Double C2 protein. A review

Trafficking proteins show limited differences in mobility across different postsynaptic spines

The function of the postsynaptic compartment is based on the presence and activity of postsynaptic receptors, whose dynamics are controlled by numerous scaffolding, signaling and trafficking proteins. Although the receptors and the scaffolding proteins have received substantial attention, the trafficking proteins have not been investigated extensively. Their mobility rates are unknown, and it is unclear how the postsynaptic environment affects their dynamics. To address this, we analyzed several trafficking proteins (α-synuclein, amphiphysin, calmodulin, doc2a, dynamin, and endophilin), estimating their movement rates in the dendritic shaft, as well as in morphologically distinct "mushroom" and "stubby" postsynapse types. The diffusion parameters were surprisingly similar across dendritic compartments, and a few differences between proteins became evident only in the presence of a synapse neck. We conclude that the movement of trafficking proteins is not strongly affected by the postsynaptic compartment, in stark contrast to the presynapse, which regulates strongly the movement of such proteins.

TC2N: A Novel Vital Oncogene or Tumor Suppressor Gene In Cancers

Several C2 domain-containing proteins play key roles in tumorigenesis, signal transduction, and mediating protein–protein interactions. Tandem C2 domains nuclear protein (TC2N) is a tandem C2 domain-containing protein that is differentially expressed in several types of cancers and is closely associated with tumorigenesis and tumor progression. Notably, TC2N has been identified as an oncogene in lung and gastric cancer but as a tumor suppressor gene in breast cancer. Recently, a large number of tumor-associated antigens (TAAs), such as heat shock proteins, alpha-fetoprotein, and carcinoembryonic antigen, have been identified in a variety of malignant tumors. Differences in the expression levels of TAAs between cancer cells and normal cells have led to these antigens being investigated as diagnostic and prognostic biomarkers and as novel targets in cancer treatment. In this review, we summarize the clinical characteristics of TC2N-positive cancers and potential mechanisms of action of TC2N in the occurrence and development of specific cancers. This article provides an exploration of TC2N as a potential target for the diagnosis and treatment of different types of cancers.

TMEM16A protein: calcium binding site and its activation mechanism

TMEM16A mediates calcium-activated transmembrane flow of chloride ion and a variety of physiological functions. The binding of cytoplasmic calcium ions of TMEM16A and the consequent conformational changes of it are the key issues to explore the relationship between its structure and function. In recent years, researchers have explored this issue through electrophysiological experiment, structure resolving, molecular dynamic simulation and other methods. The structures of TMEM16 family members resolved by cryo-Electron microscopy (cryo-EM) and X-ray crystallization provide the primarily basis for the investigation of the molecular mechanism of TMEM16A. However, the binding and activation mechanism of calcium ions in TMEM16A are still unclear and controversial. This review discusses four Ca2+ sensing sites of TMEM16A and analyze activation properties of TMEM16A by them, which will help to understand the structure-function relationship of TMEM16A and throw light on the molecular design targeting TMEM16A channel.

Overexpression of TC2N is associated with poor prognosis in gastric cancer

Background: Tac2-N (TC2N) is a tandem C2 domain-containing protein, acting as a novel oncogene or suppressor in different kinds of cancers. However, the status of TC2N expression and its significance in gastric cancer (GC) is still unclear. The present study is aimed to elucidate the clinicopathological significance and prognostic value of TC2N level in GC. Methods: We used sequencing data from the Cancer Genome Atlas (TCGA) database to analyze TC2N expression in GC by UALCAN database and Gene Expression Profiling Interactive Analysis tools (GEPIA). TC2N expression level in 12 pairs of fresh GC tissues and adjacent nontumorous tissues was detected by quantitative real-time reverse-transcription polymerase chain reaction (RT-PCR) and Western blot (WB) assays. Immunohistochemical (IHC) staining was used to detect TC2N protein expression in Paraffin-embedded tissues in our center. In vitro proliferation, migration and invasion assays were used to evaluate the effect of TC2N on functional capability of gastric cancer cells. LinkedOmics was used to identify gene expressions associated with TC2N. Results: The mRNA and protein expression of TC2N in gastric cancer were both significantly higher than normal gastric mucosa. It was also elevated in gastric cancer cells compared with normal gastric epithelium cell. In vitro assays suggested that TC2N facilitated proliferation, migration and invasion of gastric cancer cells. Bioinformatic analysis showed a widespread impact of TC2N on the transcriptome and a strong interaction with tumor associated genes. We also found that TC2N was an independent prognostic factor for long-term survival in GC patients and its high expression was evidently associated with poor overall survival and recurrence-free survival. Conclusions: Our results show that high level of TC2N correlates with poor prognosis in patients with gastric cancer and promotes the development of gastric cancer. Thus, TC2N expression can serve as a prognostic biomarker for patients with gastric cancer.

