Biology subjects

Tamburri, S.

Publications and source records attributed to Tamburri, S..

4 recordsLinked to original sources

bioRxiv2023

Structural basis of histone H2A lysine 119 deubiquitination by Polycomb Repressive Deubiquitinase BAP1/ASXL1

The maintenance of gene expression patterns during metazoan development is achieved by the actions of Polycomb group (PcG) complexes. An essential modification marking silenced genes is monoubiquitination of histone H2A lysine 119 (H2AK119Ub) deposited by the E3 ubiquitin ligase activity of the non-canonical Polycomb Repressive Complex 1. The Polycomb Repressive Deubiquitinase (PR-DUB) complex cleaves monoubiquitin from histone H2A lysine 119 (H2AK119Ub) to restrict focal H2AK119Ub at Polycomb target sites and to protect active genes from aberrant silencing. BAP1 and ASXL1, subunits that form active PR-DUB, are among the most frequently mutated epigenetic factors in human cancers, underscoring their biological importance. How PR-DUB achieves specificity for H2AK119Ub to regulate Polycomb silencing is unknown, and the mechanisms of most of the mutations in BAP1 and ASXL1 found in cancer have not been established. Here we determine a cryo-EM structure of human BAP1 bound to the ASXL1 DEUBAD domain in complex with a H2AK119Ub nucleosome. Our structural, biochemical, and cellular data reveal the molecular interactions of BAP1 and ASXL1 with histones and DNA that are critical for remodeling the nucleosome and thus establishing specificity for H2AK119Ub. These results further provide a molecular explanation for how >50 mutations in BAP1 and ASXL1 found in cancer can dysregulate H2AK119Ub deubiquitination, providing new insight into understanding cancer etiology. One Sentence SummaryWe reveal the molecular mechanism of nucleosomal H2AK119Ub deubiquitination by human BAP1/ASXL1.

biochemistry↗

bioRxiv2020

BAP1 activity regulates PcG occupancy and global chromatin condensation counteracting diffuse PCGF3/5-dependent H2AK119ub1 deposition

BAP1 is recurrently mutated or deleted in a large number of diverse cancer types, including mesothelioma, uveal melanoma and hepatocellular cholangiocarcinoma. BAP1 is the catalytic subunit of the Polycomb Repressive De-Ubiquitination complex (PR-DUB) which removes PRC1 mediated H2AK119ub1. We and others have shown that H2AK119ub1 is essential for maintaining transcriptional repression and contributes to PRC2 chromatin recruitment. However, the precise relationship between BAP1 and PRC1 remains mechanistically elusive. Using embryonic stem cells, we show that a major function of BAP1 is to restrict H2AK119ub1 deposition to target sites. This increases the stability of PcG complexes with their targets and prevents diffuse accumulation of H2AK119ub1 and H3K27me3 modifications. Loss of BAP1 results in a broad increase in H2AK119ub1 levels that are primarily dependent on PCGF3/5-PRC1 complexes with a mechanism that is reminiscent of X-chromosome inactivation. Increased genome-wide H2AK119ub1 levels titrates away PRC2 from its targets and stimulates diffuse H3K27me3 accumulation across the genome. This decreases the activity of PcG repressive machineries at physiological targets and induces a general compaction of the entire chromatin. Our findings provide evidences for a unifying model that resolves the apparent contradiction between BAP1 catalytic activity and its role in vivo, uncovering molecular vulnerabilities that could be useful for BAP1-related pathologies.

molecular biology↗

bioRxiv2020

Amyloid aggregates accumulate in melanoma metastasis driving YAP mediated tumor progression

Melanoma progression is generally associated to increased Yes-associated protein (YAP) mediated transcription. Actually, mechanical signals from the extracellular matrix are sensed by YAP, which activates proliferative genes expression, promoting melanoma progression and drug resistance. Which and how extracellular signals induce mechanotransduction is not completely understood. Herein, by secretome studies, we revealed an extracellular accumulation of amyloidogenic proteins, i.e. premelanosome protein (PMEL), together with proteins that assist amyloids maturation into fibrils. Indeed, we confirmed the presence of amyloid-like aggregates similar to those detected in Alzheimer disease. These aggregates were enriched in metastatic cell lines as well as in human melanoma biopsies, compared to their primitive counterpart. Mechanistically, we proved that beta-secretase (BACE) regulates the maturation of these aggregates and that its inhibition hampers YAP activity. Moreover, recombinant PMEL fibrils induce per se mechanotransduction promoting YAP activation. Finally, BACE inhibition affects cell proliferation and increases drug sensitivity. These results highlight the importance of amyloids for melanoma survival and the potential of beta-secretase inhibitors as new therapeutic approach to metastatic melanoma.

cancer biology↗

bioRxiv2019

Histone H2AK119 Mono-Ubiquitination is Essential for Polycomb-Mediated Transcriptional Repression

The major function of Polycomb group proteins (PcG) is to maintain transcriptional repression to preserve cellular identity. This is exerted by two distinct repressive complexes, PRC1 and PRC2, that modify histones by depositing H2AK119ub1 and H3K27me3, respectively. Both complexes are essential for development and are deregulated in several types of human tumors. PRC1 and PRC2 exist in different variants and show a complex regulatory cross-talk. However, the contribution that H2AK119ub1 plays in mediating PcG repressive functions remains largely controversial. Coupling an inducible system with the expression of a fully catalytic inactive RING1B mutant, we demonstrated that H2AK119ub1 deposition is essential to maintain PcG-target genes repressed in ESC. Loss of H2AK119ub1 induced a rapid displacement of PRC2 activity and a loss of H3K27me3 deposition. This affected both PRC2.1 and PRC2.2 variants and further correlated with a strong displacement and destabilization of canonical PRC1. Finally, we find that variant PRC1 forms can sense H2AK119ub1 deposition, which contributes to their stabilization specifically at sites where this modification is highly enriched. Overall our data place H2AK119ub1 deposition as central hub that mount PcG repressive machineries to preserve cell transcriptional identity.

molecular biology↗