O ‐GlcNAcylation modulates HBV replication through regulating cellular autophagy at multiple levels

Abstract

O-GlcNAcylation is a form of posttranslational modification, and serves various functions, including modulation of location, stability, and activity for the modified proteins. O-linked-N-acetylglucosamine (O-GlcNAc) transferase (OGT) is an essential cellular enzyme that posttranslationally modifies the cellular proteins with O-GlcNAc moiety. Early studies reported that the decreased O-GlcNAcylation regulates cellular autophagy, a process relevant for hepatitis B virus replication (HBV) and assembly. Therefore, we addressed the question how O-GlcNAcylation regulates cellular autophagy and HBV replication. Inhibition of OGT activity with a small molecule inhibitor OSMI-1 or silencing OGT significantly enhanced HBV replication and HBsAg production in hepatoma cells and primary human hepatocytes (PHHs). Western blotting analysis showed that inhibition of O-GlcNAcylation-induced endoplasmic reticulum (ER) stress and cellular autophagy, two processes subsequently leading to enhanced HBV replication. Importantly, the numbers of autophagosomes and the levels of autophagic markers LC3-II and SQSTM1/p62 in hepatoma cells were elevated after inhibition of O-GlcNAcylation. Further analysis revealed that inhibition of O-GlcNAcylation blocked autophagosome-lysosome fusion and thereby prevented autophagic degradation of HBV virions and proteins. Moreover, OSMI-1 further promoted HBV replication by inducing autophagosome formation via inhibiting the O-GlcNAcylation of Akt and mTOR. In conclusion, decreased O-GlcNAcylation enhanced HBV replication through increasing autophagosome formation at multiple levels, including triggering ER-stress, Akt/mTOR inhibition, and blockade of autophagosome-lysosome fusion.

Regulation of O-Linked N-Acetyl Glucosamine Transferase (OGT) through E6 Stimulation of the Ubiquitin Ligase Activity of E6AP

“…Our finding of enhanced OGT ubiquitination and destabilization stimulated by E6 suggests that E6 may take a different role in suppressing OGT activity by pairing with E6AP. E6-stimulated OGT ubiquitination and degradation may help to counteract the antiviral activity of OGT that has been identified as a part of the host defense mechanism against viral infection by hepatitis B virus (HBV), Kaposi’s sarcoma-associated herpesvirus (KSHV), respiratory syncytial virus (RSV), and human immunodeficiency virus (HIV-1) [ 40 , 41 , 42 , 43 , 44 , 45 ]. OGT has been found to enhance the autophagy activity of the host cells through which the HBV viral particles would be degraded, and it can also down-regulate gene expression from the HIV genome inside the host cells [ 41 , 42 , 43 , 44 ].…”

The Mechanisms of HBV-Induced Hepatocellular Carcinoma

“…In chronic infection, HBV can activate autophagy through different pathways, 100 promoting the replication of HBV and the formation and release of virus particles, thus aggravating the disease process. [101][102][103] For example, HBs can activate autophagy by triggering endoplasmic reticulum stress. 104 HBx can enhance autophagy and promote viral replication by binding to PI3KC3 or by activating miR-192-3p-XIAP signaling.…”

Metabolic mediators: How immunometabolism directs the immune response to infection

“…11 They describe an emerging connection between the hexosamine biosynthesis pathway (HBP) and a specific form of post-translational glycosylation termed O-GlcNAcylation. O-GlcNAcylation can alter functional properties of the proteins that it modifies, 12,13 and the pathway particularly targets transcription factors and epigenetic regulators. This review dovetails beautifully with the work presented by Lio and Huang, both describing the multifaceted ways in which cellular metabolism can influence genetic regulation.…”