Conserved transmembrane tyrosine residues of the TCR beta chain are required for TCR expression and function in primary T cells and hybridomas

The T cell receptor (TCR) beta7 chain transmembrane domain contains two evo lutionarily conserved tyrosines (Y), In this study, the functional basis fo r the evolutionary conservation is addressed by mutation of the residues, e xpression of the mutants in hybridoma and primary T cells, and examination of TCR signaling function. We find that the phenotype of the mutants, both surface expression and ability to signal for IL-2 production, is highly var iable in different mouse T hybridoma lines. Although we have not been able to determine the basis for these differences in the hybridomas, expression of the mutants in primary T cells provides a definitive assessment of mutan t phenotype. We show that mutation of the N-terminal Y to either leucine (L ) or alanine (A) results in low surface expression in primary T cells, whil e mutation of both N- and C-terminal Y to A or L abrogates surface expressi on. However, the more conservative mutation of both transmembrane Y to phen ylalanine maintained receptor surface expression and assembly while severel y disrupting signaling in primary T cells. Our data demonstrate that TCR be ta chain transmembrane Y are essential for TCR signal transduction as well as complex assembly. These findings suggest that protein-protein interactio ns involving membrane-spanning domains are likely relevant for TCR signal t ransduction mechanisms.