| Popis: |
The Ron receptor tyrosine kinase is a member of Met family of receptor tyrosine kinases. The ligand for Ron is hepatocyte growth factor like-protein (HGFL). Previous studies from our laboratory have shown that Ron overexpression in the mammary epithelium of mice (referred to as the MMTV-Ron) leads to mammary tumors with hundred percent incidence and were associated with a high degree of metastasis to the lung and liver. Mammary tumors from MMTV-Ron mice exhibit elevated levels of beta-catenin and its target genes. However, the requirement of beta-catenin and HGFL in tumor formation and metastatic dissemination has not been directly examined. We show that Ron and beta-catenin are coordinately elevated in human breast cancers. We also show that Ron activation induces the tyrosine phosphorylation of beta-catenin. HGFL, induced Ron activation leads to beta-catenin nuclear localization and transcriptional activity, with tyrosine residues 654 and 670 of beta-catenin being critical for these processes. We also found that HGFL-dependent Ron activation mediates upregulation of the beta-catenin target genes cyclin D1 and c-myc. Finally, we show that genetic ablation of beta-catenin in Ron-expressing breast cancer cells decreases cellular proliferation in vitro, as well as mammary tumor growth and metastasis following orthotopic transplantation into the mammary fat pad. To determine the significance of HGFL in these processes, we examined mammary tumor growth and metastasis in MMTV-Ron expressing mice with or without a targeted deletion of HGFL. Our studies show that HGFL loss significantly delayed mammary tumor initiation in this model. These changes were associated with a decrease in Ron receptor kinase activity based on kinase assays, and a reduction in mammary tumor proliferation. In addition we show for the first time that HGFL is produced in the tumor microenvironment of MMTV-Ron mice. Also blockade of HGFL, using an HGFL neutralizing antibody decreased mammary tumor growth that was associated with decreased levels in the Ron downstream signaling targets cyclin D1 and MAPK activation. Taken together, our data demonstrates that HGFL is required for Ron mediated tumor initiation, growth and metastasis and suggests that the HGFL-Ron-beta-catenin pathway is a potential therapeutic target for breast cancer. |
