Toxicity Mechanisms of the Food Contaminant Citrinin: Application of a Quantitative Yeast Model

Abstract

Mycotoxins are important food contaminants and a serious threat for human nutrition. However, in many cases the mechanisms of toxicity for this diverse group of metabolites are poorly understood. Here we apply live cell gene expression reporters in yeast as a quantitative model to unravel the cellular defense mechanisms in response to the mycotoxin citrinin. We find that citrinin triggers a fast and dose dependent activation of stress responsive promoters such as GRE2 or SOD2. More specifically, oxidative stress responsive pathways via the transcription factors Yap1 and Skn7 are critically implied in the response to citrinin. Additionally, genes in various multidrug resistance transport systems are functionally involved in the resistance to citrinin. Our study identifies the antioxidant defense as a major physiological response in the case of citrinin. In general, our results show that the use of live cell gene expression reporters in yeast are a powerful tool to identify toxicity targets and detoxification mechanisms of a broad range of food contaminants relevant for human nutrition.

Different Toxicity Mechanisms for Citrinin and Ochratoxin A Revealed by Transcriptomic Analysis in Yeast

“…We have previously shown that live cell reporter fusions in yeast are valuable and quantitative tools to characterize the acute transcriptional adaptation to CIT [28]. Here, we extend these studies to compare the impact of CIT and OTA on the induction of different stress-inducible genes.…”

“…Moreover, OTA-induced transcription of GRE2 or SOD2 was already maximal at concentrations around 200 ppm (497 μM). We next tested the effect of the loss of Pdr5 function, which is a plasma membrane multidrug transporter critically involved in CIT extrusion [28]. As shown in Figure 1B, the deletion of Pdr5 provokes an enhanced transcriptional response to both CIT and OTA treatment at different doses.…”

“…Much less is known about the toxicity mechanisms of CIT, however, it has been shown to be an efficient nephrotoxin as well [22]. Several groups have contributed to the identification of possible molecular mechanisms of CIT toxicity, finding, among other consequences, the increase of oxidative stress in connection with alterations of mitochondrial function, and induction of apoptosis [23,24,25,26,27,28,29,30,31]. It has been proposed that the co-occurrence of both toxins results in synergetic effects, however no clear conclusions have been reached [32,33].…”

“…The transcriptional response to mycotoxins is likely to be transient and dose dependent, therefore any transcriptomic assay is further complicated by the selection of the optimal induction conditions. Actually, in vivo recording of transcriptional activity in Saccharomyces cerevisiae shows a transient dose–time dependent response to CIT treatment [28]. …”

Interaction of citrinin and resveratrol and their effect on Caco-2 cell growth

“…Higher concentration of citrinin in group C (CTN 250 µg*ml -1 ), in comparison to group B (CTN 100 µg*ml -1 ), caused significant (P < 0.05) reduction of Caco-2 cells, which means that anti-proliferative effects of CTN are dose-dependent. In the study of authors Pascual-Ahuir et al (2014) citrinin triggers a fast and dose dependent activation of stress responsive promoters. It has been reported that CTN stimulates ROS generation and c-Jun N-terminal kinase (JNK) activation for mitochondriadependent apoptotic signaling in human hepatoma G2 cells, and these apoptotic biochemical events are blocked by pretreatment with resveratrol, which exerts antioxidant effects (Chen and Chan, 2009).…”