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

Abstract

The pre-T cell receptor (pre-TCR) promotes the development of thymocytes with productive rearrangement at the TCR β chain locus by signaling in a ligand-independent fashion. The TCR β chain associates with the invariant pre-Tα (pTα) chain, which bears specific charged residues in the extracellular portion mediating pre-TCR self-oligomerization. In recombinase-deficient thymocytes, calnexin (CNX) associated with CD3 chains is inefficiently retained in the endoplasmic reticulum (ER) and weakly expressed in the plasma membrane. Deliberate cross-linking of CNX/CD3 complexes mimics pre-TCR signaling. Here, we show that, analogously to the pTα chain, surface CNX is palmitoylated and that CD3 prominently accumulated in 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 the palmitoylated cytoplasmic tail from the pTα chain in recombinant CNX strikingly improved the pre-TCR-like signaling efficiency of CNX/CD3 in rafts. This study indicates that lipid rafts in the plasma membrane represent proficient microdomains for the initiation of pre-TCR signaling, and supports the view that β selection by oligomerized pre-TCR is implemented by the pTα cytoplasmic tail. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.