Slit/Robo Signaling Pathway in Cancer; a New Stand Point for Cancer Treatment

Current perspectives on the multiple roles of osteoclasts: Mechanisms of osteoclast-osteoblast communication and potential clinical implications

Bone remodeling is a complex process involving the coordinated actions of osteoblasts and osteoclasts to maintain bone homeostasis. While the influence of osteoblasts on osteoclast differentiation is well established, the reciprocal regulation of osteoblasts by osteoclasts has long remained enigmatic. In the past few years, a fascinating new role for osteoclasts has been unveiled in promoting bone formation and facilitating osteoblast migration to the remodeling sites through a number of different mechanisms, including the release of factors from the bone matrix following bone resorption and direct cell-cell interactions. Additionally, considerable evidence has shown that osteoclasts can secrete coupling factors known as clastokines, emphasizing the crucial role of these cells in maintaining bone homeostasis. Due to their osteoprotective function, clastokines hold great promise as potential therapeutic targets for bone diseases. However, despite long-standing work to uncover new clastokines and their effect in vivo, more substantial efforts are still required to decipher the mechanisms and pathways behind their activity in order to translate them into therapies. This comprehensive review provides insights into our evolving understanding of the osteoclast function, highlights the significance of clastokines in bone remodeling, and explores their potential as treatments for bone diseases suggesting future directions for the field.

Genes in Axonal Regeneration

This review explores the molecular and genetic underpinnings of axonal regeneration and functional recovery post-nerve injury, emphasizing its significance in reversing neurological deficits. It presents a systematic exploration of the roles of various genes in axonal regrowth across peripheral and central nerve injuries. Initially, it highlights genes and gene families critical for axonal growth and guidance, delving into their roles in regeneration. It then examines the regenerative microenvironment, focusing on the role of glial cells in neural repair through dedifferentiation, proliferation, and migration. The concept of "traumatic microenvironments" within the central nervous system (CNS) and peripheral nervous system (PNS) is discussed, noting their impact on regenerative capacities and their importance in therapeutic strategy development. Additionally, the review delves into axonal transport mechanisms essential for accurate growth and reinnervation, integrating insights from proteomics, genome-wide screenings, and gene editing advancements. Conclusively, it synthesizes these insights to offer a comprehensive understanding of axonal regeneration's molecular orchestration, aiming to inform effective nerve injury therapies and contribute to regenerative neuroscience.

Cancer Cell-Type-Dependent Modifications of Metastatic Parameters by SLIT2-ROBO1 and RHOA cAMP Signaling in Response to TGFβ1 and FGF2

The epithelial to mesenchymal transition (EMT) is a multistep process involving structural and functional alterations that are required for cancer metastasis, as well as loss of epithelial markers (e.g., E-cadherin/CDH1) and gain of mesenchymal markers (e.g., N-cadherin/CDH2, vimentin/VIM). Pathological events modify cell-cell interactions, cell-matrix adhesion and extra cellular matrix integrity leading to cell migration, evasion from the primary tumor and augmented invasiveness in the metastatic niche. This transformation is modulated by multiple paracrine factors (e.g., chemokines, growth factor), as well as SLIT2-ROBO1 signaling that collectively regulate expression of RHO GTPases (e.g., RHOA) and EMT marker genes. Yet, the roles of SLIT proteins in cancer remain enigmatic. In some cancer types, SLIT2 is anti-tumorigenic, while in other cancers it contributes towards the metastatic phenotype. Here we investigated the ambivalent metastatic activity of SLIT2 by analyzing how cAMP/RHOA signal transduction modulates SLIT-ROBO controlled metastatic parameters in response to the phosphodiesterase inhibitor IBMX (3-isobutyl-1-methylxanthine) and paracrine factors (TGF-β/TGFβ1 and FGF2). Upon SLIT2 administration cell migration and proliferation increases in colon cancer cells and decreases in cervical cancer cells, while altering cell morphology and proliferation in both cancer types. These effects are reinforced by TGF-β/TGFβ1 and FGF2, but attenuated by elevation of cAMP with IBMX, depending on the cancer cell type. Our data indicate that SLIT2 represents a potential biomarker for cancer diagnosis, prognosis, and therapy.

