Abstract
Microcystins (MCs) are hepatotoxins produced by some cyanobacteria. They are cyclic peptides that inhibit the serine/threonine protein phosphatases (PPs) PP1 and PP2A, especially PP2A. The inhibition of PP2A triggers a series of molecular events, which are responsible for most MC cytotoxic and genotoxic effects on animal cells. It is also known that MCs induce oxidative stress in cells due to the production of reactive oxygen species (ROS). However, a complete characterization of the toxic effects of MCs is still not accomplished. This study aimed to clarify additional molecular mechanisms involved in MC-LR toxicity, using Saccharomyces cerevisiae as eukaryotic model organism. First, a shotgun proteomic analysis of S. cerevisiae VL3 cells response to 1 nM, 10 nM, 100 nM, and 1 μM MC-LR was undertaken and compared to the control (cells not exposed to MC-LR). This analysis revealed a high number of proteins differentially expressed related with gene translation and DNA replication stress; oxidative stress; cell cycle regulation and carbohydrate metabolism. Inference of genotoxic effects of S. cerevisiae VL3 cells exposed to different concentrations of MC-LR were evaluated by analyzing the expression of genes Apn1, Apn2, Rad27, Ntg1, and Ntg2 (from the Base Excision Repair (BER) DNA repair system) using the Real-Time RT-qPCR technique. These genes displayed alterations after exposure to MC-LR, particularly the Apn1/Apn2/Rad27, pointing out effects of MC-LR in the Base Excision Repair system (BER). Overall, this study supports the role of oxidative stress and DNA replication stress as important molecular mechanisms of MC-LR toxicity. Moreover, this study showed that even at low-concentration, MC-LR can induce significant changes in the yeast proteome and in gene expression.
Highlights
Microcystins (MCs) are potent hepatotoxins produced by some cyanobacteria, especially by the species Microcystis aeruginosa
The analysis revealed two other clusters constituted by proteins involved in protein folding and chaperoning activity (HSP10, MGE1, CCT6, MIA40), cell redox homeostasis and oxidative stress (TRR1), proteins involved in DNA repair in response to DNA damage (FUM) and ATP synthesis and membrane transport mediated by ATP (ATP7, ATP1, VPH1, TIM11)
We present new data concerning Saccharomyces cerevisiae VL3 response to the cyanotoxin MC-LR, revealed by proteomics and gene expression
Summary
Microcystins (MCs) are potent hepatotoxins produced by some cyanobacteria, especially by the species Microcystis aeruginosa. The main aspect is that MC-LR has high affinity for serine/threonine protein phosphatases 1 (PP1) and 2A (PP2A) and binds to the catalytic subunit of these enzymes, acting as their inhibitors, especially of PP2A [3]. Another toxic effect of MC-LR is the induction of reactive oxygen species (ROS) and glutathione (GSH) depletion [7,8,9,10]. Regarding the mechanism of ROS production, Ding and Nam Ong (2003) proposed that
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