Rab14 limits the sorting of Glut4 from endosomes into insulin-sensitive regulated secretory compartments in adipocytes

Abstract

Insulin increases glucose uptake by increasing the rate of exocytosis of the facilitative glucose transporter isoform 4 (Glut4) relative to its endocytosis. Insulin also releases Glut4 from highly insulin-regulated secretory compartments (GSVs or Glut4 storage vesicles) into constitutively cycling endosomes. Previously it was shown that both overexpression and knockdown of the small GTP-binding protein Rab14 decreased Glut4 translocation to the plasma membrane (PM). To determine the mechanism of this perturbation, we measured the effects of Rab14 knockdown on the trafficking kinetics of Glut4 relative to two proteins that partially co-localize with Glut4, the transferrin (Tf) receptor and low-density-lipoprotein-receptor-related protein 1 (LRP1). Our data support the hypothesis that Rab14 limits sorting of proteins from sorting (or 'early') endosomes into the specialized GSV pathway, possibly through regulation of endosomal maturation. This hypothesis is consistent with known Rab14 effectors. Interestingly, the insulin-sensitive Rab GTPase-activating protein Akt substrate of 160 kDa (AS160) affects both sorting into and exocytosis from GSVs. It has previously been shown that exocytosis of GSVs is rate-limited by Rab10, and both Rab10 and Rab14 are in vitro substrates of AS160. Regulation of both entry into and exit from GSVs by AS160 through sequential Rab substrates would provide a mechanism for the finely tuned 'quantal' increases in cycling Glut4 observed in response to increasing concentrations of insulin.

Chronic treatment with fluoride affects the jejunum: insights from proteomics and enteric innervation analysis

“…In the network comparing 10 mgF/L vs . control groups, the isoforms 1B, 10, 12 and 14 interact with GLUT4, and especially Rab 10 and Rab 14, are required in GLUT4 translocation to the plasma membrane 56 , 57 . Their increased expression might help to explain the increased sensitivity to insulin recently reported to occur in rats with diabetes induced by streptozotocin exposed to 10 mgF/L in the drinking water 58 .…”

Hypoxia in Combination With Muscle Contraction Improves Insulin Action and Glucose Metabolism in Human Skeletal Muscle via the HIF-1α Pathway

“…A change in the proportion of GLUT4 at the cell surface might be caused by alterations in the endocytosis/exocytosis rate. Rab8A and Rab10 are involved in vesicle tethering via interaction with the exocyst, and Rab5 is involved in sorting of GLUT4 from the recycling endosome to the insulin-sensitive compartment (16)(17)(18). Rab20 is colocalized with Rab5 on endosomal membranes (19).…”

Rab8A regulates insulin‐stimulated GLUT4 translocation in C2C12 myoblasts

“…Indeed, previous studies on 3T3-L1 adipocytes demonstrated that Rab10 and Rab14 are the two relevant AS160 regulated Rab proteins [23]. Knockdown of Rab10 and Rab14 in adipocytes greatly reduces insulin-stimulated GLUT4 translocation [9,10,[23][24][25]. Furthermore, TIRFM imaging studies showed that after insulin stimulation, majority of the IRAP-pHluorin exocytic events are decorated with Rab10 signals, whereas Rab14 residents on transferrin receptor containing endosomes [10].…”