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Spatio-Temporal Manipulation of Small GTPase Activity at Subcellular Level and on Timescale of Seconds in Living Cells
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Activation of the Ras-related GTPase Rap1 by thymocyte TCR engagement and during selection

D Amsen1, A Kruisbeek, J L Bos

  • 1Division of Immunology, The Netherlands Cancer Institute, Amsterdam.

European Journal of Immunology
|November 9, 2000
PubMed

Insights

Rap1 signaling is active in thymocyte development and T-cell receptor (TCR) activation. This study reveals Rap1 activation during thymocyte positive selection, suggesting its crucial role in T-cell maturation.

Area of Science:

  • Immunology
  • Cellular Signaling
  • Molecular Biology

Background:

  • Ras GTPase signaling is vital for thymocyte development and T-cell receptor (TCR) mediated T-cell activation.
  • Rap1 signaling pathways may negatively regulate Ras-dependent pathways, indicating a potential role in T-cell regulation.

Purpose of the Study:

  • To investigate the involvement of Rap1 signaling in thymocyte TCR signaling and development.
  • To understand the activation dynamics of Rap1 and its regulators during thymocyte development.

Main Methods:

  • Assessed expression levels of Rap1 and its regulators (Cbl, Crk, C3G) in murine thymocytes.
  • Stimulated thymocytes via TCR and measured Rap1 activation, Cbl phosphorylation, and Cbl-CrkL association.
  • Investigated the role of co-stimulation (CD28) and signaling mimics (phorbol ester, calcium) on Rap1 activation.
  • Compared Rap1 activation mechanisms in thymocytes versus mature T lymphocytes.

Main Results:

  • Rap1 and its regulators are expressed in double-negative and double-positive thymocytes.
  • TCR stimulation transiently activated Rap1 in thymocytes, correlating with Cbl phosphorylation and Cbl-CrkL association.
  • CD28 co-stimulation enhanced TCR-dependent Rap1 activation; activation occurred independently of intracellular calcium mobilization in thymocytes.
  • Activated Rap1 levels were elevated in thymocytes undergoing positive selection.

Conclusions:

  • Rap1 signaling is dynamically regulated during thymocyte development and TCR signaling.
  • Rap1 activation in thymocytes differs from mature T cells, particularly regarding calcium dependence.
  • Elevated Rap1 activity during positive selection suggests a functional role in thymocyte development and selection processes.

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