5-Aminoimidazole-4-carboxamide-1-β-D-ribofuranoside Inhibits Cancer Cell Proliferation in Vitro and in Vivo via AMP-activated Protein Kinase

Avtar K. Singh,Shailendra Giri,Inderjit Singh,Ramandeep Rattan

doi:10.1074/jbc.m507443200

Abstract

5-Aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR) is widely used as an AMP-kinase activator, which regulates energy homeostasis and response to metabolic stress. Here, we investigated the effect of AICAR, an AMPK activator, on proliferation of various cancer cells and observed that proliferation of all the examined cell lines was significantly inhibited by AICAR treatment due to arrest in S-phase accompanied with increased expression of p21, p27, and p53 proteins and inhibition of PI3K-Akt pathway. Inhibition in in vitro growth of cancer cells was mirrored in vivo with increased expression of p21, p27, and p53 and attenuation of Akt phosphorylation. Anti-proliferative effect of AICAR is mediated through activated AMP-activated protein kinase (AMPK) as iodotubericidin and dominant-negative AMPK expression vector reversed the AICAR-mediated growth arrest. Moreover, constitutive active AMPK arrested the cells in S-phase by inducing the expression of p21, p27, and p53 proteins and inhibiting Akt phosphorylation, suggesting the involvement of AMPK. AICAR inhibited proliferation in both LKB and LKB knock-out mouse embryo fibroblasts to similar extent and arrested cells at S-phase when transfected with dominant negative expression vector of LKB. Altogether, these results indicate that AICAR can be utilized as a therapeutic drug to inhibit cancer, and AMPK can be a potential target for treatment of various cancers independent of the functional tumor suppressor gene, LKB.

Highlights

AMP-activated protein kinase (AMPK)2 is a highly conserved serine/ threonine protein kinase
In this study we have demonstrated that AMPK activation by AICAR results in growth arrest at S-phase due to inhibition of PI3K-Akt pathway and up-regulation of cdk inhibitors, independent of its upstream kinase LKB
2) The attenuation of cell proliferation was due to the activation of AMPK as evident from adenosine kinase inhibitor studies, the use of expression vectors and AMPK antisense experiments

Summary

Introduction

AMP-activated protein kinase (AMPK) is a highly conserved serine/ threonine protein kinase. The mechanisms of activating AMPK include direct allosteric binding of AMP to the ␥ subunits and phosphorylation, catalyzed by an upstream AMP kinase (AMPKK), recently identified to be LKB1 (STK11) (9 –11). Activation of AMPK has been related with protection from injury and apoptosis caused by myocardial ischemia [15, 16] and apoptosis due to metabolic stress [17,18,19] In these scenarios, AMPK has been proposed as an anti-apoptotic molecule. AICAR is converted to its triphosphorylated form ZMP, inside the cell, by an adenosine kinase [14], which acts as an AMP analogue and activates AMPK and its upstream kinase LKB without affecting the ATP:AMP ratio in the cell [14]. AICAR-mediated AMPK activation was found to be a proficient inhibitor of cell proliferation and the mechanism of its anti-proliferative effect may be mediated via inhibition of PI3K-Akt

Methods

Results

Conclusion