nases. These results suggest that PTK, Ras, and PKC Hepatocyte growth factor (HGF) stimulated mitogenplay roles in MAP kinase activation induced by HGF and activated protein (MAP) kinases and MAP kinase kinase that MAP kinase activation resulting in AA release is in primary cultured rat hepatocytes. Inhibitors for proinvolved in DNA synthesis in rat hepatocytes. (HEPATOLtein kinase C (PKC), Ro31-8425, H-7, and calphostin C, OGY 1996;23:1244-1253.) reduced HGF-induced MAP kinase activity. A PKC activator, phorbol myristate acetate (PMA), induced MAP kinase activation in a concentration-dependent manner.
Hepatocyte growth factor (HGF) is the most potent Protein tyrosine kinase (PTK) inhibitors, genistein, and mitogen for hepatocytes in primary culture. This ST638 also inhibited HGF-induced MAP kinase activagrowth factor also stimulates the growth of a variety tion. Furthermore, HGF increased formation of Rasr of cells, such as melanocytes, epidermal keratinocytes, guanosine triphosphate (GTP) complex, indicating Ras and renal tubular cells. [1][2][3][4][5][6][7] Thus, HGF plays an imactivation. Genistein inhibited HGF-induced Ras actiportant part in cell proliferation and tissue regeneravation, but Ro31-8425 was without effect. On the other hand, Ro31-8425 decreased HGF-induced [ 3 H]arachi-tion. The HGF receptor is the c-met proto-oncogene donic acid (AA) release and [ 3 H]thymidine incorporaproduct, 8,9 and several signaling events have been retion. Genistein also prevented [ 3 H]AA release and [ 3 H]ported after HGF receptor activation. HGF stimulates thymidine incorporation. Moreover, a commonly used the phosphorylation of phosphatidylinositol-specific phospholipase A 2 (PLA 2 ) inhibitor, quinacrine, dephospholipase Cg, 10 leading to inositol trisphosphate creased HGF-induced [ 3 H]AA release and [ 3 H]thymidine formation and an increase in intracellular Ca 2/ concenincorporation. The inhibitory profile of [ 3 H]AA release tration. 11 In contrast to rapid and transient change of was well correlated with that of [ 3 H]thymidine incorpoinositol triphosphate, 1,2-diacylglycerol formation was ration in Ro31-8425-, genistein-, and quinacrine-treated biphasic, and the second sustained phase was mainly cells. A cyclooxygenase inhibitor, indomethacin, which
caused by phosphatidylcholine hydrolysis. 12 Furthersuppressed HGF-induced DNA synthesis, had minimal effect on MAP kinase activation. In contrast, prostaglan-more, phosphatidylinositol 3-kinase is suggested to din (PG) E 1 , E 2 , or F 2a , which stimulate [ 3 H]thymidine bind to HGF receptor. 13 However, the detailed signalincorporation to the same level as that caused by HGF ing mechanism remains to be clarified.
in hepatocytes, caused very weak activation of MAP ki-
Mitogen-activated protein (MAP) kinases are activated by diverse stimuli and are thought to be implicated in a variety of cellular functions such as arachi-Abbreviations: HGF, hepatocyte growth factor; MAP, mitogen-activated donic acid (AA) release and cell growth. 14,15 It has protein; AA, arachidonic acid; PTK, protein tyrosine kinase; PKC, protein kirecently been shown that HGF activated MAP kinase C; PGs, prostaglandins; ATP, adenosine triphosphate; PMA, phorbol mynases 16,17 and AA release in primary cultured rat heparistate acetate; GDP, guanosine diphosphate; GTP, guanosine triphosphate; PBS, phosphate-buffered saline; SDS, sodium dodecyl sulfate; EGTA, ethylene tocytes. 16 However, the regulation of MAP kinases in glycol bis(b-aminoethyl ether)-N,N,N,N-tetraacetic acid; EGF, epidermal HGF-stimulated hepatocytes is not clearly understood.