Construction of HCV-core gene vector and its expression in cholangiocarcinoma

Advanced intrahepatic cholangiocarcinoma in hepatitis C virus-related decompensated cirrhosis: case report and review of the literature

A 75-year-old man with no known previous liver disease was admitted to our institution because of right pleural effusion, backache, and pain in the upper right quadrant. Physical and laboratory work-up revealed decompensated liver cirrhosis. Spiral computed tomography (CT) showed a 6-cm tumour in the right liver lobe. Serum levels of aminotransferases, prothrombin time, total bilirubin, alphafetoprotein and carcinoembryonic antigen were within normal limits. However, the patient had elevated cholestatic enzymes, diffuse hypergammaglobulinaemia, a six-fold increase in carbohydrate antigen 19-9 (CA 19-9), cryoglobulinaemia, and reactivity against hepatitis C virus (anti-HCV). Although hepatocellular carcinoma is the most common cancer in a cirrhotic patient with chronic viral hepatitis, the investigation revealed the presence of intrahepatic cholangiocarcinoma (ICC). This is a less frequently occurring primary liver tumour, the aetiology and pathogenesis of which remain unclear in the majority of cases. The coexistence of HCV liver disease and ICC might be an incidental finding, but recently some reports have shown a relatively high incidence of this tumour in patients with HCV-related cirrhosis. The current aspects regarding ICC prevalence in HCV patients, the possible aetiopathogenetic links between this tumour and HCV, and the importance for ICC detection and characterization using the enhancement patterns with quadruple-phase spiral CT scan are also discussed.

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Establishment of a transgenic cell line stably expressing human cytochrome P450 2C18 and identification of a CYP2C18 clone with exon 5 missing

AIM: The human cytochrome P-450 2C18 (CYP2C18) has been characterized. However, the protein has not been purified from liver and very little is known regarding the specific substrate of CYP2C18. In order to study its enzymatic activity for drug metabolism, the CYP2C18 cDNA was cloned and a stable CHL cell line expressing recombinant CYP 2C18 was established.

METHODS: The human CYP2C18 cDNA was amplified with reverse transcription-polymerase chain reaction (RT-PCR) from total RNAs extracted from human liver and cloned into pGEM-T vector. The cDNA segment was identified by DNA sequencing and subcloned into a mammalian expression vector pREP9. A transgenic cell line was established by transfecting the recombinant plasmid of pREP9-CYP2C18 to Chinese hamster lung (CHL) cell. The enzyme activity of CYP2C18 catalyzing oxidation of tolbutamide to hydroxytolbutamide in postmitochondrial supernant (S9) fraction of the cell was determined by high performance liquid chromatography (HPLC).

RESULTS: The amino acid sequence predicted from the cloned cDNA segment was identical to that of reported by Romkes et al^[3] (GenBank accession number: M61856, J05326). The S9 fraction of the established cell line metabolizes tolbutamide to hydroxytolbutamide. Tolbutamide hydroxylase activity was found to be 0.509 ± 0.052 μmol·min^-1·g^-1 S9 protein or 8.82 ± 0.90 mol·min^-1·mol^-1 CYP, but was undetectable in parental CHL cell. In addition, we have identified a CYP2C18 cDNA clone with exon 5 missing.

CONCLUSION: The cDNA of human CYP2C18 was successfully cloned and a cell line, CHL-CYP2C18, efficiently expressing the protein of CYP2C18, was established. A spliced variant of CYP2C18 with exon 5 missing was identified in the cloning process.

Activity of HDV ribozymes to trans-cleave HCV RNA

AIM: To explore whether HDV ribozymes have the ability to trans-cleave HCV RNA.

METHODS: Three HDV genomic ribozymes were designed and named RzC1, RzC2 and RzC3. The substrate RNA contained HCV RNA 5’-noncoding region and 5'-fragment of C region (5'-NCR-C). All the ribozymes and HCV RNA 5'-NCR-C were obtained by transcription in vitro from their DNA templates, and HCV RNA 5'-NCR-C was radiolabelled at its 5’-end. Under certain pH, temperature, appropriate concentration of Mg²⁺ and deionized formamide, these ribozymes were respectively or simultaneously mixed with HCV RNA 5'-NCR-C and reacted for a certain time. The trans-cleavage reaction was stopped at different time points, and the products were separated with polyacrylamide gel electrophoresis (PAGE), displayed by autoradiography. Percentage of trans-cleaved products was measured to indicate the activity of HDV ribozymes.

RESULTS: RzC1 and RzC2 could trans-cleave 26% and 21.8% of HCV RNA 5'-NCR-C under our reaction conditions with 2.5 mol•L^-1 deionized formamide respectively. The percentage of HCV RNA 5'-NCR-C trans-cleaved by RzC1, RzC2 or combined usage of the three ribozymes increased with time, up to 24.9%, 20.3% and 37.3% respectively at 90 min point. Almost no product from RzC3 was observed.

CONCLUSION: HDV ribozymes are able to trans-cleave specifically HCV RNA at certain sites under appropriate conditions, and combination of several ribozymes aiming at different target sites can trans-cleave the substrate more efficiently than using only one of them.

Cloning of cytochrome P-450 2C9 cDNA from human liver and its expression in CHL cells

AIM

Using bacterial, yeast, or mammalian cell expressing a human drug metabolism enzyme would seem good way to study drug metabolism-related problems. Human cytochrome P-450 2C9(CYP2C9) is a polymorphic enzyme responsible for the metabolism of a large number of clinically important drugs. It ranks among the most important drug metabolizing enzymes in humans. In order to provide a sufficient amount of the enzyme for drug metabolic research, the CYP2C9 cDNA was cloned and expressed stably in CHL cells.

METHODS

After extraction of total RNA from human liver tissue, the human CYP2C9 cDNA was amplified with reverse transcription-polymerase chain reaction (RT-PCR), and cloned into cloning vector pGEM-T. The cDNA fragment was identified by DNA sequencing and subcloned into a mammalian expression vector pREP9. A transgenic cell line was established by transfecting the recombinant vector of pREP9-CYP2C9 into CHL cells. The enzyme activity of CYP2C9 catalyzing oxidation of tolbutamide to hydroxy tolbutamide in S9 fraction of the cell was determined by high performance liquid chromatography(HPLC).

RESULTS

The amino acid sequence predicted from the cDNA segment was identical to that of CYP2C9*1, the wild type CYP2C9. However, there were two base differences, i.e. 21T>C, 1146C>T, but the encoding amino acid sequence was the same, L7, P382. The S9 fraction of the established cell line metabolizes tolbutamide to hydroxy tolbutamide; tolbutamide hydroxylase activity was found to be 0.465 +/- 0.109 micromol.min(-1).g(-1) S9 protein or 8.62 +/- 2.02mol.min(-1).mol(-1) CYP, but was undetectable in parental CHL cell.

CONCLUSION

The cDNA of human CYP2C9 was successfully cloned and a cell line of CHL- CYP2C9, efficiently expressing the protein of CYP2C9, was established.