Yeast AMP-Activated Protein Kinase Monitors Glucose Concentration Changes as well as Absolute Glucose Levels [Cell Biology]

March 13th, 2014 by Bendrioua, L., Smedh, M., Almquist, J., Cvijovic, M., Jirstrand, M., Goksor, M., Adiels, C. B., Hohmann, S.

Analysis of the time-dependent behavior of a signaling system can provide insight into its dynamic properties. We employed the nucleo-cytoplasmic shuttling of the transcriptional repressor Mig1 as readout to characterize Snf1-Mig1 dynamics in single yeast cells. Mig1 binds to promoters of target genes and mediates glucose repression. Mig1 is predominantly located in the nucleus when glucose is abundant; upon glucose depletion Mig1 is phosphorylated by the AMP-activated kinase Snf1 and exported into the cytoplasm. We used a three-channel microfluidic device to establish a high degree of control over the glucose concentration exposed to cells. Following regimes of glucose up- and downshifts we observed (1) a very rapid response reaching a new steady state within less than one minute; (2) different glucose threshold concentrations depending on glucose up- or downshifts; (3) a graded profile with increased cell-to-cell variation at threshold glucose concentrations; (4) a biphasic behavior with a transient translocation of Mig1 upon shift from high to intermediate glucose concentrations. FLIP and FRAP data demonstrate that Mig1 shuttles constantly between nucleus and cytoplasm although with different rates depending on the presence of glucose. Taken together, our data suggest that the Snf1-Mig1 system has the ability to monitor glucose concentration changes as well as absolute glucose levels. The sensitivity over a wide range of glucose levels and different glucose concentration-dependent response profiles are likely determined by the close integration of signaling with metabolism and may provide for a highly flexible and fast adaptation to an altered nutritional status.