and Prognostic Significance of PD-L2 in Diffuse Large B-Cell Lymphoma

Recent studies suggest that programmed death ligand-2 (PD-L2) constitutes an important antitumor immune response. Here, we investigated the relationship between PD-L2 expression and clinicopathological features in diffuse large B-cell lymphoma (DLBCL). Immunohistochemistry showed that positive expression of PD-L2 was observed in 45 of 181 newly diagnosed patients, including 14 cases with expression exclusively on tumor cells (TCs) and 31 cases with the expression on both TCs and immune cells (ICs) in the tumor microenvironment (TME). In 21 recurrent patients, positive expression of PD-L2 was present in six cases, including two cases with expression exclusively on TCs, and four cases with the expression on both TCs and ICs in the TME. Patients with PD-L2 tumor proportion score (TPS) ≥1% exhibited a better ECOG performance status (PS) (ECOG PS score <2, P = 0.041), lower international prognostic index (IPI) score (P < 0.001), and early Ann Arbor stage (Ann Arbor stage I or II, P = 0.010). Similarly, patients with PD-L2 immune proportion score (IPS) ≥1% also exhibited a better ECOG PS (ECOG PS score < 2, P = 0.006) and lower IPI score (P = 0.001). Survival analysis showed that patients with PD-L2 TPS ≥1% exhibited prolonged overall survival (OS) and progression-free survival (PFS). However, survival analysis showed no prognostic significance based on expression of PD-L2 on ICs in the TME. TC PD-L2 expression was significantly associated with OS (P = 0.041) and PFS (P = 0.001). In the multivariate analysis, TC PD-L2 expression was an independent prognostic risk factor for PFS (P = 0.013), but not for OS (P = 0.249). Furthermore, we found that higher TC and IC PD-L2 expression was associated with higher objective response rate (ORR). Moreover, we demonstrated that the expression level of PD-L2 was positively correlated with the expression status of M1 macrophage markers CD86. Our findings highlight PD-L2 as a promising therapeutic target in DLBCL.

Emerging concepts in PD-1 checkpoint biology

The PD-1 pathway is a cornerstone in immune regulation. While the PD-1 pathway has received considerable attention for its role in contributing to the maintenance of T cell exhaustion in chronic infection and cancer, the PD-1 pathway plays diverse roles in regulating host immunity beyond T cell exhaustion. Here, we discuss emerging concepts in the PD-1 pathway, including (1) the impact of PD-1 inhibitors on diverse T cell differentiation states including effector and memory T cell development during acute infection, as well as T cell exhaustion during chronic infection and cancer, (2) the role of PD-1 in regulating Treg cells, NK cells, and ILCs, and (3) the functions of PD-L1/B7-1 and PD-L2/RGMb/neogenin interactions. We then discuss the emerging use of neoadjuvant PD-1 blockade in the treatment of early-stage cancers and how the timing of PD-1 blockade may improve clinical outcomes. The diverse binding partners of PD-1 and its associated ligands, broad expression patterns of the receptors and ligands, differential impact of PD-1 modulation on cells depending on location and state of differentiation, and timing of PD-1 blockade add additional layers of complexity to the PD-1 pathway, and are important considerations for improving the efficacy and safety of PD-1 pathway therapeutics.

Inhibition of ROCK signaling pathway accelerates enteric neural crest cell-based therapy after transplantation in a rat hypoganglionic model

BACKGROUND

Hirschsprung's disease (HSCR) is a congenital gastrointestinal disorder, characterized by enteric ganglia absence in part or entire of the colon, due to abnormal colonization and migration of enteric neural crest cells (ENCCs) during development. Currently, besides surgery which is the main therapy for HSCR, the potential of stem cell-based transplantation was investigated as an alternative option. Although promising, it has limitations, including poor survival, differentiation, and migration of the grafted cells. We hypothesized that modulation of extracellular factors during transplantation could promote ENCCs proliferation and migration, leading to increased transplantation efficiency. Considering that the RhoA/ROCK pathway is highly involved in cytoskeletal dynamics and neurite growth, our study explored the effect of inhibition of this pathway to improve the success of ENCCs transplantation.

METHODS

Enteric neural crest cells were isolated from rat embryos and labeled with a GFP-tag. Cell viability, apoptosis, differentiation, and migration assays were performed with and without RhoA/ROCK inhibition. Labeled ENCCs were transplanted into the muscle layer of an induced hypoganglionic rat model followed by intraperitoneal injections of ROCK inhibitor. The transplanted segments were collected 3 weeks after for histological analysis.

