Tripartite Motif-Containing Protein 65 (TRIM65) Inhibits Hepatitis B Virus Transcription.

Tripartite motif (TRIM) proteins, comprising a family of over 100 members with conserved motifs, exhibit diverse biological functions. Several TRIM proteins influence viral infections through direct antiviral mechanisms or by regulating host antiviral innate immune responses. To identify TRIM proteins modulating hepatitis B virus (HBV) replication, we assessed 45 human TRIMs in HBV-transfected HepG2 cells. Our study revealed that ectopic expression of 12 TRIM proteins significantly reduced HBV RNA and subsequent capsid-associated DNA levels. Notably, TRIM65 uniquely downregulated viral pregenomic (pg) RNA in an HBV-promoter-specific manner, suggesting a targeted antiviral effect. Mechanistically, TRIM65 inhibited HBV replication primarily at the transcriptional level via its E3 ubiquitin ligase activity and intact B-box domain. Though HNF4α emerged as a potential TRIM65 substrate, disrupting its binding site on the HBV genome did not completely abolish TRIM65's antiviral effect. In addition, neither HBx expression nor cellular MAVS signaling was essential to TRIM65-mediated regulation of HBV transcription. Furthermore, CRISPR-mediated knock-out of TRIM65 in the HepG2-NTCP cells boosted HBV infection, validating its endogenous role. These findings underscore TRIM proteins' capacity to inhibit HBV transcription and highlight TRIM65's pivotal role in this process.