title: Calpain, Atg5 and Bak play important roles in the crosstalk between apoptosis and autophagy induced by influx of extracellular calcium.
abstract: Calcium (Ca(2+)) signals are involved in important checkpoints in cell death pathways and promote both apoptosis and autophagy. However, the relationship between autophagy and apoptosis in response to Ca(2+) level elevation is poorly understood. Here, we provided evidence that the influx of extracellular Ca(2+) triggered by Trichokonin VI (TK VI), an antimicrobial peptide, induced calpain-dependent apoptosis and autophagy in hepatocellular carcinoma (HCC) cells. Remarkably, TK VI preferentially induced apoptosis that was associated with calpain-mediated Bax and Atg5 cleavage, which resulted in the collapse of the mitochondrial membrane potential and cytochrome c release. Interestingly, truncated, but not full-length Atg5, associated with Bcl-xL and promoted the intrinsic pathway. Moreover, TK VI treatment induced reactive oxygen species (ROS) accumulation, an effect in which Bak might play a major role. This accumulation of ROS resulted in the subsequent disposal of damaged mitochondria within autophagosomes via Atg5-mediated and mitochondria-selective autophagy. Both the inhibition of calpain activity and Bax deficiency activated a switch that promoted an enhancement of autophagy. The inhibition of both apoptosis and autophagy significantly attenuated the TK VI cytotoxicity, indicating that the two processes had stimulatory effects during TK VI-meditated cell death. These results suggested that calpain, Bak and Atg5 were molecular links between autophagy and apoptosis and revealed novel aspects of the crosstalk between these two processes. The potential of TK VI is proposed as a promising anticancer agent for its well-characterized activity of Ca(2+) agonist and as a possible novel therapeutic strategy that acts on cancer cell mitochondria.
authors.affiliation: Marine Biotechnology Research Center, State Key Laboratory of Microbial Technology, Shandong University, Jinan 250100, People's Republic of China.
authors.forename: Mei
authors.initials: M
authors.lastname: Shi
authors.forename: Tian
authors.initials: T
authors.lastname: Zhang
authors.forename: Lei
authors.initials: L
authors.lastname: Sun
authors.forename: Yan
authors.initials: Y
authors.lastname: Luo
authors.forename: De-Hua
authors.initials: DH
authors.lastname: Liu
authors.forename: Shu-Tao
authors.initials: ST
authors.lastname: Xie
authors.forename: Xiao-Yan
authors.initials: XY
authors.lastname: Song
authors.forename: Guo-Fan
authors.initials: GF
authors.lastname: Wang
authors.forename: Xiu-Lan
authors.initials: XL
authors.lastname: Chen
authors.forename: Bai-Cheng
authors.initials: BC
authors.lastname: Zhou
authors.forename: Yu-Zhong
authors.initials: YZ
authors.lastname: Zhang
mesh_terms: D000408:Alamethicin / Q000031:analogs & derivatives / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides; D017209:Apoptosis / Q000502:physiology*; D001343:Autophagy / Q000502:physiology*; D000071187:Autophagy-Related Protein 5; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D045744:Cell Line, Tumor; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D018384:Oxidative Stress; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism*; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: C502778:ATG5 protein, human; D023181:Antimicrobial Cationic Peptides; D000071187:Autophagy-Related Protein 5; C494772:BAK1 protein, human; C494811:BCL2L1 protein, human; D008869:Microtubule-Associated Proteins; D017382:Reactive Oxygen Species; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051020:bcl-X Protein; D000408:Alamethicin; C092827:trichokonin VI; D002154:Calpain; D002118:Calcium