ETV4 promotes metastasis in response to activation of PI3-kinase and Ras signaling in a mouse model of advanced prostate cancer

Abstract

Combinatorial activation of PI3-kinase and RAS signaling occurs frequently in advanced prostate cancer and is associated with adverse patient outcome. We now report that the oncogenic Ets variant 4 (Etv4) promotes prostate cancer metastasis in response to coactivation of PI3-kinase and Ras signaling pathways in a genetically engineered mouse model of highly penetrant, metastatic prostate cancer. Using an inducible Cre driver to simultaneously inactivate Pten while activating oncogenic Kras and a fluorescent reporter allele in the prostate epithelium, we performed lineage tracing in vivo to define the temporal and spatial occurrence of prostate tumors, disseminated tumor cells, and metastases. These analyses revealed that though disseminated tumors cells arise early following the initial occurrence of prostate tumors, there is a significant temporal lag in metastasis, which is temporally coincident with the up-regulation of Etv4 expression in primary tumors. Functional studies showed that knockdown of Etv4 in a metastatic cell line derived from the mouse model abrogates the metastatic phenotype but does not affect tumor growth. Notably, expression and activation of ETV4, but not other oncogenic ETS genes, is correlated with activation of both PI3-kinase and Ras signaling in human prostate tumors and metastases. Our findings indicate that ETV4 promotes metastasis in prostate tumors that have activation of PI3-kinase and Ras signaling, and therefore, ETV4 represents a potential target of therapeutic intervention for metastatic prostate cancer. M etastasis is a highly inefficient process that involves multiple steps, including invasion of local stroma, intravasation into the bloodstream and/or lymphatic system, and extravasation into a secondary tissue, which is thought to arise as a consequence of multiple molecular/epigenetic alterations in tumor cells, as well as in the microenvironment of metastatic sites (1-4). Nonetheless, despite its inefficiency, most cancer deaths are due to metastases and our current inability to treat them once they arise. In particular, in prostate cancer, the locally invasive disease has a nearly 100% survival rate, whereas metastatic prostate cancer is very often lethal (5).Recent analyses have identified key molecular pathways that are frequently dysregulated during prostate cancer progression, as a consequence of copy number alterations, chromosomal rearrangements, and other aberrant genetic/epigenetic events (6-10). For example, loss of chromosomal region 8p21 and coincident haploinsufficiency for the NKX3.1 homeobox gene occurs frequently in precursor lesions known as prostatic intraepithelial neoplasia (PIN) and are associated with prostate cancer initiation (11,12). Another early event in prostate tumorigenesis is the formation of the TMPRSS2-ERG rearrangement, which fuses the transmembrane protease TMPRSS2 promoter with the coding region of the ETS transcription factor ERG (13, 14). The TMPRSS2-ERG fusion is highly prevalent in prostate cancer and is associated with disease out...

Loss of Androgen-Regulated MicroRNA 1 Activates SRC and Promotes Prostate Cancer Bone Metastasis

“…We previously showed that RASdependent RAL effector pathway activation in DU145 cells leads to the acquisition of bone metastasis (24). Although RAS mutations are rare in prostate cancer (26,27), RAS pathway activation correlates with prostate cancer progression, as demonstrated by analyses of patient samples for Ras transcriptomic signatures (28,29). Consistent with this, downstream pathway biomarkers of the RAS pathway activation, phospho-ERK and phosphoinositol 3-kinase (PI3K)/phospho-AKT signaling, increase during progression (18).…”

Understanding the temporal sequence of genetic events that lead to prostate cancer progression and metastasis

“…Although NPK cells expressing control and Etv4 shRNAs formed tumors in immunodeficient mice, those that expressed the Etv4 shRNA developed smaller and fewer metastases in the lung and liver. Together, the in vitro and in vivo data obtained in the mouse models, as well as that seen in the gene expression signatures of human tumors, strongly support a role for ETV4 in the metastasis of prostate cancer cells (6).…”

“…However, as the disease progresses and androgen receptor (AR) dependence is lost, these genetic lesions cooperate with signaling pathways, such those mediated by pRB, RAS/RAF, and phosphatidylinositol 3-kinase (PI3K)/PTEN/AKT, which are altered in a more "global" sense to promote metastasis (5). In PNAS, Aytes et al (6) describe the temporal progression and the consequence of molecular activation of the PI3K and RAS signaling pathways during prostate cancer metastasis. Using a unique genetically engineered mouse model of prostate cancer that allows lineage tracing, the authors demonstrate that the spread of tumor cells is an early event that actually occurs well before the onset of metastasis.…”

Relative mRNA expression of prostate-derived E-twenty-six factor and E-twenty-six variant 4 transcription factors, and of uridine phosphorylase-1 and thymidine phosphorylase enzymes, in benign and malignant prostatic tissue

“…It is now well established that PEA3 transcription factors are involved in prostate tumors and Ewing's sarcoma, as well as in other tumors, as a result of chromosomal translocations with ETV4 (8). Among the key features often found to be dysregulated in advanced prostate cancer, the PI3K and Ras pathways are altered in 40% of primary tumors and in 90% of metastatic tumors, and the combined signaling activity of these two pathways promotes the metastasis of prostate cancer through activation of ETV4 (42,43). In a study of breast cancer in humans, a positive association was observed between the overexpression of ETV4 and HER2/neu overexpression, tumor grade and greater recurrence rates (8).…”