title: Involvement of caspase 1 and its activator Ipaf upstream of mitochondrial events in apoptosis.
abstract: PTP-S2/TC45 is a nuclear protein tyrosine phosphatase that activates p53 and induces caspase 1-dependent apoptosis. We analyzed the role of ICE protease-activating factor (Ipaf), an activator of caspase 1 in p53-dependent apoptosis. We also determined the sequence of events that lead to apoptosis upon caspase 1 activation by Ipaf. PTP-S2 expression induced Ipaf mRNA in MCF-7 cells which was dependent on p53. PTP-S2-induced apoptosis was inhibited by a dominant-negative mutant of Ipaf and also by an Ipaf-directed short-hairpin RNA. Doxorubicin-induced apoptosis was potentiated by the expression of caspase 1 (but not by a catalytic mutant of caspase 1) and required endogenous Ipaf. Doxorubicin treatment of MCF-7 cells resulted in activation of exogenous caspase 1, which was partly dependent on endogenous Ipaf. An activated form of Ipaf induced caspase 1-dependent apoptosis that was inhibited by Bcl2 and also by a dominant inhibitor of caspase 9 (caspase 9s). Caspase 1-dependent apoptosis induced by doxorubicin was also inhibited by Bcl2 and caspase 9s, but caspase 1 activation by activated Ipaf was not inhibited by Bcl2. Mitochondrial membrane permeabilization was induced by caspase 1 and activated Ipaf, which was inhibited by Bcl2, but not by caspase 9s. Expression of caspase 1 with activated Ipaf resulted in the activation of Bax at mitochondria. Our results suggest that Ipaf is involved in PTP-S2-induced apoptosis and that caspase 1, when activated by Ipaf, causes release of mitochondrial proteins (cytochrome c and Omi) through Bax activation, thereby functioning as an initiator caspase.
authors.affiliation: Centre for Cellular and Molecular Biology, Hyderabad, India.
authors.forename: Subhash
authors.initials: S
authors.lastname: Thalappilly
authors.forename: Subhashini
authors.initials: S
authors.lastname: Sadasivam
authors.forename: Vegesna
authors.initials: V
authors.lastname: Radha
authors.forename: Ghanshyam
authors.initials: G
authors.lastname: Swarup
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D053468:CARD Signaling Adaptor Proteins; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D020170:Caspase 1 / Q000235:genetics / Q000378:metabolism*; D053453:Caspase 9; D020169:Caspases / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D002463:Cell Membrane Permeability; D004317:Doxorubicin / Q000378:metabolism / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005455:Fluorescent Antibody Technique; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism / Q000494:pharmacology; D015398:Signal Transduction; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D002135:Calcium-Binding Proteins; C435692:NLRC4 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; C513669:caspase 9s, human; D004317:Doxorubicin; C516649:PTPN2 protein, human; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2; D017027:Protein Tyrosine Phosphatases; C516653:Ptpn2 protein, mouse; C506433:CASP9 protein, human; C506434:Casp9 protein, mouse; D053453:Caspase 9; D020169:Caspases; D020170:Caspase 1