The IG20 gene is essential for survival of the animal and is highly expressed in human tumors and transformed cell lines.  It can encode IG20, MADD, IG20-SV2 and DENN-SV splice variants.  DENN-SV is constitutively expressed in all tissues and cells tested and highly expressed in tumor tissues and cells.  Over-expression of DENN-SV enhances proliferation and resistance to apoptosis induced by TNF-alpha, TRAIL, etoposide, vinblastine and gamma-radiation.  In contrast, over- expression of IG20 slows cell proliferation and enhances susceptibility to apoptosis induced by the above agents.  Other two variants have little or no effect on these properties.  IG20 enhanced apoptosis is mediated by enhanced recruitment of caspase 8 and FADD to the Death Inducing Signaling Complex (DISC).  In contrast, DENN-SV appears to activate cell survival characterized by NF-kappaB activation.  Once IG20 is introduced, they show reduced NFKB activity, become susceptible to TRAIL induced apoptosis, replicate slowly in vitro and fail to form tumors in nude mice.  In addition, siRNA mediated knock-down of, most likely, DENN-SV, and not IG20, induces spontaneous apoptosis of cancer cells.  These observations show that DENN-SV and IG20 function like an "oncogene" and a "tumor suppressor" respectively, and are involved in the regulation of cell proliferation and death.  Based on these observations, we hypothesize that "differential expression of IG20 and DENN-SV splice variants could render ovarian carcinoma cells either more susceptible or resistant to induced apoptosis respectively, and that the pro-apoptotic property of IG20 variant or targeted siRNA can be used to render ovarian cancer cells that are otherwise resistant become susceptible to killing by TRAIL."  In Aim-1, we will test the effects of IG20 and DENN-SV on proliferation and apoptosis of ovarian cancer cells;In Aim-2, we will determine the mechanism of action of IG20 in TRAIL/TNFa induced apoptosis and map functionally relevant domains;In Aim-3, we will investigate how DENN-SV enhances cell proliferation and resistance to apoptosis, and identify functionally relevant domains and adaptor proteins;and in Aim-4, we will study the effects of selective expression of IG20 and/or DENN-SV on cell proliferation and apoptosis using mouse embryonic fibroblasts derived from wild type and knockout mice.  These studies will lead to a clearer understanding of the mechanism of action of IG20/DENN-SV in ovarian cancer.