Project Funding Details

Genetic mutations targeting epigenetic mechanisms that modify and remodel the chromatin environment at regulatory elements are hallmarks of cancer, with epigenetic regulators representing one of the most frequently mutated families. The Polycomb machinery is the major repressive mechanism active in facultative heterochromatin. Central to this, is the mono-ubiquitination of histone H2A at Lysine 119 (H2Aub1), deposited by different forms of the Polycomb Repressive Complex 1 (PRC1) and removed by the PR-DUB complex. H2Aub1 levels are kept in check by these opposing activities with high biochemical heterogeneity through mechanisms that are poorly understood. Both activities are essential for development but do not fully display simple antagonistic phenotypes. We found that BAP1 mutated tumors and SS18-SSX driven SS represent two distinct oncogenic conditions in which H2Aub1plays a crucial role. In both cases the etiological mutations result in profound reshaping of the epigenome affecting cell transcriptional identity. This places H2Aub1 deposition and its homeostatic regulation in a central position in sustaining cancer development. Since general inhibition of PRC1 activity affects general cell viability, targeting specific forms (sub-complexes) of PRC1 could become an attractive strategy. However, we lack knowledge about the role played by the high degree of biochemical complexity that govers these activities and the underling molecular details involved in sustaining cancer development. Despite the composition of these ensembles have been characterized, very little is known about the biochemical features that govern their assembly, sustain their targeting to chromatin and enzymatic activity under physiological and pathological conditions. This information is essential to comprehend their activity and become crucial for designing new therapeutic strategies. This project aims to uncover the mechanisms that connect PcG repression to deposition of H2Aub1 in two distinct oncogenic conditions in which H2Aub1 homeostasis is disrupted: i) the frequent mutations of the tumor suppressor BAP1 - the catalytic activity of PR-DUB - reported in several cancer types; and ii) in presence of an aberrant reading of H2Aub1 modified nucleosomes by the expression of the SS18-SSX oncogenic fusion protein that drives Synovial Sarcoma (SS) development. The project will define the critical role played by PRC1 in sustaining both BAP1 mutated and SS cancer development. The project will characterize the biochemical properties of PR-DUB and PRC1 macromolecular ensembles, determining their topological assembly. We will use these biochemical information to uncover at genome-wide level the mechanisms that connect PRC1 activity with oncogenic H2Aub1 upon BAP1 loss and SS18-SSX fusion expression to uncover mechanisms of activity and associated molecular vulnerabilities. This project will provide deep molecular understanding about a central activity that sustain the oncogenic mechanisms driving the development of both BAP1-mutated and SS18-SSX tumors and their link with PRC1 activity. This information will uncover new molecular vulnerabilities and set the basis for the potential design of new therapeutic interventional projects. The project will provide unprecedented molecular understanding of the role played by PRC1 in regulating the oncogenic activities in the context of BAP1-null tumors and Synovial Sarcomas, uncovering structural and functional vulnerabilities that could be used to design new strategies for cancer therapy.