Functional characterization of an insulin-responsive glucose transporter (GLUT4) from fish adipose tissue.
Glucose transport across the plasma membrane is mediated by a family of glucose transporter proteins (GLUTs), several of which have been identified in mammalian, avian, and, more recently, in fish species. Here, we report on the cloning of a salmon GLUT from adipose tissue with a high sequence homology to mammalian GLUT4 that has been named okGLUT4. Kinetic analysis of glucose transport following expression in Xenopus laevis oocytes demonstrated a 7.6 +/- 1.4 mM K(m) for 2-deoxyglucose (2-DG) transport measured under zero-trans conditions and 14.4 +/- 1.5 mM by equilibrium exchange of 3-O-methylglucose. Transport of 2-DG by okGLUT4-injected oocytes was stereospecific and was competed by D-glucose, D-mannose, and, to a lesser extent, D-galactose and D-fructose. In addition, 2-DG uptake was inhibited by cytochalasin B and ethylidene glucose. Moreover, insulin stimulated glucose uptake in Xenopus oocytes expressing okGLUT4 and in isolated trout adipocytes, which contain the native form of okGLUT4. Despite differences in protein motifs important for insulin-stimulated translocation of mammalian GLUT4, okGLUT4 was able to translocate to the plasma membrane from intracellular localization sites in response to insulin when expressed in 3T3-L1 adipocytes. These data demonstrate that okGLUT4 is a structural and functional fish homolog of mammalian GLUT4 but with a lower affinity for glucose, which could in part explain the lower ability of fish to clear a glucose load.
Capilla
Encarnación
E
Departament de Fisiologia, Facultat de Biologia, Universitat de Barcelona, Spain.
Díaz
Mònica
M
Albalat
Amaya
A
Navarro
Isabel
I
Pessin
Jeffrey E
JE
Keller
Konrad
K
Planas
Josep V
JV
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D006801:Humans; D007328:Insulin / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins; D017684:Oncorhynchus kisutch / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D016415:Sequence Alignment
D029941:Fish Proteins; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495692:SLC2A4 protein, human; C495693:Slc2a4 protein, mouse; C495694:Slc2a4 protein, rat; D005947:Glucose