ROBO1 deficiency impairs HSPC homeostasis and erythropoiesis via CDC42 and predicts poor prognosis in MDS

Myelodysplastic syndrome (MDS) is a group of clonal hematopoietic neoplasms originating from hematopoietic stem progenitor cells (HSPCs). We previously identified frequent roundabout guidance receptor 1 (ROBO1) mutations in patients with MDS, while the exact role of ROBO1 in hematopoiesis remains poorly delineated. Here, we report that ROBO1 deficiency confers MDS-like disease with anemia and multilineage dysplasia in mice and predicts poor prognosis in patients with MDS. More specifically, Robo1 deficiency impairs HSPC homeostasis and disrupts HSPC pool, especially the reduction of megakaryocyte erythroid progenitors, which causes a blockage in the early stages of erythropoiesis in mice. Mechanistically, transcriptional profiling indicates that Cdc42, a member of the Rho-guanosine triphosphatase family, acts as a downstream target gene for Robo1 in HSPCs. Overexpression of Cdc42 partially restores the self-renewal and erythropoiesis of HSPCs in Robo1-deficient mice. Collectively, our result implicates the essential role of ROBO1 in maintaining HSPC homeostasis and erythropoiesis via CDC42.

Matrine suppresses liver cancer progression and the Warburg effect by regulating the circROBO1/miR-130a-5p/ROBO1 axis

Matrine, an effective component extracted from the traditional Chinese herb, Sophora flavescens, has been indicated to exert antitumor activity in different types of cancer. However, the role and precise mechanism of matrine in the progression of liver cancer remains largely unclear. Cell viability, cell proliferation, cell apoptosis, and Warburg effect were estimated by cell counting kit-8 assay, colony formation assay, flow cytometry assay, and glucose uptake and lactate production assay, respectively. The candidate Circular RNAs (circRNAs) were screened by integrating the Gene Expression Omnibus database (GSE155949) analysis with the online program GEO2R. A quantitative real-time polymerase chain reaction was employed to test the expression of circRNA circROBO1, microRNA miR-130a-5p, and roundabout homolog 1 (ROBO1). The interaction of circROBO1/miR-130a-5p/ROBO1 axis was predicted and confirmed by bioinformatics analysis, a dual-luciferase reporter assay, and an RNA pull-down assay. A xenograft mouse model was employed to reveal the role of matrine in vivo. Matrine repressed liver cancer cell viability, proliferation, and Warburg effect, but increased cell apoptosis in vitro. CircROBO1 and ROBO1 were upregulated, but miR-130a-5p was downregulated in liver cancer tissues. Additionally, matrine could reduce the expression of circROBO1 and ROBO1, and increase the expression of miR-130a-5p. Mechanically, overexpression of circROBO1 partly recovered the effect of matrine on liver cancer cell viability, proliferation, apoptosis, and Warburg effect by regulating the miR-130a-5p/ROBO1 axis. Matrine impeded liver cancer development by mediating the circROBO1/miR-130a-5p/ROBO1 axis, which provided a theoretical basis for the application of matrine as an effective anticancer drug for liver cancer.

Mechanism of Robo1 in the pentylenetetrazol-kindled epilepsy mouse model

The neural network hypothesis is one of the important pathogenesis of drug-resistant epilepsy. Axons guide molecules through synaptic remodeling and brain tissue remodeling, which may result in the formation of abnormal neural networks. Therefore, axon guidance plays a crucial role in disease progression. However, although Robo1 is one of the important components of axon guidance, the role of Robo1 in epilepsy remains unclear. In this study, we aimed to explore the mechanism of Robo1 in epilepsy. Male adult C57BL/6 mice were intraperitoneally injected with pentylenetetrazol to establish an epilepsy model. Lentivirus (LV) was given via intracranial injection 2 weeks before pentylenetetrazol injection. Different expressions of Robo1 between the control group, LV-mediated Robo1 short hairpin RNA group, empty vector control LV group, and normal saline group were analyzed using Western blot, immunofluorescence staining, Golgi staining, and video monitoring. Robo1 was increased in the hippocampus in the pentylenetetrazol-induced epilepsy mouse model; lentiviral Robo1 knockdown prolonged the latency of seizure and reduced the seizure grade in mice and resulted in a decrease in dendritic spine density, while the number of mature dendritic spines was maintained. We speculate that Robo1 has been implicated in the development and progression of epilepsy through its effects on dendritic spine morphology and density. Epileptic mice with Robo1 knockdown virus intervention had lower seizure grade and longer latency. Follow-up findings suggest that Robo1 may modulate seizures by affecting dendritic spine density and morphology. Downregulation of Robo1 may negatively regulate epileptogenesis by decreasing the density of dendritic spines and maintaining a greater number of mature dendritic spines.

