Tributyltin induces apoptotic signaling in hepatocytes through pathways involving the endoplasmic reticulum and mitochondria.
Tri-n-butyltin is a widespread environmental toxicant, which accumulates in the liver. This study investigates whether tri-n-butyltin induces pro-apoptotic signaling in rat liver hepatocytes through pathways involving the endoplasmic reticulum and mitochondria. Tri-n-butyltin activated the endoplasmic reticulum pathway of apoptosis, which was demonstrated by the activation of the protease calpain, its translocation to the plasma membrane, followed by cleavage of the calpain substrates, cytoskeletal protein vinculin, and caspase-12. Caspase-12 is localized to the cytoplasmic side of the endoplasmic reticulum and is involved in apoptosis mediated by the endoplasmic reticulum. Tri-n-butyltin also caused translocation of the pro-apoptotic proteins Bax and Bad from the cytosol to mitochondria, as well as changes in mitochondrial membrane permeability, events which can activate the mitochondrial death pathway. Tri-n-butyltin induced downstream apoptotic events in rat hepatocytes at the nuclear level, detected by chromatin condensation and by confocal microscopy using acridine orange. We investigated whether the tri-n-butyltin-induced pro-apoptotic events in hepatocytes could be linked to perturbation of intracellular calcium homeostasis, using confocal microscopy. Tri-n-butyltin caused changes in intracellular calcium distribution, which were similar to those induced by thapsigargin. Calcium was released from a subcellular compartment, which is likely to be the endoplasmic reticulum, into the cytosol. Cytosolic acidification, which is known to trigger apoptosis, also occurred and involved the Cl(-)/HCO(3)(-) exchanger. Pro-apoptotic events in hepatocytes were inhibited by the calcium chelator, Bapta-AM, and by a calpain inhibitor, which suggests that changes in intracellular calcium homeostasis are involved in tri-n-butyltin-induced apoptotic signaling in rat hepatocytes.
Grondin
Mélanie
M
Département de Chimie, Centre de Recherche en Toxicologie de l'environnement (TOXEN), Université du Québec à Montréal, CP 8888, Succursale Centre-Ville, Montreal, Québec, Canada H3C 3P8.
Marion
Michel
M
Denizeau
Francine
F
Averill-Bates
Diana A
DA
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D020013:Calcium Signaling / Q000187:drug effects; D002154:Calpain / Q000378:metabolism; D053454:Caspase 12 / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000187:drug effects*; D019254:Genes, bcl-2; D022781:Hepatocytes / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D018613:Microscopy, Confocal; D008930:Mitochondria, Liver / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects*; D014220:Trialkyltin Compounds / Q000633:toxicity*; D016596:Vinculin / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D051025:bcl-Associated Death Protein / Q000378:metabolism
D014220:Trialkyltin Compounds; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D016596:Vinculin; C011559:tributyltin; D002154:Calpain; D053454:Caspase 12