The emerging roles of retromer and sorting nexins in the life cycle of viruses

Retromer and sorting nexins(SNXs)transport cargoes from endosomes to the trans-Golgi network or plasma membrane.Recent studies have unveiled the emerging roles for retromer and SNXs in the life cycle of viruses,including members of Coronaviridae,Flaviviridae and Retroviridae.Key components of retromer/SNXs,such as Vps35,Vps26,SNX5 and SNX27,can affect multiple steps of the viral life cycle,including facilitating the entry of viruses into cells,participating in viral replication,and promoting the assembly of virions.Here we present a comprehensive updated review on the interplay between retromer/SNXs and virus,which will shed mechanistic insights into controlling virus infection.

Prognostic value of sorting nexin 10 weak expression in stomach adenocarcinoma revealed by weighted gene coexpression network analysis

AIM TO detect significant clusters of co-expressed genes associated with tumorigenesis that might help to predict stomach adenocarcinoma （SA） prognosis.METHODS The Cancer Genome Atlas database was used to obtain RNA sequences as well as complete clinical data of SA and adjacent normal tissues from patients. Weighted gene co-expression network analysis （WGCNA） was used to investigate the meaningful module along with hub genes. Expression of hub genes was analyzed in 362 paraffin-embedded SA biopsy tissues by immunohistochemical staining. Patients were classified into two groups （according to expression of hub genes）： Weak expression and over-expression groups. Correlation of biomarkers with clinicopathological factors indicated patient survival.RESULTS Whole genome expression level screening identified 6,231 differentially expressed genes. Twenty-four co- expressed gene modules were identified using WGCNA. Pearson＇s correlation analysis showed that the tan module was the most relevant to tumor stage （r = 0.24, P = 7 × 10 -6）. In addition, we detected sorting nexin （SNX）10 as the hub gene of the tan module. SNX10 expression was linked to T category （P = 0.042, x2= 8.708）, N category （P = 0.000, x2= 18.778）, TNM stage （P = 0.001, x2 = 16.744） as well as tumor differentiation （P = 0.000,x2= 251.930）. Patients with high SNX10 expression tended to have longer diseasefree survival （DFS; 44.97 mo vs 33.85 mo, P = 0.000） as well as overall survival （OS; 49.95 vs 40.84 mo, P = 0.000） in univariate analysis. Multivariate analysis showed that dismal prognosis could be precisely predicted clinicopathologically using SNX10 [DFS： P = 0.014, hazard ratio （HR） = 0.698, 95% confidence interval （CI）： 0.524-0.930, OS： P = 0.017, HR = 0.704, 95%CI： 0.528-0.940].CONCLUSION This study provides a new technique for screening prognostic biomarkers of SA. Weak expression of SNX10 is linked to poor prognosis, and is a suitable prognostic biomarker of SA.

The retromer component SNX6 interacts with dynactin p150Glued and mediates endosome-to-TGN transport

The retromer is a protein complex that mediates retrograde transport of transmembrane cargoes from endosomes to the trans-Golgi network （TGN）. It is comprised of a cargo-selection subcomplex of Vps26, Vps29 and Vps35 and a membrane-binding coat subcomplex of sorting nexins （SNXs）. Previous studies identified SNX1/2 as one of the components of the SNX subcomplex, and SNX5/6 as candidates for the second SNX. How the retromer-associated cargoes are recognized and transported by molecular motors are largely unknown. In this study, we found that one of SNX1/2＇s dimerization partners, SNX6, interacts with the p150Gued subunit of the dynein/dynactin motor complex. We present evidence that SNX6 is a component of the retromer, and that recruitment of the motor complex to the membrane-associated retromer requires the SNX6-pl50Gued interaction. Disruption of the SNX6-pl50Glued interaction causes failure in formation and detachment of the tubulovesicular sorting structures from endosomes and results in block of CI-MPR retrieval from endosomes to the TGN. These observations indicate that in addition to SNX1/2, SNX6 in association with the dynein/dynactin complex drives the formation and movement of tubular retrograde intermediates.

