Differential regulation of GRP78 and GLUT1 expression in 3T3-L1 adipocytes.
We tested the hypothesis that the constitutive glucose transporter (GLUT1) in 3T3-L1 adipocytes belongs to the family of glucose-regulated proteins which are transcriptionally regulated by glucose deprivation. Using cDNA probes for both GRP78 (BiP) and GLUT1, we show that the level of GRP78 mRNA increased by 15-fold within 24 h of glucose deprivation with little change in GLUT1 mRNA. The elevated GRP78 mRNA in turn led to a time-dependent increase in GRP78 protein. While glucose deprivation did not alter the expression of the normal glycoform of GLUT1, a lower molecular weight glycoform accumulated with extended deprivation. Mannose and fructose, but not galactose, prevented the induction of GRP78 and accumulation of the abnormal GLUT1. Because GRP78 acts as a chaperone in other cell systems, we also sought evidence to support this activity in 3T3-L1 adipocytes. Using the technique of co-immunoprecipitation, we demonstrate that GRP78 bound several proteins unique to the glucose-deprived state. No deprivation-specific proteins could be detected in association with GLUT1. These data lead us to conclude that GLUT1 does not display characteristics of the glucose-regulated proteins, at least in 3T3-L1 adipocytes, a widely used model for differentiation, hormone action, and nutrient control. However, the mechanisms for activating traditional members of this family appear intact.
Kitzman
H H
HH
Department of Biochemistry and Molecular Biology, University of Florida, Gainesville 32610, USA.
McMahon
R J
RJ
Aslanian
A M
AM
Fadia
P M
PM
Frost
S C
SC
D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D018076:DNA, Complementary; D000091342:Endoplasmic Reticulum Chaperone BiP; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1; D006031:Glycosylation; D006360:Heat-Shock Proteins; D051379:Mice; D018832:Molecular Chaperones / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology
D002352:Carrier Proteins; D018076:DNA, Complementary; D000091342:Endoplasmic Reticulum Chaperone BiP; D051272:Glucose Transporter Type 1; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D018832:Molecular Chaperones; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; C495678:Slc2a1 protein, mouse; D014415:Tunicamycin; D005947:Glucose