PRMT5 protein arginine methyltransferase activates Hepatitis B Virus transcription

Abstract

Hepatitis B virus (HBV) chronically infects more than 240 million people worldwide and is a major cause of severe liver diseases including hepatocellular carcinoma. One rate-limiting step in HBV replication is the transcription of pregenomic RNA (pgRNA) from cccDNA. Elucidating the regulatory mechanisms of HBV transcription might reveal new strategies for intervention. PRMT5 is a type II protein arginine methyltransferase, which symmetrically dimethylates histone and nonhistone arginines to regulate various cellular processes. In this study, we defined a positive regulatory role of PRMT5 in HBV transcription. PRMT5 transcript and protein were upregulated in HBV-infected hepatic cells and tissues. The steady-state levels of pgRNA, cccDNA and secreted HBsAg in HBV-infected HepG2-NTCP cells were elevated when PRMT5 was overexpressed, and the opposite trend was observed when PRMT5 was compromised. On one hand, PRMT5 stimulated the activity of HBV preS2/S promoter by promoting the recruitment of CREB and CRTC1 to cccDNA as a result of symmetric dimethylation of arginines in CRTC1 but not CREB. PRMT5 also interacted with HBx and they are mutually stabilized leading to the activation of HBV transcription. On the other hand, PRMT5 was also found to affect the recruitment of symmetrically dimethylated histones such as H3R2me2 and H3R8me2 to cccDNA resulting in epigenetic activation of HBV gene expression. Thus, PRMT5 targets both histone and non-histone arginines in its activation of HBV transcription. Specific PRMT5 inhibitors such as EPZ015666 effectively suppressed the production of pgRNA, cccDNA and secreted HBsAg in HBV-infected HepG2-NTCP cells. Taken together, our findings revealed not only a new function of PRMT5 as a positive regulator of HBV transcription but also a new strategy for anti-HBV therapy through pharmaceutical activation of PRMT5. Supported by Hong Kong Health and Medical Research Fund (13121052 and 14131162), Hong Kong Research Grants Council (HKU1/CRF/11G and T11-707/15-R), Hong Kong Scholars Program and S.K. Yee Medical Research Fund (2011).