Inhibition of Rab1B Impairs Trafficking and Maturation of SARS-CoV-2 Spike Protein.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) utilizes cellular trafficking pathways to process its structural proteins and move them to the site of assembly. Nevertheless, the exact process of assembly and subcellular trafficking of SARS-CoV-2 proteins remains largely unknown. Here, we have identified and characterized Rab1B as an important host factor for the trafficking and maturation of the spike protein (S) after synthesis at the endoplasmic reticulum (ER). Using confocal microscopy, we showed that S and Rab1B substantially colocalized in compartments of the early secretory pathway. Co-expression of dominant-negative (DN) Rab1B N121I leads to an aberrant distribution of S into perinuclear spots after ectopic expression and in SARS-CoV-2-infected cells caused by either structural rearrangement of the ERGIC or Golgi or missing interaction between Rab1B and S. Western blot analyses revealed a complete loss of the mature, cleaved S2 subunit in cell lysates and culture supernatants upon co-expression of DN Rab1B N121I. In sum, our studies indicate that Rab1B is an important regulator of trafficking and maturation of SARS-CoV-2 S, which not only improves our understanding of the coronavirus replication cycle but also may have implications for the development of antiviral strategies.

Prognosis, Significance and Positive Correlation of Rab1A and p-S6K/Gli1 Expression in Gastric Cancer.

BACKGROUND: Gastric Cancer (GC) is a frequently common malignancy. Recent studies have reported Rab1A as an activator of mTORC1, and the mTOR1 pathway is involved in regulating Gli1 expression in several cancers. Only a few studies have been performed to explore the relationship between Rab1A and p-S6K/Gli1in GC. METHODS: Immunohistochemistry (IHC) was performed to explore the association of Rab1A/p-S6K/Gli1 expression and prognosis in 117 GC tissue samples and adjacent normal tissues. RESULTS: Our results indicated that Rab1A/p-S6K/Gli1 was significantly overexpressed in GC tissues. High expression of Rab1A was closely related to the tumor size and the depth of tumor invasion. In addition, Rab1A expression was closely related with p-S6K/Gli1 expression in GC, and high level of Rab1A/p-S6K/Gli1 caused worse prognosis of GC patients. The univariate and multivariate analysis indicated that the expression of Rab1A was an independent prognostic factor. Moreover, both high Rab1A and p-S6K expression led to a worse prognosis when compared to a single positive expression as well as both high Rab1A/Gli1 expression also led to a worse prognosis than the single positive expression of Rab1A/Gli1. Strikingly, the overexpression of p-S6K also led to a worse prognosis in Rab1A positive patients, as did Gli1. CONCLUSION: Our results indicate that Rab1A/mTOR/S6K/Gli1 axis played a crucial role in GC, which may provide a novel field on targeted therapy of GC, especially for mTORC1-targeted therapy-resistant cancers.

Both Peripheral Blood and Urinary miR-195-5p, miR-192-3p, miR-328-5p and Their Target Genes PPM1A, RAB1A and BRSK1 May Be Potential Biomarkers for Membranous Nephropathy.

BACKGROUND To identify noninvasive diagnostic biomarkers for membranous nephropathy (MN). MATERIAL AND METHODS The mRNA microarray datasets GSE73953 using peripheral blood mononuclear cells (PBMCs) of 8 membranous nephropathy patients and 2 control patients; and microRNAs (miRNA) microarray dataset GSE64306 using urine sediments of 4 membranous nephropathy patients and 6 control patients were downloaded from the Gene Expression Omnibus database. The differentially expressed genes (DEGs) and differentially expressed miRNAs (DEMs) were respectively identified from PBMCs and urine sediments of membranous nephropathy patients, followed with functional enrichment analysis, protein-protein interaction (PPI) analysis, and miRNA-target gene analysis. Finally, the DEGs and the target genes of DEMs were overlapped to obtain crucial miRNA-mRNA interaction pairs for membranous nephropathy. RESULTS A total of 1246 DEGs were identified from PBMCs samples, among them upregulated CCL5 was found to be involved in the chemokine signaling pathway, and BAX was found to be apoptosis related; while downregulated PPM1A and CDK1 were associated with the MAPK signaling pathway and the p53 signaling pathway, respectively. The hub role of CDK1 (degree=18) and CCL5 (degree=12) were confirmed after protein-protein interaction network analysis in which CKD1 could interact with RAB1A. A total of 28 DEMs were identified in urine sediments. The 276 target genes of DEMs were involved in cell cycle arrest (PPM1A) and intracellular signal transduction (BRSK1). Thirteen genes were shared between the DEGs in PMBCs and the target genes of DEMs in urine sediments, but only hsa-miR-192-3p-RAB1A, hsa-miR-195-5p-PPM1A, and hsa-miR-328-5p-BRSK1 were negatively related in their expression level. CONCLUSIONS Both peripheral blood and urinary miR-195-5p, miR-192-3p, miR-328-5p, and their target genes PPM1A, RAB1A, and BRSK1 may be potential biomarkers for membranous nephropathy by participating in inflammation and apoptosis.

