Disease relevance of SLC5A1

• DISCUSSION: Overactivity of SGK1 may lead not only to excessive ENaC activity and hypertension but also to enhanced SGLT1 activity and obesity [1].
• We have mapped the entire human SGLT1 Na+/glucose cotransporter gene from cosmid and lambda phage clones representing a genomic region of 112 kilobases [2].
• Here, we report the employment of Escherichia coli for the functional expression, purification, and reconstitution of a human membrane protein, the human Na+/glucose cotransporter (hSGLT1) [3].
• Thus, to facilitate studies of the biology of SGLT1 function in epithelial monolayers, we engineered an epitope-tagged construct containing the YTDIEMNRLGK sequence (from the vesicular stomatitis virus G protein) [4].
• SLC5A8, a tumor suppressor gene down-regulated in human colon cancer, codes for a transporter in the Na(+)/glucose cotransporter gene family, but the definitive functional identity of the transporter protein is not known [5].

High impact information on SLC5A1

• Cotransporters harness ion gradients to drive 'active' transport of substrates into cells, for example, the Na+/glucose cotransporter (SGLT1) couples sugar transport to Na+ gradients across the intestinal brush border [6].
• Previously we showed that two sisters with GGM had a missense mutation in the SGLT1 gene [6].
• Sequence analysis of the amplified products has revealed a single missense mutation in SGLT1 which cosegregates with the GGM phenotype and results in a complete loss of Na(+)-dependent glucose transport in Xenopus oocytes injected with this complementary RNA [7].
• We have previously cloned and sequenced a Na+/glucose cotransporter from normal human ileum and shown that this gene, SGLT1, resides on the distal q arm of chromosome 22 [7].
• We have now amplified SGLT1 complementary DNA and genomic DNA from members of a family affected with GGM by the polymerase chain reaction [7].

Chemical compound and disease context of SLC5A1

• Carboxy-terminal vesicular stomatitis virus G protein-tagged intestinal Na+-dependent glucose cotransporter (SGLT1): maintenance of surface expression and global transport function with selective perturbation of transport kinetics and polarized expression [4].
• A truncated human Na(+)/glucose cotransporter (C(5), residues 407-664) was expressed and purified from Escherichia coli using a GST fusion vector and glutathione affinity chromatography [8].

Biological context of SLC5A1

• SGLT1 is comprised of 15 exons (spanning 72 kilobases); a possible evolutionary origin from a six-membrane-span ancestral precursor via a gene duplication event is suggested from comparison of exons against protein secondary structure and from sequence considerations [2].
• The role of the 15 endogenous cysteine residues was investigated by expressing SGLT1 constructs, each bearing a single mutation for an individual cysteine, in Xenopus oocytes, using two-microelectrode voltage-clamp electrophysiology and fluorescent labeling [9].
• Gastric emptying, measured in awake rats, was significantly inhibited by perfusion of the intestine with glucose (60 and 90 mg); this effect was mimicked by alpha-methyl glucose (nonmetabolizable substrate of SGLT-1 and -3) but not 2-deoxy-d-glucose (substrate for GLUT-2) or isoosmotic mannitol [10].
• (i) We measured pre-steady-state kinetics of SGLT1 using voltage-jump techniques [11].
• Our findings indicate that 1) the cell fraction isolated from fresh human milk is a suitable model for investigating gene expression in the human mammary gland and 2) lactating human mammary gland epithelial cells are supplied with monosaccharides mainly via SGLT1 [12].

Anatomical context of SLC5A1

• However, the SGLT1 protein was detected in both undifferentiated and differentiated HT-29-D4 cells suggesting that sodium-glucose cotransport was dependent on post-translational events controlling the efficient targeting of the protein in the plasma membrane [13].
• The sodium-dependent glucose transporter SGLT1 is expressed on the apical plasma membrane of fully differentiated enterocytes [13].
• More than apical: Distribution of SGLT1 in Caco-2 cells [14].
• By examining a Chinese hamster ovary-K1 cell line stably expressing either human SGLT2 or human high-affinity sodium glucose cotransporter (SGLT1), we found sergliflozin-A (active form) to be a highly selective and potent inhibitor of human SGLT2 [15].
• Further immunocytochemical investigation of SGLT1 distribution in fixed Caco-2 cells by epifluorescence and confocal microscopy revealed that the intracellular compartments containing SGLT1 were associated with microtubules [14].

