Vitamin D enhances caspase-dependent and independent TNF-induced breast cancer cell death: the role of reactive oxygen species.

Calcitriol, the hormonal form of vitamin D, enhanced TNF-induced cytotoxicity in MCF-7 breast cancer cells. It increased the induction of caspase-3-like activity and TNF-induced caspase-independent cytotoxicity in the presence of a pan-caspase inhibitor. The antioxidants N-acetylcysteine, glutathione, lipoic acid, and ascorbic acid markedly reduced the effect of the hormone on TNF-induced caspase activation, attesting to the involvement of reactive oxygen species (ROS) in the cross-talk between the hormone and the cytokine. Calcitriol augmented the drop in mitochondrial membrane potential induced by TNF as assessed by the fluorescent probe JC-1. We postulate that the interaction of TNF and calcitriol on the level of the mitochondria underlies the enhancement of TNF-induced, ROS-mediated caspase-dependent and -independent cell death.