POSSIBLE INVOLVEMENT OF P21 WAF1 IN THE GROWTH-INHIBITION OF HEPG2 CELLS INDUCED BY HEPATOCYTE GROWTH-FACTOR/

Hepatocyte growth factor (HGF) is a potent mitogen for a variety of ce ll types, but it is also known as an antimitogenic factor for several types of tumor cell lines. The biological processes by which HGF inhib its tumor cell growth remain poorly understood. Here we report a compa rative study of HGF-mediated signal transduction events between two op posite responding types of human hepatoblastoma cell lines, HuH6 and H epG2. Following serum starvation, both cell lines were cultured in hep atocyte growth medium (HGM), a chemically defined medium, in the prese nce or absence of HGF. Under these culture conditions, cell growth in HuH6 was promoted by HGF, while it was inhibited in HepG2. Phosphoryla tion of p42/mitogen-activated protein (MAP) kinase was observed within 10 min after HGF stimulation in both cell lines. The level of phospho rylated MAP kinase in HuH6 declined to basal levels after 2 hr. Howeve r, in HepG2 the phosphorylated form was detectable at 6 hr. p21/waf1 w as induced in both cell lines where levels peaked 4-6 hr after HGF sti mulation. In HuH6, a marked decrease of p2l/waf1 was observed at 8-12 hr, while a high level of p2l/waf1 was sustained for at least 24 hr in HepG2. HGF treatment depressed cdk2 activity in a time-dependent mann er in HepG2 while the activity increased in HuH6. When serum-starved H epG2 was growth stimulated with serum in the presence or absence of HG F, the cells treated with HGF underwent growth inhibition correlating with a sustained induction of p2l/waf1 and a decrease of cdk2 activity . Immunoprecipitation analysis revealed accumulation of cdk2-associate d p21/waf1 in the HGF-treated HepG2. Together, the results suggest tha t sustained induction of p21/waf1 mediates growth inhibition in HepG2 in the presence of HGF. J. Cell. Physiol. 177:130-136, 1998. (C) 1998 Wiley-Liss, Inc.