The E3 Ubiquitin Ligase SIAH1 Targets MyD88 for Proteasomal Degradation During Dengue Virus Infection

Abstract

The dengue virus presents a serious threat to human health globally and can cause severe, even life-threatening, illness. Dengue virus (DENV) is endemic on all continents except Antarctica, and it is estimated that more than 100 million people are infected each year. Herein, we further mine the data from a previously described screen for microRNAs (miRNAs) that block flavivirus replication. We use miR-424, a member of the miR-15/16 family, as a tool to further dissect the role of host cell proteins during DENV infection. We observed that miR-424 suppresses expression of the E3 ubiquitin ligase SIAH1, which is normally induced during dengue virus 2 (DENV2) infection through activation of the unfolded protein response (UPR). Specific siRNA-mediated knockdown of SIAH1 also results in inhibition of DENV replication, demonstrating that this target is at least partly responsible for the antiviral activity of miR-424. We further show that SIAH1 binds to and ubiquitinates the innate immune adaptor protein MyD88 and that the antiviral effect of SIAH1 knockdown is reduced in cells in which MyD88 has been deleted by CRISPR/Cas9 gene editing. Additionally, MyD88-dependent signaling, triggered either by DENV2 infection or the Toll-like receptor 7 (TLR7) ligand imiquimod, is increased in cells in which SIAH1 has been knocked down by miR-424 or a SIAH1specific siRNA. These observations suggest an additional pathway by which DENV2 harnesses aspects of the UPR to dampen the host innate immune response and promote viral replication.

Immunity and Viral Infections: Modulating Antiviral Response via CRISPR–Cas Systems

“…The transient knockdown of SIAH1 reconstitutes high-level IFN response and decreases DENV replication. However, CRISPR-mediated knockout of MyD88 abrogates anti-DENV IFN response and results in an increase in DENV replication [ 219 ].…”

microRNAs, the Link Between Dengue Virus and the Host Genome

“…Another study found that miR-424 inhibits expression of E3 ubiquitin ligase SIAH1 by activating unfolded protein response (UPR) during the infection of HeLa cells by DENV-2 ( Murphy Schafer et al, 2020 ). The downregulation of SIAH1 can inhibit the replication of DENV, which indicates that this target plays a role in the antiviral activity of miR-424, at least to a certain extent ( Murphy Schafer et al, 2020 ). SIAH1 binds to MyD88, an important transducing protein in the TLR signaling pathway, and ubiquitinates it.…”

“…SIAH1 binds to MyD88, an important transducing protein in the TLR signaling pathway, and ubiquitinates it. Moreover, the antiviral effect of SIAH1 is reduced in cells from which MyD88 has been deleted by CRISPR/Cas9 gene editing ( Murphy Schafer et al, 2020 ). In addition, in cells in which SIAH1 has been downregulated by miR-424 or siRNA knockout by SIAH1, the MyD88-mediated NF-kB signaling pathway is enhanced by DENV-2 infection or by imiquimod, a TLR7 ligand ( Murphy Schafer et al, 2020 ; Figure 2 ).…”

“…Moreover, the antiviral effect of SIAH1 is reduced in cells from which MyD88 has been deleted by CRISPR/Cas9 gene editing ( Murphy Schafer et al, 2020 ). In addition, in cells in which SIAH1 has been downregulated by miR-424 or siRNA knockout by SIAH1, the MyD88-mediated NF-kB signaling pathway is enhanced by DENV-2 infection or by imiquimod, a TLR7 ligand ( Murphy Schafer et al, 2020 ; Figure 2 ). This study indicates that the target SIAH1 plays an important role in the antiviral activity of miR-424 to some extent and hints us that an additional pathway by which DENV2 harnesses aspects of the UPR to dampen the host innate immune response and promote viral replication.…”

Recent Insights Into the Molecular Mechanism of Toll-Like Receptor Response to Dengue Virus Infection

“… Carvalho et al (2014) showed that higher NS1 levels in serum may induce a reduced TLR4 response to LPS. Recently, Murphy Schafer et al (2020) introduced an additional mechanism of TLR signaling disruption by DENV-2. DENV-2 infection induces SIAH1 expression, resulting in SIAH1 binding and ubiquitination of MyD88, an adaptor protein of TLR signaling, thereby dampening the host innate immune response and promoting viral replication.…”