T cell receptor-proximal signals are sustained in peripheral microclusters and terminated in the central supramolecular activation cluster

T cell receptor (TCR) signaling is initiated and sus-tained in microclusters; however, it’s not known whether signaling also occurs in the TCR-rich central supramolecular activation cluster (cSMAC). We showed that the cSMAC formed by fusion of micro-clusters contained more CD45 than microclusters and is a site enriched in lysobisphosphatidic acid, a lipid involved in sorting ubiquitinated membrane proteins for degradation. Calcium signaling via TCR was blocked within 2 min by anti-MHCp treatment and 1min by latrunculin-A treatment. TCR-MHCp inter-actions in the cSMAC survived these perturbations for 10min and hence were not sufficient to sustain signal-ing. TCR microclusters were also resistant to disrup-tion by anti-MHCp and latrunculin-A treatments. We propose that TCR signaling is sustained by stabilized microclusters and is terminated in the cSMAC, a struc-ture from which TCR are sorted for degradation. Our studies reveal a role for F-actin in TCR signaling beyond microcluster formation