Nuclear Factor-kappaB in Ovarian Cancer

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The NF-kB pathway promotes survival of cancer cells. My research in ovarian cancer began with characterizing the activation state and biological relevance of NF-kB in this disease. The NF-kB family of transcription factors is ubiquitously expressed. NF-kB signaling has been implicated in ovarian cancer, but the significance and mechanism of NF-kB signaling in ovarian cancer is unknown. There is precedent to propose that NF-kB is a critical signaling mechanism in cancer. I initially hypothesized that the NF-kB pathway is over-activated in ovarian cancers with more aggressive behavior. The NF-kB pathway was implicated in ovarian cancer proliferation and cytokine secretion in vitro, and contributed to chemoresistance of ovarian cancer cell lines. I therefore sought to determine the expression patterns and prognostic associations of NF-kB pathway proteins in primary ovarian cancer tissues. I demonstrated that overexpression of the NF-kB subunit p50 at diagnosis conveyed poor outcome in these patients. The biological relevance of NF-kB in ovarian cancer was established in my laboratory. Having demonstrated the coordinate presence of NF-kB machinery in ovarian cancers, I sought to modulate its activity. Inhibitors of NF-kB (IkBs) are tagged for degradation through the proteasome upon specific inducible phosphorylation by IkB kinases (IKKs). Therefore, targeted inhibition of IKKs could isolate NF-kB as a mechanism for ovarian cancer pathogenesis. A subset of ovarian cancer cell lines was affected by inhibition of IKKb in properties of growth, adhesion, invasion and cytokine secretion. I developed a gene expression signature of IKKb signaling in ovarian cancer using both pharmacologic and genetic manipulation of IKKb. This signature gave insight into the results of NF-kB in ovarian cancer, based on known functions of the ovarian cancer-specific target genes, and allowed me to probe established ovarian cancer databases in order to estimate the relative impact of NF-kB signaling on the survival of women with ovarian cancer. Higher NF-kB activity conveyed a worse outcome, suggesting that modulation of IKKb might benefit patients whose tumors showed elevated target gene expression. A key discovery from this work was the tissue specificity of NF-kB signaling. The 9-gene signature experimentally defined in ovarian cancer was completely different from the 11 genes I previously identified in multiple myeloma. We performed a global RNAi sensitization screen in combination with a small molecule IKKb inhibitor looking for interactions that enhanced toxicity. Our screen identified caspase 8. A similar screen in lymphoma, performed by our collaborators, found IKKa. Therefore, I hypothesize that caspase 8 is more active in ovarian cancer, in contrast to B cell lymphomas.I validated the cooperativity of IKKb and caspase 8 using a sub-lethal concentration of IKKb inhibitor with caspase 8 shRNA. I began to examine the context of caspase 8 function in ovarian cancer. First, I asked whether caspase 8 enzymatic activity was required for synergy with IKKb. A peptide inhibitor of caspase 8 cleavage activity did not affect ovarian cancer cell viability in the presence of IKKb inhibitor, indicating that this function of caspase 8 was not necessary for its cooperation with IKKb. This finding suggests that caspase 8 plays a different function to activate NF-kB in ovarian cancer.