AMPK Reverses the Mesenchymal Phenotype of Cancer Cells by Targeting the Akt–MDM2–Foxo3a Signaling Axis

Abstract

In cancer cells, the epithelial-mesenchymal transition (EMT) confers the ability to invade basement membranes and metastasize to distant sites, establishing it as an appealing target for therapeutic intervention. Here, we report a novel function of the master metabolic kinase AMPK in suppressing EMT by modulating the Akt-MDM2-Foxo3 signaling axis. This mechanistic link was supported by the effects of siRNA-mediated knockdown and pharmacological activation of AMPK on epithelial and mesenchymal markers in established breast and prostate cancer cells. Exposure of cells to OSU-53, a novel allosteric AMPK activator, as well as metformin and AICAR, was sufficient to reverse their mesenchymal phenotype. These effects were abrogated by AMPK silencing. Phenotypic changes were mediated by Foxo3a activation, insofar as silencing or overexpressing Foxo3a mimicked the effects of AMPK silencing or OSU-53 treatment on EMT, respectively. Mechanistically, Foxo3a activation led to the transactivation of the E-cadherin gene and repression of genes encoding EMT-inducing transcription factors. OSU-53 activated Foxo3a through two Akt-dependent pathways, one at the level of nuclear localization by blocking Akt- and IKKβ-mediated phosphorylation, and a second at the level of protein stabilization via cytoplasmic sequestration of MDM2, an E3 ligase responsible for Foxo3a degradation. The suppressive effects of OSU-53 on EMT had therapeutic implications illustrated by its ability to block invasive phenotypes in vitro and metastatic properties in vivo. Overall, our work illuminates a mechanism of EMT regulation in cancer cells mediated by AMPK, along with preclinical evidence supporting a tractable therapeutic strategy to reverse mesenchymal phenotypes associated with invasion and metastasis.

Proliferation and metastatic potential of endometrial cancer cells in response to metformin treatment in a high versus normal glucose environment

“…Additionally, experimental studies revealed that metformin is an effective antiestrogenic agent, inhibiting cell proliferation and leading to growth arrest, as well as inducing apoptosis in EC (17,(20)(21)(22). Furthermore, recent findings have suggested that metformin is important in suppressing the migration and invasion of cancer cells, which could prevent metastasis (23)(24)(25). However, in these studies metformin action was observed at high supra-pharmacological concentrations and without estradiol addition, an important factor in endometrial proliferative disorders.…”

The co‑treatment of metformin with flavone synergistically induces apoptosis through inhibition of PI3K/AKT pathway in breast cancer cells

“…AKT can activate eIF4E by inhibiting mTOR to enhance cyclin D1, resulting in cell cycle arrest in G1 phase (27,28). As a novel AMPK activator, metformin increases nuclear accumulation and protein stability of FoxO3a by inhibiting AKT-MDM2 signaling pathway to reduce invasive and metastatic capacity of aggressive cancer cells (29). Therefore, PI3K/AKT pathway plays a significant role in anticancer effects.…”

Role of the LKB1/AMPK pathway in tumor invasion and metastasis of cancer cells (Review)

“…The LKB1/AMPK pathway regulates invasion and metastasis via diversified signaling pathways, such as NF-κB, AKT, forkhead box O3 (Foxo3a), TGF-β and mTOR. It has been reported that AICAR activates AMPK to suppress AKT/ FOXO3 signaling, inhibiting EMT and reversing mesen- chymal characteristics of tumor cells (65). In PC3 and PC3M cells, AICAR and A769662 downregulated mTOR and S6K1 levels, and inhibited migration by activating AMPK (66).…”