Hepatitis B Virus DNA is a Substrate for the cGAS/STING Pathway but is not Sensed in Infected Hepatocytes

Abstract

Hepatitis B virus (HBV) chronic infection is a critical risk factor for hepatocellular carcinoma. The innate immune response to HBV infection is a matter of debate. In particular, viral escape mechanisms are poorly understood. Our study reveals that HBV RNAs are not immunostimulatory in immunocompetent myeloid cells. In contrast, HBV DNA from viral particles and DNA replication intermediates are immunostimulatory and sensed by cyclic GMP-AMP Synthase (cGAS) and Stimulator of Interferon Genes (STING). We show that primary human hepatocytes express DNA sensors to reduced levels compared to myeloid cells. Nevertheless, hepatocytes can respond to HBV relaxed-circular DNA (rcDNA), when transfected in sufficient amounts, but not to HBV infection. Finally, our data suggest that HBV infection does not actively inhibit the DNA-sensing pathway. In conclusion, in infected hepatocytes, HBV passively evades recognition by cellular sensors of nucleic acids by (i) producing non-immunostimulatory RNAs, (ii) avoiding sensing of its DNAs by cGAS/STING without active inhibition of the pathway.

Interplay between Hepatitis D Virus and the Interferon Response

“…In contrast to HDV, HBV replication does not activate significant innate immune responses [ 132 , 169 , 170 , 171 , 172 , 173 , 174 ]. Although some publications described HBV-induced IFN or pro-inflammatory responses [ 175 , 176 , 177 , 178 , 179 ], these responses are usually low and temporary compared to those activated by HDV.…”

“…Although some publications described HBV-induced IFN or pro-inflammatory responses [ 175 , 176 , 177 , 178 , 179 ], these responses are usually low and temporary compared to those activated by HDV. Other studies showed that HBV pgRNA and DNA could be substrates of cellular PRRs [ 174 , 175 , 178 , 179 ]. However, such RNA/DNA is likely not reachable by PRRs in the cytoplasm due to shielding by the HBV capsid ( Figure 2 ).…”

Cyclic Guanosine Monophosphate–Adenosine Monophosphate Synthase (cGAS), a Multifaceted Platform of Intracellular DNA Sensing

“…These recent data have important conceptual implications in the interaction between cGAS, cellular components, and viral DNA in the nucleus, even though no direct interaction has been observed apart for HIV capsid so far. In this context, several lines of evidence suggest that the DNA genome of hepatitis B virus (HBV) stimulates cGAS activity and triggers the activation of the cGAS-STING pathway when transfected into hepatocyte-derived cells ( 33 , 86 ). However, no induction of innate immune pathways is detected upon viral infection ( 33 , 86 ).…”

“…In this context, several lines of evidence suggest that the DNA genome of hepatitis B virus (HBV) stimulates cGAS activity and triggers the activation of the cGAS-STING pathway when transfected into hepatocyte-derived cells ( 33 , 86 ). However, no induction of innate immune pathways is detected upon viral infection ( 33 , 86 ). The “stealth” pattern of this peculiar virus was initially attributed, in addition to the absence HBV RNAs sensing, to the protection of the genome within the capsid during its transport to the nucleus ( 87 ).…”

“…According to the tissue distribution described in the Human Protein Atlas ( http://www.proteinatlas.org ), MB21D1 and cGAS protein are ubiquitously expressed with particularly high expression in epithelial cell types in the genital tract or the lungs as well as in hematopoietic cells and dendritic cells, with TMEM173 /STING presenting a quite comparable distribution pattern ( 31 , 32 ). In contrast, primary human hepatocytes express low levels of cGAS and STING ( 33 , 34 ). One putative explanation would be that low cGAS and STING expression would avoid overactivation of this pathway during hepatocyte renewal, which leads to DNA accumulation in the cytoplasm ( 34 , 35 ).…”