Hepatocyte growth factor activates the AP-1 complex: a comparison between normal and transformed rat hepatocytes

Background/Aims: Stimulation of activator protein-1 (AP-1), a Fos/Jun compl ex, is a key event in the cell response to growth factors. We have investig ated whether hepatocyte growth factor (HGF) induces differential AP-1 respo nses in normal and transformed rat hepatocytes, the 7777 cells. Methods: Primocultures of isolated hepatocytes or 7777 cells were stimulate d with HGF. Gene expression was evaluated by ribonuclease protection assay and Western blot analysis. AP-1 DNA binding activity was measured by electr ophoretic mobility shift assay, Identification of the proteins bound to the probes was made by supershift assays with specific antibodies. Cells were electroporated with plasmids containing an AP-1-dependent chloramphenicol a cetyl transferase (CAT) gene, and CAT activity was measured 24 h after trea tment with medium alone or HGF. Results: In both cell types, HGF triggered the same program of jun family m RNA activation, but distinct Fos/Jun proteins accumulated in the nucleus. H GF increased DNA-binding activity to the phorbol 12-O-tetradecanoate-13-ace tate responsive element (TRE) in both cell types, but distinct TRE-binding proteins were recruited in the AP-1 dimers, HGF also increased consistently binding to a cAMP responsive element (CRE) in hepatocytes only. Finally, H GF triggered TRE- and CRE-dependent gene activations in hepatocytes but TRE -dependent gene activation alone in 7777 cells, Conclusions: HGF-induced AP-1 activation leads to the formation of distinct dimers with different functional capacities in normal and transformed hepa tocytes, These data suggest the importance of qualitative abnormalities of the AP-1 complex for the establishment or maintainance of a transformed phe notype.