Synaptotagmin 11 scaffolds MKK7-JNK signaling process to promote stem-like molecular subtype gastric cancer oncogenesis.

BACKGROUND: Identifying biomarkers related to the diagnosis and treatment of gastric cancer (GC) has not made significant progress due to the heterogeneity of tumors. Genes involved in histological classification and genetic correlation studies are essential to develop an appropriate treatment for GC. METHODS: In vitro and in vivo lentiviral shRNA library screening was performed. The expression of Synaptotagmin (SYT11) in the tumor tissues of patients with GC was confirmed by performing Immunohistochemistry, and the correlation between the expression level and the patient's survival rate was analyzed. Phospho-kinase array was performed to detect Jun N-terminal kinase (JNK) phosphorylation. SYT11, JNK, and MKK7 complex formation was confirmed by western blot and immunoprecipitation assays. We studied the effects of SYT11 on GC proliferation and metastasis, real-time cell image analysis, adhesion assay, invasion assay, spheroid formation, mouse xenograft assay, and liver metastasis. RESULTS: SYT11 is highly expressed in the stem-like molecular subtype of GC in transcriptome analysis of 527 patients with GC. Moreover, SYT11 is a potential prognostic biomarker for histologically classified diffuse-type GC. SYT11 functions as a scaffold protein, binding both MKK7 and JNK1 signaling molecules that play a role in JNK1 phosphorylation. In turn, JNK activation leads to a signaling cascade resulting in cJun activation and expression of downstream genes angiopoietin-like 2 (ANGPTL2), thrombospondin 4 (THBS4), Vimentin, and junctional adhesion molecule 3 (JAM3), which play a role in epithelial-mesenchymal transition (EMT). SNU484 cells infected with SYT11 shRNA (shSYT11) exhibited reduced spheroid formation, mouse tumor formation, and liver metastasis, suggesting a pro-oncogenic role of SYT11. Furthermore, SYT11-antisense oligonucleotide (ASO) displayed antitumor activity in our mouse xenograft model and was conferred an anti-proliferative effect in SNU484 and MKN1 cells. CONCLUSION: SYT11 could be a potential therapeutic target as well as a prognostic biomarker in patients with diffuse-type GC, and SYT11-ASO could be used in therapeutic agent development for stem-like molecular subtype diffuse GC.

Mammalian hybrid pre-autophagosomal structure HyPAS generates autophagosomes.

The biogenesis of mammalian autophagosomes remains to be fully defined. Here, we used cellular and in vitro membrane fusion analyses to show that autophagosomes are formed from a hitherto unappreciated hybrid membrane compartment. The autophagic precursors emerge through fusion of FIP200 vesicles, derived from the cis-Golgi, with endosomally derived ATG16L1 membranes to generate a hybrid pre-autophagosomal structure, HyPAS. A previously unrecognized apparatus defined here controls HyPAS biogenesis and mammalian autophagosomal precursor membranes. HyPAS can be modulated by pharmacological agents whereas its formation is inhibited upon severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or by expression of SARS-CoV-2 nsp6. These findings reveal the origin of mammalian autophagosomal membranes, which emerge via convergence of secretory and endosomal pathways, and show that this process is targeted by microbial factors such as coronaviral membrane-modulating proteins.

Synaptotagmin 7 and SYNCRIP proteins are ubiquitously expressed in the rat brain and co-localize in Purkinje neurons.

Synaptotagmin 7 (SYT7) is ubiquitously expressed calcium sensor, involved in neuronal membrane trafficking. Immunoprecipitation experiments demonstrated that SYT7 interacts with Synaptotagmin-binding, cytoplasmic RNA-interacting protein (SYNCRIP). SYNCRIP is a component of mRNA granules, which are transported to dendrites and are prerequisite for synaptic plasticity. Given the potential significance of SYT7 regulation in processes of neurodegeneration, which are characterized by high level of synaptic vulnerability, we aimed to analyse and compare the distribution of SYT7 and SYNCRIP proteins in the adult rat striatum, hippocampus, cerebral and cerebellar cortex. We investigated the degree of SYT7-SYNCRIP co-localization in order to examine possible functional interaction of these two proteins. We found that SYT7 is abundantly distributed in neuropil of all examined anatomical areas of the brain, most prominently in axons. On the contrary, SYNCRIP had cytoplasmic somatodendritic pattern of expression, which was most prominent in the hippocampus and cerebellum. In the striatum, hippocampus and cerebral cortex SYT7 and SYNCRIP immunofluorescent signals were mutually excluded, thus diminishing the probability for their physiological interaction. In somata of Purkinje neurons in the cerebellar cortex, both SYT7 and SYNCRIP were expressed and partially co-localized suggesting possible functional connection between SYT7 and SYNCRIP proteins in Purkinje neurons.

