Apoptosis but not other activation events is inhibited by a mutation in the transmembrane domain of T cell receptor beta that impairs CD3 xi association

The transmembrane domain of T cell receptor (TCR) beta contains a conserved immunoreceptor tyrosine-based activation-like motif consisting of a duplicated YXXL sequence. The motif is also present in TCR gamma, the equivalent chain to TCR beta in gamma delta T lymphocytes but is absent in TCR alpha and TCR delta. To determine the putative role of this sequence in TCR-CD3 complex assembly and signal transduction, a TCR beta chain cDNA was mutated in the C-terminal tyrosine of the moth, cloned in an expression vector, and transfected into TCR beta-negative Jurkat cells. Transfectants of the mutated chain (MUT) expressed, on average, much less TCR-CD3 complex on the membrane than wild type TCR beta transfectants. Radiolabeling experiments suggested that the mutation caused a loose association of the CD36 chain resulting in a defective assembly. However, stimulation of high TCR-CD3 expressing wild type and MUT clones with monoclonal antibodies and Staphylococcus aureus enterotoxin B resulted in similar levels of CD25 and CD69 expression, interleukin-2 secretion, and TCR CD3 complex downregulation. By contrast, MUT cells were clearly resistant to activation-induced cell death, and they did not express CD95-ligand upon activation. These results suggest a differentiated intracellular signaling pathway leading to apoptosis in which Tyr-TM11 of the immunoreceptor tyrosine-based activation motif-like motif and CD3 zeta appear to be involved.