Vitamin K-dependent carboxylase activity, prothrombin mRNA, and prothrombin production in two cultured rat hepatoma cell lines.

The presence of under-gamma-carboxylated forms of plasma prothrombin is a marker for human primary hepatocellular carcinoma. A rat hepatoma cell line (7777) which was previously shown to secrete undercarboxylated prothrombin when grown as a solid tumor has now been grown in monolayer culture. This cell line has a decreased activity of the microsomal vitamin K-dependent carboxylase when compared to a control (H4IIEC3) hepatoma line, does not increase intracellular prothrombin concentrations in response to vitamin K depletion, and secretes undercarboxylated prothrombin even when grown in vitamin K supplemented media. Prothrombin gene expression in the 7777 cell line, as measured by prothrombin mRNA levels, was not altered in the 7777 cell line. This cell line appears to be a model for assessing the cellular alterations responsible for undercarboxylated prothrombin excretion by human hepatocellular tumors.