Synergistic induction of apoptosis in human leukemia cells (U937) exposed to bryostatin 1 and the proteasome inhibitor lactacystin involves dysregulation of the PKC/MAPK cascade.
Cotreatment with a minimally toxic concentration of the protein kinase C (PKC) activator (and down-regulator) bryostatin 1 (BRY) induced a marked increase in mitochondrial dysfunction and apoptosis in U937 monocytic leukemia cells exposed to the proteasome inhibitor lactacystin (LC). This effect was blocked by cycloheximide, but not by alpha-amanitin or actinomycin D. Qualitatively similar interactions were observed with other PKC activators (eg, phorbol 12-myristate 13-acetate and mezerein), but not phospholipase C, which does not down-regulate the enzyme. These events were examined in relationship to functional alterations in stress (eg, SAPK, JNK) and survival (eg, MAPK, ERK) signaling pathways. The observations that LC/BRY treatment failed to trigger JNK activation and that cell death was unaffected by a dominant-interfering form of c-JUN (TAM67) or by pretreatment with either curcumin or the p38/RK inhibitor, SB203580, suggested that the SAPK pathway was not involved in potentiation of apoptosis. In marked contrast, perturbations in the PKC/Raf/MAPK pathway played an integral role in LC/BRY-mediated cell death based on evidence that pretreatment of cells with bisindolylmaleimide I, a selective PKC inhibitor, or geldanamycin, a benzoquinone ansamycin, which destabilizes and depletes Raf-1, markedly suppressed apoptosis. Furthermore, ERK phosphorylation was substantially prolonged in LC/BRY-treated cells compared to those exposed to BRY alone, and pretreatment with the highly specific MEK inhibitors, PD98059, U0126, and SL327, opposed ERK activation while protecting cells from LC/BRY-induced lethality. Together, these findings suggest a role for activation and/or dysregulation of the PKC/MAPK cascade in modulation of leukemic cell apoptosis following exposure to the proteasome inhibitor LC. (Blood. 2001;97:2105-2114)
Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA, USA.
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D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000546:Amanitins / Q000494:pharmacology; D000607:Aminoacetonitrile / Q000031:analogs & derivatives; D017209:Apoptosis / Q000187:drug effects*; D016227:Benzoquinones; D054713:Bryostatins; D002070:Butadienes / Q000494:pharmacology; D003474:Curcumin / Q000494:pharmacology; D003546:Cysteine Endopeptidases; D003609:Dactinomycin / Q000494:pharmacology; D004224:Diterpenes; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D047029:Lactams, Macrocyclic; D007783:Lactones / Q000494:pharmacology*; D048670:MAP Kinase Kinase 4; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D018942:Macrolides; D008301:Maleimides / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D011809:Quinones / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000502:physiology; D010738:Type C Phospholipases / Q000494:pharmacology; D020298:U937 Cells / Q000187:drug effects* / Q000201:enzymology; D014452:Ubiquitins / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
D000546:Amanitins; D016227:Benzoquinones; D054713:Bryostatins; D002070:Butadienes; D004224:Diterpenes; D005419:Flavonoids; D007093:Imidazoles; D007211:Indoles; D047029:Lactams, Macrocyclic; D007783:Lactones; D018942:Macrolides; D008301:Maleimides; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins; D009570:Nitriles; D019384:Nucleic Acid Synthesis Inhibitors; D011480:Protease Inhibitors; D011500:Protein Synthesis Inhibitors; D011725:Pyridines; D011809:Quinones; C424127:SL 327; D013729:Terpenes; D018808:Transcription Factor AP-1; C113580:U 0126; D014452:Ubiquitins; C067713:lactacystin; D003609:Dactinomycin; C011309:mezerein; D000607:Aminoacetonitrile; C046785:bryostatin 1; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D010738:Type C Phospholipases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D003474:Curcumin; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D000111:Acetylcysteine; C001277:geldanamycin