c-Jun and c-Fos cooperate with STAT3 in IL-6-induced transactivation of the IL-6 response element (IRE)

Transcriptional activation of eukaryotic genes often requires the cooperati ve action of many proteins. The interleukin 6 (IL-6) response element (IRE) is activated by signal transducer and activator of transcription 3 (STAT3) , and stimulation with IL-6 leads to STAT3 tyr705 phosphorylation, dimeriza tion, translocation to the nucleus and transactivation of target gene promo ters containing IREs, Here, we report that IL-6 and 12-O-tetradecanoylphorb ol-13-acetate (TPA) synergistically transactivate the IRE in HepG2 cells, w hich is coupled to a strong upregulation of c-Jun and c-Fos expression by T PA via the mitogen-activated protein kinase (MAPK) pathway. Overexpression of c-Jun and c-Fos strongly enhanced STAT3-driven IRE transactivation as we ll as transactivation of the human intercellular adhesion molecule (ICAM)-1 promoter. In contrast, c-Jun mutants lacking the transactivation domain, t he DNA-binding domain, or mutants in which the serine residues 63 and 73 we re replaced by alanine, did not cooperate with STAT3. In immunoprecipitatio n experiments, a direct association of STAT3 with c-Jun and c-Fos was obser ved in response to IL-6, Furthermore, c-Jun/STAT3 and c-Fos/STAT3 complexes were detected on IRE probes in electrophoretic mobility shift assay (EMSA) experiments, but did not bind nor transactivate the TPA response element ( TRE), These results demonstrate that activator protein-1 (AP-1) transcripti on factors can cooperate with STAT3 in IRE transactivation in the absence o f direct AP-1 DNA binding. (C) 2001 Academic Press.