Essential role of STX6 in esophageal squamous cell carcinoma growth and migration

Syntaxin6 contributes to hepatocellular carcinoma tumorigenesis via enhancing STAT3 phosphorylation

BACKGROUND

Syntaxin6 (STX6) is a SNARE (Soluble N-ethylmaleimide-sensitive factor attachment protein receptors) protein complex located in the trans-Golgi network and endosomes, which is closely associated with a variety of intracellular membrane transport events. STX6 has been shown to be overexpressed in a variety of human malignant tumors such as esophageal, colorectal, and renal cell carcinomas, and participates in tumorigenesis and development.

METHODS

Based on clinical public database and clinical liver samples analysis, the expression of STX6 in hepatocellular carcinoma (HCC) tissues was investigated. The effects of STX6 on proliferation, migration and invasion of HCC cell in vitro and in vivo were evaluated through gain- and loss-of-function studies. We further performed RNA-seq analysis and protein interactome analysis, to further decifer the detailed mechanisms of STX6 in the regulation of the JAK-STAT pathway in HCC.

RESULTS

STX6 expression was upregulated in HCC tissues and its expression was highly correlated with the high histological grade of the tumor. STX6 promoted HCC cell proliferation, migration and invasion both in vitro and in vivo. Mechanistically, STX6 mediated tumor progression depending on promoting the activation of JAK-STAT signaling pathway. Receptor for activated protein kinase C (RACK1) as an essential adaptor protein mediating STX6 regulation of JAK-STAT pathway. Specifically, STX6 interacted with RACK1 and then recruited signal transducer and activator of transcription 3 (STAT3) to form a protein-binding complex and activates STAT3 transcriptional activity.

CONCLUSIONS

This study provided a novel concept that STX6 exerted oncogenic effects by activating the STAT3 signaling pathway, and STX6 might be a promising therapeutic target for HCC.

Increased STX3 transcript and protein levels were associated with poor prognosis in two independent cohorts of esophageal squamous cell carcinoma patients

BACKGROUND

Some conventional prognostic biomarkers for esophageal squamous cell carcinoma (ESCC) have the disadvantage that they have only been investigated at the level of either mRNA or protein levels or only in individual cohorts. Associations between Syntaxin 3 (STX3) expression and malignancy have been reported in several tumor types but not in ESCC. Here, we investigated the levels of both STX3 mRNA and protein, and its prognostic potential in two independent cohorts of patients with ESCC.

METHODS

STX3 mRNA levels were examined in surgical specimens by quantitative PCR in a cohort that included 176 ESCC patients. STX3 protein levels were investigated in surgically resected ESCC tissues by immunohistochemistry using tissue microarrays in a different cohort of 177 ESCC patients. Correlations were analyzed between the expression of STX3 mRNA and protein with clinicopathological factors and long-term prognosis.

RESULTS

Quantitative PCR indicated a significant association between high level of STX3 mRNA expression and lymph node involvement, pathological stage, and poor overall survival. The multivariate analysis demonstrated that high STX3 mRNA expression was independently associated with poor overall survival outcomes. Immunohistochemistry revealed that STX3 protein expression in ESCC tissues and high STX3 protein expression were also significantly correlated with unfavorable overall survival.

CONCLUSIONS

Overexpression of STX3 mRNA and protein may serve as potential prognostic biomarkers for ESCC patients.

Plasma Exosome Gene Signature Differentiates Colon Cancer from Healthy Controls

BACKGROUND

Liquid biopsies have become an integral part of cancer management as minimally invasive options to detect molecular and genetic changes. However, current options show poor sensitivity in peritoneal carcinomatosis (PC). Novel exosome-based liquid biopsies may provide critical information on these challenging tumors. In this initial feasibility analysis, we identified an exosome gene signature of 445 genes (ExoSig445) from colon cancer patients, including those with PC, that is distinct from healthy controls.

METHODS

Plasma exosomes from 42 patients with metastatic and non-metastatic colon cancer and 10 healthy controls were isolated and verified. RNAseq analysis of exosomal RNA was performed and differentially expressed genes (DEGs) were identified by the DESeq2 algorithm. The ability of RNA transcripts to discriminate control and cancer cases was assessed by principal component analysis (PCA) and Bayesian compound covariate predictor classification. An exosomal gene signature was compared with tumor expression profiles of The Cancer Genome Atlas.

