Differential function of Themis CABIT domains during T cell development.

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Themis (thymocyte positive selection adaptor) is a novel Grb2-binding protein.
• Its precise function in T cell receptor (TCR)-mediated signaling and thymocyte positive selection is debated.
• Themis possesses uncharacterized CABIT domains, a nuclear localization signal (NLS), and a proline-rich sequence (PRS).

Purpose of the Study:

• To investigate the in vivo function of Themis motifs in thymocyte positive selection.
• To determine the role of CABIT domains, NLS, and PRS in Themis's interaction with Grb2 and TCR signaling.
• To elucidate the distinct contributions of each Themis motif to T cell development.

Main Methods:

• Generation of mutant Themis transgenic mice on a Themis-deficient background.
• Analysis of Grb2 association, TCR-dependent tyrosine phosphorylation, and thymic positive selection.
• Assessment of Themis nuclear localization and dominant-negative effects on T cell development.

Main Results:

• Deletion of Core1, Core2, NLS, or PRS abolished Grb2 binding, TCR signaling, and positive selection.
• NLS and Core1 motifs are necessary for Themis nuclear localization; Core2 and PRS are not.
• ΔCore1-Themis exhibited dominant-negative inhibition of T cell development, unlike ΔCore2-Themis.

Conclusions:

• PRS, NLS, CABIT1, and CABIT2 are all indispensable for thymocyte positive selection.
• The CABIT domains (CABIT1 and CABIT2) play distinct and essential roles in Themis function.
• Understanding these motifs clarifies Themis's mechanism in T cell development and signaling.