Human BLM encodes a recQ-like DNA helicase that is important for the maintenance of genomic stability. When both copies of this gene are mutated, the resulting hereditary disease, known as Bloom's syndrome (BS), is characterized by sun-sensitivity, small stature, immunodeficiency, male infertility, and a tremendous predisposition to cancer of all sites and types. Cells from BS individuals are characterized by chromosome breakage and other chromosomal anomalies that are indicative of increased somatic recombination. Notably, telomeric associations (TAs) between homologous chromosomes are also present in non- immortalized and immortalized cells from BS individuals. Following the positional cloning of the BLM gene, our laboratory has investigated the functions of the BLM helicase in DNA double strand break repair processes such as non-homologous end joining, homologous recombination-mediated repair, and synthesis-dependent strand annealing. Our work has also suggested a role for BLM in recombination- mediated mechanisms of telomere elongation or ALT (alternative lengthening of telomeres), processes that maintain/elongate telomeres in the absence of telomerase. BLM preferentially associates with the telomere- specific binding proteins TRF1 and TRF2 in cells using ALT;its helicase activity can be modulated by these interactions. Our preliminary data identify and validate other proteins that uniquely interact with BLM and TRF2 in cells using ALT, demonstrate that these protein interactions modify enzymatic activity of BLM and its partner topoisomerase IIalpha, and show that modification of five putative phosphorylation sites can alter unwinding of DNA substrates. We hypothesize that BLM complex formation and modification occur dynamically during the specific nucleic acid transactions that are required to protect the telomere, to align chromosome sequences at homologous telomeres, to permit strand invasion and elongation, and/or ultimately to disentangle telomeres. These ideas will be investigated by analyses of BLM modification, localization and protein partnering during telomere elongation, and by modifying these interactions or modifications in vitro and in vivo using genetically engineered mice. The immediate goal of this application is to determine the mechanism by which BLM functions to maintain telomeres. This work has important implications for learning how cells maintain their genomic integrity, how they age or become immortal, and ultimately for developing better therapeutic strategies in oncology.
Inherited syndromes that predispose to cancer have provided us an opportunity to study the genes and proteins that are important for keeping normal cells from becoming neoplastic. The BLM helicase is one of these proteins, as it seems to be required to maintain stability of the human genome. Its role in the maintenance of chromosome ends is especially important, as it is these mechanisms that enable cells to gain the ability to grow indefinitely. The study of BLM therefore represents an opportunity for us to learn how we can control the growth of cancer cells in a therapeutic setting.
|Mcilhatton, Michael A; Boivin, Gregory P; Groden, Joanna (2016) Manipulation of DNA Repair Proficiency in Mouse Models of Colorectal Cancer. Biomed Res Int 2016:1414383|
|Tangeman, Larissa; McIlhatton, Michael A; Grierson, Patrick et al. (2016) Regulation of BLM Nucleolar Localization. Genes (Basel) 7:|
|McIlhatton, Michael A; Murnan, Kevin; Carson, Daniel et al. (2015) Genetic Manipulation of Homologous Recombination In Vivo Attenuates Intestinal Tumorigenesis. Cancer Prev Res (Phila) 8:650-6|
|Gocha, April Renee Sandy; Acharya, Samir; Groden, Joanna (2014) WRN loss induces switching of telomerase-independent mechanisms of telomere elongation. PLoS One 9:e93991|
|Gocha, April R S; Nuovo, Gerard; Iwenofu, Obiajulu H et al. (2013) Human sarcomas are mosaic for telomerase-dependent and telomerase-independent telomere maintenance mechanisms: implications for telomere-based therapies. Am J Pathol 182:41-8|
|Gocha, April Renee Sandy; Harris, Julia; Groden, Joanna (2013) Alternative mechanisms of telomere lengthening: permissive mutations, DNA repair proteins and tumorigenic progression. Mutat Res 743-744:142-50|
|Grierson, Patrick M; Acharya, Samir; Groden, Joanna (2013) Collaborating functions of BLM and DNA topoisomerase I in regulating human rDNA transcription. Mutat Res 743-744:89-96|
|Amunugama, Ravindra; Groden, Joanna; Fishel, Richard (2013) The HsRAD51B-HsRAD51C stabilizes the HsRAD51 nucleoprotein filament. DNA Repair (Amst) 12:723-32|
|Grierson, Patrick M; Lillard, Kate; Behbehani, Gregory K et al. (2012) BLM helicase facilitates RNA polymerase I-mediated ribosomal RNA transcription. Hum Mol Genet 21:1172-83|
|Russell, Beatriz; Bhattacharyya, Saumitri; Keirsey, Jeremy et al. (2011) Chromosome breakage is regulated by the interaction of the BLM helicase and topoisomerase IIalpha. Cancer Res 71:561-71|
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