Arsenite retards DNA break rejoining by inhibiting DNA ligation

Abstract

Arsenic has been shown to inhibit methyl methane-sulphonate (MMS)-induced DNA repair but the exact mechanism remains controversial. The purpose of this investigation is to examine which step of DNA repair is most sensitive to arsenite (As) and how As inhibits it. The results from single-cell alkaline electrophoresis, showing post-treatment with As increased DNA strand breaks in MMS-treated cells, suggest that that the excision step seems to be less sensitive to As than later steps. To test this hypothesis, hydroxyurea (Hu) plus cytosine-beta-D-arabinofuranoside (AraC) were used to block DNA polymerization, allowing the DNA strand breaks to accumulate. These experiments indicated that As had weak inhibitory effects on DNA strand break accumulation. However, As inhibited the rejoining of those DNA strand breaks which could be rejoined within 4 h after release from blockage by Hu plus AraC. To further elucidate this mechanism, a cell extract was used to compare the relative sensitivity of the various steps in DNA repair to As. The potency of the As inhibitory effect as deduced from concentration-response curves were: ligation of poly(rA).oligo(dT) > ligation of poly(dA).oligo(dT) approximately DNA polymerization > or = DNA repair synthesis > excision. As is known to inhibit the activity of pyruvate dehydrogenase by interacting with vicinal dithiol groups. Dithiothreitol could effectively remove As inhibition of both the ligation of poly(rA).oligo(dT) and the activity of pyruvate dehydrogenase but had no obvious effect on As inhibition of poly(dA).oligo(dT) ligation. Since DNA ligase III contains vicinal dithiol groups, we postulate that As may inhibit DNA break rejoining by interacting with the vicinal dithiols to inactivate DNA ligation in MMS-treated cells.

Mutagenicity of arsenic in mammalian cells: Role of reactive oxygen species

“…Previous genotoxic studies of arsenic have largely yielded negative findings for gene mutations but positive results for chromosomal aberrations (4,6,15,16). The failure of arsenic to induce gene mutations in mammalian cells has been taken as evidence that a nongenotoxic pathway is responsible for arsenic-induced cancer through either hypomethylation of DNA (32) or inhibition of DNA ligation (33). Herein we show that arsenic is indeed mutagenic to endogenous genes in mammalian cells and that it induces mostly large multilocus deletions that are mediated through ROS.…”

Arsenic Carcinogenesis in the Skin

“…The incision step and the ligation step of nucleotide excision repair were inhibited by arsenite [47]. Arsenite has been reported to decrease the DNA ligase III activity which results in DNA base excision repair [48,49] and DNA strand break rejoining [50]. Arsenic is also reported to inhibit other DNA repair regulatory proteins including DNA ligase I, DNA ligase II, DNA ligase III, DNA polymerase b, O 6 -methyl-guanine-DNA methyltransferase and poly (ADP-ribose) polymerase (PARP) [13,49,51].…”

Arsenic induces DNA damage via reactive oxygen species in human cells

“…However, its carcinogenic effects as well as noncarcinogenic effects are still not fully understood (for a review, see Rossman et al 1) ). Studies have shown that its carcinogenesis may be attributed to inhibition of DNA repair by inhibiting repair enzymes of dithiol groups [2][3][4] . Recently, it has been associated with generation of reactive oxygen species [5][6][7] .…”