Telomeres and Genome Stability

Research Interests

Telomeres protect the ends of linear eukaryotic chromosomes from being recognized as deleterious DNA double strand breaks (DSBs). Just a single DSB is able to stop cell cycle progression and activate repair processes. In contrast, all telomeres prohibit DNA repair, as it may lead to chromosome-end fusions - a source of genomic instability and a step in tumourigenesis. This fundamental function fades as telomeres get progressively shorter in cells of older people, thus limiting the capacity of tissue renewal and increasing the probability of cancer.
Our aim is to understand how telomeres block DNA repair and, when this function fails, how cells respond to unprotected chromosomes. Using fission yeast as a model system, we plan to identify key players and the mechanisms underlying these events. This way, we hope to provide important insights into the initial stages of cancer formation as well as specific candidate targets for future therapeutic intervention..

Group Members

Clara Reis	Postdoc
	Tel: 21 446 4511
Tiago Carneiro	Postdoc
	Tel: 21 446 4511
Inês Tenente	External Masters Student
	Tel: 21 446 6511
Hugo Almeida	2006 PDIGC PhD Student
	Tel: 21 446 4511
Ana Teresa Avelar	2007 PGD PhD Student
	Tel: 21 446 4514

Research Project

End-protection and DNA repair at S. pombe telomeres

Telomeres, the natural chromosome ends of eukaryotes, have unique properties that distinguish them from damage-induced DNA ends. Most human somatic cells lack telomerase, the enzyme responsible for generating telomeres. Proliferation of cells lacking telomerase leads to telomere depletion and ultimately to telomere loss. When telomere function is lost, chromosome ends are treated as DNA breaks that, in most cases, leads to cell death. If the cell survives, chromosomes will be joined by their ends yielding dicentric entities that can break upon mitosis. This, in turn, causes unequal distribution of genetic information to daughter cells as well as to the formation of new unprotected ends. The ensuing genomic instability is thought to be involved in the development of cancer. We plan to identify and characterize new components responsible for chromosome-end protection in a screen based on a novel assay designed to measure directly telomere-telomere fusions. Novel proteins and regulatory principals uncovered in this work are likely to be conserved. Understanding how telomeres are protected from DNA repair and, in its failure, how the cells respond to unprotected telomeres will provide insights to the initial stages of tumourogenesis. Identification of the key players in these events will novel targets for cancer therapy and early detection.

Funding

Association for International Cancer Research, UK

Collaborators

CEA/Saclay, Gif-Sur-Yvette, France - Stephane Marcand,

Research Project

Inhibiton of genomic instability by telomere protection

In this project, we propose to investigate the mechanisms underlying chromosome-end protection using fission yeast as a model system. My previous studies have shown that Taz1 (orthologue of the human telomere binding proteins TRF1 and TRF2) protects chromosome-ends from being recognized as deleterious breaks and used as substrates of DNA repair. The outcome of these processes at telomeres varies greatly through the cell cycle, leading to chromosome-end fusions and lethality in G1 and chromosomal rearrangements in G2. Novel proteins and their mechanisms of chromosome protection have been recapitulated in higher eukaryotes and, in particular, in human cells. The relationship between telomere function and cancer, and the multiple ways by which therapeutic intervention might be achieved through telomere manipulation, make the details of telomere capping critical issues in biology. Understanding how telomeres are protected from DNA repair and, in its failure, how the cells respond to unprotected telomeres will provide insights to the initial stages of tumourogenesis.

Funding

Fundação para a Ciência e Técnologia (FCT) Project Grant (Portugal)

Collaborators

Sussex Centre for Genome Damage and Stability, UK
- Aidan Doherty

Research Project

Identification of anti-checkpoint proteins at fission yeast telomeres

Recent work has revealed an apparent contradiction: although telomeres prohibit checkpoints and DNA repair, several components involved in these processes are, not only present at telomeres, but also critical for normal telomere function. Thus, similar to deleterious DNA ends, telomeres recruit potentially dangerous proteins to chromosome-ends. These, in turn, must be controlled in such way that checkpoints and DNA repair are prevented at telomeres. We propose to identify and characterize the mechanism that protects telomeres from being recognized as damaged DNA. We have generated two novel assays that will allow me to test directly whether a protein or a process is required for telomere protection. The first will allow us to screen for components that are involved in preventing chromosome-end fusions or DNA damage recognition. The second assay will test whether these components are sufficient to confer telomere-like protection to a newly formed DSB. Understanding how telomeres protect chromosome-ends from DNA damage checkpoints and repair and, in its failure, how the cells respond to unprotected telomeres will provide insights to the initial stages of tumourogenesis. Identification of the key players in these events will provide specific candidate targets for therapeutic intervention and possible tools for early diagnostic.

Funding

Fundação para a Ciência e Técnologia (FCT) Project Grant (Portugal)

Collaborators

Gray Institute for Radiation Oncology and Biology, University of Oxford, UK
- Tim Humphrey

Publications

Rog O., Miller K.M., Ferreira, M. G. and Cooper J. P. (2009). Sumoylation of RecQ helicase controls the fate of dysfunctional telomeres Molecular Cell 33 :559-569

Ferreira M.G. (2007). Telomeres on the Cdk roller-coster ride. Nature Cell Biology 9 :22-23

Miller K.M., Ferreira, M.G. and Cooper, J.P.. (2005). Taz1, Rap1 and Rif1 act both inter-dependently and independently to maintain telomeres EMBO Journal 24 :3128-3135

Ferreira, M.G., Miller K.M., Cooper, J.P. (2004). Indecent exposure: When telomeres become uncapped Molecular Cell 13 :7-18

Ferreira, M.G. and Cooper, J.P. (2004). Two modes of DNA double strand break repair are reciprocally regulated through the fission yeast cell cycle Genes and Development 18 :2249-54

Ferreira, M.G. and Cooper, J.P. (2001). The fission yeast Taz1 protein protects chromosomes from Ku-dependent end-to-end fusions Molecular Cell 7 :55-63

Ferreira, M.G., Santocanale, C., Drury, L.S., Diffley, J.F.X. (2000). Dbf4p, an essential S-phase promoting factor, is targeted for degradation by the Anaphase-Promoting Complex Molecular Cellular Biology 20 :242-8