Syntaxin5 is essential for survival by ensuring midgut epithelial homeostsis and regulating feeding in Locusta migratoria.

Syntaxin5 (Syx5) belongs to SNAREs family, which play important roles in fusion of vesicles to target membranes. Most of what we know about functions of Syx5 originates from studies in fungal or vertebrate cells, how Syx5 operates during the development of insects is poorly understood. In this study, we investigated the role of LmSyx5 in the gut development of the hemimetabolous insect Locusta migratoria. LmSyx5 was expressed in many tissues, with higher levels in the gut. Knockdown of LmSyx5 by RNA interference (RNAi) considerably suppressed feeding in both nymphs and adults. The dsLmSyx5-injected locusts lost body weight and finally died at a mortality of 100%. Furthermore, hematoxylin-eosin staining indicated that the midgut is deformed in dsLmSyx5-treated nymphs and the brush border in midgut epithelial cells is severely damaged, suggesting that LmSyx5 is involved in morphogenesis of the midgut. TEM further showed that the endoplasmic reticulum of midgut cells have a bloated appearance. Taken together, these results suggest that LmSyx5 is essential for midgut epithelial homeostsis that affects growth and development of L. migratoria. Thus, Syx5 is a promising RNAi target for controlling L. migratoria, and even other pests.

Golgi stress induces upregulation of the ER-Golgi SNARE Syntaxin-5, altered ßAPP processing, and Caspase-3-dependent apoptosis in NG108-15 cells.

The involvement of secretory pathways and Golgi dysfunction in neuronal cells during Alzheimer's disease progression is poorly understood. Our previous overexpression and knockdown studies revealed that the intracellular protein level of Syntaxin-5, an endoplasmic reticulum-Golgi soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE), modulates beta-amyloid precursor protein processing in neuronal cells. We recently showed that changes in endogenous Syntaxin-5 protein expression occur under stress induction. Syntaxin-5 was upregulated by endoplasmic reticulum stress but was degraded by Caspase-3 during apoptosis in neuronal cells. In addition, we showed that sustained endoplasmic reticulum stress promotes Caspase-3-dependent apoptosis during the later phase of the endoplasmic reticulum stress response in NG108-15 cells. In this study, to elucidate the consequences of secretory pathway dysfunction in beta-amyloid precursor protein processing that lead to neuronal cell death, we examined the effect of various stresses on endoplasmic reticulum-Golgi SNARE expression and beta-amyloid precursor protein processing. By using compounds to disrupt Golgi function, we show that Golgi stress promotes upregulation of the endoplasmic reticulum-Golgi SNARE Syntaxin-5, and prolonged stress causes Caspase-3-dependent apoptosis. Golgi stress induced intracellular beta-amyloid precursor protein accumulation and a concomitant decrease in total amyloid-beta production. We also examined the protective effect of the chemical chaperone 4-phenylbutylate on changes in amyloid-beta production and the activation of Caspase-3 induced by endoplasmic reticulum and Golgi stress. The compound alleviated the increase in the amyloid-beta 1-42/amyloid-beta 1-40 ratio induced by endoplasmic reticulum and Golgi stress. Furthermore, 4-phenylbutylate could rescue Caspase-3-dependent apoptosis induced by prolonged organelle stress. These results suggest that organelle stress originating from the endoplasmic reticulum and Golgi has a substantial impact on the amyloidogenic processing of beta-amyloid precursor protein and Caspase-3-dependent apoptosis, leading to neuronal cell death.

Mutations in GET4 disrupt the transmembrane domain recognition complex pathway.

