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Tyrosine phosphorylation acts as a molecular switch to full-scale activation of the eIF2alpha RNA-dependent protein

Qiaozhu Su1, Shuo Wang, Dionissios Baltzis

  • 1Lady Davis Institute for Medical Research, McGiIl University, Sir Mortimer B. Davis Jewish General Hospital, Montreal, QC, Canada H3T 1E2.

Proceedings of the National Academy of Sciences of the United States of America
|December 24, 2005
PubMed

Insights

Tyrosine phosphorylation of PKR, an eIF2alpha kinase, is crucial for its antiviral and antiproliferative functions. This phosphorylation regulates dsRNA binding, dimerization, and kinase activation, impacting protein synthesis during stress.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Virology

Background:

  • Phosphorylation of eukaryotic initiation factor-2 alpha (eIF2alpha) inhibits protein synthesis under stress.
  • Serine/threonine-protein kinase RNA-dependent (PKR) is an eIF2alpha kinase activated by double-stranded RNA (dsRNA) or viral infections.
  • PKR plays a role in the cellular response to type I interferon (IFN).

Purpose of the Study:

  • To investigate the role of tyrosine phosphorylation in the function of human PKR.
  • To determine the specific tyrosine residues involved in PKR activation and activity.
  • To elucidate the impact of tyrosine phosphorylation on PKR's biological functions, including antiviral and antiproliferative activities.

Main Methods:

  • In vitro and in vivo kinase assays to identify and characterize tyrosine phosphorylation sites on PKR.
  • Site-directed mutagenesis to assess the functional significance of specific tyrosine residues.
  • Analysis of PKR's dsRNA-binding affinity, dimerization, and eIF2alpha phosphorylation activity.
  • Evaluation of PKR's antiviral and antiproliferative effects in cellular models.

Main Results:

  • Human PKR was identified as a dual-specificity kinase, with phosphorylation observed at tyrosine residues Y101, Y162, and Y293.
  • Site-specific tyrosine phosphorylation was found to be essential for PKR's efficient dsRNA binding, dimerization, and kinase activation.
  • Tyrosine phosphorylation directly impacts PKR's ability to phosphorylate eIF2alpha.
  • The study confirmed that tyrosine phosphorylation of PKR is critical for its antiviral and antiproliferative properties by controlling translation.

Conclusions:

  • Tyrosine phosphorylation is a key regulatory mechanism for PKR activity.
  • Specific tyrosine residues mediate essential biochemical functions of PKR, including dsRNA binding and kinase activation.
  • The findings highlight the significant role of tyrosine phosphorylation in the biological outcomes mediated by PKR activation, particularly in antiviral defense and cell proliferation control.

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