A glucose starvation response governs endocytic trafficking and eisosomal retention of surface cargoes

Abstract

Eukaryotic cells adapt their metabolism to the extracellular environment. Downregulation of surface cargo proteins in response to nutrient stress reduces the burden of anabolic processes whilst elevating catabolic production in the lysosome. We use yeast to show that glucose starvation triggers a transcriptional response that simultaneously increases internalisation from the plasma membrane whilst supressing recycling from endosomes back to the surface. Nuclear export of the Mig1 transcriptional repressor in response to glucose starvation increases levels of the Yap1801/02 clathrin adaptors, which is sufficient to increase cargo internalisation. We also show Gpa1, which coordinates endosomal lipid homeostasis, is required for surface recycling of cargo. Nuclear translocation of Mig1 increases GPA2 levels and inhibits recycling, potentially by diverting Gpa1 to the surface and interfering with its endosomal role in recycling. Finally, we show glucose starvation results in transcriptional upregulation of many eisosomal factors, which serve to sequester a portion of nutrient transporters to persist the starvation period and maximise nutrient uptake upon return to replete conditions. This latter mechanism provides a physiological benefit for cells to rapidly recover from glucose starvation. Collectively, this remodelling of the surface protein landscape during glucose starvation calibrates metabolism to available nutrients.

Complementary α-arrestin-ubiquitin ligase complexes control nutrient transporter endocytosis in response to amino acids

“…Yet, not only substrate transport can induce nutrient transporter endocytosis, but also nutrient limitation, acute starvation or rapamycin treatment ( Crapeau et al, 2014 ; Hovsepian et al, 2017 ; Jones et al, 2012 ; Laidlaw et al, 2020 ; Lang et al, 2014 ; Müller et al, 2015 ; Schmidt et al, 1998 ; Yang et al, 2020 ). Starvation-induced endocytosis is part of a coordinated catabolic cascade.…”

Endosomal cargo recycling mediated by Gpa1 and Phosphatidylinositol-3-Kinase is inhibited by glucose starvation

“…Previous work has shown that in response to glucose starvation, the yeast AP180 clathrin adaptors are transcriptionally upregulated with a concomitant increase in endocytosis (Laidlaw et al, 2020). Under basal conditions in media lacking methionine, the methionine transporter Mup1 tagged with GFP localises to the plasma membrane (PM), but much of this signal is redistributed to endosomes and the vacuole upon plasmid over-expression of mCherrytagged AP180s: Yap1801-Cherry or Yap1802-mCherry (Figure 1A).…”

“…Similarly, we find shifting cells to media lacking sugar or supplemented with raffinose also results in robust inhibition of recycling (Figure 1D). Therefore, although internalization from the plasma membrane increases following glucose starvation (Laidlaw et al, 2020), two dedicated recycling reporters show glucose starvation also triggers a reduction in protein and lipid traffic from endosomes back to the PM. We propose increased internalization and decreased recycling during glucose starvation cooperate to drive vacuolar degradation of cargoes en masse in response to nutritional stress.…”

“…Mig1 is a zinc finger transcription factor that mediates glucose repression in yeast cells (Nehlin and Ronne, 1990;Lundin et al, 1994) and in response activates alternative metabolic pathways (Schüller, 2003). In addition to this, Mig1 influences membrane trafficking machinery through its repression of clathrin adaptor genes YAP1801 and YAP1802 under glucose replete conditions that stabilise endocytosis levels (Laidlaw et al, 2020). These experiments were performed in media supplemented with the alternative carbon source raffinose, which might provide a distinct osmotic potential that makes direct comparison with the finding that recycling is reduced during carbon withdrawal.…”

“…In glucose, the tuneable inhibitor of recycling Gpa2 is transcriptionally repressed, collectively maintaining high levels of surface proteins at the plasma membrane for optimal growth (Figure 5A). Upon glucose depletion, the Mig1-dependent increase in endocytosis via yeast AP180 adaptors (Laidlaw et al, 2020), would complement decreased recycling via the Glc7-Reg1 > Mig1 > GPA2 pathway to modulate the surface proteome to suit nutritional availability, increase lysosomal / vacuolar degradation and calibrate metabolic processes for cellular survival. G-protein regulators and PI3K orthologues are evolutionarily conserved (Pierce et al, 2002;Engelman et al, 2006), and although G-protein signalling is much more complex in animal cells, Gαs has been shown to regulate endosomal trafficking and surface protein function (Colombo et al, 1992(Colombo et al, , 1994Beron et al, 1995;Zheng et al, 2004;Beas et al, 2012).…”