Regulation of spontaneous and TNF/IFN-induced IL-6 expression in two human ovarian-carcinoma cell lines

Abstract

Autocrine and paracrine production of interleukin-6 (IL-6) is considered to be involved in the ongoing proliferation of ovarian-cancer cells. In view of the variability in IL-6 expression between various ovarian-cancer cells, we questioned whether differences in IL-6-gene regulation might be observed in ovarian tumor cells with and without IL-6 expression. The CAOV-3 cell line spontaneously secreted IL-6, which was enhanced by tumor necrosis factor-α (877 ± 89 vs. 8,452 ± 1,762 pg/ml, x ± sd, p < 0.01). The electrophoretic mobility shift assay (EMSA) demonstrated that basic IL-6 expression was associated with DNA binding of activator protein-I (AP-I) and nuclear factor IL-6 (NF-IL6). Nuclear factor kappa-B (NF-κB), which consisted mainly of p65-NF-κB was induced in response to TNF-α stimulation. A2780 cells did not express IL-6, either spontaneously or after stimulation with TNF-α. EMSAs, showed spontaneous AP-I but no NF-IL6 or NF-κB DNA binding. TNF-α stimulation enhanced AP-I and induced NF-κB but no NF-IL6 DNA binding in these cells. NF-IL6 protein, however, was detected in nuclear extracts of these cells by Western blotting. In contrast, IL-6-promoter transfection studies showed no difference in promoter activation between CAOV-3 and A2780. This study reveals that differential IL-6-gene expression observed in ovarian-cancer cell lines is independent of NF-IL6 activation.