TNF defers apoptosis in macrophages undergoing spontaneous or pharmacologically (thapsigargin, ceramide, CCCP, etoposide or cisplatin)-induced apoptosis, as determined by measurements of caspase-3 activity and annexin-V staining (Chapter 2). The action requires TNF interaction with TNF-R1, not TNF-R2. Survival is uniquely reliant on the activity of the NF-B signaling pathway, and does not require activities arising from the PI3K/Akt, JNK, ERK, p38 MAP kinase or iNOS pathways (Chapter 3). Further, the general anti-apoptotic property of TNF and its specific antagonism of CCCP-induced apoptosis led to the finding that TNF action prevents cytochrome c release. This protection is likely mediated through effects on components of the MPTP itself, as TNF exhibited functional redundancy with the pore inhibitor cyclosporin A, and did not modify upstream events that promote MPTP opening during apoptosis, namely ROS production, cytosolic Ca2+ increase, or a reduction of total ATP (Chapter 4). Subsequent experiments with the mRNA synthesis inhibitor, actinomycin D, and the translation inhibitor, cycloheximide revealed that the protein(s) responsible for TNF-induced survival was transcribed and translated within 1 hr. However, western analyses provided no convincing evidence of the involvement of Mn-SOD, cIAP-1, XIAP, Bcl-2 or A1 in TNF cytoprotection (Chapter 5). Rather, microarray experiments identified the consistent induction of an early response gene, pim-1, within 30 min of TNF exposure (Chapter 6). This result was verified at the protein level with a specific Pim-1 antibody. Evidence was also found for induction of the anti-apoptotic protein A20, but only at mRNA level. Parthenolide, wortmannin, SP600125, PD98059, SB203580 or L-NAME1 acted against TNF-induced Pim-1 expression in a pattern that exactly matched the effects of these inhibitors on TNF-induced survival. That is, only parthenolide-mediated inactivation of NF-B abolished TNF-induced induction of Pim-1. TNF also stimulated the rapid phosphorylation (inactivation) of the pro-apoptotic BH3-only protein, Bad at Ser112 in a manner sensitive to NF-B inhibition, but not PI3K/Akt, JNK, ERK or p38 MAP kinase inhibition (Chapter 7). As Bad is a known substrate of Pim-1 and Bad 1 Parthenolide, wortmannin, SP600125, PD98059 and SB203580 are inhibitors of the NF-B, PI3K/Akt, JNK, ERK and p38 MAP kinase pathways, respectively. L-NAME inhibits iNOS. NF-B- and mitochondria-linked signaling events that contribute to TNF action in deferring physiological and chemotherapeutic drug-induced apoptosis in macrophages ii phosphorylation occurred coincident with Pim-1 upregulation, it is likely that Pim-1 kinase activity mediates the inactivation of Bad. The overall data therefore supports a model in which TNF ligation of TNF-R1 at the cell surface results in intracellular NF- B activation, leading to the induction of Pim-1 mRNA and protein, and the ensuing phosphorylation of Bad. Inactivation of pro-apoptotic Bad increases the resistance threshold of mitochondria to apoptotic insults, thereby reducing the occurrence of mitochondrial permeability transition, cytochrome c release and subsequent caspase-3 activation.
| Identifer | oai:union.ndltd.org:ADTP/232706 |
| Date | January 2008 |
| Creators | Lo, Susan Z. Y. |
| Publisher | University of Western Australia. School of Medicine and Pharmacology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Susan Z.Y. Lo, http://www.itpo.uwa.edu.au/UWA-Computer-And-Software-Use-Regulations.html |
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