SNX32 is a host restriction factor that degrades African swine fever virus CP204L via the RAB1B-dependent autophagy pathway

African swine fever virus (ASFV) causes a highly contagious and deadly disease in domestic pigs and European wild boars, posing a severe threat to the global pig industry. ASFV CP204L, a highly immunogenic protein, is produced during the early stages of ASFV infection. However, the impact of CP204L protein-interacting partners on the outcome of ASFV infection is poorly understood. To accomplish this, coimmunoprecipitation and mass spectrometry analysis were conducted in ASFV-infected porcine alveolar macrophages (PAMs). We have demonstrated that sorting nexin 32 (SNX32) is a CP204L-binding protein and that CP204L interacted and colocalized with SNX32 in ASFV-infected PAMs. ASFV growth and replication were promoted by silencing SNX32 and suppressed by overexpressing SNX32. SNX32 degraded CP204L by recruiting the autophagy-related protein Ras-related protein Rab-1b (RAB1B). RAB1B overexpression inhibited ASFV replication, while knockdown of RAB1B had the opposite effect. Additionally, RAB1B, SNX32, and CP204L formed a complex upon ASFV infection. Taken together, this study demonstrates that SNX32 antagonizes ASFV growth and replication by recruiting the autophagy-related protein RAB1B. This finding extends our understanding of the interaction between ASFV CP204L and its host and provides new insights into exploring the relationship between ASFV infection and autophagy.IMPORTANCEAfrican swine fever (ASF) is a highly contagious and acute hemorrhagic viral disease with a high mortality near 100% in domestic pigs. ASF virus (ASFV), which is the only member of the family Asfarviridae, is a dsDNA virus of great complexity and size, encoding more than 150 proteins. Currently, there are no available vaccines against ASFV. ASFV CP204L represents the most abundantly expressed viral protein early in infection and plays an important role in regulating ASFV replication. However, the mechanism by which the interaction between ASFV CP204L and host proteins affects ASFV replication remains unclear. In this study, we demonstrated that the cellular protein SNX32 interacted with CP204L and degraded CP204L by upregulating the autophagy-related protein RAB1B. In summary, this study will help us understand the interaction mechanism between CP204L and its host upon infection and provide new insights for the development of vaccines and antiviral drugs.

Circ_RBM23 knockdown suppresses chemoresistance, proliferation, migration and invasion of sorafenib-resistant HCC cells through miR-338-3p/RAB1B axis

BACKGROUND

Circular RNA RNA-binding motif protein 23 (circ_RBM23; ID: hsa_circ_0000524) is a novel regulator in hepatocellular carcinoma (HCC). Herein, we planned to investigate its role in sorafenib resistance in HCC.

METHOD

Levels of circ_RBM23, microRNA (miR)-338-3p, Ras-related GTPase-trafficking protein (RAB1B), Snail and E-cadherin were detected by real-time quantitative PCR and western blotting. Sorafenib resistant (SR) HCC cells (Huh7/SR and SK-HEP-1/SR) were established by acquisition of sorafenib resistance, and cell functions were measured by MTT assay, Edu assay, colony formation assay, apoptosis assay, transwell assay, and in vivo xenograft formation assay. Crosslink between miR-338-3p and circ_RBM23 or RAB1B was confirmed by bioinformatics analysis and dual-luciferase reporter assay.

RESULTS

Circ_RBM23 upregulation was discovered in the tissues of SR patients and SR cells, which was accompanied with miR-338-3p downregulation and RAB1B upregulation. The 50% inhibitory concentration (IC₅₀) of sorafenib in SR cells was greatly suppressed by interfering circ_RBM23 or reinforcing miR-338-3p, allied with this was the inhibition of EdU-positive cell rate, colony formation and migration/invasion abilities under sorafenib treatment, as well as the enhancement of apoptotic rate. Moreover, circ_RBM23 inhibition delayed tumor growth of Huh7/SR cells under sorfanib treatment in vivo.

CONCLUSION

Circ_RBM23 promoted chemoresistance, malignant proliferation, migration and invasion of SR HCC cells by modulating miR-338-3p/RAB1B axis.

LINC00173 facilitates tumor progression by stimulating RAB1B-mediated PA2G4 and SDF4 secretion in nasopharyngeal carcinoma

An increasing number of studies have found that long non-coding RNA (lncRNA) play important roles in driving the progression of nasopharyngeal carcinoma (NPC). Our microarray screening revealed that expression of the lncRNA long intergenic non-protein coding RNA 173 (LINC00173) was upregulated in NPC. However, its role and mechanism in NPC have not yet been elucidated. In this study, we demonstrate that high LINC00173 expression indicated a poor prognosis in NPC patients. Knockdown of LINC00173 significantly inhibited NPC cell proliferation, migration and invasion in vitro. Mechanistically, LINC00173 interacted and colocalized with Ras-related protein Rab-1B (RAB1B) in the cytoplasm, but the modulation of LINC00173 expression did not affect the expression of RAB1B at either the mRNA or protein levels. Instead, relying on the stimulation of RAB1B, LINC00173 could facilitate the extracellular secretion of proliferation-associated 2G4 (PA2G4) and stromal cell-derived factor 4 (SDF4; also known as 45-kDa calcium-binding protein) proteins, and knockdown of these proteins could reverse the NPC aggressive phenotype induced by LINC00173 overexpression. Moreover, in vivo LINC00173-knockdown models exhibited a marked slowdown in tumor growth and a significant reduction in lymph node and lung metastases. In summary, LINC00173 serves as a crucial driver for NPC progression, and the LINC00173-RAB1B-PA2G4/SDF4 axis might provide a potential therapeutic target for NPC patients.

