Ron-receptor tyrosine kinase in tumorigenesis and metastasis

Targeting Receptor Tyrosine Kinases as a Novel Strategy for the Treatment of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) comprises a group of aggressive and heterogeneous breast carcinoma. Chemotherapy is the mainstay for the treatment of triple-negative tumors. Nevertheless, the success of chemotherapeutic treatments is limited by their toxicity and development of acquired resistance leading to therapeutic failure and tumor relapse. Hence, there is an urgent need to explore novel targeted therapies for TNBC. Receptor tyrosine kinases (RTKs) are a family of transmembrane receptors that are key regulators of intracellular signaling pathways controlling cell proliferation, differentiation, survival, and motility. Aberrant activity and/or expression of several types of RTKs have been strongly connected to tumorigenesis. RTKs are frequently overexpressed and/or deregulated in triple-negative breast tumors and are further associated with tumor progression and reduced survival in patients. Therefore, targeting RTKs could be an appealing therapeutic strategy for the treatment of TNBC. This review summarizes the current evidence regarding the antitumor activity of RTK inhibitors in preclinical models of TNBC. The review also provides insights into the clinical trials evaluating the use of RTK inhibitors for the treatment of patients with TNBC.

The Roles of Tumor-Associated Macrophages in Prostate Cancer

The morbidity of prostate cancer (PCa) is rising year by year, and it has become the primary cause of tumor-related mortality in males. It is widely accepted that macrophages account for 50% of the tumor mass in solid tumors and have emerged as a crucial participator in multiple stages of PCa, with the huge potential for further treatment. Oftentimes, tumor-associated macrophages (TAMs) in the tumor microenvironment (TME) behave like M2-like phenotypes that modulate malignant hallmarks of tumor lesions, ranging from tumorigenesis to metastasis. Several clinical studies indicated that mean TAM density was higher in human PCa cores versus benign prostatic hyperplasia (BPH), and increased biopsy TAM density potentially predicts worse clinicopathological characteristics as well. Therefore, TAM represents a promising target for therapeutic intervention either alone or in combination with other strategies to halt the “vicious cycle,” thus improving oncological outcomes. Herein, we mainly focus on the fundamental aspects of TAMs in prostate adenocarcinoma, while reviewing the mechanisms responsible for macrophage recruitment and polarization, which has clinical translational implications for the exploitation of potentially effective therapies against TAMs.

Tumor cell intrinsic RON signaling suppresses innate immune responses in breast cancer through inhibition of IRAK4 signaling

Increasing evidence suggests that cancer cells require both alterations in intrinsic cellular processes and the tumor microenvironment for tumor establishment, growth, and progression to metastatic disease. Despite this, knowledge of tumor-cell intrinsic molecular mechanisms controlling both tumor cell processes as well as the tumor microenvironment is limited. In this study, we provide evidence demonstrating the novel role of RON signaling in regulating breast cancer initiation, progression, and metastasis through modulation of tumor cell intrinsic processes and the tumor microenvironment. Using clinically relevant models of breast cancer, we show that RON signaling in the mammary epithelial tumor cells promotes tumor cell survival and proliferation as well as an immunopermissive microenvironment associated with decreased M1 macrophage, natural killer (NK) cell, and CD8+ T cell recruitment. Moreover, we demonstrate that RON signaling supports these phenotypes through novel mechanisms involving suppression of IRAK4 signaling and inhibition of type I Interferons. Our studies indicate that activation of RON signaling within breast cancer cells promotes tumor cell intrinsic growth and immune evasion which support breast cancer progression and highlight the role of targeting RON signaling as a potential therapeutic strategy against breast cancer.

Prostate Epithelial RON Signaling Promotes M2 Macrophage Activation to Drive Prostate Tumor Growth and Progression

Effective treatment of advanced prostate cancer persists as a significant clinical need as only 30% of patients with distant disease survive to 5 years after diagnosis. Targeting signaling and tumor cell-immune cell interactions in the tumor microenvironment has led to the development of powerful immunotherapeutic agents, however, the prostate tumor milieu remains impermeable to these strategies highlighting the need for novel therapeutic targets. In this study, we provide compelling evidence to support the role of the RON receptor tyrosine kinase as a major regulator of macrophages in the prostate tumor microenvironment. We show that loss of RON selectively in prostate epithelial cells leads to significantly reduced prostate tumor growth and metastasis and is associated with increased intratumor infiltration of macrophages. We further demonstrate that prostate epithelial RON loss induces transcriptional reprogramming of macrophages to support expression of classical M1 markers and suppress expression of alternative M2 markers. Interestingly, our results show epithelial RON activation drives upregulation of RON expression in macrophages as a positive feed-forward mechanism to support prostate tumor growth. Using 3D coculture assays, we provide additional evidence that epithelial RON expression coordinates interactions between prostate tumor cells and macrophages to promote macrophage-mediated tumor cell growth. Taken together, our results suggest that RON receptor signaling in prostate tumor cells directs the functions of macrophages in the prostate tumor microenvironment to promote prostate cancer. IMPLICATIONS: Epithelial RON is a novel immunotherapeutic target that is responsible for directing the macrophage antitumor immune response to support prostate tumor growth and progression.

MST1R (RON) expression is a novel prognostic biomarker for metastatic progression in breast cancer patients

PURPOSE

This study evaluates the prognostic significance of MST1R (RON) expression in breast cancer with respect to disease progression, long-term survival, subtype, and association with conventional prognostic factors.

METHODS

The approach includes interrogation of survival and tumor staging with paired MST1R RNA expression from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets. Protein expression evaluation was performed using immunohistochemistry (IHC) staining of MST1R on breast cancer tissue samples from the Cancer Diagnosis Program Breast Cancer Progression tissue microarray and locally obtained breast tumor tissue samples analyzed with paired survival, metastasis, and subtype.