Protein Interaction Domains and Post-Translational Modifications: Structural Features and Drug Discovery Applications

Background:

Many pathways regarding healthy cells and/or linked to diseases onset and progression depend on large assemblies including multi-protein complexes. Protein-protein interactions may occur through a vast array of modules known as protein interaction domains (PIDs).

Objective:

This review concerns with PIDs recognizing post-translationally modified peptide sequences and intends to provide the scientific community with state of art knowledge on their 3D structures, binding topologies and potential applications in the drug discovery field.

Method:

Several databases, such as the Pfam (Protein family), the SMART (Simple Modular Architecture Research Tool) and the PDB (Protein Data Bank), were searched to look for different domain families and gain structural information on protein complexes in which particular PIDs are involved. Recent literature on PIDs and related drug discovery campaigns was retrieved through Pubmed and analyzed.

Results and Conclusion:

PIDs are rather versatile as concerning their binding preferences. Many of them recognize specifically only determined amino acid stretches with post-translational modifications, a few others are able to interact with several post-translationally modified sequences or with unmodified ones. Many PIDs can be linked to different diseases including cancer. The tremendous amount of available structural data led to the structure-based design of several molecules targeting protein-protein interactions mediated by PIDs, including peptides, peptidomimetics and small compounds. More studies are needed to fully role out, among different families, PIDs that can be considered reliable therapeutic targets, however, attacking PIDs rather than catalytic domains of a particular protein may represent a route to obtain selective inhibitors.

Pan-Cancer Multiomics Analysis of TC2N Gene Suggests its Important Role(s) in Tumourigenesis of Many Cancers

BACKGROUND

Role of TC2N in carcinogenesis has been largely unfathomed until recently when it was identified as a novel oncogene in lung cancer. Subsequently, a tumour suppressor role of TC2N was reported in breast cancer. It is therefore highly relevant to investigate TC2N molecular partners/mechanisms on a larger scale including a wider range of tumour types.

METHODS

We investigated TC2N mRNA expression, its promoter methylation levels, effects of TC2N transcription on overall patient survival, somatic mutations in TC2N gene and correlation between TC2N mRNA expression and other cancer genes in pan-cancer by using data available from the Cancer Genome Atlas (TCGA) and the Genotype Tissue Expression (GTEx) databases.

RESULTS

TC2N mRNA expression was differentially regulated in 9/33 TCGA tumour types. Of these 9 tumours, 5 tumour types (cholangiocarcinoma, ovarian-serous-cystadenocarcinoma, rectal-adenocarcinoma, stomach-adenocarcinoma and thymoma) had significantly higher TC2N mRNA expression while 4 (pheochromocytoma-and-paraganglioma, skin-cutaneous-melanoma, thyroid-carcinoma and uterine-carcinosarcoma) had significantly lower TC2N mRNA expression compared to matched and normal controls. TC2N promoter was hypermethylated in most cancers while hypomethylated in head-and-neck-squamous-cell-carcinoma and kidney-renal-clear-cell carcinoma. TC2N transcription was positively correlated with transcription of several other cancer genes including genes from Myc, cell-cycle, Nrf2, Wnt, PI3K, Hippo, Notch, TGFβ and RAS/RTK pathways. Poor prognosis was associated with higher TC2N mRNA levels in pancreatic-adenocarcinoma and brain-lower-grade-glioma and lower TC2N mRNA levels in kidney-renal-clear-cell-carcinoma, mesothelioma, sarcoma and skin-cutaneous melanoma. Functional protein partners of TC2N were identified as STX2, SMEK1, SMEK2, STXBP5, SCARA5, MMRN1, CATSPER2, CATSPERB, CLEC4M and STAB2. Many of these proteins are key players in carcinogenesis of various cancers. Highest pathogenic somatic mutation rates in TC2N were found in skin-cutaneous-melanoma, uterine-corpus-endometrial-carcinoma, colon-endocervical-adenocarcinoma, bladder-urothelial-carcinoma and breast-invasive-carcinoma.

