Differential regulation of GRP78 and GLUT1 expression in 3T3-L1 adipocytes

✍ Scribed by Harvey H. Kitzman; Robert J. McMahon; Ara M. Aslanian; Payal M. Fadia; Susan C. Frost

• Publisher: Springer
• Year: 1996
• Tongue: English
• Weight: 825 KB
• Volume: 162
• Category: Article
• ISSN: 0300-8177
• DOI: 10.1007/bf00250995

✦ Synopsis

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.