title: Induction of tumor necrosis factor by bryostatin 1 is involved in synergistic interactions with paclitaxel in human myeloid leukemia cells.
abstract: Interactions between the protein kinase C (PKC) activator/down-regulator bryostatin 1 and paclitaxel have been examined in human myeloid leukemia cells (U937) and in highly paclitaxel-resistant cells ectopically expressing a Bcl-2 phosphorylation loop-deleted protein (Delta Bcl-2). Treatment (24 hours) of wild-type cells with paclitaxel (eg, 5 to 20 nM) in combination with 10 nM bryostatin 1 induced a marked increase in mitochondrial damage (eg, cytochrome c and Smac/DIABLO [second mitochondria-derived activator of caspases/direct IAP binding protein with low pI] release), caspase activation, Bid cleavage, and apoptosis; moreover, bryostatin 1 circumvented the block to paclitaxel-induced mitochondrial injury and apoptosis conferred by ectopic expression of the loop-deleted protein. Coadministration of tumor necrosis factor (TNF) soluble receptors, or ectopic expression of CrmA or dominant-negative caspase-8, abrogated potentiation of paclitaxel-induced mitochondrial injury and apoptosis by bryostatin 1, implicating the extrinsic apoptotic pathway in this process. Similar events occurred in HL-60 leukemia cells. Potentiation of paclitaxel-induced apoptosis in wild-type and mutant cells by bryostatin 1 was associated with increases in TNF-alpha mRNA and protein and was mimicked by exogenous TNF-alpha. Coadministration of the selective PKC inhibitor GFX (1 microM) blocked the increase in TNF-alpha mRNA levels and apoptosis in bryostatin 1/paclitaxel-treated cells. Lastly, synchronization of cells in G(2)M increased their sensitivity to TNF-alpha-associated lethality. Collectively, these findings indicate that in U937 cells, bryostatin 1 promotes paclitaxel-mediated mitochondrial injury and apoptosis, and circumvents resistance to cell death conferred by loss of the Bcl-2 phosphorylation domain, through the PKC-dependent induction of TNF-alpha. They further suggest that this process is amplified by paclitaxel-mediated arrest of cells in G(2)M, where they are more susceptible to TNF-alpha-induced lethality.
authors.affiliation: Department of Biochemistry, Division of Hematology/Oncology, Virginia Commonwealth University/Medical College of Virginia, Richmond 23298, USA.
authors.forename: Shujie
authors.initials: S
authors.lastname: Wang
authors.forename: Zhiliang
authors.initials: Z
authors.lastname: Wang
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D051023:BH3 Interacting Domain Death Agonist Protein; D054713:Bryostatins; D002352:Carrier Proteins / Q000378:metabolism; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D016195:G2 Phase / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D019254:Genes, bcl-2; D018922:HL-60 Cells / Q000187:drug effects; D006801:Humans; D007783:Lactones / Q000494:pharmacology*; D018942:Macrolides; D008928:Mitochondria / Q000187:drug effects; D008954:Models, Biological; D009000:Monocytes / Q000187:drug effects; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D017239:Paclitaxel / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D017384:Sequence Deletion; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis* / Q000235:genetics / Q000494:pharmacology; D020298:U937 Cells / Q000187:drug effects; D051020:bcl-X Protein
chemical_list: D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; C494811:BCL2L1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D054713:Bryostatins; D002352:Carrier Proteins; D007783:Lactones; D018942:Macrolides; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011993:Recombinant Fusion Proteins; D014409:Tumor Necrosis Factor-alpha; D051020:bcl-X Protein; C046785:bryostatin 1; D011493:Protein Kinase C; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D017239:Paclitaxel