Hepatitis B virus Core protein nuclear interactome identifies SRSF10 as a host RNA-binding protein restricting HBV RNA production

Abstract

Despite the existence of a preventive vaccine, chronic infection with Hepatitis B virus (HBV) affects more than 250 million people and represents a major global cause of hepatocellular carcinoma (HCC) worldwide. Current clinical treatments, in most of cases, do not eliminate viral genome that persists as a DNA episome in the nucleus of hepatocytes and constitutes a stable template for the continuous expression of viral genes. Several studies suggest that, among viral factors, the HBV core protein (HBc), well-known for its structural role in the cytoplasm, could have critical regulatory functions in the nucleus of infected hepatocytes. To elucidate these functions, we performed a proteomic analysis of HBc-interacting host-factors in the nucleus of differentiated HepaRG, a surrogate model of human hepatocytes. The HBc interactome was found to consist primarily of RNA-binding proteins (RBPs), which are involved in various aspects of mRNA metabolism. Among them, we focused our studies on SRSF10, a RBP that was previously shown to regulate alternative splicing (AS) in a phosphorylation-dependent manner and to control stress and DNA damage responses, as well as viral replication. Functional studies combining SRSF10 knockdown and a pharmacological inhibitor of SRSF10 phosphorylation (1C8) showed that SRSF10 behaves as a restriction factor that regulates HBV RNAs levels and that its dephosphorylated form is likely responsible for the anti-viral effect. Surprisingly, neither SRSF10 knock-down nor 1C8 treatment modified the splicing of HBV RNAs but rather modulated the level of nascent HBV RNA. Altogether, our work suggests that in the nucleus of infected cells HBc interacts with multiple RBPs that regulate viral RNA metabolism. Our identification of SRSF10 as a new anti-HBV restriction factor offers new perspectives for the development of new host-targeted antiviral strategies.

HBV Core Protein Is in Flux between Cytoplasmic, Nuclear, and Nucleolar Compartments

“…Cp has notably strong interaction with SR protein kinases (which have nuclear and cytoplasmic localization) ( 52 – 54 ). A recent examination of the nuclear RNA-dependent interactome of HBV Cp found a statistically significant number of interactions with ribosomal proteins (enriched in the nucleolus) and spliceosomal proteins (enriched in nuclear speckles) ( 55 ). The biological relevance of Cp nucleolar localization and interactions with resident proteins needs to be addressed.…”

Systematic Analysis Identifies a Specific RNA-Binding Protein-Related Gene Model for Prognostication and Risk-Adjustment in HBV-Related Hepatocellular Carcinoma

“…Because of the high risk of recurrence and metastasis, the 5-year survival probabilities of advanced HCC are still undesirable. The epidemiology of HCC is affected by underlying liver diseases especially hepatitis B virus (HBV) ( Chabrolles et al, 2020 ). It has been estimated that HBV infection is responsible for 50% of HCC worldwide ( Li et al, 2019 ).…”

“…Over 1,500 human RBPs have been discovered, which possess 600 structure-specific RNA-binding domains ( Schneider et al, 2019 ). Most of them are characterized by evolutionary conservatism and ubiquitous expression to maintain cellular homeostasis ( Chabrolles et al, 2020 ). Genetic and proteomic data highlight that alterations in RBP expression display profound implications on HCC ( Lin et al, 2019 ).…”

Interplay Between CMGC Kinases Targeting SR Proteins and Viral Replication: Splicing and Beyond

“…Besides being involved in nucleocapsid formation in the cytoplasm, the HBV Core protein is also abundantly present in the nucleus of infected hepatocytes where it may regulate viral gene expression ( Akiba et al, 1987 ; Zhang et al, 2016 ). A recent proteomic analysis indicated that the nuclear interactome of Core was mainly composed by cellular RBPs and in particular by SR proteins, one of which, SRSF10 displays an antiviral activity ( Chabrolles et al, 2020 ). Unexpectedly, however, depleting SRSF10 or provoking its dephosphorylation does not affect HBV RNA splicing but rather modulates the level of nascent HBV RNA.…”