KEY RESULTS

Our results showed that inhibition of ROCK increased viable cell number, differentiation, and migration of ENCCs in vitro. Moreover, transplantation of labeled ENCCs into the hypoganglionic model showed enhanced distribution of grafted ENCCs, upon treatment with ROCK inhibitor.

CONCLUSIONS AND INFERENCES

ROCK inhibitors influence ENCCs growth and migration in vitro and in vivo, and should be considered to improve the efficiency of ENCCs transplantation.

miR-93-5p enhances migration and invasion by targeting RGMB in squamous cell carcinoma of the head and neck

Invasion and metastasis represent the primary causes of therapeutic failure in patients diagnosed with squamous cell carcinoma of the head and neck (SCCHN). Therefore, disease prediction and inhibition of invasion and metastasis are critical for enhancing the survival of patients with SCCHN. Our previous study revealed that increased expression of miR-93-5p is associated with poor prognosis in SCCHN; however, the mechanism underlying the oncogenic functions of miR-93-5p in SCCHN migration and invasion remains unclear. Using qPCR analyses, transwell assays, and scratch tests, we demonstrated that expression of ectopic miR-93-5p induced the migration and invasion of SCCHN, and this was accompanied by corresponding alterations in biomarkers and transcription factors specific for epithelial-mesenchymal transition (EMT). Luciferase reporter assays were used to demonstrate that miR-93-5p directly targeted the 3' UTR of RGMB, and we further found that the tumor-promoting functions of miR-93-5p were partly mediated by targeting RGMB, whose downregulation also promoted the migration and invasion of SCCHN. Overall, our results indicate that miR-93-5p acts as an oncogene in the regulation of migration and invasion by suppressing RGMB in SCCHN. These findings provide novel evidence that miR-93-5p may serve as a valuable predictive biomarker and potential intervention target in patients with SCCHN.

MicroRNA-4472 Promotes Tumor Proliferation and Aggressiveness in Breast Cancer by Targeting RGMA and Inducing EMT

BACKGROUND

Breast cancer is the most common cause of cancer-related death in women worldwide. MicroRNA (miRNA) ectopic expression has been reported to be involved in the regulation of gene expression in breast cancer. We screened several differentially expressed miRNAs associated with breast cancer chemoresistance, growth, and metastasis using a miRNA microarray. Increased expression of miR-4472 has been associated with larger breast tumors and chemoresistance. However, the biologic function of miR-4472 and its molecular mechanisms in cancer progression have not yet been reported.

MATERIALS AND METHODS

Real-time quantitative polymerase chain reaction was used to measure the expression of miR-4472 in breast cancer tissue and cell lines. The biologic functions of miR-4472 and its target gene were explored using Transwell, cell proliferation, and flow cytometry assays. Bioinformatics tools, dual-luciferase reporter assays, and Western blot were used to identify the target genes of miR-4472. Western blot was used to explain the participation of miR-4472 and target gene in epithelial-to-mesenchymal transition.

RESULTS

miR-4472 was significantly upregulated in highly metastatic breast cancer tissues, and its expression was positively associated with larger tumor size and advanced pTNM stage. miR-4472 promoted breast cancer cell metastasis and growth. Repulsive guidance molecule A (RGMA) was a direct target gene of miR-4472. RGMA was identified as a suppressor in cancer metastasis. miR-4472 downregulated expression of RGMA and promoted epithelial-to-mesenchymal transition by suppressing E-cadherin and initiating vimentin, β-catenin, and Slug.

CONCLUSIONS

miR-4472 contributes to the progression of breast cancer by regulating RGMA expression and inducing epithelial-to-mesenchymal transition, indicating that miR-4472/RGMA might serve as a therapeutic target for breast cancer.

