Current Papers in Liver Disease - July, 1997

By Howard J. Worman, M. D.
Columbia University

This is a past issue of Current Papers in Liver Disease.

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Ktistaki, E., and Talianidis, I. 1997. Modulation of hepatic gene expression by hepatocyte nuclear factor 1. Science. 277:109-112.

Liver-specific gene expression is regulated by several liver-enriched transcription factors (proteins that increase the synthesis of RNA from their DNA genes) including HNF-1, C/EBP, HNF-3 and HNF-4. HNF-1 is known to activate genes that contain HNF-1 promoters but to inhibit other genes, including its own, that contain HNF-4 promoters and lack HNF-1 promoters. In this study, the authors show that HNF-1 inhibits NHF-4 by binding to the main transcription activation domain of HNF-4. HNF-1 can therefore both activate and repress liver-specific genes during development. This work is another piece of the complex puzzle of how a liver cell becomes a liver cell.

Moirand, R., Adams, P. C., Bicheler, V., Brissot, P., and Deugnier, Y. 1997. Clinical features of genetic hemochromatosis in women compared with men. Annals of Internal Medicine. 127:105-110.

Hereditary hemochromatosis is an inherited disorder of metabolism that leads to iron overload in many organs of the body, including the liver where it can lead to cirrhosis. Hemochromatosis has an estimated prevalence of about 1 in 300 in populations of European ancestry. A candidate gene on chromosome 6, responsible for at least 85% of cases of hereditary hemochromatosis, has been characterized (see Feder et al. Nature Genetics. 13:399-408 in the September, 1996 Current Papers in Liver Disease). Individuals with mutations in both copies of this gene develop the disease. It has long been thought that women have less severe expression of hemochromatosis because of menstrual blood loss which leads to decreased iron overload. This hypothesis, however, has never been validated by a systematic examination of a large group of patients. In this study, 176 women and 176 men with hereditary hemochromatosis from France and Canada were examined for age at presentation, clinical symptoms, transferrin saturation and ferritin index (serum biochemical indicators of iron overload) and liver iron content. The authors found that men and women were diagnosed with hemochromatosis at the same age (48 to 50 years old). Liver iron content was similar in men and women. Women generally had lower serum ferritin concentrations (suggestive of lower total body iron content) and during treatment by phlebotomy (blood drawing to lower body iron), generally had less iron removed. Compared with women, men had a higher incidence of cirrhosis and diabetes mellitus (from iron deposition in the pancreas). Compared with men, women had a higher incidence of fatigue and skin pigmentation. Liver iron content was higher in women who had stopped menstruating prior to the age of 50 than those who stopped after age 50. Serum ferritin and transferrin saturation were normal in 6.2% of women, but 0% of men, who were identified by family screening when the disease was diagnosed in a relative. This suggests that some women with hereditary hemochromatosis may not have suggestive serum biochemical abnormalities. From this study, it appears that homozygous hemochromatosis is slightly underexpressed in women, but that women can present with severe disease at the same age as men. Women also tend to have different clinical features than men. The reasons for this are unclear. One drawback of the study was that the incidence of concurrent chronic viral hepatitis and alcohol abuse, risk factors for cirrhosis that are more common in men, was not assessed.

Maier-Dobersberger, T., Ferenci, P., Polli, C., Balac, P., Dienes, H. P., Kaserer, K., Datz, C., Vogel, W., and Gangl, A. 1997. Detection of the His1069 mutation in Wilson disease by rapid polymerase chain reaction. Annals of Internal Medicine. 127:21-26.

Wilson disease is caused by mutations mutations in the ATP7B gene on chromosome 13. More than 50 different mutations (changes in the gene sequence) have been found to cause Wilson disease. As a result of this genetic heterogeneity, molecular diagnosis is difficult unless the specific mutation in a family member is known. Of the 50 mutations, some are more common than others. In this paper, Maier-Dobersberger et al. use a polymerase chain reaction-based assay to show that 61% of Austrian patients have a particular mutation in which the amino acid histidine at position 1069 of the protein encoded by the ATP7B gene is changed to glutamine. Patients with this mutation tend to develop symptoms in their mid teens. In 83 patients from 72 families, 20, including five siblings, were homozygous (had two copies of the abnormal gene) for this mutation. Thirty-three patients, including four siblings, were compound heterozygotes, with a histidine to glutamine mutation in one gene and another mutation in their other. This mutation was not detected in 30 patients, including two siblings. Of 98 patient relatives, heterozygosity (the presence of only one mutant gene) was confirmed in 46. These results show that the histidine to glutamine 1069 mutation is relatively common in patients with Wilson disease of European ancestry. They also show that polymerase chain reaction-based testing for a known mutation can be used in infants and children to help differentiate subjects who have Wilson disease (homozygotes and compound heterozygotes) from carriers (heterozygotes).

Chang, M.-H., Chen, C.-J., Lai, M.-S., Hsu, H.-M., Wu, T.-C., Kong, M.-S., Liang, D.-C., Shau, W.-Y., Chen, D.-S., for the Taiwan Childhood Hepatoma Study Group. 1997. Universal hepatitis B vaccination in Taiwan and the incidence of hepatocellular carcinoma in children. New England Journal of Medicine. 336:1855-1859.

