Different modes of sodium-d-glucose cotransporter-mediated d-glucose uptake regulation in Caco-2 cells

Abstract

We recently reported that a considerable amount of the sodium-d-glucose cotransporter SGLT1 present in Caco-2 cells, a model for human enterocytes, is located in intracellular compartments attached to microtubules. A similar distribution pattern was also observed in enterocytes in thin sections from human jejunum, highlighting the validity of the Caco-2 cell model. Fluorescent surface labeling of live Caco-2 cells revealed that the intracellular compartments containing SGLT1 were accessible by endocytosis. To elucidate the role of endosomal SGLT1 in the regulation of sodium-dependent d-glucose uptake into enterocytes, we compared SGLT1-mediated D-glucose uptake into Caco-2 cells with the subcellular distribution of SGLT1 after challenging the cells with different stimuli. Incubation (90 min) of Caco-2 cells with mastoparan (50 microM), a drug that enhances apical endocytosis, shifted a large amount of SGLT1 from the apical membrane to intracellular sites and significantly reduced sodium-dependent alpha-[(14)C]methyl-D-glucose uptake (-60%). We also investigated the effect of altered extracellular D-glucose levels. Cells preincubated (1 h) with d-glucose-free medium exhibited significantly higher sodium-dependent alpha-[(14)C]methyl-D-glucose uptake (+45%) than did cells preincubated with high d-glucose medium (100 mM, 1 h). Interestingly, regulation of SGLT1-mediated d-glucose uptake into Caco-2 cells by extracellular D-glucose levels occurred without redistribution of cellular SGLT1. These data suggest that, pharmacologically, d-glucose uptake can be regulated by a shift of SGLT1 between the plasma membrane and the endosomal pool; however, regulation by the physiological substrate d-glucose can be explained only by an alternative mechanism.

Pancreatic α-Amylase Controls Glucose Assimilation by Duodenal Retrieval through N-Glycan-specific Binding, Endocytosis, and Degradation

“…Subsequently, Khoursandi et al (21) reported that the intracellular compartments containing SGLT1 are accessible by endocytosis during incubation of the cells for 30 min at 37°C. Incubation of Caco-2 cells with mastoparan, a drug that enhances apical endocytosis, shifted a large amount of SGLT1 from the apical membrane to intracellular sites and significantly reduced sodium-dependent glucose uptake (Ϫ60%) (21). These papers showed that SGLT1 is internalized from the apical surface to the endosomes of Caco-2 cells by incubation of the cells for 30 min at 37°C and that most intracellular SGLT1 remains in the intracellular reserve pools.…”

Tripeptides of RS1 (RSC1A1) Inhibit a Monosaccharide-dependent Exocytotic Pathway of Na+-d-Glucose Cotransporter SGLT1 with High Affinity

“…In this work the authors did not distinguish whether the SGLT1 protein in the plasma membrane or the turnover of SGLT1 was increased. In another study in which Caco-2 cells were preincubated for 1 h with 100 mM D-glucose, a 45% decrease of phlorizin inhibitable AMG uptake was observed (20). The authors proposed that this down-regulation is due to increased endocytosis, however, no significant changes of the intracellular distribution of SGLT1 could be detected.…”

“…Cyclic AMP, protein kinase A, protein kinase C (PKC), 3 and phosphoinositol 3-kinase are involved in the regulatory pathways (13,14,16). It has been shown that SGLT1 can be regulated by changes in transcription (12,17,18), mRNA stability (19), intracellular trafficking (14,16,20,21), and transporter activity (22). However, the individual regulatory pathways, their cross-talk, and their physiological importance are not understood.…”

Transepithelial glucose transport and Na+/K+ homeostasis in enterocytes: an integrative model

“…Studies have revealed intracellular stores of SGLT1 (38,39), which are thought to play a role in the regulation of SGLT1-mediated glucose uptake. SGLT1 has also been shown to be rapidly upregulated by sweet taste receptors (76).…”