The aim or our research is to understand how genome stability is maintained in response to DNA double-strand breaks.
Exposure to ionizing radiation (IR) can cause chromosome breaks, in which both DNA strands are broken. In addition to causing cell death (the desired outcome during radiation therapy) such lesions can also cause chromosomal rearrangements, a hallmark of cancer cells, which can lead to oncogene activation or tumour suppressor loss. We are examining the mechanisms and determinants of DNA double-strand break (DSB) repair in normal cells, and how misrepair can lead to chromosomal rearrangements, genome instability and cancer.
DNA is tightly wrapped up around proteins called histones to form chromatin. We have studied a chromatin mark, (histone H3 methylated on lysine 36), which is frequently lost in human cancers, most notably in more than 50% of high grade pediatric gliomas (childhood brain tumours). From our studies using fission yeast (Schizosaccharomyces pombe) we have found this mark to have an important role in DSB repair. Further, we identified a role for this chromatin mark in human cells in facilitating DSB repair within active genes across the genome and its loss leads to aberrant DSB repair associated with loss of genetic material. These findings are helping us understand how DNA damage can lead to chromosomal rearrangements, thus promoting tumorigenesis.
Further, we have exploited powerful genetic approaches (synthetic lethality) in yeast and human cells to identify drugs, which specifically kill cancer cells that are deficient in this chromatin mark. Using this novel combination of approaches we are now translating our findings into the clinic.
Modulating chromatin through histone methylation orchestrates repair of DNA double-strand breaks. SETD2-dependent trimethylation of histone H3 lysine 36 (H3K36me3) is associated with active genes. Following a DNA double strand break (zigag), this chromatin mark promotes accurate repair by homologous recombination (HR) through recruitment of repair factors to the break-site. In the absence of this chromatin mark these factors are not recruited efficiently and instead the break is repaired by error-prone microhomology-mediated end joining (MMEJ) leading to mutations in active genes.
Tim Humphrey is a senior group leader at the MRC-CRUK Oxford Institute for Radiation Oncology. Tim performed his doctoral studies at the University of Oxford and was an EMBO and HFSP post-doctoral research fellow at Harvard Medical School before returning to the UK to become a group leader at the MRC Genome Stability Unit, Oxfordshire. He was awarded tenure in 2003, and in 2008 he moved to the Gray Institute in Oxford and heads the Chromosome Integrity Group. As Director of Studies, he oversaw the development of the Institute’s graduate studies research programme.
Deepak K Jha, Sophia X Pfister, Timothy C Humphrey, Brian D Strahl. SET-ting the stage for DNA repair, Nat Struct Mol Biol, 2014 vol. 21 (8) pp. 655-7
Pfister,S.X., Ahrabi,S., Zalmas,PL., Sarkar,S., Aymard,F., Bachrati, C.Z., Helleday,T., Legube, G., La Thangue, N.B., Porter, A.C.G., and Humphrey,T. C. SETD2-Dependent Histone H3K36 Trimethylation Is Required for Homologous Recombination Repair and Genome Stability, Cell Reports (2014), View report.
Chen-Chun Pai, Rachel S Deegan, Csenge Gal, Lakxmi Subramanian, Sovan Sarkar, Elizabeth J Blaikley, Carol Walker, Lydia Hulme, Eric Bernhard, Sandra Codlin, Jürg Bähler, Robin Allshire, Simon Whitehall and Timothy C Humphrey(2014). A histone H3K36 chromatin switch coordinates DNA double-strand break repair pathway choice. Nature Communications (5):4091 10.1038/ncomms5091
Elizabeth J. Blaikley, Helen Tinline-Purvis, Torben R. Kasparek, Samuel Marguerat, Sovan Sarkar, Lydia Hulme, Sharon Hussey, Boon-Yu Wee, Rachel S. Deegan, Carol A. Walker, Chen-Chun Pai, Jürg Bähler, Takuro Nakagawa and Timothy C. Humphrey (2014) The DNA damage checkpoint pathway promotes extensive resection and nucleotide synthesis to facilitate homologous recombination repair and genome stability in fission yeast. Nucleic Acids Res 42 (9): 56445-56
Torben R Kasparek, Timothy C Humphrey DNA double-strand break repair pathways, chromosomal rearrangements and cancer. Semin Cell Dev Biol. 2011 Oct;22(8):886-97. Epub 2011 Oct 17.
Sara Ahrabi, PhD Student
Chen-Chun Pai, Postdoctoral Researcher
Sovan Sarkar, Postdoctoral Researcher
Carol Walker, Research Assistant