Osteosarcoma cell intrinsic PD-L2 signals promote invasion and metastasis via the RhoA-ROCK-LIMK2 and autophagy pathways

Known as co-stimulatory molecule, programmed death ligand-2 (PD-L2) contributes to T-cell exhaustion by interaction with programmed death-1 (PD-1) receptor, but its tumor cell-intrinsic signal effects have been little investigated. PD-L2 expression was detected by immunohistochemistry in 18 pairs of primary osteosarcoma tissues and matching lung metastasis tissues. We also investigated the effects of PD-L2 knockdown on osteosarcoma both in vitro and in vivo. In our study, PD-L2 expression was elevated in lung metastases compared with primary osteosarcoma according to an immunohistochemistry assay. Wound-healing and transwell assays revealed that PD-L2 knockdown  leaded to inhibition of migration and invasion of human osteosarcoma cells in vitro. Mechanistically, we demonstrated that PD-L2 knockdown attenuated migration and invasion by inactivating RhoA-ROCK-LIMK2 signaling, suppressing epithelial–mesenchymal transition (EMT), and inhibiting autophagy by decreasing beclin-1 expression. In support of these observations, beclin-1 knockdown also inhibited activation of the RhoA-ROCK-LIMK2 pathway, leading to autophagy inhibition-induced blockade of migration and invasion. Depletion of PD-L2 in KHOS cells markedly weakens pulmonary metastatic potential in vivo by orthotopic transplantation of nude mice. Our study reveals a pro-metastatic functional mechanism for PD-L2 in osteosarcoma. Furthermore, we demonstrate a regulatory role for PD-L2 on autophagy, as well as a relationship between autophagy and metastasis in osteosarcoma, which may represent a potential therapeutic target for osteosarcoma.

Identification of methylation sites and signature genes with prognostic value for luminal breast cancer

Background

Robust and precise molecular prognostic predictors for luminal breast cancer are required. This study aimed to identify key methylation sites in luminal breast cancer, as well as precise molecular tools for predicting prognosis.

Methods

We compared methylation levels of normal and luminal breast cancer samples from The Cancer Genome Atlas dataset. The relationships among differentially methylated sites, corresponding mRNA expression levels and prognosis were further analysed. Differentially expressed genes in normal and cancerous samples were analysed, followed by the identification of prognostic signature genes. Samples were divided into low- and high-risk groups based on the signature genes. Prognoses of low- and high-risk groups were compared. The Gene Expression Omnibus dataset were used to validate signature genes for prognosis prediction. Prognosis of low- and high-risk groups in Luminal A and Luminal B samples from the TCGA and the Metabric cohort dataset were analyzed. We also analysed the correlation between clinical features of low- and high- risk groups as well as their differences in gene expression.

Results

Fourteen methylation sites were considered to be related to luminal breast cancer prognosis because their methylation levels, mRNA expression and prognoses were closely related to each other. The methylation level of SOSTDC1 was used to divide samples into hypo- and hyper-methylation groups. We also identified an mRNA signature, comprising eight transcripts, ESCO2, PACSIN1, CDCA2, PIGR, PTN, RGMA, KLK4 and CENPA, which was used to divide samples into low- and high-risk groups. The low-risk group showed significantly better prognosis than the high-risk group. A correlation analysis revealed that the risk score was an independent prognostic factor. Low- and high- risk groups significantly correlated with the survival ratio in Luminal A samples, but not in Luminal B samples on the basis of the TCGA and the Metabric cohort dataset. Further functional annotation demonstrated that the differentially expressed genes were mainly involved in cell cycle and cancer progression.

Conclusions

We identified several key methylation sites and an mRNA signature for predicting luminal breast cancer prognosis. The signature exhibited effective and precise prediction of prognosis and may serve as a prognostic and diagnostic marker for luminal breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4314-9) contains supplementary material, which is available to authorized users.

Analysis of the miRNA-mRNA-lncRNA network in human estrogen receptor-positive and estrogen receptor-negative breast cancer based on TCGA data

Estrogen receptor-positive (ER⁺) and ER-negative (ER^-) subtypes of breast cancer have distinct clinical outcomes because they respond differentially to endocrine therapies. We aimed to comprehensively analyze differentially expressed microRNA (miRNAs), long non-coding RNAs (lncRNAs) and mRNAs in different ER subtypes as well as to identify prognosis-related RNAs. The expression levels of miRNAs, lncRNAs, and mRNAs between breast cancer and normal samples were compared using data from The Cancer Genome Atlas database. Differentially expressed miRNAs, lncRNAs and mRNAs between ER⁺ and ER^- samples were also screened. An ER subtype-related miRNA-lncRNA-mRNA network was constructed. lncRNAs and mRNAs in this network were further subjected to an analysis of their associations with patient prognosis. Sets of differentially expressed miRNAs, lncRNAs, and miRNAs between breast cancer and normal samples were identified among which 14 miRNAs, 78 lncRNAs, and 475 mRNAs were differentially expressed between ER subtypes. Relationships between these RNAs were analyzed. The resultant ER subtype-related miRNA-lncRNA-mRNA network consisted of 14 nodes, among which LINC0092 and chromosome 2 open reading frame 71 (C2orf71) were correlated with better prognosis of breast cancer. LINC0092 was co-expressed with SFRP1 and RGMA and regulated by hsa-miR-449a and hsa-miR-452-5p. C2orf71 was co-expressed with LINC00511 and regulated by hsa-miR-184. Cross-talk among differentially expressed miRNAs, lncRNAs, and miRNAs may be an important feature in ER⁺ and ER^- subtypes of breast cancer. LINC0092 and C2orf71, two of these cross-talking RNAs, may serve as novel prognostic predictor of breast cancer because of their close associations with prognosis.

