The Origin of Genome Instability in Cancer: Role of the Fragile Site Gene Product FHIT

The transformation of normal cells to cancer cells involves multiple steps mediated by the acquisition of mutations, selection and clonal expansion of cells with favorable mutations. Most cancers exhibit remarkable genomic instability, defined as an elevated rate of genetic mutation at the single nucleotide and chromosome levels. Genomic instability is a facilitating hallmark of cancer in that it raises the probability of generating cancer-promoting mutations. Multiple factors contribute to the genome instability phenotypes seen in cancer, but the molecular processes initiating instability in sporadic cancer are unknown. In dysplastic cells, genomic alterations are first seen at chromosome fragile sites. These fragile sites are exquisitely sensitive to agents that stress DNA replication forks, and thus, it is thought that replicative stress is a major source of genome instability in cancer. A frequent and very early genetic alteration in precancerous cells is deletion within fragile site FRA3B, which overlaps exons of the large FHIT gene, resulting in loss of FHIT protein expression. Here it is shown that loss of FHIT expression triggers endogenous replication stress hindering replication fork progression and inducing fork stalling and collapse. Consequently, FHIT-deficient cells develop spontaneous DNA breaks and chromosome instability. Mechanistically, FHIT loss-induced replication stress is due to an imbalance in the deoxyribonucleotide triphosphate pool and an insufficient supply of thymidine triphosphate. FHIT up-regulates the S-phase-specific expression of thymidine kinase 1, a component of the pyrimidine salvage pathway for the production of thymidine triphosphate. Balanced precursors of DNA are needed for efficient and accurate DNA replication, and notably restoration of nucleotide balance rescues DNA replication defects in FHIT-deficient cells.Under selective pressure, FHIT-deficient clones enabled by oncogenic mutations emerge with newly acquired precancerous phenotypes, suggesting that FHIT loss-induced genome instability facilitates tumorigenesis. Collectively, these findings support a model where loss of FHIT expression initiates genomic instability in dysplastic lesions, linking alterations at chromosome fragile sites to the origin of genome instability and cancer progression.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Integrated Biomedical Science Graduate Program

Grantor dc:publisher

The Ohio State University

Year dc:date

2013

Author dc:creator

• Saldivar, Joshua Charles

Contributors dc:contributor

• Huebner, Kay

• Biomedical Research
• Cellular Biology
• Genetics
• Molecular Biology
• Genome instability
• replication stress
• common fragile sites
• FRA3B
• FHIT
• thymidine kianse
• dNTP

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=osu1366133042

OAI identifier oai:identifier

oai:etd.ohiolink.edu:osu1366133042