1-Formyl-β-carboline Derivatives Block Newcastle Disease Virus Proliferation through Suppressing Viral Adsorption and Entry Processes

The multifaceted interactions between Newcastle disease virus proteins and host proteins: a systematic review

Newcastle disease virus (NDV) typically induces severe illness in poultry and results in significant economic losses for the worldwide poultry sector. NDV, an RNA virus with a single-stranded negative-sense genome, is susceptible to mutation and immune evasion during viral transmission, thus imposing enormous challenges to avian health and poultry production. NDV is composed of six structural proteins and two nonstructural proteins that exert pivotal roles in viral infection and antiviral responses by interacting with host proteins. Nowadays, there is a particular focus on the mechanisms of virus-host protein interactions in NDV research, yet a comprehensive overview of such research is still lacking. Herein, we briefly summarize the mechanisms regarding the effects of virus-host protein interaction on viral infection, pathogenesis, and host immune responses. This review can not only enhance the present comprehension of the mechanism underlying NDV and host interplay, but also furnish a point of reference for the advancement of antiviral measures.

Entry of Newcastle disease virus into host cells: an interplay among viral and host factors

Newcastle disease (ND) is a major burden for the poultry industry worldwide, especially in developing countries. The virus that causes this disease, Newcastle disease virus (NDV), is also an effective vector for the development of novel human and animal vaccines and a promising oncolytic virus for cancer therapy. The mechanism of entry of NDV into host cells is of particular interest because it has a significant impact on the infectivity, host range, and pathogenicity of the virus. Here, we present an overview of the entry of NDV into cells, focusing on the interplay among viral and host factors involved in this process. In particular, recent research revealing novel features of NDV attachment to cells, the identification of viral and cellular components that regulate binding of the virus to cells, and the emerging role of novel cellular routes of NDV entry are discussed. More importantly, some of the remaining gaps in our understanding of NDV entry and some fundamental questions for research efforts in the future are also highlighted.

Canthin-6-one analogs block Newcastle disease virus proliferation via suppressing the Akt and ERK pathways

Newcastle disease virus, a member of the Paramyxoviridae family, causes significant economic losses in poultry worldwide. To identify novel antiviral agents against NDV, 36 canthin-6-one analogs were evaluated in this study. Our data showed that 8 compounds exhibited excellent inhibitory effects on NDV replication with IC50 values in the range of 5.26 to 11.76 μM. Besides, these analogs inhibited multiple NDV strains with IC50 values within 12 μM and exerted antiviral activity against peste des petits ruminants virus (PPRV) and canine distemper virus (CDV). Among these analogs, 16 presented the strongest anti-NDV activity (IC50 = 5.26 μM) and minimum cytotoxicity (CC50 > 200 μM) in DF-1 cells. Furthermore, 16 displayed antiviral activity in different cell lines. Our results showed that 16 did not affect the viral adsorption while it can inhibit the entry of NDV by suppressing the Akt pathway. Further study found that 16-treatment inhibited the NDV-activated ERK pathway, thereby promoting the expression of interferon-related genes. Our findings reveal an antiviral mechanism of canthin-6-one analogs through inhibition of the Akt and ERK signaling pathways. These results point to the potential value of canthin-6-one analogs to serve as candidate antiviral agents for NDV.

3-Amide-β-carbolines block the cell cycle by targeting CDK2 and DNA in tumor cells potentially as anti-mitotic agents

β-Carboline alkaloids are natural and synthetic products with outstanding antitumor activity. C3 substituted and dimerized β-carbolines exert excellent antitumor activity. In the present research, 37 β-carboline derivatives were synthesized and characterized. Their cytotoxicity, cell cycle, apoptosis, and CDK2- and DNA-binding affinity were evaluated. β-Carboline monomer M3 and dimer D4 showed selective activity and higher cytotoxicity in tumor cells than in normal cells. Structure-activity relationships (SAR) indicated that the amide group at C3 enhanced the antitumor activity. M3 blocked the A549 (IC50 = 1.44 ± 1.10 μM) cell cycle in the S phase and inhibited A549 cell migration, while D4 blocked the HepG2 (IC50 = 2.84 ± 0.73 μM) cell cycle in the G0/G1 phase, both of which ultimately induced apoptosis. Furthermore, associations of M3 and D4 with CDK2 and DNA were proven by network pharmacology analysis, molecular docking, and western blotting. The expression level of CDK2 was downregulated in M3-treated A549 cells and D4-treated HepG2 cells. Moreover, M3 and D4 interact with DNA and CDK2 at sub-micromolar concentrations in endothermic interactions caused by entropy-driven adsorption processes, which means that the favorable entropy change (ΔS > 0) overcomes the unfavorable enthalpy change (ΔH > 0) and drives the spontaneous reaction (ΔG < 0). Overall, these results clarified the antitumor mechanisms of M3 and D4 through disrupting the cell cycle by binding DNA and CDK2, which demonstrated the potential of M3 and D4 as novel antiproliferative drugs targeting mitosis.

