Down-modulation of Bcl-XL,release of cytochrome c and sequential activation of caspases during honokiol-induced apoptosis in human squamous lung cancer CH27 cells

Honokiol is a phenolic compound purified from Magnolia officinalis, which induced the apoptotic cell death in several types of human cancer cells. In the present study, the molecular mechanism of honokiol-mediated apoptotic process was examined in human squamous lung cancer CH27 cells. Here, we found that honokiol-induced apoptotic cell death was accompanied by upregulation of Bad and downregulation of Bcl-XL, while honokiol had no effect on the levels of Bcl-2, Bcl-XS, Bag-1, Bax and Bak proteins. Moreover, honokiol treatment caused the release of mitochondrial cytochrome c to cytosol and sequential activation of caspases. Proteolytic activation of caspase-3 and cleavage of PARP, an in vivo substrate for caspase-3, were observed in honokiol-treated CH27 cells. Furthermore, treatment with caspase inhibitors z-DEVD-fmk and z-VAD-fmk markedly blocked honokiol-induced apoptosis. These results demonstrated that modulation of Bcl-XL and Bad proteins, release of mitochondrial cytochrome c and activation of caspase-3, participated in honokiol-triggered apoptotic process in human squamous lung cancer CH27 cells.