Hz. Liu et al., ATP-SENSITIVE BINDING OF A 70-KDA CYTOSOLIC PROTEIN TO THE GLUCOSE-TRANSPORTER IN RAT ADIPOCYTES, The Journal of biological chemistry, 270(14), 1995, pp. 7869-7875
We have identified a 70-kDa cytosolic protein (GTBP70) in rat adipocyt
es that binds to glutathione S-transferase fusion proteins correspondi
ng to the cytoplasmic domains of the facilitative glucose transporter
isoforms Glut1, Glut2, and Glut4. GTBP70 did not bind to irrelevant fu
sion proteins, indicating that the binding is specific to the glucose
transporter. GTBP70 binding to the glucose transporter showed little i
soform specificity but was significantly subdomain-specific; it bound
to the C-terminal domain and the central loop, but not to the N-termin
al domain of Glut4. The GTBP70 binding to Glut4 was not affected by th
e presence of 2 mM EDTA, 2.4 mM Ca2+, or 150 mm K+. The binding was in
hibited by ATP in a dose-dependent manner, with 50% inhibition at 10 m
M ATP. This inhibition was specific to ATP, as ADP and AMP-PCP (adenos
ine 5'-(beta,gamma-methylenetriphosphate)) were without effect. GTBP70
did not react with antibodies against phosphotyrosine, phosphothreoni
ne, or phosphoserine, suggesting that it is not a phosphoprotein. The
binding of GTBP70 to Glut4 was not affected by the pretreatment of adi
pocytes with insulin. When these experiments were repeated using rat h
epatocyte cytosols, no ATP-sensitive 70-kDa protein binding to the glu
cose transporter fusion proteins was evident, suggesting that either G
TBP70 expression or its function is cell-specific. These findings stro
ngly suggest the possibility that GTBP70 may play a key role in glucos
e transporter regulation in insulin target cells such as adipocytes.