Inhibition of TLR4-Induced IκB Kinase Activity by the RON Receptor Tyrosine Kinase and Its Ligand, Macrophage-Stimulating Protein

Abstract

The RON receptor tyrosine kinase regulates the balance between classical (M1) and alternative (M2) macrophage activation. In primary macrophages, the ligand for Ron, macrophage-stimulating protein (MSP), inhibits the expression of inducible NO synthase, a marker of classically activated macrophages, whereas promoting the expression of arginase I, a marker of alternative activation. Ron−/− mice express increased levels of IL-12, a product of classically activated macrophages, after endotoxin administration, resulting in increased serum IFN-γ levels and enhanced susceptibility to septic shock. In this study, we demonstrate that MSP inhibits LPS-induced IL-12p40 expression, and this inhibition is dependent on the docking site tyrosines in Ron. To further define this inhibition, we examined the effect of Ron on signaling pathways downstream of Ron. We found that MSP does not inhibit the MyD88-independent activation of IFN regulatory factor 3 and production of IFN-β in response to LPS, nor does it inhibit MyD88-dependent TGF-β–activated kinase phosphorylation or MAPK activation in primary macrophages. However, the induction of IκB kinase activity, IκB degradation, and DNA binding of NF-κB after LPS stimulation is delayed in the presence of MSP. In addition, Ron inhibits serine phosphorylation of p65 and NF-κB transcriptional activity induced by LPS stimulation of TLR4. Finally, MSP inhibits the NF-κB–dependent upregulation of the nuclear IκB family member, IκBζ, a positive regulator of secondary response genes including IL-12p40. LPS also induces expression of Ron and an N-terminally truncated form of Ron, Sf-Ron, in primary macrophages, suggesting that the upregulation of Ron by LPS could provide classical feedback regulation of TLR signaling.

The Ron Receptor Tyrosine Kinase Regulates Macrophage Heterogeneity and Plays a Protective Role in Diet-Induced Obesity, Atherosclerosis, and Hepatosteatosis

“…The degree of inflammation at these sites correlates with the ratio of M1/M2 macrophages as broadly defined, and an imbalance of these populations results in disease progression (34)(35)(36). We have previously shown that Ron regulates the balance of inflammatory versus reparative macrophages both in vitro and in vivo (14)(15)(16). In order to determine whether Ron plays a role in the progression of obesity-associated disease, we placed 6-wk-old male mice on an HFD for up to 18 wk.…”

“…NF-kB and Stat1 promote an inflammatory phenotype in macrophages by coordinately inducing inflammatory gene expression. Ron inhibits the activation of NF-kB in response to LPS by targeting the ubiquitination of TNFR-associated factor 6 and the nuclear localization of NF-kB (16,18,19). Ron also inhibits IFN-g-induced Stat1 phosphorylation, associated with the upregulation of the inhibitors of cytokine signaling, suppressor of cytokine signaling 1 and 3 (12,20).…”

“…The Ron receptor tyrosine kinase is expressed on tissue-resident macrophages, where it inhibits pathogen-and cytokine-induced inflammatory gene expression (12)(13)(14)(15)(16)(17). NF-kB and Stat1 promote an inflammatory phenotype in macrophages by coordinately inducing inflammatory gene expression.…”

Inhibition of RON kinase potentiates anti-CTLA-4 immunotherapy to shrink breast tumors and prevent metastatic outgrowth

“…16,26 In macrophages, activation of RON by MSP results in attenuation of immune responses. 29–33 Previously, we and others have shown that host RON signaling negatively regulates antitumor immunity in mouse models of cancer. 31,34,35 Importantly, host RON was critical for conversion of micrometastatic lesions into overt clinical metastases, a step that is thought to be rate-limiting in the deadly metastatic cascade.…”

Whole-exome sequencing identifies MST1R as a genetic susceptibility gene in nasopharyngeal carcinoma

“…MST1R encodes a cell surface receptor for macrophage-stimulating 1 (MST1, also known as MSP) with tyrosine kinase activity. Previous studies show that MST1R plays a critical function in host defense: (i) It is predominantly expressed in the tissue-resident macrophages, which promote tissue repair and inhibit inflammation by repressing the production of proinflammatory molecules induced by pathogens (14)(15)(16)(17) and (ii) MST1R expression is detected in the ciliated epithelial cells in the normal nasal mucosa, and activation of MST1R signaling can increase the ciliary motility to prevent chronic infection (18). Previous studies and our WES data strongly support the role of MST1R as an NPC susceptibility gene.…”