SERCA Modulators Reveal Distinct Signaling and Functional Roles of T Lymphocyte Ca 2+ Stores.

The allosteric SERCA (Sarcoplasmic/Endoplasmic Reticulum Ca ²⁺ -ATPase) activator CDN1163 has been recently added to the group of pharmacological tools for probing SERCA function. We chose to investigate the effects of the compound on T lymphocyte Ca ²⁺ stores, using the well-described Jurkat T lymphocyte as a reliable cell system for Ca ²⁺ signaling pathways. Our study identified the lowest concentrations of the SERCA inhibitors thapsigargin (TG) and 2,5-di-( tert butyl)-1,4-benzohydroquinone (tBHQ) capable of releasing Ca ²⁺ , permitting the differentiation of the TG-sensitive SERCA 2b Ca ²⁺ store from the tBHQ-sensitive SERCA 3 Ca ²⁺ store. We proceeded to test the effects of CDN1163 on Ca ²⁺ stores, examining specific actions on the SERCA 2b and SERCA 3 Ca ²⁺ pools using our low-dose SERCA blocker regimen. In contrast to previous work, we find CDN1163 exerts complex time-sensitive and SERCA isoform-specific actions on Ca ²⁺ stores. Surprisingly, short-term exposure (0-30 min) to CDN1163 perturbs T cell Ca ²⁺ stores by suppressing Ca ²⁺ uptake with diminished Ca ²⁺ release from the SERCA 2b-controlled store. Concomitantly, we find evidence for a SERCA-activating effect of CDN1163 on the SERCA-3 regulated store, given the observation of increased Ca ²⁺ release inducible by low-dose tBHQ. Intriguingly, longer-term (>12 h) CDN1163 exposure reversed this pattern, with increased Ca ²⁺ release from SERCA 2b-regulated pools yet decreased Ca ²⁺ release responses from the tBHQ-sensitive SERCA 3 pool. Indeed, this remodeling of SERCA 2b Ca ²⁺ stores with longer-term CDN1163 exposure also translated into the compound's ability to protect Jurkat T lymphocytes from TG but not tBHQ-induced growth suppression.