UHRF1 and the DNA Damage Response

Our DNA is under constant threat from endogenous and exogenous damaging agents. Our cells have evolved a network of signaling pathways and repair mechanisms that detect and counteract this threat, collectively referred to as the DNA damage response. Cells that lose the ability to cope with DNA damage risk the acquisition of deleterious changes to DNA sequence or structure. I initially set out to identify and characterize candidate proteins that interact with Mus81-Eme1, an endonuclease that processes DNA intermediates that arise from aberrant or stalled DNA replication. I focused on one interesting candidate protein known as Nuclear protein 95 (Np95) which now is called UHRF1 (Ubiquitin-like, containing PHD and RING finger domains, 1). Although previous studies demonstrate the importance of Mus81-Eme1 enzyme in DNA repair, genome integrity, and tumor suppression, little is known about how the enzyme acts together with other components of signaling pathways that comprise the DNA damage response. My findings in chapter two characterized this interaction and linked Mus81-Eme1 with UHRF1 in the cellular response to DNA damage. Although UHRF1 levels have been linked with sensitivity to antineoplastic agents, a direct role for UHRF1 in the DNA damage response had not been elucidated or reported. Accordingly, the third chapter of my thesis focuses on investigating the role of UHRF1 in the cellular response to DNA damage caused by exposure to γ-irradiation. Our findings for chapter three indicate that (i) UHRF1 is crucial for the cellular iii response to double strand breaks caused by γ-irradiation and that (ii) UHRF1 is critical for maintenance of chromosome integrity. Recent studies have now implicated UHRF1 in processes required for heterochromatin replication. This protein has been shown to play a role in the replication of heterochromatin by helping to replicate DNA methylation patterns and playing a role in propagating the epigenetic mark known as histone 3 lysine 9 trimethylation (H3K9me3). H3K9me3 has been shown to play a role in a signaling pathway involved in the repair of DNA damage in heterochromatic regions. In the fourth chapter of my thesis, we hypothesize that UHRF1 is playing a role in a pathway that responds to DSB damage in heterochromatic regions of chromatin. Our results indicate that a loss of UHRF1 results in a loss of heterochromatic H3K9me3 and heterochromatin associated HP1β. Our findings support the idea that epigenetic alterations maintained by UHRF1 contribute to signals that relax heterochromatin to facilitate access for repair factors. In summary, findings presented in this thesis shed light on processes that protect cells from DNA damage caused by radiation and chemotherapy and safeguard genome integrity.

Department dc:contributor.department

Pharmacology

Year dc:date.issued

2012

Author dc:creator

• Mistry, Helena

Advisor dc:contributor.advisor

• McPherson, John Peter

Language dc:language.iso

en_ca

Handle dc:identifier.uri

http://hdl.handle.net/1807/31868

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/31868