RESULTS

Unsupervised PCA using exosomal genes with greatest expression variance showed stark separation between controls and patient samples. Using separate training and test sets, gene classifiers were constructed capable of discriminating control and patient samples with 100% accuracy. Using a stringent statistical threshold, 445 DEGs fully delineated control from cancer samples. Furthermore, 58 of these exosomal DEGs were found to be overexpressed in colon tumors.

CONCLUSIONS

Plasma exosomal RNAs can robustly discriminate colon cancer patients, including patients with PC, from healthy controls. ExoSig445 can potentially be developed as a highly sensitive liquid biopsy test in colon cancer.

Investigation of genetic variants and causal biomarkers associated with brain aging

Delta age is a biomarker of brain aging that captures differences between the chronological age and the predicted biological brain age. Using multimodal data of brain MRI, genomics, and blood-based biomarkers and metabolomics in UK Biobank, this study investigates an explainable and causal basis of high delta age. A visual saliency map of brain regions showed that lower volumes in the fornix and the lower part of the thalamus are key predictors of high delta age. Genome-wide association analysis of the delta age using the SNP array data identified associated variants in gene regions such as KLF3-AS1 and STX1. GWAS was also performed on the volumes in the fornix and the lower part of the thalamus, showing a high genetic correlation with delta age, indicating that they share a genetic basis. Mendelian randomization (MR) for all metabolomic biomarkers and blood-related phenotypes showed that immune-related phenotypes have a causal impact on increasing delta age. Our analysis revealed regions in the brain that are susceptible to the aging process and provided evidence of the causal and genetic connections between immune responses and brain aging.

Role of STX6 as a prognostic factor associated with immune infiltration in hepatocellular carcinoma

Syntaxin 6 (STX6), a soluble N-ethylmaleimide-sensitive factor-activating receptor protein, has formed an increasing part of cancer research. However, to the best of our knowledge, the role of STX6 in hepatocellular carcinoma (HCC) is still unclear. In the present study, data from multiple bioinformatics databases, including The Cancer Genome Atlas, Gene Expression Omnibus, Kaplan-Meier plotter, Tumor Immune Estimation Resource (TIMER) and Gene Expression Profiling Integrative Analysis (GEPIA2), and immunohistochemistry (IHC) were utilized to assess the role of STX6 in HCC. The results demonstrated that STX6 expression was upregulated in HCC tissues compared with normal tissues. STX6 expression was significantly associated with tumor size, Edmondson grade and α-fetoprotein (AFP) level. Furthermore, survival analysis demonstrated that high STX6 expression was significantly associated with poor prognosis in patients with HCC. Furthermore, assessment of the immune infiltrates demonstrated that CD163 expression was positively correlated with the STX6 level when analyzed using the TIMER and GEPIA2 databases. IHC results further demonstrated this association. Furthermore, compared with the typically used AFP, STX6 could have an improved diagnostic value in the diagnosis of HCC. In conclusion, STX6 expression was not only positively associated with poor prognosis but may also be involved in the immune inflammatory reaction in HCC. STX6 may become a potential therapeutic and diagnosis maker for patients with HCC.

Syntaxin 18 regulates the DNA damage response and epithelial-to-mesenchymal transition to promote radiation resistance of lung cancer

Radiotherapy is an important modality in lung cancer treatment. Despite advances in treatment planning and dose delivery, patient benefit is still limited by in-field relapse and metastatic recurrence. Simultaneous application of cisplatinum-based chemotherapy leads to moderately improved outcomes, thus providing proof-of-concept for radiosensitization strategies in lung cancer. In an unbiased functional genetic screen for radiosensitization targets in lung cancer, we identified syntaxin 18, a protein involved in retrograde vesicular transport between the Golgi apparatus and endoplasmic reticulum, as mediator of radioresistance. Downregulation of endogenous syntaxin 18 specifically reduced clonogenic survival of radioresistant and radiosensitive lung cancer cells following X-radiation. Gene expression programs regulating DNA repair, mitotic checkpoints and mitosis were altered in isogenic cells with reduced syntaxin 18 expression. Functionally, this translated into impaired DNA damage-induced cell cycle checkpoints leading to cell death by mitotic catastrophe. Interestingly, downregulation of syntaxin 18 in lung cancer cells also impaired expression of markers of epithelial-mesenchymal-transition, and reduced migration and invasion capacity. These findings suggest that syntaxin 18 is a key player regulating genes responsible for controlling the growth of the primary tumor as well as metastases upon radiotherapy of lung cancer. They provide a promising lead for biologically rational radiosensitization strategies impacting on radiation-induced cell death as well as metastasis.

