Sorting nexin 27 interacts with the Cytohesin associated scaffolding protein (CASP) in lymphocytes

CASP is a small cytokine-inducible protein, primarily expressed in hematopoetic cells, which associates with members of the Cytohesin/ARNO family of guanine nucleotide-exchange factors. Cytohesins activate ARFs, a group of GTPases involved in vesicular initiation. Functionally, CASP is an adaptor protein containing a PDZ domain, a coiled-coil, and a potential carboxy terminal PDZ-binding motif that we sought to characterize here. Using GST pulldowns and mass spectrometry we identified the novel interaction of CASP and sorting nexin 27 (SNX27). In lymphocytes, CASP's PDZ-binding motif interacts with the PDZ domain of SNX27. This protein is a unique member of the sorting nexin family of proteins, a group generally involved in the endocytic and intracellular sorting machinery. Endogenous SNX27 and CASP co-localize at the early endosomal compartment in lymphocytes and also in transfection studies. These results suggest that endosomal SNX27 may recruit CASP to orchestrate intracellular trafficking and/or signaling complexes.     

A presynaptic endosomal trafficking pathway controls synaptic growth signaling

Structural remodeling of synapses in response to growth signals leads to long-lasting alterations in neuronal function in many systems. Synaptic growth factor receptors alter their signaling properties during transit through the endocytic pathway, but the mechanisms controlling cargo traffic between endocytic compartments remain unclear. Nwk (Nervous Wreck) is a presynaptic F-BAR/SH3 protein that regulates synaptic growth signaling in Drosophila melanogaster. In this paper, we show that Nwk acts through a physical interaction with sorting nexin 16 (SNX16). SNX16 promotes synaptic growth signaling by activated bone morphogenic protein receptors, and live imaging in neurons reveals that SNX16-positive early endosomes undergo transient interactions with Nwk-containing recycling endosomes. We identify an alternative signal termination pathway in the absence of Snx16 that is controlled by endosomal sorting complex required for transport (ESCRT)-mediated internalization of receptors into the endosomal lumen. Our results define a presynaptic trafficking pathway mediated by SNX16, NWK, and the ESCRT complex that functions to control synaptic growth signaling at the interface between endosomal compartments.     

An essential role for SNX1 in lysosomal sorting of protease-activated receptor-1: evidence for retromer-, Hrs-, and Tsg101-independent functions of sorting nexins

Sorting nexin 1 (SNX1) and SNX2 are the mammalian homologues of the yeast Vps5p retromer component that functions in endosome-to-Golgi trafficking. SNX1 is also implicated in endosome-to-lysosome sorting of cell surface receptors, although its requirement in this process remains to be determined. To assess SNX1 function in endocytic sorting of protease-activated receptor-1 (PAR1), we used siRNA to deplete HeLa cells of endogenous SNX1 protein. PAR1, a G-protein-coupled receptor, is proteolytically activated by thrombin, internalized, sorted predominantly to lysosomes, and efficiently degraded. Strikingly, depletion of endogenous SNX1 by siRNA markedly inhibited agonist-induced PAR1 degradation, whereas expression of a SNX1 siRNA-resistant mutant protein restored agonist-promoted PAR1 degradation in cells lacking endogenous SNX1, indicating that SNX1 is necessary for lysosomal degradation of PAR1. SNX1 is known to interact with components of the mammalian retromer complex and Hrs, an early endosomal membrane-associated protein. However, activated PAR1 degradation was not affected in cells depleted of retromer Vps26/Vps35 subunits, Hrs or Tsg101, an Hrs-interacting protein. We further show that SNX2, which dimerizes with SNX1, is not essential for lysosomal sorting of PAR1, but rather can regulate PAR1 degradation by disrupting endosomal localization of endogenous SNX1 when ectopically expressed. Together, our findings establish an essential role for endogenous SNX1 in sorting activated PAR1 to a distinct lysosomal degradative pathway that is independent of retromer, Hrs, and Tsg101.     

