Differential role of calcium in tumour necrosis factor-mediated apoptosis and secretion of granulocyte-macrophage colony-stimulating factor in a T cell hybridoma

The authors investigated the dependence on extracellular and intracellular free Ca2+ in the induction of apoptosis and secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF) by tumour necrosis factor (TNF) in a rat/mouse T cell hybridoma PC60 R55/R75, using the Ca2+ chelators EGTA and BAPTA/AM, respectively. TNF-induced apoptosis still occurred in the absence of free Ca2+, while GM-CSF production required the continuous presence of Ca2+. The latter was also true for GM-CSF production driven by interleukin 1 (IL-1). The dependence on Ca2+ in the induction of GM-CSF, but not of apoptosis, was further confirmed by the inhibition of TNF- or IL-1-induced cytokine production by cyclosporin A or FK506, drugs that block the Ca2+/calmodulin-dependent protein Ser/Thr phosphatase calcineurin. This differential requirement for Ca2+ illustrates the partial functional redundancy between TNF and IL-1, showing the activation of cytokine gene expression through a Ca(2+)-dependent activation of calcineurin, and a Ca(2+)-independent activation of apoptosis, exerted solely by TNF.