Overexpression of Apaf-1 promotes apoptosis of untreated and paclitaxel- or etoposide-treated HL-60 cells

Charles Perkins, Caryn N. Kim, Guofu Fang, Kapil Bhalla

Research output: Contribution to journalArticle

97 Scopus citations

Abstract

Recent studies have demonstrated that Apaf-1 is the adaptor molecule which in the presence of cytosolic cytochrome c (cyt c) and dATP interacts with procaspase-9, resulting in the sequential cleavage and activity of caspase-9 and caspase-3, followed by apoptosis. In the present studies, we determined the effect of enforced overexpression of Apaf-1 on the apoptotic threshold in the human myeloid leukemia HL-60 cells. Our findings demonstrate that both transient and stable transfections resulted in a 2.5-fold higher expression of Apaf-1, which was associated with approximately a 5-fold increase in the percentage of apoptosis in the transfectants (HL-60/Apaf-1) as compared with the control HL-60/neo cells. In cells overexpressing either Bcl-2 or Bcl-x(L), transient overexpression of Apaf-1 did not induce apoptosis. Stably overexpressing Apaf-1 levels significantly sensitized HL- 60/Apaf-1 cells to apoptosis induced by clinically achievable concentrations of paclitaxel or etoposide (P < 0.01). This increase in paclitaxel- or etoposide-induced apoptosis of HL-60/Apaf-1 cells was not associated with any significant alterations in Bcl-2, Bcl-x(L), Bax, Fas, or Fas ligand expression. It was, however, clearly associated with caspase-9 cleavage, as well as the poly(ADP-ribose) polymerase and DFF45 cleavage activity of caspase-3. Coexpression of the catalytically inactive, dominant-negative, mutant caspase-9, XIAP, or treatment with the caspase inhibitor, zVAD, significantly inhibited the increase in apoptosis of HL-60/Apaf-1 cells (P < 0.01). These data indicate that the intracellular levels of Apaf-1 is an important molecular determinant of the threshold for apoptosis induced by paclitaxel and etoposide.

Original languageEnglish (US)
Pages (from-to)4561-4566
Number of pages6
JournalCancer research
Volume58
Issue number20
StatePublished - Oct 15 1998

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

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