TRAF6 regulates TCR signaling via interaction with and modification of LAT adapter

Abstract TNF receptor-associated factor 6 (TRAF6) is an essential ubiquitin E3 ligase in immune responses, but its function in adaptive immunity is not well understood. Here we show that TRAF6 is recruited to the peripheral ring of the T cell immunological synapse in Jurkat T cells or human primary CD4+ T cells conjugated with SEE-pulsed B cells. This recruitment depends on TRAF6 interacting with linker for activation of T cells (LAT) via its TRAF domain. Although LAT was indispensable for TCR/CD28-induced TRAF6 ubiquitination and its ligase activity, RNA interference-induced TRAF6 knockdown in T cells decreased TCR/CD28-induced LAT ubiquitination, tyrosine-phosphorylation. Overexpression of TRAF6 or its catalytically inactive form C70A promoted and decreased, respectively, LAT tyrosine-191 phosphorylation upon stimulation. Moreover, LAT was ubiquitinated at Lysine-88 by TRAF6 via K63-linked chain. In addition, TRAF6 was required for and synergized with LAT to promote the TCR/CD28-induced activation of NFAT. These results reveal a novel function and mechanism of TRAF6 action in the TCR-LAT signaling pathway distinct from its role in TCR-induced NF-κB activation, and indicate LAT also play an adapter role in TCR/CD28-induced activation of TRAF6.