RESUMEN
BACKGROUND: To construct the full-length complementary DNA of HCV genome from an HCV infected patient. METHODS: Four HCV gene fragments (1.6, 3.5, 2.4 kb and 2.6 kb) were amplified by RT-PCR from serum of a Chinese patient and fused and connected together to produce a 9.2 kb subgenomic fragment, which was further cloned into a cassette vector with fixed 5-prime and 3-prime termini of HCV to make the full-length cDNA. The cDNA heterogeneity was analyzed by comparing the sequences of 4 isolated HVR1 regions. The prokaryotic expressed Core, NS3 protease, NS3 helicase were detected for their specific reactivities with patient serum by Western blot analysis. And the protease activity of NS3 was evaluated in a cell-based NS3/4A-SEAP expression system. RESULTS: The cDNA covered the near full-length of HCV genome from the patient's serum. The difference among HVR1 regions indicated no selection of HCV variants during RT-PCR and the quasi-species characteristic of the amplified cDNA. The prokaryotic expressed viral proteins could be identified by patient serum. In the NS3/4A-SEAP system, NS3 could cleave the 4A-4B site between NS4A and SEAP proteins and resulted in the secretion of SEAP in culture media. CONCLUSION: These results suggest that the cloned HCV cDNA encodes a complete and functional open reading frame and will be useful for further construction of infectious cDNA clone.
Asunto(s)
ADN Complementario/genética , Genoma Viral , Hepacivirus/genética , Hepatitis C/virología , Secuencia de Bases , Clonación Molecular , Humanos , Datos de Secuencia Molecular , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
AIM: To establish an efficient, sensitive, cell-based assay system for NS3 serine protease in an effort to study further the property of hepatitis C virus (HCV) and develop new antiviral agents. METHODS: We constructed pCI-neo-NS3/4A-SEAP chimeric plasmid, in which the secreted alkaline phosphatase (SEAP) was fused in-frame to the downstream of NS4A/4B cleavage site. The protease activity of NS3 was reflected by the activity of SEAP in the culture media of transient or stable expression cells. Stably expressing cell lines were obtained by G418 selection. Pefabloc SC, a potent irreversible serine protease inhibitor, was used to treat the stably expressing cell lines to assess the system for screening NS3 inhibitors. To compare the activity of serine proteases from 1b and 1a, two chimeric clones were constructed and introduced into both transient and stable expression systems. RESULTS: The SEAP activity in the culture media could be detected in both transient and stable expression systems, and was apparently decreased after Pefabloc SC treatment. In both transient and stable systems, NS3/4A-SEAP chimeric gene from HCV genotype 1b produced higher SEAP activity in the culture media than that from 1a. CONCLUSION: The cell-based system is efficient and sensitive enough for detection and comparison of NS3 protease activity, and screening of anti-NS3 inhibitors. The functional difference between NS3/4A from 1a and 1b subtypes revealed by this system provides a clue for further investigations.