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The activation of Csk by CD4 interferes with TCR-mediated activatory signaling
Barbara Marinari1, Luca Simeoni, Burkhart Schraven
1Department of Cellular and Developmental Biology, La Sapienza University, I-00185 Rome, Italy.
Abstract:
CD4-Lck recruitment to TCR/CD3, as well as Lck activation is essential for T cell activation. Indeed, the blockage of CD4-Lck recruitment to TCR during antigen recognition exerts a drastic inhibitory effect on T cell activation by interfering with both early and late phases of T cell signaling. In the present work, we report a novel inhibitory mechanism by which CD4 can shut down proximal T cell-activating signals. Indeed, we show that upon ligation of CD4 by antibodies the inhibitory kinase, p50(csk), is strongly induced and prolonged during the time. In contrast, p50(csk) was not activated when TCR and CD4 were properly engaged by their ligands. We also demonstrate that anti-CD4 treatment stimulated Csk kinase associated to the membrane adapter, PAG/Cbp, without affecting the total amount of Csk bound to PAG/Cbp. As a consequence, early tyrosine phosphorylation events as well as downstream signaling pathways leading to IL-2 gene expression induced by TCR were inhibited in anti-CD4 pretreated cells. We suggest a new model to explain the activation of negative signals by CD4 molecule.
Insights
Antibodies targeting CD4 can inhibit T cell activation by inducing the p50(csk) inhibitory kinase. This blocks T cell receptor (TCR) signaling pathways, preventing IL-2 gene expression and T cell activation.
Area of Science:
- Immunology
- Cell Signaling
Background:
- T cell activation relies on CD4-Lck recruitment to the T cell receptor (TCR)/CD3 complex.
- Blocking CD4-Lck interaction inhibits T cell activation by disrupting early and late signaling phases.
Purpose of the Study:
- To investigate a novel inhibitory mechanism by which CD4 can suppress proximal T cell-activating signals.
- To elucidate the role of CD4 ligation by antibodies in regulating T cell signaling.
Main Methods:
- Investigated the activation of the inhibitory kinase p50(csk) upon CD4 ligation by antibodies.
- Assessed Csk kinase association with the membrane adapter PAG/Cbp.
- Analyzed early tyrosine phosphorylation events and downstream signaling pathways, including IL-2 gene expression.
Main Results:
- Antibody-mediated CD4 ligation strongly induced and prolonged p50(csk) activation.
- p50(csk) was not activated when TCR and CD4 were properly engaged by their natural ligands.
- Anti-CD4 treatment stimulated Csk kinase associated with PAG/Cbp, inhibiting TCR-induced phosphorylation and IL-2 expression.
Conclusions:
- CD4, when ligated by antibodies, can activate the inhibitory kinase p50(csk), leading to suppression of T cell activation.
- This study proposes a new model for CD4-mediated negative signaling in T cells.
- Understanding this mechanism offers insights into regulating T cell responses.