title: UCN-01 (7-hydroxystauorsporine) blocks PMA-induced maturation and reciprocally promotes apoptosis in human myelomonocytic leukemia cells (U937).
abstract: Interactions between the protein kinase inhibitor UCN-01 and the PKC activator phorbol ester (PMA) have been examined in relation to differentiation and apoptosis in human myelomonocytic leukemia cells (U937). Coadministratation of 100 nM UCN-01 with a low concentration of PMA e.g., 2 nM, inhibited rather than promoted differentiation, reflected by reduced surface expression of the monocytic maturation marker CD11b and diminished cell adherence. Instead, administration of UCN-01 with PMA led to a marked increase in mitochondrial injury (e.g, cytochrome c release), activation of caspases-3 and -8, Bid cleavage, PARP degradation, and apoptosis, accompanied by a substantial reduction in viability and clonogenic survival. These phenomena were associated with multiple perturbations in cell cycle regulatory events, including abrogation of p21(CIP1) induction, p27(KIP1) cleavage, down-regulation of cyclin D1, dephosphorylation (activation) of p34cdc2, and degradation of underphosphorylated pRb. Potentiation of PMA-mediated apoptosis was partially mimicked by caffeine suggesting the involvement of Chk1 in the potentiation of apoptosis. Induction of cell death by UCN-01 and PMA was increased in cells stably expressing a p21(CIP1) mRNA antisense construct, suggesting that p21(CIP1) expression may protect cells from the lethal effects of this drug combination. Finally, ectopic expression of a Bcl-2 but not dominant-negative caspase-8 protected cells from UCN-01/PMA-mediated apoptosis, suggesting the lethal effects of this combination primarily involves the mitochondrial rather than the TNF-related extrinsic apoptotic pathway. Taken together, these findings suggest that UCN-01 disrupts a variety of cell cycle events in leukemic cells exposed to the maturation-inducing agent PMA, causing cells to engage an apoptotic rather than a differentiation-related program.
authors.affiliation: Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Rahmani
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000470:Alkaloids / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D015153:Blotting, Western; D002273:Carcinogens; D002454:Cell Differentiation; D002470:Cell Survival; D002986:Clinical Trials as Topic; D003574:Cytochrome c Group / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005799:Genes, Dominant; D006801:Humans; D007938:Leukemia / Q000188:drug therapy; D008954:Models, Biological; D019311:Staurosporine / Q000031:analogs & derivatives; D013755:Tetradecanoylphorbol Acetate; D013997:Time Factors; D014407:Tumor Cells, Cultured; D020298:U937 Cells
chemical_list: D000470:Alkaloids; D000970:Antineoplastic Agents; D002273:Carcinogens; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; C054852:7-hydroxystaurosporine; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate