Using a Yeast Model to Decipher the Toxicity of Organochlorinated Pesticides

Exposure to organochlorinated pesticides (OCPs) has been linked to neurotoxicity, endocrine disruption, and cancer, but the cellular mechanisms of toxicity behind these effects remain largely unknown. It was hypothesized that a chemical genomics approach using a Saccharomyces cerevisiae gene deletion library could help elucidate the cellular mechanisms by which various OCPs induce toxicity. Pools of deletion strains were exposed in triplicate for five and fifteen generations to the IC₂₀, 50% IC₂₀, and 25% IC₂₀ OCP concentrations. The oligo sequences unique to each deletion strain were PCR-amplified and hybridized to TAG4 arrays to identify sensitive, unaffected, and resistant strains. The overrepresented biological terms within the data assisted in the selection of individual deletion strains for growth curve experiments. It is demonstrated here that genes involved in transcriptional elongation, nitrogen utilization, and amino acid sensing are necessary for resistance to the toxaphene OCP, a profile very similar to that for the GMP synthesis inhibitors 6-azauracil and mycophenolic acid. Preliminary analyses for the dieldrin OCP indicate that autophagy and components of the pyruvate dehydrogenase complex are critical for cell survival under dieldrin exposure. Future investigations will refine the mechanism(s) in yeast and perhaps examine how the knockout or knockdown of orthologs in higher organisms, such as C. elegans or human cell lines, affects OCP toxicity.