CONCLUSION

Our findings unravel several un-explored avenues related to the role of TC2N in tumourigenesis of several cancers, suggesting TC2N as an important player and a potential candidate for tumour-therapy.

Doc2b Ca2+ binding site mutants enhance synaptic release at rest at the expense of sustained synaptic strength

Communication between neurons involves presynaptic neurotransmitter release which can be evoked by action potentials or occur spontaneously as a result of stochastic vesicle fusion. The Ca²⁺-binding double C₂ proteins Doc2a and –b were implicated in spontaneous and asynchronous evoked release, but the mechanism remains unclear. Here, we compared wildtype Doc2b with two Ca²⁺ binding site mutants named DN and 6A, previously classified as gain- and loss-of-function mutants. They carry the substitutions D218,220N or D163,218,220,303,357,359A respectively. We found that both mutants bound phospholipids at low Ca²⁺ concentrations and were membrane-associated in resting neurons, thus mimicking a Ca²⁺-activated state. Their overexpression in hippocampal primary cultured neurons had similar effects on spontaneous and evoked release, inducing high mEPSC frequencies and increased short-term depression. Together, these data suggest that the DN and 6A mutants both act as gain-of-function mutants at resting conditions.

Tac2-N acts as a novel oncogene and promotes tumor metastasis via activation of NF-κB signaling in lung cancer

BACKGROUND

High rates of recurrence and metastasis are the major cause of the poor outcomes for patients with lung cancer. In previous research, we have demonstrated that Tac2-N promotes tumor growth by suppressing p53 signaling in lung cancer. Beyond that, other biological functions and clinical significance of Tac2-N in lung cancer progression are still unknown.

METHODS

Tissue microarrays of 272 lung cancer patients were constructed to assess the association of Tac2-N expression and prognosis of lung cancer patients with different clinical stages. The protein expression of Tac2-N in metastatic and non-metastatic specimens were detected by IHC. In vitro migration and invasion and in vivo nude mice metastasis model were used to evaluate the effect of Tac2-N ectopic expression on metastasis capability of lung cancer cells. The downstream signaling pathway of Tac2-N was explored using luciferase reporter assays and WB.

RESULTS

The expression of Tac2-N was associated with advanced stages, but not with early stages (P = 0.513). Tac2-N expression is sharply overexpressed in metastatic tumors compared with non-metastatic tumors. In vitro and in vivo assays suggested that Tac2-N facilitated migration and invasion of lung cancer cells in vitro and promoted tumor metastasis in vivo. Mechanistically, Tac2-N increased the degradation of IκB by promoting its phosphorylation, and subsequently activated NF-κB activity by facilitating the nuclear translocation of NF-κB and stimulating the transcription of targets, MMP7 and MMP9. Notably, the C2B domain of Tac2-N was crucial for Tac2-N to activate NF-κB signal. Blockage of NF-κB by shRNA or inhibitor attenuates the function of Tac2-N in the promotion of metastasis.

CONCLUSIONS

Our study provided proof of principle to show that Tac2-N serves as a novel oncogene gene and plays an important role in the progression and metastasis of lung cancer.

TC2N, a novel oncogene, accelerates tumor progression by suppressing p53 signaling pathway in lung cancer

