Glucose-6-Phosphate Upregulates Txnip Expression by Interacting With MondoA

Abstract

The major metabolic fates of glucose in cells are glycolysis and the pentose phosphate pathway, and they share the first step: converting glucose to glucose-6-phosphate (G6P). Here, we show that G6P can be sensed by the transcription factor MondoA/Mlx to modulate Txnip expression. Endogenous knockdown and EMSA (gel migration assay) analyses both confirmed that G6P is the metabolic intermediate that activates the heterocomplex MondoA/Mlx to elicit the expression of Txnip. Additionally, the three-dimensional structure of MondoA is modeled, and the binding mode of G6P to MondoA is also predicted by in silico molecular docking and binding free energy calculation. Finally, free energy decomposition and mutational analyses suggest that certain residues in MondoA, GKL139-141 in particular, mediate its binding with G6P to activate MondoA, which signals the upregulation of the expression of Txnip.

Normal and Neoplastic Growth Suppression by the Extended Myc Network

“…MondoA–Mlx binding then directly induces the transcription of at least three glycolytic genes, namely, those for hexokinase II, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase and lactate dehydrogenase A, although in a manner that recognizes consensus E-boxes rather than ChoREs [ 40 ]. Given that the PKLR gene is also a target for ChREBP and Myc, and likely for MondoA as well [ 68 , 76 , 77 , 117 , 302 , 313 , 346 ], these findings suggest that significant control over glycolysis is supervised by both arms of the Extended Myc Network in ways that match proliferation with appropriate levels of glucose oxidation, ATP production, mitochondrial function and anabolic substrate supply.…”

“…This “Mlx Network”, also comprised of bHLH-ZIP factors, contained the Myc-like proteins ChREBP (“carbohydrate response element binding protein”) and MondoA and their own dedicated heterodimerization partner, the Max-related Mlx, which together formed the Network’s positively-acting arm [ 31 , 56 , 57 , 58 ] ( Figure 1 ). Unlike Myc and Max, which are nuclear proteins, ChREBP, MondoA and Mlx are “conditionally nuclear” in that they translocate to the nucleus only upon binding metabolites such as glucose, glucose-6-phosphate, fructose 2,6-bisphosphate, lactate and adenosine [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 40 , 42 , 56 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ]. The cytosolic location of MondoA and ChREBP is also not random; rather, amphipathic helical domains in the C-termini of these factors allow them to interact with intracytoplasmic lipid droplets and presumably serve as sensors of intracellular lipid content [ 69 ].…”

Normal and Neoplastic Growth Suppression by The Extended Myc Network

“…MondoA-Mlx binding then directly induces the transcription of at least three glycolytic genes, namely, those for hexokinase II, 6-phosphofructo-2kinase/fructose-2,6-bisphosphatase and lactate dehydrogenase A, although in a manner that recognizes consensus Eboxes rather than ChoREs [47]. Given that the PKLR gene is also a target for ChREBP and Myc, and likely for MondoA as well [55,63,64,104,299,310,342], these findings suggest that significant control over glycolysis is supervised by both arms of the Extended Myc Network in ways that match proliferation with appropriate levels of glucose oxidation, ATP production, mitochondrial function and anabolic substrate supply.…”

“…A potential connection between TXNIP's role as glycolytic regulator and that of an oxido-reductase has been demonstrated by studies showing TXNIP to be inducible by adenosine-containing molecules, including adenosine itself, ATP and NADH in ways that cooperate with glucose [40,54]. A more extensive role for TXNIP (and indirectly for MondoA and ChREBP) as a TS in several cancer types has recently emerged although it appears to involve more than simply its negative regulation of glucose uptake [55,374]. For example, TXNIP stabilizes the cyclin-dependent kinase inhibitor p27 KIP1 [375].…”

“…1). Unlike Myc and Max, which are nuclear proteins, ChREBP, MondoA and Mlx are cytoplasmic but translocate to the nucleus in response to the binding of metabolites such as glucose, glucose-6-phosphate, fructose 2,6-bisphosphate, lactate and adenosine [33,34,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55]. In fact, the cytosolic location of MondoA and ChREBP is not random; rather amphipathic helical domains in the C-termini of these factors allow them to interact with intracytoplasmic lipid droplets and presumably serve as sensors of intracellular lipid content [56].…”