No 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 ...

Previous studies from our laboratory demonstrated that the hepatocyte-specific transcriptional activity of the hepatocyte growth factor-like protein/macrophage stimulating protein (HGFL) promoter is modulated in HepG2 cells by the first 135 base pairs (bp) upstream of the HGFL transcriptional start site. Gel mobility shift and transactivation assays demonstrated that hepatocyte nuclear factor-4 (HNF-4) binds to this region and is responsible, in part, for the liver-specific expression of this gene in HepG2 cells. In an attempt to understand the in vivo mechanism regulating the expression of HGFL, a series of transgenic mice were generated that contained four different regions upstream of the HGFL promoter attached to the coding sequences for chloramphenicol acetyltransferase (CAT). Interestingly, upstream promoter sequences, containing as little as 104 bp upstream of the translational start site, were able to drive reporter expression and protein production specifically in kidney and liver tissue. Strikingly, when the first exon and intron of the HGFL gene was inserted downstream of the 135 bp promoter element, only liver-specific expression was observed. These studies indicate that short sequences upstream of HGFL can drive efficient expression in kidney and liver tissue, and that sequences in the first intron of the HGFL gene contain regulatory elements that direct kidney-specific transcriptional repression in vivo and aid in the proper recapitulation of HGFL expression in mice.