Hsa_circ_0010220 regulates miR-198/Syntaxin 6 axis to promote osteosarcoma progression

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hsa_circ_0010220 expression is increased in osteosarcoma.

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hsa_circ_0010220 knockdown represses cell proliferation, migration and invasion.

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hsa_circ_0010220 regulates Syntaxin 6 via miR-198.

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hsa_circ_0010220 silence decreases xenograft tumor growth.

Background

Circular RNAs (circRNAs) are a class of endogenous RNAs that are involved in osteosarcoma progression. Hsa_circ_0010220 (circ_0010220) is a circRNA generated by gene Rho Guanine Nucleotide Exchange Factor 10 Like (ARHGEF10L) and is upregulated in osteosarcoma, but its functional role in osteosarcoma is limited studied. This study aimed to illustrate the regulatory mechanism underlying circ_0010220 in osteosarcoma.

Methods

51 paired tumor and normal tissues were obtained from osteosarcoma patients. circ_0010220, microRNA (miR)-198 and Syntaxin 6 (STX6) abundances were examined by quantitative reverse transcription polymerase chain reaction and western blot. Cell proliferation, cell cycle, apoptosis, migration and invasion were analyzed via Cell Counting Kits-8 (CCK-8), colony formation, flow cytometry and transwell analyses. Target relationship was verified via dual-luciferase reporter analysis, RNA immunoprecipitation and pull-down. The in vivo function was analyzed using a xenograft model.

Results

Circ_0010220 was elevated in osteosarcoma tissues and cells, and was related to the lower survival rate of osteosarcoma patients. Circ_0010220 knockdown inhibited cell proliferation, migration and invasion, but induced cell cycle arrest and apoptosis in vitro. Besides, circ_0010220 silence curbed the growth of xenograft osteosarcoma tumors in vivo. Mechanistic research revealed that miR-198 is a target of circ_0010220, and directly targets STX6. Moreover, circ_0010220 upregulated the expression of STX6 by sponging miR-198 to regulate cell proliferation, migration, invasion, cell cycle, and apoptosis.

Conclusion

Circ_0010220 contributes to osteosarcoma progression through mediating miR-198/STX6 axis, which might be a novel therapeutic target for osteosarcoma therapy.

Suppression of complement component 2 expression by hepatitis B virus contributes to the viral persistence in chronic hepatitis B patients

Previously, we identified rare missense mutations of complement component 2 (C2) to be associated with chronic hepatitis B (CHB) by exome sequencing. However, up to now, little is known about the role of C2 in CHB. In the present study, we aimed to perform preliminary exploration about the underlying role of C2 in CHB. Serum samples from 113 CHB patients and 30 healthy controls, and liver biopsy samples from 5 CHB patients and 3 healthy controls were obtained from the Third Affiliated Hospital of Sun Yat-sen University between January 2018 and January 2020. HepG2.2.15 and HepG2-NTCP cells infected with HBV were used to examine the influence of HBV infection on C2 expression. IFN-treated HepG2.2.15 cells were used to assess the effect of IFN on C2 expression. C2-overexpressing or C2-silencing HepG2.2.15 cells were constructed to evaluate the effect of C2 on HBV infection. Western blot and RT-qPCR were used to measure C2 expression in biopsy samples. HBeAg and HBsAg in culture medium and C2 of serum samples were measured by ELISA. HBV-DNA was measured by RT-qPCR. GSE84044, GSE54747 and GSE27555 were downloaded from GEO. C2 expression in liver tissue and serum was significantly lower in CHB patients compared to healthy controls, and significantly higher C2 expression was found in CHB patients with lower ALT, AST, Scheuer grade and stages compared to CHB patients with higher ALT, AST, Scheuer grades and Scheuer stage. Besides, HBV infection could decrease C2 expression by increasing expression of Sp1 and reducing expression of HDAC4. Moreover, C2 could enhance the anti-virus effect of IFN on HepG2.2.15 cells and also inhibit HBV replication in HepG2.2.15 cells by inhibition of p38-MAPK signalling pathway. In conclusion, HBV may promote viral persistence in CHB patients by inhibiting C2 expression.

