Background The chromosomes in all living organisms are under constant attack from reactive chemical species that can damage the structural integrity of the DNA. All cells, therefore, devote considerable energy to both preventing and repairing DNA structural abnormalities. Despite this, thousands of DNA lesions still arise daily in each human cell. The majority of these lesions pose no threat to cell viability, but their cumulative effect in a long-lived species influences lifespan and the incidence of age-related diseases such as cancer and neurodegeneration.
Our laboratory investigates the biochemical, molecular and cell biological functions of DNA repair factors in eukaryotic cells and how these factors act to maintain chromosome stability. In particular, we focus on those genes that, when defective, give rise to disorders in humans associated with the premature onset of aging and/or age-associated diseases such as cancer.
In recent years, a major focus has been on characterization of BLM, the protein defective in Bloom's syndrome, a disorder associated with an elevated incidence of cancers of all types. The BLM gene encodes a DNA helicase of the RecQ family, which has important roles in DNA replication and repair via the homologous recombination pathway. We combine analysis of the biochemical properties of BLM with both studies in human cells lacking BLM and studies of SGS1, the budding yeast ortholog of BLM.
Following our recent move from the University of Oxford to the Center for Healthy Aging in the ICMM, we have re-aligned many of our studies to focus on the aging process in humans. Fortunately, chromosome maintenance pathways, including those involving RecQ helicases, are known to impact directly on the rate of human aging. This can be seen most strikingly in human disorders associated with accelerated aging, such as Werner's syndrome (WS). In WS, loss of the RecQ helicase encoded by the WRN gene leads to early onset, multi-organ aging.
Current Project Areas
(i) Biochemical analysis of RecQ helicases We use purified recombinant proteins and defined DNA substrates to investigate the functions of RecQ helicases and their partner proteins in DNA replication and homologous recombination repair. For example, we discovered and re-constituted biochemically a pathway for processing recombination intermediates that requires BLM. This is a process called Holliday junction dissolution.
Model for the role of BLM in the dissolution of double Holliday junctions
ii) Factors required for the regulation of homologous recombination We are using molecular genetics and biochemistry to characterize factors, such as FBH1, that regulate the efficiency of homologous recombination repair.
(iii) Cellular responses to DNA damage We are analyzing the role of selected post-translational modifications of proteins in regulating the cellular response to DNA damage and other stresses occurring during DNA replication.
(iv) Characterization of a novel class of anaphase bridge structure. Through analyzing the localization of BLM, we identified a class of ultra-fine anaphase bridges that link sister chromatids at either centromeres or fragile site loci. This latter class (see photo) have foci for the FANCD2 protein at their termini. FANCD2 is a protein required for the so-called Fanconi anaemia pathway for DNA repair. We are investigating the source of these bridges, and how BLM helps to resolve them. BLM acts alongside a SNF2 family protein called PICH, which we are analyzing biochemically and functionally through the use of PICH-depleted human cells and chicken DT-40 cell knock-out mutants. We are also investigating how phosphorylation of BLM and PICH in mitosis regulates their function.
(v) Use of yeast to study chromosome maintenance pathways Because the pathways we analyze are highly conserved, we can use budding yeast as a model organism to conduct detailed genetic characterization of the BLM ortholog, Sgs1. These studies also enable the use of techniques, such as 2-dimensional DNA replication gel analysis and genome-wide screens to be conducted. For example, we have created a system for site-specific blockade of DNA replication, and are analyzing proteins recruited to the site of blockade and the mechanism by which the blockade is overcome.
The Danish National Research Foundation, The Nordea Foundation Center for Healthy Aging, The European Research Council, The European Union and The Danish Council for Independent Research (Medical Sciences and Natural Sciences).
Drs Guillermo Montoya and Niels Mailand, Center for Protein Research, University of Copenhagen, Denmark.
Dr. Keith Caldecott, Genome Damage and Stability Centre, University of Sussex, UK.
Dr. Chuna Choudhary, Center for Protein Research, University of Copenhagen, Denmark.
Dr Michael Lisby, University of Copenhagen, Denmark.
Drs Claudia and Jiri Lukas, Center for Protein Research, University of Copenhagen, Denmark.
Dr. Erich Nigg, Biocenter, Basel, Switzerland.
Drs Erwin Peterman and Gijs Wuite, Free University of Amsterdam, The Netherlands.
Dr. Nicolas Thomä, FMI, Basel, Switzerland.
