Despite the many advances made in breast cancer research and treatments, breast cancer remains one of the deadliest diseases plaguing women worldwide. While many findings on genetic mutations and their role in predisposing people to breast cancer have been uncovered, we are just beginning to understand the extent to which epigenetic regulators promote tumorigenic phenotypes, metastasis, and chemotherapeutic resistance. Moreover, new experimental tools offer the ability to address questions we were previously unable to assess. My project takes advantage of a new mouse model to understand the role of a proto-oncogenic, transcriptional co-regulator, TRIM24, in mammary gland development and disease.
We previously reported an unknown binding partner and negative regulator of p53, Tripartite Motif protein 24 (TRIM24). TRIM24 is a multifunctional protein, which acts as a co-regulator of estrogen receptor, a histone reader with tandem PHD and Bromo domains, and a ubiquitin E3-ligase targeting p53 by its RING domain. TRIM24 is over-expressed in human breast cancers, which is correlated with poor patient survival. Previous in cellulo studies in our lab show that TRIM24 over-expression leads to transformation of immortalized human mammary epithelial cells. However, whether over-expression of TRIM24 drives cancer development in vivo remains unknown. To address this gap in our knowledge, we developed a physiologically relevant mouse model to determine if over-expression of TRIM24 promotes tumor development in mammary epithelial cells, consistent with TRIM24 function as an oncogene. We hypothesize that TRIM24 acts as an oncogene in the mammary gland.
To test this hypothesis, we generated transgenic mice, which in the presence of cre-recombinase, conditionally over-express mouse TRIM24 fused to a C-terminal FLAG epitope tag. Our studies reveal that increased expression of Trim24 in the mouse mammary gland is sufficient to drive tumorigenesis by 8 months of age. To facilitate genome wide and targeted therapeutic studies, I developed multiple primary cell lines (tumor and normal mammary epithelia) from each genotype. Colony formation and proliferation assays indicate that over-expression of TRIM24 gives cells a survival and proliferative advantage. RNA-deep sequencing and genome-wide binding profiles of these tumor-derived cell lines reveal that TRIM24 over-expression may be a direct driver of the epithelial-mesenchymal transition (EMT). These data corroborate unpublished in cellulo data from our lab, which implicate TRIM24 as a metastasis-promoting protein through its ability to activate EMT gene expression. Furthermore, we have observed an over-representation of metaplastic breast carcinomas (MpBC), a rare and devastatingly aggressive disease that has an EMT signature, in profiles of tumors generated in our mouse model. We have performed exome-sequencing, RNA-sequencing and immunohistochemistry on mice, which are currently being compared to human MpBC patient samples with the end goal of identifying the common alterations and substantiate TRIM24 as a player in the development of the MpBC phenotype. Finally, we present our mouse model as a useful tool to test the efficacy of potential therapeutics targeting MpBC and other breast cancers.