RESULTS

Data from TCGA (n = 774) show poorer relapse-free survival (RFS) in patients with high MST1R expression (P = 0.32) and no difference in MST1R expression based on tumor stage (P = 0.77) or nodal status (P = 0.94). Patients in the GEO-derived Kaplan-Meier Plotter microarray dataset demonstrate the association of MST1R and poorer overall survival (n = 1402, P = 0.018) and RFS in patients receiving chemotherapy (n = 798, P = 0.041). Patients with high MST1R expression display worse overall survival (P = 0.01) and receiver operator characteristic (ROC) analysis demonstrate the predictive capacity of increased MST1R with early death (P = 0.0017) in IHC-stained samples. Paired IHC-stained breast tumor samples from the primary versus metastatic site show MST1R expression is associated with metastatic progression (P = 0.032), and ROC analysis supports the predictive capacity of MST1R in metastatic progression (P = 0.031). No associations of MST1R with estrogen receptor (ER), progesterone receptor (PR), both ER and PR, HER2 positivity, or triple-negativity were found (P = 0.386, P = 0.766, P = 0.746, P = 0.457, P = 0.947, respectively).

CONCLUSIONS

MST1R expression has prognostic value in breast cancer with respect to survival and metastatic progression. MST1R expression is not associated with tumor stage, nodal status, or subtype.

An exome-wide rare variant analysis of Korean men identifies three novel genes predisposing to prostate cancer

Since prostate cancer is highly heritable, common variants associated with prostate cancer have been studied in various populations, including those in Korea. However, rare and low-frequency variants have a significant influence on the heritability of the disease. The contributions of rare variants to prostate cancer susceptibility have not yet been systematically evaluated in a Korean population. In this work, we present a large-scale exome-wide rare variant analysis of 7,258 individuals (985 cases with prostate cancer and 6,273 controls). In total, 19 rare variant loci spanning 7 genes contributed to an association with prostate cancer susceptibility. In addition to replicating previously known susceptibility genes (e.g., CDYL2, MST1R, GPER1, and PARD3B), 3 novel genes were identified (FDR q < 0.05), including the non-coding RNAs ENTPD3-AS1, LOC102724438, and protein-coding gene SPATA3. Additionally, 6 pathways were identified based on identified variants and genes, including estrogen signaling pathway, signaling by MST1, IL-15 production, MSP-RON signaling pathway, and IL-12 signaling and production in macrophages, which are known to be associated with prostate cancer. In summary, we report novel genes and rare variants that potentially play a role in prostate cancer susceptibility in the Korean population. These observations demonstrated a path towards one of the fundamental goals of precision medicine, which is to identify biomarkers for a subset of the population with a greater risk of disease than others.

Expression of RON in colorectal cancer and its relationships with tumor cell behavior and prognosis

Aims and background

The aims of the current study were to evaluate whether recepteur d'origine nantais (RON) affects tumor cell behavior and oncogenic signaling pathways in colorectal cancer, and to examine the relationship of its expression with various clinicopathological parameters and patient survival.

Methods

Immunohistochemistry, Western blot and RT-PCR were used to detect the expression of the RON gene in human colorectal cancer tissue. To study the biological role of RON in tumor cell behavior and cellular signaling pathways, we used small interfering RNA (siRNA) to knock down RON gene expression in human colorectal cancer cell lines.

Results

Knockdown of RON inhibited the induction of the invasive growth phenotype and the activation of oncogenic signaling pathways including Akt, MAPK and β-catenin. RON overexpression was associated with tumor size, lymphovascular invasion, depth of invasion, lymph node metastasis, distant metastasis, tumor stage and poor survival.

Conclusions

These results suggest that RON overexpression may help in predicting poor clinical outcomes in colorectal cancer.

Methylisoindigo and Its Bromo-Derivatives Are Selective Tyrosine Kinase Inhibitors, Repressing Cellular Stat3 Activity, and Target CD133+ Cancer Stem Cells in PDAC

Indirubin is an active component of the herbal ingredient ‘Danggui Longhui wan’, which was used for the treatment of inflammation and chronic myeloid leukemia in China. The recent study showed its derivative methylisoindigo (also known as meisoindigo) preferentially targeting cancer stem cells (CSCs) in interference with AMPK and LKB1, the cellular metabolic sensors. In this study, we screened the effect of meisoindigo on a panel of 300 protein kinases and found that it selectively inhibited Stat3-associated tyrosine kinases and further confirmed its activity in cell based assays. To gain a deeper insight into the structure–activity relationship we produced 7 bromo-derivatives exhausting the accessible positions on the bisindole backbone except for in the 4-position due to the space limitation. We compared their anti-proliferative effects on tumor cells. We found that 6-bromomeisoindigo showed improved toxicity in company with increased Stat3 inhibition. Moreover, we detected that 6-bromomeisoindigo induced apoptosis of 95% of CD133+ pancreatic cancer cells. Considering that CD133 is a common marker highly expressed in a range of CSCs, our results imply the potential application of 6-bromomeisoindigo for the treatment of CSCs in different types of cancers.