MiR-135a inhibits non-small cell lung cancer progression by suppressing RAB1B expression and the RAS pathway

Lung cancer is the most common tumor in China and worldwide. Despite advances in diagnosis and therapy, it still represents the most lethal malignancy in industrialized countries. The study of regulatory noncoding RNAs has deepened our understanding of cancer on the molecular and clinical level. In this article, it showed that miR-135a was aberrantly downregulated in non-small cell lung cancer (NSCLC) cells in comparison with normal bronchial epithelial cells, and the expression of miR-135a inhibited proliferation, invasion and metastasis of NSCLC cells in vitro. Moreover, it was demonstrated that miR-135a inhibited the expression of multiple components (including RAS, Raf1, Rac1 and RhoA) of the RAS pathway via RAB1B, which was a novel target of miR-135a. The expression of miR-135a and RAB1B could effectively predict the clinical outcomes of NSCLC. In summary, miR-135a might function as a suppressor of NSCLC cells, and thus could be used as a potential therapeutic target.

The small GTPase RAB1B promotes antiviral innate immunity by interacting with TNF receptor-associated factor 3 (TRAF3)

Innate immune detection of viral nucleic acids during viral infection activates a signaling cascade that induces type I and type III IFNs as well as other cytokines, to generate an antiviral response. This signaling is initiated by pattern recognition receptors, such as the RNA helicase retinoic acid-inducible gene I (RIG-I), that sense viral RNA. These sensors then interact with the adaptor protein mitochondrial antiviral signaling protein (MAVS), which recruits additional signaling proteins, including TNF receptor-associated factor 3 (TRAF3) and TANK-binding kinase 1 (TBK1), to form a signaling complex that activates IFN regulatory factor 3 (IRF3) for transcriptional induction of type I IFNs. Here, using several immunological and biochemical approaches in multiple human cell types, we show that the GTPase-trafficking protein RAB1B up-regulates RIG-I pathway signaling and thereby promotes IFN-β induction and the antiviral response. We observed that RAB1B overexpression increases RIG-I-mediated signaling to IFN-β and that RAB1B deletion reduces signaling of this pathway. Additionally, loss of RAB1B dampened the antiviral response, indicated by enhanced Zika virus infection of cells depleted of RAB1B. Importantly, we identified the mechanism of RAB1B action in the antiviral response, finding that it forms a protein complex with TRAF3 to facilitate the interaction of TRAF3 with mitochondrial antiviral signaling protein. We conclude that RAB1B regulates TRAF3 and promotes the formation of innate immune signaling complexes in response to nucleic acid sensing during RNA virus infection.

TBC1D20 mediates autophagy as a key regulator of autophagosome maturation

In humans, loss of TBC1D20 (TBC1 domain family, member 20) protein function causes Warburg Micro syndrome 4 (WARBM4), an autosomal recessive disorder characterized by congenital eye, brain, and genital abnormalities. TBC1D20-deficient mice exhibit ocular abnormalities and male infertility. TBC1D20 is a ubiquitously expressed member of the family of GTPase-activating proteins (GAPs) that increase the intrinsically slow GTP-hydrolysis rate of small RAB-GTPases when bound to GTP. Biochemical studies have established TBC1D20 as a GAP for RAB1B and RAB2A. However, the cellular role of TBC1D20 still remains elusive, and there is little information about how the functional loss of TBC1D20 causes clinical manifestations in WARBM4-affected children. Here we evaluate the role of TBC1D20 in cells carrying a null mutant allele, as well as TBC1D20-deficient mice, which display eye and testicular abnormalities. We demonstrate that TBC1D20, via its RAB1B GAP function, is a key regulator of autophagosome maturation, a process required for maintenance of autophagic flux and degradation of autophagic cargo. Our results provide evidence that TBC1D20-mediated autophagosome maturation maintains lens transparency by mediating the removal of damaged proteins and organelles from lens fiber cells. Additionally, our results show that in the testes TBC1D20-mediated maturation of autophagosomes is required for autophagic flux, but is also required for the formation of acrosomes. Furthermore TBC1D20-deficient mice, while not mimicking severe developmental brain abnormalities identified in WARBM4 affected children, display disrupted neuronal autophagic flux resulting in adult-onset motor dysfunction. In summary, we show that TBC1D20 has an essential role in the maturation of autophagosomes and a defect in TBC1D20 function results in eye, testicular, and neuronal abnormalities in mice implicating disrupted autophagy as a mechanism that contributes to WARBM4 pathogenesis.

Loss of RAB1B promotes triple-negative breast cancer metastasis by activating TGF-β/SMAD signaling

Triple-negative breast cancer (TNBC) is a highly aggressive tumor subtype associated with a poor prognosis. The mechanism involved in TNBC progression remains largely unknown. To date, there are no effective therapeutic targets for this tumor subtype. In this study, by performing quantitative proteomic analyses in highly metastatic and parental breast cancer cell line, we found that RAB1B, a member of the RAS oncogene family, was significantly down-regulated in highly metastatic breast cancer cells. Moreover, down-regulation of RAB1B was also found to promote the proliferation and migration of TNBC cells in vitro and in vivo. Mechanistically, loss of RAB1B resulted in elevated expression of TGF-β receptor 1 (TβR1) through decreased degradation of ubiquitin, increased levels of phosphorylated SMAD3 and TGF-β-induced epithelial-mesenchymal transition (EMT). Furthermore, low RAB1B expression correlated with poor prognosis in breast cancer patients. Taken together, our findings reveal that RAB1B acts as a metastasis suppressor in TNBC by regulating the TGF-β/SMAD signaling pathway and RAB1B may serve as a novel biomarker of prognosis and the response to anti-tumor therapeutics for patients with TNBC.