Gene and sequence specificity of DNA damage induction and repair: consequences for mutagenesis

Skin cells and tissue are capable of using L-ergothioneine as an integral component of their antioxidant defense system

The cellular defense system against harmful levels of reactive oxygen species consists of antioxidant enzymatic activities and small nonenzymatic molecules. L-ergothioneine has long been recognized as a potent and stable low-molecular-weight antioxidant that humans consume with diet and that accumulates in cells normally subjected to high levels of oxidative stress. As L-ergothioneine is plasma membrane-impermeative, its protective function is restricted to cells that express the L-ergothioneine-specific receptor/transporter OCTN1. Here we report for the first time that both as resident skin cells and in culture, epidermal keratinocytes synthesize OCTN1, which enables them to internalize and accumulate L-ergothioneine. This accumulation confers upon the cells an increased antioxidant potential. Consequently, it reduces the levels of reactive oxygen species and DNA, protein, and lipid damage in keratinocytes subjected to solar-simulating UV oxidative stress. Our results suggest that L-ergothioneine not only prevents oxidative damage but also may enable DNA repair in the UV-irradiated cells. The diminished oxidative damage to cellular constituents limits the apoptotic response and results in increased cell viability. The cells' ability to take up, accumulate, and utilize the potent antioxidant L-ergothioneine positions this naturally occurring amino acid and its receptor/transporter as an integral part of the antioxidative defense system of the skin.

Efficient repair of bleomycin-induced double-strand breaks in barley ribosomal genes

Ability of barley ribosomal genes to cope with damage produced in vivo by the radiomimetic agent bleomycin was investigated. Repair kinetics of bleomycin-induced double-strand breaks in ribosomal and total genomic DNA was compared. Induction and repair of double-strand breaks in defined regions of the ribosomal genes was also analyzed. Preferential sensitivity of barley linker DNA towards bleomycin treatment in vivo was established. Relatively higher yield of initially induced double-strand breaks in genomic DNA in comparison to ribosomal DNA was also found. Fragments containing intergenic spacers of barley rRNA genes displayed higher sensitivity to bleomycin than the coding sequences. No heterogeneity in the repair of DSB between transcribed and non-transcribed regions of ribosomal genes was detected. Data indicate that DSB repair in barley rDNA, although more efficient than in genomic DNA, does not correlate with the activity of nucleolus organizer regions.