nderstood. We know that on the supported planar bilayer system WASP is required to maintain a stable synapse and PKC-θ contributes to symmetry breaking (Sims et al., 2007). Symmetry breaking in the contact plane leads to polarity and in a migrating cells this process is based two opposing actin-myosin networks-the lamellipodium dominated by Rac and a high F-actin:myosin II ratio and the uropod dominated by Rho and a low F-actin:myosin II ratio (Xu et al., 2003). Thus, we have speculated that myosin II may be a target in symmetry breaking. PKC-θ phosphorylates WASP interacting protein (WIP) and regulates its interaction with myosin II (Krzewski et al., 2006). WASP also interacts with this complex. One hypothesis is that myosin II activation via WIP phosphorylation leads to contraction of the pSMAC actin network leading to local thinning and breakdown, whereas WASP may either antagonize this myosin II activation or induced ventral actin polymerization to repair the pSMAC and restore symmetry after its been broken. 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 sug