The protein containing the C2 domain has been well documented for its essential roles in endocytosis, cellular metabolism and cancer. Tac2-N (TC2N) is a tandem C2 domain-containing protein, but its function, including its role in tumorigenesis, remains unknown. Here, we first identified TC2N as a novel oncogene in lung cancer. TC2N was preferentially upregulated in lung cancer tissues compared with adjacent normal lung tissues. High TC2N expression was significantly associated with poor outcome of lung cancer patients. Knockdown of TC2N markedly induces cell apoptosis and cell cycle arrest with repressing proliferation in vitro, and suppresses tumorigenicity in vivo, whereas overexpression of TC2N has the opposite effects both in vitro and in vivo. Using a combination of TCGA database and bioinformatics, we demonstrate that TC2N is involved in regulation of the p53 signaling pathway. Mechanistically, TC2N attenuates p53 signaling pathway through inhibiting Cdk5-induced phosphorylation of p53 via inducing Cdk5 degradation or disrupting the interaction between Cdk5 and p53. Moreover, the blockade of p53 attenuates the function of TC2N knockdown in the regulation of cell proliferation and apoptosis. In addition, downregulated TC2N is involved in the apoptosis of lung cancer cells induced by doxorubicin, leading to p53 pathway activation. Overall, these findings uncover a role for the p53 inactivator TC2N in regulating the proliferation and apoptosis of lung cancer cells. Our present study provides novel insights into the mechanism of tumorigenesis in lung cancer.

Doc2b Protects β-Cells Against Inflammatory Damage and Enhances Function

Loss of functional β-cell mass is an early feature of type 1 diabetes. To release insulin, β-cells require soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes, as well as SNARE complex regulatory proteins like double C2 domain-containing protein β (Doc2b). We hypothesized that Doc2b deficiency or overabundance may confer susceptibility or protection, respectively, to the functional β-cell mass. Indeed, Doc2b^+/- knockout mice show an unusually severe response to multiple-low-dose streptozotocin (MLD-STZ), resulting in more apoptotic β-cells and a smaller β-cell mass. In addition, inducible β-cell-specific Doc2b-overexpressing transgenic (βDoc2b-dTg) mice show improved glucose tolerance and resist MLD-STZ-induced disruption of glucose tolerance, fasting hyperglycemia, β-cell apoptosis, and loss of β-cell mass. Mechanistically, Doc2b enrichment enhances glucose-stimulated insulin secretion (GSIS) and SNARE activation and prevents the appearance of apoptotic markers in response to cytokine stress and thapsigargin. Furthermore, expression of a peptide containing the Doc2b tandem C2A and C2B domains is sufficient to confer the beneficial effects of Doc2b enrichment on GSIS, SNARE activation, and apoptosis. These studies demonstrate that Doc2b enrichment in the β-cell protects against diabetogenic and proapoptotic stress. Furthermore, they identify a Doc2b peptide that confers the beneficial effects of Doc2b and may be a therapeutic candidate for protecting functional β-cell mass.

DNA promoter methylation-dependent transcription of the double C2-like domain β (DOC2B) gene regulates tumor growth in human cervical cancer

Double C2-like domain β (DOC2B) gene encodes for a calcium-binding protein, which is involved in neurotransmitter release, sorting, and exocytosis. We have identified the promoter region of the DOC2B gene as hypermethylated in pre-malignant, malignant cervical tissues, and cervical cancer cell lines by methylation-sensitive dimethyl sulfoxide-polymerase chain reaction and bisulfite genome sequencing; whereas, it was unmethylated in normal cervical tissues (p < 0.05). The promoter hypermethylation was inversely associated with mRNA expression in SiHa, CaSki, and HeLa cells and treatment with demethylating agent 5-aza-2-deoxycytidine restored DOC2B expression. The region -630 to +25 bp of the DOC2B gene showed robust promoter activity by a luciferase reporter assay and was inhibited by in vitro artificial methylation with Sss1 methylase prior to transient transfections. Overexpression of the DOC2B gene in SiHa cells when compared with controls showed significantly reduced colony formation, cell proliferation, induced cell cycle arrest, and repressed cell migration and invasion (p < 0.05). Ectopic expression of DOC2B resulted in anoikis-mediated cell death and repressed tumor growth in a nude mice xenograft model (p < 0.05). DOC2B expressing cells showed a significant increase in intracellular calcium level (p < 0.05), impaired AKT1 and ERK1/2 signaling, and induced actin cytoskeleton remodeling. Our results show that promoter hypermethylation and silencing of the DOC2B gene is an early and frequent event during cervical carcinogenesis and whose reduced expression due to DNA promoter methylation may lead to selective cervical tumor growth.

