Control of hepatitis B virus at the level of transcription.

Hepatitis B virus (HBV) is tightly controlled by a number of noncytotoxic mechanisms. This control occurs within the host hepatocyte at different steps of the HBV replication cycle. HBV persists by establishing a nuclear minichromosome, HBV cccDNA, serving as a transcription template for the viral pregenome and viral mRNAs. Nucleoside/nucleotide analogues widely used for antiviral therapy as well as most antiviral cytokines act at steps after transcription of HBV RNAs and thus can control virus replication but do not directly affect its gene expression. Control of HBV at the level of transcription in contrast is able to restrict both, HBV replication and gene expression. In the review, we focus on how HBV is controlled at the level of transcription. We discuss how the composition of transcription factors determines HBV gene expression and replication and how this may be influenced by antivirally active substances, e.g. the cytokine IL-6 or helioxanthin analogues, or by the differentiation state of the hepatocyte.