Adaptive activation of EFNB2/EPHB4 axis promotes post-metastatic growth of colorectal cancer liver metastases by LDLR-mediated cholesterol uptake

The microenvironment of distant organ plays vital roles in regulating tumor metastases. However, little is known about the crosstalk between metastasized tumor cells and target organs. Herein, we found that EFNB2 expression was upregulated in liver metastases (LM) of colorectal cancer (CRC), but not in pulmonary metastases (PM) or primary CRC tumors. EFNB2 played a tumor-promoting role in CRC LM in vitro and in vivo. Through forward signaling, EFNB2-promoted CRC LM by interacting with the EPHB4 receptor. EFNB2/EPHB4 axis enhances LDLR-mediated cholesterol uptake in CRC LM. Subsequently, EFNB2/EPHB4 axis promotes LDLR transcription by regulating STAT3 phosphorylation. Blocking LDLR reversed the role of the EFNB2/EPHB4 axis in promoting CRC LM. Using clinical data, survival analysis revealed that the survival time of patients with CRC LM was decreased in patients with high EFNB2 expression, compared with low EFNB2 expression. Inhibition of the EFNB2/EPHB4 axis markedly prolonged the survival time of BALB/c nude mice with CRC LM with a high cholesterol diet. These findings revealed a key step in the regulation of cholesterol uptake by EFNB2/EPHB4 axis and its tumor-promoting role in CRC LM.

miR-152-3p impedes the malignant phenotypes of hepatocellular carcinoma by repressing roundabout guidance receptor 1

BACKGROUND

miR-152-3p functions as a tumour suppressor in the progression of hepatic tumorigenesis. Herein, we further discussed the prognostic significance and immune infiltration of miR-152-3p and its potential gene target in hepatocellular carcinoma (HCC).

METHODS

The Cancer Genome Atlas (TCGA), Integrative Molecular Database of Hepatocellular Carcinoma (HCCDB), Human Protein Atlas (HPA) and Kaplan-Meier Plotter databases were used to evaluate miR-152-3p and roundabout guidance receptor 1 (ROBO1) expression, prognosis and immune infiltration. In vitro cell experiments, including cell proliferation and apoptosis, were evaluated using Cell Counting Kit 8 (CCK8) and terminal-deoxynucleotidyl transferase-mediated nick end labelling (TUNEL) assays.

RESULTS

Up-regulation of ROBO1 functioned as an oncogene associated with poor prognosis, immune cell enrichment and cell proliferation in HCC. ROBO1 was significantly positively correlated with the enrichment of multiple immune cells and their biomarkers. Enrichment of type-2 T-helper (Th2) cells is an unfavourable biomarker of HCC prognosis. GSEA revealed that ROBO1 correlated with apoptosis, mitosis and carcinogenic signalling pathways. Suppression of cell proliferation and the enhancement of cell apoptosis by miR-152-3p mimics were counteracted by overexpression of ROBO1 in HCC cells.

CONCLUSION

ROBO1 expression is positively correlated with multiple immune checkpoint molecules, suggesting that ROBO1 may be a potential drug target to enhance the potency of immunotherapy. The miR-152-3p/ROBO1 signalling axis contributes to malignant progression and provides a prospective immunotherapeutic target for HCC.

Robo recruitment of the Wave regulatory complex plays an essential and conserved role in midline repulsion

The Roundabout (Robo) guidance receptor family induces axon repulsion in response to its ligand Slit by inducing local cytoskeletal changes; however, the link to the cytoskeleton and the nature of these cytoskeletal changes are poorly understood. Here, we show that the heteropentameric Scar/Wave Regulatory Complex (WRC), which drives Arp2/3-induced branched actin polymerization, is a direct effector of Robo signaling. Biochemical evidence shows that Slit triggers WRC recruitment to the Robo receptor's WRC-interacting receptor sequence (WIRS) motif. In Drosophila embryos, mutants of the WRC enhance Robo1-dependent midline crossing defects. Additionally, mutating Robo1's WIRS motif significantly reduces receptor activity in rescue assays in vivo, and CRISPR-Cas9 mutagenesis shows that the WIRS motif is essential for endogenous Robo1 function. Finally, axon guidance assays in mouse dorsal spinal commissural axons and gain-of-function experiments in chick embryos demonstrate that the WIRS motif is also required for Robo1 repulsion in mammals. Together, our data support an essential conserved role for the WIRS-WRC interaction in Robo1-mediated axon repulsion.

