MODULATION OF THE HUMAN INTERLEUKIN-6 PROMOTER (IL-6) AND TRANSCRIPTION FACTOR-C/EBP BETA (NF-IL6) ACTIVITY BY P53 SPECIES

Constitutive up-regulation of interleukin-6 (IL-6) gene expression is observed in many neoplastic cell lines. The contribution of mutations in p53 to the up-regulation of the IL-6 promoter was evaluated in transient transfection experiments. In HeLa cells, wild-type (wt) human or murine p53 preferentially repressed the IL-6 promoter. The p53 mutants Val-135 and Phe-132 up-regulated IL-6 promoter activity in these cells at both 32.5 and 37-degrees-C. The temperature-sensitive Val-135 mutant was not only not inhibitory or ''wt-like'' at the lower temperature, but had gained a transcriptional activator phenotype which was temperature-independent in HeLa cells. The functional DNA target for transcriptional modulation of the IL-6 promoter by p53 species included the multiple cytokine- and second messenger-response element (-173 to -145); point mutations in the transcription factor C/EBPbeta-binding site within the second messenger-response element largely blocked the ability of p53 mutants Val-135 and Phe-132 to up-regulate this promoter. The up-regulation of IL-6 promoter constructs by co-transfection into HeLa cells of a C/EBPbeta constitutive expression vector was blocked in a dominant negative manner by wt p53. In contrast, the p53 mutants Val-135 and Phe-132 further enhanced C/EBPbeta-mediated up-regulation of IL-6 promoter constructs. The modulation of C/EBPbeta function by p53 species provides a basis for the involvement of p53 not only in the regulation of cytokine synthesis but also in the altered responsiveness of tumor cells to cytokines.