In the present study, we found that
celastrol, a natural compound with well-known apoptosis-inducing effect, could also induce paraptosis-like cytoplasmic vacuolization in
cancer cell lines including HeLa cells, A549 cells and PC-3 cells derived from cervix, lung and prostate, respectively. Further study using HeLa cells indicated that the vacuoles induced by
celastrol might be derived from dilation of endoplasmic reticulum. And, in
celastrol-treated cells, markers of autophagy such as transformation of
microtubule-associated protein 1 light chain 3 (LC3)I to LC3II and LC3 punctates formation were identified. Interestingly, autophagy inhibitors could not interrupt but enhance the induction of cytoplasmic vacuolization. Furthermore, MAPK pathways were activated by
celastrol and inhibitors of
MEK and p38 pathways could prevent the formation of cytoplasmic vacuolization.
Celastrol treatment also induced G2/M cell cycle arrest and apoptosis in HeLa cells. In conclusion,
celastrol induced a kind of paraptosis accompanied by autophagy and apoptosis in
cancer cells. The coincidence of apoptosis and autophagy together with paraptosis might contribute to the unique characteristics of paraptosis in
celastrol-treated cells such as the dependence of paraptosis on MAPK pathways and dynamic change of LC3
proteins. Both paraptosis and apoptosis could contribute to the cell death induced by
celastrol while autophagy might serve as a kind of survival mechanism. The potency of
celastrol to induce paraptosis, apoptosis and autophagy at the same dose might be related to its capability to affect a variety of pathways including
proteasome, ER stress and Hsp90.