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Published on: March 22, 2012

TCR subunit specificity of CTLA-4-mediated signaling

Eric Siu1, Beatriz M Carreno, Joaquín Madrenas

  • 1The FOCIS Centre for Clinical Immunology and Immunotherapeutics, Robarts Research Institute, London, Ontario, Canada N6A 5K8.

Journal of Leukocyte Biology
|September 16, 2003
PubMed

Insights

Cytotoxic T-lymphocyte-associated antigen (CTLA)-4 negatively regulates T cell responses. This study shows CTLA-4 inhibits T cell activation by engaging with CD3-epsilon, not just TCR-zeta, indicating broader target specificity.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Signaling

Background:

  • Cytotoxic T-lymphocyte-associated antigen (CTLA)-4 is a T cell receptor that down-regulates immune responses.
  • The precise mechanism of CTLA-4-mediated negative signaling remains unclear.
  • A recent hypothesis proposed CTLA-4 inhibits T cell activation by dephosphorylating the T cell receptor (TCR)-zeta chain via recruitment of tyrosine phosphatase-2.

Purpose of the Study:

  • To investigate the mechanism of CTLA-4-mediated negative signaling.
  • To test the hypothesis that CTLA-4 specifically targets the TCR-zeta chain for dephosphorylation.
  • To determine if CTLA-4's inhibitory action is restricted to TCR-zeta or extends to other components of the T cell receptor complex.

Main Methods:

  • Generation of stably transfected T cell clones expressing doxycycline-inducible CTLA-4.
  • Construction of fusion proteins: CD25:TCR-zeta (CD25-zeta) and CD25:CD3-epsilon (CD25-epsilon).
  • Ligation of CD25-zeta or CD25-epsilon to induce T cell activation (measured by ERK activation and IL-2 production).
  • Coligation of CTLA-4 with CD25-zeta or CD25-epsilon to assess inhibitory effects.

Main Results:

  • Ligation of CD25-zeta or CD25-epsilon induced T cell activation, evidenced by extracellular signal-regulated kinase (ERK) activation and interleukin (IL)-2 production.
  • Coligation of CTLA-4 with either CD25-zeta or CD25-epsilon significantly inhibited ERK activation and IL-2 production.
  • These findings demonstrate that CTLA-4's inhibitory effect is not specific to TCR-zeta but can also be triggered by CD3-epsilon.

Conclusions:

  • CTLA-4 does not exclusively inhibit signals originating from the TCR-zeta chain.
  • CTLA-4 can inhibit T cell activation mediated by CD3-epsilon signaling.
  • The target specificity of CTLA-4 appears to be determined by its coligation with various transmembrane receptors, rather than solely by intracellular mediators.

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