Homozygous K5Cre transgenic mice have wavy hair and accelerated malignant progression in a murine model of skin carcinogenesis.

Mice with conditional gene deletions have been extremely valuable in allowing investigators to study the genes of interest in a tissue-specific manner. The Cre-loxP recombination system provides a powerful tool to produce targeted rearrangements of particular genes. The keratin 5-Cre recombinase (K5Cre) transgenic mouse line has been used to generate skin specific gene deletions. We found that the K5Cre mice display a unique phenotype when bred to homozygosity. The K5Cre(+/+) mice have a wavy hair coat and curly whiskers. Histologically, the hair follicles appear disoriented. Over time, the K5Cre(+/+) mice develop patches of alopecia. These mice are also runted when compared to wild-type controls. Fostering the K5Cre(+/+) pups to wild-type mothers results in normal weight gain, suggesting a maternal defect in milk production. When the K5Cre(+/+) mammary glands were examined, we not only found a significant decrease in the number of mammary branches in the virgin females, but also a greater number of quiescent alveoli units in the lactating glands. When the K5Cre(+/+) mice were bred to v-Ha-ras (Tg . AC) transgenic mice, the resulting Tg . AC(+/-) K5Cre(+/+) offspring were utilized in a chemically induced skin carcinogenesis model. The mice were treated with 2.5 microg of 12-O-tetradecanoylphorbol-13-acetate (TPA) weekly for 10 wk. No difference was observed in the time to onset of papilloma formation, the number of papillomas and the average papilloma volume between the Tg . AC(+/-) K5Cre(+/+) mice and their corresponding controls. Surprisingly, however, the K5Cre(+/+) papillomas displayed an accelerated tendency to malignant progression; in addition, the frequency of malignant transformation of the papillomas is significantly enhanced. Although the K5Cre(+/+) mice resemble waved-1 and -2 mutants, the molecular basis for the K5Cre(+/+) phenotype is probably different. In conclusion, we discovered a unique phenotype associated with the K5Cre(+/+) transgenic line.

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

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-gamma 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-gamma 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.

Mammary-specific Ron receptor overexpression induces highly metastatic mammary tumors associated with beta-catenin activation.

Activated growth factor receptor tyrosine kinases (RTK) play pivotal roles in a variety of human cancers, including breast cancer. Ron, a member of the Met RTK proto-oncogene family, is overexpressed or constitutively active in 50% of human breast cancers. To define the significance of Ron overexpression and activation in vivo, we generated transgenic mice that overexpress a wild-type or constitutively active Ron receptor in the mammary epithelium. In these animals, Ron expression is significantly elevated in mammary glands and leads to a hyperplastic phenotype by 12 weeks of age. Ron overexpression is sufficient to induce mammary transformation in all transgenic animals and is associated with a high degree of metastasis, with metastatic foci detected in liver and lungs of >86% of all transgenic animals. Furthermore, we show that Ron overexpression leads to receptor phosphorylation and is associated with elevated levels of tyrosine phosphorylated beta-catenin and the up-regulation of genes, including cyclin D1 and c-myc, which are associated with poor prognosis in patients with human breast cancers. These studies suggest that Ron overexpression may be a causative factor in breast tumorigenesis and provides a model to dissect the mechanism by which the Ron induces transformation and metastasis.