The transmembrane domain recognition complex (TRC) targets cytoplasmic C-terminal tail-anchored (TA) proteins to their respective membranes in the endoplasmic reticulum (ER), Golgi, and mitochondria. It is composed of three proteins, GET4, BAG6, and GET5. We identified an individual with compound heterozygous missense variants (p.Arg122His, p.Ile279Met) in GET4 that reduced all three TRC proteins by 70% to 90% in his fibroblasts, suggesting a possible defect in TA protein targeting. He presented with global developmental delay, intellectual disabilities, seizures, facial dysmorphism, and delayed bone age. We found the TA protein, syntaxin 5, is poorly targeted to Golgi membranes compared to normal controls. Since GET4 regulates ER to Golgi transport, we hypothesized that such transport would be disrupted in his fibroblasts, and discovered that retrograde (but not anterograde) transport was significantly reduced. Despite reduction in the three TRC proteins, their mRNA levels were unchanged, suggesting increased degradation in patient fibroblasts. Treating fibroblasts with the FDA-approved proteasome inhibitor, bortezomib (10 nM), restored syntaxin 5 localization and nearly normalized the levels of all three TRC proteins. Our study identifies the first individual with GET4 mutations.

Inhibition of diverse opportunistic viruses by structurally optimized retrograde trafficking inhibitors.

Opportunistic viruses are a major problem for immunosuppressed individuals, particularly following organ or stem cell transplantation. Current treatments are non-existent or suffer from problems such as high toxicity or development of resistant strains. We previously published that a trafficking inhibitor that targets a host protein greatly reduces the replication of human cytomegalovirus. This inhibitor was also shown to be moderately effective against polyomaviruses, another family of opportunistic viruses. We have developed a panel of analogues for this inhibitor and have shown that these analogues maintain their high efficacy against HCMV, while substantially lowering the concentration required to inhibit polyomavirus replication. By targeting a host protein these compounds are able to inhibit the replication of two very different viruses. These observations open up the possibility of pan-viral inhibitors for immunosuppressed individuals that are effective against multiple, diverse opportunistic viruses.

p115-SNARE interactions: a dynamic cycle of p115 binding monomeric SNARE motifs and releasing assembled bundles.

Tethering factors regulate the targeting of membrane-enclosed vesicles under the control of Rab GTPases. p115, a golgin family tether, has been shown to participate in multiple stages of ER/Golgi transport. Despite extensive study, the mechanism of action of p115 is poorly understood. SNARE proteins make up the machinery for membrane fusion, and strong evidence shows that function of p115 is directly linked to its interaction with SNAREs. Using a gel filtration binding assay, we have demonstrated that in solution p115 stably interacts with ER/Golgi SNAREs rbet1 and sec22b, but not membrin and syntaxin 5. These binding preferences stemmed from selectivity of p115 for monomeric SNARE motifs as opposed to SNARE oligomers. Soluble monomeric rbet1 can compete off p115 from coat protein II (COPII) vesicles. Furthermore, excess p115 inhibits p115 function in trafficking. We conclude that monomeric SNAREs are a major binding site for p115 on COPII vesicles, and that p115 dissociates from its SNARE partners upon SNAREpin assembly. Our results suggest a model in which p115 forms a mixed p115/SNARE helix bundle with a monomeric SNARE, facilitates the binding activity and/or concentration of the SNARE at prefusion sites and is subsequently ejected as SNARE complex formation and fusion proceed.

ER stress response in NG108-15 cells involves upregulation of syntaxin 5 expression and reduced amyloid ß peptide secretion.

Endoplasmic reticulum (ER) stress plays a role in the pathogenesis of neurodegenerative diseases such as Alzheimer׳s disease (AD). We previously showed that manipulation of the ER-Golgi-soluble N-ethylmaleimide-sensitive factor-attachment protein receptors (ER-Golgi SNARE) syntaxin 5 (Syx5) causes changes in Golgi morphology and the processing of AD-related proteins. To understand the pathophysiologic significance of these phenomena, we examined whether the expression of Syx5 is altered by ER stress. De novo synthesis of ER-Golgi SNARE Syx5 and Bet1 was induced by various ER stressors. Elevated expression of Syx5 and Bet1 was associated with increased levels of these proteins in vesicular components, including ER-Golgi-intermediate-compartment/vesicular tubular clusters. In addition, ER stress diminished amyloid ß (Aß) peptide secretion. Knockdown of Syx5 expression enhanced the secretion of Aß peptides under condition without ER stress. Moreover, diminished Aß peptide secretion resulting from ER stress was significantly reversed by Syx5 knockdown. These findings suggest that Syx5 plays important roles in ß-amyloid precursor protein processing and in the ER stress response that precedes apoptotic cell death and may be involved in the crosstalk between these two pathways.