Calcium sensing in exocytosis

Neurotransmitters, neuropeptides and hormones are released through regulated exocytosis of synaptic vesicles and large dense core vesicles. This complex and highly regulated process is orchestrated by SNAREs and their associated proteins. The triggering signal for regulated exocytosis is usually an increase in intracellular calcium levels. Besides the triggering role, calcium signaling modulates the precise amount and kinetics of vesicle release. Thus, it is a central question to understand the molecular machineries responsible for calcium sensing in exocytosis. Here we provide an overview of our current understanding of calcium sensing in neurotransmitter release and hormone secretion.

Duplication 16p11.2 in a child with infantile seizure disorder

Submicroscopic recurrent 16p11.2 rearrangements are associated with several neurodevelopmental disorders, including autism, mental retardation, and schizophrenia. The common 16p11.2 region includes 24 known genes, of which 22 are expressed in the developing human fetal nervous system. As yet, the mechanisms leading to neurodevelopmental abnormalities and the broader phenotypes associated with deletion or duplication of 16p11.2 have not been clarified. Here we report a child with spastic quadriparesis, refractory infantile seizures, severe global developmental delay, hypotonia, and microcephaly, and a de novo 598 kb 16p11.2 microduplication. Family history is negative for any of these features in parents and immediate family members. Sequencing analyses showed no mutations in DOC2A, QPRT, and SEZ6L2, genes within the duplicated 16p11.2 region that have been implicated in neuronal function and/or seizure related phenotypes. The child's clinical course is consistent with a rare seizure disorder called malignant migrating partial seizure disorder of infancy, raising the possibility that duplication or disruption of genes in the 16p11.2 interval may contribute to this severe disorder.

DOC2B, C2 domains, and calcium: A tale of intricate interactions

Ca(+2)-dependent exocytosis involves vesicle docking, priming, fusion, and recycling. This process is performed and regulated by a vast number of synaptic proteins and depends on proper protein-protein and protein-lipid interactions. Double C2 domain (DOC2) is a protein family of three isoforms found while screening DNA libraries with a C2 probe. DOC2 has three domains: the Munc13-interacting domain and tandem C2s (designated C2A and C2B) connected by a short polar linker. The C2 domain binds phospholipids in a Ca(2+)-dependent manner. This review focuses on the ubiquitously expressed isoform DOC2B. Sequence alignment of the tandem C2 protein family in mouse revealed high homology (81%) between rabphilin-3A and DOC2B proteins. We created a structural model of DOC2B's C2A based on the crystal structure of rabphilin-3A with and without calcium and found that the calcium-binding loops of DOC2B move upon calcium binding, enabling efficient plasma membrane penetration of its C2A. Here, we discuss the potential relation between the DOC2B bioinformatical model and its function and suggest a possible working model for its interaction with other proteins of the exocytotic machinery, including Munc13, Munc18, and syntaxin.

Calcium-sensing beyond neurotransmitters: functions of synaptotagmins in neuroendocrine and endocrine secretion

Neurotransmitters, neuropeptides and hormones are released through the regulated exocytosis of SVs (synaptic vesicles) and LDCVs (large dense-core vesicles), a process that is controlled by calcium. Synaptotagmins are a family of type 1 membrane proteins that share a common domain structure. Most synaptotagmins are located in brain and endocrine cells, and some of these synaptotagmins bind to phospholipids and calcium at levels that trigger regulated exocytosis of SVs and LDCVs. This led to the proposed synaptotagmin-calcium-sensor paradigm, that is, members of the synaptotagmin family function as calcium sensors for the regulated exocytosis of neurotransmitters, neuropeptides and hormones. Here, we provide an overview of the synaptotagmin family, and review the recent mouse genetic studies aimed at understanding the functions of synaptotagmins in neurotransmission and endocrine-hormone secretion. Also, we discuss potential roles of synaptotagmins in non-traditional endocrine systems.

DOC2b is a SNARE regulator of glucose-stimulated delayed insulin secretion

Insulin secretion is precisely regulated by blood glucose with unique biphasic pattern. The regulatory mechanism of the second-phase insulin release is unclear. In this study, we report that DOC2b (double C2 domain protein isoform b), a SNARE related protein, was associated with insulin vesicles and translocated to plasma membrane within several minutes upon high-glucose stimulation followed by an interaction with syntaxin4, but not syntaxin1. This binding specificity and the time course of DOC2b translocation were suitable for the regulation of second-phase insulin release. Increased DOC2b expression enhanced glucose-stimulated insulin secretion. In contrast, silencing DOC2b inhibited delayed release of insulin, without affecting rapid (approximately 7min) phase secretion. Interestingly, DOC2b had no effects on KCl-triggered insulin release. These data suggest that DOC2b may be a regulator for delayed (second-phase) insulin secretion in MIN6 cells.

