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Human In Vitro Suppression as Screening Tool for the Recognition of an Early State of Immune Imbalance
14:01

Human In Vitro Suppression as Screening Tool for the Recognition of an Early State of Immune Imbalance

Published on: July 22, 2011

PAG/Cbp suppression reveals a contribution of CTLA-4 to setting the activation threshold in T cells

Michal Smida1, Clemens Cammann, Slavyana Gurbiel

  • 1Institute of Molecular and Clinical Immunology, Otto-von-Guericke University, Leipziger Strasse 44, Magdeburg, 39120, Germany. jon.lindquist@med.ovgu.de.

Cell Communication and Signaling : CCS
|April 23, 2013
PubMed
Abstract

Insights

Loss of PAG protein in T cells unexpectedly halts lymphocyte activation, revealing a novel fail-safe mechanism involving CTLA-4 regulation.

Area of Science:

  • Immunology
  • Cell Biology
  • Oncology

Background:

  • PAG/Cbp protein regulates Src family kinases (SFKs) by recruiting Csk to the plasma membrane, controlling cellular activation.
  • SFKs are implicated as oncogenes, prompting investigation into the role of PAG in lymphocyte transformation.

Purpose of the Study:

  • To investigate the consequences of PAG loss in primary human T cells using RNA interference.
  • To determine if PAG depletion leads to lymphocyte transformation due to enhanced SFK activity.

Main Methods:

  • RNA interference (RNAi) was employed to deplete PAG in primary human T cells.
  • T cell signaling pathways, including Src kinase activity and T-cell receptor (TCR) signaling, were analyzed.
  • Phosphorylation of CTLA-4 and recruitment of Shp-1 phosphatase were assessed.

Main Results:

  • PAG depletion enhanced Src kinase activity and proximal TCR signaling, consistent with the loss of a negative regulator.
  • Contrary to expectations, PAG-suppressed T cells exhibited unresponsiveness, not hyper-proliferation.
  • This unresponsiveness was mediated by Fyn-dependent hyper-phosphorylation of CTLA-4, leading to Shp-1 recruitment.
  • Simultaneous suppression of CTLA-4 restored T cell proliferation.

Conclusions:

  • A novel fail-safe mechanism regulating T cell activation has been identified.
  • CTLA-4 plays a previously unrecognized role in establishing the T cell activation threshold.

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