Newcastle disease virus activates the PI3K/AKT signaling pathway by targeting PHLPP2 degradation to delay cell apoptosis and promote viral replication

Newcastle disease (ND) is a highly pathogenic, contagious, and fatal infectious disease in poultry caused by the Newcastle disease virus (NDV). The PI3K/AKT signaling pathway is a phosphorylation cascade that participates in regulating several cellular functions. Viruses reportedly regulate the course of infection through the PI3K/AKT axis. Here, we aimed to analyze the pathogenesis of NDV infection mediated by the PI3K/AKT signaling pathway activation. We found that NDV infection can phosphorylate AKT to activate the PI3K/AKT axis both in vitro and in vivo. Flow cytometry and Caspase-3 activity assay showed that NDV infection could inhibit cell apoptosis. The activation or inhibition of the PI3K/AKT signaling pathway activity significantly inhibited or promoted NDV-mediated apoptosis. Furthermore, inhibition of cell apoptosis significantly promoted NDV replication. Overall, our results showed that NDV infection activates the PI3K/AKT signaling pathway and inhibits cell apoptosis, thus promoting viral replication. In this context, the reduced expression of PHLPP2 protein mediated by NDV infection could be inhibited by MG132. PHLPP2 expression reversely and positively regulated NDV replication and cell apoptosis, respectively. These results indicated that NDV infection-mediated activation of the PI3K/AKT signaling pathway and the inhibition of apoptosis depend on the ubiquitin-proteasome degradation of the PHLPP2 protein. Co-IP and indirect immunofluorescence results showed that NDV V protein could interact with PHLPP2 protein, indicating that NDV targeted PHLPP2 protein degradation through V protein to activate the PI3K/AKT signaling pathway. This study deepens our understanding of the molecular mechanisms of NDV infection, providing a theoretical basis for ND prevention and control.

Direct interaction of the molecular chaperone GRP78/BiP with the Newcastle disease virus hemagglutinin-neuraminidase protein plays a vital role in viral attachment to and infection of culture cells

Introduction

Glucose Regulated Proteins/Binding protein (GRP78/Bip), a representative molecular chaperone, effectively influences and actively participates in the replication processes of many viruses. Little is known, however, about the functional involvement of GRP78 in the replication of Newcastle disease virus (NDV) and the underlying mechanisms.

Methods

The method of this study are to establish protein interactomes between host cell proteins and the NDV Hemagglutinin-neuraminidase (HN) protein, and to systematically investigate the regulatory role of the GRP78-HN protein interaction during the NDV replication cycle.

Results

Our study revealed that GRP78 is upregulated during NDV infection, and its direct interaction with HN is mediated by the N-terminal 326 amino acid region. Knockdown of GRP78 by small interfering RNAs (siRNAs) significantly suppressed NDV infection and replication. Conversely, overexpression of GRP78 resulted in a significant increase in NDV replication, demonstrating its role as a positive regulator in the NDV replication cycle. We further showed that the direct interaction between GRP78 and HN protein enhanced the attachment of NDV to cells, and masking of GRP78 expressed on the cell surface with specific polyclonal antibodies (pAbs) inhibited NDV attachment and replication.

Discussion

These findings highlight the essential role of GRP78 in the adsorption stage during the NDV infection cycle, and, importantly, identify the critical domain required for GRP78-HN interaction, providing novel insights into the molecular mechanisms involved in NDV replication and infection.