Small-molecule agonists of SHIP1 inhibit the phosphoinositide 3-kinase pathway in hematopoietic cells

Because phosphoinositide 3-kinase (PI3K) plays a central role in cellular activation, proliferation, and survival, pharmacologic inhibitors targeting components of the PI3K pathway are actively being developed as therapeutics for the treatment of inflammatory disorders and cancer. These targeted drugs inhibit the activity of either PI3K itself or downstream protein kinases. However, a previously unexplored, alternate strategy is to activate the negative regulatory phosphatases in this pathway. The SH2-containing inositol-5′-phosphatase SHIP1 is a normal physiologic counter-regulator of PI3K in immune/hematopoietic cells that hydrolyzes the PI3K product phosphatidylinositiol-3,4,5-trisphosphate (PIP3). We now describe the identification and characterization of potent and specific small-molecule activators of SHIP1. These compounds represent the first small-molecule activators of a phosphatase, and are able to activate recombinant SHIP1 enzyme in vitro and stimulate SHIP1 activity in intact macrophage and mast cells. Mechanism of activation studies with these compounds suggest that they bind a previously undescribed, allosteric activation domain within SHIP1. Furthermore, in vivo administration of these compounds was protective in mouse models of endotoxemia and acute cutaneous anaphylaxis, suggesting that SHIP1 agonists could be used therapeutically to inhibit the PI3K pathway.

Doc2beta is a novel Munc18c-interacting partner and positive effector of syntaxin 4-mediated exocytosis

The widely expressed Sec/Munc18 (SM) protein Munc18c is required for SNARE-mediated insulin granule exocytosis from islet beta cells and GLUT4 vesicle exocytosis in skeletal muscle and adipocytes. Although Munc18c function is known to involve binding to the t-SNARE Syntaxin 4, a paucity of Munc18c-binding proteins has restricted elucidation of the mechanism by which it facilitates these exocytosis events. Toward this end, we have identified the double C2 domain protein Doc2beta as a new binding partner for Munc18c. Unlike its granule/vesicle localization in neuronal cells, Doc2beta was found principally in the plasma membrane compartment in islet beta cells and adipocytes. Moreover, co-immunoprecipitation and GST interaction assays showed Doc2beta-Munc18c binding to be direct and complexes to be devoid of Syntaxin 4. Supporting the notion of Munc18c binding with Syntaxin 4 and Doc2beta in mutually exclusive complexes, in vitro competition with Syntaxin 4 effectively displaced Munc18c from binding to Doc2beta. The second C2 domain (C2B) of Doc2beta and an N-terminal region of Munc18c were sufficient to confer complex formation. Disruption of endogenous Munc18c-Doc2beta complexes by addition of the Doc2beta binding domain of Munc18c (residues 173-255) was found to selectively inhibit glucose-stimulated insulin release. Moreover, increased expression of Doc2beta enhanced glucose-stimulated insulin secretion by approximately 40%, whereas siRNA-mediated depletion of Doc2beta attenuated insulin release. All changes in secretion correlated with parallel alterations in VAMP2 granule docking with Syntaxin 4. Taken together, these data support a model wherein Munc18c transiently switches from association with Syntaxin 4 to association with Doc2beta at the plasma membrane to facilitate exocytosis.

Calcium sensitivity of neurotransmitter release differs at phasic and tonic synapses