Nonmuscle Myosin Heavy Chain IIA Is a Critical Factor Contributing to the Efficiency of Early Infection of Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel phlebovirus in the Bunyaviridae family. Most patients infected by SFTSV present with fever and thrombocytopenia, and up to 30% die due to multiple-organ dysfunction. The mechanisms by which SFTSV enters multiple cell types are unknown. SFTSV contains two species of envelope glycoproteins, Gn (44.2 kDa) and Gc (56 kDa), both of which are encoded by the M segment and are cleaved from a precursor polypeptide (about 116 kDa) in the endoplasmic reticulum (ER). Gn fused with an immunoglobulin Fc tag at its C terminus (Gn-Fc) bound to multiple cells susceptible to the infection of SFTSV and blocked viral infection of human umbilical vein endothelial cells (HUVECs). Immunoprecipitation assays following mass spectrometry analysis showed that Gn binds to nonmuscle myosin heavy chain IIA (NMMHC-IIA), a cellular protein with surface expression in multiple cell types. Small interfering RNA (siRNA) knockdown of NMMHC-IIA, but not the closely related NMMHC-IIB or NMMHC-IIC, reduced SFTSV infection, and NMMHC-IIA specific antibody blocked infection by SFTSV but not other control viruses. Overexpression of NMMHC-IIA in HeLa cells, which show limited susceptivity to SFTSV, markedly enhanced SFTSV infection of the cells. These results show that NMMHC-IIA is critical for the cellular entry of SFTSV. As NMMHC-IIA is essential for the normal functions of platelets and human vascular endothelial cells, it is conceivable that NMMHC-IIA directly contributes to the pathogenesis of SFTSV and may be a useful target for antiviral interventions against the viral infection.     

Towards a molecular understanding of endosomal trafficking by Retromer and Retriever

Endosomes are dynamic intracellular compartments that control the sorting of a constant stream of different transmembrane cargos either for ESCRT‐mediated degradation or for egress and recycling to compartments such as the Golgi and the plasma membrane. The recycling of cargos occurs within tubulovesicular membrane domains and is facilitated by peripheral membrane protein machineries that control both membrane remodelling and selection of specific transmembrane cargos. One of the primary sorting machineries is the Retromer complex, which controls the recycling of a large array of different cargo molecules in cooperation with various sorting nexin (SNX) adaptor proteins. Recently a Retromer‐like complex was also identified that controls plasma membrane recycling of cargos including integrins and lipoprotein receptors. Termed “Retriever,” this complex uses a different SNX family member SNX17 for cargo recognition, and cooperates with the COMMD/CCDC93/CCDC22 (CCC) complex to form a larger assembly called “Commander” to mediate endosomal trafficking. In this review we focus on recent advances that have begun to provide a molecular understanding of these two distantly related transport machineries.     

Sorting nexin 27 protein regulates trafficking of a p21-activated kinase (PAK) interacting exchange factor (β-Pix)-G protein-coupled receptor kinase interacting protein (GIT) complex via a PDZ domain interaction

Sorting nexin 27 (SNX27) is a 62-kDa protein localized to early endosomes and known to regulate the intracellular trafficking of ion channels and receptors. In addition to a PX domain, SNX27 is the only sorting family member that contains a PDZ domain. To identify novel SNX27-PDZ binding partners, we performed a proteomic screen in mouse principal kidney cortical collecting duct cells using a GST-SNX27 fusion construct as bait. We found that β-Pix (p21-activated kinase-interactive exchange factor), a guanine nucleotide exchange factor for the Rho family of small GTPases known to regulate cell motility directly interacted with SNX27. The association of β-Pix and SNX27 is specific for β-Pix isoforms terminating in the type-1 PDZ binding motif (ETNL). In the same screen we also identified Git1/2 as a potential SNX27 interacting protein. The interaction between SNX27 and Git1/2 is indirect and mediated by β-Pix. Furthermore, we show recruitment of the β-Pix·Git complex to endosomal sites in a SNX27-dependent manner. Finally, migration assays revealed that depletion of SNX27 from HeLa and mouse principal kidney cortical collecting duct cells significantly decreases cell motility. We propose a model by which SNX27 regulates trafficking of β-Pix to focal adhesions and thereby influences cell motility.     

The PX-domain protein SNX17 interacts with members of the LDL receptor family and modulates endocytosis of the LDL receptor

Sorting nexins (SNXs) comprise a family of proteins characterized by the presence of a phox-homology domain, which mediates the association of these proteins with phosphoinositides and recruits them to specific membranes or vesicular structures within cells. Although only limited information about SNXs and their functions is available, they seem to be involved in membrane trafficking and sorting processes by directly binding to target proteins such as certain growth factor receptors. We show that SNX17 binds to the intracellular domain of some members of the low-density lipoprotein receptor (LDLR) family such as LDLR, VLDLR, ApoER2 and LDLR-related protein. SNX17 resides on distinct vesicular structures partially overlapping with endosomal compartments characterized by the presence of EEA1 and rab4. Using rhodamine-labeled LDL, it was possible to demonstrate that during endocytosis, LDL passes through SNX17-positive compartments. Functional studies on the LDLR pathway showed that SNX17 enhances the endocytosis rate of this receptor. Our results identify SNX17 as a novel adaptor protein for LDLR family members and define a novel mechanism for modulation of their endocytic activity.     

