Induces CD27-mediated apoptosis. Inhibits BCL2L1 isoform Bcl-x(L) anti-apoptotic activity. Inhibits activation of NF-kappa-B and promotes T-cell receptor-mediated apoptosis (By similarity). Isoform 1 binds 3 zinc ions. Isoform 2 binds 2 zinc ions. Binds through its N-terminal region to the C-terminus of CD27 and to PXMP2/PMP22. Binds to the C-terminus of TNFRSF18/GITR. Isoform 1 binds to BCL2L1/BCLX isoform Bcl-x(L) but not to BAX. In the nucleus, accumulates in dot-like structures. Highly expressed in testis, heart, liver, lung, and muscle, and less in kidney, spleen and brain. By p53, camptothecin, stroke injury and infection with coxsackievirus B3. This up-regulation is sufficient to induce apoptosis in neural tissue. Phosphorylated by ABL2/ARG in response to oxidative stress. Mouse isoform 2 has been shown to have no pro-apoptotic activity.