title: PKC inhibition is involved in trichosanthin-induced apoptosis in human chronic myeloid leukemia cell line K562.
abstract: Trichosanthin (TCS), a type I ribosome-inactivating protein, induces cell death in various cell types including several tumor cell lines. However, the mechanism remains largely uncharacterized. In this study, we investigated the possible mechanism underlying its cytotoxicity by using human chronic myeloid leukemia cell line K562. We found that TCS induced apoptosis in K562 cells in a time- and concentration-dependent manner and can be blocked by caspase-3 inhibitors. Interestingly, TCS treatment induced a transient elevation in intracellular calcium concentration and a slow increase in reactive oxygen species production, while calcium chelators and antioxidants had no obvious effect on TCS-induced apoptosis, suggesting that calcium changes and reactive oxygen species may not be involved in TCS-mediated apoptosis in K562 cells. Instead we found that TCS partly inhibited PKC activity. Indeed, the PKC activator, PMA, inhibited while the PKC inhibitor, calphostin c, enhanced TCS-induced apoptosis. These PKC modulators had similar effects on TCS-induced cleavage of caspase-3, and caspase-3 inhibitors prevented calphostin c-enhanced apoptosis induced by TCS. In summary, we conclude that TCS induces apoptosis in K562 cells partly via PKC inhibition and caspase-3 activation.
authors.affiliation: Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Science, Graduate School of the Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Li
authors.forename: Xuechun
authors.initials: X
authors.lastname: Xia
authors.forename: Huiling
authors.initials: H
authors.lastname: Nie
authors.forename: Mark A
authors.initials: MA
authors.lastname: Smith
authors.forename: Xiongwei
authors.initials: X
authors.lastname: Zhu
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D053148:Caspase 3 / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D018613:Microscopy, Confocal; D009281:Naphthalenes / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D017382:Reactive Oxygen Species; D015978:Trichosanthin / Q000494:pharmacology*
chemical_list: D009281:Naphthalenes; D047428:Protein Kinase Inhibitors; D017382:Reactive Oxygen Species; D015978:Trichosanthin; D011493:Protein Kinase C; D053148:Caspase 3; C058819:calphostin C; D002118:Calcium