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Assessment of Mitochondrial Functions and Cell Viability in Renal Cells Overexpressing Protein Kinase C Isozymes
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Protein phosphatase 2A-linked and -unlinked caspase-dependent pathways for downregulation of Akt kinase triggered by

W Liu1, A A Akhand, K Takeda

  • 1Department of Immunology, Nagoya University Graduate School of Medicine, Showa-ku, Nagoya, Japan.

Cell Death and Differentiation
|June 20, 2003
PubMed

Insights

4-hydroxynonenal (HNE) triggers apoptosis by downregulating Akt signaling through caspase-dependent pathways. This involves protein phosphatase 2A (PP2A) activation and Src kinase inhibition, revealing a feedback loop in apoptosis.

Area of Science:

  • Cellular signaling
  • Apoptosis research
  • Biochemistry

Background:

  • Akt (protein kinase B) is crucial in cell survival and proliferation.
  • 4-hydroxynonenal (HNE) is an aldehyde linked to oxidative stress and apoptosis.
  • Caspase-dependent apoptosis involves a cascade of proteases.

Purpose of the Study:

  • To elucidate the signal pathways regulating Akt activity during HNE-induced apoptosis.
  • To investigate the role of protein phosphatase 2A (PP2A) and caspases in Akt downregulation.
  • To identify feedback mechanisms in HNE-triggered apoptosis.

Main Methods:

  • Jurkat cells treated with HNE.
  • Analysis of Akt phosphorylation at Ser473.
  • Inhibition studies using okadaic acid (PP2A inhibitor) and DEVD-CHO (caspase-3 inhibitor).
  • Measurement of PP2A activity and its association with Akt.
  • Assessment of Src kinase activity and Akt cleavage.

Main Results:

  • HNE treatment decreased Akt activity via dephosphorylation at Ser473.
  • This dephosphorylation was blocked by PP2A and caspase-3 inhibitors.
  • HNE increased PP2A activity and PP2A-Akt association, dependent on caspase-3.
  • Caspase-3 activation led to decreased Src kinase activity and partial Akt cleavage.
  • Two distinct caspase-dependent pathways for Akt downregulation were identified.

Conclusions:

  • HNE induces apoptosis through caspase-dependent downregulation of Akt signaling.
  • PP2A activation and Src kinase inhibition are key components of this pathway.
  • These findings reveal a positive feedback mechanism regulating HNE-induced apoptosis.

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