Despite significant advances in understanding the biochemical basis of nucleotide excision repair (NER), there is no cure for individuals with Xeroderma pigmentosum, Cockayne Syndrome, Fanconi Anemia, and other DNA repair defects. Current therapy is focused on relieving symptoms and improving quality of life. The ubiquitin/proteasome system (UPS) of interacellular protein degradation has been extensively studied, and is implicated in cell cycle control, stress response, signal transduction, and DNA repair. We determined that the NER protein Rad4 is highly unstable, and is rapidly degraded by the proteasome. Remarkably, a number of additional DNA repair proteins have protein degradation functions, including Rad6, Rad7, Rad16 and FANCL. My laboratory has, for the past 15 years, investigated the role of protein degradation in DNA repair. We determined that Rad4 is stabilized when it forms a complex with the DNA repair factor, Rad23. Rad23 can also bind the proteasome and deliver ubiquitinated substrates. We recently discovered that the localization of proteasomes at the nuclear periphery is required for DNA repair. The studies proposed here will use genetic, biochemical and cell biological approaches to investigate the role of the UPS in nucleotide excision repair. We will characterize the proteins that traffic proteasomes, and determine how nuclear substrates, including Rad4, are targeted to the proteasome. These mechanistic studies are expected to have a broad impact, as they will show that proteasome trafficking represents a previously unknown regulatory process in intracellular protein degradation.

Public Health Relevance

The primary objective of the proposed studies is to investigate the role of protein degradation in DNA repair. Xeroderma pigmentosum and Cockayne Syndrome are well studied DNA repair defects for which there is no treatment or cure. Our studies could pave the way towards identification of candidate proteins and biochemical functions that can be targeted by therapeutic agents.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Radiation Therapeutics and Biology Study Section (RTB)
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Okano, Paul
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Rbhs-Robert Wood Johnson Medical School
Schools of Medicine
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Liang, Ruei-Yue; Chen, Li; Ko, Bo-Ting et al. (2014) Rad23 interaction with the proteasome is regulated by phosphorylation of its ubiquitin-like (UbL) domain. J Mol Biol 426:4049-60
Chen, Li; Madura, Kiran (2014) Degradation of specific nuclear proteins occurs in the cytoplasm in Saccharomyces cerevisiae. Genetics 197:193-7
Chen, Li; Madura, Kiran (2014) Yeast importin-? (Srp1) performs distinct roles in the import of nuclear proteins and in targeting proteasomes to the nucleus. J Biol Chem 289:32339-52
Joshi, Kishore Kumar; Chen, Li; Torres, Nidza et al. (2011) A proteasome assembly defect in rpn3 mutants is associated with Rpn11 instability and increased sensitivity to stress. J Mol Biol 410:383-99
Kipen, Howard M; Gandhi, Sampada; Rich, David Q et al. (2011) Acute decreases in proteasome pathway activity after inhalation of fresh diesel exhaust or secondary organic aerosol. Environ Health Perspect 119:658-63
Chen, Li; Romero, Lizbeth; Chuang, Show-Mei et al. (2011) Sts1 plays a key role in targeting proteasomes to the nucleus. J Biol Chem 286:3104-18
Chandra, Abhishek; Chen, Li; Liang, Huiyan et al. (2010) Proteasome assembly influences interaction with ubiquitinated proteins and shuttle factors. J Biol Chem 285:8330-9
Chandra, Abhishek; Chen, Li; Madura, Kiran (2010) Synthetic lethality of rpn11-1 rpn10? is linked to altered proteasome assembly and activity. Curr Genet 56:543-57
Geetha, Thangiah; Seibenhener, M Lamar; Chen, Li et al. (2008) p62 serves as a shuttling factor for TrkA interaction with the proteasome. Biochem Biophys Res Commun 374:33-7
Chen, Li; Madura, Kiran (2008) Centrin/Cdc31 is a novel regulator of protein degradation. Mol Cell Biol 28:1829-40

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