A soluble LAT deletion mutant inhibits T-cell activation: reduced recruitment of signalling molecules to glycolipid-enriched microdomains

The type III transmembrane adaptor protein linker for activation of T cells (LAT) is essential for membrane recruitment of signalling molecules follow ing TCR activation. Here we show that although LAT deleted in the transmemb rane domain is completely soluble, it can be tyrosine phosphorylated after anti-CD3 stimulation or pervanadate treatment. Overexpression of this delet ion mutant in transiently transfected Jurkat TAg cells inhibits transcripti onal activation of nuclear factor of activated T cells (NF-AT)/AP-1 reporte r construct in a concentration dependent manner. Furthermore, by selection of transiently transfected cells, a clear reduction of TCR-induced CD69 exp ression was observed in cells expressing the mutant. These dominant negativ e effects seemed to be dependent both on the ability of the membrane deleti on mutant to reduce phosphorylation of endogenous LAT and to reduce interac tion of endogenous LAT with PLC-gamma1 and Grb2 Consistent with this, the r edistribution of PLC-gamma1 and Grb2 to glycolipid-enriched microdomains. c alled lipid rafts, after stimulation was inhibited when the soluble form of LAT was overexpressed. We suggest that the dominant negative effect is cau sed by the ability of the mutant to sequester signalling molecules in cytos ol and thereby inhibit redistribution of signalling molecules to lipid raft s upon T-cell activation. (C) 2001 Elsevier Science Inc. All rights reserve d.