HBx represses WDR77 to enhance HBV replication by DDB1-mediated WDR77 degradation in the liver

Abstract

Rationale: Hepatitis B x protein (HBx) is required to initiate and maintain the replication of hepatitis B virus (HBV). Protein arginine methyltransferases 5 (PRMT5) negatively regulates HBV transcription. WD repeat domain 77 protein (WDR77) greatly enhances the methyltransferase activity of PRMT5. However, the role of WDR77 in the modulation of cccDNA transcription and HBV replication is poorly understood. In this study, we investigated the mechanism by which HBx modulated HBV replication involving WDR77 in the liver. Methods: A human liver-chimeric mouse model was established. Immunohistochemistry (IHC) staining, Western blot analysis, Southern blot analysis, Northern blot analysis, immunofluorescence assays, ELISA, RT-qPCR, CoIP assays, and ChIP assays were performed in human liver-chimeric mouse model, primary human hepatocytes (PHHs), HepG2-NTCP, dHepaRG and HepG2 cell lines. Results: HBV infection and HBx expression remarkably reduced the protein levels of WDR77 in human liver-chimeric mice and HepG2-NTCP cells. WDR77 restricted cccDNA transcription and HBV replication in PHHs and HepG2-NTCP cells. Mechanically, WDR77 enhanced PRMT5-triggered symmetric dimethylation of arginine 3 on H4 (H4R3me2s) on the cccDNA minichromosome to control cccDNA transcription. HBx drove the cellular DDB1-containing E3 ubiquitin ligase to degrade WDR77 through recruiting WDR77, leading to the disability of methyltransferase activity of PRMT5. Thus, HBx promoted HBV replication by driving a positive feedback loop of HBx-DDB1/WDR77/PRMT5/H4R3me2s/cccDNA/HBV/HBx in the liver. Conclusions: HBx attenuates the WDR77-mediated HBV repression by driving DDB1-induced WDR77 degradation in the liver. Our finding provides new insights into the mechanism by which HBx enhances HBV replication in the liver.

Pathogenicity and virulence of Hepatitis B virus

“…The binding of HBx to PRMT1 inhibits the protein methylation activity of PRMT1 and relieves this suppression to enhance HBV gene expression[ 72 ]. Moreover, HBx induces DDB1 to degrade WD repeat domain 77 protein (WDR77), which enhances the methyltransferase activity and represses HBV replication[ 232 ]. A recent study also showed that HBx recruited m 6 A methyltransferase complexes to promote the co-transcriptional m 6 A modification of viral RNAs, which was discussed in section 3.3.7 above[ 233 ].…”

TRIM26 inhibits hepatitis B virus replication by promoting HBx degradation and TRIM26 genetic polymorphism predicts PegIFNα treatment response of HBeAg‐positive chronic hepatitis B Patients

“…19 In this study, we demonstrated that TRIM26 inhibited the replication of HBV, this was verified by the decrease of HBsAg, HBcAg, HBV total RNA and HBV methyltransferase activity and the enhancement of cccDNA transcriptional activity. 39 HBx promotes the transcription of cccDNA by recruiting DDB1 and promoting SMC5/6 to ubiquitin-mediated degradation, 9 whereas siRNA drugs and PegIFNα can reverse this process. 32 In addition, HBx-mediated degradation of SMC5/6 also has an impact on the process of the repair of host DNA doublestrand breaks, so as to promote tumorigenesis.…”

“…As an encoding product of cccDNA, HBx has been demonstrated to inhibit the transcription of cccDNA in a large number of studies. Yuan et al found that HBx recruits WDR77 to degrade by binding with E3 ubiquitin ligase DDB1, resulting in the loss of PRMT5 methyltransferase activity and the enhancement of cccDNA transcriptional activity 39 . HBx promotes the transcription of cccDNA by recruiting DDB1 and promoting SMC5/6 to ubiquitin‐mediated degradation, 9 whereas siRNA drugs and PegIFNα can reverse this process 32 .…”

Hepatitis B virus X protein promotes epithelial-mesenchymal transition of hepatocellular carcinoma cells by regulating SOCS1

“…Among HBV proteins, HBV X protein (HBx) plays a major role in the development and pathogenesis of HCC ( 5 ). HBx is a multifunctional regulatory protein essential for viral replication that requires various host cellular components ( 6 , 7 ). HBx is also a promiscuous protein involved in cell cycle regulation, transactivation of genes related to cell growth, oncogenic transformation, and metastasis.…”