Alcohol Intake and Alcohol-SNP Interactions Associated with Prostate Cancer Aggressiveness

Excessive alcohol intake is a well-known modifiable risk factor for many cancers. It is still unclear whether genetic variants or single nucleotide polymorphisms (SNPs) can modify alcohol intake's impact on prostate cancer (PCa) aggressiveness. The objective is to test the alcohol-SNP interactions of the 7501 SNPs in the four pathways (angiogenesis, mitochondria, miRNA, and androgen metabolism-related pathways) associated with PCa aggressiveness. We evaluated the impacts of three excessive alcohol intake behaviors in 3306 PCa patients with European ancestry from the PCa Consortium. We tested the alcohol-SNP interactions using logistic models with the discovery-validation study design. All three excessive alcohol intake behaviors were not significantly associated with PCa aggressiveness. However, the interactions of excessive alcohol intake and three SNPs (rs13107662 [CAMK2D, p = 6.2 × 10-6], rs9907521 [PRKCA, p = 7.1 × 10-5], and rs11925452 [ROBO1, p = 8.2 × 10-4]) were significantly associated with PCa aggressiveness. These alcohol-SNP interactions revealed contrasting effects of excessive alcohol intake on PCa aggressiveness according to the genotypes in the identified SNPs. We identified PCa patients with the rs13107662 (CAMK2D) AA genotype, the rs11925452 (ROBO1) AA genotype, and the rs9907521 (PRKCA) AG genotype were more vulnerable to excessive alcohol intake for developing aggressive PCa. Our findings support that the impact of excessive alcohol intake on PCa aggressiveness was varied by the selected genetic profiles.

The potential of Slit2 as a therapeutic target for central nervous system disorders

Introduction: Slit2 is an extracellular matrix protein that regulates migration of developing axons during central nervous system (CNS) development. Roundabout (Robo) receptors expressed by various cell types in the CNS, mediate intracellular signal transduction pathways for Slit2. Recent studies indicate that Slit2 plays important protective roles in a myriad of processes such as cell migration, immune response, vascular permeability, and angiogenesis in CNS pathologies. Areas covered: This review provides an overview of the diverse functions of Slit2 in CNS disorders and discusses the potential of Slit2 as a therapeutic target. We reviewed preclinical studies reporting the role of Slit2 in various CNS disease models, transgenic animal research, and rodent models that utilized Slit2 as a therapy. Expert opinion: Slit2 exerts a wide array of beneficial effects ranging from anti-migration, blood-brain barrier (BBB) protection, inhibition of peripheral immune cell infiltration, and anti-apoptosis in various disease models. However, a dual role of Slit2 in endothelial permeability has been observed in transgenic animals. Further research on Slit2 will be crucial including key issues such as effects of transgenic overexpression versus exogenous Slit2, function of Slit2 dependent on cellular expression of Robo receptors and the underlying pathology for potential clinical translation.

Research Progress on Slit/Robo Pathway in Pancreatic Cancer: Emerging and Promising

Pancreatic cancer is a highly malignant digestive system tumor which is the leading cause of cancer-related deaths. The basic and clinical research of pancreatic cancer has made great progress in recent years, and kinds of signaling pathways have been found in the tumorigenesis and progression in pancreatic cancer. The Slit glycoprotein (Slit) and Roundabout receptor (Robo) signaling pathway acts as a neural targeting factor with the axonal remnant, axon guidance, and inhibition of neuronal migration in the nervous system. In recent years, it has been found that the Slit/Robo signaling pathway has different degrees of expression changes in various tumor cells. In different tumor cells, the signaling pathway gene expression is different and regulates tumor angiogenesis, cell invasion, metastasis, and nerve infiltration. Herein, we summarize the mechanisms of the Slit/Robo pathway in the development and progression of pancreatic cancer, in order to have more understanding of the role of Slit/Robo in pancreatic cancer.

Expression patterns of SLIT/ROBO mRNAs reveal a characteristic feature in the entorhinal-hippocampal area of macaque monkeys

OBJECTIVE

SLITs are secreted glycoproteins that bind to Roundabouts (ROBOs) which are a family member of transmembrane receptors. SLIT signaling has well-conserved roles in mediating axon repulsion in a developing nervous system. We previously reported that SLIT1 mRNA is enriched in middle layers of the prefrontal cortex of macaque monkeys in a developmentally regulated manner. Other SLIT (SLIT2 and SLIT3) mRNAs showed preferential expressions in the prefrontal cortex with a distinct laminar pattern. To obtain further clues to the role of SLIT signaling in the organization of the primate brain, we performed ISH analysis of SLIT and ROBO mRNAs using adult macaque brain tissues.

RESULTS

In this study, we examined the expression patterns of SLITs and ROBOs (ROBO1 and ROBO2) in other brain regions, and found intense and characteristic expression patterns of these genes in the entorhinal-hippocampal area. In situ hybridization analysis revealed that SLIT1 and SLIT2 mRNAs showed marked complementary distribution in the entorhinal cortex. SLIT and ROBO mRNAs were widely expressed in the hippocampus with modest regional preference. These findings suggest that each SLIT gene has a specialized role that is particularly important for prefrontal as well as hippocampal connectivity in the primate cortex.