Our laboratory is interested in the molecular basis underlying the response of eukaryotic cells to environmental stress. We are using the yeast Saccharomyces cerevisiae as a model organism for the cell and molecular biological response of eukaryotic cells to two different types of environmental challenges, cytotoxic drugs and oxidative stress. We have found that the cellular response to each of these stress regimens is modulated by the action of transcriptional regulatory proteins and often involves the expression of ATP binding cassette (ABC) transporter proteins. A brief description of each research area is presented below. More detail can be found by clicking on the link of interest and publications on these areas are listed here.
A major problem in the chemotherapy of cancer is the appearance of drug resistant tumor cells. Often these drug resistant tumors exhibit broad range tolerance to several structurally unrelated cytotoxic drugs. This ability to tolerate a variety of different drugs is referred to as multidrug resistance. One of the best understood mechanisms behind the acquistion of multidrug resistance involves the overproduction of an ABC transporter protein designated MDR1. This membrane protein acts as an ATP-dependent drug pump and prevents the accumulation of toxic levels of target compounds. Saccharomyces cerevisiae also exhibits loci that can be altered to give rise to multidrug resistance (referred to in this organism as pleiotropic drug resistance). We are also expanding our studies into the human pathogenic fungus Candida glabrata which can acquire a multidrug resistance phenotype that is highly related to that seen in S. cerevisiae. Along with analyses of the transcriptional regulatory systems involved in control of fungal multidrug resistance, we are interested in the function and activity of proteins encoded by target genes. We have isolated an ABC transporter-encoding gene (YOR1) from S. cerevisiae that is regulated by the PDR system and are analyzing the trafficking of this protein through the secretory pathway. Our goal is to use Yor1p trafficking as a model for the delivery of ABC transporters to their final destination in eukaryotic cells.
Regulation of Membrane Lipid Composition
Many studies on multidrug resistance have clearly demonstrated the importance of transporter proteins in regulating drug concentrations inside cells. Less well understood but arguably even more important is the contribution made by the membranes that separate the cytoplasm from the extracellular milleu. Work from our laboratory and others indicated that genes encoding enzymes involved in biosynthesis of plasma membrane lipids called sphingolipds are important transcriptional targets of the PDR system. Changes in the level of these lipids have important consequence to drug resistance and trafficking of membrane proteins.
An inescapable challenge posed to all cells growing under aerobic conditions is the production of reactive oxygen species that can damage intracellular components. To deal with this problem, cells elaborate a variety of different proteins and small molecules that are directed towards maintaining normal intracellular redox balance. In S. cerevisiae, transcriptional control of many of these oxidative stress resistance components is provided by the transcription factor Yap1p. We are studying how Yap1p is activated upon oxidative stress challenge as well as the downstream target genes that are important in maintenance of redox balance.