The neuronal guidance cue Slit2 induces targeted migration and may play a role in brain metastasis of breast cancer cells

Involvement of neuronal factors in tumor angiogenesis and the shaping of the cancer microenvironment

Emerging evidence suggests that nerves within the tumor microenvironment play a crucial role in regulating angiogenesis. Neurotransmitters and neuropeptides released by nerves can interact with nearby blood vessels and tumor cells, influencing their behavior and modulating the angiogenic response. Moreover, nerve-derived signals may activate signaling pathways that enhance the production of pro-angiogenic factors within the tumor microenvironment, further supporting blood vessel growth around tumors. The intricate network of communication between neural constituents and the vascular system accentuates the potential of therapeutically targeting neural-mediated pathways as an innovative strategy to modulate tumor angiogenesis and, consequently, neoplastic proliferation. Hereby, we review studies that evaluate the precise molecular interplay and the potential clinical ramifications of manipulating neural elements for the purpose of anti-angiogenic therapeutics within the scope of cancer treatment.

Concomitant induction of SLIT3 and microRNA-218-2 in macrophages by toll-like receptor 4 activation limits osteoclast commitment

BACKGROUND

Toll-like receptor 4 (TLR4) conducts a highly regulated inflammatory process by limiting the extent of inflammation to avoid toxicity and tissue damage, even in bone tissues. Thus, it is plausible that strategies for the maintenance of normal bone-immunity to prevent undesirable bone damage by TLR4 activation can exist, but direct evidence is still lacking.

METHODS

Osteoclast precursors (OCPs) obtained from WT or Slit3-deficient mice were differentiated into osteoclast (OC) with macrophage colony-stimulating factor (M-CSF), RANK ligand (RANKL) and lipopolysaccharide (LPS) by determining the number of TRAP-positive multinuclear cells (TRAP+ MNCs). To determine the alteration of OCPs population, fluorescence-activated cell sorting (FACS) was conducted in bone marrow cells in mice after LPS injection. The severity of bone loss in LPS injected WT or Slit3-deficient mice was evaluated by micro-CT analysis.

RESULT

We demonstrate that TLR4 activation by LPS inhibits OC commitment by inducing the concomitant expression of miR-218-2-3p and its host gene, Slit3, in mouse OCPs. TLR4 activation by LPS induced SLIT3 and its receptor ROBO1 in BMMs, and this SLIT3-ROBO1 axis hinders RANKL-induced OC differentiation by switching the protein levels of C/EBP-β isoforms. A deficiency of SLIT3 resulted in increased RANKL-induced OC differentiation, and the elevated expression of OC marker genes including Pu.1, Nfatc1, and Ctsk. Notably, Slit3-deficient mice showed expanded OCP populations in the bone marrow. We also found that miR-218-2 was concomitantly induced with SLIT3 expression after LPS treatment, and that this miRNA directly suppressed Tnfrsf11a (RANK) expression at both gene and protein levels, linking it to a decrease in OC differentiation. An endogenous miR-218-2 block rescued the expression of RANK and subsequent OC formation in LPS-stimulated OCPs. Aligned with these results, SLIT3-deficient mice displayed increased OC formation and reduced bone density after LPS challenge.

CONCLUSION

Our findings suggest that the TLR4-dependent concomitant induction of Slit3 and miR-218-2 targets RANK in OCPs to restrain OC commitment, thereby avoiding an uncoordinated loss of bone through inflammatory processes. These observations provide a mechanistic explanation for the role of TLR4 in controlling the commitment phase of OC differentiation. Video Abstract.

The SLIT/ROBO Pathway in Liver Fibrosis and Cancer

Liver fibrosis is a common outcome of most chronic liver insults/injuries that can develop into an irreversible process of cirrhosis and, eventually, liver cancer. In recent years, there has been significant progress in basic and clinical research on liver cancer, leading to the identification of various signaling pathways involved in tumorigenesis and disease progression. Slit glycoprotein (SLIT)1, SLIT2, and SLIT3 are secreted members of a protein family that accelerate positional interactions between cells and their environment during development. These proteins signal through Roundabout receptor (ROBO) receptors (ROBO1, ROBO2, ROBO3, and ROBO4) to achieve their cellular effects. The SLIT and ROBO signaling pathway acts as a neural targeting factor regulating axon guidance, neuronal migration, and axonal remnants in the nervous system. Recent findings suggest that various tumor cells differ in SLIT/ROBO signaling levels and show varying degrees of expression patterns during tumor angiogenesis, cell invasion, metastasis, and infiltration. Emerging roles of the SLIT and ROBO axon-guidance molecules have been discovered in liver fibrosis and cancer development. Herein, we examined the expression patterns of SLIT and ROBO proteins in normal adult livers and two types of liver cancers: hepatocellular carcinoma and cholangiocarcinoma. This review also summarizes the potential therapeutics of this pathway for anti-fibrosis and anti-cancer drug development.

The rexinoid V-125 reduces tumor growth in preclinical models of breast and lung cancer

Rexinoids are ligands which activate retinoid X receptors (RXRs), regulating transcription of genes involved in cancer-relevant processes. Rexinoids have anti-neoplastic activity in multiple preclinical studies. Bexarotene, used to treat cutaneous T cell lymphoma, is the only FDA-approved rexinoid. Bexarotene has also been evaluated in clinical trials for lung and metastatic breast cancer, wherein subsets of patients responded despite advanced disease. By modifying structures of known rexinoids, we can improve potency and toxicity. We previously screened a series of novel rexinoids and selected V-125 as the lead based on performance in optimized in vitro assays. To validate our screening paradigm, we tested V-125 in clinically relevant mouse models of breast and lung cancer. V-125 significantly (p < 0.001) increased time to tumor development in the MMTV-Neu breast cancer model. Treatment of established mammary tumors with V-125 significantly (p < 0.05) increased overall survival. In the A/J lung cancer model, V-125 significantly (p < 0.01) decreased number, size, and burden of lung tumors. Although bexarotene elevated triglycerides and cholesterol in these models, V-125 demonstrated an improved safety profile. These studies provide evidence that our screening paradigm predicts novel rexinoid efficacy and suggest that V-125 could be developed into a new cancer therapeutic.

ROBO1 protein expression is independently associated with biochemical recurrence in prostate cancer patients who underwent radical prostatectomy in Asian patients

Background

The purpose of this study is to investigate the correlation between ROBO1 expression and prostate cancer aggressiveness.

Methods

ROBO1 expression was evaluated in normal prostate epithelial cells (PrEC) and different prostate cancer cell lines by Western blot analysis. The migration and invasion of native and ROBO1 knockdown cells were evaluated using migration chambers and a Matrigel-coated membrane, respectively. Samples from 145 patients who underwent radical prostatectomy between June 2000 and June 2008, were retrieved from the paraffin files for tissue microarray (TMA) with immunohistochemical analysis. Biochemical recurrence (BCR)-free survival curves were estimated using the Kaplan-Meier and Cox regression methods in two groups of patients classified according to the degree of ROBO1 expression (low or high expression).

Results

ROBO1 is highly expressed in the prostate cancer cell lines. All ROBO1 knockdown cells (PC3, 22Rv1 and DU 145) showed markedly decreased migration and invasiveness compared to native cells. In 145 patients with radical prostatectomy, the Kaplan-Meier curves and log-rank test for BCR-free survival stratified by ROBO1 expression in organ-confined (pT2) or not (pT3), showed significant differences in 10-year survival between the ROBO1 high and low expression groups (87.2% versus 52.6% in pT2; P=0.047, 51.0% versus 36.9% in pT3; P=0.033). The multivariable-adjusted model showed a markedly increased hazard ratio (HR) in patients with high ROBO1 expression compared to the patients with low ROBO1expression in every model.

Conclusions

ROBO1 may play an important role in the migration and invasion of prostate cancer cells, and was independently associated with BCR.

