The role of p38 MAP kinase in the synergistic cytotoxic action of calcitriol and TNF-alpha in human breast cancer cells.

Calcitriol, the hormonal form of Vitamin D, potentiates the activity of some agents of the anti-cancer immune system including tumor necrosis factor-alpha (TNF-alpha). Different signaling pathways activated by TNF-alpha may be targets for calcitriol action. Activation of p38 MAP kinase was shown to have both pro- and anti-apoptotic actions in TNF-alpha-induced programmed cell death depending on cell context. Treatment of MCF-7 breast cancer cells with TNF-alpha resulted in activation of p38 MAP kinase that persisted for at least 24h. Whereas calcitriol had no effect on the earlier phase of p38 MAP kinase activation (up to 1h), it inhibited the activation of this pathway between one and 24h after exposure to TNF-alpha. Both calcitriol and the p38 MAP kinase inhibitor SB203580 enhanced TNF-alpha-induced cytotoxicity and drop in mitochondrial membrane potential, but their combined effect was sub-additive. Taken together, these findings suggest that p38 MAP kinase plays an anti-apoptotic role in TNF-alpha-induced cytotoxicity in MCF-7 cells and that the synergistic interaction between TNF-alpha and calcitriol, leading to mitochondrial damage and subsequent cell death, is partially due to modulation of this signaling pathway.