Abstract
C-terminally truncated hepatitis B virus (HBV) middle size surface proteins (MHBst) has been shown to be a transcriptional activator and may be relevant to hepatocarcinogenesis by transactivating gene expression. In the present study, a pcDNA3.1(−)-MHBst167 vector coding for MHBst truncated at amino acid 167 (MHBst167) was constructed and transfected into the HepG2 hepatoma cell line. mRNA and protein expression of MHBst167 in the cells was detected by reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis. A cDNA library of genes transactivated by the truncated protein in HepG2 cells was made in pGEM-T Easy using suppression subtractive hybridization. The cDNAs were sequenced and analyzed with BLAST searching against the sequences in GenBank. The results showed that certain sequences, such as that of human proto-oncogene c-Myc, may be involved in tumor development. An expression vector pCAT3/c-Myc containing the chloramphenicol acetyltransferase (CAT) gene under the control of a c-Myc promoter was generated, and the transcriptional transactivating effect of MHBst167 on the c-Myc promoter was investigated by RT-PCR and western blotting. MHBst167 was found to upregulate the transcriptional activity of the promoter, as well as transcription and translation of c-Myc. MHBst167 was also shown to transactivate SV40 immediate early promoter, and transcriptionally transactivate the expression of human c-Myc. These findings provide new directions for studying the biological functions of MHBst167, and for a better understanding of the tumor development mechanisms of HBV infection.
Highlights
Worldwide, hepatitis B virus (HBV) is an important pathogen causing both acute and chronic liver diseases
DNA sequencing results indicated that the recombinant vector contained HBV DNA fragment encoding the truncated middle surface protein in‐frame and the sequence was completely correct
The results showed that chloramphenicol acetyltransferase (CAT) gene expression exhibited an approximately linear association with the quantity of reporter vector used in transfection (Fig. 2A)
Summary
Hepatitis B virus (HBV) is an important pathogen causing both acute and chronic liver diseases. The integrated HBV DNA can encode two types of transcriptional transactivators: The well studied HBxAg and the preS2 transactivators, large hepatitis B virus surface proteins (LHBs) and C‐terminally truncated middle size surface proteins (MHBst) [4,5,6]. Considerable advances have been made in the fields of transcriptional transactivation of MHBst; the molecular basis of MHBst‐dependent transcriptional transactivation remains enigmatic. Studies in this area will provide a better understanding of the association between HBV and host hepatocytes, and pave the way for elucidating the pathogenesis of HBV‐related HCC. The association between the human proto‐oncogene c‐Myc and MHBst167 was discussed
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