Chromosomal rearrangements are a common genomic abnormality found in tumor cells, which can alter the normal function of the genes involved, thus contributing to cancer development. Despite their prevalence, much remains unknown about the mechanisms that form translocations. Several commonly occurring chromosomal rearrangements, RET/PTC, AKAP9/BRAF, STRN/ALK, ETV6/NTRK3 and several NTRK1 gene fusions, contribute to the development of papillary thyroid carcinomas (PTC), a major type of thyroid cancer. In the US general population, thyroid cancer is the fastest increasing type of cancer. Its incidence has increased 4 to 7-fold in US Air Force active-duty personnel compared to the general population, even though overall cancers are less frequent in military personnel. We have demonstrated for the first time that DNA breaks at chromosomal fragile sites participate directly in the generation of oncogenic RET/PTC1 rearrangements in human thyroid cells. Fragile sites are sensitive to a range of chemicals, and have been identified in the regions of deletions and chromosomal rearrangements. All partner genes participating in PTC rearrangements are located in known fragile sites. Several environmental exposures, which are daily encountered by the general population and/or intensified in military personnel, such as benzene (in explosives, jet and automobile exhausts, and napalm) and diethylnitrosamine (in cigarette smoke and pesticides), also induce fragile site breakage. Many of them, including benzene, show a positive association with the risk of thyroid cancer. We hypothesize that these agents alone or in combination contribute to the increased incidence of thyroid cancer. In this proposal, we will investigate whether environmental exposures generate RET fragility, leading to RET/PTC rearrangements in human thyroid cells by examining a variety of environmental and therapeutic agents known to induce fragile sites, and will expand this study to other PTC-specific rearrangements as well. Next, we will identify the mechanism of fragile site-mediated RET/PTC rearrangements in response to these environmental exposures, by determining whether the formation of secondary structures during DNA replication contribute to RET gene instability in the formation of RET/PTC rearrangements. Then, to work towards clinical application of DNA fragility to a DNA diagnostic test, we will test whether breakage of RET and other rearrangement-participating genes in normal cells of PTC patients with rearrangements is higher than that in normal individuals, as a means to evaluate individual susceptibility to PTC. This proposal will have significant impact on our understanding of the direct role of environmental factors in the RET/PTC and other rearrangements of thyroid cancers. These mechanistic studies will provide new knowledge to better understand fragile site breakage and its role in sporadic cancer initiation. Further, using data on preferential breakage properties of rearrangement-participating genes to create a DNA test can potentially be extended to other cancers caused by fragile site-mediated rearrangements.

Public Health Relevance

Gene rearrangements, a common cause of papillary thyroid carcinomas, are an excellent model to study the mechanisms of chromosomal rearrangement in cancer cells, which remain poorly understood. We propose to investigate the ability of environmental and chemotherapeutic agents to generate RET/PTC and other PTC- specific rearrangements, identify the mechanism of fragile site-mediated RET/PTC rearrangements in response to these agents, and develop a DNA test of RET, BARF, ALK, NTRK1, and NTRK3 breakage to monitor high-risk populations. This work will deepen our understanding of the molecular mechanisms of chromosomal rearrangements in cancer cells, and eventually lead to the development of novel diagnostic measures for malignant tumors caused by the mechanism of chromosomal rearrangements.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA113863-08
Application #
9325293
Study Section
Molecular and Cellular Endocrinology Study Section (MCE)
Program Officer
Witkin, Keren L
Project Start
2006-03-13
Project End
2019-08-31
Budget Start
2017-09-01
Budget End
2018-08-31
Support Year
8
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of Virginia
Department
Biochemistry
Type
Schools of Medicine
DUNS #
065391526
City
Charlottesville
State
VA
Country
United States
Zip Code
22904
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Lehman, Christine E; Dillon, Laura W; Nikiforov, Yuri E et al. (2017) DNA fragile site breakage as a measure of chemical exposure and predictor of individual susceptibility to form oncogenic rearrangements. Carcinogenesis 38:293-301
Thys, Ryan G; Lehman, Christine E; Pierce, Levi C T et al. (2015) DNA secondary structure at chromosomal fragile sites in human disease. Curr Genomics 16:60-70
Dillon, Laura W; Pierce, Levi C T; Ng, Maggie C Y et al. (2013) Role of DNA secondary structures in fragile site breakage along human chromosome 10. Hum Mol Genet 22:1443-56
Dillon, Laura W; Pierce, Levi C T; Lehman, Christine E et al. (2013) DNA topoisomerases participate in fragility of the oncogene RET. PLoS One 8:e75741
Dillon, Laura W; Lehman, Christine E; Wang, Yuh-Hwa (2012) The role of fragile sites in sporadic papillary thyroid carcinoma. J Thyroid Res 2012:927683
Gandhi, M; Dillon, L W; Pramanik, S et al. (2010) DNA breaks at fragile sites generate oncogenic RET/PTC rearrangements in human thyroid cells. Oncogene 29:2272-80
Dillon, Laura W; Burrow, Allison A; Wang, Yuh-Hwa (2010) DNA instability at chromosomal fragile sites in cancer. Curr Genomics 11:326-37
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Hagerman, Katharine A; Ruan, Haihe; Edamura, Kerrie Nichol et al. (2009) The ATTCT repeats of spinocerebellar ataxia type 10 display strong nucleosome assembly which is enhanced by repeat interruptions. Gene 434:29-34

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