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.
Department of Biochemistry and Molecular Biology, University of Florida, Gainesville 32610, USA.
H H
HH
Kitzman
R J
RJ
McMahon
A M
AM
Aslanian
P M
PM
Fadia
S C
SC
Frost
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