SPECIAL SEMINAR - Dr Sébastien LEON, Research Director CNRS/Paris Diderot University - Jacques MONOD Institute (IJM) PARIS

A quest for the mysterious signal regulating AMPK activity in yeast

Dr Sébastien LEON

Research Director CNRS/Paris Diderot University
Jacques MONOD Institute (IJM)
Team Membrane trafficking, ubiquitin and signaling

Abstract
Glucose acts both as a nutrient and a signaling molecule. This is particularly true in the yeast Saccharomyces cerevisiae, which has evolved in sugar-rich ecological niches. In yeast, the presence of glucose drives metabolism toward fermentation by repressing the expression of genes involved in the utilization of alternative carbon sources and in respiratory metabolism (« glucose repression »). This ensures the preferential use of glucose through fermentation over any other carbon source.
At the core of this mechanism is the yeast orthologue of 5’-AMP-activated kinase (AMPK), known as Snf1. Snf1 is thought to have evolved primarily as a glucose sensor rather than an energy sensor. Glucose presence inhibits Snf1 activity, whereas glucose depletion triggers its activation and initiates a transcriptional program that enables the utilization of non-glucose carbon sources. Although the exact nature of the signal by which glucose regulates Snf1 activity remains unknown, early steps of glucose metabolism appear to be required. In particular, a PP1 phosphatase complex, responsible for dephosphorylating and thereby inactivating Snf1, plays an essential role in conveying the glucose signal to promote Snf1 inhibition.
We performed a genetic screen using the toxic glucose analog 2-deoxyglucose (2DG) to identify regulators of this pathway and to develop tools for elucidating the mechanisms by which glucose exerts its effect in the glucose repression pathway. Specifically, we identified point mutations in genes encoding AMPK and PP1 that abolish the cellular response to 2DG. Further analysis of these mutants suggests that Reg1 plays a central role in sensing the presence of glucose or 2DG, through mechanisms that we now aim to elucidate.