HIV‑1 downregulates the expression and phosphorylation of receptor tyrosine kinase by targeting the NF‑κB pathway

Macrophages are major targets of human immunodeficiency virus (HIV) and can act as long-term reservoirs of the virus. Chronic HIV-1 infection is associated with dysregulated inflammation. Recepteur d'origine nantais (RON) is expressed in tissue resident macrophages and functions to maintain inflammatory homeostasis. The present study aimed to compare the expression of RON on HIV-positive and -negative participants, and to investigate the mechanism by which HIV-1 influences the expression and function of RON in the JLTRG T cell line. The levels of RON and the RON ligand, macrophage-stimulating protein (MSP), in the peripheral blood of HIV-1-positive patients that were receiving (n=22) or not receiving highly active anti-retroviral therapy (HAART) (n=82) and 37 healthy control participants were determined by enzyme-linked immunosorbent assay. Expression of RON and MSP in the JLTRG T cell line was assessed by western blotting and the subcellular location was analyzed by fluorescence microscopy. JLTRG cells were co-cultured with a cell line that stably expresses HIV, H9/HTLV-IIIB, and alterations in the levels of RON and nuclear factor-κB (NF-κB) in JLTRG cells were assessed by western blotting. The expression of RON and MSP were significantly different in the serum of HIV-1- positive patients that were receiving HAART compared with those not receiving HAART (P<0.05) and healthy control patients (P<0.01). RON was detected in JLTRG cells, and was shown to be downregulated by HIV-1 infection. HIV-1 infection of JLTRG cells also reduced NF-κB phosphorylation. Thus, HIV-1 was shown to downregulate the expression and phosphorylation of RON by targeting the NF-κB pathway.

Effect of Recepteur d'Origine Nantais expression on chemosensitivity and tumor cell behavior in colorectal cancer

Recepteur d'Origine Nantais (RON) expression is known to induce oncogenic properties including tumor cell growth, survival, motility, angiogenesis and chemoresistance. In the present study, we evaluated whether RON affects chemosensitivity and oncogenic behavior of colorectal cancer cells and investigated its prognostic value in colorectal cancer. To evaluate the impact of RON on chemosensitivity and tumor cell behavior, we treated colorectal cancer cells with small interfering RNAs specific to RON. This was followed by flow cytometric analyses and migration, Matrigel invasion and endothelial tube formation assays. The expression of RON was investigated by immunohistochemistry in colorectal cancer tissues. TUNEL assay and immunohistochemical staining for CD34 and D2-40 were deployed to determine apoptosis, angiogenesis and lymphangiogenesis. RON knockdown enhanced 5-fluorouracil (FU)-induced apoptosis by upregulating the activities of caspases and expression of proapoptotic genes. Moreover, it enhanced 5-FU-induced cell cycle arrest by decreasing the expression of cyclins and cyclin‑dependent kinases and inducing that of p21. Furthermore, RON knockdown augmented the 5-FU-induced inhibition of invasion and migration of colorectal cancer cells. The β-catenin signaling cascade was blocked by RON knockdown upon 5-FU treatment. RON knockdown also decreased endothelial tube formation and expression of VEGF-A and HIF-1α and increased angiostatin expression. Furthermore, it inhibited lymphatic endothelial cell tube formation and the expression of VEGF-C and COX-2. RON expression was observed to be associated with age, tumor size, lymphovascular and perineural invasion, tumor stage, lymph node and distant metastasis, and poor survival rate. The mean microvessel density value of RON-positive tumors was significantly higher than that of RON-negative ones. These results indicate that RON is associated with tumor progression by inhibiting chemosensitivity and enhancing angiogenesis in colorectal cancer.

Downregulation of Foxc2 enhances apoptosis induced by 5-fluorouracil through activation of MAPK and AKT pathways in colorectal cancer

The chemotherapy drug 5-fluorouracil (5-FU) is fundamental for the treatment of colorectal cancer (CRC); however, drug resistance to 5-FU may occasionally occur. Abnormal expression of Forkhead box C2 gene (Foxc2) has been identified in several human cancers, but the role of Foxc2 in the progression of CRC remains unclear. The present study established a stable Foxc2-short hairpin (sh)RNA cell line, which was confirmed by western blot analysis and quantitative polymerase chain reaction. The Foxc2-shRNA cells were treated with 5-FU and the cell viability was determined by an MTT assay. Western blot analysis was performed to investigate the signaling pathway involved in 5-FU treatment. The present study identified that 5-FU increased the percentage of apoptotic CRC cells among the Foxc2/RNA interference-transfected cells compared with cells transfected with an empty vector. Therefore, the downregulation of Foxc2, induced by 5-FU, may enhance apoptosis by the downregulation of apoptotic factors, including B cell lymphoma-2 and pro-caspase-3, in Foxc2-shRNA CRC cells. Furthermore, the mitogen-activated protein kinase (MAPK) and phosphatidylinositide 3-kinases/protein kinase B (PI3K/AKT) pathways were essential for the sensitization effect of Foxc2 to 5-FU treatment. Overall, these findings reveal the mechanisms behind Foxc2 depletion and 5-FU treatment of CRC and suggest that Foxc2 enhances resistance to apoptosis, induced by 5-FU, through the activation of MAPK and P13K/AKT pathways, and may serve as a valuable clinical prognostic marker for CRC.

Hepatocyte growth factor-like protein is required for prostate tumor growth in the TRAMP mouse model

The Ron receptor is deregulated in a variety of cancers. Hepatocyte growth factor-like protein (HGFL) is the ligand for Ron and is constitutively secreted from hepatocytes into the circulation. While a few recent reports have emerged analyzing ectopic HGFL overexpression in cancer cells, no studies have examined the effect of host-produced HGFL in tumorigenesis. To examine HGFL function in prostate cancer, the TRAMP mouse model, which is predisposed to develop prostate tumors, was utilized. Prostate tumors from TRAMP mice exhibit elevated levels of HGFL, which correlated with upregulation in human prostate cancer. To directly implicate HGFL in prostate tumorigenesis, TRAMP mice deficient in HGFL (HGFL-/-TRAMP+) were generated. HGFL-/- TRAMP+ mice developed significantly smaller prostate tumors compared to controls. Analysis of HGFL-/- tumors revealed reduced tumor vascularization. No differences in cancer cell proliferation were detected between HGFL-/- TRAMP+ and HGFL+/+ TRAMP+ mice. However, a significant increase in cancer cell death was detected in HGFL-/- TRAMP+ prostates which correlated with decreased pro-survival targets. In vitro analysis demonstrated robust STAT3 activation resulting in Bcl2-dependent survival following treatment of prostate cancer cells with HGFL. These data document a novel function for endogenous HGFL in prostate cancer by imparting a critical survival signal to tumor cells.

