Ian Cowell

Institute for Cell and Molecular Biosciences

Newcastle University

E-mail i.g.cowell@ncl.ac.uk

 

 

Research Interests - Chromosomes, chromatin dynamics and genome stability.

The genetic material of eukaryotic cells is organized into chromosomes. These highly organized but dynamic structures support the stable maintenance and faithful replication of the genome, while at the same time permitting transcription and the execution of genetic programs. How these processes occur and how they are coordinated are fundamental questions in modern biology, with great significance for the understanding of conditions such as cancer and aging.

Mechanisms of chromosomal translocation in leukaemia.

Therapy-related leukaemia is a rare but unfortunate side effect of otherwise successful treatment for primary cancers using DNA damage-inducing anti-cancer drugs. Leukaemia cells from these cases display chromosome aberrations, including characteristic recurrent chromosome translocations, and these genetic lesions are thought to be causative or at least early contributory events in the generation of  these leukaemias. How and why recurrent translocations occur in therapy-related and de novo leukaemia is unknown, but the mechanism presumably involves chromosome breakage and incorrect rejoining. To better understand this process we are using interphase in situ hybridization (iFISH) and immunological techniques to probe the chromosome and chromatin dynamics of the regions involved. This work is carried out in Prof. Caroline Austin's laboratory as part of a Leukaemia and Lymphoma Research program grant. 

Biology of topoisomerase II-mediated DNA damage.

Topoisomerase II is an essential enzyme that allows the passage of one DNA duplex through another. This involves an enzyme-bridged DNA double-strand break (DSB) which is normally transient and which is re-ligated after the passage of the second duplex. This enzyme-bridged break is stabilized by topoisomerase II poisons, and the resultant topoisomerase II-DNA complexes and DSBs account for the cytotoxic properties of the drugs. Topoisomerase poisons such as etoposide, epirubicin, mitoxantrone and mAMSA are of great clinical importance and are widely used in cancer therapy. Stabilised covalent topoisomerase II-DNA complexes can be repaired by the cell in a process that usually ends in the non homologous end joining (NHEJ) DNA double-strand break pathway. We are investigating the steps required before NHEJ can reseal the topoisomerase-induced break, using amongst others the TARDIS assay to quantify topoisomerase adducts in genomic DNA (14)

Changes in chromatin and nuclear organization associated with DNA damage and genome stability.

The histone variant H2A.X is rapidly phosphorylated after cellular exposure to DNA-damaging agents such as ionizing radiation or the topoisomerase poison etoposide, resulting in chromatin domains enriched for phosphorylated H2A.X (gammaH2AX) around sites of double-strand DNA breaks. I previously showed that heterochromatin is a barrier to H2AX phosphorylation (10) and work subsequently published in Molecular Cell and Nature has confirmed this, showing that removal of the heterochromatin protein HP1 is a necessary part of the DNA damage response. Histone deacetylase inhibitors (HDACIs) cause histone hyperacetylation and alter the properties of heterochromatin relieving the block to H2AX phosphorylation. DNA topoisomerase II poisons such as etoposide are mainstream cytotoxic anticancer drugs, and recently it has been shown that their cytotoxic effects can be potentiated by HDACIs. In Professor Austin's laboratory we are interested in the interactions between histone deacetylase inhibitors, DNA topoisomerase II poisons and heterochromatin with the aim of better understanding the action of this class of drugs.We have recently shown that HDACIs cause a redistribution of topoisomerase II beta from heterochromatin to euchromatin in mouse cells and a change in the genomic distribution topoisomerase-mediated DNA damage (13).

Targeting DNA-repair proteins as a means to improve the efficacy of anti-cancer treatments.

I contributed to work validating the PIKK kinases DNA-PKcs and ATM as drug targets for anti-cancer therapies (7,8 & 12) and with Drs Durkacz and Wilmore in the NICR at Newcastle on an LLR-funded project to determine the role of DNA damage-inducible kinases in the cellular responses to nucleoside analogues used in leukaemia therapy (12).

Histone lysine methylation and the function of chromodomain proteins.

Work I started at Newcastle and then continued at the Babraham and the Roslin Institutes focused on histone modifications and the function of chromodomain proteins (2-4). Chromodomain proteins, particularly the heterochromatin protein HP1 bind to, and form the “readout” for modifications including trimethylation of histone H3 at lysine 9. I was amongst the first to report the evolutionarily widespread occurrence of chromatin domains enriched for histone H3 trimethylated at lysine 9, and the association of this epigenetic modification with heterochromatin and a transcriptionally silent state (5). Current work includes studying the relationship between the epigenetic status of genomic regions and their response to DNA damage induced by agents such as topoisomerase II poisons or ionizing radiation (13) (see above).

