Characterization of the Inhibitor of KappaB Kinase (IKK) Complex in Granulosa Cell Tumors of the Ovary and Granulosa Cell Tumor-Derived Cell Lines

Granulosa cell tumors of the ovary (GCT) are a distinct, hormonally active subset of ovarian cancers. Although it has recently been shown that similar to 97 % of all adult GCT harbor a novel somatic missense mutation in the FOXL2 gene, given its almost universal presence, it does not explain differences in tumor stage and/or recurrence. The nuclear factor kappaB (NF kappa B) transcription factor is constitutively active in two human GCT-derived cell lines, COV434 and KGN, which are useful in vitro models to investigate juvenile and adult GCT, respectively. This study aimed to determine the molecular basis and pathogenetic significance of this aberrant NF kappa B activity. Selective chemical inhibitors were used to target candidate components of the pathway. The constitutive activity was blocked by two independent inhibitors of I kappa B alpha phosphorylation, suggesting that aberrant activation occurs upstream of this point. NF kappa B inhibition resulted in a dose-dependent decrease in cell proliferation and viability and a dose-dependent increase in apoptosis. Inhibitors of earlier components of the pathway were without effect. Two independent inhibitors of inhibitor of kappaB kinase (IKK)beta, a catalytic subunit of the NF kappa B activation complex, were unable to inhibit the constitutive activity, but surprisingly also ligand-induced activity. These findings suggest a central role for IKK beta; however, no mutations or altered expression of the IKK beta, IKK alpha, or IKK gamma genes was observed in the cell lines or in a panel of human GCT samples. This study highlights unresolved issues in understanding the pathogenesis of GCT and in the use of the COV434 and KGN cells lines as model systems.