Zachary A Duck

Many fungi have evolved mechanisms to assess environmental nutrient availability prior to the energy-intensive process of mating. In this study, we examined one such system in Saccharomyces cerevisiae, involving a glucose-sensing pathway mediated by Gpr1p and the pheromone-induced mating pathway. Initially we observed that the mating pathway in MATa cells is sensitive to environmental glucose depletion. This phenomenon can be partially reversed with a high glucose spike, but not with the addition of low levels of glucose. Deletion of the low-affinity glucose receptor, Gpr1p, eliminated this glucose-induced recovery of pheromone responsiveness. We then determined the impact of GPR1 deletion on the mating pathway and observed that, in all end points studied, the mating pathway response to pheromone is reduced in the absence of Gpr1p. Similarly, elimination of the Gα for Gpr1p, Gpa2p, resulted in reduction in pheromone sensitivity in all assays studied. The negative effect of removing Gpr1p on mating pathway activation could be recovered by overexpressing the mating receptor, Ste2p. Furthermore, Ste2p levels are reduced in the absence of glucose and GPR1. These data suggest that activity of the GPCR-mediated mating pathway in S. cerevisiae is modulated by extracellular glucose concentrations through the only other GPCR in MATa cells, Gpr1p.

3‐hydroxy‐3‐methylglutaryl coenzyme A reductase inhibitors (statins) are prominent cholesterol lowering maintenance drugs that have been previously implicated in altering gene expression in several targets including hepatocyte derived cell lines (Hepatoma HepG2). Statin‐dependent changes in expression have been implicated in a wide range of categories including molecular transporters. However, detailed analysis of how drugs affect expression levels has yet to be performed for many of these transporters. The effect of statins on the expression of the hepatic drug transporters Organic Anion Transporter Protein (OATP) 1B1 and 1B3 was assessed in native expression (T84 cells) and overexpression (transfected Human Embryonic Kidney (HEK) cells) systems, using quantitative Polymerase Chain Reaction (qPCR) after incubation with Simvastatin, Rosuvastatin, Lovastatin, Atorvastatin, and Pitavastatin. Expression of both OATP 1B1 and OATP 1B3 were shown to decrease in both native expression and overexpression systems with statin treatment. Rosuvastatin decreased transporter levels to the greatest extent. These results provide new insights into the role of statins in hepatic drug transport.

Nutrient sensing and mating are clearly linked in a number of different fungal species. The mechanisms by which these two processes interact appear to differ in different species. We have observed that glucose sensing and mating are closely linked in Saccharomyces cerevisiae, with disruptions in the glucose sensing pathway causing reduction in mating pathway activity. In this study we sought to determine the mechanisms by which this reduction occurs. In a series of gene replacement experiments we have shown that overexpressing the mating receptor in glucose receptor (Gpr1) deficient cells restores the mating pathway. Likewise, overexpression of the g protein associated with glucose sensing, Gpa2, is able to restore the mating pathway in Gpr1蜐 cells. These effects seem to be independent of the activity of the g‐protein. Dominant negative effects were seen with some modified forms of Gpr1. We propose a mechanism of interaction that involves the formation of a complex involving potentially Ste2, Gpr1, Gpa2, and Gpa1. This research was funded by the NSF, Project #0952519

Mating in Saccharomyces cerevisiae is an energy intensive process, so it follows that yeast cells would want to assess sugar availability prior to mating. Our lab has determined that optimal mating efficiency is dependent on a glucose sensing pathway mediated by the G‐protein coupled receptor, Gpr1. In this study we systematically assessed the impact of deficiencies in all known participants in the Gpr1 pathway on the mating pathway. The results indicated that many components of the glucose sensing pathway are necessary for optimal function of the mating pathway. To determine potential reciprocal effects, we assessed the impact of deficiencies in all known participants in the mating pathway on the glucose sensing pathway. The results indicated that the glucose sensing pathway was also dependent on many of the components of the mating pathway for complete activity. This analysis indicates significant interdependence between yeast mating and glucose sensing through Gpr1, and points to at least two levels of interaction between these two pathways. This research was funded by the National Science Foundation, Award #: 0952519.