Dr. Grant Stewart received his first degree in Cellular and Molecular Pathology at the University of Bristol (1996). He subsequently joined the laboratory of Professor Malcolm Taylor at the University of Birmingham to do a Ph.D. studying the heterogeneity of the chromosomal instability syndrome, Ataxia-Telangiectasia (A-T), and the role of the ATM (Ataxia-Telangiectasia Mutated) gene in sporadic leukaemia. During the course of his Ph.D., he identified mutations in DNA double strand break (DSB) gene, hMRE11, also contributed to the development of a syndrome similar to A-T (A-T-like disorder or ATLD), firmly establishing a genetic link between the hMre11 DSB repair complex and ATM.
Continuing his growing interest in the cellular response to DNA damage, he moved in 2002, with a European Molecular Biology Organisation (EMBO) Long Term Fellowship, to the laboratory of Professor Stephen Elledge at Baylor College of Medicine (Houston, Texas). Whilst at Baylor, he identified a novel DNA double strand break repair protein called Mediator of DNA Damage Checkpoint 1 (MDC1) and demonstrated it played a role in recruiting other DSB responsive proteins to the sites of DNA breaks to facilitate repair and cell cycle checkpoint activation.
In 2005 Dr. Grant Stewart moved back to the University of Birmingham with a CR-UK Career Development Fellowship to start up his own laboratory investigating the function of the DNA DSB repair proteins, MDC1 and 53BP1, during the cellular response to DNA damage and also how defects in pathways controlled by these proteins contribute to human disease and tumourigenesis. Recently his group has identified a novel human immunodeficiency syndrome associated with defective repair of DNA DSBs called RIDDLE syndrome. ‘RIDDLE’ is an acronym describing its common clinical features: Radiosensitivity, ImmunoDeficiency, Dysmorphic facial features and LEarning difficulties. Through a collaboration his laboratory was able to identify the gene mutated in RIDDLE syndrome as RNF168 and that the encoded protein facilitates the recruitment of DSB repair proteins, such as 53BP1 and BRCA1, to sites of DNA damage by promoting relaxation of the chromatin structure surrounding the break.
Despite these findings, very little is known about the function of RNF168 during the cellular response to DNA DSBs and how defects in this pathway contribute to human immunodeficiency. Currently Dr. Grant Stewart’s laboratory is focusing on RIDDLE syndrome and determining how RNF168 and the ubiquitin/SUMO system functions in the cell to coordinate DNA DSB repair, which is in part funded by CR-UK and a Lister Institute Research Prize.
The cellular response to DNA double strand breaks (DSB) is a complex, integrated network of pathways that function to preserve the integrity of the genome. Following the recognition of DNA damage, a cascade of repair protein recruitment is initiated that is essential for the timely and accurate repair of the DNA lesion. This occurs in a highly ordered, hierarchical manner, principally controlled by mediator proteins, such as MDC1 and 53BP1. Mediator proteins function as molecular scaffolds that facilitate the recruitment and localized activation of repair and checkpoint proteins within the microenvironment surrounding the damage.
Access of repair proteins to sites of DNA damage requires the controlled relaxation of the surrounding chromatin. This process is regulated by the post-translational modification of histones adjacent to the DNA break, which involves enzymes that coordinate protein phosphorylation, ubiquitylation, SUMOylation, methylation and acetylation.
The research ongoing in the laboratory of Dr. Grant Stewart centres on understanding how the cell coordinates the relocalisation of repair/checkpoint proteins to the sites of DNA damage and how defects in this pathway contributes to the development of human disease and cancer. The identification of mutations in the RNF168 gene as the underlying genetic cause of the human immunodeficiency disorder, RIDDLE Syndrome, by Dr. Stewart’s laboratory has highlighted the importance of the ubiquitin system in facilitating repair of programmed DNA breaks that occur during immune system development. Based on this, research projects within Dr. Stewart’s laboratory currently focus on determining how the ubiquitin/SUMO system regulates the recognition and repair of DNA damage, the identification of novel proteins that function to regulate this process and whether components of this pathway are mutated in human syndromes characterised by nervous/immune system abnormalities and cancer predisposition.
1. Stewart GS**, Stankovic T, Byrd PJ, Wechsler T, Miller ES, Huissoon A, Drayson MT, West SC, Elledge SJ, Taylor AM. (2007). RIDDLE immunodeficiency syndrome is linked to defects in 53BP1-mediated DNA damage signaling. Proc Natl Acad Sci U S A. 104:16910-5. (** Corresponding author)
2. Spycher C, Miller ES, Townsend K, Pavic L, Morrice NA, Janscak P, Stewart GS, Stucki M. (2008). Constitutive phosphorylation of MDC1 physically links the MRE11/RAD50/NBS1 complex to damaged chromatin. J. Cell Biol. 181:227-40
3. Blackford AN, Bruton RK, Dirlik O, Stewart GS, Taylor AMR, Dobner T, Grand RJA, and Turnell AS (2008) A role for E1B-AP5 in ATR signalling pathways during adenovirus infection J. Virol. 82:7640-52
4. Stewart GS**, Panier S, Townsend K, Al-Hakim AK, Kolas NK, Miller ES, Nakada S, Ylanko J, Olivarius S, Mendez M, Oldreive C, Wildenhain J, Tagliaferro A, Pelletier L, Taubenheim N, Durandy A, Byrd PJ, Stankovic T, Taylor AMR, Durocher D**. (2009) The gene mutated in the RIDDLE syndrome mediates a ubiquitin-dependent signalling cascade at sites of DNA damage. Cell 136:420–434 (** Corresponding author)
5. Townsend K, Dyson H, Blackford AN, Miller ES, Chapman JR, Sedgwick GG, Barone G, Turnell AS, Stewart GS. (2009). Mediator of DNA damage checkpoint 1 (MDC1) regulates mitotic progression. J. Biol. Chem. 284:33939-33948
6. Noon AT, Shibata A, Rief N, Löbrich M, Stewart GS, Jeggo PA, Goodarzi AA. (2009). 53BP1-dependent robust, localized KAP-1 phosphorylation is essential for heterochromatic DNA double strand break repair. Nat. Cell Biol. 12:177-84.
7. Lilley CE, Chaurushiya MS, Suh J, Panier S, Stewart GS, Durocher D, Weitzman MD. (2009). A viral E3 ligase targets RNF8 and RIDDLIN/RNF168 to control histone ubiquitination and the cellular DNA damage response. EMBO J. 29:943-55.
8. Blackford AN, Patel RN, Forrester NA, Theil K, Groitl P, Stewart GS, Taylor AMR, Morgan IM, Dobner T, Grand RJA, Turnell AS. (2010) Adenovirus E4orf6 inhibits ATR activation by promoting TOPBP1 degradation. Proc Natl Acad Sci U S A. 107:12251-6.