Evidence for a role of SNX16 in regulating traffic between the early and later endosomal compartments

Sorting nexins (SNXs) are a growing family of proteins characterized by the presence of a PX domain. The PX domain mediates membrane association by interaction with phosphoinositides. The SNXs are generally believed to participate in membrane trafficking, but information regarding the function of individual proteins is limited. In this report, we describe the major characteristics of one member, SNX16. SNX16 is a novel 343-amino acid protein consisting of a central PX domain followed by a potential coiled-coil domain and a C-terminal region. Like other sorting nexins, SNX16 associates with the membrane via the PX domain which interacts with the phospholipid phosphatidylinositol 3-phosphate. We show via biochemical and cellular studies that SNX16 is distributed in both early and late endosome/lysosome structures. The coiled-coil domain is necessary for localization to the later endosomal structures, as mutant SNX16 lacking this domain was found only in early endosomes. Trafficking of internalized epidermal growth factor was also delayed by this SNX16 mutant, as these cells showed a delay in the segregation of epidermal growth factor in the early endosome for its delivery to later compartments. In addition, the coiled-coil domain is shown here to be important for homo-oligomerization of SNX16. Taken together, these results suggest that SNX16 is a sorting nexin that may function in the trafficking of proteins between the early and late endosomal compartments.     

Abstrakt interacts with and regulates the expression of sorting nexin-2

Protein sorting through vesicular compartments is highly regulated to maintain the integrity and signaling of intracellular organelles in eukaryotic cells. Sorting Nexin-2 (SNX2) is involved in protein sorting in the trans-Golgi network, endosome, and/or lysosome compartments, with loss of function leading to defect in protein sorting and stress on organelles. To investigate the function of SNX2, we have identified the DEAD-box helicase Abstrakt (Abs) as an SNX2-interacting protein. The N-terminal domain of Abs interacts with the phox homology (PX) domain of SNX2 suggesting that PX domains may also participate in protein-protein interaction. Interestingly, both proteins undergo nucleocytoplasmic shuttling, and this process is responsive to serum withdrawal for Abs. Finally, expression of Abs reduced the cellular expression of SNX2 without altering its steady state mRNA levels. This unexpected interaction provides a novel mechanism whereby expression of proteins involved in membrane trafficking could be regulated by an RNA helicase.     

Sorting Nexin 11 Regulates Lysosomal Degradation of Plasma Membrane TRPV3

The trafficking of ion channels to/from the plasma membrane is considered an important mechanism for cellular activity and an interesting approach for disease therapies. The transient receptor potential vanilloid 3 (TRPV3) ion channel is widely expressed in skin keratinocytes, and its trafficking mechanism to/from the plasma membrane is unknown. Here, we report that the vesicular trafficking protein sorting nexin 11 (SNX11) downregulates the level of the TRPV3 plasma membrane protein. Overexpression of SNX11 causes a decrease in the level of TRPV3 current and TRPV3 plasma membrane protein in TRPV3‐transfected HEK293T cells. Subcellular localizations and western blots indicate that SNX11 interacts with TRPV3 and targets it to lysosomes for degradation, which is blocked by the lysosomal inhibitors chloroquine and leupeptin. Both TRPV3 and SNX11 are highly expressed in HaCaT cells. We show that TRPV3 agonists‐activated Ca²⁺ influxes and the level of native TRPV3 total protein in HaCaT cells are decreased by overexpression of SNX11 and increased by knockdown of SNX11. Our findings reveal that SNX11 promotes the trafficking of TRPV3 from the plasma membrane to lysosomes for degradation via protein‐protein interactions, which demonstrates a previously unknown function of SNX11 as a regulator of TRPV3 trafficking from the plasma membrane to lysosomes.     

