ZNF638 represses the transcription of HBV closed circular DNA involving HUSH complex-mediated histone modifications of epigenetic silencing

Hepatitis B virus (HBV) infection poses a critical threat to public health burden worldwide. The covalently closed circular DNAs (cccDNAs) of HBV was known to form microchromosomes and interact with host epigenetic factors. The aim of the present study is to elucidate the mechanisms of ZNF638, as a transcription factor participating viral epigenetic regulations, for its role in the suppression of HBV cccDNA transcription. Using chromatin immunoprecipitation and nuclear HBV cccDNA pulldown assays to determine ZNF638 binding sites. ZNF638’s regulatory effects on HBV in HBV cell models are examined by FISH-IF, qRT-PCR, and ELISA assays. The effect of ZNF638 deficiency on HBV inhibition through HBV-targeting siRNA delivery was evaluated in an in vivo model of HBV transgenic mice. It was found that ZNF638 was able to bind the preS and S gene regions of HBV, repressing the transcription of cccDNA upon increased modification of H3K9me3 mediated by SETDB1. HUSH complex was demonstrated to involve in the epigenetic silencing of cccDNA transcription. Subcutaneous injection of ZNF638 siRNA significantly compromised the efficacy of HBV RNAi therapy in vivo. We conclude that ZNF638 is a repressive host factor to inhibit the transcription of HBV DNAs and potently attenuate HBV infection. The binding of ZNF638 to specific regions for recruiting HUSH complex to write H3K9me3 histone marks is required for the epigenetic silencing of cccDNA transcription.