Lithium chloride could aggravate brain injury caused by 3-nitropropionic acid.

Lithium, a well-known drug for the treatment of bipolar disorder, may also have the ability to reduce neurodegeneration and stimulate cell proliferation. Systemic injection of mitochondrial toxin 3-nitropropionic acid (3NPA) is known to induce a relatively selective, Huntington disease-like brain injury. The aim of this study was to determine the effect of lithium chloride (LiCl) on brain injury caused by 3NPA. Female adult Wistar rats were pre-treated with LiCl (127 mg/kg) 1 day before the first injection of 3NPA (28 mg/kg), and then for 8 days with the same treatment but receiving LiCl 1 hour before 3NPA. Control groups were pre-treated accordingly, with LiCl or with normal saline, but were not treated with 3NPA. Staining for cytochrome c oxidase activity and in situ hybridization autoradiography of synaptotagmin-4 and -7 mRNAs were used to evaluate brain injury caused by 3NPA. There was a significant reduction of body weight in the 3NPA+LiCl group (79%) compared to the 3NPA group (90%, p = 0.031) and both control groups (100%, p = 0.000). Densitometric evaluation of cytochrome c oxidase staining and in situ hybridization autoradiograms revealed that the pre-treatment with LiCl caused an increase in striatal lesion for about 40% (p = 0.049). Moreover, the lesion was observed also in the hippocampus of three animals from the 3NPA+LiCl group and in two animals from the 3NPA group. However, there were no differences between the LiCl and saline group in any of the measured parameters. We concluded that the pre-treatment with a relatively nontoxic dose of LiCl could aggravate brain injury caused by 3NPA.

Reduced thrombosis in Klkb1-/- mice is mediated by increased Mas receptor, prostacyclin, Sirt1, and KLF4 and decreased tissue factor.

The precise mechanism for reduced thrombosis in prekallikrein null mice (Klkb1(-/-)) is unknown. Klkb1(-/-) mice have delayed carotid artery occlusion times on the rose bengal and ferric chloride thrombosis models. Klkb1(-/-) plasmas have long-activated partial thromboplastin times and defective contact activation-induced thrombin generation that partially corrects upon prolonged incubation. However, in contact activation-induced pulmonary thromboembolism by collagen/epinephrine or long-chain polyphosphate, Klkb1(-/-) mice, unlike F12(-/-) mice, do not have survival advantage. Klkb1(-/-) mice have reduced plasma BK levels and renal B2R mRNA. They also have increased expression of the renal receptor Mas and plasma prostacyclin. Increased prostacyclin is associated with elevated aortic vasculoprotective transcription factors Sirt1 and KLF4. Treatment of Klkb1(-/-) mice with the Mas antagonist A-779, COX-2 inhibitor nimesulide, or Sirt1 inhibitor splitomicin lowers plasma prostacyclin and normalizes arterial thrombosis times. Treatment of normal mice with the Mas agonist AVE0991 reduces thrombosis. Klkb1(-/-) mice have reduced aortic tissue factor (TF) mRNA, antigen, and activity. In sum, Klkb1(-/-) mice have a novel mechanism for thrombosis protection in addition to reduced contact activation. This pathway arises when bradykinin delivery to vasculature is compromised and mediated by increased receptor Mas, prostacyclin, Sirt1, and KLF4, leading to reduced vascular TF.

Altered expression of synaptotagmin 13 mRNA in adult mouse brain after contextual fear conditioning.

Contextual fear memory processing requires coordinated changes in neuronal activity and molecular networks within brain. A large number of fear memory-related genes, however, still remain to be identified. Synaptotagmin 13 (Syt13), an atypical member of synaptotagmin family, is highly expressed in brain, but its functional roles within brain have not yet been clarified. Here, we report that the expression of Syt13 mRNA in adult mouse brain was altered following contextual fear conditioning. C57BL/6 mice were exposed to a novel context and stimulated by strong electrical footshock according to a contextual fear conditioning protocol. After 24 h, the mice were re-exposed to the context without electrical footshock for the retrieval of contextual fear memory. To investigate the relationship between Syt13 and contextual fear memory, we carried out in situ hybridization and analyzed gene expression patterns for Syt13 at four groups representing temporal changes in brain activity during contextual fear memory formation. Contextual fear conditioning test induced significant changes in mRNA levels for Syt13 within various brain regions, including lateral amygdala, somatosensory cortex, piriform cortex, habenula, thalamus, and hypothalamus, during both acquisition and retrieval sessions. Our data suggest that Syt13 may be involved in the process of contextual fear memory.

