• phosphatidylcholine-specific phospholipase C;
  • phorbol ester;
  • all-transretinoic acid;
  • hepatocarcinoma

The biological significance of phosphatidylcholine-specific phospholipase C (PC-PLC) in hepatocarcinogenesis and the proliferation and differentiation of rat liver cancer cells was investigated. The Ca2+-dependent activities of PC-PLC gradually increased during N-nitrosodiethylamine (DEN)-induced hepatocarcinogenesis and peaked at weeks 18–20 when the tumour formed. There was a close relationship between Ca2+-dependent PC-PLC activities and cellular DNA content, membranous γ-glutamyltranspeptidase (γ-GT), and tyrosine protein kinase. In contrast, Ca2+-independent PC-PLC activities decreased during hepatocarcinogenesis. Similarly, when CBRH-7919 rat liver cancer cells were treated with phorbol 12-myristate 13-acetate, a proliferation stimulator of the cells, γ-GT and Ca2+-dependent activities of PC-PLC and the expression of α-fetoprotein increased significantly. However, when these cells were induced by retinoic acid to differentiate, Ca2+-dependent PC-PLC and γ-GT activities decreased significantly, together with α-fetoprotein expression. There was a close relationship between Ca2+-dependent PC-PLC and γ-GT activities during differentiation as there was during proliferation. We suppose that Ca2+-dependent PC-PLC is involved in rat hepatocarcinogenesis induced by DEN and that it plays an important role in the phorbol ester-induced proliferation or retinoic acid-induced differentiation of liver cancer cells.