Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

12-2007

Committee Chair or Co-Chairs

Yue Zou

Committee Members

David A. Johnson, Douglas P. Thewke, John J. Laffan, Peter J. Rice

Abstract

The genome of mammalian cells is under constant attack from DNA-damaging agents. To maintain genomic integrity, cells activate an array of pathways primarily consisting of DNA repair and DNA damage checkpoints. Human replication protein A (RPA), a single-stranded DNA (ssDNA) binding protein, is essential for almost all DNA metabolic pathways. However, the role of RPA in nucleotide excision repair (NER), a DNA repair pathway for removing bulky DNA lesions, remains elusive. In this study, the binding of RPA to a battery of well-defined ssDNA substrates has been systematically examined using fluorescence spectroscopy. The results showed that RPA has a lower binding affinity for damaged ssDNA than for non-damaged ssDNA, and there was no direct contact between RPA residues and the lesion itself. These findings will help define the roles of RPA in DNA damage recognition in NER. In cells, RPA undergoes hyperphosphorylation in the N-terminus of RPA32 subunit after DNA damage. In this study, the hyperphosphorylation-induced conformational changes of RPA have been probed using mass spectrometry-based protein foot-printing, fluorescence spectroscopy and limited proteolysis. The data show that upon hyperphosphorylation RPA undergoes a subtle structural change involving its DNA-binding domain B (DBD-B), reducing its affinity for short ssDNA. These results suggest that hyperphosphorylation may modulate RPA functions by altering DBD-B-mediated RPA-DNA/protein interactions. Cellular accumulation of DNA damage has been widely implicated in premature aging. In Hutchinson-Gilford progeria syndrome (HGPS) and restrictive dermopathy (RD), premature aging is caused by defective maturation of lamin A and linked to accumulation of DNA double-strand breaks (DSBs). However, how lamin A dysfunction leads to genome instability and premature aging is not understood. Here evidence showed that in HGPS and RD fibroblasts DNA damage checkpoints are persistently activated and recruitment of repair factors to DSBs was impaired. Strikingly, xeroderma pigmentosum group A (XPA), a unique NER protein, formed foci and colocalized with the unrepairable DSBs in the patient cells. RNAi knockdown of XPA in HGPS cells significantly restored DSB repair. These results indicate that XPA dysfunction may play an important role in accumulating DSBs in HGPS, implicating a potential strategy for treatment of these premature aging diseases.

Document Type

Dissertation - Open Access

Copyright

Copyright by the authors.

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