Hepatitis B viral DNA is methylated in liver tissues.
The mechanisms that regulate hepatitis B virus (HBV) replication within the liver are poorly understood. Given that methylation of CpG islands regulates gene expression in human tissues, we sought to identify CpG islands in HBV-DNA and to determine if they are methylated in human tissues. In silico analysis demonstrated three CpG islands in HBV genotype A sequences, two of which were of particular interest because of their proximity to the HBV surface gene start codon (island 1) and to the enhancer 1/X gene promoter region (island 2). Human sera with intact virions that were largely unmethylated were used to transfect HepG2 cells and HBV-DNA became partially methylated at both islands 1 and 2 by day 6 following exposure of HepG2 to virus. Examination of three additional human sera and 10 liver tissues showed no methylation in sera but tissues showed methylation of island 1 in six of 10 cases and of island 2 in five of 10 cases. The cell line Hep3B, with integrated HBV, showed complete methylation of island 1 but no methylation of island 2. In conclusion, HBV-DNA can be methylated in human tissues and methylation may play an important role in regulation of HBV gene expression.
Vivekanandan
P
P
Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
Thomas
D
D
Torbenson
M
M
D045744:Cell Line, Tumor; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D004279:DNA, Viral / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D006509:Hepatitis B / Q000097:blood* / Q000503:physiopathology / Q000821:virology; D006514:Hepatitis B Surface Antigens / Q000032:analysis; D006515:Hepatitis B virus / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008099:Liver / Q000378:metabolism / Q000821:virology*
D004279:DNA, Viral; D006514:Hepatitis B Surface Antigens