The heterologous expression of Escherichia coli MutT enzyme is involved in the protection against oxidative stress in Leishmania braziliensis.

BACKGROUND Oxidative stress is responsible for generating DNA lesions and the 8-oxoguanine (8-oxoG) is the most commonly lesion found in DNA damage. When this base is incorporated during DNA replication, it could generate double-strand DNA breaks and cellular death. MutT enzyme hydrolyzes the 8-oxoG from the nucleotide pool, preventing its incorporation during DNA replication. OBJECTIVES To investigate the importance of 8-oxoG in Leishmania infantum and L. braziliensis, in this study we analysed the impact of heterologous expression of Escherichia coli MutT (EcMutT) enzyme in drug-resistance phenotype and defense against oxidative stress. METHODS Comparative analysis of L. braziliensis and L. infantum H2O2 tolerance and cell cycle profile were performed. Lines of L. braziliensis and L. infantum expressing EcMutT were generated and evaluated using susceptibility tests to H2O2 and SbIII, cell cycle analysis, γH2A western blotting, and BrdU native detection assay. FINDINGS Comparative analysis of tolerance to oxidative stress generated by H2O2 showed that L. infantum is more tolerant to exogenous H2O2 than L. braziliensis. In addition, cell cycle analysis showed that L. infantum, after treatment with H2O2, remains in G1 phase, returning to its normal growth rate after 72 h. In contrast, after treatment with H2O2, L. braziliensis parasites continue to move to the next stages of the cell cycle. Expression of the E. coli MutT gene in L. braziliensis and L. infantum does not interfere in parasite growth or in susceptibility to SbIII. Interestingly, we observed that L. braziliensis EcMutT-expressing clones were more tolerant to H2O2 treatment, presented lower activation of γH2A, a biomarker of genotoxic stress, and lower replication stress than its parental non-transfected parasites. In contrast, the EcMutT is not involved in protection against oxidative stress generated by H2O2 in L. infantum. MAIN CONCLUSIONS Our results showed that 8-oxoG clearance in L. braziliensis is important to avoid misincorporation during DNA replication after oxidative stress generated by H2O2.

DNA lesions that block transcription induce the death of Trypanosoma cruzi via ATR activation, which is dependent on the presence of R-loops.

Trypanosoma cruzi is the etiological agent of Chagas disease and a peculiar eukaryote with unique biological characteristics. DNA damage can block RNA polymerase, activating transcription-coupled nucleotide excision repair (TC-NER), a DNA repair pathway specialized in lesions that compromise transcription. If transcriptional stress is unresolved, arrested RNA polymerase can activate programmed cell death. Nonetheless, how this parasite modulates these processes is unknown. Here, we demonstrate that T. cruzi cell death after UV irradiation, a genotoxic agent that generates lesions resolved by TC-NER, depends on active transcription and is signaled mainly by an apoptotic-like pathway. Pre-treated parasites with α-amanitin, a selective RNA polymerase II inhibitor, become resistant to such cell death. Similarly, the gamma pre-irradiated cells are more resistant to UV when the transcription processes are absent. The Cockayne Syndrome B protein (CSB) recognizes blocked RNA polymerase and can initiate TC-NER. Curiously, CSB overexpression increases parasites' cell death shortly after UV exposure. On the other hand, at the same time after irradiation, the single-knockout CSB cells show resistance to the same treatment. UV-induced fast death is signalized by the exposition of phosphatidylserine to the outer layer of the membrane, indicating a cell death mainly by an apoptotic-like pathway. Furthermore, such death is suppressed in WT parasites pre-treated with inhibitors of ataxia telangiectasia and Rad3-related (ATR), a key DDR kinase. Signaling for UV radiation death may be related to R-loops since the overexpression of genes associated with the resolution of these structures suppress it. Together, results suggest that transcription blockage triggered by UV radiation activates an ATR-dependent apoptosis-like mechanism in T. cruzi, with the participation of CSB protein in this process.