The Golgi complex of dopaminergic enteric neurons is fragmented in a hemiparkinsonian rat model.

Since gastrointestinal disorders are early consequences of Parkinson's disease (PD), this disease is clearly not restricted to the central nervous system (CNS), but also significantly affects the enteric nervous system (ENS). Large aggregates of the protein α-synuclein forming Lewy bodies, the prototypical cytopathological marker of this disease, have been observed in enteric nervous plexuses. However, their value in early prognosis is controversial. The Golgi complex (GC) of nigral neurons appears fragmented in Parkinson's disease, a characteristic common in most neurodegenerative diseases. In addition, the distribution and levels of regulatory proteins such as Rabs and SNAREs are altered, suggesting that PD is a membrane traffic-related pathology. Whether the GC of enteric dopaminergic neurons is affected by the disease has not yet been analyzed. In the present study, dopaminergic neurons in colon nervous plexuses behave as nigral neurons in a hemiparkinsonian rat model based on the injection of the toxin 6-OHDA. Their GCs are fragmented, and some regulatory proteins' distribution and expression levels are altered. The putative mechanisms of the transmission of the neurotoxin to the ENS are discussed. Our results support the possibility that GC structure and the level of some proteins, especially syntaxin 5, could be helpful as early indicators of the disease. RESEARCH HIGHLIGHTS: The Golgi complexes of enteric dopaminergic neurons appear fragmented in a Parkinson's disease rat model. Our results support the hypothesis that the Golgi complex structure and levels of Rab1 and syntaxin 5 could be helpful as early indicators of the disease.

STX5 Inhibits Hepatocellular Carcinoma Adhesion and Promotes Metastasis by Regulating the PI3K/mTOR Pathway.

Background and Aims: Syntaxin 5 (STX5) is a member of the syntaxin or target-soluble SNAP receptor (t-SNARE) family and plays a critical role in autophagy. However, its function and molecular mechanism in tumor cell migration are still unknown. The role of STX5 in influencing hepatocellular carcinoma (HCC) is an important topic in our research. Methods: By using quantitative reverse transcription polymerase chain reaction (qPCR), western blotting, and immunohistochemical analysis of RNA and protein in tissues, we comprehensively evaluated data sets from public databases and clinical patient cohorts for STX5. The correlation of STX5 expression with the clinicopathological characteristics of HCC patients were assessed. In addition, we predicted signal pathways from differentially expressed genes (DEGs) and the Cancer Genome Atlas (TCGA) databases, and confirmed the prediction using integrated transcriptome and RNA-seq. We further investigated the underlying mechanisms of STX5 in the migration and adhesion of HCC cells both in vitro and in vivo. Results: In the TCGA dataset and our patient cohort, STX5 levels were significantly higher in HCC tissues than in adjacent normal liver tissues. At the same time, high expression of STX5 predicted worse prognosis in patients with liver cancer. High expression of STX5 indicates the decrease of adhesion and the increase of migration of HCC cells, and the conversion of epithelial-mesenchymal transition (EMT) in vitro via PI3K/mTOR pathway activation. Conversely, when Sirolimus, a phosphoinositide 3-kinase (PI3K)/AKT/mechanistic target of rapamycin (mTOR) inhibitor acts on cells simultaneously, STX5 overexpression-mediated enhancement of HCC metastasis is reversed. Double-negative regulation of STX5 and mTOR further enhanced the inhibitory effect of STX5 on HCC metastasis. In vivo, STX5 knockdown inhibited the metastasis of HCC cells. Conclusions: Our study demonstrates a novel research result that STX5 promotes HCC metastasis through PI3K/mTOR pathway. We believe that combined inhibition of STX5 and mTOR is a potential treatment for effectively prolonging patient survival and inhibiting HCC metastasis.

Syntaxin 5-dependent phosphorylation of the small heat shock protein Hsp42 and its role in protein quality control.