The DEK oncogene promotes cellular proliferation through paracrine Wnt signaling in Ron receptor-positive breast cancers

Disease progression and recurrence are major barriers to survival for breast cancer patients. Understanding the etiology of recurrent or metastatic breast cancer and underlying mechanisms is critical for the development of new treatments and improved survival. Here, we report that two commonly overexpressed breast cancer oncogenes, Ron (Recepteur d'Origine Nantaise) and DEK, cooperate to promote advanced disease through multipronged effects on β-catenin signaling. The Ron receptor is commonly activated in breast cancers, and Ron overexpression in human disease stimulates β-catenin nuclear translocation and is an independent predictor of metastatic dissemination. Dek is a chromatin-associated oncogene whose expression has been linked to cancer through multiple mechanisms, including β-catenin activity. We demonstrate here that Dek is a downstream target of Ron receptor activation in murine and human models. The absence of Dek in the MMTV-Ron mouse model led to a significant delay in tumor development, characterized by decreased cell proliferation, diminished metastasis and fewer cells expressing mammary cancer stem cell markers. Dek complementation of cell lines established from this model was sufficient to promote cellular growth and invasion. Mechanistically, Dek expression stimulated the production and secretion of Wnt ligands to sustain an autocrine/paracrine canonical β-catenin signaling loop. Finally, we show that Dek overexpression promotes tumorigenic phenotypes in immortalized human mammary epithelial MCF10A cells and, in the context of Ron receptor activation, correlates with disease recurrence and metastasis in patients. Overall, our studies demonstrate that DEK overexpression, due in part to Ron receptor activation, drives breast cancer progression through the induction of Wnt/β-catenin signaling.

Variant RONΔ160 of the RON receptor tyrosine kinase promotes the growth and invasion in vitro and in vivo in gastric cancer cell lines

BACKGROUND

Recepteur d'origine nantais (RON) is a receptor tyrosine kinase whose overexpression has been observed in human gastric cancers. This study aimed to determine whether overexpression of the variant RONΔ160 could induce tumorigenicity of gastric cancer cells in vitro or in vivo, and whether its specific small molecule inhibitor (Compound I) could inhibit the effect of RONΔ160.

METHODS

We constructed human gastric cancer cell line MGC-803 that was stably transfected with a recombinant plasmid expressing RONΔ160, and the effect of RONΔ160 overexpression and macrophage-stimulating protein (MSP) activation on proliferation, migration and invasion abilities of MGC-803 cells were evaluated. Tumor-bearing mice with gastric cancer cells were used to analyze the effects of RONΔ160 overexpression and Compound I on implanted tumor growth.

RESULTS

In vitro, overexpression of RONΔ160 in MGC-803 cells resulted changes to their cell morphology, and promoted cell proliferation, migration and invasion. In addition, overexpression of RONΔ160 increased the proportion of cells in the S phase. The effect of RONΔ160 was significantly enhanced by induction of MSP inducing (p < 0.05). In vivo, RONΔ160 promoted the growth of MGC-803 cells in nude mice, including increased tumor size and weight, and lower tumor incubation period. The Compound I inhibited the tumorigenic abilities of RONΔ160 (p <0.05).

CONCLUSIONS

The results indicate that overexpression of the variant RONΔ160 altered the phenotype and tumorigenicity of MGC-803 cells. Its specific small molecule inhibitor could inhibit the effect of RONΔ160. Therefore, the variant RONΔ160 may become a potential therapeutic target for gastric cancer.

Chrysin inhibits cell invasion by inhibition of Recepteur d'origine Nantais via suppressing early growth response-1 and NF-κB transcription factor activities in gastric cancer cells

Cell invasion is one of crucial reasons for cancer metastasis and malignancy. Recepteur d'origine Nantais (RON) has been reported to play an important role in the cancer cell invasion process. High accumulation and activation of RON has been implicated in gastric adenocarcinoma AGS cells. Chrysin is a naturally occurring phytochemical, a type of flavonoid, which has been reported to suppress tumor metastasis. However, the effects of chrysin on RON expression in gastric cancer are not well studied. In the present study, we examined whether chrysin affects RON expression in gastric cancer, and if so, its underlying mechanism. We examined the effect of chrysin on RON expression and activity, via RT-PCR, promoter study, and western blotting in human gastric cancer AGS cells. Chrysin significantly inhibited endogenous and inducible RON expression in a dose-dependent manner. After demonstrating that Egr-1 and NF-κB are the critically required transcription factors for RON expression, we discovered that chrysin suppressed Egr-1 and NF-κB transcription factor activities. Additionally, the phorbol-12-myristate-13-acetate- (PMA) induced cell invasion was partially abrogated by chrysin and an RON antibody. Our results suggest that chrysin has anticancer effects at least by suppressing RON expression through blocking Egr-1 and NF-κB in gastric cancer AGS cells.

FOXC2 promotes colorectal cancer proliferation through inhibition of FOXO3a and activation of MAPK and AKT signaling pathways

Abnormal expression of FOXC2 has been found in several human cancers. However, the role of FOXC2 in the progression of colorectal cancer (CRC) has not been well characterized. In analysis of 206 CRC specimens, we revealed that both high expression and nuclear localization of FOXC2 were correlated to aggressive characteristics and poor survival of patients with CRC. FOXC2 promoted cell proliferation through activation of MAPK and AKT pathways, subsequently down-regulating p27, up-regulating cyclin D1 and p-FOXO3a. Furthermore, FOXC2 nuclear localization was required for its promotion of cell proliferation. These findings suggest that FOXC2 plays an essential role in CRC progression and may serve as a valuable clinical prognostic marker of this disease.