Neuropeptide exocytosis involving synaptotagmin-4 and oxytocin in hypothalamic programming of body weight and energy balance.

Hypothalamic neuropeptides play essential roles in regulating energy and body weight balance. Energy imbalance and obesity have been linked to hypothalamic signaling defects in regulating neuropeptide genes; however, it is unknown whether dysregulation of neuropeptide exocytosis could be critically involved. This study discovered that synaptotagmin-4, an atypical modulator of synaptic exocytosis, is expressed most abundantly in oxytocin neurons of the hypothalamus. Synaptotagmin-4 negatively regulates oxytocin exocytosis, and dietary obesity is associated with increased vesicle binding of synaptotagmin-4 and thus enhanced negative regulation of oxytocin release. Overexpressing synaptotagmin-4 in hypothalamic oxytocin neurons and centrally antagonizing oxytocin in mice are similarly obesogenic. Synaptotagmin-4 inhibition prevents against dietary obesity by normalizing oxytocin release and energy balance under chronic nutritional excess. In conclusion, the negative regulation of synaptotagmin-4 on oxytocin release represents a hypothalamic basis of neuropeptide exocytosis in controlling obesity and related diseases.

Exogenous expression of synaptotagmin XIII suppresses the neoplastic phenotype of a rat liver tumor cell line through molecular pathways related to mesenchymal to epithelial transition.

The molecular pathogenesis of hepatocellular carcinoma is well-studied but not completely understood. We utilized a microcell-hybrid model of tumor suppression in rat liver tumor cells to facilitate the identification of liver tumor suppressor genes located on human chromosome 11. These investigations confirmed a liver tumor suppressor locus at human 11p11.2, identified Wt1 as a potential effector of 11p11.2-mediated tumor suppression, and subsequently identified human SYT13 as a strong candidate for the 11p11.2 liver tumor suppressor gene. In the studies presented here, we introduced SYT13 into the GN6TF rat liver tumor cell line to characterize a functional role for SYT13 in this model system. Transfected clones expressing an SDS-resistant dimer form of the SYT13 protein displayed induction of Wt1 gene expression and a significant attenuation of the neoplastic phenotype exhibited by the parental tumor cell line. Saturation densities and anchorage-independent growth of SYT13 dimer-positive cell lines were reduced in vitro, and tumorigenicity was significantly decreased or ablated in syngeneic host rats in vivo. In addition, restoration of the contact-inhibited, epithelioid morphology observed in normal liver epithelial cells accompanied ectopic expression of the SYT13 protein dimer, suggesting that SYT13 may be mediating an epithelial differentiation coordinate with tumor suppression in these cells. Accordingly, the expression of E-cadherin (Cdh1) mRNA was increased >100-fold in SYT13-dimer-positive cell lines and the Cdh1 transcriptional repressor Snail was decreased >3-fold in these cells compared to the parental tumor cells. These studies combine to suggest that SYT13 is a liver tumor suppressor gene and that its function may be mediated through pathways implicated in mesenchymal to epithelial transition.

Upregulation of synaptotagmin IV inhibits transmitter release in PC12 cells with targeted synaptotagmin I knockdown.

BACKGROUND: The function of synaptotagmins (syt) in Ca2+-dependent transmitter release has been attributed primarily to Ca2+-dependent isoforms such as syt I. Recently, syt IV, an inducible Ca2+-independent isoform has been implicated in transmitter release. We postulated that the effects of syt IV on transmitter release are dependent on the expression of syt I. RESULTS: To test this, we increased syt IV expression in PC12 cells by either upregulation with forskolin treatment or overexpression with transfection. Two separately generated stable PC12 cell lines with syt I expression abolished by RNAi targeting were used and compared to control cells. We measured catecholamine release from single vesicles by amperometry and neuropeptide Y release from populations of cells by an immunoassay. In syt I targeted cells with forskolin-induced syt IV upregulation, amperometry measurements showed a reduction in the number of release events and the total amount of transmitter molecules released per cell. In cells with syt IV overexpressed, similar amperometry results were obtained, except that the rate of expansion for full fusion was slowed. Neuropeptide Y (NPY) release from syt I knockdown cells was decreased, and overexpression of syt IV did not rescue this effect. CONCLUSIONS: These data support an inhibitory effect of syt IV on release of vesicles and their transmitter content. The effect became more pronounced when syt I expression was abolished.

