Base Excision Repair of Chemotherapeutically-Induced Alkylated DNA Damage Predominantly Causes Contractions of Expanded GAA Repeats Associated with Friedreich's Ataxia

Authors

Yanhao Lai, Department of Chemistry and Biochemistry, Florida International University, Miami, Florida; Department of Environmental and Occupational Health, West China School of Public Health, Sichuan University, Chengdu, People’s Republic of ChinaFollow
Jill M. Beaver, Department of Chemistry and Biochemistry, Florida International UniversityFollow
Karla Lorente, Department of Chemistry and Biochemistry, Florida International UniversityFollow
Jonathan Melo, Department of Chemistry and Biochemistry, Florida International UniversityFollow
Shyama Ramjagsingh, Department of Chemistry and Biochemistry, Florida International University
Irina U. Agoulnik, Department of Cellular Biology and Pharmacology, Florida International UniversityFollow
Zunzhen Zhang, Sichuan UniversityFollow
Yuan Liu, Department of Chemistry and Biochemistry, Florida International University, Miami, FloridaFollow

Date of this Version

4-1-2014

Document Type

Article

Abstract

Expansion of GAA·TTC repeats within the first intron of the frataxin gene is the cause of Friedreich's ataxia (FRDA), an autosomal recessive neurodegenerative disorder. However, no effective treatment for the disease has been developed as yet. In this study, we explored a possibility of shortening expanded GAA repeats associated with FRDA through chemotherapeutically-induced DNA base lesions and subsequent base excision repair (BER). We provide the first evidence that alkylated DNA damage induced by temozolomide, a chemotherapeutic DNA damaging agent can induce massive GAA repeat contractions/deletions, but only limited expansions in FRDA patient lymphoblasts. We showed that temozolomide-induced GAA repeat instability was mediated by BER. Further characterization of BER of an abasic site in the context of (GAA)₂₀ repeats indicates that the lesion mainly resulted in a large deletion of 8 repeats along with small expansions. This was because temozolomide-induced single-stranded breaks initially led to DNA slippage and the formation of a small GAA repeat loop in the upstream region of the damaged strand and a small TTC loop on the template strand. This allowed limited pol β DNA synthesis and the formation of a short 5'-GAA repeat flap that was cleaved by FEN1, thereby leading to small repeat expansions. At a later stage of BER, the small template loop expanded into a large template loop that resulted in the formation of a long 5'-GAA repeat flap. Pol β then performed limited DNA synthesis to bypass the loop, and FEN1 removed the long repeat flap ultimately causing a large repeat deletion. Our study indicates that chemotherapeutically-induced alkylated DNA damage can induce large contractions/deletions of expanded GAA repeats through BER in FRDA patient cells. This further suggests the potential of developing chemotherapeutic alkylating agents to shorten expanded GAA repeats for treatment of FRDA.

Comments

This article was originally published in PLoS One.

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 License.

Recommended Citation

Lai Y, Beaver JM, Lorente K, Melo J, Ramjagsingh S, Agoulnik IU, et al. (2014) Base Excision Repair of Chemotherapeutically-Induced Alkylated DNA Damage Predominantly Causes Contractions of Expanded GAA Repeats Associated with Friedreich's Ataxia. PLoS ONE 9(4): e93464. doi:10.1371/journal.pone.0093464