The small heat shock protein Hsp42 and the t-SNARE protein Sed5 have central roles in the sequestration of misfolded proteins into insoluble protein deposits in the yeast Saccharomyces cerevisiae. However, whether these proteins/processes interact in protein quality control (PQC) is not known. Here, we show that Sed5 and anterograde trafficking modulate phosphorylation of Hsp42 partially via the MAPK kinase Hog1. Such phosphorylation, specifically at residue S215, abrogated the co-localization of Hsp42 with the Hsp104 disaggregase, aggregate clearance, chaperone activity, and sequestration of aggregates to IPOD and mitochondria. Furthermore, we found that Hsp42 is hyperphosphorylated in old cells leading to a drastic failure in disaggregation. Old cells also displayed a retarded anterograde trafficking, which, together with slow aggregate clearance and hyperphosphorylation of Hsp42, could be counteracted by Sed5 overproduction. We hypothesize that the breakdown of proper PQC during yeast aging may, in part, be due to a retarded anterograde trafficking leading to hyperphosphorylation of Hsp42.

Activity of the SNARE Protein SNAP29 at the Endoplasmic Reticulum and Golgi Apparatus.

Snap29 is a conserved regulator of membrane fusion essential to complete autophagy and to support other cellular processes, including cell division. In humans, inactivating SNAP29 mutations causes CEDNIK syndrome, a rare multi-systemic disorder characterized by congenital neuro-cutaneous alterations. The fibroblasts of CEDNIK patients show alterations of the Golgi apparatus (GA). However, whether and how Snap29 acts at the GA is unclear. Here we investigate SNAP29 function at the GA and endoplasmic reticulum (ER). As part of the elongated structures in proximity to these membrane compartments, a pool of SNAP29 forms a complex with Syntaxin18, or with Syntaxin5, which we find is required to engage SEC22B-loaded vesicles. Consistent with this, in HeLa cells, in neuroepithelial stem cells, and in vivo, decreased SNAP29 activity alters GA architecture and reduces ER to GA trafficking. Our data reveal a new regulatory function of Snap29 in promoting secretory trafficking.

Hitchhiking on vesicles: a way to harness age-related proteopathies?

Central to proteopathies and leading to most age-related neurodegenerative disorders is a failure in protein quality control (PQC). To harness the toxicity of misfolded and damaged disease proteins, such proteins are either refolded, degraded by temporal PQC, or sequestered by spatial PQC into specific, organelle-associated, compartments within the cell. Here, we discuss the impact of vesicle trafficking pathways in general, and syntaxin 5 in particular, as key players in spatial PQC directing misfolded proteins to the surface of vacuole and mitochondria, which facilitates their clearance and detoxification. Since boosting vesicle trafficking genetically can positively impact on spatial PQC and make cells less sensitive to misfolded disease proteins, we speculate that regulators of such trafficking might serve as therapeutic targets for age-related neurological disorders.

Syntaxin 5 Is Required for the Formation and Clearance of Protein Inclusions during Proteostatic Stress.

Spatial sorting to discrete quality control sites in the cell is a process harnessing the toxicity of aberrant proteins. We show that the yeast t-snare phosphoprotein syntaxin5 (Sed5) acts as a key factor in mitigating proteotoxicity and the spatial deposition and clearance of IPOD (insoluble protein deposit) inclusions associates with the disaggregase Hsp104. Sed5 phosphorylation promotes dynamic movement of COPII-associated Hsp104 and boosts disaggregation by favoring anterograde ER-to-Golgi trafficking. Hsp104-associated aggregates co-localize with Sed5 as well as components of the ER, trans Golgi network, and endocytic vesicles, transiently during proteostatic stress, explaining mechanistically how misfolded and aggregated proteins formed at the vicinity of the ER can hitchhike toward vacuolar IPOD sites. Many inclusions become associated with mitochondria in a HOPS/vCLAMP-dependent manner and co-localize with Vps39 (HOPS/vCLAMP) and Vps13, which are proteins providing contacts between vacuole and mitochondria. Both Vps39 and Vps13 are required also for efficient Sed5-dependent clearance of aggregates.

Stx5-Mediated ER-Golgi Transport in Mammals and Yeast.

