HGF-mediated apoptosis via p53/bax-independent pathway activating JNK1

Current studies have indicated both positive and negative roles for the hep atocyte growth factor (HGF)/c-met receptor signaling system in tumor develo pment. Recently, we have shown that HGF has the capacity to induce both gro wth inhibition and programmed cell death in aflatoxin-transformed (AFLB8) r at liver epithelial cells. Using the same cell line, we have now investigat ed a potential mechanism for HGF-induced apoptosis, Immunoblot analysis of bcl-2 gene family member (bax, bcl-2, bclX-s/l) expression showed no correl ation with HGF treatment, suggesting that HGF-mediated apoptosis is bar ind ependent. Following HGF treatment retinoblastoma protein (pRB) was present in the hypophosphorylated state, HGF treatment increased cyclin A, cyclin G 1 and nuclear transcriptional factor (NF kappa B) protein expression. Howev er, electrophoretic mobility shift analysis showed that NF kappa B activity decreased with HGF treatment, Under these apoptotic conditions, c-Jun N-te rminal kinase (JNK1) and extracellular signal-regulated kinase (ERK2) were activated with lower level activation of ERK2, while no involvement of phos phatidylinositol-3 kinase was observed. Epidermal growth factor (EGF) was n ot protective, and actually induced cells to undergo apoptosis to a level s imilar to that of HGF alone or EGF/HGF in combination. These results sugges t the possibility of cross-talk between HGF/c-met and EGF/EGFR signaling pa thways, and the involvement of JNK1 induction in HGF-mediated apoptotic cel l death.