Identification and Characterization of Multiple TRIM Proteins That Inhibit Hepatitis B Virus Transcription

Shijian Zhang,Jim Z Wu,Guang Yang,Ju-Tao Guo

doi:10.1371/journal.pone.0070001

Shijian Zhang, Jim Z Wu + Show 2 more

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https://doi.org/10.1371/journal.pone.0070001

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Abstract

Tripartite motif (TRIM) proteins constitute a family of over 100 members that share conserved tripartite motifs and exhibit diverse biological functions. Several TRIM proteins have been shown to restrict viral infections and regulate host cellular innate immune responses. In order to identify TRIM proteins that modulate the infection of hepatitis B virus (HBV), we tested 38 human TRIMs for their effects on HBV gene expression, capsid assembly and DNA synthesis in human hepatoma cells (HepG2). The study revealed that ectopic expression of 8 TRIM proteins in HepG2 cells potently reduced the amounts of secreted HBV surface and e antigens as well as intracellular capsid and capsid DNA. Mechanistic analyses further demonstrated that the 8 TRIMs not only reduced the expression of HBV mRNAs, but also inhibited HBV enhancer I and enhancer II activities. Studies focused on TRIM41 revealed that a HBV DNA segment spanning nucleotide 1638 to nucleotide 1763 was essential for TRIM41-mediated inhibition of HBV enhancer II activity and the inhibitory effect depended on the E3 ubiquitin ligase activity of TRIM41 as well as the integrity of TRIM41 C-terminal domain. Moreover, knockdown of endogenous TRIM41 in a HepG2-derived stable cell line significantly increased the level of HBV preC/C RNA, leading to an increase in viral core protein, capsid and capsid DNA. Our studies have thus identified eight TRIM proteins that are able to inhibit HBV transcription and provided strong evidences suggesting the endogenous role of TRIM41 in regulating HBV transcription in human hepatoma cells.

Highlights

Tripartite motif (TRIM) proteins are RING-type E3 ligases
In contradiction to a previous report which showed that TRIM22 inhibited hepatitis B virus (HBV) gene transcription in human hepatoma cells [11], our study did not reveal any significant effect of TRIM22 on HBV protein expression and DNA replication (Fig. 1), which is, consistent with a recent report by Mao and colleagues [30]
Using the HBV genome transiently transfected cell culture system, we identified eight members of TRIM family proteins that significantly reduced all the viral gene products, including viral mRNA, protein, capsid and capsid DNA, upon ectopic expression in HepG2 cells (Figs. 1 and 2)

Summary

Introduction

Tripartite motif (TRIM) proteins are RING-type E3 ligases. These proteins share a conserved N-terminal structure consisting of a RING finger domain, one or two B boxes, a putative coiledcoil domain, and a variable C terminus. Several TRIM proteins are interferon (IFN) inducible and can restrict viral infections [5]. TRIM5a, being one of the most highly implicated TRIM family proteins in cell-intrinsic antiviral immunity, restricts the infection of various retroviruses, such as human immunodeficiency virus 1 (HIV-1) and murine leukemia virus (MLV) [6,7,8]. TRIM56 restricts the infection of bovine viral diarrhea virus via interaction with the viral N-terminal protease [13]. A screen of 55 human and mouse TRIM proteins identified more than 20 TRIMs that inhibited the early or late events of HIV-1 and/or MLV replication cycle [14]

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