Bone morphogenetic proteins, breast cancer, and bone metastases: striking the right balance

Bone morphogenetic proteins (BMPs) belong to the TGF-β super family, and are essential for the regulation of foetal development, tissue differentiation and homeostasis and a multitude of cellular functions. Naturally, this has led to the exploration of aberrance in this highly regulated system as a key factor in tumourigenesis. Originally identified for their role in osteogenesis and bone turnover, attention has been turned to the potential role of BMPs in tumour metastases to, and progression within, the bone niche. This is particularly pertinent to breast cancer, which commonly metastasises to bone, and in which studies have revealed aberrations of both BMP expression and signalling, which correlate clinically with breast cancer progression. Ultimately a BMP profile could provide new prognostic disease markers. As the evidence suggests a role for BMPs in regulating breast tumour cellular function, in particular interactions with tumour stroma and the bone metastatic microenvironment, there may be novel therapeutic potential in targeting BMP signalling in breast cancer. This review provides an update on the current knowledge of BMP abnormalities and their implication in the development and progression of breast cancer, particularly in the disease-specific bone metastasis.

B7-DC (PD-L2) costimulation of CD4+ T-helper 1 response via RGMb

The role of B7-DC in T-cell responses remains controversial because both coinhibitory and costimulatory functions have been reported in various experimental systems in vitro and in vivo. In addition to interacting with the coinhibitory receptor PD-1, B7-DC has also been shown to bind repulsive guidance molecule b (RGMb). The functional consequences of the B7-DC/RGMb interaction, however, remain unclear. More than a decade ago, we reported that replacement of a murine B7-DC mutant lysine with serine (K113S) at positive 113 resulted in a loss of binding capacity to PD-1. Nevertheless, K113S remained costimulatory for T cells in vitro, implicating a dual functionality for B7-DC in T-cell responses. Here we show that recombinant K113S protein interacts with RGMb with a similar affinity to wild-type B7-DC. More importantly, K113S costimulates CD4⁺ T-cell responses via RGMb and promotes Th1 polarization. RGMb is expressed on the surface of naive mouse T cells, macrophages, neutrophils and dendritic cells. Finally, K113S/RGMb costimulation suppresses Th2-mediated asthma and ameliorates small airway inflammation and lung pathology in an experimental mouse model. Our findings indicate that RGMb is a costimulatory receptor for B7-DC. These findings from the K113S variant provide not only a possible explanation for the B7-DC-triggered contradictory effects on T-cell responses, but also a novel approach to investigate the B7-DC/PD-1/RGMb axis. Recombinant K113S or its derivatives could potentially be developed as an agonist for RGMb to costimulate the Th1 response without triggering PD-1-mediated T-cell inhibition.

Integrated Genetic, Epigenetic, and Transcriptional Profiling Identifies Molecular Pathways in the Development of Laterally Spreading Tumors

Laterally spreading tumors (LST) are colorectal adenomas that develop into extremely large lesions with predominantly slow progression to cancer, depending on lesion subtype. Comparing and contrasting the molecular profiles of LSTs and colorectal cancers offers an opportunity to delineate key molecular alterations that drive malignant transformation in the colorectum. In a discovery cohort of 11 LSTs and paired normal mucosa, we performed a comprehensive and unbiased screen of the genome, epigenome, and transcriptome followed by bioinformatics integration of these data and validation in an additional 84 large, benign colorectal lesions. Mutation rates in LSTs were comparable with microsatellite-stable colorectal cancers (2.4 vs. 2.6 mutations per megabase); however, copy number alterations were infrequent (averaging only 1.5 per LST). Frequent genetic, epigenetic, and transcriptional alterations were identified in genes not previously implicated in colorectal neoplasia (ANO5, MED12L, EPB41L4A, RGMB, SLITRK1, SLITRK5, NRXN1, ANK2). Alterations to pathways commonly mutated in colorectal cancers, namely, the p53, PI3K, and TGFβ pathways, were rare. Instead, LST-altered genes converged on axonal guidance, Wnt, and actin cytoskeleton signaling. These integrated omics data identify molecular features associated with noncancerous LSTs and highlight that mutation load, which is relatively high in LSTs, is a poor predictor of invasive potential.