Newcastle disease virus forms inclusion bodies with features of liquid-liquid phase separation

Formation of inclusion bodies (IBs) is a hallmark of infections with negative-strand RNA viruses. Although the Newcastle disease virus (NDV) IBs had been observed in the 1950s, the characteristics of NDV IBs remained largely unknown. Here, we show that NDV infection triggers the formation of IBs that contain newly synthesized viral RNA. The structures of NDV IBs, observed by electron microscopy, were not membrane-bound. Fluorescence recovery after photobleaching a region of NDV IBs occurred rapidly, and IBs were dissolved by 1,6-hexanediol treatment, demonstrating they exhibited properties consistent with liquid-liquid phase separation (LLPS). We find the nucleoprotein (NP) and phosphoprotein (P) are sufficient to generate IB-like puncta, with the N arm domain and N core region of NP and the C terminus of P playing important roles in this process. In summary, our findings suggest that NDV forms IBs containing viral RNA, and provide insights into the formation of NDV IBs.

A bivalent β-carboline derivative inhibits macropinocytosis-dependent entry of pseudorabies virus by targeting the kinase DYRK1A

Pseudorabies virus (PRV) has become a "new life-threatening zoonosis" since the human-originated PRV strain was first isolated in 2020. To identify novel anti-PRV agents, we screened a total of 107 β-carboline derivatives and found 20 compounds displaying antiviral activity against PRV. Among them, 14 compounds showed better antiviral activity than acyclovir. We found that compound 45 exhibited the strongest anti-PRV activity with an IC₅₀ value of less than 40 nM. Our in vivo studies showed that treatment with 45 significantly reduced the viral loads and protected mice challenged with PRV. To clarify the mode of action of 45, we conducted a time of addition assay, an adsorption assay, and an entry assay. Our results indicated that 45 neither had a virucidal effect nor affected viral adsorption while significantly inhibiting PRV entry. Using the FITC-dextran uptake assay, we determined that 45 inhibits macropinocytosis. The actin-dependent plasma membrane protrusion, which is important for macropinocytosis, was also suppressed by 45. Further, the kinase DYRK1A was predicted to be a potential target for 45. The binding of 45 to DYRK1A was confirmed by DARTS and CETSA. Further analysis revealed that knockdown of DYRK1A by siRNA suppressed PRV macropinocytosis and the TNFα-induced formation of protrusions. These results suggested that 45 could restrain PRV macropinocytosis by targeting DYRK1A. Together, these findings reveal a unique mechanism through which β-carboline derivatives restrain PRV infection, pointing to their potential value in the development of anti-PRV agents. Our data also reveal a potential target for designing novel macropinocytosis inhibitors.

9-Butyl-Harmol Exerts Antiviral Activity against Newcastle Disease Virus through Targeting GSK-3β and HSP90β

The paramyxoviruses represent a large family of human and animal pathogens that cause significant health and economic burdens worldwide. However, there are no available drugs against the virus. β-carboline alkaloids are a family of naturally occurring and synthetic products with outstanding antiviral activities. Here, we examined the antiviral effect of a series of β-carboline derivatives against several paramyxoviruses, including Newcastle disease virus (NDV), peste des petits ruminants virus (PPRV), and canine distemper virus (CDV). Among these derivatives, 9-butyl-harmol was identified as an effective antiviral agent against these paramyxoviruses. Further, a genome-wide transcriptome analysis in combination with target validation strategies reveals a unique antiviral mechanism of 9-butyl-harmol through the targeting of GSK-3β and HSP90β. On one hand, NDV infection blocks the Wnt/β-catenin pathway to suppress the host immune response. 9-butyl-harmol targeting GSK-3β dramatically activates the Wnt/β-catenin pathway, which results in the boosting of a robust immune response. On the other hand, NDV proliferation depends on the activity of HSP90. The L protein, but not the NP protein or the P protein, is proven to be a client protein of HSP90β, rather than HSP90α. 9-butyl-harmol targeting HSP90β decreases the stability of the NDV L protein. Our findings identify 9-butyl-harmol as a potential antiviral agent, provide mechanistic insights into the antiviral mechanism of 9-butyl-harmol, and illustrate the role of β-catenin and HSP90 during NDV infection. IMPORTANCE Paramyxoviruses cause devastating impacts on health and the economy worldwide. However, there are no suitable drugs with which to counteract the viruses. We determined that 9-butyl-harmol could serve as a potential antiviral agent against paramyxoviruses. Until now, the antiviral mechanism of β-carboline derivatives against RNA viruses has rarely been studied. Here, we found that 9-butyl-harmol exerts dual mechanisms of antiviral action, with its antiviral activities being mediated by two targets: GSK-3β and HSP90β. Correspondingly, the interaction between NDV infection and the Wnt/β-catenin pathway or HSP90 is demonstrated in this study. Taken together, our findings shed light on the development of antiviral agents against paramyxoviruses, based on the β-carboline scaffold. These results present mechanistic insights into the polypharmacology of 9-butyl-harmol. Understanding this mechanism also deepens the host-virus interaction and reveals new drug targets for anti-paramyxoviruses.

