u-0126 and mezerein

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)

Topics: Acetylcysteine; Amanitins; Aminoacetonitrile; Apoptosis; Benzoquinones; Bryostatins; Butadienes; Curcumin; Cysteine Endopeptidases; Dactinomycin; Diterpenes; Drug Synergism; Enzyme Activation; Flavonoids; Humans; Imidazoles; Indoles; JNK Mitogen-Activated Protein Kinases; Lactams, Macrocyclic; Lactones; Macrolides; Maleimides; MAP Kinase Kinase 4; MAP Kinase Signaling System; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases; Multienzyme Complexes; Neoplasm Proteins; Nitriles; Nucleic Acid Synthesis Inhibitors; p38 Mitogen-Activated Protein Kinases; Protease Inhibitors; Proteasome Endopeptidase Complex; Protein Kinase C; Protein Synthesis Inhibitors; Proto-Oncogene Proteins c-raf; Pyridines; Quinones; Terpenes; Tetradecanoylphorbol Acetate; Transcription Factor AP-1; Type C Phospholipases; U937 Cells; Ubiquitins