IMPLICATIONS

The novel genetic, epigenetic, and transcriptional changes associated with LST development reveal important insights into why some adenomas do not progress to cancer. The finding that LSTs exhibit a mutational load similar to colorectal carcinomas has implications for the validity of molecular biomarkers for assessing cancer risk. Mol Cancer Res; 14(12); 1217-28. ©2016 AACR.

Genome-wide association study revealed genomic regions related to white/red earlobe color trait in the Rhode Island Red chickens

Background

Earlobe color is a naturally and artificially selected trait in chicken. As a head furnishing trait, it has been selected as a breed characteristic. Research has demonstrated that white/red earlobe color was related to at least three loci and sex-linked. However, there has been little work to date to identify the specific genomic regions and genes response to earlobe color in Rhode Island Red chickens. Currently, it is possible to identify the genomic regions responsible for white/red earlobe in Rhode Island Red chicken to eliminate this gap in knowledge by using genome-wide association (GWA) analysis.

Results

In the present study, genome-wide association (GWA) analysis was conducted to explore the candidate genomic regions response to chicken earlobe color phenotype. Hens with red dominant and white dominant earlobe was used for case-control analysis by Illumina 600 K SNP arrays. The GWA results showed that 2.38 Mb genomic region (50.13 to 52.51 Mb) with 282 SNPs on chromosome Z were significantly correlated to earlobe color, including sixteen known genes and seven anonymous genes. The sixteen genes were PAM, SLCO4C1, ST8SIA4, FAM174A, CHD1, RGMB, RIOK2, LIX1, LNPEP, SHB, RNF38, TRIM14, NANS, CLTA, GNE, and CPLX1.

Conclusions

The study has revealed the white/red earlobe trait is polygenic and sex-linked in Rhode Island Red chickens. In the genome significant ~2.38 Mb region, twenty-three genes were found and some of them could play critical roles in the formation of white/red earlobe color, especially gene SLCO4C1. Taken together, the candidate genes findings herein can help elucidate the genomic architecture of response to white/red earlobe and provide a new insight on mechanisms underlying earlobe color in Rhode Island Red chickens and other breeds.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0422-1) contains supplementary material, which is available to authorized users.

Smad6 determines BMP-regulated invasive behaviour of breast cancer cells in a zebrafish xenograft model

The transforming growth factor-β (TGF-β) family is known to play critical roles in cancer progression. While the dual role of TGF-β is well described, the function of bone morphogenetic proteins (BMPs) is unclear. In this study, we established the involvement of Smad6, a BMP-specific inhibitory Smad, in breast cancer cell invasion. We show that stable overexpression of Smad6 in breast cancer MCF10A M2 cells inhibits BMP signalling, thereby mitigating BMP6-induced suppression of mesenchymal marker expression. Using a zebrafish xenograft model, we demonstrate that overexpression of Smad6 potentiates invasion of MCF10A M2 cells and enhances the aggressiveness of breast cancer MDA-MB-231 cells in vivo, whereas a reversed phenotype is observed after Smad6 knockdown. Interestingly, BMP6 pre-treatment of MDA-MB-231 cells induced cluster formation at the invasive site in the zebrafish. BMP6 also stimulated cluster formation of MDA-MB-231 cells co-cultured on Human Microvascular Endothelial Cells (HMEC)-1 in vitro. Electron microscopy illustrated an induction of cell-cell contact by BMP6. The clinical relevance of our findings is highlighted by a correlation of high Smad6 expression with poor distant metastasis free survival in ER-negative cancer patients. Collectively, our data strongly indicates the involvement of Smad6 and BMP signalling in breast cancer cell invasion in vivo.