The Ron receptor tyrosine kinase activates c-Abl to promote cell proliferation through tyrosine phosphorylation of PCNA in breast cancer

Multiple growth pathways lead to enhanced proliferation in malignant cells. However, how the core machinery of DNA replication is regulated by growth signaling remains largely unclear. The sliding clamp proliferating cell nuclear antigen (PCNA) is an indispensable component of the DNA machinery responsible for replicating the genome and maintaining genomic integrity. We previously reported that epidermal growth factor receptor (EGFR) triggered tyrosine 211 (Y211) phosphorylation of PCNA, which in turn stabilized PCNA on chromatin to promote cell proliferation. Here we show that the phosphorylation can also be catalyzed by the non-receptor tyrosine kinase c-Abl. We further demonstrate that, in the absence of EGFR, signaling to PCNA can be attained through the activation of the Ron receptor tyrosine kinase and the downstream non-receptor tyrosine kinase c-Abl. We show that Ron and c-Abl form a complex, and that activation of Ron by its ligand, hepatocyte growth factor-like protein (HGFL), stimulates c-Abl kinase activity, which in turn directly phosphorylates PCNA at Y211 and leads to an increased level of chromatin-associated PCNA. Correspondingly, HGFL-induced Ron activation resulted in Y211 phosphorylation of PCNA while silencing of c-Abl blocked this effect. We show that c-Abl and Y211 phosphorylation of PCNA is an important axis downstream of Ron, which is required for cell proliferation. Treatment with a specific peptide that inhibits Y211 phosphorylation of PCNA or with the c-Abl pharmacological inhibitor imatinib suppressed HGFL-induced cell proliferation. Our findings identify the pathway of Ron-c-Abl-PCNA as a mechanism of oncogene-induced cell proliferation, with potentially important implications for development of combination therapy of breast cancer.

Myeloid-specific expression of Ron receptor kinase promotes prostate tumor growth

Ron receptor kinase (MST1R) is important in promoting epithelial tumorigenesis, but the potential contributions of its specific expression in stromal cells have not been examined. Herein, we show that the Ron receptor is expressed in mouse and human stromal cells of the prostate tumor microenvironment. To test the significance of stromal Ron expression, prostate cancer cells were orthotopically implanted into the prostates of either wild-type or Ron tyrosine kinase deficient (TK(-/-); Mst1r(-/-)) hosts. In TK(-/-) hosts, prostate cancer cell growth was significantly reduced as compared with tumor growth in TK(+/+) hosts. Prostate tumors in TK(-/-) hosts exhibited an increase in tumor cell apoptosis, macrophage infiltration and altered cytokine expression. Reciprocal bone marrow transplantation studies and myeloid cell-specific ablation of Ron showed that loss of Ron in myeloid cells is sufficient to inhibit prostate cancer cell growth. Interestingly, depletion of CD8(+) T cells, but not CD4(+) T cells, was able to restore prostate tumor growth in hosts devoid of myeloid-specific Ron expression. These studies show a critical role for the Ron receptor in the tumor microenvironment, whereby Ron loss in tumor-associated macrophages inhibits prostate cancer cell growth, at least in part, by derepressing the activity of CD8(+) T cells.

EGCG inhibits recepteur d'origine nantais expression by suppressing Egr-1 in gastric cancer cells

Abnormal accumulation and activation of the recepteur d'origine nantais (RON) has been implicated in epithelial tumor carcinogenesis. In the present study, we examined the effect of epigallocatechin-3-gallate (EGCG), the major green tea catechin, on the induction of RON and tumor growth in human gastric cancer. EGCG inhibited phorbol 12-myristate 13-acetate (PMA)-induced RON expression and reduced RON transcriptional activity. However, (-)-epigalloca-techin (EGC), (-)-epicatechin gallate (ECG) and (-)‑epicatechin (EC) did not affect RON expression. Experiments with deleted and site-directed mutagenesis of the RON promoter indicated that Egr-1 binding sites in the RON promoter may be the EGCG‑response element acting as a cis-element in gastric cancer cells. EGCG also inhibited PMA-induced Egr-1 expression and DNA binding in a dose-dependent manner. Furthermore, gastric cancer cells pretreated with PMA showed markedly enhanced invasiveness, which was partially abrogated by EGCG and siRNA-targeted RON and Egr-1. EGCG significantly reduced tumor growth in an in vivo tumor model, whereas RON expression was downregulated. These results suggest that EGCG may exert at least part of its anticancer effect by controlling RON expression through suppression of Egr-1 activation.

Upregulation of recepteur d'origine nantais tyrosine kinase and cell invasiveness via early growth response-1 in gastric cancer cells

Abnormal accumulation and activation of the recepteur d'origine nantais (RON) has been implicated in carcinogenesis of epithelial tumors. RON expression was induced by the tumor promoter, phorbol 12-myristate 13-acetate (PMA), in gastric adenocarcinoma AGS cells. Studies with deleted and site-directed mutagenesis of Egr-1 promoter and with expression vectors encoding Egr-1 confirmed that Egr-1 is essential for RON expression. In addition, AGS cells pretreated with PMA showed remarkably enhanced invasiveness, which was partially abrogated by siRNA-targeted RON and Egr-1. These results suggest that tumor promoter induces RON expression via Egr-1, which, in turn, stimulates cell invasiveness in AGS cells.

