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 B-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.

Gene alterations in tumor cells that confer the ability to grow under nutrient-and mitogen-deficient conditions constitute a competitive advantage that leads to more-aggressive forms of cancer. The atypical protein kinase C (PKC) isoform, PKC, has been shown to interact with the signaling adapter p62, which is important for Ras-induced lung carcinogenesis. Here we show that PKC-deficient mice display increased Ras-induced lung carcinogenesis, suggesting a new role for this kinase as a tumor suppressor in vivo. We also show that Ras-transformed PKC-deficient lungs and embryo fibroblasts produced more interleukin-6 (IL-6), which we demonstrate here plays an essential role in the ability of Ras-transformed cells to grow under nutrient-deprived conditions in vitro and in a mouse xenograft system in vivo. We also show that PKC represses histone acetylation at the C/EBP␤ element in the IL-6 promoter. Therefore, PKC, by controlling the production of IL-6, is a critical signaling molecule in tumorigenesis.

Overexpression of the Ron receptor tyrosine kinase has recently been shown in a wide variety of human cancers. However, no studies have examined Ron receptor expression or function during prostate tumorigenesis. We report here that Ron is highly expressed in human prostate adenocarcinoma and metastatic lymph nodes compared to normal prostate or benign prostate hyperplasia. Furthermore, we show that Ron is overexpressed in PC-3 and DU145 prostate cancer cell lines, and that levels of angiogenic chemokines produced by prostate cancer cells positively correlates with Ron expression. Knockdown of Ron in PC-3 or DU145 cells results in a significant decrease in angiogenic chemokine production and is associated with decreased activation of the transcription factor NF-kappaB. Moreover, exogenous overexpression of Ron in LNCaP cells is sufficient to induce a significant increase in angiogenic chemokines that can be abrogated by inhibition of NF-kappaB signaling. Given that the function of angiogenic chemokines is important in the development of new blood vessels, we also examined the ability of Ron to modulate endothelial cell migration. Our data show that knockdown of Ron in prostate cancer cells results both in significantly less endothelial cell chemotaxis compared to Ron-expressing cells in vitro as well as in reduced tumor growth and decreased microvessel density following orthotopic transplantation into the prostate in vivo. In total, our data suggest that the Ron receptor is important in modulating prostate tumor growth by modulating angiogenic chemokine production and subsequent endothelial cell recruitment.

The atypical PKC-interacting protein, Par-4, inhibits cell survival and tumorigenesis in vitro, and its genetic inactivation in mice leads to reduced lifespan, enhanced benign tumour development and low-frequency carcinogenesis. Here, we demonstrate that Par-4 is highly expressed in normal lung but reduced in human lung cancer samples. We show, in a mouse model of lung tumours, that the lack of Par-4 dramatically enhances Ras-induced lung carcinoma formation in vivo, acting as a negative regulator of Akt activation. We also demonstrate in cell culture, in vivo, and in biochemical experiments that Akt regulation by Par-4 is mediated by PKCf, establishing a new paradigm for Akt regulation and, likely, for Ras-induced lung carcinogenesis, wherein Par-4 is a novel tumour suppressor.

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