A multiple-oscillator mechanism underlies antigen-induced Ca2+ oscillations in Jurkat T-cells

Abstract

T-cell receptor stimulation triggers cytosolic Ca²⁺ signaling by inositol-1,4,5-trisphosphate (IP₃)-mediated Ca²⁺ release from the endoplasmic reticulum (ER) and Ca²⁺ entry through Ca²⁺ release-activated Ca²⁺ (CRAC) channels gated by ER-located stromal-interacting molecules (STIM1/2). Physiologically, cytosolic Ca²⁺ signaling manifests as regenerative Ca²⁺ oscillations, which are critical for nuclear factor of activated T-cells-mediated transcription. In most cells, Ca²⁺ oscillations are thought to originate from IP₃ receptor-mediated Ca²⁺ release, with CRAC channels indirectly sustaining them through ER refilling. Here, experimental and computational evidence support a multiple-oscillator mechanism in Jurkat T-cells whereby both IP₃ receptor and CRAC channel activities oscillate and directly fuel antigen-evoked Ca²⁺ oscillations, with the CRAC channel being the major contributor. KO of either STIM1 or STIM2 significantly reduces CRAC channel activity. As such, STIM1 and STIM2 synergize for optimal Ca²⁺ oscillations and activation of nuclear factor of activated T-cells 1 and are essential for ER refilling. The loss of both STIM proteins abrogates CRAC channel activity, drastically reduces ER Ca²⁺ content, severely hampers cell proliferation and enhances cell death. These results clarify the mechanism and the contribution of STIM proteins to Ca²⁺ oscillations in T-cells.

Keywords: CD3; CRAC; IP3; Jurkat; NFAT1; Orai; SOCE; STIM1; STIM2; calcium; oscillations.