Associations of SLC5A1 with chemical compounds

• By using immunogold labeling at the electron microscopy level, we demonstrated that phorbol myristyl acetate induced the redistribution of SGLT1 protein from intracellular sites to the plasma membrane [13].
• When exposed to a maleimide-based fluorescent probe, wt SGLT1 was not significantly labeled but mutants C255A and C511A could be clearly labeled, indicating an accessible cysteine residue [9].
• The Na+/glucose cotransporter (SGLT1) is an archetype for the SLC5 family, which is comprised of Na+-coupled transporters for sugars, myo-inositol, choline, and organic anions [9].
• On the contrary phlorizin, the well-established inhibitor of SGLT1, decreased intrinsic fluorescence by a maximum of 50%, and induced a blue shift of maximum (5 nm) [16].
• Kinetic analysis of hSGLT1 in proteoliposomes revealed sodium-dependent, secondary active, phlorizin-sensitive, and stereospecific alpha-methyl-d-glucopyranoside transport, demonstrating its full catalytic activity [16].

Physical interactions of SLC5A1

• The sodium-dependent glucose transporter SGLT1 played a role in apical (mucosal) to basolateral (serosal) transport and transport in the opposite direction was dependent on the multidrug resistance-associated protein MRP2 [17].

Regulatory relationships of SLC5A1

• We showed that SGLT1 was positively regulated by Cl- and that optimal activity of CFTR was dependent on the presence of glucose [18].
• SGLT1 alone is able to translocate glucose together with sodium; however, RS1 increases the Vmax of transport expressed by SGLT1 [19].

Other interactions of SLC5A1

• Voltage-clamp experiments in oocytes expressing hSGLT1 demonstrated that hRS1 reduced the maximal substrate-induced currents but did not change substrate activation, membrane potential dependence, Na(+) dependence or substrate selectivity of hSGLT1 [20].
• This review considers the structure and function of two premier members, SGLT1 and SGLT2, and their role in intestinal glucose absorption and renal glucose reabsorption [21].
• At least three, and up to six, Na+-dependent glucose transporters (SGLT1-SGLT6; gene name SLC5A) have been identified [22].
• RESULTS: Southern blot analysis of the amplicions revealed the expression of SGLT1 mRNA but not of GLUT1 mRNA in milk epithelial cells [12].
• The abundance of mRNAs encoding the Na(+)-glucose cotransporter isoform SGLT1 and the facilitative glucose transporter isoforms GLUT2 and GLUT5 is developmentally modulated with highest levels in adult small intestine [23].

Analytical, diagnostic and therapeutic context of SLC5A1

• An SGLT1 missense mutation underlies hereditary glucose/galactose malabsorption, characterized by potentially fatal diarrhea; conversely, oral rehydration therapy exploits normal transport to alleviate life-threatening diarrhea of infectious origin [2].
• Purified hSGLT1 migrates on SDS-PAGE with an apparent mass of 55 kDa [16].
• The position of the maximum intrinsic tryptophan fluorescence and titration with hydrophilic collisional quenchers KI, acrylamide, and trichloroethanol suggested that most of Trps in hSGLT1 in solution are in a hydrophobic environment [16].
• We have used a cosmid probe for fluorescence in situ hybridization, which refines the localization to 22q13.1, and provide an example of the utility of the SGLT1 probe as a diagnostic for genetic diseases associated with translocations of chromosome 22 [24].
• Furthermore, the presence of SGLT1 was tested by an ELISA assay employing newly developed epitope specific antibodies [14].

References