Molecular models of induced DNA premutational damage and mutational pathways for the carcinogen 4-nitroquinoline 1-oxide and its metabolites

Polyphosphate is a key factor for cell survival after DNA damage in eukaryotic cells

Cells require extra amounts of dNTPs to repair DNA after damage. Polyphosphate (polyP) is an evolutionary conserved linear polymer of up to several hundred inorganic phosphate (Pi) residues that is involved in many functions, including Pi storage. In the present article, we report on findings demonstrating that polyP functions as a source of Pi when required to sustain the dNTP increment essential for DNA repair after damage. We show that mutant yeast cells without polyP produce less dNTPs upon DNA damage and that their survival is compromised. In contrast, when polyP levels are ectopically increased, yeast cells become more resistant to DNA damage. More importantly, we show that when polyP is reduced in HEK293 mammalian cell line cells and in human dermal primary fibroblasts (HDFa), these cells become more sensitive to DNA damage, suggesting that the protective role of polyP against DNA damage is evolutionary conserved. In conclusion, we present polyP as a molecule involved in resistance to DNA damage and suggest that polyP may be a putative target for new approaches in cancer treatment or prevention.

Using DNA damage sensitivity phenotypes to characterize mutations affecting proteasome function

Most mutants affected either in the proteasome biogenesis or function accumulate polyubiquitylated proteins and display growth defects at 37°C or in the presence of canavanine, an arginine analog that impairs protein synthesis. We uncovered a new striking phenotype related to DNA damage for some proteasome mutants: mutant strains grew better than the wild type in the presence of specific genotoxic agents (4NQO, Cpt, and MMS). Hyperresistance to 4NQO or Cpt is a new sensitive tool to detect proteasomal defects. Here, we describe simple methods that can be used to show and quantitatively measure this phenotype in budding yeast.

Accumulation of polycyclic aromatic hydrocarbon-induced single strand breaks is attributed to slower rejoining processes by DNA polymerase inhibitor, cytosine arabinoside in CHO-K1 cells

We demonstrate a successful induction of DNA single strand breaks in CHO-K1 cells by cocultivation with mouse embryonic fibroblasts (MEF) during exposure to benzo(a)pyrene (BP) or 3-methylcholanthrene (MC). When compared to those induced by methyl methanesulfonate (MMS), the DNA single strand breaks induced by BP and MC were markedly accumulated by post-incubation with cytosine arabinoside (araC) and were much more delayed in their rejoining. These results suggest that the active metabolites of BP or MC produced by cocultivation with MEF or microsomal fraction (S-15) result in the formation of large DNA adducts which require an active participation of DNA polymerase alpha(delta) in the polymerization step of excision repair for their removal.

Exposure to low concentrations of mutagens alters the mutagenic and lethal effects of 4-nitroquinoline-N-oxide and mitomycin C in Escherichia coli

Mitomycin C and 4-nitroquinoline-N-oxide are two mutagens which can induce the SOS DNA repair system in Escherichia coli. Growth of E. coli B/r strain WP2, or its uvrA- derivative, in very low concentrations of either mutagen led to the increased sensitization to the lethal and/or mutagenic effects of a subsequent challenge with the same mutagen. These phenomena were not observed in either the recA- or lexA- derivatives of the parent strain. Induction of the adaptive response repair pathway by prior cultivation in low concentrations of N-methyl-N'-nitro-N-nitrosoguanidine reduced both the mutagenic and lethal effects of a subsequent challenge with mitomycin C but not 4-nitroquinoline-N-oxide.