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Coordinated dual cleavages induced by the proteasome regulator PA28 lead to dominant MHC ligands

T P Dick1, T Ruppert, M Groettrup

  • 1Department of Tumorvirus-Immunology, German Cancer Research Center, Heidelberg, Federal Republic of Germany.

Cell
|July 26, 1996
PubMed

Insights

The proteasome regulator PA28 enhances the proteasome

Area of Science:

  • * Molecular biology
  • * Immunology
  • * Biochemistry

Background:

  • * The eukaryotic 20S proteasome is a multi-subunit protease complex.
  • * The proteasome is involved in antigen presentation and protein degradation.
  • * PA28 (proteasome activator 28) is an interferon-gamma-inducible regulator that associates with the 20S proteasome.

Purpose of the Study:

  • * To investigate the effect of PA28 on the kinetics of product generation by the 20S proteasome.
  • * To elucidate the mechanism by which PA28 alters proteasome cleavage patterns.
  • * To determine if PA28 optimizes the generation of T-cell epitopes.

Main Methods:

  • * Kinetic analysis of peptide degradation by 20S proteasomes with and without PA28.
  • * Analysis of peptide products generated from specific protein substrates (mouse cytomegalovirus pp89 and JAK1 kinase).

Main Results:

  • * In the absence of PA28, the 20S proteasome primarily generates single-cleavage peptides.
  • * PA28 promotes a coordinated double-cleavage mechanism, leading to immediate generation of doubly cleaved products.
  • * PA28 significantly enhances the production of major histocompatibility complex (MHC) ligands and their precursors.

Conclusions:

  • * PA28 profoundly alters the cleavage mechanism of the 20S proteasome.
  • * PA28 optimizes the generation of dominant T-cell epitopes by enhancing MHC ligand precursor production.
  • * This suggests a crucial role for PA28 in adaptive immunity and antigen presentation.

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