The COG Complex, Rab6 and COPI Define a Novel Golgi Retrograde Trafficking Pathway that is Exploited by SubAB Toxin

Toxin trafficking studies provide valuable information about endogenous pathways of intracellular transport. Subtilase cytotoxin (SubAB) is transported in a retrograde manner through the endosome to the Golgi and then to the endoplasmic reticulum (ER), where it specifically cleaves the ER chaperone BiP/GRP78 (Binding immunoglobin protein/Glucose-Regulated Protein of 78 kDa). To identify the SubAB Golgi trafficking route, we have used siRNA-mediated silencing and immunofluorescence microscopy in HeLa and Vero cells. Knockdown (KD) of subunits of the conserved oligomeric Golgi (COG) complex significantly delays SubAB cytotoxicity and blocks SubAB trafficking to the cis Golgi. Depletion of Rab6 and β-COP proteins causes a similar delay in SubAB-mediated GRP78 cleavage and did not augment the trafficking block observed in COG KD cells, indicating that all three Golgi factors operate on the same 'fast' retrograde trafficking pathway. SubAB trafficking is completely blocked in cells deficient in the Golgi SNARE Syntaxin 5 and does not require the activity of endosomal sorting nexins SNX1 and SNX2. Surprisingly, depletion of Golgi tethers p115 and golgin-84 that regulates two previously described coat protein I (COPI) vesicle-mediated pathways did not interfere with SubAB trafficking, indicating that SubAB is exploiting a novel COG/Rab6/COPI-dependent retrograde trafficking pathway.     

Sorting motifs in the intracellular domain of the low density lipoprotein receptor interact with a novel domain of sorting nexin-17

The low density lipoprotein (LDL) receptor plays a major role in maintaining human plasma cholesterol levels and mutations in the gene cause familial hypercholesterolemia. The LDL receptor (LDLR) pathway has been well characterized, but little is known of proteins involved in its complex intracellular sorting and trafficking. Sorting nexin 17 (SNX17) has recently been implicated in LDLR intracellular trafficking. We show here that endogenous SNX17 is highly expressed in several cell types and is localized partially in early endosomes. We found that the PX domain of SNX17 is required for its endosomal localization but does not interact directly with the LDL receptor. A novel domain containing a FERM-like domain of SNX17 is needed for its interaction with the LDL receptor. Mutations in the NPXY motif of the LDL-receptor cytoplasmic tail that disrupt internalization also disrupt its interaction with SNX17, whereas mutations elsewhere had little effect. When transiently overexpressed in Chinese hamster ovary cells, SNX17 localized to large vesicular structures and disrupted normal trafficking of the LDL receptor in a PX domain-dependent manner. These results suggest that SNX17 plays a role in the cellular trafficking of the LDL receptor through interaction with the NPVY motif in its cytoplasmic domain and interaction of the PX domain with subcellular membrane compartments.     

SNX-BAR-mediated endosome tubulation is co-ordinated with endosome maturation

Endosomal sorting is essential for cell homeostasis. Proteins targeted for degradation are retained in the maturing endosome vacuole while others are recycled to the cell surface or sorted to the biosynthetic pathway via tubular transport carriers. Sorting nexin (SNX) proteins containing a BAR (for Bin-Amphiphysin-Rvs) domain are key regulators of phosphoinositide-mediated, tubular-based endosomal sorting, but how such sorting is co-ordinated with endosomal maturation is not known. Here, using well-defined Rab GTPases as endosomal compartment markers, we have analyzed the localization of SNX1 [endosome-to-trans-Golgi network (TGN) transport as part of the SNX-BAR-retromer complex], SNX4 (cargo-recycling from endosomes to the plasma membrane) and SNX8 (endosomes-to-TGN trafficking in a retromer-independent manner). We show that these SNX-BARs are primarily localized to early endosomes, but display the highest frequency of tubule formation at the moment of early-to-late endosome transition: the Rab5-to-Rab7 switch. Perturbing this switch shifts SNX-BAR tubulation to early endosomes, resulting in SNX1-decorated tubules that lack retromer components VPS26 and VPS35, suggesting that both early and late endosomal characteristics of the endosome are important for SNX-BAR-retromer-tubule formation. We also establish that SNX4, but not SNX1 and SNX8, is associated with the Rab11-recycling endosomes and that a high frequency of SNX4-mediated tubule formation is observed as endosomes undergo Rab4-to-Rab11 transition. Our study therefore provides evidence for fine-tuning between the processes of endosomal maturation and the formation of endosomal tubules. As tubulation is required for SNX1-, SNX4- and SNX8-mediated sorting, these data reveal a previously unrecognized co-ordination between maturation and tubular-based sorting.     

