title: Modulation of 1-[beta-D-arabinofuranosyl] cytosine-induced apoptosis in human myeloid leukemia cells by staurosporine and other pharmacological inhibitors of protein kinase C.
abstract: We have examined the effects of both nonspecific and highly selective pharmacological inhibitors of protein kinase C (PKC) on the capacity of a 6-h exposure to 1-[beta-D-arabinofuranosyl]cytosine (ara-C; 10 microM) to induce apoptotic DNA fragmentation and cell death in the human myeloid leukemia cell lines HL-60 and U937. Staurosporine, a highly potent, nonspecific inhibitor of PKC (20-50 nM), uniquely potentiated ara-C-related degradation of DNA to oligonucleosomal fragments in both cell lines (i.e., 2- to 3-fold), but was ineffective when given alone at these concentrations. In contrast, co-administration of the nonspecific PKC inhibitor H7 and two highly selective PKC inhibitors, calphostin C and chelerythrine, also increased the extent of DNA fragmentation observed in ara-C-treated cells, but these effects were evident only at inhibitor concentrations that were by themselves sufficient to induce DNA damage. Agarose gel electrophoresis demonstrated that cells co-exposed to staurosporine and ara-C exhibited considerably more pronounced internucleosomal DNA cleavage than did cells exposed to ara-C alone; moreover, this effect was suppressed by Zn2+ (1 mM) and the permeant Ca2+ chelator BAPTA-AM (50 microM). Potentiation of ara-C-related DNA fragmentation by subeffective concentrations of staurosporine was accompanied by a pronounced increase in the morphological features characteristic of apoptosis. A synergistic interaction between staurosporine and ara-C with respect to inhibition of clonogenicity in both HL-60 and U937 cells was demonstrated by median dose-effect analysis. The actions of staurosporine did not result from enhanced ara-C metabolism, as preincubation of cells with concentrations of this agent that potentiated ara-C actions (e.g., 20-50 nM) did not increase intracellular levels of the lethal metabolite ara-CTP. Lastly, preexposure of HL-60 and U937 cells to staurosporine did not block ara-C-mediated upregulation of c-jun, an oncogene whose increased expression has been temporally associated with ara-C-induced apoptosis. Together, these findings indicate that staurosporine exhibits a unique pattern of potentiation of ara-C-related apoptosis in human myeloid leukemias, and provide a rationale for exploring the antileukemic potential of this combination regimen.
authors.affiliation: Department of Medicine, Medical College of Virginia, Richmond 23298-0230.
authors.forename: S
authors.initials: S
authors.lastname: Grant
authors.forename: A J
authors.initials: AJ
authors.lastname: Turner
authors.forename: T M
authors.initials: TM
authors.lastname: Bartimole
authors.forename: P A
authors.initials: PA
authors.lastname: Nelms
authors.forename: V C
authors.initials: VC
authors.lastname: Joe
authors.forename: W D
authors.initials: WD
authors.lastname: Jarvis
mesh_terms: D000470:Alkaloids / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001085:Arabinofuranosylcytosine Triphosphate / Q000378:metabolism; D003561:Cytarabine / Q000494:pharmacology*; D004249:DNA Damage; D004357:Drug Synergism; D015870:Gene Expression / Q000187:drug effects; D016758:Genes, jun / Q000187:drug effects; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000188:drug therapy* / Q000473:pathology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D019311:Staurosporine; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D000470:Alkaloids; D003561:Cytarabine; D001085:Arabinofuranosylcytosine Triphosphate; D011493:Protein Kinase C; D019311:Staurosporine