Discovery of Cancer-Specific and Independent Prognostic Gene Subsets of the Slit-Robo Family Using TCGA-PANCAN Datasets

The Slit-Robo family of axon guidance molecules works in concert, playing important roles in organ development and cancer. Expressions of individual Slit-Robo genes have been used in calculating univariable hazard ratios (HR_uni) for predicting cancer prognosis in the literature. However, Slit-Robo members do not act independently; hence, hazard ratios from multivariable Cox regression (HR_multi) on the whole gene set can further lead to identification of cancer-specific, novel, and independent prognostic gene pairs or modules. Herein, we obtained mRNA expressions of the Slit-Robo family consisting of four Robos (ROBO1/2/3/4) and three Slits (SLIT1/2/3), along with four types of survival outcome across cancers found in the Cancer Genome Atlas (TCGA). We used cluster heat maps to visualize closely associated pairs/modules of prognostic genes across 33 different cancers. We found a smaller number of significant genes in HR_multi than in HR_uni, suggesting that the former analysis was less redundant. High ROBO4 expression emerged as relatively protective within the family, in both types of HR analyses. Multivariable Cox regression, on the other hand, revealed significantly more HR signatures containing Slit-Robo pairs acting in opposing directions than those containing Slit-Slit or Robo-Robo pairs for disease-specific survival. Furthermore, we discovered, through the online app SmulTCan's lasso regression, Slit-Robo gene subsets that significantly differentiated between high- versus low-risk prognosis patient groups, particularly for renal cancers and low-grade glioma. The statistical pipeline reported herein can help test independent and significant pairs/modules within a codependent gene family for cancer prognostication, and thus should also prove useful in personalized/precision medicine research.

SLIT2/ROBO signaling in tumor-associated microglia and macrophages drives glioblastoma immunosuppression and vascular dysmorphia

SLIT2 is a secreted polypeptide that guides migration of cells expressing Roundabout 1 and 2 (ROBO1 and ROBO2) receptors. Herein, we investigated SLIT2/ROBO signaling effects in gliomas. In patients with glioblastoma (GBM), SLIT2 expression increased with malignant progression and correlated with poor survival and immunosuppression. Knockdown of SLIT2 in mouse glioma cells and patient-derived GBM xenografts reduced tumor growth and rendered tumors sensitive to immunotherapy. Tumor cell SLIT2 knockdown inhibited macrophage invasion and promoted a cytotoxic gene expression profile, which improved tumor vessel function and enhanced efficacy of chemotherapy and immunotherapy. Mechanistically, SLIT2 promoted microglia/macrophage chemotaxis and tumor-supportive polarization via ROBO1- and ROBO2-mediated PI3K-γ activation. Macrophage Robo1 and Robo2 deletion and systemic SLIT2 trap delivery mimicked SLIT2 knockdown effects on tumor growth and the tumor microenvironment (TME), revealing SLIT2 signaling through macrophage ROBOs as a potentially novel regulator of the GBM microenvironment and immunotherapeutic target for brain tumors.

ROBO2 hampers malignant biological behavior and predicts a better prognosis in pancreatic adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a fatalmalignant cancer with extremely poor prognosis and high mortality. Genome wide studies show that Slit/Robo signaling pathway takes a major effect in the oncogenesis and progression of pancreatic cancer. However, the function and mechanism of ROBO2 in the development of PDAC remains unclear.

METHODS

In present study, we use Western blot and real-time polymerase chain reaction (RT-PCR) to detect the expression of ROBO2 in pancreatic cell lines. Cell proliferation,Transwellmigration and invasion were conducted inAsPC-1, MIA PaCa-2 and PANC-1cell lines. RNA sequencing, bioinformatics analysisand Western blot were used to explore its mechanism and potential target molecules. The expression of ROBO2 in 95 tumor tissues was detected by immunohistochemistry.

RESULTS

ROBO2 expression was downregulated in PDAC cell lines and tissue samples. A high expression of ROBO2 was associated with better prognosis. Upregulation of ROBO2 inhibited PDAC cell proliferation, migration, and invasion. However, we found theoppositeresults in the ROBO2 downregulation group. In addition, the function of ROBO2 on cell proliferation was further affirmed by the animal model. Finally, the results of RNA sequencing indicated that ROBO2 partly promoted the antitumor activity by inhibiting ECM1 in PDAC.

CONCLUSIONS

Our work suggests that ROBO2 inhibits tumor progression in PDAC and may serve as a predictive biomarker and therapeutic target in PDAC.

PRRG4 promotes breast cancer metastasis through the recruitment of NEDD4 and downregulation of Robo1

Metastasis is responsible for the death of most breast cancer patients. Robo1 has been implicated as a tumor suppressor for various cancers including breast cancer. However, it is not well understood how Robo1 expression is regulated during tumorigenesis. In this study, we uncovered that the transmembrane proline rich γ-carboxyglutamic acid protein 4 (PRRG4) promotes breast cancer metastasis by downregulating Robo1. Analysis of mRNA expression data in The Cancer Genome Atlas and immunohistochemistry assay on breast tumor samples showed that PRRG4 expression was higher in breast tumors than in normal breast tissues. Experiments with PRRG4 knockdown and overexpression revealed that PRRG4 promoted migration and invasion of breast cancer cells, and enhanced metastasis in an experimental metastasis model. Mechanistically, we found that PRRG4 via its LPSY and PPPY motifs recruited the E3 ubiquitin ligase NEDD4, which induced ubiquitination and degradation of Robo1, thus contributing to migration and invasion of breast cancer cells. In addition, PRRG4 interacted with and enhanced protein tyrosine kinase Src and FAK activation. Overall, our data support a model that PRRG4 via NEDD4 downregulates the Robo1, resulting in the activation of Src and FAK and promoting breast cancer metastasis. PRRG4 may be a novel target for treating metastatic breast cancer.

SLIT2 Overexpression in Periodontitis Intensifies Inflammation and Alveolar Bone Loss, Possibly via the Activation of MAPK Pathway

SLIT2, a member of neuronal guidance cues, has been reported to regulate inflammation and cancer progression. Periodontitis is an oral inflammatory disease that degenerates periodontal tissue, alveolar bone and tooth. This study aims to explore the expression pattern of SLIT2 in periodontitis and its role in disease progression and bone loss. Gingival tissue of 20 periodontitis patients and 20 healthy-controls was obtained. Ligature-induced periodontitis (LIP) mice-model was developed in Slit2-Tg and wild-type mice. The effect of SLIT2 on inflammation, immune cell infiltration, M1 macrophage polarization, and alveolar bone loss in periodontitis was analyzed extensively. In periodontitis-affected gingival-tissue, SLIT2 expression was 4.4-fold higher compared to healthy-volunteers. LIP enhanced SLIT2 expression in mice periodontitis-affected periodontal tissue (PAPT) and blood circulation of wild-type mice by 4. 6-, and 5.0-fold, respectively. In Slit2-Tg-mice PAPT, SLIT2 expression was 1.8-fold higher compared to wild-type mice. Micro-CT and histomorphometric analysis revealed a 1.3-fold higher cement-enamel-junction to the alveolar-bone-crest (CEJ-ABC) distance and alveolar bone loss in LIP Slit2-Tg-mice compare to LIP wild-type mice. Results from RNA-sequencing, RT-qPCR, and ELISA showed a higher expression of Cxcr2, Il-18, TNFα, IL-6, and IL-1β in Slit2-Tg-mice PAPT compared to wild-type-mice. Slit2-Tg-mice PAPT showed a higher number of osteoclasts, M1 macrophages, and the upregulation of Robo1 expression. Slit2-Tg-mice PAPT showed upregulation of M1 macrophage marker CD16/32 and osteoclastogenic markers Acp5, Ctsk, and Nfatc1, but osteogenic markers (Alp, Bglap) remained unchanged. Immunohistochemistry unveiled the higher vasculature and infiltration of leucocytes and macrophages in Slit2-Tg-mice PAPT. RNA-sequencing, GO-pathway enrichment analysis, and western blot analysis revealed the activation of the MAPK signaling pathway in Slit2-Tg mice PAPT. In conclusion, SLIT2 overexpression in periodontitis intensifies inflammation, immune cells infiltration, M1 macrophage polarization, osteoclastogenesis, and alveolar bone loss, possibly via activation of MAPK signaling, suggesting the role of SLIT2 on exacerbation of periodontitis and alveolar bone loss.

