Abstract
Sodium taurocholate cotransporting polypeptide (NTCP) is expressed at the surface of human hepatocytes and functions as an entry receptor of hepatitis B virus (HBV). Recently, we have reported that epidermal growth factor receptor (EGFR) is involved in NTCP-mediated viral internalization during the cell entry process. Here, we analyzed which function of EGFR is essential for mediating HBV internalization. In contrast to the reported crucial function of EGFR-downstream signaling for the entry of hepatitis C virus (HCV), blockade of EGFR-downstream signaling proteins, including mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K), and signal transducer and activator of transcription (STAT), had no or only minor effects on HBV infection. Instead, deficiency of EGFR endocytosis resulting from either a deleterious mutation in EGFR or genetic knockdown of endocytosis adaptor molecules abrogated internalization of HBV via NTCP and prevented viral infection. EGFR activation triggered a time-dependent relocalization of HBV preS1 to the early and late endosomes and to lysosomes in concert with EGFR transport. Suppression of EGFR ubiquitination by site-directed mutagenesis or by knocking down two EGFR-sorting molecules, signal-transducing adaptor molecule (STAM) and lysosomal protein transmembrane 4β (LAPTM4B), suggested that EGFR transport to the late endosome is critical for efficient HBV infection. Cumulatively, these results support the idea that the EGFR endocytosis/sorting machinery drives the translocation of NTCP-bound HBV from the cell surface to the endosomal network, which eventually enables productive viral infection.
Highlights
Sodium taurocholate cotransporting polypeptide (NTCP) is expressed at the surface of human hepatocytes and functions as an entry receptor of hepatitis B virus (HBV)
These results suggest that epidermal growth factor receptor (EGFR) activation supports HBV infection
We examined the significance of these signaling pathways in the infection of HBV as well as hepatitis C virus (HCV) as a reference: EGFR has been reported to facilitate HCV entry through activation of Ras and phosphoinositide 3-kinase (PI3K)-Akt [12, 13]
Summary
Suppression of EGFR ubiquitination by site-directed mutagenesis or by knocking down two EGFR-sorting molecules, signal-transducing adaptor molecule (STAM) and lysosomal protein transmembrane 4 (LAPTM4B), suggested that EGFR transport to the late endosome is critical for efficient HBV infection These results support the idea that the EGFR endocytosis/sorting machinery drives the translocation of NTCP-bound HBV from the cell surface to the endosomal network, which eventually enables productive viral infection. EGFR has been reported to play a pivotal role in the entry mechanism of different classes of viruses, such as human cytomegalovirus, hepatitis C virus (HCV), and respiratory syncytial virus [7] In such cases, virus entry essentially requires EGFR-triggered activation of the downstream signaling, including that leading to actin rearrangement necessary to the migration of internalized viral particles to the site of replication (see “Discussion”). We analyze the function of EGFR that essentially regulates the NTCP-mediated viral entry
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