Novel autoregulatory function of hepatitis B virus M protein on surface gene expression.
The hepatitis B virus surface gene consists of a single open reading frame divided into three coding regions: pre-S1, pre-S2, and S. By alternate translation at each of the three initiation codons, L, M, and S proteins can be synthesized. Studies have shown that M protein is not essential for viral replication, virion morphogenesis, or in vitro infectivity. In this study, we show that native M protein can regulate surface gene expression at the transcriptional level. The regulatory effect of M protein is mediated through the CCAAT box within the S promoter. Deletion mapping analysis indicated that the transactivating effect of M protein is mediated through amino acids 1-57 of M protein (the MHBs(au) domain), although its maximal transactivation activity coincides with that of the pre-S2 domain. This conclusion is supported by the fact that disruption of the putative V8 protease site at the pre-S2/S domain junction not only rendered M protein incapable of transactivating the S promoter but also inactivated its nuclear translocation potential. Immunoprecipitation and immunoblot experiments demonstrated that pre-S2 interacts with the three subunits of the CCAAT box-binding factor/nuclear factor Y, the cognate binding protein of the CCAAT box. These results demonstrate and define a novel regulatory role of M protein, which, under natural conditions, may undergo a proteolytic process to generate an MHBs(au) species that will be translocated inside the nucleus, where it will interact with the CCAAT box-binding factor to regulate surface gene expression. Because the CCAAT box is located at a fixed position within numerous promoters, these observations might provide a plausible explanation for hepatitis B virus-associated hepatocarcinogenesis.
Huang
Tsurng-Juhn
TJ
Institute of Basic Medical Sciences, Medical College, National Cheng Kung University, Tainan, Taiwan.
Lu
Cheng-Chan
CC
Tsai
Jui-Chen
JC
Yao
Wei-Jen
WJ
Lu
Xuanyong
X
Lai
Ming-Derg
MD
Liu
Hsiao-Sheng
HS
Shiau
Ai-Li
AL
D001483:Base Sequence; D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism / Q000821:virology*; D002467:Cell Nucleus / Q000378:metabolism; D002918:Chymotrypsin / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D017353:Gene Deletion; D015967:Gene Expression Regulation, Viral; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006514:Hepatitis B Surface Antigens / Q000378:metabolism / Q000502:physiology*; D006515:Hepatitis B virus / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008156:Luciferases / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D017931:DNA Primers; D006514:Hepatitis B Surface Antigens; D049452:Green Fluorescent Proteins; D012313:RNA; D008156:Luciferases; D002918:Chymotrypsin