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Essential role of PACT-mediated PKR activation in tunicamycin-induced apoptosis

Madhurima Singh1, Vennece Fowlkes, Indhira Handy

  • 1Department of Biological Sciences, University of South Carolina, 700 Sumter Street, Columbia, SC 29208, USA.

Journal of Molecular Biology
|November 15, 2008
PubMed

Insights

PACT activates PKR, a key player in endoplasmic reticulum (ER) stress-induced apoptosis. PACT-PKR activation is essential for tunicamycin-induced cell death, highlighting a new therapeutic target.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Apoptosis Research

Background:

  • Cellular stresses, including disrupted calcium homeostasis and protein misfolding, trigger apoptosis via endoplasmic reticulum (ER) stress.
  • Tunicamycin, a protein glycosylation inhibitor, is a known inducer of ER stress and apoptosis.

Purpose of the Study:

  • To investigate the role of double-stranded RNA (dsRNA)-activated protein kinase (PKR) and its activator PACT in tunicamycin-induced apoptosis.
  • To elucidate the mechanism by which PACT influences PKR activation and subsequent cell death pathways.

Main Methods:

  • Utilized tunicamycin to induce ER stress in cellular models.
  • Examined the phosphorylation status of PACT and its interaction with PKR.
  • Assessed apoptosis, eIF2alpha phosphorylation, and CHOP induction in wild-type, PACT-null, and PKR-null cells.
  • Performed reconstitution experiments by reintroducing PKR and PACT expression in null cells.

Main Results:

  • PACT is phosphorylated upon tunicamycin treatment, leading to direct interaction and activation of PKR.
  • PACT-mediated PKR activation is critical for tunicamycin-induced apoptosis.
  • PACT-null and PKR-null cells exhibit significant resistance to tunicamycin, with impaired eIF2alpha phosphorylation and CHOP induction.
  • Reconstitution of PKR and PACT restores tunicamycin sensitivity.

Conclusions:

  • PACT-induced PKR activation is an essential signaling pathway in tunicamycin-induced apoptosis.
  • This pathway plays a crucial role in ER stress response and cell death.
  • Targeting the PACT-PKR interaction may offer therapeutic strategies for diseases involving ER stress.

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