Nuclear Localization of Robo is Associated with Better Survival in Bladder Cancer

The Slit-Robo pathway has shown to be altered in several malignant diseases. However, its role in bladder cancer is poorly understood. Therefore, we aimed to assess the tissue expression of Robo1 and Robo4 as well as their ligand Slit2 in different stages of bladder cancer to explore possible changes of Slit-Robo signalling during the progression of bladder cancer. Robo1, Robo4 and Slit2 gene expressions were analyzed in 92 frozen bladder cancer tissue samples by using reverse transcription quantitative real-time PCR. Immunohistochemical analyses were performed on 149 formalin-fixed and paraffin-embedded bladder cancer tissue samples. Results were correlated with the clinical and follow-up data by performing both univariable and multivariable analyses. Robo1 and Robo4 nuclear staining intensitiy was significantly higher in low stage and low grade bladder cancer. Elevated Robo1 nuclear staining was associated with better disease-specific survival (DSS) (p = 0.045). Similarly, stronger Robo4 nuclear staining tended to be associated with longer DSS (p = 0.061). We found higher Robo1 and Slit2 gene expression levels in advanced stages of bladder cancer (p = 0.007 and p < 0.001). High Slit2 gene expression was correlated with significantly shorter DSS (p < 0.005), while Robo1 and Robo4 gene expressions were not associated with patients' prognosis. Our results demonstrate that the nuclear expression of Robo1 and Robo4 is associated with a favourable prognosis suggesting that its translocation into the nucleus represent a posttranslational regulation process which may exhibit an antitumor effect in bladder cancer.

Slit2 signaling contributes to cholestatic fibrosis in mice by activation of hepatic stellate cells

Liver Cholestasis is a widespread disease of broad etiologies and ultimately results in fibrosis, which is still lacking effective therapeutic strategies. Activation of hepatic stellate cells (HSCs) is the key event of liver fibrosis. Here, we aimed to investigate the effect and mechanism of the Slit2 signaling in cholestasis-induced liver fibrosis. Our findings revealed that the serum levels and hepatic expression of Slit2 were significantly increased in patients with primary biliary cirrhosis (PBC). Additionally, Slit2-Tg mice were much more vulnerable to BDL-induced liver injury and fibrosis compared to WT control. Slit2 up-regulation by Slit2 recombinant protein induced proliferation, and inhibited apoptosis of human HSCs cell line LX-2 via p38 and ERK signaling pathway, resulting in the activation of HSCs. In contrast, Slit2 down-regulation by siRNA silencing inhibit the activation of HSCs. In conclusion, Slit2 is involved in the activation of HSCs and liver fibrogenesis, highlighting Slit2 as a potential therapeutic target for liver fibrosis.

Activation of Slit2/Robo1 Signaling Promotes Tumor Metastasis in Colorectal Carcinoma through Activation of the TGF-β/Smads Pathway

Slit2 (slit guidance ligand 2), a ligand of the Roundabout1 (Robo1) transmembrane receptor, is often overexpressed in colorectal carcinomas (CRCs). In this study, we performed data mining in the Metabolic gEne RApid Visualizer (MERAV) database and found that Slit2 and TGF-β1 (Transforming growth factor-β1) are highly expressed in carcinomas relative to those in tumor-free tissues from healthy volunteers or wild type mice. Furthermore, expression of Slit2 and TGF-β1 in CRCs increases with pathological stages. Serum levels of Slit2 in patients with CRC and in ApcMin/+ mice with spontaneous intestinal adenoma were significantly increased compared with those in healthy controls. Specific blockage of Slit2 binding to Robo1 inactivated TGF-β/Smads signaling and inhibited tumor cell migration and metastasis, which can be partially restored by treatment with TGF-β1. However, specific inhibition of TGF-β1/Smads signaling reduced CRC tumor cell migration and invasion without affecting cell proliferation. This study suggests that activation of Slit2/Robo1 signaling in CRC induces tumor metastasis partially through activation of the TGF-β/Smads pathway.

Targeting the SLIT/ROBO pathway in tumor progression: molecular mechanisms and therapeutic perspectives

The SLITs (SLIT1, SLIT2, and SLIT3) are a family of secreted proteins that mediate positional interactions between cells and their environment during development by signaling through ROBO receptors (ROBO1, ROBO2, ROBO3, and ROBO4). The SLIT/ROBO signaling pathway has been shown to participate in axonal repulsion, axon guidance, and neuronal migration in the nervous system and the formation of the vascular system. However, the role of the SLIT/ROBO pathway has not been thoroughly clarified in tumor development. The SLIT/ROBO pathway can produce both beneficial and detrimental effects in the growth of malignant cells. It has been confirmed that SLIT/ROBO play contradictory roles in tumorigenesis. Here, we discuss the tumor promotion and tumor suppression roles of the SLIT/ROBO pathway in tumor growth, angiogenesis, migration, and the tumor microenvironment. Understanding these roles will help us develop more effective cancer therapies.

The Role of the Slit/Robo Signaling Pathway

The Slit family is a family of secreted proteins that play important roles in various physiologic and pathologic activities via interacting with Robo receptors. Slit/Robo signaling was first identified in the nervous system, where it functions in neuronal axon guidance; nevertheless, an increasing number of studies have shown that Slit/Robo signaling even regulates other activities, such as angiogenesis, inflammatory cell chemotaxis, tumor cell migration and metastasis. Although the precise role of the ligand-receptor in organisms has been obscure and the conclusions drawn are sometimes paradoxical, tremendous advances in understanding the Slit/Robo signaling pathway have been made. As such, our review summarizes the characteristics of the Slit/Robo signaling pathway and its role in various cell types.

Molecular targets for tivantinib (ARQ 197) and vasculogenic mimicry in human melanoma cells

Tivantinib (TivB) was reported previously to target MET and microtubule assembly in different cells resulting in cytotoxicity. However, its other cellular targets remain unknown, especially the proteins involved in focal adhesion and cytoskeletal organization. We studied the effect of TivB on vinculin a focal adhesion protein, and RhoC, a GTPase which promote the reorganization of cytoskeleton. Biomolecules involved in vasculogenic mimicry (VM) previously not reported in melanoma, and their susceptibility to TivB was also evaluated. TivB affects the viability and apoptosis of human melanoma cells depending on the cell type. Vinculin and RhoC were increased in the presence of TivB and affected the integrity of actin filaments and altered the cellular morphology. TivB disrupts the VM exhibited by melanoma cells in 3D matrix. Roundabout Guidance Receptor 4 (Robo4), a receptor protein implicated in axonal guidance and angiogenesis and its ligand Slit2 are expressed in human C8161 and WM793 melanoma cells, but absent in other melanoma cells including normal melanocytes. VM is more prominent in C8161 cells and could be blocked by siRNA mediated silencing of Robo4 mRNA, but TivB does not affect Robo4 in C8161 cells. Immunoblot analysis indicated no changes in Robo4 and Slit2 protein expression, however, both vinculin and RhoC protein increased in TivB treated melanoma cells. These results suggest that TivB affects cell cytoskeleton and morphology by altering proteins such as vinculin and RhoC. Our studies indicate TivB could target molecules other than MET in melanoma cells, which may provide insight into its alternate mechanism of action.

The Expression of the SLIT-ROBO Family in Adult Patients with Acute Myeloid Leukemia

INTRODUCTION

SLIT-ROBO is a ligand-receptor family of neuronal guidance cues that has been involved in pathological and physiological angiogenesis. SLIT-ROBO expression is altered in many tumours. However, no data exist about the role of the whole family in acute myelogenous myeloid leukemia (AML).

PURPOSE

Herein, we assessed the expression of all SLIT-ROBO family in bone marrow (BM) biopsy of AML patients and control group on both protein and RNA levels.

METHODS

The paraffin-embedded tissue blocks were subjected to immunohistochemistry for SLIT1, SLIT2, SLIT3, ROBO1, ROBO2, ROBO3, and ROBO4. Microvessel density (MVD) was evaluated by CD34 immunohistochemistry. An in silico analysis using The Cancer Genome Atlas data repository was conducted for assessment of RNA level.

