Endoplasmic Reticulum Protein SCAP Inhibits Dengue Virus NS2B3 Protease by Suppressing Its K27-Linked Polyubiquitylation

Abstract

Dengue viruses (DENVs) are an emerging threat to global public health. The NS2B3 protease complex of DENV has recently been shown to cleave the antiviral protein STING and thereby subvert the innate immune signaling to facilitate virus replication. Whether host cells have a mechanism to counteract this virus-mediated immunosuppression is unclear. We discovered that the K27-linked polyubiquitination of NS3 protein facilitates its recruitment of NS2B, the formation of NS2B3, and consequently the enhanced cleavage of STING. However, an endoplasmic reticulum (ER) protein, SCAP, through binding to NS2B protein, inhibits the ubiquitination of NS3, rendering NS2B3 protease incapable of binding and cleaving STING. Importantly, ectopic expression of SCAP impaired DENV infection, whereas silencing of SCAP potentiated DENV infection. Collectively, this study uncovered a novel function of SCAP of counteracting the inhibitory action of DENV NS2B3 protease on STING signaling, suggesting that modulation of SCAP levels may have therapeutic implications. IMPORTANCE This study reports the first ubiquitylation target protein in DENV, the NS3 protein, and the unique role of K27-linked polyubiquitylation in NS3's ability to recruit NS2B and formation of the NS2B3 protease complex. Additionally, this study identified novel functions of the ER protein SCAP: one is to compete with NS2B for binding to STING, and the other is to inhibit the ubiquitination of NS3. Both of these functions protect STING from being cleaved by the NS2B3 protease and thus contribute to host antiviral response.

Species-specific disruption of STING-dependent antiviral cellular defenses by the Zika virus NS2B3 protease

“…Here, we provide direct evidence that ZIKV also targets the cGAS/STING pathway by cleaving STING, impairing the cells' ability to induce ISGs in response to cGAMP, but not poly(I:C), stimulation. Proteolytic inactivation of STING appears to be a general mechanism shared by several other flaviviruses, including JEV, DENV (38)(39)(40)54), and WNV, but not live-attenuated or virulent YFV. We found that the residues R78 and G79, located within the cytoplasmic loop of STING, are critical determinants for NS2B3-mediated cleavage.…”

TRIM21 Promotes Innate Immune Response to RNA Viral Infection through Lys27-Linked Polyubiquitination of MAVS

“…For example, upon DNA virus infection, K27-linked polyubiquitination of cGAS and STING can restrict the replication of viruses (54,55). In contrast, K27-linked polyubiquitination of dengue virus NS3 protein enhances the cleavage of STING by the NS2B3 protease complex, promoting viral replication (71).…”

RNA‐virus proteases counteracting host innate immunity

“…Recently, Liu et al . reported that the full‐length DENV NS3 (including the C‐terminal helicase), but not the NS2B, can be modified by Lys27‐linked polyubiquitination when co‐transfecting Ub and NS3 in HEK 293T cells. The ubiquitinated NS3 facilitates recruitment of NS2B, that is, the formation of the NS2B/NS3 protease, thereby enhancing the cleavage of STING.…”

“…The ubiquitinated NS3 facilitates recruitment of NS2B, that is, the formation of the NS2B/NS3 protease, thereby enhancing the cleavage of STING. Furthermore, these authors found that the ER protein SCAP (sterol regulatory element‐binding protein (SREBP) cleavage‐activating protein) can bind NS2B and inhibit polyubiquitination of NS3, thus disrupting the formation of NS2B/NS3 pro and the cleavage of STING .…”