Tissue-based quantitative proteome analysis of human hepatocellular carcinoma using tandem mass tags.

CONTEXT AND OBJECTIVE: Human hepatocellular carcinoma (HCC) is a severe malignant disease, and accurate and reliable diagnostic markers are still needed. This study was aimed for the discovery of novel marker candidates by quantitative proteomics. METHODS AND RESULTS: Proteomic differences between HCC and nontumorous liver tissue were studied by mass spectrometry. Among several significantly upregulated proteins, translocator protein 18 (TSPO) and Ras-related protein Rab-1A (RAB1A) were selected for verification by immunohistochemistry in an independent cohort. For RAB1A, a high accuracy for the discrimination of HCC and nontumorous liver tissue was observed. CONCLUSION: RAB1A was verified to be a potent biomarker candidate for HCC.

Mining the thiol proteome for sulfenic acid modifications reveals new targets for oxidation in cells.

Oxidation of cysteine to sulfenic acid has emerged as a biologically relevant post-translational modification with particular importance in redox-mediated signal transduction; however, the identity of modified proteins remains largely unknown. We recently reported DAz-1, a cell-permeable chemical probe capable of detecting sulfenic acid modified proteins directly in living cells. Here we describe DAz-2, an analogue of DAz-1 that exhibits significantly improved potency in vitro and in cells. Application of this new probe for global analysis of the sulfenome in a tumor cell line identifies most known sulfenic acid modified proteins: 14 in total, plus more than 175 new candidates, with further testing confirming oxidation in several candidates. The newly identified proteins have roles in signal transduction, DNA repair, metabolism, protein synthesis, redox homeostasis, nuclear transport, vesicle trafficking, and ER quality control. Cross-comparison of these results with those from disulfide, S-glutathionylation, and S-nitrosylation proteomes reveals moderate overlap, suggesting fundamental differences in the chemical and biological basis for target specificity. The combination of selective chemical enrichment and live-cell compatibility makes DAz-2 a powerful new tool with the potential to reveal new regulatory mechanisms in signaling pathways and identify new therapeutic targets.

Rab1 defines a novel pathway connecting the pre-Golgi intermediate compartment with the cell periphery.

The function of the pre-Golgi intermediate compartment (IC) and its relationship with the endoplasmic reticulum (ER) and Golgi remain only partially understood. Here, we report striking segregation of IC domains in polarized PC12 cells that develop neurite-like processes. Differentiation involves expansion of the IC and movement of Rab1-containing tubules to the growth cones of the neurites, whereas p58- and COPI-positive IC elements, like rough ER and Golgi, remain in the cell body. Exclusion of Rab1 effectors p115 and GM130 from the neurites further indicated that the centrifugal, Rab1-mediated pathway has functions that are not directly related to ER-to-Golgi trafficking. Disassembly of COPI coats did not affect this pathway but resulted in missorting of p58 to the neurites. Live cell imaging showed that green fluorescent protein (GFP)-Rab1A-containing IC elements move bidirectionally both within the neurites and cell bodies, interconnecting different ER exit sites and the cis-Golgi region. Moreover, in nonpolarized cells GFP-Rab1A-positive tubules moved centrifugally towards the cell cortex. Hydroxymethylglutaryl-CoA reductase, the key enzyme of cholesterol biosynthesis, colocalized with slowly sedimenting, Rab1-enriched membranes when the IC subdomains were separated by velocity sedimentation. These results reveal a novel pathway directly connecting the IC with the cell periphery and suggest that this Rab1-mediated pathway is linked to the dynamics of smooth ER.