Mechanism of the abnormal vitamin k-dependent γ-carboxylation process in human hepatocellular carcinomas

Abstract

Background. An important marker for hepatocellular carcinoma is the presence of des‐γ‐carboxy (abnormal) prothrombin. However, the molecular basis for the reduced carboxylation of prothrombin is unknown. Methods. Two groups of patients were defined according to the absence (Group I, n = 7) or presence (Group II, n = 8) of des‐γ‐carboxy prothrombin. The enzymatic activity of y‐carboxylase and the total microsomal prothrombin concentration were determined in all tumors. The kinetic parameters for the synthetic peptide Phe‐Leu‐Glu‐Glu‐Leu (FLEEI.) were measured in eight tumors. The γ‐carboxylase mRNA expression was evaluated by Northern blot analysis in 12 of 15 tumors. In addition, the total vitamin K content (K, K, epoxide, and menaquinones 4‐10) in 10 tumors was investigated by high performance liquid chromatography. Results. Concentrations of menaquinones 4‐10 were normal in the nontumorous part of the liver but significantly decreased (P = 0.02) in all the tumors (Groups I and II). This decrease was more severe in Group II (P = 0.02). The tumors in Group I had normal or increased γ‐carboxylase activity and increased mRNA expression (P < 0.02) as compared with their nontumorous counterparts. The tumors in Group II were heterogeneous. Five tumors displayed low y‐carboxylase activity, associated with low mRNA expression in two, whereas two others had high γ carboxylase activity and mRNA expression. The concentration of FLEEL at half‐maximal velocity was normal in all the tumors examined (Groups I and II), and a relation was found between the level of expression of γ‐carboxylase and the maximal velocity for FLEEL carboxylation in the tumors in Group II (r = 0.98; P < 0.01). The microsomal content of normal prothrombin was within normal limits in all tumors (Groups I and II). Conclusions. Tumor vitamin K content has a critical role in the synthesis of des‐γ‐carboxy prothrombin. Furthermore, the γ‐carboxylase defect, which is observed in some secreting tumors, is the result of the defective gene expression of a normal enzyme and not the consequence of the presence of a competitive inhibitor. It is possible that a 75% reduction in γ‐carboxylase gene expression could take a part in the secretion of des‐γ‐carboxy prothrombin, but this mechanism is not predominant.

K vitamins, PTP antagonism, and cell growth arrest

“…This does not seem to be related to dietary factors and does not yet have prognostic significance. Several studies have suggested that there may be a functional deficit in vitamin K available to hepatoma cells, resulting in a diminished capacity to carboxylate prothrombin on glutamic acid residues, and HCC tissue samples have been found to have a lower concentration of K vitamin in the surrounding tissue Huisse et al, 1994). In addition, the clinical administration of high doses of vitamin K to HCC patients who produce elevated levels of DCP, results in restoration of carboxylation activity, as judged by dramatic decreases of DCP levels to normal (Furukawa et al, 1992;Carr, 1994).…”

Growth inhibitory actions of prothrombin on normal hepatocytes: Influence of matrix

“…The best known is alpha-fetoprotein, which we have found to be elevated in about 50% of our HCC patients (Virji et al, 1992). By contrast, the more recently recognized marker DCP (des-γ carboxy prothrombin) has been found to be increased in over 70% of patients with HCC, although it is less specific than AFP, since it is also increased in biliary diseases and by the anticoagulant action of warfarin (Weitz et al, 1993;Huisse et al, 1994;Liebman et al, 1984;Nakao et al, 1991;Liebman et al, 1989;Li et al, 2002,Lefrere et al, 1987,Shah et al, 1987Tsai et al, 1990). The action of warfarin has been identified to be on the vitamin K cycle, in which oxidized vitamin K cannot be cycled back to the reduced and physiologically active form (Fasco et al, 1982), when warfarin was present.…”

“…As a result, the underlying normal liver produces mature prothrombin, but HCCs within that liver produce under-carboxylated or immature prothrombin, DCP, one of the more useful HCC serum markers (Weitz et al, 1993;Huisse et al, 1994;Liebman et al, 1984;Nakao et al, 1991;Liebman et al, 1989;Li et al, 2002). The biological significance of this has never been clear, but it has recently been suggested that immature prothrombin or DCP has HCC growth promoting properties (Suzuki et al, 2005).…”

Vitamin K Contents in Liver Tissue of Hepatocellular Carcinoma Patients

“…The mechanism causing the elevation of serum PIVKA-II levels in hepatocellular carcinoma patients is proposed to be as follows; (1) vitamin K deficiency in local cancerous tissue due to an abnormal vitamin K uptake of hepatic cancer cells [17][18][19] ; (2) excessive production of a prothrombin precursor (PIVKA) in hepatic cancer cells [18][19][20] ; (3) decline of γ-glutamylcarboxylase activity in hepatic cancer cells 20) ; (4) decline of the ability to use vitamin K due to oxidation-reduction cycle abnormality in hepatic cancer cells; or (5) prothrombin gene abnormality in hepatic cancer cells. 20,21) But details of the mechanism are not known.…”