Sorting nexins--unifying trends and new perspectives

The sorting nexins (SNXs) are a family of PX domain-containing proteins found in yeast and mammalian cells that have been proposed to regulate intracellular trafficking. Mammalian SNXs have been suggested to function variously in pro-degradative sorting, internalization, endosomal recycling, or simply in endosomal sorting. In yeast, the defining function for these proteins is a regulation of cargo retrieval. Here we examine recent data on the SNX family of proteins and attempt to draw out unifying themes between the work performed in yeast and mammalian systems.     

Viral Bimolecular Fluorescence Complementation: A Novel Tool to Study Intracellular Vesicular Trafficking Pathways

The Human Immunodeficiency Virus type 1 (HIV-1) accessory protein Nef interacts with a multitude of cellular proteins, manipulating the host membrane trafficking machinery to evade immune surveillance. Nef interactions have been analyzed using various in vitro assays, co-immunoprecipitation studies, and more recently mass spectrometry. However, these methods do not evaluate Nef interactions in the context of viral infection nor do they define the sub-cellular location of these interactions. In this report, we describe a novel bimolecular fluorescence complementation (BiFC) lentiviral expression tool, termed viral BiFC, to study Nef interactions with host cellular proteins in the context of viral infection. Using the F2A cleavage site from the foot and mouth disease virus we generated a viral BiFC expression vector capable of concurrent expression of Nef and host cellular proteins; PACS-1, MHC-I and SNX18. Our studies confirmed the interaction between Nef and PACS-1, a host membrane trafficking protein involved in Nef-mediated immune evasion, and demonstrated co-localization of this complex with LAMP-1 positive endolysosomal vesicles. Furthermore, we utilized viral BiFC to localize the Nef/MHC-I interaction to an AP-1 positive endosomal compartment. Finally, viral BiFC was observed between Nef and the membrane trafficking regulator SNX18. This novel demonstration of an association between Nef and SNX18 was localized to AP-1 positive vesicles. In summary, viral BiFC is a unique tool designed to analyze the interaction between Nef and host cellular proteins by mapping the sub-cellular locations of their interactions during viral infection.     

Sorting Out the Sorting Functions of Endosomes in Arabidopsis

In animals, sorting of membrane proteins following their internalization from the plasma membrane (PM) by endocytosis occurs through a series of different endosomal compartments. In plants, how and where these sorting events take place is still poorly understood and our current view of the endocytic pathway still largely relies on analogies made from the animal system. However, extensive differences seem to exist between animal and plant endosomal functions, as exemplified by the role of the trans-Golgi network (TGN) as an early endosomal compartment in plants or the functional diversification of conserved sorting complexes. By using the Arabidopsis root tip as a reference model, we and other have begun to shed light on the complexity of the plant endocytic pathways. Notably, we have recently characterized the functions of an endosomal compartment, the SNX1-endosomes, also referred to as the prevacuolar compartment (PVC) or multivesicular bodies (MVB), in the sorting of different cargo proteins, including two related auxin-efflux carriers, PIN1 and PIN2. We have shown that routing decisions take place at this endosomal level, such as the sorting of PIN2 toward the lytic vacuole for degradation or PIN1 toward the PM for recycling.Key Words: Arabidopsis, intracellular trafficking, endocytic recycling, endosomes, MVB, PVC, VPS29, SNX, PIN, cell polarity     

Reggies/flotillins interact with Rab11a and SNX4 at the tubulovesicular recycling compartment and function in transferrin receptor and E-cadherin trafficking

The lipid raft proteins reggie-1 and -2 (flotillins) are implicated in membrane protein trafficking but exactly how has been elusive. We find that reggie-1 and -2 associate with the Rab11a, SNX4, and EHD1–decorated tubulovesicular recycling compartment in HeLa cells and that reggie-1 directly interacts with Rab11a and SNX4. Short hairpin RNA–mediated down-regulation of reggie-1 (and -2) in HeLa cells reduces association of Rab11a with tubular structures and impairs recycling of the transferrin–transferrin receptor (TfR) complex to the plasma membrane. Overexpression of constitutively active Rab11a rescues TfR recycling in reggie-deficient HeLa cells. Similarly, in a Ca²⁺ switch assay in reggie-depleted A431 cells, internalized E-cadherin is not efficiently recycled to the plasma membrane upon Ca²⁺ repletion. E-cadherin recycling is rescued, however, by overexpression of constitutively active Rab11a or SNX4 in reggie-deficient A431 cells. This suggests that the function of reggie-1 in sorting and recycling occurs in association with Rab11a and SNX4. Of interest, impaired recycling in reggie-deficient cells leads to de novo E-cadherin biosynthesis and cell contact reformation, showing that cells have ways to compensate the loss of reggies. Together our results identify reggie-1 as a regulator of the Rab11a/SNX4-controlled sorting and recycling pathway, which is, like reggies, evolutionarily conserved.     

