title: Apoptosis triggered by Rv1818c, a PE family gene from Mycobacterium tuberculosis is regulated by mitochondrial intermediates in T cells.
abstract: Ectopic expression of the Mycobacterium tuberculosis PE-family gene Rv1818c, triggers apoptosis in the mammalian Jurkat T cells, which is blocked by anti-apoptotic protein Bcl-2. Although complete overlap is not observed, a considerable proportion of cellular pools of ectopically expressed Rv1818c localizes to mitochondria. However, recombinant Rv1818c does not trigger release of cytochrome c from isolated mitochondria even though Rv1818c protein induced apoptosis of Jurkat T cells. Apoptosis induced by Rv1818c is blocked by the broad-spectrum caspase inhibitory peptide zVAD-FMK. Unexpectedly, Rv1818c-induced apoptosis is not blocked in a Jurkat sub-clone deficient for caspase-8 (JI 9.2) or in cells where caspase-9 function is inhibited or expression of caspase-9 reduced by siRNA, arguing against a central role for these caspases in Rv1818c-induced apoptotic signaling. Depleting cellular pools of the mitochondrial protein Smac/DIABLO substantially reduces apoptosis consistent with mitochondrial involvement in this death pathway. We present evidence that Rv1818c-induced apoptosis is blocked by the co-transfection of an endogenous inhibitor of caspase activation, XIAP in T cells. Additionally, Rv1818c is released into extracellular environment via exosomes secreted by M. tuberculosis infected BM-DC's and macrophages. Furthermore, the extracellular Rv1818c protein can be detected in T cells co-cultured with infected BM-DC's. Taken together, these data suggest that Rv1818c-induced apoptotic signaling is likely regulated in part by the Smac-dependent activation of caspases in T cells.
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, C.V. Raman Avenue, Malleswaram, Bangalore, Karnataka 560012, India. balaji@mcbl.iisc.ernet.in <balaji@mcbl.iisc.ernet.in>
authors.forename: Kithiganahalli N
authors.initials: KN
authors.lastname: Balaji
authors.forename: Girija
authors.initials: G
authors.lastname: Goyal
authors.forename: Yeddula
authors.initials: Y
authors.lastname: Narayana
authors.forename: Madduri
authors.initials: M
authors.lastname: Srinivas
authors.forename: Rashmi
authors.initials: R
authors.lastname: Chaturvedi
authors.forename: Saleemulla
authors.initials: S
authors.lastname: Mohammad
mesh_terms: D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D001854:Bone Marrow Cells; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D003713:Dendritic Cells; D004789:Enzyme Activation; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D019169:Jurkat Cells; D008264:Macrophages; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D008928:Mitochondria / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D013601:T-Lymphocytes / Q000378:metabolism
chemical_list: D000942:Antigens, Bacterial; D051017:Apoptosis Regulatory Proteins; D001426:Bacterial Proteins; C412403:DIABLO protein, human; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; C440642:PE-PGRS protein, Mycobacterium; D020169:Caspases