en. PKC-θ mediated synapse breaking seems like a negative feedback loop because the other major activity of PKC-θ in T cells is activation of NFkB and other transcription factors. Thus, the functional consequences of synapse stabilization as a result of PKC-θ inhibition can only be studied in pre-armed effector cells, which don’t need to activate transcription for function.
The cSMAC was initially shown to contain PKC-θ and Lck, two kinases that are important for T cell activation (Monks et al., 1998). This suggested that the cSMAC might be involved in sustained signaling. Our early studies on planar bilayers demonstrated that TCR signaling was initiated before the cSMAC was formed based on cytoplasmic Ca2+ elevation at a time point where TCR-MHC-peptide interactions were focused in the periphery (Grakoui et al., 1999). This was more explicitly demonstrated with a specific phopho-Lck antibody, which revealed early TCR signaling in the periphery of the nascent synapse, but not at the cSMAC. This led to the suggestion that the cSMAC might be involved in signal termination (Lee et al., 2003). Computer models suggested that signals in response to weaker ligands might survive in the cSMAC due to a less aggressive attack by ubiquitin ligases. As discussed below this preservation of signaling in the cSMAC may also depend upon a reorganization of F-actin to fill in the normally F-actin depleted central area (Cemerski et al., 2008; Lee et al., 2003). The enigma with peripheral signaling in the immunological synapse was that TCR was not clearly associated with the signaling. This issue was resolved with TIRFM, which greatly increased the contrast of imaging of the cell-planar bilayer interface, as described above, but the discovery of the late submicron TCR microclusters that formed in the dSMAC and moved to the pSMAC over ~ 2 minutes.
The movement of microcluster was interesting for what it said about actin dynamics, but the signaling behavior was even more interesting. Varma repeated the Valittuti experiment of blocking 