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Requirement for Daxx in mature T-cell proliferation and activation

J Leal-Sanchez1, A Couzinet, A Rossin

  • 1Equipe Labellisée par La Ligue Nationale Centre le Cancer Institute of Signalling, Developmental Biology and Cancer Research, CNRS UMR 6543, Nice, France.

Cell Death and Differentiation
|November 4, 2006
PubMed

Insights

The protein Daxx regulates T-cell homeostasis by promoting Fas-mediated cell death and suppressing T-cell receptor (TCR)-induced proliferation. Blocking Daxx function enhances T-cell responses, revealing its critical role in immune regulation.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Death Pathways

Background:

  • The protein Daxx (also known as DAXX) is implicated in apoptosis signaling, particularly Fas-mediated cell death, through the activation of apoptosis signal-regulating kinase 1 (ASK1) and downstream MAPKs (JNK and p38).
  • The essential role of Daxx in vivo has been challenging to study due to the embryonic lethality of daxx-deficient mice.

Purpose of the Study:

  • To investigate the in vivo function of Daxx in T-lymphocyte homeostasis using a transgenic mouse model expressing a dominant-negative form of Daxx (Daxx-DN) in T cells.
  • To elucidate the mechanisms by which Daxx influences Fas-mediated apoptosis and T-cell receptor (TCR) signaling.

Main Methods:

  • Generation of transgenic mice expressing a dominant-negative Daxx (Daxx-DN) specifically in the T-cell lineage.
  • Analysis of Daxx recruitment to the Fas receptor upon Fas ligand (FasL) engagement.
  • Assessment of T-cell proliferation and survival following Fas-induced cell death and TCR stimulation in Daxx-DN T cells.
  • Evaluation of LAT and ZAP70 phosphorylation and recruitment to the TCR complex.

Main Results:

  • Daxx is recruited to the Fas receptor upon FasL engagement.
  • Expression of Daxx-DN in activated T cells confers protection against Fas-induced cell death by inhibiting the formation of the death-inducing signaling complex.
  • Despite altered Fas signaling, normal lymphocyte development and homeostasis were observed.
  • Daxx-DN T-lymphocytes exhibited enhanced proliferative responses upon both in vitro and in vivo stimulation.
  • This increased proliferation correlated with augmented tyrosine phosphorylation of LAT and ZAP70, and favored their recruitment to the TCR complex.

Conclusions:

  • Daxx acts as a critical regulator of T-lymphocyte homeostasis.
  • Daxx negatively impacts TCR-induced T-cell proliferation and promotes Fas-mediated cell death.
  • Modulating Daxx function offers a potential strategy for manipulating T-cell responses.

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