Abstract

Phospholipase C isozymes (PLCs) play a role in ligand-mediated signal transduction for cellu- lar activity such as proliferation and differentation. However, their biological significance of in carcinogenesis or tumor progression is not fully estabilished, although PLC-rl is known to be related to the cell growth or the oncogene. We examined the relative content of PLC-rl in human hepatocellular carcinoma (HCC) and the adjacent non tumorous liver tissue, by immunoperoxidase staining of paraffin embedded sections. Among 32 cases, 25 demonstrated s significant decrease of PLC-rl content in comparison to the adjacent nontumorous tissue. Seven cases revealed no remarkable change in PLC-rl expression. There was no HCC expressing higher level of PLC-rl. We also performed image cytometric studies to evaluate the relationship between the DNA ploidy pattern and the PLC-yl content. Interestingly, the tumors showing a decreased PLC-rl expression, were mostly diploid and tetraploid (except 3 cases) in contrast to those tumors showing no change in PLC-rl content which were exclusively aneuploid. The results suggest that PLC-rl expression is closely related to DNA ploidy of the tumor, and that there may be two different mechanisms of hepatocarcinogenesis: one is related to PLC-rl associated signal trasduction system, and the other is independent of PLC-rl.

• Keywords: Hepatocarcinogenesis, PLC-rl, Signal transduction, DNA ploidy