Role of casein kinase 1 in the glucose sensor-mediated signaling pathway in yeast.
BACKGROUND
In yeast, glucose-dependent degradation of the Mth1 protein, a corepressor of the glucose transporter gene (HXT) repressor Rgt1, is a crucial event enabling expression of several HXT. This event occurs through a signaling pathway that involves the Rgt2 and Snf3 glucose sensors and yeast casein kinase 1 and 2 (Yck1/2). In this study, we examined whether the glucose sensors directly couple with Yck1/2 to convert glucose binding into an intracellular signal that leads to the degradation of Mth1.


RESULTS
High levels of glucose induce degradation of Mth1 through the Rgt2/Snf3 glucose signaling pathway. Fluorescence microscopy analysis indicates that, under glucose-limited conditions, GFP-Mth1 is localized in the nucleus and does not shuttle between the nucleus and cytoplasm. If glucose-induced degradation is prevented due to disruption of the Rgt2/Snf3 pathway, GFP-Mth1 accumulates in the nucleus. When engineered to be localized to the cytoplasm, GFP-Mth1 is degraded regardless of the presence of glucose or the glucose sensors. In addition, removal of Grr1 from the nucleus prevents degradation of GFP-Mth1. These results suggest that glucose-induced, glucose sensor-dependent Mth1 degradation occurs in the nucleus. We also show that, like Yck2, Yck1 is localized to the plasma membrane via C-terminal palmitoylation mediated by the palmitoyl transferase Akr1. However, glucose-dependent degradation of Mth1 is not impaired in the absence of Akr1, suggesting that a direct interaction between the glucose sensors and Yck1/2 is not required for Mth1 degradation.


CONCLUSIONS
Glucose-induced, glucose sensor-regulated degradation of Mth1 occurs in the nucleus and does not require direct interaction of the glucose sensors with Yck1/2.
Pasula
Satish
S
The Mississippi Functional Genomics Network, Department of Biological Sciences, The University of Southern Mississippi, Hattiesburg, MS 39406, USA.
Chakraborty
Samujjwal
S
Choi
Jae H
JH
Kim
Jeong-Ho
JH
D000217:Acyltransferases / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D047389:Casein Kinase I / Q000378:metabolism / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D044783:F-Box Proteins / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; D044783:F-Box Proteins; C118806:MTH1 protein, S cerevisiae; C102114:RGT1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C071032:GRR1 protein, S cerevisiae; D000217:Acyltransferases; C107846:AKR1 protein, S cerevisiae; D044767:Ubiquitin-Protein Ligases; D047389:Casein Kinase I; C479664:YCK1 protein, S cerevisiae; C479666:YCK2 protein, S cerevisiae; D005947:Glucose