β-Carboline dimers inhibit the tumor proliferation by the cell cycle arrest of sarcoma through intercalating to Cyclin-A2

β-Carbolines are potentially strong alkaloids with a wide range of bioactivities, and their dimers exhibit stronger antitumor activity other than the monomers. However, the detailed mechanisms of the β-carboline dimers in inhibiting sarcoma (SARC) remain unclear. The results showed that β-carboline-3-carboxylic acid dimers Comp1 and Comp2, which were synthesized in our lab and modified at the N⁹ position and linked at the C³ position, exhibited effective inhibition activity on MG-63 proliferation (IC_{50 =} 4.6μM). Meanwhile, the large scale transcriptome profiles of SARC from The Cancer Genome Atlas (TCGA) were analyzed, and found that abnormal expression of genes relevant to apoptosis, cell cycle, and signaling pathways of Hedgehog, HIF, Ras involved in the SARC pathogenesis. Interestingly, both dimers could promote the apoptosis and arrest the cell cycle in S phase to inhibit proliferation of MG-63. Moreover, Comp1 and Comp2 inhibited the expression CDK2, CCNA2, DBF4, and PLK1 associated with various immune cells and cell cycle in MG-63. Remarkably, drug-target interaction network analysis showed that numerous proteins involved in cell cycle were the potential targets of Comp1 and Comp2, especially CCNA2. Further molecular docking, isothermal titration calorimetry (ITC) and Cellular Thermal Shift Assay (CETSA) confirmed that both dimers could directly interact with CCNA2, which is significantly correlated with CD4+ T cells, by strong hydrophobic interactions (K_d=5.821 ×10⁶ N). Meanwhile, the levels of CCNA2 and CDK2 were inhibited to decrease in MG-63 by both dimer treatments at transcription and protein levels, implying that Comp1 and Comp2 blocked the interaction between CCNA2 and CDK2 through competitive binding with CCNA2 to arrest the cell cycle of MG-63 cells in the S phase. Additionally, the transcriptome profiles of β-carboline-treated mice from Gene Expression Omnibus (GEO) were obtained, and found that similar antitumor mechanism was shared among β-carboline derivatives. Overall, our results elucidated the antitumor mechanisms of Comp1 and Comp2 through dual-suppressing the function of CCNA2 to profoundly arrest cell cycle of MG-63, then effectively inhibited cell proliferation of MG-63. These results provide new insights into the antitumor mechanism of β-carboline dimers and new routes of various novel cancer-related drug targets for future possible cancer therapy.

The canonical Wnt/β-catenin signaling pathway facilitates pseudorabies virus proliferation and enhances virus-induced autophagy

Pseudorabies virus (PRV) is a swine herpesvirus with a broad host range that causes significant economic losses worldwide. The Wnt/β-catenin signaling pathway is reportedly involved in multiple viruses' proliferation. In this study, we demonstrated that PRV infection significantly activated the Wnt/β-catenin signaling and promoted the nuclear translocation of β-catenin. Applying specific chemical inhibitors (FH535 and iCRT14) caused a remarkable decrease in PRV titers in various cell lines. Knockdown of β-catenin by siRNA also reduced the proliferation of PRV. On the contrary, treatment with lithium chloride (LiCl), an inhibitor of GSK3β, stimulated the Wnt/β-catenin signaling pathway and enhanced the PRV proliferation. Similarly, overexpression of β-catenin promoted PRV proliferation and reversed the antiviral effect of FH535. Moreover, LiCl promoted PRV-induced autophagy, whereas FH535 and iCRT14 showed converse effects. These findings suggest that PRV infection stimulates the canonical Wnt/β-catenin signaling pathway, facilitating PRV proliferation and regulating virus-induced autophagy. These data also provide potential targets for developing antiviral agents against PRV.