The short form of RON is expressed in acute myeloid leukemia and sensitizes leukemic cells to cMET inhibitors

Several receptor tyrosine kinases (TKs) are involved in the pathogenesis of acute myeloid leukemia (AML). Here, we have assessed the expression of the Recepteur d'Origine Nantais (RON) in leukemic cell lines and samples from AML patients. In a series of 86 AML patients, we show that both the full length and/or the short form (sf) of RON are expressed in 51% and 43% of cases, respectively. Interestingly, sfRON is not expressed in normal CD34+ hematopoietic cells and induces part of its oncogenic signaling through interaction with the Src kinase Lyn. sfRON-mediated signaling in leukemic cells also involves mTORC1, the proapoptotic bcl2-family member, BAD, but not the phosphatidylinositol 3-kinase/Akt pathway. Furthermore, the expression of sfRON was specifically downregulated by 5-azacytidine (AZA). Conversely, AZA could induce the expression of sfRON in sfRON-negative leukemic cells suggesting that the activity of this drug in AML and myelodysplastic syndromes could involve modulation of TKs. cMET/RON inhibitors exhibited an antileukemic activity exclusively in AML samples and cell lines expressing sfRON. These results might support clinical trials evaluating cMET/RON inhibitors in AML patients expressing sfRON.

Ron receptor-dependent gene regulation in a mouse model of endotoxin-induced acute liver failure

BACKGROUND

Prior experimentation has shown that loss of the tyrosine kinase (TK) signaling domain of the Ron receptor leads to marked hepatocyte protection in a model of lipopolysaccharide-induced acute liver failure (ALF) in D-galactosamine (GalN)-sensitized mice. The aim of this study was to identify the role of Ron in the regulation of hepatic gene expression.

METHODS

Microarray analyses were performed on liver RNA isolated sequentially from wild-type (WT) and TK-/- mice during the progression of ALF. Gene array data were validated using Western and immunohistochemistry analyses as well as with ex vivo culture systems.

RESULTS

At baseline, 101 genes were differentially expressed between WT and TK-/- livers, which regulate processes involved in hypoxia, proliferation, apoptosis and metabolism. One hour after ALF induction, WT livers exhibited increased cytokine expression compared to TK-/- livers, and after 4 hours, an induction of suppressor of cytokine signaling (SOCS) genes as well as JAK-STAT pathway activation were prominent in TK-/- livers compared to controls.

CONCLUSION

Our studies suggest a novel hepato-protective mechanism in Ron TK-/- mice wherein increased and sustained SOCS production and JAK-STAT activation in the hepatocyte may inhibit the destructive proinflammatory milieu and promote survival factors which blunt hepatic death and the ensuing development of ALF.

Expression of the receptor tyrosine kinase recepteur d'origine nantais and its association with tumor progression in hypopharyngeal cancer

BACKGROUND

The purpose of this study was to investigate expression of recepteur d'origine nantais (RON) in human hypopharyngeal squamous cell carcinoma (SCC) and to determine whether RON affects tumor cell behavior in hypopharyngeal SCC cell line and if this would serve as a target for molecular therapy in a preclinical model.

METHODS

Reverse transcriptase-polymerase chain reaction, immunohistochemistry, Western blotting, cell invasion, migration, proliferation, and apoptosis assays were used to assess alteration of RON expression and its impact to cancer progression in human hypopharyngeal SCC.

RESULTS

Immunoreactivity of RON was observed in hypopharyngeal SCC tissues relative to adjacent normal mucosa in all cases. RON protein expression was significantly increased in metastatic lymph nodes than nonmetastatic lymph nodes by Western blotting. Knockdown of RON resulted in significantly reduced cell invasion, migration, and proliferation in human hypopharyngeal SCC cells. Knockdown of RON enhanced cell apoptosis through activation of caspase 3, caspase 7, and poly ADP-ribose polymerase (PARP).

CONCLUSION

These results indicate that knockdown of RON expression may be associated with the reversal of invasive phenotype in hypopharyngeal SCC.

Knockdown of RON inhibits AP-1 activity and induces apoptosis and cell cycle arrest through the modulation of Akt/FoxO signaling in human colorectal cancer cells

BACKGROUND/AIMS

Altered Recepteur d'Origine nantais (RON) expression transduces signals inducting invasive growth phenotype that includes cell proliferation, migration, matrix invasion, and protection of apoptosis in human cancer cells. The aims of the current study were to evaluate whether RON affects tumor cell behavior and cellular signaling pathways including activator protein-1 (AP-1) and Akt/forkhead box O (FoxO) in human colorectal cancer cells.

METHODS

To study the biological role of RON on tumor cell behavior and cellular signaling pathways in human colorectal cancer, we used small interfering RNA (siRNA) to knockdown RON gene expression in human colorectal cancer cell line, DKO-1.

RESULTS

Knockdown of RON diminished migration, invasion, and proliferation of human colorectal cancer cells. Knockdown of RON decreased AP-1 transcriptional activity and expression of AP-1 target genes. Knockdown of RON activated cleaved caspase-3, -7, -9, and PARP, and down-regulated the expression of Mcl-1, survivin and XIAP, leading to induction of apoptosis. Knockdown of RON induced cell cycle arrest in the G2/M phase of cancer cells by an increase of p27 and a decrease of cyclin D3. Knockdown of RON inhibited the phosphorylation of Akt/FoxO signaling proteins such as Ser473 and Thr308 of Akt and FoxO1/3a.

CONCLUSIONS

These results indicate that knockdown of RON inhibits AP-1 activity and induces apoptosis and cell cycle arrest through the modulation of Akt/FoxO signaling in human colorectal cancer cells.