Long Noncoding RNA RGMB-AS1 Indicates a Poor Prognosis and Modulates Cell Proliferation, Migration and Invasion in Lung Adenocarcinoma

Lung cancer is the most common cause of cancer-related mortality worldwide. It is a complex disease involving multiple genetic and epigenetic alterations. The development of transcriptomics revealed the important role of long non-coding RNAs (lncRNAs) in lung cancer occurrence and development. Here, microarray analysis of lung adenocarcinoma tissues showed the abnormal expression of lncRNA RGMB-AS1. However, the role of lncRNA RGMB-AS1 in lung adenocarcinoma remains largely unknown. We showed that upregulation of lncRNA RGMB-AS1 was significantly correlated with differentiation, TNM stage, and lymph node metastasis. In lung adenocarcinoma cells, downregulation of lncRNA RGMB-AS1 inhibited cell proliferation, migration, invasion, and caused cell cycle arrest at the G1/G0 phase. In vivo experiments showed that lncRNA RGMB-AS1 downregulation significantly suppressed the growth of lung adenocarcinoma. The expression of lncRNA RGMB-AS1 was inversely correlated with that of repulsive guidance molecule b (RGMB) in lung adenocarcinoma tissues, and UCSC analysis and fluorescence detection assay indicated that lncRNA RGMB-AS1 may be involved in the development of human lung adenocarcinoma by regulating RGMB expression though exon2 of RGMB. In summary, our findings indicate that lncRNA RGMB-AS1 may play an important role in lung adenocarcinoma and may serve as a potential therapeutic target.

The role of the Rho/ROCK signaling pathway in inhibiting axonal regeneration in the central nervous system

The Rho/Rho-associated coiled-coil containing protein kinase (Rho/ROCK) pathway is a major signaling pathway in the central nervous system, transducing inhibitory signals to block regeneration. After central nervous system damage, the main cause of impaired regeneration is the presence of factors that strongly inhibit regeneration in the surrounding microenvironment. These factors signal through the Rho/ROCK signaling pathway to inhibit regeneration. Therefore, a thorough understanding of the Rho/ROCK signaling pathway is crucial for advancing studies on regeneration and repair of the injured central nervous system.

Study on expression of lncRNA RGMB-AS1 and repulsive guidance molecule b in non-small cell lung cancer

Background

The relationships between lncRNAs and tumors have currently become one of the focuses on cancer studies. However, there are a few studies about lncRNAs in non-small cell lung cancer (NSCLC) at present.

Methods

Microarray analysis was designed to study the expression patterns of lncRNAs in three pairs of NSCLC tissues. The expression of lncRNA RGMB-AS1 and repulsive guidance molecule b (RGMB) were detected in 72 paired NSCLC tissues and adjacent normal tissues by qRT-PCR assay. The relations of lncRNA RGMB-AS1 and RGMB expression with clinicopathological factors of NSCLC patients were explored. A549 and SPC-A-1 cells were transfected with siRNA of lncRNA RGMB-AS1 and negative control. RGMB expression level was detected by qRT-PCR assay and western blot analysis.

Results

The results of microarray found that 571 lncRNAs were differentially expressed in NSCLC tissues (Fold change cut-off: 5.0, P < 0.05), including 304 upregulated and 267 downregulated lncRNAs. The results of qRT-PCR showed that lncRNA RGMB-AS1 expression was significantly higher in NSCLC tissues than in adjacent normal tissues (P < 0.05), while RGMB mRNA showed an opposite trend (P < 0.05). Correlation analysis indicated that the expression of lncRNA RGMB-AS1and RGMB mRNA were inversely correlated (R² = 0.590, P < 0.05). While lncRNA RGMB-AS1 and RGMB expression levels in NSCLC tissues were associated with the occurrence of differentiation status, lymph node metastases and TNM stage (P < 0.05). Transfection with siRNA of lncRNA RGMB-AS1, subsequent results showed that RGMB mRNA and protein expression were upregulated (P < 0.05) in A549 and SPC-A-1 cells compared to the control groups.

Conclusion

We identified lncRNA RGMB-AS1 was upregulated and RGMB was downregulated in NSCLC patients. Both were related to differentiation status, lymph node metastases and TNM stage. Studies also indicated that lncRNA RGMB-AS1and RGMB were inversely correlated.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/7911587521528276

Expression of repulsive guidance molecule b (RGMb) in the uterus and ovary during the estrous cycle in rats

