Hepatocyte growth factor induces transglutaminase activity that negatively regulates the growth signal in primary cultured hepatocytes.

Transglutaminase (TGase) activity increased 2.5-fold at 6 h after treatment of rat hepatocytes with 117 nM hepatocyte growth factor (HGF). In the same manner, putrescine incorporation into proteins of cells occurred in HGF-treated cells but did not in those pretreated with monodansylcadaverine (MDC), a TGase inhibitor, even in the presence of HGF. These results suggest that HGF-induced TGase was active and catalyzed some cross-linkage reaction. Cycloheximide completely blocked the increase in TGase activity induced by HGF, suggesting that HGF stimulated de novo synthesis of TGase within 6 h. Both [35S]methionine incorporation and Northern blotting analyses supported this possibility. Pretreatment of cells with MDC additionally increased HGF-induced DNA synthesis and the ratio of cells in S-phase. Similarly, TGase antisense oligonucleotide inhibited de novo synthesis of TGase, resulting in increase in the ratio of S-phase cells in the presence of HGF. Analyses of cross-linking of HGF to the receptor indicated that the antisense oligonucleotide inhibited the downregulation of HGF receptor subsequent to HGF-addition. These results provide the first evidence for inducibility of de novo synthesis of TGase by HGF and suggest that TGase negatively regulates the growth signal of HGF through the downregulation of receptor.