The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) syntaxin 5 (Stx5) in mammals and its ortholog Sed5p in Saccharomyces cerevisiae mediate anterograde and retrograde endoplasmic reticulum (ER)-Golgi trafficking. Stx5 and Sed5p are structurally highly conserved and are both regulated by interactions with other ER-Golgi SNARE proteins, the Sec1/Munc18-like protein Scfd1/Sly1p and the membrane tethering complexes COG, p115, and GM130. Despite these similarities, yeast Sed5p and mammalian Stx5 are differently recruited to COPII-coated vesicles, and Stx5 interacts with the microtubular cytoskeleton, whereas Sed5p does not. In this review, we argue that these different Stx5 interactions contribute to structural differences in ER-Golgi transport between mammalian and yeast cells. Insight into the function of Stx5 is important given its essential role in the secretory pathway of eukaryotic cells and its involvement in infections and neurodegenerative diseases.

ER and Golgi stresses increase ER-Golgi SNARE Syntaxin5: Implications for organelle stress and ßAPP processing.

Unresolved endoplasmic reticulum (ER) stress causes neuronal death and has been implicated in neurodegenerative conditions such as Alzheimer's disease (AD). However, the mechanisms by which stress signals propagate from the ER through the Golgi apparatus and their effects on the transport and processing of AD-related proteins, such as ß-amyloid precursor protein (ßAPP), are unknown. We recently found that in the NG108-15 cell line, ER stress upregulates ER-Golgi-soluble N-ethylmaleimide-sensitive factor-attachment protein receptors (ER-Golgi SNAREs) Syx5 and Bet1. In the present study, we examined the effects of apoptosis and ER stress inducers on the expression of ER-Golgi SNARE proteins and cell viability in a primary culture of rat hippocampal neurons. An apoptosis inducer significantly downregulated the expression of ER-Golgi SNARE Syx5. ER-stress inducers upregulated the expression of Syx5 isoforms and Bet1 proteins via de novo synthesis of their mRNA transcripts. Knockdown of Syx5 during apoptosis or ER stress induction enhanced vulnerability of neurons. Additionally, we examined the effects of Golgi stress on Syx5 expression and ßAPP processing. Golgi stress also induced upregulation of ER-Golgi SNARE Syx5, and concomitantly, suppressed amyloid-ß peptide secretion. These findings suggest that Syx5 is a potential stress responsive factor that participates in ßAPP processing and the survival pathways of neuronal cells.

Investigation of diagnostic potentials of nine different biomarkers in endometriosis.

OBJECTIVE: To investigate the diagnostic potentials of the serum levels of nine different biomarkers in endometriosis. STUDY DESIGN: In this case-controlled, prospective clinical study, 80 women underwent laparoscopy or laparotomy with a preliminary diagnosis of chronic pelvic pain, severe secondary dysmenorrhea, infertility, pelvic endometriosis or pelvic mass. The 60 women with confirmed pelvic endometriosis constituted the endometriosis group, and the other 20 women without endometriosis constituted the control group. Preoperative blood samples were obtained for serum biomarker measurements. Serum levels of nine different serum biomarkers including α-enolase, macrophage migration inhibitory factor, leptin, interleukin-8, anti-endometrial antibody, phosphoinositide dependent protein kinase 1, CA125, syntaxin-5, and laminin-1 were measured concurrently and compared between the control and endometriosis groups, and among control group and endometriosis subgroups including stage I, stage II, stage III and stage IV endometriosis. RESULTS: The serum levels of α-enolase, macrophage migration inhibitory factor, leptin, interleukin-8 and antiendometrial antibodies showed a statistically significant difference neither between control and endometriosis groups nor among control group and endometriosis subgroups. The serum levels of CA125, syntaxin-5 and laminin-1 showed a statistically significant difference both between the control and endometriosis groups (p<0.01) and among control group and endometriosis subgroups (p<0.01). Serum levels of laminin-1 in stage II and IV endometriosis; syntaxin-5 in stage I and II endometriosis; and CA125 in stage III and IV endometriosis were found to have the different levels compared to control group. CONCLUSIONS: These findings show that the concurrent measurement of CA125, syntaxin-5 and laminin-1 might be a useful non-invasive test in strengthening the diagnosis of endometriosis and in predicting its severity.