CGH analysis of mouse mammary gland tumors from eight genetically-engineered mouse models

Background. Oncogene overexpression in primary cells often triggers the induction of a cellular safeguard response promoting senescence or apoptosis. Secondary cooperating genetic events are generally required for oncogene induced tumorigenesis to overcome these biologic obstacles. We employed array CGH for 8 genetically-engineered mouse models of mammary cancer to identify loci that might harbor genes that enhance oncogene-induced tumorigenesis. Results. Unlike many other mammary tumor models, the MMTV-Myc tumors displayed few CNVs except for amplification of distal mouse chromosome 11 in 80% of the tumors (syntenic to human 17q23-qter often amplified in human breast cancer). Analyses of candidate genes located in this region identified JMJD6 as an epigenetic regulatory gene that cooperates with Myc to enhance tumorigenesis. It suppresses Myc-induced apoptosis under varying stress conditions through inhibition of p19ARF mRNA and protein, leading to reduced levels of p53. JMJD6 binds to the p19ARF promoter and exerts its inhibitory function through demethylation of H4R3me2a. JMJD6 overexpression in MMTV-Myc cell lines increases tumor burden, induces EMT and greatly enhances tumor metastasis. Importantly, we demonstrate that co-expression of high levels of JMJD6 and MYC is associated with poor prognosis for human ER+ breast cancer patients. Conclusions. A novel epigenetic mechanism has been identified for how JMJD6 cooperates with Myc during oncogenic transformation. Combined high expression of Myc and JMJD6 confers a more aggressive phenotype in mouse and human tumors. Given the pleotropic pro-tumorigenic activities of JMJD6, it may be useful as a prognostic factor and a therapeutic target for Myc-driven mammary tumorigenesis. 5-6 mammary gland tumors for each model were subjected to CGH analysis. The same mouse mammary gland tumor models were used as described in Zhu M, Yi M, Kim CH, Deng C, Li Y, Medina D, Stephens RM, Green JE: Integrated miRNA and mRNA expression profiling of mouse mammary tumor models identifies miRNA signatures associated with mammary tumor lineage. Genome Biol 2011, 12:R77.