Nucleotide sequence of prothrombin gene in abnormal prothrombin-producing hepatocellular carcinoma cell lines

A protein induced by vitamin K absence or antagonist II, PIVKA-II is synthesized in the liver and possesses a structure similar to prothrombin except that ten glutamic acid residues in amino-terminal Gla domain are not completely gamma-carboxylated and are functionally inactive. This protein can be detected in the plasma of patients with hepatocellular carcinoma (HCC) and used as a new tumor marker. To analyze the mechanism of PIVKA-II production in HCC tissue, the prothrombin gene of PIVKA-II-secreting HCC cell lines was sequenced to detect the mutation in the Gla domain and carboxylase recognition site of leader sequence located on exons I and II that may cause the inhibition of carboxylation. Exons I and II and donor and acceptor site of intron I of the prothrombin gene in two HCC cell lines, PLC/PRF/5 and huH-2, were analyzed by polymerase chain reaction (PCR), and the product was sequenced directly. In addition, RNA samples of these cell lines were used for complementary DNA synthesis, followed by PCR and sequencing. The nucleotide sequences of the Gla domain in both HCC cell lines were conserved. One nucleotide change was detected at nt.554 (adenine to guanine), but this did not influence the amino acid sequence. Splicing sites between exons I and II, the leader sequence of the precursor prothrombin, and protease target sites also were conserved as the reported prothrombin gene, and mutations reported for other des-gamma-carboxy coagulation factors were not detected. These results also were confirmed by DNA analysis of seven human fresh-frozen samples (three PIVKA-II-positive HCC samples and four control specimens). The mechanism of PIVKA-II production in HCC is still unclear, but it is not caused by mutation in the prothrombin gene.