Calcium mobilization is both required and sufficient for initiating chromatin decondensation during activation of peripheral T-cells

• Chromatin rapidly decondenses during T-cell activation.
• Mobilization of intracellular calcium is required for proper chromatin decondensation.
• Activation-induced decondensation occurs independently of NFAT activation.
• Extracellular calcium is dispensable for the induction of chromatin decondensation.
• Mobilization of intracellular calcium is sufficient to induce chromatin decondensation.

Antigen engagement of the T-cell receptor (TCR) induces a rapid and dramatic decondensation of chromatin that is necessary for T-cell activation. This decondensation makes T-cells competent to respond to interleukin-2 providing a mechanism to ensure clonotypic proliferation during an immune response. Using murine T-cells, we investigated the mechanism by which TCR signaling can initiate chromatin decondensation, focusing on the role of calcium mobilization. During T-cell activation, calcium is first released from intracellular stores, followed by influx of extracellular calcium via store operated calcium entry. We show that mobilization of intracellular calcium is required for TCR-induced chromatin decondensation. However, the decondensation is not dependent on the activity of the downstream transcription factor NFAT. Furthermore, we show that the influx of extracellular calcium is dispensable for initiating chromatin decondensation. Finally, we show that mobilization of calcium from intracellular stores is sufficient to induce decondensation, independent of TCR engagement. Collectively, our data suggest that chromatin decondensation in peripheral T-cells is controlled by modulating intracellular calcium levels