Sorting nexin 8 regulates endosome-to-Golgi transport

Sorting nexin 8 (SNX8) belongs to the sorting nexin protein family, whose members are involved in endocytosis and endosomal sorting and signaling. The function of SNX8 has so far been unknown. Here, we have investigated the role of SNX8 in intracellular transport of the bacterial toxin Shiga toxin (Stx) and the plant toxin ricin. After being endocytosed, these toxins are transported retrogradely from endosomes, via the Golgi apparatus and the endoplasmic reticulum (ER), into the cytosol, where they exert their toxic effect. Interestingly, our experiments show that SNX8 regulates the transport of Stx and ricin differently; siRNA-mediated knockdown of SNX8 significantly increased the Stx transport to the trans-Golgi network (TGN), whereas ricin transport was slightly inhibited. We also found that SNX8 colocalizes with early endosome antigen 1 (EEA1) and with retromer components, suggesting an endosomal localization of SNX8 and supporting our finding that SNX8 is involved in endosomal sorting.     

Overexpression of a novel sorting nexin, SNX15, affects endosome morphology and protein trafficking

Sorting nexin (SNX) 15 is a novel member of the SNX family of proteins. Although the functions of most SNXs have not yet been determined, several family members (e.g., SNX1, SNX2, SNX3, and SNX8) are orthologs of yeast proteins involved in protein trafficking. Overexpression of myc-tagged SNX15 in COS-7 cells altered the morphology of several endosomal compartments. In transient transfection experiments, myc-SNX15 was first seen in small punctate spots and small ring structures. Later, myc-SNX15 was found in larger rings. Finally, myc-SNX15 was observed in large, amorphous membrane-limited structures. These structures contained proteins from lysosomes, late endosomes, early endosomes, and the trans-Golgi network. However, the morphology of the endoplasmic reticulum and Golgi was not affected by overexpression of myc-SNX15. In myc-SNX15-overexpressing cells, the endocytosis of transferrin was severely inhibited and endocytosis of tac-trans-Golgi network (TGN) 38 and tac-furin was slowed. In addition, the recycling of internalized tac-TGN38 and tac-furin was also inhibited. Both the morphological and biochemical data indicate that SNX15 plays a crucial role in trafficking through the endocytic pathway. This is the first demonstration that a mammalian SNX protein is involved in protein trafficking.     

Proteasome Inhibitor PS-341 Effectively Blocks Infection by the Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome(SFTS) is an emerging hemorrhagic fever disease caused by SFTSV, a newly discovered phlebovirus that is named after the disease. Currently, no effective vaccines or drugs are available for use against SFTSV infection, as our understanding of the viral pathogenesis is limited. Bortezomib(PS-341), a dipeptideboronic acid analog, is the first clinically approved proteasome inhibitor for use in humans. In this study, the antiviral efficacy of PS-341 against SFTSV infection was tested in human embryonic kidney HEK293 T(293 T) cells. We employed four different assays to analyze the antiviral ability of PS-341 and determined that PS-341 inhibited the proliferation of SFTSV in 293 T cells under various treatment conditions. Although PS-341 did not affect the virus absorption, PS-341 treatment within a non-toxic concentration range resulted in a significant reduction of progeny viral titers in infected cells.Dual-luciferase reporter assays and Western blot analysis revealed that PS-341 could reverse the SFTSV-encoded nonstructural protein(NS) mediated degradation of retinoic acid-inducible gene-1(RIG-I), thereby antagonizing the inhibitory effect of NSs on interferons and blocking virus replication. In addition, we observed that inhibition of apoptosis promotes virus replication. These results indicate that targeting of cellular interferon pathways and apoptosis during acute infection might serve as the bases of future therapeutics for the treatment of SFTSV infections.