PROTEIN-KINASE-C DEPENDENT AND INDEPENDENT MECHANISMS CONTROLLING RATTROPHOBLAST CELL-DNA SYNTHESIS AND DIFFERENTIATION

Trophoblast giant cells are the steroidogenic cells of the rat placent a. In this study, the role of protein kinase C signalling pathways in the control of DNA synthesis and differentiation-dependent progesteron e biosynthesis by trophoblast cells were investigated. Rcho-1 trophobl ast cells, derived from a rat choriocarcinoma, can be experimentally m anipulated to proliferate or differentiate and provide a useful model for studying trophoblast giant cell endocrine differentiation. The rol e of protein kinase C signal transduction was examined through the tre atment of Rcho-1 trophoblast cells with isoquinolinesulfonamide deriva tives (H7, a protein kinase C inhibitor; HA1004, a control compound), chelytherine (a protein kinase C inhibitor), and phorbol esters (prote in kinase C activators). Treatment with H7 significantly attenuated DN A synthesis in proliferating and differentiating trophoblast cells and accelerated the acquisition of progesterone biosynthetic capabilities by trophoblast cells. Treatment with HA1004, the related but function ally distinct isoquinolone, did not significantly affect trophoblast D NA synthesis or proliferation and only weakly increased progesterone a ccumulation Chelytherine significantly inhibited trophoblast cell prol iferation but failed to influence trophoblast progesterone production significantly. The phorbol ester, 12-O-tetradecanoylphorbol acetate, d id not significantly influence progesterone accumulation. H7 did not s ignificantly influence the concentration of either P450scc or the mRNA encoding it in Rcho-1 trophoblast cells, or the transcriptional activ ity of the P450scc gene. The results indicate that signalling pathways sensitive to protein kinase C are involved in the control of trophobl ast cell proliferation. Differentiation-dependent production of proges terone is sensitive to H7 but appears to be independent of protein kin ase C and occurs at a stage other than P450scc expression.