Morphological changes of T cells following formation of the immunological synapse modulate intracellular calcium signals

Sustained Ca2+ influx through plasma membrane Ca2+ released-activated Ca2+ (CRAC) channels is essential for T cell activation. Since inflowing Ca2+ inactivates CRAC channels, T cell activation is only possible if Ca2+-dependent inactivation is prevented. We have previously reported that sustained Ca2+ influx through CRAC channels requires both mitochondrial Ca2+ uptake and mitochondrial translocation towards the plasma membrane in order to prevent Ca2+-dependent channel inactivation. Here, we show that morphological changes following formation of the immunological synapse (IS) modulate Ca2+ influx through CRAC channels. Cell shape changes were dependent on the actin cytoskeleton, and they sustained Ca2+ entry by bringing mitochondria and the plasma membrane in closer proximity. The increased percentage of mitochondria beneath the plasma membrane following shape changes occurred in all 3 dimensions and correlated with an increase in the amplitude of Ca2+ signals. The shape change-dependent mitochondrial localization close to the plasma membrane prevented CRAC channel inactivation even in T cells in which dynein motor protein-dependent mitochondria movements towards the plasma membrane were completely abolished, highlighting the importance of the shape change-dependent control of Ca2+ influx. Our results suggest that morphological changes do not only facilitate an efficient contact with antigen presenting cells but also strongly modulate Ca2+ dependent T cell activation.