RESULTS

Acute myeloid leukemia patients were generally high expressers of ROBO1 and ROBO2 compared to the controls (p < 0.0001, p < 0.001, respectively). In contrast, low expression of SLIT1, SLIT2, and SLIT3 ligands has been noted more commonly in AML than in control BM samples (p < 0.0001, p = 0.003, and p = 0.001, respectively). ROBO4 expression correlated with MVD. The in silico analysis showed a poor prognostic value of high ROBO3 and low SLIT2 RNA levels (p = 0.0003 and p = 0.0008, respectively), as well as high ROBO3 and ROBO4 RNA levels in cytogenetic poor risk groups of patients (p = 0.0029 and p = 0.0003, respectively).

CONCLUSIONS

These data indicate that SLIT-ROBO family members play a role in the biology of AML. Low expression of SLIT in BM of AML patients may suggest its expression alterations in AML. Increased expression of ROBO1 and ROBO2 in AML patients suggests their participation in AML pathogenesis.

ADP-ribosylation factor-like 4A interacts with Robo1 to promote cell migration by regulating Cdc42 activation

Cell migration is a highly regulated event that is initiated by cell membrane protrusion and actin reorganization. Robo1, a single-pass transmembrane receptor, is crucial for neuronal guidance and cell migration. ADP-ribosylation factor (Arf)-like 4A (Arl4A), an Arf small GTPase, functions in cell morphology, cell migration, and actin cytoskeleton remodeling; however, the molecular mechanisms of Arl4A in cell migration are unclear. Here, we report that the binding of Arl4A to Robo1 modulates cell migration by promoting Cdc42 activation. We found that Arl4A interacts with Robo1 in a GTP-dependent manner and that the Robo1 amino acid residues 1394-1398 are required for this interaction. The Arl4A-Robo1 interaction is essential for Arl4A-induced cell migration and Cdc42 activation but not for the plasma membrane localization of Robo1. In addition, we show that the binding of Arl4A to Robo1 decreases the association of Robo1 with the Cdc42 GTPase-activating protein srGAP1. Furthermore, Slit2/Robo1 binding down-regulates the Arl4A-Robo1 interaction in vivo, thus attenuating Cdc42-mediated cell migration. Therefore, our study reveals a novel mechanism by which Arl4A participates in Slit2/Robo1 signaling to modulate cell motility by regulating Cdc42 activity.

Inhibitory effect of SLIT2 on granulosa cell proliferation mediated by the CDC42-PAKs-ERK1/2 MAPK pathway in the prehierarchical follicles of the chicken ovary

The SLIT2 ligand and ROBO receptors of the SLIT/ROBO pathway are expressed in hen ovarian follicles and have been shown to play critical roles in ovary development, cell proliferation and apoptosis in mammals. However, the exact roles of SLIT2 and the molecular mechanisms of chicken follicle development remain poorly understood. Here, we discovered that high levels of SLIT2 suppress FSHR, GDF9, STAR and CYP11A1 mRNA and protein expression in granulosa cells (GCs) and cell proliferation (p < 0.01). However, these inhibitory effects can be abolished by the siRNA-mediated knockdown of the ROBO1 and ROBO2 receptors. Furthermore, the activity of CDC42, which is a key Rho GTPase in the SLIT/ROBO pathway, is regulated by the ligand SLIT2 because the intrinsic GTPase activation activity of CDC42 is activated or repressed by regulating SRGAP1 expression (p < 0.01). The effects of the SLIT2 overexpression on GC proliferation and phosphorylation of the B-RAF, RAF1 and ERK1/2 kinases were completely abrogated by knocking down endogenous PAK1 and partially abrogated by the knockdown of PAK2 and PAK3 in the GCs. Collectively, our findings indicate that SLIT2 suppresses GC proliferation, differentiation and follicle selection mainly by a mechanism involving ROBO1 and ROBO2 and that this suppression is mediated by the CDC42-PAKs-ERK1/2 MAPK signaling cascade in the prehierarchical follicles of the chicken ovary.

Development of Microplatforms to Mimic the In Vivo Architecture of CNS and PNS Physiology and Their Diseases

Understanding the mechanisms that govern nervous tissues function remains a challenge. In vitro two-dimensional (2D) cell culture systems provide a simplistic platform to evaluate systematic investigations but often result in unreliable responses that cannot be translated to pathophysiological settings. Recently, microplatforms have emerged to provide a better approximation of the in vivo scenario with better control over the microenvironment, stimuli and structure. Advances in biomaterials enable the construction of three-dimensional (3D) scaffolds, which combined with microfabrication, allow enhanced biomimicry through precise control of the architecture, cell positioning, fluid flows and electrochemical stimuli. This manuscript reviews, compares and contrasts advances in nervous tissues-on-a-chip models and their applications in neural physiology and disease. Microplatforms used for neuro-glia interactions, neuromuscular junctions (NMJs), blood-brain barrier (BBB) and studies on brain cancer, metastasis and neurodegenerative diseases are addressed. Finally, we highlight challenges that can be addressed with interdisciplinary efforts to achieve a higher degree of biomimicry. Nervous tissue microplatforms provide a powerful tool that is destined to provide a better understanding of neural health and disease.

Robo1 and vimentin regulate radiation-induced motility of human glioblastoma cells

Glioblastoma is a primary brain tumor with a poor prognosis despite of many treatment regimens. Radiotherapy significantly prolongs patient survival and remains the most common treatment. Slit2 and Robo1 are evolutionarily conserved proteins involved in axon guidance, migration, and branching of neuronal cells. New studies have shown that Slit2 and Robo1 could play important roles in leukocyte chemotaxis and glioblastoma cell migration. Therefore, we investigated whether the Slit2/Robo1 complex has an impact on the motility of glioblastoma cells and whether irradiation with therapeutic doses modulates this effect. Our results indicate that photon irradiation increases the migration of glioblastoma cells in vitro. qPCR and immunoblotting experiments in two different glioblastoma cell lines (U-373 MG and U-87 MG) with different malignancy revealed that both Slit2 and Robo1 are significantly lower expressed in the cell populations with the highest motility and that the expression was reduced after irradiation. Overexpression of Robo1 significantly decreased the motility of glioblastoma cells and inhibited the accelerated migration of wild-type cells after irradiation. Immunoblotting analysis of migration-associated proteins (fascin and focal adhesion kinase) and of the epithelial-mesenchymal-transition-related protein vimentin showed that irradiation affected the migration of glioblastoma cells by increasing vimentin expression, which can be reversed by the overexpression of Slit2 and Robo1. Our findings suggest that Robo1 expression might counteract migration and also radiation-induced migration of glioblastoma cells, a process that might be connected to mesenchymal-epithelial transition.

Suppression of Slit3 induces tumor proliferation and chemoresistance in hepatocellular carcinoma through activation of GSK3β/β-catenin pathway

Background

It is essential to understand the mechanisms responsible for hepatocellular carcinoma (HCC) progression and chemoresistance in order to identify prognostic biomarkers as well as potential therapeutic avenues. Recent findings have shown that SLIT3 appears to function as a novel tumor suppressor gene in various types of cancers, yet its clinical correlation and role in HCC has not been understood clearly.

Methods

We determined the transcript levels of Slit3 in tumor and adjacent normal tissues within two cohorts (N = 40 and 25) of HCC patients, and correlated the gene expression with the clinicopathological data. Subsequently, the functional effects and underlying molecular mechanisms of Slit3 overexpression and/or repression were studied using cell-line and mouse models.

Results

Our results demonstrated a repression in Slit3 expression in nearly 50% of the HCC patients, while the overall expression of Slit3 inversely correlated with the size of the tumor in both cohorts of patients. Stable down-regulation of Slit3 in HCC cell-lines induced cell proliferation in vitro and tumor growth in vivo, while stable Slit3 overexpression repressed these effects. Molecular investigations showed that the stable Slit3 repression-induced cell proliferation was associated with a higher expression of β-catenin and a repressed GSK3β activity. Moreover, Slit3-repression induced chemoresistance to sorafenib, oxaliplatin and 5-FU through impairment of β-catenin degradation and induction of cyclin D3 and survivin levels. The effects induced by stable Slit3-repression were diminished by transient repression of β-catenin by siRNA approach.

