Research article

AMPK exerts dual regulatory effects on the PI3K pathway

Rong Tao¹ , Jun Gong² , Xixi Luo³ , Mengwei Zang⁴ , Wen Guo⁴ , Rong Wen⁵ and Zhijun Luo^2,4

¹  Department of Medicine, Molecular Medicine PhD Program, Boston University School of Medicine, 715 Albany Street, Evans 643, Boston, MA 02118, USA

²  Department of Biochemistry, Boston University School of Medicine, 715 Albany Street, Evans 643, Boston, MA 02118, USA

³  Department of Medicine, Section of Hematology and Oncology, University of Chicago, 5812 South Ellis Avenue, Chicago, IL 60637, USA

⁴  Department of Medicine, Boston University School of Medicine, 610 Albany Street, Boston, MA 02118, USA

⁵  Bascom Palmer Eye Institute, University of Miami, Miller School of Medicine, 1638 NW 10th Avenue, Miami, FL 33136, USA

author email corresponding author email

Journal of Molecular Signaling 2010, 5:1doi:10.1186/1750-2187-5-1

Published:	18 February 2010

Abstract

Background

AMP-activated protein kinase (AMPK) is a fuel-sensing enzyme that is activated when cells experience energy deficiency and conversely suppressed in surfeit of energy supply. AMPK activation improves insulin sensitivity via multiple mechanisms, among which AMPK suppresses mTOR/S6K-mediated negative feedback regulation of insulin signaling.

Results

In the present study we further investigated the mechanism of AMPK-regulated insulin signaling. Our results showed that 5-aminoimidazole-4-carboxamide-1 ribonucleoside (AICAR) greatly enhanced the ability of insulin to stimulate the insulin receptor substrate-1 (IRS1)-associated PI3K activity in differentiated 3T3-F442a adipocytes, leading to increased Akt phosphorylation at S473, whereas insulin-stimulated activation of mTOR was diminished. In 3T3-F442a preadipocytes, these effects were attenuated by expression of a dominant negative mutant of AMPK α1 subunit. The enhancing effect of ACIAR on Akt phosphorylation was also observed when the cells were treated with EGF, suggesting that it is regulated at a step beyond IR/IRS1. Indeed, when the cells were chronically treated with AICAR in the absence of insulin, Akt phosphorylation was progressively increased. This event was associated with an increase in levels of phosphatidylinositol -3,4,5-trisphosphate (PIP3) and blocked by Wortmannin. We then expressed the dominant negative mutant of PTEN (C124S) and found that the inhibition of endogenous PTEN per se did not affect phosphorylation of Akt at basal levels or upon treatment with AICAR or insulin. Thus, this result suggests that AMPK activation of Akt is not mediated by regulating phosphatase and tensin homologue (PTEN).

Conclusion

Our present study demonstrates that AMPK exerts dual effects on the PI3K pathway, stimulating PI3K/Akt and inhibiting mTOR/S6K.