Different modes of sodium-D-glucose cotransporter-mediated D-glucose uptake regulation in Caco-2 cells.
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.
Khoursandi
Saeed
S
Max Planck Institute of Molecular Physiology, Otto-Hahn-Str. 11, 44227 Dortmund, Germany.
Scharlau
Daniel
D
Herter
Peter
P
Kuhnen
Cornelius
C
Martin
Dirk
D
Kinne
Rolf K H
RK
Kipp
Helmut
H
D018938:Caco-2 Cells; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D011992:Endosomes / Q000378:metabolism; D020895:Enterocytes / Q000378:metabolism / Q000648:ultrastructure; D045604:Extracellular Fluid / Q000378:metabolism; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins; D007583:Jejunum / Q000648:ultrastructure; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D010455:Peptides; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology*; D051269:Sodium-Glucose Transporter 1; D014862:Wasp Venoms / Q000494:pharmacology
D036341:Intercellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; D010455:Peptides; C495674:SLC5A1 protein, human; D051269:Sodium-Glucose Transporter 1; D014862:Wasp Venoms; C037500:mastoparan; D005947:Glucose