title: The role of individual caspases in cell death induction by taxanes in breast cancer cells.
abstract: BACKGROUND
  In previous study we showed that caspase-2 plays the role of an apical caspase in cell death induction by taxanes in breast cancer cells. This study deals with the role of other caspases. We tested breast cancer cell lines SK-BR-3 (functional caspase-3) and MCF-7 (nonfunctional caspase-3).
  
  
  RESULTS
  Using western blot analysis we demonstrated the activation of initiator caspase-8 and -9 as well as executioner caspase-6 and -7 in both tested cell lines after application of taxanes (paclitaxel, SB-T-1216) at death-inducing concentrations. Caspase-3 activation was also found in SK-BR-3 cells. Employing specific siRNAs after taxane application, suppression of caspase-3 expression significantly increased the number of surviving SK-BR-3 cells. Inhibition of caspase-7 expression also increased the number of surviving SK-BR-3 and MCF-7 cells. On the other hand, suppression of caspase-8 and caspase-9 expression had no significant effect on cell survival. However, caspase-9 seemed to be involved in the activation of caspase-3 and caspase-7. Caspase-3 and caspase-7 appeared to activate mutually. Furthermore, we observed a significant decrease in mitochondrial membrane potential (flow cytometric analysis) and cytochrome c release (confocal microscopy, western blot after cell fractionation) from mitochondria in SK-BR-3 cells. No such changes were observed in MCF-7 cells after taxane treatment.
  
  
  CONCLUSIONS
  We conclude that the activation of apical caspase-2 results in the activation of caspase-3 and -7 without the involvement of mitochondria. Caspase-9 can be activated directly via caspase-2 or alternatively after cytochrome c release from mitochondria. Subsequently, caspase-9 activation can also lead to caspase-3 and -7 activations. Caspase-3 and caspase-7 activate mutually. It seems that there is also a parallel pathway involving mitochondria that can cooperate in taxane-induced cell death in breast cancer cells.
authors: Department of Cell and Molecular Biology, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
authors: Michael
authors: M
authors: Jelínek
authors: Department of Cell and Molecular Biology, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
authors: Kamila
authors: K
authors: Balušíková
authors: Department of Cell and Molecular Biology, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
authors: Martina
authors: M
authors: Schmiedlová
authors: Department of Cell and Molecular Biology, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
authors: Vlasta
authors: V
authors: Němcová-Fürstová
authors: Department of Cell and Molecular Biology, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
authors: Jan
authors: J
authors: Šrámek
authors: Department of Cell and Molecular Biology, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
authors: Jitka
authors: J
authors: Stančíková
authors: Institute of Chemical Biology and Drug Discovery, State University of New York at Stony Brook, Stony Brook, NY USA.
authors: Ilaria
authors: I
authors: Zanardi
authors: Institute of Chemical Biology and Drug Discovery, State University of New York at Stony Brook, Stony Brook, NY USA.
authors: Iwao
authors: I
authors: Ojima
authors: Department of Cell and Molecular Biology, Third Faculty of Medicine, Charles University, Prague, Czech Republic.
authors: Jan
authors: J
authors: Kovář
keywords: Breast cancer; Caspases; Cell death; Taxanes