Conclusion

This study suggests that Slit3 acts as a tumor suppressor in HCC by repressing the tumor growth and thus tumor progression. Low Slit3 level indicates a poor response of HCC cells to chemotherapy. Restoration or overexpression of Slit3 is a potential therapeutic approach to repress the tumor growth and enhance the efficacy of chemotherapeutic agents.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4326-5) contains supplementary material, which is available to authorized users.

A Traveling Wave Ion Mobility Spectrometry (TWIMS) Study of the Robo1-Heparan Sulfate Interaction

Roundabout 1 (Robo1) interacts with its receptor Slit to regulate axon guidance, axon branching, and dendritic development in the nervous system and to regulate morphogenesis and many cell functions in the nonneuronal tissues. This interaction is known to be critically regulated by heparan sulfate (HS). Previous studies suggest that HS is required to promote the binding of Robo1 to Slit to form the minimal signaling complex, but the molecular details and the structural requirements of HS for this interaction are still unclear. Here, we describe the application of traveling wave ion mobility spectrometry (TWIMS) to study the conformational details of the Robo1-HS interaction. The results suggest that Robo1 exists in two conformations that differ by their compactness and capability to interact with HS. The results also suggest that the highly flexible interdomain hinge region connecting the Ig1 and Ig2 domains of Robo1 plays an important functional role in promoting the Robo1-Slit interaction. Moreover, variations in the sulfation pattern and size of HS were found to affect its binding affinity and selectivity to interact with different conformations of Robo1. Both MS measurements and CIU experiments show that the Robo1-HS interaction requires the presence of a specific size and pattern of modification of HS. Furthermore, the effect of N-glycosylation on the conformation of Robo1 and its binding modes with HS is reported. Graphical Abstract ᅟ.

Antagonizing miR-218-5p attenuates Wnt signaling and reduces metastatic bone disease of triple negative breast cancer cells

Wnt signaling is implicated in bone formation and activated in breast cancer cells promoting primary and metastatic tumor growth. A compelling question is whether osteogenic miRNAs that increase Wnt activity for bone formation are aberrantly expressed in breast tumor cells to support metastatic bone disease. Here we report that miR-218-5p is highly expressed in bone metastases from breast cancer patients, but is not detected in normal mammary epithelial cells. Furthermore, inhibition of miR-218-5p impaired the growth of bone metastatic MDA-MB-231 cells in the bone microenvironment in vivo. These findings indicate a positive role for miR-218-5p in bone metastasis. Bioinformatic and biochemical analyses revealed a positive correlation between aberrant miR-218-5p expression and activation of Wnt signaling in breast cancer cells. Mechanistically, miR-218-5p targets the Wnt inhibitors Sclerostin (SOST) and sFRP-2, which highly enhances Wnt signaling. In contrast, delivery of antimiR-218-5p decreased Wnt activity and the expression of metastasis-related genes, including bone sialoprotein (BSP/IBSP), osteopontin (OPN/SPP1) and CXCR-4, implicating a Wnt/miR-218-5p regulatory network in bone metastatic breast cancer. Furthermore, miR-218-5p also mediates the Wnt-dependent up-regulation of PTHrP, a key cytokine promoting cancer-induced osteolysis. Antagonizing miR-218-5p reduced the expression of PTHrP and Rankl, inhibited osteoclast differentiation in vitro and in vivo, and prevented the development of osteolytic lesions in a preclinical metastasis model. We conclude that pathological elevation of miR-218-5p in breast cancer cells activates Wnt signaling to enhance metastatic properties of breast cancer cells and cancer-induced osteolytic disease, suggesting that miR-218-5p could be an attractive therapeutic target for preventing disease progression.

miR-218 suppresses epithelial-to-mesenchymal transition by targeting Robo1 and Ecop in lung adenocarcinoma cells

AIM

Although, miR-218 has been implicated in epithelial-to-mesenchymal transition process, the detailed mechanisms of miR-218 involvement in epithelial-to-mesenchymal transition in human lung adenocarcinoma cell are still unclear.

MATERIALS & METHODS

miR-218 function assays and its target gene analysis were performed.

RESULTS

miR-218 suppresses human lung adenocarcinoma cell migration and invasion and inhibits its target gene, Ecop and Robo1 expression, which subsequently suppresses NF-κB activity and its downstream targets.

CONCLUSION

miR-218 inhibits human lung adenocarcinoma cell migration and invasion via the suppression of Ecop and Robo1 expression, thus suggesting that miR-218 could serve as a potential therapeutic target.

Gene expression profiling of brain metastatic cell from triple negative breast cancer: Understanding the molecular events

Brain metastatic triple negative breast cancer (BM-TNBC) is afflicted with unfavorable prognosis. However, the molecular events underlying BM-TNBC remain largely unknown. In the present study, we conducted gene expression microarray analysis using the triple negative breast cancer cell line MDA-MB-231 and its brain metastatic derivative (MDA-MB-231Brm). Results of microarray analysis showed that a total of 4296 genes were differentially expressed, of which 2433 genes were up-regulated and 1863 genes were down-regulated. Gene Ontology (GO), KEGG pathway and protein-protein interaction (PPI) analyses indicated differentially expressed genes functionally categorized as genes of signal transduction, multicellular organismal development, ion transport, nervous system development, plasma membrane, extracellular region, calcium ion binding, GTP binding neuroactive ligand-receptor interaction. The validity of the microarray results was verified by quantitative real-time PCR analysis of twelve representative genes. The present findings revealed molecular basis and events associated with brain metastasis in TNBC, which will potentially contribute to the understanding of underlying mechanism and develop therapeutic targets.

[MiR-218 Inhibits Migration and Invasion of Lung Cancer Cell by Regulating Robo1 Expression]

BACKGROUND

To explore the function and the potential molecular mechanism of miR-218 in lung cancer cell.

METHODS

The expression of miR-218 mRNA was determined by real-time PCR in lung cancer tissues, adjacent tissues and lung cancer cells. Transwell assay was used to detect the migration and invasion of A549 cell after transfected with Anti-miR-218 or negative control and HC4006 cell after transfected with miR-218 mimics and miR-218 negative control. Targetscan and MiRanda were used to calculate the potential targets of miR-218 and Luciferase reporter assay was performed to identify that the Robo1 was one target genes of miR-218. Transwell assay was used to detect whether miR-218 regulated the invasion of lung cancer cell transfected with anti-miR-218 or negative control via Robo1.

RESULTS

The expression of miR-218 in the lung cancer tissues was significantly lower than that in the adjacent tissues (P<0.05). Inhibition of miR-218 improved the migration and invasion of A549 cell. Overexpression of miR-218 suppressed the migration and invasion of HCC4006 cell. The co-transfection of anti-miR-218 or miR-218 mimics and the Robo1 3'UTR increased or reduced the luciferase activity of Robo1 compared with the control group (P<0.05). Inhibition of miR-218 and Robo1 recovered the invaded cells of A549. Overexpression of miR-218 and inhibition of Robo1 reduced the number of the invased cells of HCC4006. These results suggested that miR-218 banded Robo1 directly and inhibited lung cancer cell invasion by targeting Robo1.