Cotrafficking of SV2 and synaptotagmin at the synapse.

Synaptic vesicles are specialized cycling endosomes that contain a unique constellation of membrane proteins. Proteins are sorted to vesicles by short amino acid sequences that serve as binding sites for clathrin adaptor proteins. Here we show that a tyrosine-based endocytosis motif in the vesicle protein SV2 is required for trafficking to synaptic vesicles of both SV2 and the calcium sensor protein synaptotagmin. Aberrant neurotransmission in cultured hippocampal neurons lacking SV2 was rescued by expression of wild-type SV2A, but not by SV2A-Y46A, a mutant containing a disrupted endocytosis motif in SV2A's cytoplasmic N terminus. Neurons expressing SV2A-Y46A had significantly more SV2 on the plasma membrane, indicating reduced internalization. A screen for proteins that preferentially bound wild-type SV2A identified multiple endocytosis-related proteins, and in vitro binding studies confirmed binding to the clathrin adaptors AP2, EPS15, and amphiphysin 2/Bin1. Neurons lacking SV2 contained less synaptotagmin and had a higher proportion of synaptotagmin on the plasma membrane. Expression of either wild-type SV2A or SV2A-Y46A restored synaptotagmin expression levels; however, only wild-type SV2A restored a normal proportion of synaptotagmin on the plasma membrane. These findings indicate that SV2 influences the expression and trafficking of synaptotagmin via separate mechanisms. Synaptic vesicles immunoisolated from SV2A/B double knock-out mice had significantly less synaptotagmin than vesicles isolated from wild-type mice. Our results indicate that SV2 plays a major role in regulating the amount of synaptotagmin in synaptic vesicles and provide an explanation for the observation that synapses lacking SV2 have fewer vesicles competent for calcium-induced fusion.

The effects of GABA transporter inhibition on synaptophysin and synaptotagmin expression in diazepam tolerance.

BACKGROUND: In light of the differential interactions seen between benzodiazepine, GABA transporter (GAT) inhibition and drug tolerance, the locomotor effects of a GAT1-specific inhibitor (SKF89976A) following diazepam tolerance were analysed and compared with the concomitant expression of synaptic vesicle proteins implicated in synaptic plasticity. METHODS: Male PVG/OlaHsd rats were chronically dosed with diazepam to produce tolerance, and the expression of mRNA for synaptophysin and synaptotagmin were analysed in the hippocampus by means of in situ hybridisation. The action of the GAT inhibitor SKF89976A on the expression of these mRNAs, and on open field behaviour was subsequently observed. RESULTS: The results show an unexpected sedative effect of GAT-inhibition in diazepam-tolerant rats. The expression data show a significant effect of diazepam treatment on synaptophysin expression, which is reversible by SKF89976A treatment. CONCLUSIONS: The increased synaptophysin expression in the hippocampus of diazepam-tolerant rats may indicate a role for modulation of transmitter release, synaptic plasticity and learning in pharmacological tolerance. The reversibility of this effect following acute GAT inhibition suggests a complicated relationship between the benzodiazepine-binding site and other synaptic GABA-binding sites. Furthermore, the sedative behavioural effect of the GAT inhibitor in diazepam-tolerant rats is an unusual observation with implications for the treatment of drug-tolerant individuals.

Effects of methylphenidate: the cellular point of view.

The psychostimulant methylphenidate (MPH) is the first choice of treatment in attention-deficit hyperactivity disorder and is based mainly on inhibition of dopamine transporter (DAT). Nonetheless, the complete cellular effects of MPH are still unknown. We attempted to determine whether MPH influences neurotransmitter levels, synaptic gene expression, and cell proliferation in a dose-dependent manner in rat pheochromocytoma cells (PC12) lacking DAT. PC12 were treated in a dose-dependent manner with MPH. Gene expression level of synaptotagmin (Syt) 1 and 4, syntaxin 1a (Stx1a), and synaptic vesicle glycoprotein 2C (SV2C) was measured using quantitative real-time RT-PCR. Different Neurotransmitter release was measured using high-performance liquid chromatography (HPLC). Differences in cell proliferation were evaluated via BrdU incorporation. Treatment with low-dose MPH (1-100 nM) altered intra-/extracellular neurotransmitter levels, down-regulated all investigated genes as well as enhanced cell proliferation significantly. These data point to diverse effects of MPH on cell metabolism independent of inhibiting DAT.

Apolipoproteins D and E3 exert neurotrophic and synaptogenic effects in dorsal root ganglion cell cultures.