RON is associated with tumor progression via the inhibition of apoptosis and cell cycle arrest in human gastric cancer

The recepteur d'origine nantais (RON) receptor tyrosine kinase is overexpressed in epithelial cancers, including gastric cancer. The aims of the present study were to evaluate whether RON affects tumor cell behaviors and oncogenic signaling pathways, and to document the relationship of its expression with various clinicopathological parameters in gastric cancer. The biological role of RON in tumor cell behaviors and oncogenic signaling pathways was investigated by using small interfering RNA in gastric cancer cell lines including AGS and MKN28. The expression of RON in gastric cancer tissues was investigated by using reverse transcription polymerase chain reaction and immunohistochemistry. Knockdown of RON suppressed tumor cell migration and invasion in AGS and MKN28, induced apoptosis through modulation of anti-apoptotic and pre-apoptotic genes and induced cell cycle arrest by decreasing cyclin D1, cyclin D3 and CDK4, and by inducing p21 and p27 expression. Signaling cascades, including Akt and mitogen-activated protein kinase (MAPK), were significantly blocked by knockdown of RON. Expression of RON was significantly associated with tumor size, depth of invasion, lymph node metastasis, tumor stage and poor survival. These results indicate that RON is associated with tumor progression via the inhibition of apoptosis and cell cycle arrest in human gastric cancer.

Novel function of transcription factor Nrf2 as an inhibitor of RON tyrosine kinase receptor-mediated cancer cell invasion

Recepteur d' origine nantais (RON), a tyrosine kinase receptor, is aberrantly expressed in human tumors and promotes cancer cell invasion. RON receptor activation is also associated with resistance to tamoxifen treatment in breast cancer cells. Nrf2 is a positive regulator of cytoprotective genes. Using chromatin immunoprecipitation (ChIP) and site-directed mutagenesis studies of the RON promoter, we identified Nrf2 as a negative regulator of RON gene expression. High Nrf2 and low RON expression was observed in normal mammary tissue whereas high RON and low or undetectable expression of Nrf2 was observed in breast tumors. The Nrf2 inducer sulforaphane (SFN) as well as ectopic Nrf2 expression or knock-down of the Nrf2 negative regulator keap1, which stabilizes Nrf2, inhibited RON expression and invasion of carcinoma cells. Consequently, our studies identified a novel functional role for Nrf2 as a "repressor" and RON kinase as a molecular target of SFN, which mediates the anti-tumor effects of SFN. These results are not limited to breast cancer cells since the Nrf2 inducer SFN stabilized Nrf2 and inhibited RON expression in carcinoma cells from various tumor types.

MSP-induced RON activation upregulates uPAR expression and cell invasiveness via MAPK, AP-1 and NF-κB signals in gastric cancer cells

Overexpression of recepteur d'Origine nantais (RON) and urokinase plasminogen activator receptor (uPAR) have been observed in human gastric cancers. However, the interaction between RON and uPAR in gastric cancer is unclear. The present study investigated the effect of macrophage-stimulating protein (MSP, the RON ligand) on uPAR expression and the underlying signal pathways in human gastric cancer AGS cells. uPAR messenger RNA expression was induced by MSP in a time- and concentration-dependent manner. MSP also induced uPAR promoter activity. The introduction of RON-specific small interfering RNA (siRNA) significantly affected the MSP-induced uPAR transcription. Deleted and site-directed mutagenesis studies demonstrated the involvement of the binding sites of transcription factor nuclear factor-kappaB (NF-κB) and activator protein (AP)-1 in the MSP-induced uPAR expression. Studies with expression vectors encoding mutated-type NF-κB signaling molecules and AP-1 decoy confirmed that NF-κB and AP-1 were essential for the MSP-induced uPAR expression. In addition, MSP induced the activation of extracellular signal-regulated kinase-1/2 (Erk-1/2), c-Jun amino terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK). Dominant-negative mutants (K97M and TAM67) and specific inhibitors of Erk-1/2 and JNK were able to suppress the MSP-induced uPAR expression. AGS cells pretreated with MSP showed a remarkably enhanced invasiveness, which was partially abrogated by siRNA-targeted RON and uPAR-neutralizing antibodies. The above results suggest that MSP induces uPAR expression via MAPK, AP-1 and NF-κB signaling pathways and, in turn, stimulates cell invasiveness in human gastric cancer AGS cells.

Identification of a novel series of potent RON receptor tyrosine kinase inhibitors

A novel series of N-(3-fluoro-4-(2-substituted-thieno[3,2-b]pyridin-7-yloxy)phenyl)-1-phenyl-5-(trifluoromethyl)-1H-pyrazole-4-carboxamides targeting RON receptor tyrosine kinase was designed and synthesized. SAR study of the series allowed us to identify compounds possessing either inhibitory activity of RON kinase enzyme in the low nanomolar range with low residual activity against the closely related c-Met or potent dual inhibitory activity against RON and c-Met, with no significant activity against VEGFR2 in both cases.

The Ron receptor tyrosine kinase is not required for adenoma formation in Apc(Min/+) mice

The Ron receptor tyrosine kinase is overexpressed in approximately half of all human colon cancers. Increased Ron expression positively correlates with tumor progression, and reduction of Ron levels in human colon adenocarcinoma cells reverses their tumorigenic properties. Nearly all colon tumors demonstrate loss of the adenomatous polyposis coli (APC) tumor suppressor, an early initiating event, subsequently leading to beta-catenin stabilization. To understand the role of Ron in early stage intestinal tumorigenesis, we generated Apc-mutant (Apc(Min/+)) mice with and without Ron signaling. Interestingly, we report here that significantly more Apc(Min/+) Ron-deficient mice developed higher tumor burden than Apc(Min/+) mice with wild-type Ron. Even though baseline levels of intestinal crypt proliferation were increased in the Apc(Min/+) Ron-deficient mice, loss of Ron did not influence tumor size or histological appearance of the Apc(Min/+) adenomas, nor was beta-catenin localization changed compared to Apc(Min/+) mice with Ron. Together, these data suggest that Ron may be important in normal intestinal tissue homeostasis, but that the expression of this receptor is not required for the formation and growth of adenomas in Apc(Min/+) mice.