Retromer-Mediated Protein Sorting and Vesicular Trafficking

Retromer is an evolutionarily conserved multimeric protein complex that mediates intracellular transport of various vesicular cargoes and functions in a wide variety of cellular processes including polarized trafficking,developmental signaling and lysosome biogenesis.Through its interaction with the Rab GTPases and their effectors,membrane lipids,molecular motors,the endocytic machinery and actin nucleation promoting factors,retromer regulates sorting and trafficking of transmembrane proteins from endosomes to the trans-Golgi network（TGN） and the plasma membrane.In this review.I highlight recent progress in the understanding of relromer-medialed protein sorting and vesicle trafficking and discuss how retromer contributes to a diverse set of developmental,physiological and pathological processes.

SNX11 Identified as an Essential Host Factor for SFTS Virus Infection by CRISPR Knockout Screening

Severe fever with thrombocytopenia syndrome virus(SFTSV)is a highly pathogenic tick-borne bunyavirus that causes lethal infectious disease and severe fever with thrombocytopenia syndrome(SFTS)in humans.The molecular mechanisms and host cellular factors required for SFTSV infection remain uncharacterized.Using a genome-wide CRISPR-based screening strategy,we identified a host cellular protein,sorting nexin 11(SNX11)which is involved in the intracellular endosomal trafficking pathway,as an essential cell factor for SFTSV infection.An SNX11-KO HeLa cell line was established,and SFTSV replication was significantly reduced.The glycoproteins of SFTSV were detected and remained in later endosomal compartments but were not detectable in the endoplasmic reticulum(ER)or Golgi apparatus.pH values in the endosomal compartments of the SNX11-KO cells increased compared with the pH of normal HeLa cells,and lysosomal-associated membrane protein 1(LAMP1)expression was significantly elevated in the SNX11-KO cells.Overall,these results indicated that penetration of SFTSV from the endolysosomes into the cytoplasm of host cells was blocked in the cells lacking SNX11.Our study for the first time provides insight into the important role of the SNX11 as an essential host factor in the intracellular trafficking and penetrating process of SFTSV infection via potential regulation of viral protein sorting,membrane fusion,and other endocytic machinery.

Involvement of SNX1 in regulating EGFR endocytosis in a gefitinib-resistant NSCLC cell lines

The drug gefitinib, a specific inhibitor of EGFR tyrosine kinase, has been shown to suppress the activation of EGFR signaling for survival and cell proliferation in non-small cell lung cancer cell lines. For many years, EGFR endocytosis has served as a model for investigating ligand-induced, receptor-mediated endocytosis. On EGF stimulation, EGFR is internalized and transported via clathrin-coated vesicles to early endosomes, and EGFR then recruits and phosphorylates signaling molecules, leading to the activation of downstream signaling such as MAPK/PI3K/AKT pathways-an important mechanism for regulating cell growth. Once delivered to the lysosomes, EGFR is degraded to terminate intracellular EGFR signaling via endocytosis;this process is known as receptor downregulation. Therefore, the endocytosis of EGFR is closely related with attenuation of intracellular EGFR signaling. Alternatively, EGFR is returned to cell surface from early endosomes for the continued signaling. Previous reports revealed that a competent EGF-induced endocytosis of EGFR followed by its rapid downregulation efficiently proceeds in the gefitinib-sensitive NSCLC cell lines. In contrast, gefitinib-resistant cell lines showed that EGFR endocytosis is impaired and the internalized EGFR is aggregated in the early endosomes, which is associated with the overexpressed sorting nexin 1 (SNX1), initially identified as a protein that interacts with EGFR. Thus dysregulated EGFR endocytosis is implicated in gefitinib resistance, as it leads to uncontrolled signal transduction. At present, the therapeutic relevance of EGFR endocytosis with regard to drug resistance in lung cancer has not been clarified. This review focused on the mechanism for EGFR endocytosis associated with SNX1 trafficking in gefitinib-resistant lung cancer cells.