Christine E. Bulawa

Complementary whole-genome technologies reveal the cellular response to proteasome inhibition by PS-341

Although the biochemical targets of most drugs are known, the biological consequences of their actions are typically less well understood. In this study, we have used two whole-genome technologies in Saccharomyces cerevisiae to determine the cellular impact of the proteasome inhibitor PS-341. By combining population genomics, the screening of a comprehensive panel of bar-coded mutant strains, and transcript profiling, we have identified the genes and pathways most affected by proteasome inhibition. Many of these function in regulated protein degradation or a subset of mitotic activities. In addition, we identified Rpn4p as the transcription factor most responsible for the cells ability to compensate for proteasome inhibition. Used together, these complementary technologies provide a general and powerful means to elucidate the cellular ramifications of drug treatment.

Chs1 of Candida albicans is an essential chitin synthase required for synthesis of the septum and for cell integrity

CaCHS1 of the fungal pathogen Candida albicans encodes an essential chitin synthase that is required for septum formation, viability, cell shape and integrity. The CaCHS1 gene was inactivated by first disrupting one allele using the ura‐blaster protocol, then placing the remaining allele under the control of the maltose‐inducible, glucose‐repressible MRP1 promoter. Under repressing conditions, yeast cell growth continued temporarily, but daughter buds failed to detach from parents, resulting in septumless chains of cells with constrictions defining contiguous compartments. After several generations, a proportion of the distal compartments lysed. The conditional Δchs1 mutant also failed to form primary septa in hyphae; after several generations, growth stopped, and hyphae developed swollen balloon‐like features or lysed at one of a number of sites including the hyphal apex and other locations that would not normally be associated with septum formation. CHS1 therefore synthesizes the septum of both yeast and hyphae and also maintains the integrity of the lateral cell wall. The conditional mutant was avirulent under repressing conditions in an experimental model of systemic infection. Because this gene is essential in vitro and in vivo and is not present in humans, it represents an attractive target for the development of antifungal compounds.

Novel small-molecule inhibitors of RNA polymerase III

ABSTRACT A genetic approach utilizing the yeast Saccharomyces cerevisiae was used to identify the target of antifungal compounds. This analysis led to the identification of small molecule inhibitors of RNA polymerase (Pol) III from Saccharomyces cerevisiae. Three lines of evidence show that UK-118005 inhibits cell growth by targeting RNA Pol III in yeast. First, a dominant mutation in the g domain of Rpo31p, the largest subunit of RNA Pol III, confers resistance to the compound. Second, UK-118005 rapidly inhibits tRNA synthesis in wild-type cells but not in UK-118005 resistant mutants. Third, in biochemical assays, UK-118005 inhibits tRNA gene transcription in vitro by the wild-type but not the mutant Pol III enzyme. By testing analogs of UK-118005 in a template-specific RNA Pol III transcription assay, an inhibitor with significantly higher potency, ML-60218, was identified. Further examination showed that both compounds are broad-spectrum inhibitors, displaying activity against RNA Pol III transcription systems derived from Candida albicans and human cells. The identification of these inhibitors demonstrates that RNA Pol III can be targeted by small synthetic molecules.

Detection of compounds that rescue Rab1-synuclein toxicity.

Recent studies implicate a disruption in Rab-mediated protein trafficking as a possible contributing factor to neurodegeneration in Parkinsons disease (PD). Misfolding of the neuronal protein alpha-synuclein (asyn) is implicated in PD. Overexpression of asyn results in cell death in a wide variety of model systems, and in several organisms, including yeast, worms, flies, and rodent primary neurons, this toxicity is suppressed by the overproduction of Rab proteins. These and other findings suggest that asyn interferes with Rab function and provide new avenues for PD drug discovery. This chapter describes two assay formats that have been used successfully to identify small molecules that rescue asyn toxicity in yeast. The 96-well format monitors rescue by optical density and is suitable for screening thousands of compounds. A second format measures viable cells by reduction of the dye alamarBlue, a readout that is compatible with 96-, 384-, and 1536-well plates allowing the screening of large libraries (>100,000 compounds). A secondary assay to eliminate mechanistically undesirable hits is also described.