J Korean Diabetes Assoc.  2000 Aug;24(4):404-412.

Effect of Overexpression of Gi Proteins on Insulin Actions in 3T3-L1 Adipocytes

• Son HS
• Cha BY
• Moon SD
• Lee JM
• Hong OK
• Chang SA
• Ahn YB
• Yoon KH
• Lee KW
• Son HY
• Kang SK

Abstract

BACKGROUND: It has been reported that G proteins are involved in biological actions of insulin. Especially, Gi protein is more associated with insulin actions than Gs proteins. Gi protein has at least three different subtypes of Gi 1, Gi 2 and Gi 3 protein. However, it is not certain which subtypes of Gi proteins are associated with biological actions of insulin.
METHODS
To investigate which subtypes of Gi proteins are associated with insulin action, we overexpressed three different kinds of Gi protein, Gi 1, Gi 2 and Gi 3 protein, in 3T3-L1 adipocytes using DNA-polylysine-adenovirus complex transfection method. After incubating for 2 hours, 3T3-L1 adipocytes were treated with 100 nM insulin for the evaluation of biological actions of insulin. Moreover, to elucidate insulin stimulated insulin receptor autophosphorylation and IRS-1 phosphorylation, 3T3-L1 adipocytes were stimulated with 100 nM insulin for 10 minutes, homogenized and immunoprecipitated with anti-phosphotyrosine antibody.
RESULTS
Transfection with Gi 2 gene resulted in increment in insulin-stimulated [3H]2-deoxyglucose (DOG) uptake without affecting basal 2-DOG uptake, but not with Gi 1 and Gi 3 gene transfection. There was unchanged glycogen synthesis rate in all three Gialphasubtypes. Insulin-induced increments of insulin receptor autophos phorylation and IRS-1 phosphorylation were found in Gi 2 protein overexpressed group, only.
CONCLUSION
These results suggest that Gi 2 protein may be associated with regulation of biological actions of insulin.

Keyword

Insulin; Gi protein; 2-DOG uptake; Glycogen synthesis; IRS-1; Insulin receptor -subunit

MeSH Terms

Adipocytes*
Glycogen
GTP-Binding Proteins
Insulin*
Phosphorylation
Receptor, Insulin
Transfection
GTP-Binding Proteins
Glycogen
Insulin
Receptor, Insulin