Syntaxin 6-mediated exosome secretion regulates enzalutamide resistance in prostate cancer

Prostate cancer (PCa) deaths are typically the result of metastatic castration-resistant PCa (mCRPC). Recently, enzalutamide (Enz), an oral androgen receptor inhibitor, was approved for treating patients with mCRPC. Invariably, all PCa patients eventually develop resistance against Enz. Therefore, novel strategies aimed at overcoming Enz resistance are needed to improve the survival of PCa patients. The role of exosomes in drug resistance has not been fully elucidated in PCa. Therefore, we set out to better understand the exosome's role in the mechanism underlying Enz-resistant PCa. Results showed that Enz-resistant PCa cells (C4-2B, CWR-R1, and LNCaP) secreted significantly higher amounts of exosomes (2-4 folds) compared to Enz-sensitive counterparts. Inhibition of exosome biogenesis in resistant cells by GW4869 and dimethyl amiloride strongly decreased their cell viability. Mechanistic studies revealed upregulation of syntaxin 6 as well as its increased colocalization with CD63 in Enz-resistant PCa cells compared to Enz-sensitive cells. Syntaxin 6 knockdown by specific small interfering RNAs in Enz-resistant PCa cells (C4-2B and CWR-R1) resulted in reduced cell number and increased cell death in the presence of Enz. Furthermore, syntaxin 6 knockdown significantly reduced the exosome secretion in both Enz-resistant C4-2B and CWR-R1 cells. The Cancer Genome Atlas analysis showed increased syntaxin 6 expressions associated with higher Gleason score and decreased progression-free survival in PCa patients. Importantly, IHC analysis showed higher syntaxin 6 expression in cancer tissues from Enz-treated patients compared to Enz naïve patients. Overall, syntaxin 6 plays an important role in the secretion of exosomes and increased survival of Enz-resistant PCa cells.

Nitric Oxide Generated by Tumor-Associated Macrophages Is Responsible for Cancer Resistance to Cisplatin and Correlated With Syntaxin 4 and Acid Sphingomyelinase Inhibition

Tumor microenvironment is fundamental for cancer progression and chemoresistance. Among stromal cells tumor-associated macrophages (TAMs) represent the largest population of infiltrating inflammatory cells in malignant tumors, promoting their growth, invasion, and immune evasion. M2-polarized TAMs are endowed with the nitric oxide (NO)-generating enzyme inducible nitric oxide synthase (iNOS). NO has divergent effects on tumors, since it can either stimulate tumor cells growth or promote their death depending on the source of it; likewise the role of iNOS in cancer differs depending on the cell type. The role of NO generated by TAMs has not been investigated. Using different tumor models in vitro and in vivo we found that NO generated by iNOS of M2-polarized TAMs is able to protect tumor cells from apoptosis induced by the chemotherapeutic agent cisplatin (CDDP). Here, we demonstrate that the protective effect of NO depends on the inhibition of acid sphingomyelinase (A-SMase), which is activated by CDDP in a pathway involving the death receptor CD95. Mechanistic insights indicate that NO actions occur via generation of cyclic GMP and activation of protein kinase G (PKG), inducing phosphorylation of syntaxin 4 (synt4), a SNARE protein responsible for A-SMase trafficking and activation. Noteworthy, phosphorylation of synt4 at serine 78 by PKG is responsible for the proteasome-dependent degradation of synt4, which limits the CDDP-induced exposure of A-SMase to the plasma membrane of tumor cells. This inhibits the cytotoxic mechanism of CDDP reducing A-SMase-triggered apoptosis. This is the first demonstration that endogenous NO system is a key mechanism through which TAMs protect tumor cells from chemotherapeutic drug-induced apoptosis. The identification of the pathway responsible for A-SMase activity downregulation in tumors leading to chemoresistance warrants further investigations as a means to identify new anti-cancer molecules capable of specifically inhibiting synt4 degradation.

