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.

Macrophage-mediated RON signaling supports breast cancer growth and progression through modulation of IL-35.

Tumor associated macrophages (TAMs) play a major role in regulating mammary tumor growth and in directing the responses of tumor infiltrating leukocytes in the microenvironment. However, macrophage-specific mechanisms regulating the interactions of macrophages with tumor cells and other leukocytes that support tumor progression have not been extensively studied. In this study, we show that the activation of the RON receptor tyrosine kinase signaling pathway specifically in macrophages supports breast cancer growth and metastasis. Using clinically relevant murine models of breast cancer, we demonstrate that loss of macrophage RON expression results in decreases in mammary tumor cell proliferation, survival, cancer stem cell self-renewal, and metastasis. Macrophage RON signaling modulates these phenotypes via direct effects on the tumor proper and indirectly by regulating leukocyte recruitment including macrophages, T-cells, and B-cells in the mammary tumor microenvironment. We further show that macrophage RON expression regulates the macrophage secretome including IL-35 and other immunosuppressive factors. Overall, our studies implicate activation of RON signaling in macrophages as a key player in supporting a thriving mammary pro-tumor microenvironment through novel mechanisms including the augmentation of tumor cell properties through IL-35.

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.