Mitochondria-dependent and -independent mechanisms in tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis are both regulated by interferon-γ in human breast tumour cells

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL/APO-2L) induces apoptosis in a variety of tumour cells upon binding to death receptors TRAIL-R1 and TRAIL-R2. Here we describe the sensitization by interferon (IFN)-γ to TRAIL-induced apoptosis in the breast tumour cell lines MCF-7 and MDA-MB231. IFN-γ promoted TRAIL-mediated activation of caspase-8, Bcl-2 interacting domain death agonist (Bid) degradation, Bcl-2-associated X protein (Bax) translocation to mitochondria, cytochrome c release to the cytosol and activation of caspase-9 in these cell lines. No changes in the expression of TRAIL receptors were observed upon IFN-γ treatment. Overexpression of Bcl-2 in MCF-7 cells completely inhibited IFN-γ-induced sensitization to TRAIL-mediated cell death. Interestingly, TRAIL-induced apoptosis was also clearly enhanced by IFN-γ in caspase-3-overexpressing MCF-7 cells, in the absence of Bax translocation to mitochondria and cytochrome c release to the cytosol. In summary, our results suggest that IFN-γ facilitates TRAIL-induced activation of mitochondria-regulated as well as mitochondria-independent apoptotic pathways in breast tumour cells.