Repulsive guidance molecule b (RGMb; a.k.a. Dragon), initially identified in the embryonic dorsal root ganglion, is the first member of the RGM family shown to enhance bone morphogenetic protein (BMP) signaling by acting as a BMP co-receptor. BMP signaling has been demonstrated to play an important role in the reproductive organs. Our previous study found that RGMb was expressed in the reproductive axis, but whether RGMb expression in reproductive organs changes across the estrous cycle remains unknown. Here, we show in the rat that RGMb mRNA expression in the uterus was significantly higher during metesterus and diestrus than during proestrus and estrus. Western blotting indicated that RGMb protein was significantly lower during estrus compared with the other three stages. Immunohistochemistry revealed that RGMb protein was mainly localized to the uterine luminal and glandular epithelial cells of the endometrium. RGMb mRNA and protein in the ovary remained unchanged during the estrous cycle. RGMb protein was expressed in the oocytes of all follicles. Weak staining for RGMb protein was also found in corpora lutea. RGMb was not detected in granulosa cells and stromal cells. Taken together, RGMb expression in the uterus and ovary across the estrus cycle demonstrate that RGMb may be involved in the regulation of uterine function, follicular development as well as luteal activity.

Tumour angiogenesis and repulsive guidance molecule b: a role in HGF- and BMP-7-mediated angiogenesis

Hepatocyte growth factor (HGF) is a key growth factor linked to promoting cancer progression and angiogenesis. The present study identifies repulsive guidance molecule b (RGMb), a bone morphogenetic protein (BMP) co-receptor, as a gene whose expression is regulated by HGF and explores the potential of RGMb to contribute to the process of angiogenesis. Microarray analysis was used to identify HGF responsive genes in HECV endothelial cells, identifying RGMb. RGMb was subsequently targeted using a ribozyme transgene system and its role in angiogenesis assessed using in vitro and in vivo assays. The importance of RGMb in pro-angiogenic responses to HGF and BMP-7 was also assessed. Microarray analysis identified RGMb as a gene upregulated as a result of HGF treatment. Knockdown of RGMb, in HECV cells, had minimal effects on tubule formation, brought about a general, although non-significant increase in cell growth and enhanced cell migration. Similarly, no significant effect of RGMb knockdown was found in vivo using a co-inoculation angiogenesis model. Knockdown of RGMb was, however, found to reduce the responsiveness of HECV cells to HGF treatment and particularly to BMP-7 treatment in regard to the enhanced migratory and tubule formation brought about by these treatments in vitro. Our results indicate that RGMb expression can be influenced by HGF treatment. Whilst this molecule appears to have minimal impact on angiogenic traits individually, it demonstrates an involvement in propagating pro-angiogenic effects of HGF and particularly BMP-7 and thus, may play a role in regulating angiogenic responses to HGF and BMP-7.

RGMb is a novel binding partner for PD-L2 and its engagement with PD-L2 promotes respiratory tolerance

Interaction between the inhibitory molecule PD-L2 on dendritic cells and repulsive guidance molecule b (RGMb) on lung macrophages is required to establish respiratory tolerance.

We report that programmed death ligand 2 (PD-L2), a known ligand of PD-1, also binds to repulsive guidance molecule b (RGMb), which was originally identified in the nervous system as a co-receptor for bone morphogenetic proteins (BMPs). PD-L2 and BMP-2/4 bind to distinct sites on RGMb. Normal resting lung interstitial macrophages and alveolar epithelial cells express high levels of RGMb mRNA, whereas lung dendritic cells express PD-L2. Blockade of the RGMb–PD-L2 interaction markedly impaired the development of respiratory tolerance by interfering with the initial T cell expansion required for respiratory tolerance. Experiments with PD-L2–deficient mice showed that PD-L2 expression on non–T cells was critical for respiratory tolerance, but expression on T cells was not required. Because PD-L2 binds to both PD-1, which inhibits antitumor immunity, and to RGMb, which regulates respiratory immunity, targeting the PD-L2 pathway has therapeutic potential for asthma, cancer, and other immune-mediated disorders. Understanding this pathway may provide insights into how to optimally modulate the PD-1 pathway in cancer immunotherapy while minimizing adverse events.