Dr Alessandro Vindigni, St. Louis University, USA.
Dr Stephen West, Cancer Research UK, London Research Institute, UK
Dr. Lily Hui-Ching Wang, National Tsing Hua University, Taiwan
Dr Shunichi Takeda, Kyoto University, Kyoto, Japan
Drs Songmin Ying and Huahao Shen, Zhejiang University, China
Wu, L. and Hickson, I.D. (2003) The Bloom's syndrome helicase suppresses crossing over during homologous recombination. Nature, 426, 870-874.
Davies, S.L., North, P.S. and Hickson, I.D. (2007) Role for BLM in replication fork re-start and suppression of origin firing following replicative stress. Nature Structural and Molecular Biology, 14, 677-679.
Chan, K-L., Palmai-Pallag, T., Ying, S. and Hickson, I.D. (2009) Replication stress induces sister-chromatid bridging at fragile site loci in mitosis. Nature Cell Biology. 11, 753-760.
Chu, W-K. and Hickson, I.D. (2009) RecQ helicases: multifunctional genome caretakers. Nature Reviews Cancer 9, 644-654.
Cejka, P., Plank, J.L., Bachrati, C.Z., Hickson, I.D. and Kowalczykowski, S.C. (2010) Rmi1 stimulates decatenation of double Holliday junctions during dissolution by Sgs1-Top3. Nature Structural and Molecular Biology 17, 1377-1383.
Lukas, C., Savic, V., Bekker-Jensen, S., Doil, C., Neumann, B., Pedersen, R.S., Grofte, M., Chan, K-L., Hickson, I.D., Bartek, J. and Lukas, J. (2011) 53BP1 nuclear bodies form around DNA lesions generated by mitotic transmission of chromosomes under replication stress. Nature Cell Biology 13, 243-253.
Mankouri, H.W., Ashton, T.M. and Hickson, I.D. (2011) Holliday junction-containing DNA structures persist in cells lacking Sgs1 or Top3 following exposure to DNA damage. Proc. Natl. Acad. Sci. U.S.A. 108, 4944-4949.
Ying, S., Minocherhomji, S., Chan, K.L., Palmai-Pallag, T., Chu, W.K., Wass, T., Mankouri H.W., Liu, Y. and Hickson, I.D. (2013) MUS81 promotes common fragile site expression. Nature Cell Biology 15, 1001-1007.
Biebricher, A., Hirano, S., Enzlin, J.H., Wiechens, N., Streicher, W.W., Huttner, D., Wang, L.H-H., Nigg, E.A., Owen-Hughes, T., Liu, Y., Peterman, E., Wuite, G.J.L. and Hickson, I.D. (2013) PICH: A DNA translocase Specially Adapted for Processing Anaphase Bridge DNA. Molecular Cell 51, 691-701.
Bocquet, N., Bizard, A.H., Abdulrahman, W., Larsen, N.B., Faty, M., Cavadini, I., Bunker, R., Kowalczykowski, S.C., Cejka, P., Hickson, I.D. and Thomä, N. (2014) Structural and mechanistic insight into Holliday junction dissolution by topoisomerase IIIa and RMI1. Nature Structural and Molecular Biology 21, 261-268.
Larsen, N.B., Sass, E., Suski, C., Mankouri, H.W. and Hickson, I.D. (2014) The E. coli Tus-Ter replication fork barrier causes site-specific DNA replication perturbation in yeast. Nature Communications 5, 3574.
Minocherhomji, S., Ying, S., Bjerregaard, V.A., Bursomanno, S., Aleliunaite, A., Wu, W., Mankouri, H.W., Shen, H., Liu, Y. and Hickson, I.D. (2015) Replication stress activates DNA repair synthesis in mitosis. Nature 528, 286-290.
Nielsen, C.F., Huttner, D., Bizard, A.H., Hirano, S., Li, T-N., Palmai-Pallag, T., Bjerregaard, V.A., Liu, Y., Nigg, E.A., Wang, L.H-C. and Hickson, I.D. (2015) PICH promotes sister chromatid disjunction in mitosis: evidence of functional co-operation with topoisomerase II. Nature Communications 6, 8962.
Ian D. Hickson
The Danish National Research Foundation
The Nordea Foundation Center for Healthy Aging
The European Research Council
The European Union
The Danish Council for Independent Research (Medical Sciences and Natural Sciences).