Differential regulation of IL-6 promoter activity in a human ovarian-tumor cell line transfected with various p53 mutants:Involvement of AP-1

In human ovarian carcinomas, the p53 tumor-suppressor gene Is frequently mutated. Interleukin-6 (IL-6) in these rumors is known to stimulate tumor cell proliferation, In order to evaluate the effect of several p53 phenotypes on the IL-6 promoter activity, the human ovarian wild-type (wt)-p53 cell line A2780 was stably transfected with an empty plasmid (CMV) or (m)-175-, m-248 or m-273-p53. Electrophoretic mobility-shift assays revealed differences in activator protein-1 (AP-1) DNA-binding activity in the various clones. The CMV and m-273 clone had comparable amounts of AP-1. The m-175 clone displayed the least and m-248 the most pronounced AP-1 binding. Supershift analysis of AP-1/DNA complexes with antibodies against: the AP-1 sub-units, c-Fos, FosB, Fra-1, Fra-2, c-Jun, JunB, and JunD, revealed that the AP-1/DNA complexes in the various clones had different: compositions. Era proteins were basically present only in m-175 and m-248 AP-1. IL-6-promoter activity was evaluated in the presence and absence of the AP-1 binding site which showed that the m-175-transfected clone has a transcriptional suppressing AP-1, whereas the CMV and the m 273 clones have an activating AP-1. Exposure of the p53 clones to tumor-necrosis factor-alpha (TNF-alpha) clearly altered the AP-1/DNA complex composition. IL-6-promoter activity was enhanced by TNF-alpha irrespective of the presence of an AP-1 binding site, while the degree of activation differed in the various clones, being most pronounced in the m-17S and m-248 clones. The results demonstrate that the basic and activated IL-6-promoter activity is differently regulated In the various p53 clones, possibly due to alterations in the AP-1 composition. Int. J. Cancer 81:236-242, 1999. (C) 1999 Wiley-Liss, Inc.