Co-cultures of 3T3-L1 adipocytes with neurons from the rat dorsal root ganglia (DRG) showed enhanced neuritogenesis and synaptogenesis. Microarray analysis for upregulated genes in adipocyte/DRG co-cultures currently points to apolipoproteins D and E (ApoD, ApoE) as influential proteins. We therefore tested adipocyte-secreted cholesterol and the carrier proteins ApoD and ApoE3. Cholesterol, ApoD, and ApoE3 each increased neurite outgrowth and upregulated the expression of presynaptic synaptophysin and synaptotagmin, as well as the postsynaptic density protein 95. The neurotrophic effects of ApoD and ApoE3 were associated with an increased expression of the low-density lipoprotein receptor and apolipoprotein E receptor 2. Simultaneous treatment with receptor-associated protein, an apolipoprotein receptor antagonist, inhibited the neurotrophic function of both apolipoproteins. The application of ApoD, ApoE3, and cholesterol to DRG cell cultures corresponded with increased expression of the chemokine stromal cell-derived factor 1 and its receptor CXC chemokine receptor 4 (CXCR4). Surprisingly, the inhibition of CXCR4 by the antagonistic drug AMD3100 decreased the apolipoprotein/cholesterol dependent neurotrophic effects. We thus assume that apolipoprotein-induced neuritogenesis in DRG cells interferes with CXCR4 signaling, and that adipocyte-derived apolipoproteins might be helpful in nerve repair.

Re-expression of tumorigenicity after attenuation of human synaptotagmin 13 in a suppressed microcell hybrid cell line.

Human chromosome 11p11.2 contains a putative liver tumor suppressor locus that was identified using a microcell hybrid cell line-based model of tumor suppression. Transcription mapping of suppressed microcell hybrid cell lines suggests that human SYT13 represents a strong candidate for the 11p11.2 tumor suppressor gene. Other evidence suggests that the putative 11p11.2 tumor suppressor gene (SYT13 or some other) may modulate the tumorigenic potential of neoplastic liver cell lines through direct or indirect regulation of the rat Wt1 tumor suppressor gene. To characterize a functional role for SYT13 in liver tumor suppression, we employed RNAi to attenuate SYT13 expression in a suppressed microcell hybrid cell line (GN6TF-11neoCX4). SYT13-attenuated cells display aggressive phenotypic properties that are similar to or indistinguishable from the parental tumor cells (GN6TF), including altered cellular morphologies, disrupted contact inhibition, elevated saturation densities, restoration of anchorage-independent growth and increased tumorigenicity in vivo. Moreover, SYT13 attenuation and re-expression of tumorigenicity in GN6TF-11neoCX4-derived cell lines was accompanied by a significant decrease of Wt1 expression. In contrast, the phenotypic properties of scrambled-control cells were similar to the suppressed microcell hybrid cells and Wt1 expression was unaffected. These observations combine to establish that: i) human SYT13 functions as a liver tumor suppressor gene that complements a molecular defect in GN6TF rat liver tumor cells resulting in a normalized cellular phenotype in vitro and suppression of tumorigenicity in vivo; ii) RNAi-mediated attenuation of SYT13 expression restores the neoplastic phenotype of GN6TF-11neoCX4 microcell hybrid cells, consistent with the function of a liver tumor suppressor gene; and iii) loss of Wt1 expression is important for the re-establishment of tumorigenic potential by GN6TF-11neoCX4 microcell hybrid cells after attenuation of SYT13.

Gene expression profiling in human null cell pituitary adenoma tissue.

It is estimated that up to one in five individuals develops pituitary gland tumors, despite the common occurrence of these tumors, the pathogenetic mechanisms underlying their development mainly remain unknown. We studied the gene expression in null cell adenomas compared with normal pituitary by expressed sequence tags (EST) sequencing and cDNA microarray on large scale. Both approaches of EST sequencing and microarray analysis showed that 17 genes were differentially expressed in human null cell pituitary adenoma tissues, among which 14 genes were overexpressed and three genes were underpressed. Five of the genes with potential oncogenic significance by RT-real time quantitative PCR. Synaptotagmin (SYT) are integral membrane proteins of synaptic vesicles considered to serve as Ca(2+) sensors in the process of vesicular trafficking and exocytosis. Calcium binding to participates in triggering neurotransmitter release at the synapse. In view of our finding that SYT is overexpressed in null cell adenomas, these tumors may be capable of secreting some unknown hormones or peptides. ATP5B and MDH1 were involved in the energy metabolism, whose overexpression in null cell adenomas provide us with a new perspective of exploring the oncogenesis of these tumors. All of these data may contribute to the understanding of null cell adenoma formation and development.