title: Endoplasmic reticulum stress-induced apoptosis in Leishmania through Ca2+-dependent and caspase-independent mechanism.
abstract: Numerous reports have shown that mitochondrial dysfunctions play a major role in apoptosis of Leishmania parasites, but the endoplasmic reticulum (ER) stress-induced apoptosis in Leishmania remains largely unknown. In this study, we investigate ER stress-induced apoptotic pathways in Leishmania major using tunicamycin as an ER stress inducer. ER stress activates the expression of ER-localized chaperone protein BIP/GRP78 (binding protein/identical to the 78-kDa glucose-regulated protein) with concomitant generation of intracellular reactive oxygen species. Upon exposure to ER stress, the elevation of cytosolic Ca(2+) level is observed due to release of Ca(2+) from internal stores. Increase in cytosolic Ca(2+) causes mitochondrial membrane potential depolarization and ATP loss as ablation of Ca(2+) by blocking voltage-gated cation channels with verapamil preserves mitochondrial membrane potential and cellular ATP content. Furthermore, ER stress-induced reactive oxygen species (ROS)-dependent release of cytochrome c and endonuclease G from mitochondria to cytosol and subsequent translocation of endonuclease G to nucleus are observed. Inhibition of caspase-like proteases with the caspase inhibitor benzyloxycarbonyl-VAD-fluoromethyl ketone or metacaspase inhibitor antipain does not prevent nuclear DNA fragmentation and phosphatidylserine exposure. Conversely, significant protection in tunicamycin-induced DNA degradation and phosphatidylserine exposure was achieved by either pretreatment of antioxidants (N-acetyl-L-cysteine, GSH, and L-cysteine), chemical chaperone (4-phenylbutyric acid), or addition of Ca(2+) chelator (1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid-acetoxymethyl ester). Taken together, these data strongly demonstrate that ER stress-induced apoptosis in L. major is dependent on ROS and Ca(2+)-induced mitochondrial toxicity but independent of caspase-like proteases.
authors.affiliation: Division of Structural Biology and Bio-informatics, Indian Institute of Chemical Biology, 4, Raja S.C. Mullick Road, Kolkata-700 032, India.
authors.forename: Subhankar
authors.initials: S
authors.lastname: Dolai
authors.forename: Swati
authors.initials: S
authors.lastname: Pal
authors.forename: Rajesh K
authors.initials: RK
authors.lastname: Yadav
authors.forename: Subrata
authors.initials: S
authors.lastname: Adak
mesh_terms: D000255:Adenosine Triphosphate / Q000235:genetics / Q000378:metabolism; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism*; D020169:Caspases / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics; D018320:Leishmania major / Q000235:genetics / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000235:genetics; D051336:Mitochondrial Membranes / Q000378:metabolism; D015800:Protozoan Proteins / Q000096:biosynthesis / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology; D056811:Unfolded Protein Response
chemical_list: D000900:Anti-Bacterial Agents; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D015800:Protozoan Proteins; D017382:Reactive Oxygen Species; C436924:glucose regulated protein 78, Leishmania donovani; D014415:Tunicamycin; D000255:Adenosine Triphosphate; D020169:Caspases; D002118:Calcium