Gene transcription analysis of Saccharomyces cerevisiae exposed to neocarzinostatin protein– chromophore complex reveals evidence of DNA damage, a potential mechanism of resistance, and consequences of prolonged exposure

The natural product neocarzinostatin (NCS), a protein–small molecule complex, exhibits potent antiproliferative activity in mammalian cells but has little apparent effect on the growth of the unicellular eukaryotic organism, Saccharomyces cerevisiae. Here, we show by whole-genome transcription profiling experiments that incubation of S. cerevisiae with NCS leads to dramatic and wide-ranging modifications in the expression profile of yeast genes. Approximately 18% of yeast transcripts are altered by 2-fold or more within 4 h of treatment with NCS. Analysis of the observed transcription profile provides evidence that yeast rapidly and continuously overexpress multiple DNA-damage repair genes during NCS exposure. Perhaps to meet the energetic requirements of continuous DNA-damage repair, yeast cells enter respiration upon prolonged exposure to NCS, although grown in nutrient-rich medium. The NCS protein component is readily transported into S. cerevisiae, as demonstrated by fluorescence microscopy of yeast treated with fluorescently labeled NCS. Transcription profiling experiments with neocarzinostatin protein alone implicate a specific resistance mechanism in yeast that targets the NCS protein component, one involving the nonclassical export pathway. These experiments provide a detailed picture of the effects of exposure to NCS upon yeast and the mechanisms they engage as a response to this protein–small molecule DNA-damaging agent.