title: Inactive caspase 3 activates Akt in human leukemia cells susceptible or resistant to apoptosis induced by phorbol ester.
abstract: Phorbol 12-myristate 13-acetate (PMA) is a protein kinase C (PKC) activator and tumor promoter that induces terminal differentiation in human myeloid leukemia cells. We undertook to characterize phorbol ester-activated PKC-mediated cell cycle arrest and apoptosis. In the present studies, we determined the effect of high intracellular levels of the anti-apoptosis Bcl-2 protein on caspase 3 activation and cyctochrome c release during phorbol ester 12-myristate 13-acetate (PMA)-induced apoptosis. For this, we used the U937 cells, Bcl-2 overexpressed U937 cells (U937/Bcl-2) and the PMA-resistant derivative cell line R-U937. The G1 arrest of U937 cells and U937/Bcl-2 cells induced by treatment with 20 nM PMA is associated with cyclin A down-regulation and accumulation of p21, cdks inhibitor. However, PMA had no effect on the levels of cyclin A expression and p21 expression under the same conditions of time and concentration of PMA in the R-U937 cells. Treatment with 20 nM PMA for 24 h produced morphological features of apoptosis and DNA fragmentation in U937 and U937/Bcl-2 cells, but not in R-U937 cells. This was associated with the caspase 3 activation and cyctochrome c release. R-U937 cells exhibited less cytochrome c release and sustained phosphorylation level of Akt during PMA-induced apoptosis. These findings indicate that R-U937 cells are resistant to PMA-induced apoptosis by a mechanism of the signaling defect in the activation of the caspase 3 that is involved in the execution of apoptosis.
authors.affiliation: Department of Pediatrics, Yeungnam University Medical Center, Taegu, Korea.
authors.forename: Jeong-Ok
authors.initials: JO
authors.lastname: Hah
authors.forename: Kyung-Ah
authors.initials: KA
authors.lastname: Lee
authors.forename: Yun Jung
authors.initials: YJ
authors.lastname: Choi
authors.forename: Won-Duck
authors.initials: WD
authors.lastname: Kim
authors.forename: Jong-Wook
authors.initials: JW
authors.lastname: Park
authors.forename: Taeg Kyu
authors.initials: TK
authors.lastname: Kwon
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002273:Carcinogens / Q000494:pharmacology*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects*; D004789:Enzyme Activation; D019254:Genes, bcl-2; D006801:Humans; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014162:Transfection; D020298:U937 Cells
chemical_list: D002273:Carcinogens; D011518:Proto-Oncogene Proteins; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011493:Protein Kinase C; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D013755:Tetradecanoylphorbol Acetate