Short-form Ron receptor is required for normal IFN-γ production in concanavalin A-induced acute liver injury

Abstract

Abrogation of Ron receptor tyrosine kinase function results in defects in macrophage activation and dysregulated acute inflammatory responses in vivo. Several naturally occurring constitutively active alternative forms of Ron have been identified, including from primary human tumors and tumor cell lines. One of these alternative forms, short-form (SF) Ron, is generated from an alternative start site in intron 10 of the Ron gene that eliminates most of the extracellular portion of the receptor and is overexpressed in several human cancers. To test the physiological significance of SF-Ron in vivo, mice were generated that solely express the full-length form of Ron (FL-Ron). Our results show that elimination of the capacity to express SF-Ron in vivo leads to augmented production of IFN-␥ from splenocytes following stimulation ex vivo with either concanavalin A or anti-CD3/T cell receptor monoclonal antibody. Moreover, in a concanavalin A-induced murine model of acute liver injury, FL-Ron mice have increased production of serum INF-␥ and serum alanine aminotransferase levels and worsened liver histology and overall survival compared with wild-type control mice. Taken together, these results suggest for the first time that SF-Ron impacts the progression of inflammatory immune responses in vivo and further support a role for the Ron receptor and its various forms in liver pathophysiology.receptor tyrosine kinases; regulation of cytokine production; animal models of liver injury RECEPTOR TYROSINE KINASES (RTK) play a critical role in multiple biological functions including immune system regulation. The Ron receptor is a member of a distinct family of multifunctional RTKs that also includes c-Met. Activation of Ron and Met results in pleiotropic biological responses, including a set of properties allowing cells to undergo "invasive growth" (4, 13, 33). In addition, Ron receptor activity is critical for proper modulation of inflammatory responses to toxic insults in vivo, including the necroinflammatory hepatic injury in an endotoxin-mediated murine model of acute liver failure (5,11,12,27).When mouse Ron (mRon) cDNA was cloned from hematopoietic stem cells, an alternative 1.9-kb short-form Ron (SF-Ron) transcript was identified in addition to the 4.8-kb full-length Ron (FL-Ron) mRNA transcript (9). SF-Ron is expressed in human lung, ovary, and tissues of the gastrointestinal tract and several human cancers and cancer cell lines; however, the tissue-specific expression of SF-Ron has not been fully characterized (1,7,9,22). The transcription start site for SF-Ron mRNA has been localized to intron 10 of the mRon gene (21, 30), and SF-Ron mRNA encodes a truncated Ron protein that possesses a truncated extracellular domain and the entire transmembrane and cytoplasmic tyrosine kinase domains. SF-Ron displays constitutive tyrosine kinase activity (1, 6), and overexpression of SF-Ron results in loss of an epithelial phenotype and aggressive cell behavior (1). Moreover, mouse strains that express SF-Ron transcript in adult bone ...

Pseudomonas aeruginosa Exotoxin A-Induced Hepatotoxicity: An Animal Model in Rats

“…Therefore, the appearance of IL-10 increase is indicative of hepatocyte recovery. Recently, the treatment of LPS plus PEA, LPS alone, or Con-A resulted in a significant increase in INF-γ in mouse study [4,25]. In our study, a trace amount of INF-γ was detected, but not dose or time dependent, though.…”

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

“…The gene encoding Ron contains an internal promoter that drives expression of an N-terminally truncated form of Ron that lacks the extracellular ligand binding domain but retains the transmembrane and kinase domains (Sf-Ron). The inflammatory defects observed in mice harboring an Sf-Ron–specific deletion support the concept that, like the full-length RON receptor, Sf-Ron also plays a critical role in the regulation of macrophage activation (30). To determine whether LPS regulates the expression of Ron and/or Sf-Ron in macrophages, we stimulated primary peritoneal macrophages with LPS and examined Ron and Sf-Ron expression by real-time PCR (Fig.…”

Ron-Receptor Tyrosine Kinase In Tumorigenesis and Metastasis

“…Recent studies have also suggested that SF-Ron has nonredundant biological functions relative to full-length Ron in the progression of inflammatory immune responses in vivo. These observations suggest that the function of SF-Ron is biologically distinct from that of the fulllength receptor and may participate in tumorigenesis [25].…”

“…Variants of Ron have been identified in both normal and malignant tissues. In mice, short-form (SF-)Ron is naturally expressed in select cells and tissues including expression in the spleen and in splenic T cells, bone marrow, testes, lung, ovary, peritoneal macrophages, and in several hematopoietic cells including stem cells [24,25]. SF-Ron is generated from an alternative start site located in intron 10 of the Ron gene and generates a Ron protein containing only a small extracellular portion along with the transmembrane and intracellular domains.…”

“…A recent report has shown that the expression of full length Ron and SF-Ron may be the result of variations in the methylation patterns within two distinct CpG islands in the Ron proximal promoter, wherein widespread hypermethylation associates with lack of full length Ron expression whereas hypermethylation of the distal island associates with transcriptional activity of SF-Ron [26]. In vivo, SF-Ron confers susceptibility to Friend virus-induced erythroleukemia and SF-Ron kinase activity is required for erythropoietin-independent expansion of erythroid progenitors in response to Friend virus [25,27]. SF-Ron is also expressed in human ovarian and breast cancers as well as in several human cancer cell lines derived from the pancreas, breast, ovary, lung and leukemias [24].…”