Akt/PKB signaling regulates cigarette smoke-induced pulmonary epithelial-mesenchymal transition

Abstract

Objectives: Cigarette smoke (CS) is a major risk factor for the development of lung cancer and chronic obstructive pulmonary disease (COPD). Epithelial-mesenchymal transition (EMT) is found in invasive or metastatic phenotypes in lung cancer and COPD. MK-2206, a pan Akt inhibitor, has failed in clinical trials for solid tumors when administered alone at tolerated doses, but it has been shown to have synergistic effects when applied with certain molecular targeted agents. In this study, we investigated the working mechanism of MK-2206 in CS-induced pulmonary EMT both in vivo and in vitro.

Materials and methods: The expression of Akt, epithelial-mesenchymal transition (EMT) markers and signaling proteins were analyzed by immunohistochemistry, real-time PCR and Western blot in cigarette smoke extract (CSE)-treated pulmonary epithelia and CS-treated lung tissues in mice.

Results and conclusion: We demonstrated that exposure of the epithelium to CSE and exposure of the mice to CS can induce EMT by activating the Akt signaling pathway. Intragastric application of MK-2206 at a low dose (50 mg/kg) reversed the changes of the key indicators of EMT in the lungs of CS-exposed mice, including TGF-β1, α-SMA, vimentin, MMP-9, MMP-2, S100A4, collagen deposition, and E-cadherin. MK-2206 at a non-cytotoxic concentration (0.5 μM) or Akt knockdown consistently reversed the changes of the key indicators of EMT in the pulmonary epithelia. Moreover, we found that the effects of Akt inhibition or knockdown on the CS/CSE-induced EMT acted via the TGF-β1/Akt/Smad/mTOR and Akt/P38 MAPK pathways. Taken together, our data offer a novel perspective on the molecular mechanism of Akt for CS-induced EMT. This finding may enhance the understanding of the mechanism behind the synergistic use of a low dose of MK-2206 to achieve antitumor efficacy with reduced adverse reactions in patients with lung cancer and COPD.

Keywords: Akt signaling; Cigarette smoking; Epithelial-mesenchymal transition; Lung cancer; TGF-β1.