Chronic hepatitis B virus (HBV) infection is associated with the development of hepatocellular carcinoma. In Southeast Asia, HBV infection is endemic and hepatocellular carcinoma is a common causes of cancer death. In 1984, Taiwan launched a nationwide vaccination program to control hepatitis B. This program reduced the hepatitis B surface antigen carrier rate in children from about 10% to 1% within 10 years of implementation (Chen et al. 1996. Journal of the American Medical Association. 276:906-908; see November, 1996 Current Papers). In the present study, the authors report that universal hepatitis B vaccination reduces that incidence of hepatocellular carcinoma in children. The average annual incidence of hepatocellular carcinoma in children 6 to 14 years of age declined from 0.70 per 100,000 between 1981 and 1986 to 0.57 between 1986 and 1990 and 0.36 between 1990 and 1994. The rates of death from hepatocellular carcinoma similarly decreased. The incidence in children 6 to 9 years of age declined from 0.52 per 100,000 for those born between 1974 and 1984 to 0.13 per 100,000 for those born between 1984 and 1986. This landmark study shows that mass vaccination can reduce the incidence of a specific cancer in humans and further strengthens the association between HBV infection and liver cancer. The results also lend strong support to the argument for worldwide, universal hepatitis B vaccination.

Gale, M. J., Jr., Korth, M. J., Tang, N. M., Tan, S.-L., Hopkins, D. A., Dever, T. E., Polyak, S. J., Gretch, D. R., and Katze, M. G. 1997. Evidence that hepatitis C virus resistance to interferon is mediated through repression of the PKR protein kinase by the nonstructural 5A protein. Virology. 230:217-127.

Enomoto and colleagues have previously shown that mutations in a region of the hepatitis C virus NS5A gene, particularly in genotype 1b isolates, correlate with increased sensitivity to interferon treatment [see April, 1996 Current Papers]. This finding has since been confirmed by several other investigators [see March, 1997 Current Papers]. This region of NS5A that presumably mediates resistance to interferon treatment has been termed the interferon-sensitivity determining region (ISDR). How ISDR mediates resistance to interferon is not known. In the present study, Gale et al. present evidence that the ISDR interacts with an anti-viral enzyme called PKR protein kinase that is induced in host cells by interferon. Using several different biochemical methods, they demonstrate that NS5A represses PKR through a direct interaction with its catalytic domain and that the inhibition and interaction require the ISDR. These results suggest that hepatitis C virus may avoid some of the antiviral effects of interferon by inactivating PKR. They also provide an explanation as to why mutations in the ISDR correlate with enhanced sensitivity to interferon treatment.

Yao, N., Hesson, T., Cable, M., Hong, Z., Kwong, A. D., Le, H. V., and Weber, P. C. 1997. Structure of the hepatitis C virus RNA helicase domain. Nature Structural Biology. 4:463-467.

The hepatitis C virus (HCV) is a single stranded RNA virus. The RNA genome encodes one large polyprotein that is processed by cellular and viral proteases into several structural and enzymatic proteins necessary for viral replication. One such viral enzyme is a helicase that unwinds duplex RNA during genomic replication. In this study, the authors used X-ray crystallography to determine the structure of the HCV helicase. Their structural analysis revealed a molecule with distinct nucleotide triphosphatase and RNA binding domains. The structure suggests that the helicase initially recognizes the 3' single-strand region of the RNA substrate by a conserved arginine-rich sequence in the RNA binding domain. Based on homology to regions in other enzymes, they speculate that rotation of parts of the helicase may be coupled to nucleotide triphosphate hydrolysis during the helicase catalytic cycle. Knowledge of the structure of the HCV helicase and its functionally important domains could lead to the development of specific inhibitors using rational drug design that may be ultimately used in patients to prevent HCV replication.

Paulusma, C. C., Kool, M., Bosma, P. J., Scheffer, G. L., Borg, F. T., Scheper, R. J., Tytgat, G. N. J., Borst, P., Baas, F., and Oude Elferink, R. P. J. 1997. A mutation in the human canalicular multispecific organic anion transporter gene causes the Dubin-Johnson syndrome. Hepatology. 25:1539-1542.

Last year (see April, 1996 Current Papers), Paulusma et al. (Science. 271:1126-1128) demonstrated that point mutations in the rat gene encoding cMOAT, a protein homologous to multidrug resistance-associated protein that transports bilirubin from the liver cell to the bile, caused chronic conjugated hyperbilirubinemia in the TR- rat. The phenotype of the TR- rat is almost identical to that seen in the human disease Dubin-Johnson syndrome, an inherited disease characterized by conjugated hyperbilirubinemia common in individuals of Persian Jewish decent. As a result, the authors speculated that mutations in the human homologue of rat cMOAT caused Dubin-Johnson syndrome. In the present paper, the same group reports on the isolation of the complementary DNA for the human homologue of rat cMOAT. Using antibodies against cMOAT, they show that the protein was present in the bile canaliculi of normal human liver but absent from the liver of a patient with Dubin-Johnson. They then show that a patient with Dubin-Johnson syndrome has a point mutation in the cMOAT gene that results in a premature termination codon. These results, along with the previous studies in the TR- rat, show that mutations in the gene encoding cMOAT, a bile canalicular organic anion transport protein, cause the Dubin-Johnson syndrome.