The Ron receptor tyrosine kinase positively regulates angiogenic chemokine production in prostate cancer cells

Overexpression of the Ron receptor tyrosine kinase has recently been shown in a wide variety of human cancers. However, no studies have examined Ron receptor expression or function during prostate tumorigenesis. We report here that Ron is highly expressed in human prostate adenocarcinoma and metastatic lymph nodes compared to normal prostate or benign prostate hyperplasia. Furthermore, we show that Ron is overexpressed in PC-3 and DU145 prostate cancer cell lines, and that levels of angiogenic chemokines produced by prostate cancer cells positively correlates with Ron expression. Knockdown of Ron in PC-3 or DU145 cells results in a significant decrease in angiogenic chemokine production and is associated with decreased activation of the transcription factor NF-kappaB. Moreover, exogenous overexpression of Ron in LNCaP cells is sufficient to induce a significant increase in angiogenic chemokines that can be abrogated by inhibition of NF-kappaB signaling. Given that the function of angiogenic chemokines is important in the development of new blood vessels, we also examined the ability of Ron to modulate endothelial cell migration. Our data show that knockdown of Ron in prostate cancer cells results both in significantly less endothelial cell chemotaxis compared to Ron-expressing cells in vitro as well as in reduced tumor growth and decreased microvessel density following orthotopic transplantation into the prostate in vivo. In total, our data suggest that the Ron receptor is important in modulating prostate tumor growth by modulating angiogenic chemokine production and subsequent endothelial cell recruitment.

The Ron receptor tyrosine kinase negatively regulates mammary gland branching morphogenesis

The Ron receptor tyrosine kinase is expressed in normal breast tissue and is overexpressed in approximately 50% of human breast cancers. Despite the recent studies on Ron in breast cancer, nothing is known about the importance of this protein during breast development. To investigate the functional significance of Ron in the normal mammary gland, we compared mammary gland development in wild-type mice to mice containing a targeted ablation of the tyrosine kinase (TK) signaling domain of Ron (TK-/-). Mammary glands from RonTK-/- mice exhibited accelerated pubertal development including significantly increased ductal extension and branching morphogenesis. While circulating levels of estrogen, progesterone, and overall rates of epithelial cell turnover were unchanged, significant increases in phosphorylated MAPK, which predominantly localized to the epithelium, were associated with increased branching morphogenesis. Additionally, purified RonTK-/- epithelial cells cultured ex vivo exhibited enhanced branching morphogenesis, which was reduced upon MAPK inhibition. Microarray analysis of pubertal RonTK-/- glands revealed 393 genes temporally impacted by Ron expression with significant changes observed in signaling networks regulating development, morphogenesis, differentiation, cell motility, and adhesion. In total, these studies represent the first evidence of a role for the Ron receptor tyrosine kinase as a critical negative regulator of mammary development.

Recepteur d'origine nantais tyrosine kinase is a direct target of hypoxia-inducible factor-1alpha-mediated invasion of breast carcinoma cells

Hypoxia-inducible factor-1alpha (HIF-1alpha) overexpression was shown to be associated with invasion and metastasis of tumors and tumor cell lines. The identification of molecular targets that contribute to HIF-1alpha-mediated invasion is under intensive investigation. We have analyzed the role of recepteur d'origine nantais (RON), a tyrosine kinase receptor for macrophage-stimulating protein (MSP) that plays a role in breast cancer cell invasion as one of the molecular targets of HIF-1alpha. Analysis of a panel of breast cancer cell lines indicated a correlation between HIF-1alpha and RON expression. Treatment of HIF-1alpha- and RON-positive breast cancer cells with HIF-1alpha inhibitor, echinomycin, led to the inhibition of HIF-1alpha activity and RON expression. We have identified HIF-1alpha binding site on the RON promoter. Chromatin immunoprecipitation analysis and site-directed mutagenesis of the RON promoter confirmed the binding of HIF-1alpha to RON promoter. HIF-1alpha inhibitor-, echinomycin-, or short hairpin RNA-mediated selective knockdown of HIF-1alpha or HIF-1alpha target RON tyrosine kinase abrogated RON gene expression, and the RON ligand macrophage-stimulating protein mediated invasion of breast cancer cells. Consequently, the data presented herein demonstrated RON as a novel molecular target of HIF-1alpha and suggest a potential therapeutic role for HIF-1alpha or RON tyrosine kinase inhibitors in the blockade of RON tyrosine kinase-mediated invasion of carcinoma cells.

RON receptor tyrosine kinase in human gliomas: expression, function, and identification of a novel soluble splice variant

Malignant gliomas are incurable because of their diffuse infiltration of the surrounding brain. The recepteur d'origine nantais (RON) receptor tyrosine kinase is highly expressed in several epithelial cancer types and mediates tumorigenic, pro-invasive as well as metastatic effects. Analyzing RON expression in human gliomas, we found that different splice variants with known oncogenic activity are expressed in glioblastomas (GBM). In addition, the RON ligand macrophage-stimulating protein (MSP) is secreted by cultured GBM cells. MSP showed no mitogenic effect on GBM cells but displayed significant chemotactic activity for several GBM cell lines. We identified a novel splice variant, RONDelta90, which is generated by a transcript missing exon 6. As a result of a frameshift, translation is terminated in exon 7, resulting in a truncated soluble protein. RONDelta90 transcripts are expressed in normal human brain as well as in low grade astrocytomas but only in approximately 50% of highly malignant astrocytomas. In addition, RONDelta90 is detectable in supernatants of GBM cell lines. We cloned the RONDelta90 cDNA, and purified the recombinant protein from transfected cells. RONDelta90 inhibited MSP-induced phosphorylation of cellular RON and also attenuated basal activation levels. In addition, RONDelta90 inhibited MSP-induced glioma cell migration as well as random motility. To conclude, RONDelta90 is a novel soluble receptor variant with antagonistic activity that may act as a physiological modulator of RON signaling. The expression of several oncogenic RON splice variants in malignant gliomas suggests that these could represent candidate targets for treatment with agents inhibiting RON activity.