title: In lymphatic cells par-4 sensitizes to apoptosis by down-regulating bcl-2 and promoting disruption of mitochondrial membrane potential and caspase activation.
abstract: Inhibition of apoptosis is a hallmark of malignancies of the hematopoetic system. Previous studies in nonhematopoetic cells demonstrated that the prostate-apoptosis-response-gene-4 (Par-4) is up-regulated in cells undergoing programmed cell death and that Par-4 exerts its proapoptotic effect by down-regulating Bcl-2. After showing the aberrant expressional pattern of Par-4 in neoplastic lymphocytes as well as demonstrating inverse expressional patterns of Par-4 and Bcl-2 in malignant cells of patients suffering from acute lymphocytic leukemia, we assessed the functional consequences of Par-4 overexpression during apoptosis in Jurkat T lymphocytes. We show that in lymphatic cells Par-4 overexpression decreases the level of Bcl-2, whereas Bax, the proapoptotic counterpart of Bcl-2, retains unaltered levels. Moreover, Par-4 overexpression is accompanied by cleavage of poly(ADP-ribose) polymerase (PARP). Despite these effects, overexpression of Par-4 alone is not sufficient to induce apoptosis but markedly increases the rate of apoptosis on treatment with different chemotherapeutic agents. On chemotherapeutic treatment Par-4 overexpression enhances disruption of mitochondrial membrane potential, PARP-cleaving activity, as well as activation of caspase-3. The hypothesis of caspase-dependency of Par-4-promoted apoptosis is additionally supported by demonstrating complete abrogation of programmed cell death after pretreatment with a broad spectrum caspase-inhibitor. On inhibition of caspase-3 overexpression of Par-4 enables lymphatic cells to alternatively activate caspases-9, -6, and -7 by diminishing the influence of the inhibitors of apoptosis proteins (IAPs) cIAP1 and XIAP. Our study is the first to identify Par-4 as a proapoptotic protein in lymphatic cells, outlining a model of action evaluating the role of Bcl-2/Bax, as well as demonstrating the impact of Par-4 expression on PARP cleavage, disruption of mitochondrial membrane potential, caspase activation, and interactions with inhibitors of apoptosis proteins.
authors.affiliation: Department of Medicine III, Johann Wolfgang Goethe-University Hospital, 60590 Frankfurt am Main, Germany.
authors.forename: Simone
authors.initials: S
authors.lastname: Boehrer
authors.forename: Kai U
authors.initials: KU
authors.lastname: Chow
authors.forename: Florian
authors.initials: F
authors.lastname: Beske
authors.forename: Natasa
authors.initials: N
authors.lastname: Kukoc-Zivojnov
authors.forename: Elena
authors.initials: E
authors.lastname: Puccetti
authors.forename: Martin
authors.initials: M
authors.lastname: Ruthardt
authors.forename: Christine
authors.initials: C
authors.lastname: Baum
authors.forename: Vivek M
authors.initials: VM
authors.lastname: Rangnekar
authors.forename: Dieter
authors.initials: D
authors.lastname: Hoelzer
authors.forename: Paris S
authors.initials: PS
authors.lastname: Mitrou
authors.forename: Eckhart
authors.initials: E
authors.lastname: Weidmann
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D003561:Cytarabine / Q000494:pharmacology; D015536:Down-Regulation; D004317:Doxorubicin / Q000494:pharmacology; D004789:Enzyme Activation; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D019169:Jurkat Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis* / Q000235:genetics; D014162:Transfection
chemical_list: D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; D061945:Caspase Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D019253:Proto-Oncogene Proteins c-bcl-2; C101296:prostate apoptosis response-4 protein; D003561:Cytarabine; D004317:Doxorubicin; D011065:Poly(ADP-ribose) Polymerases; D020169:Caspases