RGMb is a novel binding partner for PD-L2 and its engagement with PD-L2 promotes respiratory tolerance

We report that programmed death ligand 2 (PD-L2), a known ligand of PD-1, also binds to repulsive guidance molecule b (RGMb), which was originally identified in the nervous system as a co-receptor for bone morphogenetic proteins (BMPs). PD-L2 and BMP-2/4 bind to distinct sites on RGMb. Normal resting lung interstitial macrophages and alveolar epithelial cells express high levels of RGMb mRNA, whereas lung dendritic cells express PD-L2. Blockade of the RGMb-PD-L2 interaction markedly impaired the development of respiratory tolerance by interfering with the initial T cell expansion required for respiratory tolerance. Experiments with PD-L2-deficient mice showed that PD-L2 expression on non-T cells was critical for respiratory tolerance, but expression on T cells was not required. Because PD-L2 binds to both PD-1, which inhibits antitumor immunity, and to RGMb, which regulates respiratory immunity, targeting the PD-L2 pathway has therapeutic potential for asthma, cancer, and other immune-mediated disorders. Understanding this pathway may provide insights into how to optimally modulate the PD-1 pathway in cancer immunotherapy while minimizing adverse events.

Anti-Müllerian hormone recruits BMPR-IA in immature granulosa cells

Anti-Müllerian hormone (AMH) is a member of the TGF-β superfamily secreted by the gonads of both sexes. This hormone is primarily known for its role in the regression of the Müllerian ducts in male fetuses. In females, AMH is expressed in granulosa cells of developing follicles. Like other members of the TGF-β superfamily, AMH transduces its signal through two transmembrane serine/threonine kinase receptors including a well characterized type II receptor, AMHR-II. The complete signalling pathway of AMH involving Smads proteins and the type I receptor is well known in the Müllerian duct and in Sertoli and Leydig cells but not in granulosa cells. In addition, few AMH target genes have been identified in these cells. Finally, while several co-receptors have been reported for members of the TGF-β superfamily, none have been described for AMH. Here, we have shown that none of the Bone Morphogenetic Proteins (BMPs) co-receptors, Repulsive guidance molecules (RGMs), were essential for AMH signalling. We also demonstrated that the main Smad proteins used by AMH in granulosa cells were Smad 1 and Smad 5. Like for the other AMH target cells, the most important type I receptor for AMH in these cells was BMPR-IA. Finally, we have identified a new AMH target gene, Id3, which could be involved in the effects of AMH on the differentiation of granulosa cells and its other target cells.

Repulsive guidance molecules (RGMs) and neogenin in bone morphogenetic protein (BMP) signaling

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor-beta (TGFβ) superfamily. BMPs mediate a highly conserved signal transduction cascade through the type-I and type-II serine/threonine kinase receptors and intracellular Smad proteins, which regulate multiple developmental and homeostatic processes. Mutations in this pathway can cause various diseases in humans, such as skeletal disorders, cardiovascular diseases, and various cancers. Multiple levels of regulation, including extracellular regulation, help to ensure proper spatiotemporal control of BMP signaling in the right cellular context. The family of repulsive guidance molecules (RGMs) and the type-I transmembrane protein neogenin, a paralog of DCC (Deleted in Colorectal Cancer), have been implicated in modulating the BMP pathway. In this review, we discuss the properties and functions of RGM proteins and neogenin, focusing on their roles in the modulation of BMP signal transduction.

Spatiotemporal expression of repulsive guidance molecules (RGMs) and their receptor neogenin in the mouse brain

Neogenin has been implicated in a variety of developmental processes such as neurogenesis, neuronal differentiation, apoptosis, migration and axon guidance. Binding of repulsive guidance molecules (RGMs) to Neogenin inhibits axon outgrowth of different neuronal populations. This effect requires Neogenin to interact with co-receptors of the uncoordinated locomotion-5 (Unc5) family to activate downstream Rho signaling. Although previous studies have reported RGM, Neogenin, and/or Unc5 expression, a systematic comparison of RGM and Neogenin expression in the developing nervous system is lacking, especially at later developmental stages. Furthermore, information on RGM and Neogenin expression at the protein level is limited. To fill this void and to gain further insight into the role of RGM-Neogenin signaling during mouse neural development, we studied the expression of RGMa, RGMb, Neogenin and Unc5A-D using in situ hybridization, immunohistochemistry and RGMa section binding. Expression patterns in the primary olfactory system, cortex, hippocampus, habenula, and cerebellum were studied in more detail. Characteristic cell layer-specific expression patterns were detected for RGMa, RGMb, Neogenin and Unc5A-D. Furthermore, strong expression of RGMa, RGMb and Neogenin protein was found on several major axon tracts such as the primary olfactory projections, anterior commissure and fasciculus retroflexus. These data not only hint at a role for RGM-Neogenin signaling during the development of different neuronal systems, but also suggest that Neogenin partners with different Unc5 family members in different systems. Overall, the results presented here will serve as a framework for further dissection of the role of RGM-Neogenin signaling during neural development.