Defining a fundamental role for histone methylation in preventing DNA damage-induced replication catastrophe

点击翻译按钮获取中文摘要

Duplication of the cell's genome is essential for the continuation of life, and this must occur in an efficient and well-timed manner to ensure that each daughter cell gets the correct amount of genetic material. The presence of damage within the cell's DNA can slow or stall the DNA replication machinery, preventing the timely completion of genome duplication. This can result in either cell death, if the unrepaired damage is too great, or transfer of the damage into the daughter cells when the cell divides, which can cause mutations. The accumulation of DNA damage and mutations over time is a fundamental part of the process in which normal healthy cells undergo transformation into tumour cells. It is therefore clear that problems with repairing damage that occurs during DNA replication are a significant cause of human disease and cancer.To prevent genetic damage from persisting, cells have evolved a highly complex network of cellular pathways that recognise and repair DNA damage. One of the most important DNA repair pathways that functions during DNA replication is the Fanconi Anaemia (FA) pathway. The FA pathway is named after the rare human disease, Fanconi Anaemia, which is associated with severe clinical symptoms such as growth retardation, limb malformation, brain abnormalities, progressive bone marrow failure leading to anaemia and an increased predisposition for developing cancer. To date, it has been found that mutations in any one of 16 different genes, all working within the same pathway, can give rise to FA. The study of rare human syndromes, such as FA, has dramatically increased our knowledge about how DNA repair pathways protect the cell from genetic damage, and the consequences when this process fails. However, despite our progress, we still do not fully understand some fundamental aspects of how these pathways function or indeed whether additional factors exist that are yet to be discovered. Indeed, patients suffering from an FA-like disorder have been identified in whom the disease-causing mutation has yet to be discovered.In this respect, we have identified a new protein (PFAP; Putative Fanconi Anaemia Protein) that functions to help repair DNA damage that arises during DNA replication. Interestingly, the defects caused by loss of PFAP are strikingly similar to those observed in cells from FA patients, suggesting that PFAP functions within the FA pathway, and may even be mutated in patients exhibiting FA-like symptoms. In addition, we have discovered that PFAP binds to an enzyme called HMT-1 (Histone Methyltransferase 1), whose primary role is to modify the structure of proteins surrounding DNA (called chromatin) through a process called methylation. Strikingly, loss of HMT-1 gives rise to the same problems as we observed in cells lacking PFAP, indicative of a biochemical link between 'chromatin methylation' and the FA repair pathway.Whilst we know that chromatin methylation can alter the way cells respond to certain types of DNA damage, it is unknown how it affects the FA pathway. Therefore, this application aims to investigate this, using three different approaches. Firstly, we aim to establish where PFAP functions within the FA pathway and ascertain whether PFAP is mutated in cells derived from patients exhibiting an FA-like disorder. Secondly, we aim to understand how PFAP controls DNA replication in the presence of DNA damage. Lastly, we aim to determine if chromatin methylation carried out by PFAP/HMT-1 contributes to how replication-associated DNA damage is repaired.The proposed research on this fundamental and highly conserved aspect of the cellular response to DNA damage has the potential to make a significant long-term impact on improving human health and wellbeing. In addition to furthering our understanding of how normal cells transform into tumour cells, it could also aid the diagnosis of FA-like disorders and/or facilitate the development of new chemotherapeutic drugs to treat cancer.