CONCLUSIONS

MiR-218 inhibited the migration and invasion of lung cancer cells through regulating Robo1 expression.
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Slit2 suppresses endothelial cell proliferation and migration by inhibiting the VEGF-Notch signaling pathway

Slit homolog 2 (Slit2) is distributed in various tissues and participates in numerous cellular processes; however, the role of Slit2 in the regulation of angiogenesis remains controversial, since it has previously been reported to exert proangiogenic and antiangiogenic activities. The present study aimed to investigate the effects of Slit2 on vascular endothelial cell proliferation and migration in vitro, and to reveal the possible underlying signaling pathway. Aortic endothelial cells were isolated from Sprague Dawley rats and cultured. Cell proliferation assay, cell migration assay, immunocytochemistry and small interfering RNA transfection were subsequently performed. The results demonstrated that exogenous Slit2 administration markedly suppressed TNF-α-induced endothelial cell proliferation and migration in vitro. In addition, TNF-α application upregulated the protein expression levels of vascular endothelial growth factor (VEGF) and Notch in RAECs, whereas Slit2 administration downregulated VEGF and Notch expression in RAECs cultured in TNF-α conditioned medium. Further studies indicated that knockdown of VEGF suppressed the effects of TNF-α on the induction of RAEC proliferation and migration. VEGF knockdown-induced inhibition of RAEC proliferation and migration in TNF-α conditioned medium was also achieved without Slit2 administration. Furthermore, VEGF knockdown markedly decreased Notch1 and Notch2 expression. These results indicated that Slit2 suppresses TNF-α-induced vascular endothelial cell proliferation and migration in vitro by inhibiting the VEGF-Notch signaling pathway. Therefore, Slit2 may inhibit the proliferation and migration of endothelial cells during vascular development.

Pathogenesis of Breast Cancer Metastasis to Brain: a Comprehensive Approach to the Signaling Network

There is a general consensus that breast cancer is a rising trend disease in the world. It is one of the most common cancer types and is the leading cause of death among women's cancers. There are several reasons for this high rate of mortality including metastasis which is responsible for about 90 % of cancer-related mortality. Therefore, recognition and understanding of metastatic process is important, and by considering the key role of pathophysiological route in metastasis as a multistep cascade of "invasion-metastasis," it might modify and improve our insight toward this complex phenomenon. Moreover, it can provide novel approaches for designing advanced targeted therapies. The present work aimed to review the published papers regarding molecular basis of metastatic process of breast cancer to brain metastasis, especially related genes and signaling network. Furthermore, the use of molecular aspects of metastatic breast cancer to brain was discussed in horizon of future treatment of breast cancer.

The emerging role of Slit-Robo pathway in gastric and other gastro intestinal cancers

Gastric cancer remains one of the most common cancers worldwide and one of the leading cause for cancer-related deaths. Due to the high frequency of metastasis, it is still one of the most lethal malignancies in which kinds of signaling pathways are involved in. The Roundabout (ROBO) receptors and their secreted SLIT glycoprotein ligands, which were originally identified as important axon guidance molecules, have implication in the regulation of neurons and glia, leukocytes, and endothelial cells migration. Recent researches also put high emphasis on the important roles of the Slit-Robo pathway in tumorigenesis, cancer progression and metastasis. Herein we provide a comprehensive review on the role of these molecules and their associated signaling pathway in gastric and other gastrointestinal cancers. Improved knowledge of the Slit-Robo signaling pathway in gastric carcinoma will be useful for deep understanding the mechanisms of tumor development and identifying ideal targets of anticancer therapy in gastric carcinoma.

Activation of Slit2-Robo1 signaling promotes liver fibrosis

BACKGROUND & AIMS

The secretory protein Slit2 and its receptor Robo1 are believed to regulate cell growth and migration. Here, we aimed to determine whether Slit2-Robo1 signaling mediates the pathogenesis of liver fibrosis.

METHODS

Serum levels of Slit2 in patients with liver fibrosis were determined by ELISA. Liver fibrosis was induced in wild-type (WT), Slit2 transgenic (Slit2-Tg) and Robo1(+/-)Robo2(+/-) double heterozygotes (Robo1/2(+/-)) mice by carbon tetrachloride (CCl4). The functional contributions of Slit2-Robo1 signaling in liver fibrosis and activation of hepatic stellate cells (HSCs) were investigated using primary mouse HSCs and human HSC cell line LX-2.

RESULTS

Significantly increased serum Slit2 levels and hepatic expression of Slit2 and Robo1 were observed in patients with liver fibrosis. Compared to WT mice, Slit2-Tg mice were much more vulnerable to CCl4-induced liver injury and more readily develop liver fibrosis. Development of hepatic fibrosis in Slit2-Tg mice was associated with a stronger hepatic expression of collagen I and α-smooth muscle actin (α-SMA). However, liver injury and hepatic expression of collagen I and α-SMA were attenuated in CCl4-treated Robo1/2(+/-) mice in response to CCl4 exposure. In vitro, Robo1 neutralizing antibody R5 and Robo1 siRNA downregulated phosphorylation of Smad2, Smad3, PI3K, and AKT in HSCs independent of TGF-β1. R5 and Robo1 siRNA also inhibited the expression of α-SMA by HSCs. Finally, the protective effect of R5 on the CCl4-induced liver injury and fibrosis was further verified in mice.

CONCLUSIONS

Slit2-Robo1 signaling promotes liver injury and fibrosis through activation of HSCs.

Function of Slit/Robo signaling in breast cancer

Slit and Robo are considered tumor suppressors because they are frequently inactivated in various tumor tissue. These genes are closely correlated with CpG hypermethylation in their promoters. The Slit/Robo signaling pathway is reportedly involved in breast cancer development and metastasis. Overexpression of Slit/ Robo induces its tumor suppressive effects possibly by inactivating the β-catenin/LEF/TCF and PI3K/Akt signaling pathways or by altering β-catenin/E-cadherin-mediated cell-cell adhesion in breast cancer cells. Furthermore, loss of Slit proteins or their Robo receptors upregulates the CXCL12/CXCR4 signaling axis in human breast carcinoma. In addition, this pathway regulates the distant migration of breast cancer cells not only by mediating the phosphorylation of the downstream molecules of CXCL12/CXCR4 and srGAPs, such as PI3K/ Src, RAFTK/ Pyk2, and CDC42, but also by regulating the activities of MAP kinases. This review includes recent studies on the functions of Slit/Robo signaling in breast cancer and its molecular mechanisms.

Low Expression of Slit2 and Robo1 is Associated with Poor Prognosis and Brain-specific Metastasis of Breast Cancer Patients

Brain metastasis is a significant unmet clinical problem in breast cancer treatment. It is always associated with poor prognosis and high morbidity. Recently, Slit2/Robo1 pathway has been demonstrated to be involved in the progression of breast carcinoma. However, until present, there are no convincing reports that suggest whether the Slit2/Robo1 axis has any role in brain metastasis of breast cancer. In this study, we investigated the correlation between Slit2/Robo1 signaling and breast cancer brain metastasis for the first time. Our results demonstrated that (1) Invasive ductal carcinoma patients with low expression of Slit2 or Robo1 exhibited worse prognosis and brain-specific metastasis, but not liver, bone or lung. (2) Lower expression of Slit2 and Robo1 were observed in patients with brain metastasis, especially in their brain metastasis tumors, compared with patients without brain metastasis. (3) The interval from diagnosis of breast cancer to brain metastasis and brain metastasis to death were both much shorter in patients with low expression of Slit2 or Robo1 compared with the high expression group. Overall, our findings indicated that Slit2/Robo1 axis possibly be regarded as a significant clinical parameter for predicting brain metastasis in breast cancer patients.

Slit/Robo pathway: a promising therapeutic target for cancer

Axon guidance molecules, slit glycoprotein (Slit) and Roundabout receptor (Robo), have implications in the regulation of physiological processes. Recent studies indicate that Slit and Robo also have important roles in tumorigenesis, cancer progression and metastasis. The Slit/Robo pathway can be considered a master regulator for multiple oncogenic signaling pathways. Herein, we provide a comprehensive review on the role of these molecules and their associated signaling pathways in cancer progression and metastasis. Overall, the current available data suggest that the Slit/Robo pathway could be a promising target for development of anticancer drugs.

