Actin polymerization‐dependent activation of Cas‐L promotes immunological synapse stability

Abstract

The immunological synapse formed between a T cell and an antigen presenting cell is important for cell-cell communication during T cell mediated immune responses. Immunological synapse formation begins with stimulation of the T cell receptor (TCR). TCR microclusters are assembled and transported to the center of the immunological synapse in an actin polymerization-dependent process. However, the physical link between TCR and actin remains elusive. Here we show that lymphocyte-specific Crk-associated substrate (Cas-L), a member of a force sensing protein family, is required for transport of TCR microclusters and for establishing synapse stability. We found that Cas-L is phosphorylated at TCR microclusters in an actin polymerization-dependent fashion. Furthermore, Cas-L participates in a positive feedback loop leading to amplification of Ca2+ signaling, inside-out integrin activation, and actomyosin contraction. We propose a new role for Cas-L in T cell activation as a mechanical transducer linking TCR microclusters to the underlying actin network and coordinating multiple actin dependent structures in the immunological synapse. Our studies highlight the importance of mechanotransduction processes in T cell mediated immune responses.

DOCK8 enforces immunological tolerance by promoting IL-2 signaling and immune synapse formation in Tregs

“…This was accompanied by decreased recruitment to the IS of phosphotyrosine proteins, including phospho-ZAP70. In addition, accumulation at the IS of the mechanosensor pCASL, which is essential for the establishment of IS stability (81), and of TALIN, a known DOCK8 interactor crucial for IS stability, was reduced in Dock8 -/-Tregs. DOCK8-deficient Tregs were significantly less efficient at transendocytosis of CD86 from CHO cells, a system that relies on Treg interactions with CD86 exclusively These findings suggest that DOCK8 has a critical role in the formation of a stable IS between Tregs and DCs and in transendocytosis.…”

Lymphocyte mechanotransduction: The regulatory role of cytoskeletal dynamics in signaling cascades and effector functions

“…Specifically, DOCK8 deficiency was correlated with low actin foci formation, and lower phosphorylation levels of the mechanosensory molecule CasL (a member of the mechanosensitive CAS family). Accordingly, a separate study showed that actin polymerization is important for CasL phosphorylation in TCR MCs, highlighting the function of CasL in bridging between mechanical forces and the T‐cell cytoskeleton . Besides actin filaments and myosin motor proteins, microtubules were also recently observed to regulate T‐cell traction forces .…”

“…Accordingly, a separate study showed that actin polymerization is important for CasL phosphorylation in TCR MCs, highlighting the function of CasL in bridging between mechanical forces and the T-cell cytoskeleton. 155 Besides actin filaments and myosin motor proteins, microtubules were also recently observed to regulate T-cell traction forces. 156 In this case, inhibiting microtubule dynamics led to an increase in T-cell traction stress, and it was found that microtubules induce this effect by regulation of myosin II phosphorylation, and inhibition of ARF.…”

Mediating signaling response to actin‐mediated forces: Cas‐L is causal in the T‐cell response to forces triggered by antigen presentation

“…The immunological synapse of a T cell represents one such microcosm of signaling, regulating signals at the interface with the antigen‐presenting cell to dictate T‐cell fate and to provide a conduit for T‐cell‐mediated cytotoxicity. In this issue of ICB , Santos et al 1 show how initial T‐cell receptor (TCR) signals control actomyosin contractility to mediate molecular trafficking in the immunological synapse. The back‐and‐forth between chemical and physical signals described here provides a fascinating glimpse of complex biophysical events that might well be prevalent throughout biology.…”

“…The findings by Santos et al 1 were obtained using total internal reflection fluorescence (TIRF) microscopy on lipid bilayers. This technology is widely used, and the combination of high resolution and precise control of TCR signaling has proven very powerful.…”