Elucidating the Mechanisms and Regulation of TCOF1 in the Pathogenesis of Breast Cancer

Description

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer for which chemotherapy is the main treatment option. Unfortunately, chemotherapeutic agents usually have high toxicity in patients. Therefore, there is an urgent clinical need to identify novel therapeutic targets for TNBC. It has been shown recently that super-enhancers play an important role in upregulating the expression of cancer driver genes. However, an understanding of super-enhancers in different subtypes of breast cancer, and their functional significance in tumorigenesis, are lacking. Using a bioinformatics approach, we have uncovered TNBC-specific super-enhancers and genes regulated by these elements. In our preliminary studies, deletion of the putative super-enhancer of a nucleolar phosphoprotein TCOF1 by Crispr/Cas9 resulted in significant decrease of TCOF1 expression, providing the first evidence of a gene regulated by a breast tumor subtype-specific super-enhancer. The role of TCOF1 in the pathogenesis of cancer has not been identified. This project is based on the premise that TCOF1 is overexpressed in 28% of TNBC, and upregulation of TCOF1 is a predictor of poor survival in breast cancer patients. In our preliminary studies, inducible knockout of TCOF1 reduces colony formation, spheroid growth in 3D culture, as well as tumor growth in xenograft models. Mechanistically, our data also suggest that TCOF1 plays an important role in the methylation of rRNA, which may confer selectivity for translating subpools of transcripts. Interestingly, our in silico analysis uncovered a putative Akt phosphorylation site (S1350) on TCOF1. We further showed that phosphorylation of TCOF1 in TNBC cells is inhibited by Akt inhibitors. Together with our previous studies which indicated a specific function of Akt3 in TNBC growth, we hypothesize that super-enhancer-driven overexpressed TCOF1 is phosphorylated by Akt3, and TCOF1 in turn induces translational reprogramming and TNBC growth. This application has three specific aims. Aim 1: We will examine the role of TCOF1 in promoting translation of a subset of transcripts that confer growth and survival advantages for TNBC cells. Aim 2: We will elucidate the regulation of TCOF1 by subtype-specific super-enhancer in tumor lines as well as in clinical samples. We also propose to identify TCOF1 as a novel Akt3 substrate. Aim 3: The physiological relevance of super-enhancer-driven overexpression of TCOF1 in TNBC growth and survival will be examined using xenograft models. By collaborating with a team of experts in bioinformatics, epigenetics and molecular profiling of clinical tumors, I am confident that these proposed studies will further advance our understanding of TCOF1 signaling in TNBC tumorigenesis at the molecular, cellular andin vivolevels. They will also address the unexplored role of subtype-specific super-enhancers in breast cancer. Importantly, by identifying TCOF1 as a novel Akt3-specific substrate, our study will be beneficial for the development of new therapeutic intervention against TNBC.