The Single-Strand DNA Binding Activity of Human PC4 Prevents Mutagenesis and Killing by Oxidative DNA Damage

Abstract

Human positive cofactor 4 (PC4) is a transcriptional coactivator with a highly conserved single-strand DNA (ssDNA) binding domain of unknown function. We identified PC4 as a suppressor of the oxidative mutator phenotype of the Escherichia coli fpg mutY mutant and demonstrate that this suppression requires its ssDNA binding activity. Saccharomyces cerevisiae mutants lacking their PC4 ortholog Sub1 are sensitive to hydrogen peroxide and exhibit spontaneous and peroxide-induced hypermutability. PC4 expression suppresses the peroxide sensitivity of the yeast sub1⌬ mutant, suggesting that the human protein has a similar function. A role for yeast and human proteins in DNA repair is suggested by the demonstration that Sub1 acts in a peroxide resistance pathway involving Rad2 and by the physical interaction of PC4 with the human Rad2 homolog XPG. We show that XPG recruits PC4 to a bubble-containing DNA substrate with a resulting displacement of XPG and formation of a PC4-DNA complex. We discuss the possible requirement for PC4 in either global or transcription-coupled repair of oxidative DNA damage to mediate the release of XPG bound to its substrate.Oxidative DNA damage and the mutations it causes have been implicated in a number of human diseases, including cancer and neurodegenerative diseases, and are a contributing factor to aging (6,12,35,36). Thus, a thorough understanding of genes involved in the prevention and repair of oxidative DNA damage and its mutagenic consequences is important to our understanding of the mechanisms mitigating these diseases and exacerbating normal degenerative processes associated with aging.Oxidative DNA damage results from the interaction of reactive oxygen species (ROS) with DNA. ROS are produced as by-products of normal aerobic metabolism and by exogenous factors, such as ionizing radiation and chemical oxidants (6,12,35,36). The deleterious consequences of ROS to an organism's genetic material are held in check by proteins that prevent or repair oxidative DNA damage (7,12,13,15,21). Unrepaired oxidative lesions result in increased mutagenesis, lethality, and apoptosis (23,27). A balance between DNA repair and damage prevention mechanisms and ROS production is required to maintain a low spontaneous mutation rate. Factors that increase ROS production, reduce ROS detoxification, or factors that affect repair of oxidative DNA lesions result in increased mutagenesis. This is best demonstrated in Escherichia coli; mutations that inactivate the fpg and mutY genes, whose products repair the predominant oxidative lesion 8-oxoguanine (8-oxoG) and its mispaired intermediate 8-oxoG:A, respectively, result in a mutator phenotype that specifically increases GC3 TA transversion mutagenesis (37).In this study, we screened a human cDNA library and describe the isolation and characterization of the human transcription positive cofactor 4 (PC4) gene as a suppressor of oxidative mutagenesis in the E. coli fpg mutY strain. We demonstrate that PC4 and its Saccharomyces cerevisiae ortholog SUB1 are requi...

Genome-wide location analysis reveals a role for Sub1 in RNA polymerase III transcription

“…S6B). Consistently, SUB1 is a nonessential gene and its deletion does not interfere with the cell growth rate in exponentially growing cells (1,8). All these results suggest the existence of regulatory mechanisms that compensate for the decreased neosynthesis of Pol III transcripts caused by the absence of Sub1 to maintain a wild type pool of tRNA in the cell.…”

Suppression of UV-induced apoptosis by the human DNA repair protein XPG

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Human positive coactivator 4 is a potential novel therapeutic target in non-small cell lung cancer

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