Intracellular Redistribution of Nucleolin upon Interaction with the CD3ε Chain of the T Cell Receptor Complex

T cell activation through the antigen receptor (TCR) involves the cytoplasmic tails of the CD3 subunits CD3gamma, CD3delta, CD3epsilon, and CD3zeta. Whereas the biological significance of the cytoplasmic tails of these molecules is suggested, in part, by their evolutionarily conserved sequences, their interactions with signal transduction molecules are not completely understood. We used affinity chromatography columns of glutathione S-transferase fused to the CD3epsilon cytoplasmic tail to isolate proteins that specifically interact with this subunit. In this way, we identified the shuttling protein nucleolin as a specific CD3epsilon-interacting molecule. Using competition studies and affinity chromatography on peptide columns, we were able to identify a central proline-rich sequence as the nucleolin-interacting sequence in CD3epsilon. Transfection in COS cells of wild type CD3epsilon, but not of nonbinding mutants of CD3epsilon, resulted in redistribution of nucleolin from the nucleus and nucleoli to the cytoplasm. This property was transferred to a CD8 protein chimera by appending the cytoplasmic tail of CD3epsilon. We also found that nucleolin associated with the TCR complex. This association was increased upon TCR engagement, suggesting that the CD3epsilon/nucleolin interaction may have a role in T cell activation.