title: Decreased expression and function of sodium-glucose co-transporter 2 from a novel C-terminal mutation: a case report.
abstract: BACKGROUND
  Familial renal glucosuria (FRG) is characterized by persistent glucosuria in the presence of normal serum glucose concentrations, and the absence of other impairments of tubular function. Mutations in the sodium-glucose co-transporter 2 (SGLT2) gene (SLC5A2) are causative of FRG the long-term outcome of which is well know. In the search for potential new drug targets for SGLT2 inhibitors with which to treat the diabetes, expressional and functional studies of SGLT2 have been the focus of attention, but reports of these are rare. Furthermore, it is well known that the alleles in the C-terminal are very important for the expression and function in some genes. However, little is known about the effect of mutation in SLC5A2 C- terminal.
  
  
  METHODS
  Here, we identified a FRG patient with urine glucose excretion 7.56 g/day and a novel SLC5A2 missense mutation, c.1891G > A/p.(E631K), by DNA sequencing. Expression and function of the mutant SGLT2 (631 K) fused to green fluorescent protein (GFP) were verified by western blotting, confocal laser microscopy, and transport activity assays in cultured HEK293 cells. Although wild-type SGLT2-GFP and 631 K mutant-GFP fusion proteins were properly expressed in a punctate pattern in the cell membrane, and co-localized with the cell membrane marker DiIC18(3), the expression of the mutant fusion protein was obviously decreased (24 %). Moreover, the uptake activity of the mutant SGLT2 631 K-GFP fusion protein was significantly decreased compared with wild-type (3629 ± 1082 vs. 7926 ± 1153, P < 0.001).
  
  
  CONCLUSIONS
  These results suggest that the SLC5A2 C-terminal is very important for protein expression. We speculate that the observed reduced expression of the mutant transporter led to a decrease in transport of the glucose analog 2-(N-(7-nitrobenz-2-oxa-1,3- diazol-4-yl)amino)-2-deoxyglucose. The current study provides a starting point for further investigations of the SGLT2 molecular mechanism in FRG families, and offers functional insights into the development of anti-diabetes drugs.
authors.affiliation: Renal Division, Inner Mongolia People's Hospital, Hohhot, 010017, P.R. China. lanlife@163.com.
authors.forename: Lei
authors.initials: L
authors.lastname: Yu
authors.affiliation: Computer & Information Engineering College, Inner Mongolia Normal University, Hohhot, 010022, China.
authors.forename: Qiaozhi
authors.initials: Q
authors.lastname: Xu
authors.affiliation: Renal Division, Peking University First Hospital, Peking University Institute of Nephrology, Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, 100034, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Hou
authors.affiliation: Renal Division, Peking University First Hospital, Peking University Institute of Nephrology, Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, 100034, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000328:Adult; D015153:Blotting, Western; D005260:Female; D006030:Glycosuria, Renal / Q000235:genetics*; D049452:Green Fluorescent Proteins; D057809:HEK293 Cells; D006801:Humans; D018613:Microscopy, Confocal; D020125:Mutation, Missense; D017422:Sequence Analysis, DNA; D051297:Sodium-Glucose Transporter 2 / Q000235:genetics* / Q000378:metabolism
chemical_list: C089180:SLC5A2 protein, human; D051297:Sodium-Glucose Transporter 2; C485192:green fluorescent protein, Aequorea victoria; D049452:Green Fluorescent Proteins
keywords: Familial renal glucosuria; SGLT2; SLC5A2