HISTONEDDR

ROLE OF HISTONE MODIFICATIONS IN DNA DAMAGE RESPONSE IN MAMMALS

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 Obiettivo del progetto (Objective)

'After DNA damage a signal must be created to recruit DNA repair factors to the lesion. Then the repair machinery needs to gain access to DNA and chromatin should be properly reassembled. DNA assembly with histones to form chromatin creates a physically limits the access to DNA. Alterations of chromatin that do not affect the DNA sequence constitute the epigenetic level of regulation of DNA metabolism. Among them, the post-translational modification of histones can directly regulate chromatin structure and they can also recruit different proteins to DNA serving as signaling and docking points. There is not much information regarding the role of these modifications in DNA damage response (DDR). This project looks forward to gaining insight into the role of histone H3K79 and histone H4K20 methylation in recuiting DNA repair factors. 53BP1 has been proposed to be recruited to the lesions by methylation of H3K79 and/or H4K20, although the mechanism is not still clear. In yeast, Dot1, the enzyme responsible for H3K79 methylation, is required for a normal DDR. As a second objective we would like to analyze the potential modifications of H3K56 in mammalian cells and determine if they have a function in DDR. Also in yeast, it has been described that H3K56 acetylation is necessary for the re-assembly of chromatin after repair. In mammals it seems that methylation of this residue takes place instead of acetylation. However the role of these marks has not been well studied in mammals. We will employ in vitro cell culture to analyze the exposure of these marks after DNA damage, the changes in localization or protein interactions of the enzymes responsible for them and to identify proteins that create or recognize these marks. Additionally KO mice will be used to analyze the physiological relevance of the results in vivo. All these studies are highly relevant to the EU, as they imply the interconnection of two priority fields in EU (both of them have a European Network).'

Introduzione (Teaser)

Histone modifications constitute a well-established epigenetic mechanism that controls gene expression without altering the genetic material. Understanding how these marks on the histones are placed and their functional consequences was the subject of a European study.

Descrizione progetto (Article)

DNA is found in cells associated with proteins known as histones, in the form of chromatin. Although initially envisaged as mere structural components, it is now well established that histones are actively involved in DNA metabolism, transcription and repair. A plethora of histone modifications have been described (methylation, acetylation, and phosphorylation) but their functional role is still under investigation.

Researchers of the EU-funded ?Role of histone modifications in dna damage response in mammals? (HISTONEDDR) proposal focused on SCML2, a poorly described reader of histone modifications. SCML2 is a homologue of the Drosophila Polycomb family of proteins which form complexes implicated in transcriptional repression.

SCML2 interacts with lysine residues of histones H4 or H3, and these modifications have been linked to the DNA damage response. Experimental analysis of the two SCML2 isoforms unveiled structural differences and altered subcellular localisation patterns. One of the isoforms (SCML2B) was shown to regulate cell cycle progression through direct contact with cell-cycle related genes.

The SCML2A isoform contains the chromatin-binding domain. It mediates gene repression by using a combination of RNA binding, methylated lysine recognition and interaction with the Polycomb complex PRC1. Furthermore, both SCML2 isoforms were found to interact with USP7, a specific protease which stabilises members of the histone modification complex PRC1 as well as the tumour suppressor p53 under stress conditions.

Overall, the HISTONEDDR study findings provide the first link between the mammalian Polycomb system and the cell cycle machinery. Both PRC1 and USP7 are implicated in various diseases and in ageing. Project activities bring us a step closer to comprehending the mechanism underlying their pathological impact.