Requirement for non-regulated, constitutive calcium influx in macrophage survival signaling.

The phosphatidylinositol-3-kinase (PI3K)/AKT axis and the Nuclear Factor kappa B (NFκB) pathway play critical roles in macrophage survival. In cells other than macrophages proper operation of those two pathways requires Ca²(+) influx into the cell, but if that is the case in macrophages remains unexplored. In the present work we used THP-1-derived macrophages and a pharmacological approach to examine for the first time the role of constitutive, non-regulated Ca²(+) influx in PI3K/AKT and NFκB signaling. Blocking constitutive function of Ca²(+)-permeable channels with the organic channel blocker SKF96365 completely prevented phosphorylation of IκBα, AKT and its downstream target BAD in TNFα-treated macrophages. A similar effect was observed upon treating macrophages with the calmodulin (CAM) inhibitor W-7 or the calmodulin-dependent kinase II (CAMKII) inhibitor KN-62. In addition, pre-treating macrophages with SKF96365 significantly enhanced TNFα-induced apoptosis. Our findings suggest that in THP-1-derived macrophages survival signaling depends, to a significant extent, on constitutive Ca²(+) influx presumably through a mechanism that involves the CAM/CAMKII axis as a coupling component between constitutive Ca²(+) influx and activation of survival signaling.