Free Radical Biology & Medicine 2014 April 4. [Epub ahead of print] [Link]
He H, Kamp DW, Li D, Lin Z, Liu G, Liu T, Wang Y, Yang L, Zhao B, Zhou X.
Clinical Research Center, Affiliated Hospital of Guangdong Medical College, Zhanjiang, 524001, China, Department of Hematology, The Second Affiliated Hospital, Medical School of Xi’an Jiaotong University, Xi’an 710004, Shanxi, China, Department of Medicine, Northwestern University Feinberg School of Medicine and Jesse Brown VA Medical Center, 240 E. Huron, McGaw M-330, Chicago, IL 60611, USA, Clinical Research Center, Affiliated Hospital of Guangdong Medical College, Zhanjiang, 524001
Chrysotile asbestos is closely associated with excess mortality from pulmonary diseases such as lung cancer, mesothelioma, and asbestosis. Although multiple mechanisms in which chrysotile asbestos fibers induce pulmonary disease have been identified, the role of autophagy in human lung epithelial cells has not been examined. In the present study, we evaluated whether chrysotile asbestos induces autophagy in A549 human lung epithelial cells, and then analyzed the possible underlying molecular mechanism. Chrysotile asbestos-induced autophagy in A549 cells based on a series of biochemical and microscopic autophagy markers. We observed that asbestos increased A549 cell microtubule-associated protein 2 light chains 3 (LC3-II) expression, an autophagy marker, in conjunction with dephosphorylation of phospho-AKT, phospho-mTOR, and phospho-P70s6k. Notably, AKT1/AKT2 double knockout (AKT DKO) murine embryonic fibroblasts (MEFs) had negligible asbestos-induced LC3-II expression supporting a crucial role for AKT signaling. Chrysotile asbestos also led to the phosphorylation/activation of Jun N-terminal kinase (JNK) and p38 MAPK. Pharmacologic inhibition of JNK, but not p38 MAPK, dramatically inhibited the protein expression of LC3-II. Moreover, JNK2-/- MEFs but not JNK1-/- MEFs blocked LC3-II levels induced by chrysotile asbestos. In addition, NAC, an antioxidant, attenuated chrysotile asbestos-induced dephosphorylation of p-AKT and completely abolished phosphorylation/activation of JNK. Finally, we demonstrated that chrysotile asbestos-induced apoptosis was not affected by the presence of the autophagy inhibitors 3-methyladenine (3-MA) or ATG5(autophagy-related gene 5) siRNA, indicating that chrysotile asbestos-induced autophagy may be adaptive rather than prosurvival. Our findings demonstrate that AKT/mTOR and JNK2 signaling pathways are required for chrysotile asbestos-induced autophagy. These data provide a mechanistic basis for possible future clinical applications targeting these signaling pathways in the management of asbestos-induced lung disease.