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

Abstract

The processes controlling targeting of glucose transporters to apical and basolateral membranes of polarized cells are complex and not‐well understood. We have engineered SGLT1 and GLUT4 constructs linked to fluorescent proteins to highlight the differences in transporter expression and trafficking, in real time, in different cell types. Activity was assessed in parallel using a FRET glucose sensor. In COS cells and HEK cells, SGLT1 was distributed between the plasma membrane and intracellular compartments, but there was little expression in CHO cells. Trafficking was investigated using the lysosome inhibitors NH 4Cl (10 mmol/L) and chloroquine (150 μmol/L) and the proteasome inhibitors MG‐262 (1 μmol/L) and lactacystin (5 μmol/L). Lysosome inhibitors caused SGLT1 accumulation into intracellular bodies, whereas proteasome inhibitors induced SGLT1 accumulation in the plasma membrane, even in CHO cells. Our data suggest that a fraction of SGLT1 is rapidly degraded by lysosomes and never reached the plasma membrane; another fraction reaches the membrane and is subsequently degraded by lysosomes following internalization. The latter process is regulated by the ubiquitin/proteasome pathway, acting at a late stage of the lysosomal pathway. Using the cholesterol inhibitor Mβ CD (3 mmol/L), a dominant negative dynamin (K44A) and caveolin, we showed that SGLT1 internalization is lipid raft‐mediated, but caveolin‐independent. In contrast, GLUT4 internalization is dynamin‐dependent, but cholesterol‐independent. The physiological relevance of these data is discussed in terms of differential membrane compartmentalization of the transporters and expression under stress conditions.

Role of Caveolin-1 in Diabetes and Its Complications

“…Another study showed that CAV1 increases the expression, activity, and transport of SGLT1 to the cell membrane in Xenopus oocytes [206]. However, a new study showed that SGLT1 internalization is lipid raft-dependent but CAV1-independent in HEK and COS cells [207]. Though CAV1 tends to improve glycemic control and associated complications via its interaction with various drug targets and downstream signaling molecules, its potential use as an antidiabetic drug requires further in-depth studies.…”

Starch digestion in the upper gastrointestinal tract of humans

“…Glucose is transported from the small intestinal lumen, through the epithelium into the underlying serosa. The sodium‐dependent glucose transporter (SGLT1) is most abundant in the small intestine epithelium and is believed to allow glucose and galactose to cross the luminal epithelium into the small intestinal absorptive cells . SGLT1 undergoes a succession of conformational changes in response to the binding of sodium ions and glucose .…”

“…The sodium‐dependent glucose transporter (SGLT1) is most abundant in the small intestine epithelium and is believed to allow glucose and galactose to cross the luminal epithelium into the small intestinal absorptive cells . SGLT1 undergoes a succession of conformational changes in response to the binding of sodium ions and glucose . It appears that each glucose molecule requires the binding of two sodium ions .…”

Solute carrier 5A5 regulates systemic glucose homeostasis by mediating glucose absorption in the Drosophila midgut

“…The incorporation of SGLT1 in the plasma membrane is balanced by the endocytosis of SGLT1 from the plasma membrane. SGLT1 has been documented to be endocytosed from the plasma membrane of cultured cells in a clathrin-and caveolin-independent manner (Ghezzi et al, 2017). Following endocytosis, SGLT1 could be targeted to the lysosomes for proteolysis or recycled back to the plasma membrane (Ghezzi et al, 2017).…”

“…SGLT1 has been documented to be endocytosed from the plasma membrane of cultured cells in a clathrin-and caveolin-independent manner (Ghezzi et al, 2017). Following endocytosis, SGLT1 could be targeted to the lysosomes for proteolysis or recycled back to the plasma membrane (Ghezzi et al, 2017). While these results have provided evidence supporting that endocytosis and the downstream lysosomal degradation and recycling are important intracellular trafficking pathways that regulate the availability of SGLT1 in the plasma membrane, they were obtained from in vitro work that utilized cultured cells which are not models for human enterocytes.…”