 

Selected Publications

14. Cowell, I. G., Tilby, M. and Austin, C. A. (2011) An overview of the visualisation and quantitation of low and high MW DNA adducts using the trapped in agarose DNA immunostaining (TARDIS) assay. Mutagenesis 26 253-260.

13. Cowell, I. G., Papaergiorgio, N., Padget, K., Watter, G. P. and Austin, C. A. (2011) Histone deacetylase inhibition redistributes topoisomerase IIβ from heterochromatin to euchromatin. Nucleus 2 61-71.

12. Willmore, E., Elliott, S.L., Mainou-Fowler, T., Summerfield, G.P., Jackson, G.H., O'Neill, F., Lowe, C., Carter, A., Harris, R., Pettitt, A.R.,Cano-Soumillac, C.,Griffin, R. J., Cowell, I. G., Austin, C. A. and Durkacz, B. W. (2008). DNA-dependent protein kinase is a therapeutic target and an indicator of poor prognosis in B-cell chronic lymphocytic leukemia. Clin Cancer Res 14, 3984-3992.

11. Toyoda, E., Kagaya, S., Cowell, I.G., Kurosawa, A., Kamoshita, K., Nishikawa, K., Iiizumi, S., Koyama, H., Austin, C.A., and Adachi, N. (2008). NK314, a topoisomerase II inhibitor that specifically targets the alpha isoform. J Biol Chem 283, 23711-23720.

10. Cowell, I.G., Sunter, N.J., Singh, P.B., Austin, C.A., Durkacz, B.W., and Tilby, M.J. (2007). gammaH2AX foci form preferentially in euchromatin after Ionising-radiation. PLoS ONE 2, e1057.

9. Leontiou, C., Watters, G.P., Gilroy, K.L., Heslop, P., Cowell, I.G., Craig, K., Lightowlers, R.N., Lakey, J.H., and Austin, C.A. (2007). Differential selection of acridine resistance mutations in human DNA topoisomerase IIbeta is dependent on the acridine structure. Mol Pharmacol 71, 1006-1014.

8. Zhao, Y., Thomas, H.D., Batey, M.A., Cowell, I.G., Richardson, C.J., Griffin, R.J., Calvert, H.A., Newell, D.R., Smith, G.C.M., and Curtin, N.J. (2006). Preclinical evaluation of a potent novel DNA-dependent protein kinase (DNA-PK) inhibitor, NU7441. Cancer Res 66, 5354-5362.

7. Cowell, I.G., Durkacz, B.W., and Tilby, M.J. (2005). Sensitization of breast carcinoma cells to ionizing radiation by small molecule inhibitors of DNA-dependent protein kinase and ataxia telangiectsia mutated. Biochem Pharmacol 71, 13-20.

6. Brown, J.P., Singh, P.B., and Cowell, I.G. (2003). Composite cis-acting epigenetic switches in eukaryotes: lessons from Drosophila Fab-7 for the Igf2-H19 imprinted domain. Genetica 117, 199-207.

5. Cowell, I.G., Aucott, R., Mahadevaiah, S.K., Burgoyne, P.S., Huskisson, N., Bongiorni, S., Prantera, G., Fanti, L., Pimpinelli, S., Wu, R., et al. (2002). Heterochromatin, HP1 and methylation at lysine 9 of histone H3 in animals. Chromosoma 111, 22-36.

4. Filesi, I., Cardinale, A., van Der, S.S., Cowell, I.G., Singh, P.B., and Biocca, S. (2002). Loss of Heterochromatin Protein 1 (HP1) chromodomain function in mammalian cells by intracellular antibodies causes cell death. J. Cell Sci. 115, 1803-1813.

3. Scholzen, T., Endl, E., Wohlenberg, C., van Der, S.S., Cowell, I.G., Gerdes, J., and Singh, P.B. (2002). The Ki-67 protein interacts with members of the heterochromatin protein 1 (HP1) family: a potential role in the regulation of higher-order chromatin structure. J. Pathol. 196, 135-144.

2.Wang, G., Ma, A., Chow, C.M., Horsley, D., Brown, N.R., Cowell, I.G., and Singh, P.B. (2000). Conservation of heterochromatin protein 1 function. Mol Cell Biol 20, 6970-6983.