RNA interference toward UMP1 induces proteasome inhibition in Saccharomyces cerevisiae: evidence for protein oxidation and autophagic cell death

The proteasome is a large intracellular protease that is responsible for a large portion of intracellular proteolysis, in particular the degradation of a majority of short-lived and oxidized proteins. Inhibition of proteasome function occurs in response to multiple stressors, with proteasome inhibition sufficient for the induction of a wide range of cytotoxic processes. Although considerable advances have been made in the understanding of the proteasome, and the effects of proteasome inhibition, our understanding of these topics in Saccharomyces cerevisiae has been slowed by the inability of proteasome inhibitors to penetrate and/or be retained in S. cerevisiae. Expression of UMP1 is necessary for proteasome assembly in S. cerevisiae, and in the present study we examined the effectiveness of RNA interference for UMP1 as a means of achieving proteasome inhibition in S. cerevisiae. Induction of RNA interference for UMP1 resulted in a dramatic decrease in UMP1 at the protein level, which was not observed in cells transformed with control vector. RNA interference caused an impairment in proteasome function, and increase in protein oxidation, with proteins involved in both stress response and energy metabolism showing increased oxidation. Interestingly, RNA interference induced cell death that seemed to be autophagic in nature, suggesting possible cross talk between the proteasome and the autophagic proteolytic pathways. Taken together, these data indicate that RNA interference may be a useful model with which to study the effects of proteasome inhibition in S. cerevisiae and demonstrate the ability of proteasome inhibition to induce cytotoxic alterations in S. cerevisiae.