Elevated Slit2 Activity Impairs VEGF-Induced Angiogenesis and Tumor Neovascularization in EphA2-Deficient Endothelium

Angiogenic remodeling during embryonic development and in adult tissue homeostasis is orchestrated by cooperative signaling between several distinct molecular pathways, which are often exploited by tumors. Indeed, tumors upregulate proangiogenic molecules while simultaneously suppressing angiostatic pathways to recruit blood vessels for growth, survival, and metastatic spread. Understanding how cancers exploit proangiogenic and antiangiogenic signals is a key step in developing new, molecularly targeted antiangiogenic therapies. While EphA2, a receptor tyrosine kinase (RTK), is required for VEGF-induced angiogenesis, the mechanism through which these pathways intersect remains unclear. Slit2 expression is elevated in EphA2-deficient endothelium, and here it is reported that inhibiting Slit activity rescues VEGF-induced angiogenesis in cell culture and in vivo, as well as VEGF-dependent tumor angiogenesis, in EphA2-deficient endothelial cells and animals. Moreover, blocking Slit activity or Slit2 expression in EphA2-deficient endothelial cells restores VEGF-induced activation of Src and Rac, both of which are required for VEGF-mediated angiogenesis. These data suggest that EphA2 suppression of Slit2 expression and Slit angiostatic activity enables VEGF-induced angiogenesis in vitro and in vivo, providing a plausible mechanism for impaired endothelial responses to VEGF in the absence of EphA2 function.

IMPLICATIONS

Modulation of angiostatic factor Slit2 by EphA2 receptor regulates endothelial responses to VEGF-mediated angiogenesis and tumor neovascularization.

MicroRNA-218 inhibits cell invasion and migration of pancreatic cancer via regulating ROBO1

miRNA-218 is a highlighted tumor suppressor and its underlying role in tumor progression is still unknown. Here, we restored the expression of miRNA-218 in pancreatic cancer to clarify the function and potent downstream pathway of miRNA-218. The expressions of both miRNA-218 and its potent target gene ROBO1 were revealed by RT-PCR and western blotting analysis. Transfection of miRNA-218 precursor mimics and luciferase assay were performed to elucidate the regulation mechanism between miRNA-218 and ROBO1. Cells, stably expressing miRNA-218 followed by forced expression of mutant ROBO1, were established through co-transfections of both lentivirus vector and plasmid vector. The cell migration and invasion abilities were evaluated by migration assay and invasion assay respectively. An increased expression of ROBO1 was revealed in cell BxPC-3-LN compared with cell BxPC-3. Elevated expression of miRNA-218 would suppress the expression of ROBO1 via complementary binding to a specific region within 3'UTR of ROBO1 mRNA (sites 971-978) in pancreatic cancer cells. Stably restoring the expression of miRNA-218 in pancreatic cancer significantly downregulated the expression of ROBO1 and effectively inhibited cell migration and invasion. Forced expression of mutant ROBO1 could reverse the repression effects of miRNA-218 on cell migration and invasion. Consequently, miRNA-218 acted as a tumor suppressor in pancreatic cancer by inhibiting cell invasion and migration. ROBO1 was a functional target of miRNA-218's downstream pathway involving in cell invasion and migration of pancreatic cancer.

Axon guidance factor SLIT2 inhibits neural invasion and metastasis in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) metastasizes by neural, vascular, and local invasion routes, which limit patient survival. In nerves and vessels, SLIT2 and its ROBO receptors constitute repellent guidance cues that also direct epithelial branching. Thus, the SLIT2-ROBO system may represent a key pinch point to regulate PDAC spread. In this study, we examined the hypothesis that escaping from repellent SLIT2-ROBO signaling is essential to enable PDAC cells to appropriate their local stromal infrastructure for dissemination. Through immunohistochemical analysis, we detected SLIT2 receptors ROBO1 and ROBO4 on epithelia, nerves, and vessels in healthy pancreas and PDAC specimens, respectively. SLIT2 mRNA expression was reduced in PDAC compared with nontransformed pancreatic tissues and cell lines, suggesting a reduction in SLIT2-ROBO pathway activity in PDAC. In support of this interpretation, restoring the SLIT2 expression in SLIT2-deficient PDAC cells inhibited their bidirectional chemoattraction with neural cells, and more specifically, impaired unidirectional PDAC cell navigation along outgrowing neurites in models of neural invasion. Restoring autocrine/paracrine SLIT2 signaling was also sufficient to inhibit the directed motility of PDAC cells, but not their random movement. Conversely, RNA interference-mediated silencing of ROBO1 stimulated the motility of SLIT2-competent PDAC cells. Furthermore, culture supernatants from SLIT2-competent PDAC cells impaired migration of endothelial cells (human umbilical vein endothelial cells), whereas an N-terminal SLIT2 cleavage fragment stimulated such migration. In vivo investigations of pancreatic tumors with restored SLIT2 expression demonstrated reduced invasion, metastasis, and vascularization, with opposing effects produced by ROBO1 silencing in tumor cells or sequestration of endogenous SLIT2. Analysis of clinical specimens of PDAC showed that those with low SLIT2 mRNA expression exhibited a higher incidence and a higher fraction of tumor-infiltrated lymph nodes. Taken together, our findings argue that disrupting SLIT2-ROBO signaling in PDAC may enhance metastasis and predispose PDAC cells to neural invasion.

Roundabout receptors

Roundabout receptors (Robo) and their Slit ligands were discovered in the 1990s and found to be key players in axon guidance. Slit was initially described s an extracellular matrix protein that was expressed by midline glia in Drosophila. A few years later, it was shown that, in vertebrates and invertebrates, Slits acted as chemorepellents for axons crossing the midline. Robo proteins were originally discovered in Drosophila in a mutant screen for genes involved in the regulation of midline crossing. This ligand-receptor pair has since been implicated in a variety of other neuronal and non-neuronal processes ranging from cell migration to angiogenesis, tumourigenesis and even organogenesis of tissues such as kidneys, lungs and breasts.

Characterization of the interaction between Robo1 and heparin and other glycosaminoglycans

Roundabout 1 (Robo1) is the cognate receptor for secreted axon guidance molecule, Slits, which function to direct cellular migration during neuronal development and angiogenesis. The Slit2-Robo1 signaling is modulated by heparan sulfate, a sulfated linear polysaccharide that is abundantly expressed on the cell surface and in the extracellular matrix. Biochemical studies have further shown that heparan sulfate binds to both Slit2 and Robo1 facilitating the ligand-receptor interaction. The structural requirements for heparan sulfate interaction with Robo1 remain unknown. In this report, surface plasmon resonance (SPR) spectroscopy was used to examine the interaction between Robo1 and heparin and other GAGs and determined that heparin binds to Robo1 with an affinity of ~650 nM. SPR solution competition studies with chemically modified heparins further determined that although all sulfo groups on heparin are important for the Robo1-heparin interaction, the N-sulfo and 6-O-sulfo groups are essential for the Robo1-heparin binding. Examination of differently sized heparin oligosaccharides and different GAGs also demonstrated that Robo1 prefers to bind full-length heparin chains and that GAGs with higher sulfation levels show increased Robo1 binding affinities.

Immunohistochemical prediction of brain metastases in patients with advanced breast cancer: the role of Rad51

BACKGROUND

There are no clinically useful biomarkers predictive of brain metastases (BM) in breast cancer. In this study, we investigated the correlation between expression of selected proteins in the primary tumor and the risk of BM in patients with metastatic breast cancer (MBC).

METHODS

The study included 198 MBC patients (96 with and 102 without BM). Using tissue microarrays derived from the primary tumor, we assessed by immunohistochemical expression of ER, PR, HER2, Ki-67, CK5/6, EGFR, HER3, CXCR4, Rad51, E-cadherin, and claudin 3 and 4.

RESULTS

Ki-67 ≥14% (hazard ratio [HR] 2.76; P < 0.001), cytoplasmic expression of Rad51 (HR 1.87; P = 0.014) and ER-negativity (HR 1.72; P = 0.029) were associated with increased risk of BM in the multivariate analysis. A three-biomarker profile including ER, Ki-67 and Rad51 vs. other subtypes combined yielded an HR of 4.43 (P < 0.001).

CONCLUSIONS

ER-negativity, cytoplasmic expression of Rad51 and high Ki-67 are associated with increased risk of BM.

