NEDD4 Induces K48-Linked Degradative Ubiquitination of Hepatitis B Virus X Protein and Inhibits HBV-Associated HCC Progression

Abstract

Neural precursor cell expressed developmentally downregulated gene 4 (NEDD4) plays two opposite roles in carcinogenesis. It has been reported that NEDD4 inhibits hepatocellular carcinoma (HCC) progression; however, little is known about its potential function and molecular mechanism in HCC in the context of hepatitis B virus (HBV) infection. In this study, we analyzed NEDD4 expression in 199 HCC specimens with or without HBV infection and observed that NEDD4 expression was unrelated to HBV exposure in HCC tumor tissue but that high NEDD4 expression conferred better overall survival (OS) and progression-free survival (PFS) than low NEDD4 expression in patients with HBV-associated HCC. Upregulation of NEDD4 inhibited proliferation, migration and invasion in HBV-related HCC cell lines. We demonstrated that NEDD4 interacts with HBV X protein (HBx) and that HBx upregulation could reverse the suppression of proliferation and mobility induced by NEDD4 overexpression. Furthermore, we confirmed that NEDD4 induced the degradation of HBx in a ubiquitin/proteasome-dependent manner via K48-linked ubiquitination. Our findings suggest that NEDD4 exerts a tumor-suppressive effect in HBV-associated HCC by acting as an E3 ubiquitin ligase for HBx degradation and provide new insights into the function of NEDD4.

Cathepsin K promotes the proliferation of hepatocellular carcinoma cells through induction of SIAH1 ubiquitination and degradation

“…For example, NEDD4 can promote the growth and motility of HCC cells by regulating large tumor suppressor gene 1 (LATS1) and phosphate and tension homology deleted on chromosome ten (PTEN)/PI3K/AKT 7 , 28 , 29 ; NEDD4 induces degradative ubiquitination of the hepatitis B virus X protein and inhibits HBV-associated HCC progression. 30 In the present study, we found that NEDD4 and SIAH1 form a complex and that NEDD4 might induce the degradative ubiquitination of SIAH1. We verified that CTSK could also form complexes with NEDD4.…”

RBCK1 promotes the stabilization of HBx by linear ubiquitination to drive the progression of HBV-associated hepatocellular carcinoma

“…5C, D). Furthermore, using ubiquitination assays, we noticed that RBCK1-knockdown increased K48-linked ubiquitination of HBx, which has been reported to mediate the proteasomal degradation of HBx [12,23], but decreased the M1-Ubi (Fig. 5E), which may mediate the stability of HBx.…”

“…The versatile UPS components, in turn, regulated the stability of HBx via direct or indirect mechanisms [11]. HBx is an unstable protein that is ubiquitinated and rapidly degraded by the proteasome pathway to maintain a very low intracellular level [12,13]. Clinical reports have presented HBx as a possible diagnostic marker by demonstrating its expression in 40% of sera and 85% of liver tissue samples from patients with HCC [14].…”

Deubiquitinase OTUD5 Promotes Hepatitis B Virus Replication by Removing K48-linked Ubiquitination of HBV core/precore and Up-regulating HNF4ɑ Expressions through Inhibiting the ERK1/2 /Mitogen-activated Protein Kinase Pathway

“…4). Posttranslational regulation of hepatitis B virus structural proteins had been an important cellular process during HBV infection, for example, TRIM21 inhibited HBV replication through ubiquitin-mediated proteasomal degradation of HBx 28 , NEDD4 prohibited HBV infection by mediating K48-linked degradation of HBx and inhibits HBV-associated HCC 29 . In addition, deubiquitinating enzyme VCPIP1 binds to HBx protein and promotes stabilization of HBx in a ubiquitin-independent manner by recruiting the PSMC3 in vivo 30 .…”