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Okadaic acid induces apoptosis through double-stranded RNA-dependent protein kinase/eukaryotic initiation

Hiroyuki Morimoto1, Hirohiko Okamura, Kaya Yoshida

  • 1Department of Anatomy, School of Dentistry, The University of Tokushima, Kuramoto, Tokushima 770-8504, Japan. morimoto@dent.tokushima-u.ac.jp

Journal of Biochemistry
|December 31, 2004
PubMed

Insights

Okadaic acid, a phosphatase inhibitor, triggers apoptosis in MG63 cells by activating PKR and eIF-2alpha, leading to decreased anti-apoptotic protein expression and blocked protein synthesis. This highlights the role of phosphatases in cell death pathways.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Double-stranded RNA-dependent protein kinase (PKR) is crucial for the cellular antiviral response.
  • PKR phosphorylates eukaryotic translation initiation factor 2alpha (eIF-2alpha), inhibiting protein synthesis.
  • Protein phosphatases play a role in regulating cellular processes, including apoptosis.

Purpose of the Study:

  • To investigate the functional relationship between protein phosphatases and apoptosis.
  • To examine the effect of okadaic acid, a phosphatase inhibitor, on apoptosis in MG63 cells.
  • To elucidate the role of PKR and eIF-2alpha phosphorylation in okadaic acid-induced apoptosis.

Main Methods:

  • Treatment of MG63 cells with varying concentrations of okadaic acid (20 nM and 100 nM).
  • Western blot analysis to assess the phosphorylation levels of PKR and eIF-2alpha.
  • Evaluation of NF-kappaB activation and expression of pro-apoptotic proteins (Fas and Bax).

Main Results:

  • 100 nM okadaic acid, but not 20 nM, induced apoptosis in MG63 cells.
  • Higher okadaic acid concentration increased phosphorylated PKR, which subsequently phosphorylated eIF-2alpha, inhibiting translation.
  • NF-kappaB activation was observed at 100 nM okadaic acid; however, Fas and Bax expression remained unaffected.

Conclusions:

  • Inhibition of protein phosphatase activity by okadaic acid induces apoptosis in MG63 cells.
  • The mechanism involves the PKR and eIF-2alpha pathway, leading to decreased anti-apoptotic protein expression.
  • PKR-mediated inhibition of translation contributes to okadaic acid-induced apoptosis.

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