The deubiquitinating enzyme USP25 binds tankyrase and regulates trafficking of the facilitative glucose transporter GLUT4 in adipocytes

Abstract

Key to whole body glucose homeostasis is the ability of fat and muscle cells to sequester the facilitative glucose transporter GLUT4 in an intracellular compartment from where it can be mobilized in response to insulin. We have previously demonstrated that this process requires ubiquitination of GLUT4 while numerous other studies have identified several molecules that are also required, including the insulin-responsive aminopeptidase IRAP and its binding partner, the scaffolding protein tankyrase. In addition to binding IRAP, Tankyrase has also been shown to bind the deubiquinating enzyme USP25. Here we demonstrate that USP25 and Tankyrase interact, and colocalise with GLUT4 in insulin-sensitive cells. Furthermore depletion of USP25 from adipocytes reduces cellular levels of GLUT4 and concomitantly blunts the ability of insulin to stimulate glucose transport. Collectively, these data support our model that sorting of GLUT4 into its insulin-sensitive store involves a cycle of ubiquitination and subsequent deubiquitination.

CHC22 clathrin mediates traffic from early secretory compartments for human GLUT4 pathway biogenesis

“…So rodents must rely simply on coalescence of relevant cargo (GLUT4, IRAP, and p115) in the ERGIC to segregate them from other proteins constitutively leaving the secretory pathway and this is likely less efficient, perhaps with some GLUT4 directly accessing the cell surface for rapid reuptake in the absence of insulin (Martin et al, 2000). In this case, population of the rodent GSC with GLUT4 is mainly a result of the retrograde recycling pathway, in which sortilin and IRAP have been shown to participate (Jordens et al, 2010;Pan et al, 2017Pan et al, , 2019Sadler et al, 2019). In the case of human cells, CHC22 can actively capture GLUT4 and partners for diversion to the GSC, providing a more robust route to GSC formation following biosynthesis, with the GSC also replenished with GLUT4 by the endocytic-retrograde recycling pathway.…”

Structure, function and regulation of mammalian glucose transporters of the SLC2 family

“…However, collectively the retention mechanisms appear to involve a series of interacting, adapter and tethering proteins including TUG, sortilin, golgi associated, gamma adaptin ear containing, ARF-binding protein 2 (GGA2), p115 and insulin-responsive aminopeptidase (IRAP), the clathrin heavy chain (CHC) components CHC17 and CHC22 [ 26 , 32 , 177 ]. The enzyme tankarase, UBC9 (ubiquitinylation) and USP25 (deubiquitnylation) also appear to be involved in post-translational control of GLUT4 traffic and sorting [ 124 , 127 , 177 , 227 ]. Figure 1 summarises the compartments in which GLUT4 is localised, together with the GLUT4-vesicle-interacting proteins which control GLUT4 retention and sorting.…”

Metabolic Modulation to Treat Cardiac Diseases: Role for Membrane Substrate Transporters

“…Another potential approach is to exploit the emerging role of post-translational modifications of both CD36 and GLUT4 in their localization and functioning. Thus, CD36 undergoes a number of posttranslational modifications including palmitoylation, O-GlcNAcylation and ubiquitination, which may influence its subcellular recycling and/or functioning 41 , while GLUT4 trafficking (in adipocytes) is regulated, among others, by (de)ubiquitination 42 . Disclosure of the putatively complex role of post-translational modifications on CD36 and GLUT4 functioning is likely to generate additional approaches for their application as metabolic modulation targets.…”