Recombinase-deficient T cell development by selective accumulation of CD3 into lipid rafts

The pre-T cell receptor (pre-TCR) promotes development of thymocyte with productive rearrangement at T cell receptor β chain locus by signaling in a ligand-independent fashion. The TCR β chain associates with the invariant pre-T α (pTα) chain, which bears specific charged residues in the extracellular portion mediating pre-TCR self-oligomerization. In recombinase-deficient thymocyte, calnexin (CNX) associated with CD3 chains is inefficiently retained in the endoplasmic reticulum and weakly expressed in the plasma membrane. Deliberate cross-linking of CNX/CD3 complexes mimics pre-TCR signaling. Here we show that analogously to pTα chain, surface CNX is palmitoylated and that CD3 prominently accumulated into lipid rafts upon cross-linking. Mutant CNX isoforms devoid of ER retention determined pre-TCR-like signaling and simulated β selection only when stably translocating CD3 to lipid rafts. Inclusion of palmitoylated cytoplasmic tail from pTα chain in recombinant CNX strikingly improved pre-TCR-like signaling efficiency of CNX/CD3 into rafts. This study indicates that lipid rafts in the plasma membrane represent proficient microdomains for initiation of pre-TCR signaling and supports the view that β selection by oligomerized pre-TCR is implemented by pTα cytoplasmic tail.