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HSCARG downregulates NF-?B signaling by interacting with USP7 and inhibiting NEMO ubiquitination.

ABSTRACT: Nuclear factor ?B (NF-?B) signaling is a central pathway that participates in a variety of key processes, including immunity, inflammation, cell growth and differentiation. The activity of NF-?B is strictly regulated by a cluster of proteins, and modifications of these proteins either promote or suppress signal transduction at various steps. Here we demonstrated that HSCARG suppresses TNF?-stimulated NF-?B signaling under physiological conditions. We elucidated the detailed mechanism through which HSCARG inhibits NF-?B activation. HSCARG interacts with NEMO and suppresses polyubiquitination of NEMO by interacting with the deubiquitinase USP7. HSACRG attenuates its inhibitory effect on NEMO ubiquitination in USP7 knockdown cells, and inhibition of NEMO polyubiquitination by USP7 is impaired in HSCARG(-/-) cells as well. Moreover, we demonstrated that USP7 is a negative regulator of TNF?-stimulated NF-?B activity. Altogether, our data indicate that HSCARG and USP7 function in concert in inhibiting polyubiquination of NEMO, thus inhibiting NF-?B activity.

SUBMITTER: Li T

PROVIDER: S-EPMC4047896 | biostudies-other | 2014 May

REPOSITORIES: biostudies-other

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HSCARG downregulates NF-κB signaling by interacting with USP7 and inhibiting NEMO ubiquitination.

Li T T Guan J J Li S S Zhang X X Zheng X X

Cell death & disease 20140515

Nuclear factor κB (NF-κB) signaling is a central pathway that participates in a variety of key processes, including immunity, inflammation, cell growth and differentiation. The activity of NF-κB is strictly regulated by a cluster of proteins, and modifications of these proteins either promote or suppress signal transduction at various steps. Here we demonstrated that HSCARG suppresses TNFα-stimulated NF-κB signaling under physiological conditions. We elucidated the detailed mechanism through whi ...[more]

PMID: 24832601

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Project description:Viruses have adopted diverse strategies to suppress antiviral responses. Hepatitis B virus (HBV), a virus that is prevalent worldwide, manipulates the host's innate immune system to evade scavenging. It is reported that the hepatitis B e antigen (HBeAg) can interfere with NF-?B activity, which then leads to high viral loads, while HBV with the G1896A mutation remains infectious without the production of HBeAg but can induce more severe proinflammatory response and liver damage. The aim of current work was to study the molecular mechanism by which HBeAg suppresses interleukin-1? (IL-1?)-stimulated NF-?B activity, which leads to the suppression of the innate immune responses to HBV infection. Our study revealed that HBeAg could interact with NEMO, a regulatory subunit associated with I?B kinase, which regulates the activation of NF-?B. HBeAg suppressed the IL-1?-induced tumor necrosis factor (TNF)-associated factor 6 (TRAF6)-dependent K63-linked ubiquitination of NEMO, thereby downregulating NF-?B activity and promoting virus replication. We further demonstrated the inhibitory effect of HBeAg on the NF-?B signaling pathway using primary human hepatocytes, HBV-infected HepG2-NTCP cells, and clinical liver samples. Our study reveals a molecular mechanism whereby HBeAg suppresses IL-1?-induced NF-?B activation by decreasing the TRAF6-dependent K63-linked ubiquitination of NEMO, which may thereby enhance HBV replication and promote a persistent infection.IMPORTANCE The role of HBeAg in inflammatory responses during the infection of hepatitis B virus (HBV) is not fully understood, and several previous reports with regard to the NF-?B pathway are controversial. In this study, we showed that HBeAg could suppress both Toll-like receptor 2 (TLR2)- and IL-1?-induced activation of NF-?B in cells and clinical samples, and we further revealed novel molecular mechanisms. We found that HBeAg can associate with NEMO, the regulatory subunit for I?B kinase (IKK) that controls the NF-?B signaling pathway, and thereby inhibits TRAF6-mediated K63-linked ubiquitination of NEMO, resulting in downregulation of NF-?B activity and promotion of virus replication. In contrast, the HBeAg-negative HBV mutant can induce higher levels of NF-?B activity. These results are important for understanding the HBV-induced pathogenesis of chronic hepatitis and indicate that different clinical measures should be considered to treat HBeAg-positive and HBeAg-negative infections. Our findings represent a conceptual advance in HBV-related suppression of NF-?B signaling.

Project description:BackgroundUTP-glucose-1-phosphoryl transferase (UGPase) catalyzes the synthesis of UDP-glucose, which is essential for generating the glycogen needed for the synthesis of bacterial lipopolysaccharide (LPS) and capsular polysaccharide, which play important roles in bacterial virulence. However, the molecular function of UGPase in Brucella is still unknown.ResultsIn this study, the ubiquitination modification of host immune-related protein in cells infected with UGPase-deleted or wild-type Brucella was analyzed using ubiquitination proteomics technology. The ubiquitination modification level and type of NF-κB Essential Modulator (NEMO or Ikbkg), a molecule necessary for NF-κB signal activation, was evaluated using Coimmunoprecipitation, Western blot, and dual-Luciferase Assay. We found 80 ubiquitin proteins were upregulated and 203 ubiquitin proteins were downregulated in cells infected with B. melitensis 16 M compared with those of B. melitensis UGPase-deleted strain (16 M-UGPase-). Moreover, the ubiquitin-modified proteins were mostly enriched in the categories of regulation of kinase/NF-κB signaling and response to a bacterium, suggesting Brucella UGPase inhibits ubiquitin modification of related proteins in the host NF-κB signaling pathway. Further analysis showed that the ubiquitination levels of NEMO K63 (K63-Ub) and Met1 (Met1-Ub) were significantly increased in the 16 M-UGPase--infected cells compared with that of the 16 M-infected cells, further confirming that the ubiquitination levels of NF-κB signaling-related proteins were regulated by the bacterial UGPase. Besides, the expression level of IκBα was decreased, but the level of p-P65 was significantly increased in the 16 M-UGPase--infected cells compared with that of the 16 M- and mock-infected cells, demonstrating that B. melitensis UGPase can significantly inhibit the degradation of IκBα and the phosphorylation of p65, and thus suppressing the NF-κB pathway.ConclusionsThe results of this study showed that Brucella melitensis UGPase inhibits the activation of NF-κB by modulating the ubiquitination of NEMO, which will provide a new scientific basis for the study of immune mechanisms induced by Brucella.

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HSCARG downregulates NF-?B signaling by interacting with USP7 and inhibiting NEMO ubiquitination.

Publications

HSCARG downregulates NF-κB signaling by interacting with USP7 and inhibiting NEMO ubiquitination.

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