Cockayne syndrome complementation group B (CSB)
protein is engaged in transcription-coupled repair (TCR) of UV induced DNA damage and its deficiency leads to progressive multisystem degeneration and
premature aging. Here, we show that human CSB-deficient cells are hypersensitive to physiological concentrations (1-10 microM) of a lipid peroxidation product, trans-4-hydroxy-2-nonenal (HNE), and in response to HNE they develop a higher level of sister chromatid exchanges (SCEs) in comparison to the wild-type cells. HNE-
DNA adducts block in vitro transcription by
T7 RNA polymerase, as well as by HeLa cell-free extracts. Treatment of wild-type cells with 1-20 microM HNE causes dephosphorylation of the CSB
protein, which stimulates its
ATPase activity necessary for TCR. However, high HNE concentrations (100-200 microM) inhibit in vitro CSB
ATPase activity as well as the transcription machinery in HeLa cell-free extracts. Cell lines expressing CSB
protein mutated in different
ATPase domains exhibit different sensitivities to HNE. The motif II mutant, which binds
ATP, but is defective in
ATP hydrolysis was as sensitive to HNE as CSB-null cells. In contrast, motif V mutant cells were as sensitive to HNE as were the cells bearing wild-type
protein, while motif VI mutant cells showed intermediate sensitivity to HNE. These mutants exhibit decreased
ATP binding, but retain residual
ATPase activity. Homology modeling suggested that
amino acids mutated in motifs II and VI are localized closer to the
ATP binding site than
amino acids mutated in
ATPase motif V. These results suggest that HNE-
DNA adducts are extremely toxic endogenous DNA lesion, and that their processing involves CSB. When these lesions are not removed from the transcribed
DNA strand due to CSB gene mutation or CSB
protein inactivation by high, pathological HNE concentrations, they may contribute to accelerated aging.