Title: Investigation of chromatin-bound CBX2-associated protein complexes in advanced cancer
Funder: The Academy of Medical Sciences

Abstract: This innovative proposal aims to elucidate the chromatin-binding profile and chromatin-bound protein interactions of the epigenetic reader protein, CBX2, in cancer. The study will utilise the cutting-edge techniques such as CUT&RUN-sequencing, quantitative multiplex rapid immunoprecipitation mass spectrometry of endogenous proteins (qPLEX-RIME), and a novel loci-specific proteomics approach (CRISPR affinity purification in situ of regulator elements (CAPTURE)), to determine the oncogenic function of CBX2 and validate its potential as a novel therapeutic target. CBX2 is part of the polycomb repressive complex 1 (PRC1), which is an epigenetic regulator comprising a diverse range of protein sub-units. Different PRC1 compositions regulate distinct transcriptomic profiles in different cell contexts; however, the role of these distinct PRC1 complexes is unknown. CBX2 recognises H3K27me3 marks to direct CBX2-associated PRC1 to target genomic regions. Expression of CBX2 is elevated in numerous cancers and it is most significantly upregulated in aggressive disease; including triple negative breast cancer (TNBC) and castrate resistant prostate cancer (CRPC). In both of these cancer types, CBX2 regulates similar signalling pathways, leading to the hypothesis that CBX2-associated PRC1 has a common oncogenic function in different forms of advanced disease. This study will compare CBX2 DNA-binding and CBX2-associated PRC1 composition in TNBC, CRPC and non-transformed cell lines, as well as breast and prostate patient derived xenograft tissue, to identify the direct CBX2-regulatory profile in different cell contexts, and determine if a common oncogenic CBX2-complex exists. Understanding these aspects of CBX2 functionality are fundamental to determining its potential as a therapeutic target in multiple cancer types.

Lay abstract: Genes within our DNA provide the instructions for producing proteins - which are molecules that carry out life's functions. Epigenetics is a biological mechanism that controls which genes are “switched on” or “switched off” – thereby telling cells which proteins to produce and when. In healthy cells, epigenetics is tightly controlled to ensure that the correct genes are switched on at the right time. In cancer cells, however, the pattern of which genes are switched on/off changes dramatically. We therefore believe that altered epigenetic control plays a key role in cancer development; however, there remains a major knowledge gap in this area. A protein called CBX2, which is involved in epigenetic control, has been found at significantly higher levels in hard-to-treat cancers compared with healthy cells. We know that CBX2 works in tandem with other proteins to regulate epigenetics, but we do not know how it specifically works in cancer. We believe that CBX2, and the proteins it works with, could be targeted with drugs to treat cancer. My research proposal aims to use detailed biochemical analysis to, i) identify which genes CBX2 switches on and off in cancer compared to healthy cells, and ii) identify if there is a difference in the proteins CBX2 works with in cancer compared to healthy cells. Understanding these aspects of CBX2 function will enable us to determine if CBX2 is a genuine therapeutic target, and will help us to identify much needed new therapeutic targets to improve quality of life for cancer patients.

Research activity codes: 2.1 BIOLOGICAL AND ENDOGENOUS FACTORS
Health categories: CANCER AND NEOPLASMS