Abstract
A recently established cellular model for the rare small cell carcinoma of the ovary hypercalcemic type (SCCOHT-1) was characterized in comparison to ovarian adenocarcinoma cells (NIH:OVCAR-3 and SK-OV-3). The different cancer populations exhibited a common sensitivity in acidic pH milieu and a continuous proliferation in alkaline medium of pH 8.0-9.0. In the presence of elevated Ca2+ concentrations, the ovarian cancer cells demonstrated a progressively reduced proliferation within 72 h in contrast to other tumor types such as breast cancer cells. This significant growth inhibition was calcium-specific since the proliferation was unaffected after culture of the ovarian cancer cells in the presence of similar concentrations of other cations. The Ca2+ effects on the ovarian cancer cells were associated with marked differences in the activation of intracellular signaling pathways including enhanced phosphorylation of the p42/44 MAP kinase (Thr202/Tyr204). Further analysis of the signaling pathway revealed a significantly enhanced Ca2+-dependent and p42/44 MAP kinase activation-mediated prostaglandin E2 (PGE2) production in SK-OV-3 and SCCOHT-1 and to a lesser extent in NIH:OVCAR-3 cells. Vice versa, exogenous PGE2 did not affect the proliferative capacity of the ovarian cancer cells and inhibition of the Ca2+-mediated MAP kinase activation did not abolish the Ca2+-mediated cytotoxicity. Collectively, these data suggest that multiple pathways are activated by exogenous Ca2+ in the different ovarian cancer cells, including a specific MAP kinase signaling cascade with subsequent PGE2 production and a parallel pathway for the induction of cell death.