STX3 represses the stability of the tumor suppressor PTEN to activate the PI3K-Akt-mTOR signaling and promotes the growth of breast cancer cells

Syntaxin 3, also known as STX3, is a protein encoded by the STX3 gene in humans. This protein is one of the fundamental components of the exocytotic machinery required for the docking and fusion of secretory granules with the plasma membrane. The roles of STX3 in human breast cancer remains elusive. Here we report that STX3 acts as an oncogenic protein in human breast cancer. We analyzed the expression of STX3 in 148 patients with breast cancer. The mRNA and protein levels of STX3 are significantly up-regulated in human breast cancer compared with matched adjacent non-cancer tissues. The up-regulation of STX3 is correlated with high disease stage and predicts overall and disease-free survival in patients with breast cancer. Lentivirus-mediated knockdown of STX3 represses in vitro proliferation and colony formation and in vivo growth of breast cancer cells, whereas STX3 overexpression promotes the growth of breast cancer cells in vitro and in vivo. We find that STX3 promotes the proliferation of breast cancer cells by increasing the activation of the Akt-mTOR signaling, and Akt inhibitor Ipatasertib or MK-2206 represses STX3 effects on the growth of breast cancer cells. Further mechanism study shows that STX3 binds to PTEN and increases PTEN ubiquitination and degradation, thus leading to activation of the PI3K-Akt-mTOR signaling. Therefore, STX3 promotes the growth of breast cancer cells by regulating the PTEN-PI3K-Akt-mTOR signaling.

SNARE proteins in membrane trafficking

SNAREs are the core machinery mediating membrane fusion. In this review, we provide an update on the recent progress on SNAREs regulating membrane fusion events, especially the more detailed fusion processes dissected by well-developed biophysical methods and in vitro single molecule analysis approaches. We also briefly summarize the relevant research from Chinese laboratories and highlight the significant contributions on our understanding of SNARE-mediated membrane trafficking from scientists in China.

Argonaute CLIP Defines a Deregulated miR-122-Bound Transcriptome that Correlates with Patient Survival in Human Liver Cancer

MicroRNA-122, an abundant and conserved liver-specific miRNA, regulates hepatic metabolism and functions as a tumor suppressor, yet systematic and direct biochemical elucidation of the miR-122 target network remains incomplete. To this end, we performed Argonaute crosslinking immunoprecipitation (Argonaute [Ago]-CLIP) sequencing in miR-122 knockout and control mouse livers, as well as in matched human hepatocellular carcinoma (HCC) and benign liver tissue to identify miRNA target sites transcriptome-wide in two species. We observed a majority of miR-122 binding on 3' UTRs and coding exons followed by extensive binding to other genic and non-genic sites. Motif analysis of miR-122-dependent binding revealed a G-bulged motif in addition to canonical motifs. A large number of miR-122 targets were found to be species specific. Upregulation of several common mouse and human targets, most notably BCL9, predicted survival in HCC patients. These results broadly define the molecular consequences of miR-122 downregulation in hepatocellular carcinoma.

Annexin A6-A multifunctional scaffold in cell motility

Annexin A6 (AnxA6) belongs to a highly conserved protein family characterized by their calcium (Ca²⁺)-dependent binding to phospholipids. Over the years, immunohistochemistry, subcellular fractionations, and live cell microscopy established that AnxA6 is predominantly found at the plasma membrane and endosomal compartments. In these locations, AnxA6 acts as a multifunctional scaffold protein, recruiting signaling proteins, modulating cholesterol and membrane transport and influencing actin dynamics. These activities enable AnxA6 to contribute to the formation of multifactorial protein complexes and membrane domains relevant in signal transduction, cholesterol homeostasis and endo-/exocytic membrane transport. Hence, AnxA6 has been implicated in many biological processes, including cell proliferation, survival, differentiation, inflammation, but also membrane repair and viral infection. More recently, we and others identified roles for AnxA6 in cancer cell migration and invasion. This review will discuss how the multiple scaffold functions may enable AnxA6 to modulate migratory cell behavior in health and disease.