SRC points the way to biomarkers and chemotherapeutic targets

The role of Src in tumorigenesis has been extensively studied since the work of Peyton Rous over a hundred years ago. Src is a non-receptor tyrosine kinase that plays key roles in signaling pathways controlling tumor cell growth and migration. Src regulates the activities of numerous molecules to induce cell transformation. However, transformed cells do not always migrate and realize their tumorigenic potential. They can be normalized by surrounding nontransformed cells by a process called contact normalization. Tumor cells need to override contact normalization to become malignant or metastatic. In this review, we discuss the role of Src in cell migration and contact normalization, with emphasis on Cas and Abl pathways. This paradigm illuminates several chemotherapeutic targets and may lead to the identification of new biomarkers and the development of effective anticancer treatments.

miR-218 directs a Wnt signaling circuit to promote differentiation of osteoblasts and osteomimicry of metastatic cancer cells

MicroRNAs (miRNAs) negatively and post-transcriptionally regulate expression of multiple target genes to support anabolic pathways for bone formation. Here, we show that miR-218 is induced during osteoblast differentiation and has potent osteogenic properties. miR-218 promotes commitment and differentiation of bone marrow stromal cells by activating a positive Wnt signaling loop. In a feed forward mechanism, miR-218 stimulates the Wnt pathway by down-regulating three Wnt signaling inhibitors during the process of osteogenesis: Sclerostin (SOST), Dickkopf2 (DKK2), and secreted frizzled-related protein2 (SFRP2). In turn, miR-218 expression is up-regulated in response to stimulated Wnt signaling and functionally drives Wnt-related transcription and osteoblast differentiation, thereby creating a positive feedback loop. Furthermore, in metastatic breast cancer cells but not in normal mammary epithelial cells, miR-218 enhances Wnt activity and abnormal expression of osteoblastic genes (osteomimicry) that contribute to homing and growth of cells metastatic to bone. Thus, miR-218/Wnt signaling circuit amplifies both the osteoblast phenotype and osteomimicry-related tumor activity.

Silencing of miRNA-218 promotes migration and invasion of breast cancer via Slit2-Robo1 pathway

MiRNAs play an important role in regulating tumor migration and invasion, and abnormal expression of miRNAs occurs in various kinds of human cancers. In this essay, it is reported that the level of miRNA-218 decreases in metastatic breast cancer cells, moreover, miRNA-218 suppresses breast cancer cells migration and invasion through binding Robo1 (one of Slit receptors) to its 3'UTR. MiRNA-218 restoration suppresses Robo1 expression and inhibits breast cancer cells invasion and migration. What the results describe is that the function of Robo1 regulated by miRNA-218 may provide a new strategy for inhibiting migration and invasion of breast cancer cells.

Slits affect the timely migration of neural crest cells via Robo receptor

BACKGROUND

Neural crest cells emerge by delamination from the dorsal neural tube and give rise to various components of the peripheral nervous system in vertebrate embryos. These cells change from non-motile into highly motile cells migrating to distant areas before further differentiation. Mechanisms controlling delamination and subsequent migration of neural crest cells are not fully understood. Slit2, a chemorepellant for axonal guidance that repels and stimulates motility of trunk neural crest cells away from the gut has recently been suggested to be a tumor suppressor molecule. The goal of this study was to further investigate the role of Slit2 in trunk neural crest cell migration by constitutive expression in neural crest cells.

RESULTS

We found that Slit gain-of-function significantly impaired neural crest cell migration while Slit loss-of-function favored migration. In addition, we observed that the distribution of key cytoskeletal markers was disrupted in both gain and loss of function instances.

CONCLUSIONS

These findings suggest that Slit molecules might be involved in the processes that allow neural crest cells to begin migrating and transitioning to a mesenchymal type.

Identification of pluripotent and adult stem cell genes unrelated to cell cycle and associated with poor prognosis in multiple myeloma

Gene expression-based scores used to predict risk in cancer frequently include genes coding for DNA replication, repair or recombination. Using two independent cohorts of 206 and 345 previously-untreated patients with Multiple Myeloma (MM), we identified 50 cell cycle-unrelated genes overexpressed in multiple myeloma cells (MMCs) compared to normal human proliferating plasmablasts and non-proliferating bone marrow plasma cells and which have prognostic value for overall survival. Thirty-seven of these 50 myeloma genes (74%) were enriched in genes overexpressed in one of 3 normal human stem cell populations--pluripotent (18), hematopoietic (10) or mesenchymal stem cells (9)--and only three genes were enriched in one of 5 populations of differentiated cells (memory B lymphocytes, T lymphocytes, polymorphonuclear cells, monocytes, osteoclasts). These 37 genes shared by MMCs and adult or pluripotent stem cells were used to build a stem cell score ((SC)score), which proved to be strongly prognostic in the 2 independent cohorts of patients compared to other gene expression-based risk scores or usual clinical scores using multivariate Cox analysis. This finding highlights cell cycle-unrelated prognostic genes shared by myeloma cells and normal stem cells, whose products might be important for normal and malignant stem cell biology.

The dyslexia candidate gene DYX1C1 is a potential marker of poor survival in breast cancer

Background

The dyslexia candidate gene, DYX1C1, shown to regulate and interact with estrogen receptors and involved in the regulation of neuronal migration, has recently been proposed as a putative cancer biomarker. This study was undertaken to assess the prognostic value and therapy-predictive potential of DYX1C1 mRNA and protein expression in breast cancer.

Methods

DYX1C1 mRNA expression was assessed at the mRNA level in three independent population-derived patient cohorts. An association to estrogen/progesterone receptor status, Elston grade, gene expression subtype and lymph node status was analyzed within these cohorts. DYX1C1 protein expression was examined using immunohistochemistry in cancer and normal breast tissue. The statistical analyses were performed using the non-parametric Wilcoxon rank-sum test, ANOVA, Fisher's exact test and a multivariate proportional hazard (Cox) model.

Results

DYX1C1 mRNA is significantly more highly expressed in tumors that have been classified as estrogen receptor α and progesterone receptor-positive. The expression of DYX1C1 among the molecular subtypes shows the lowest median expression within the basal type tumors, which are considered to have the worst prognosis. The expression of DYX1C1 is significantly lower in tumors graded as Elston grade 3 compared with grades 1 and 2. DYX1C1 protein is expressed in 88% of tumors and in all 10 normal breast tissues examined. Positive protein expression was significantly correlated to overall survival (Hazard ratio 3.44 [CI 1.84-6.42]) of the patients but not to any of the variables linked with mRNA expression.

Conclusion

We show that the expression of DYX1C1 in breast cancer is associated with several clinicopathological parameters and that loss of DYX1C1 correlates with a more aggressive disease, in turn indicating that DYX1C1 is a potential prognostic biomarker in breast cancer.

Slit-Robo GTPase-activating proteins are differentially expressed in murine dorsal root ganglia: modulation by peripheral nerve injury

The Slit-Robo GTPase-activating proteins (srGAPs) play an important role in neurite outgrowth and axon guidance; however, little is known about its role in nerve regeneration after injury. Here, we studied the expression of srGAPs in mouse dorsal root ganglia (DRG) following sciatic nerve transection (SNT) using morphometric and immunohistochemical techniques. Reverse transcriptase polymerase chain reaction and Western blot analysis indicated that srGAP1 and srGAP3, but not srGAP2, were expressed in normal adult DRG. Following unilateral SNT, elevated mRNA and protein levels of srGAP1 and srGAP3 were detected in the ipsilateral relative to contralateral L(3-4) DRGs from day 3 to day 14. Immunohistochemical results showed that srGAP1 and srGAP3 were largely expressed in subpopulations of DRG neurons in naïve DRGs. However, after SNT, srGAP3 in neurons was significantly increased in the ipsilateral relative to contralateral DRGs, which peaked at day 7 to day 14. Interestingly, DRG neurons with strong srGAP3 labeling also coexpressed Robo2 after peripheral nerve injury. These results suggest that srGAPs are differentially expressed in murine DRG and srGAP3 are the predominant form. Moreover, srGAP3 may participate in Slit-Robo signaling in response to peripheral nerve injury or the course of nerve regeneration.