Celastrol induces apoptosis in non-small-cell lung cancer A549 cells through activation of mitochondria- and Fas/FasL-mediated pathways

Celastrol is a natural compound extracted from the traditional Chinese medicinal herb, Tripterygium wilfordii Hook. It has attracted interests for its potential anti-inflammatory and antitumor effects. However, the molecular mechanisms of celastrol-induced apoptosis in cancer cells remain unclear. In this study, we investigated the effects of celastrol on the human non-small-cell lung cancer (NSCLC) cell line A549 in vitro. Celastrol caused a dose- and time-dependent growth inhibition of A549 cells with an IC₅₀ of 2.12 μM at 48 h treatment. Celastrol induced A549 cells apoptosis as confirmed by annexin V/propidium iodide staining and DNA fragmentation. Celastrol-induced apoptosis was characterized by cleavage of caspase-9, caspase-8, caspase-3, and PARP protein, increased Fas and FasL expression, and a reduction in the mitochondrial membrane potential. Furthermore, celastrol induced the release of cytochrome c. Celastrol also up-regulated the expression of pro-apoptotic Bax, down-regulated anti-apoptotic Bcl-2, and inhibited Akt phosphorylation. These results demonstrate that celastrol can induce apoptosis of human NSCLC A549 cells through activation of both mitochondria- and FasL-mediated pathways.