Apical Localization of Sodium-Dependent Glucose Transporter SGLT1 is Maintained by Cholesterol and Microtubules

Abstract

A GFP-labeled sodium-dependent glucose transporter SGLT1 (SGLT-GFP) was transfected into MDCK cells. SGLT-GFP was localized at the apical membrane in confluent cells. When cellular cholesterol was depleted by methyl-β-cyclodextrin (MβCD) treatment, the localization of SGLT-GFP gradually switched from apical to whole plasma membrane. Time-lapse microscopy revealed that the effect of MβCD appeared within 30 min, and that the transition of SGLT-GFP to the whole plasma membrane was completed within 2 hr after the administration. Immunofluorescence microscopy revealed that the tight junction framework remained steady during this process. The effect of MβCD on SGLT-GFP localization was counter­balanced by the addition of cholesterol into the culture medium. Disruption of microtubules by colcemid also perturbed SGLT-GFP localization. SGLT-GFP localized to the whole plasma membrane by colcemid treatment, and apical localization was restored within 1 hr after ­removal of colcemid. Inhibition of protein synthesis by cycloheximide had no effect on the transition of SGLT-GFP induced by the MβCD or colcemid. These results indicated that the apical localization of SGLT-GFP is maintained by cellular cholesterol and microtubules, possibly with an apical recycling machinery.

Desmosome Assembly and Cell-Cell Adhesion Are Membrane Raft-dependent Processes

“…Four-hour treatment in MCD dramatically decreased the strength of cell-cell junctions. Similar to tight junction maintenance in MCD medium (41), desmosomes were still preserved on the plasma membrane even after 4-h treatment in MCD. Decreases in the strength of cell-cell junctions may be a consequence of reduced interaction between the desmosomal proteins.…”

Real‐time imaging of sodium glucose transporter (SGLT1) trafficking and activity in single cells

“…Accordingly, based on the observation that M β CD decreases both the activity and insertion of SGLT1 into the apical membrane, it has been suggested that cellular cholesterol stabilizes SGLT1 into the apical membrane (Suzuki et al. ). The GTPase dynamin regulates both the clathrin and caveolin‐dependent pathways, but more importantly, does not regulate the lipid raft endocytotic pathway, which is caveolin‐independent (Achiriloaie et al.…”

Interaction of glucose transporters SGLT1 and GLUT2 with cytoskeleton in enterocytes and Caco2 cells during hexose absorption

“…It was shown that SGLT1 trans porter is associated with endosomes connected with microtubules (Wright et al, 1997;Kipp et al, 2003;Khoursandi et al, 2004). Microtubule depolymeriza tion was accompanied with impaired SGLT1 transport (Suzuki et al, 2006). Diminished SGLT1 content in the brush border and suppressed glucose absorption at the microtubule depolymerization with unaltered total SGLT1 expression (Canania et al, 2006) are evidence in favor of the existence of the hypothesized link between the transporter and microtubules.…”

“…Transporter incidence in various cell areas occurs by protein synthesis de novo (Gouyon et al, 2003), as well as by translocation of existing transporters inside the cells (Khoursandi et al, 2004;Habold et al, 2005;Suzuki et al, 2006). These processes can be considered to be correlated with microtubule reorganization and redistribution.…”