Heterotypic interaction of CRTAM with Necl2 induces cell adhesion on activated NK cells and CD8⁺ T cells

Abstract

NK cells and CD8⁺ T cells exhibit cytotoxicity and cytokine production upon recognizing target cells through cell–cell interaction. We screened the molecules involved in the recognition and regulation of these cells using cDNA subtraction between naive and activated NK cells. We identified class I-restricted T cell-associated molecule (CRTAM), a two Ig domain-bearing surface receptor, as a molecule rapidly and transiently expressed on NK cells and CD8⁺ T cells upon activation. CRTAM is expressed as a dimer on the cell surface, and its expression is transcriptionally regulated. Using an expression-cloning system, we then further identified Nectin-like (Necl) molecule 2, a three Ig domain-containing receptor, as a ligand of CRTAM. While Necl2 mediates homotypic interaction, CRTAM interacts with Necl2 but not with CRTAM itself. The heterotypic CRTAM–Necl2 interaction has a higher affinity than the homotypic Necl2 interaction. Although there was no clear alteration in the cytotoxic function of the NK cells and CD8⁺ T cells against the Necl2-expressing target cells, T cells expressing CRTAM tightly bound to Necl2-expressing cells. CRTAM⁺ cells did not induce homotypic aggregation but they did exert strong heterotypic binding with Necl2⁺ cells, which was inhibited by the addition of the CRTAM-Ig fusion protein. These results suggest that the heterotypic interaction between CRTAM and Necl2 plays an important role in the adhesion, interaction or migration of NK cells and CD8⁺ T cells upon stimulation.

cell adhesion, expression cloning, Ig superfamily, subtraction

APC    antigen-presenting cell, BS³    Bis(sulfosuccinimidyl) suberate, CRTAM    class I-restricted T cell-associated molecule, ITAM    immunoreceptor tyrosine-based activation motif, ITIM    immunoreceptor tyrosine-based inhibitory motif, SHIP    SH2-domein-containing inositol polyphosphate 5-phosphatase, SHP    SH2-domein-containing protein tyrosine phosphatase, LFA    leukocyte function-associated antigen, Necl    nectin-like, RT    reverse transcription, Tg    transgenic