Siva binds to the CD27 cytoplasmic tail. It has a DD homology region, a box-B-like ring finger, and a zinc finger-like domain. Overexpression of Siva in various cell lines induces apoptosis, suggesting an important role for Siva in the CD27-transduced apoptotic pathway [1]. Siva-1 binds to and inhibits BCL-X(L)-mediated protection against UV radiation-induced apoptosis. Indeed, the unique amphipathic helical region (SAH) present in Siva-1 is required for its binding to BCL-X(L) and sensitising cells to UV radiation. Natural complexes of Siva-1/BCL-X(L) are detected in HUT78 and murine thymocyte, suggesting a potential role for Siva-1 in regulating T cell homeostasis [2]. This family contains both Siva-1 and the shorter Siva-2 lacking the sequence coded by exon 2. It has been suggested that Siva-2 could regulate the function of Siva-1 [3].

1: CD27, a member of the tumor necrosis factor receptor family, induces apoptosis and binds to Siva, a proapoptotic protein. Prasad KV, Ao Z, Yoon Y, Wu MX, Rizk M, Jacquot S, Schlossman SF; Proc Natl Acad Sci U S A 1997;94:6346-6351. PMID:9177220

2: Siva-1 binds to and inhibits BCL-X(L)-mediated protection against UV radiation-induced apoptosis. Xue L, Chu F, Cheng Y, Sun X, Borthakur A, Ramarao M, Pandey P, Wu M, Schlossman SF, Prasad KV; Proc Natl Acad Sci U S A 2002;99:6925-6930. PMID:12011449

3: Murine Siva-1 and Siva-2, alternate splice forms of the mouse Siva gene, both bind to CD27 but differentially transduce apoptosis. Yoon Y, Ao Z, Cheng Y, Schlossman SF, Prasad KV; Oncogene 1999;18:7174-7179. PMID:10597319