Calcium influx through CRAC channels controls actin organization and dynamics at the immune synapse.

Catherine A Hartzell,Katarzyna I Jankowska,Richard S Lewis,Janis K Burkhardt

doi:10.7554/elife.14850

Catherine A Hartzell, Katarzyna I Jankowska + Show 2 more

Open Access

https://doi.org/10.7554/elife.14850

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Abstract

T cell receptor (TCR) engagement opens Ca(2+) release-activated Ca(2+) (CRAC) channels and triggers formation of an immune synapse between T cells and antigen-presenting cells. At the synapse, actin reorganizes into a concentric lamellipod and lamella with retrograde actin flow that helps regulate the intensity and duration of TCR signaling. We find that Ca(2+) influx is required to drive actin organization and dynamics at the synapse. Calcium acts by promoting actin depolymerization and localizing actin polymerization and the actin nucleation promotion factor WAVE2 to the periphery of the lamellipod while suppressing polymerization elsewhere. Ca(2+)-dependent retrograde actin flow corrals ER tubule extensions and STIM1/Orai1 complexes to the synapse center, creating a self-organizing process for CRAC channel localization. Our results demonstrate a new role for Ca(2+) as a critical regulator of actin organization and dynamics at the synapse, and reveal potential feedback loops through which Ca(2+) influx may modulate TCR signaling.

Highlights

Soon after a T cell encounters cognate antigen on an antigen-presenting cell (APC), it spreads out over the cell’s surface, forming a tightly apposed structure known as the immune synapse (Bromley et al, 2001; Yokosuka and Saito, 2010; Dustin, 2008)
To study the location and redistribution of the population of STIM1/Orai1 complexes positioned at the synapse, Jurkat T cells expressing STIM1 labeled with mCherry and Orai1 labeled with EGFP (Orai1-EGFP) were stimulated on coverslips coated with anti-CD3 mAb (Bunnell et al, 2001)
Because ER tubule movement is influenced by centripetal actin flow (Figure 2C), we examined the effect of Ca2+o removal on ER tubule distribution and dynamics at the Jurkat cell synapse

Summary

Introduction

Soon after a T cell encounters cognate antigen on an antigen-presenting cell (APC), it spreads out over the cell’s surface, forming a tightly apposed structure known as the immune synapse (Bromley et al, 2001; Yokosuka and Saito, 2010; Dustin, 2008). TCRs assemble with scaffolding and signaling proteins to form microclusters in the dSMAC which migrate centripetally towards the cSMAC (Grakoui et al, 1999; Krummel et al, 2000; Campi et al, 2005; Varma et al, 2006; Yokosuka et al, 2005). As they move, TCR microclusters activate a MAP kinase cascade and Ca2+ influx through Ca2+ release-activated Ca2+ (CRAC) channels, both of which are essential to initiate gene expression programs that drive T cell proliferation and differentiation (Feske et al, 2001).

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