The efficacy of synaptic transmission varies greatly among synaptic contacts. We have explored the origins of differences between phasic and tonic crustacean neuromuscular junctions. Synaptic boutons of a phasic motor neuron release three orders of magnitude more quanta to a single action potential and show strong depression to a train, whereas tonic synapses are nearly unresponsive to single action potentials and display an immense facilitation. Phasic and tonic synapses display a similar nonlinear dependence on extracellular [Ca2+]. We imposed similar spatially uniform intracellular [Ca2+] ([Ca2+]i) steps in phasic and tonic synapses by photolysis of presynaptic caged calcium. [Ca2+]i was measured fluorometrically while transmitter release was monitored electrophysiologically from single boutons in which the [Ca2+]i was elevated. Phasic synapses released the readily releasable pool (RRP) of vesicles at a much higher rate and with a shorter delay than did tonic synapses. Comparison of several kinetic models of molecular events showed that a difference in Ca2+-sensitive priming of vesicles in the RRP combined with a revision of the kinetic Ca2+-binding sequence to the secretory trigger produced the best fit to the markedly different responses to Ca2+ steps and action potentials and of the characteristic features of synaptic plasticity in phasic and tonic synapses. The results reveal processes underlying one aspect of synaptic diversity that may also regulate changes in synaptic strength during development and learning and memory formation.

Calcium concentration threshold and translocation kinetics of EGFP-DOC2B expressed in cultured Aplysia neurons

The double C2 domain protein family (DOC2) is characterized by two calcium-binding domains (C2). Upon binding to calcium, the affinity of the protein to phospholipids is significantly increased, leading to translocation of the protein from the cytosol to the plasma membrane. These properties, and the binding domain of DOC2B to Munc13, suggested that DOC2B could play a role in augmentation and potentiation of synaptic release. Nevertheless, the level of the free intracellular calcium concentration ([Ca(2+)](i)) which triggers its translocation under in vivo conditions, is not known. Using cultured Aplysia neurons that express rat EGFP-DOC2B, we found that the [Ca(2+)](i) increment necessary to induce EGFP-DOC2B translocation is approximately 200 nM in the bulk of the cytoplasm. The rate of EGFP-DOC2B recruitment to the plasma membrane is slower than the [Ca(2+)](i) elevation rate, while the detachment of EGFP-DOC2B from it is faster than the calcium removal. The extent of EGFP-DOC2B translocation to the plasma membrane reflects local submembrane [Ca(2+)](i). Our observations are consistent with the view that DOC2B can participate in the regulation of neurotransmitter release. It should be noted that EGFP-DOC2B could be used as a tool to map sub-membrane calcium dynamics under physiological conditions.

Scholastic achievement: a multivariate analysis of nutritional, intellectual, socioeconomic, sociocultural, familial, and demographic variables in Chilean school-age children

OBJECTIVE

We determined relative effects of nutritional status, intellectual ability, exposure to mass media, and socioeconomic, sociocultural, familial, demographic, and educational variables on scholastic achievement (SA).

METHODS

This was a cross-sectional study. Exposure to mass media and nutritional, intellectual, socioeconomic, sociocultural, familial, demographic, and educational factors, including approximately 2000 variables, were measured in a representative and proportional sample of 4509 school-age children from elementary and high schools in Chile's Metropolitan Region. The field study was carried out between 1986 and 1987, and data processing, which lasted 15 y, was completed in 2002.

RESULTS

Within the total sample, intellectual ability, level of maternal schooling, head circumference-for-age Z score, book reading, in-door plumbing, level of paternal schooling, type of school, quality of housing, height-for-age Z score, and calcium intake were the independent variables with the greatest explanatory power in SA variance (r(2) = 0.508). In most grades, IA was the independent variable with the greatest explanatory power in SA variance. In adolescents in their fourth year of high school and whose physical growth and intellectual development processes are consolidated, intellectual ability, age, head circumference-for-age Z score, book reading, type of school, and level of paternal schooling were the independent variables with the greatest explanatory power in SA variance (r(2) = 0.60).

CONCLUSIONS

These findings show that SA is conditioned by multiple factors depending on the characteristics of school-age children, their families, and the educational system. Nutritional indicators of past nutrition are significantly associated with SA, especially head circumference-for-age Z score. This information may be useful for health and educational planning.

Ca(2+)-induced recruitment of the secretory vesicle protein DOC2B to the target membrane

Ca(2+)-dependent fusion of transport vesicles at their target can be enhanced by intracellular Ca2+ and diacylglycerol. Diacylglycerol induces translocation of the vesicle priming factor Munc13 and association of the secretory vesicle protein DOC2B to the membrane. Here we demonstrate that a rise in intracellular Ca2+ is sufficient for a Munc13-independent recruitment of DOC2B to the target membrane. This novel mechanism occurred readily in the absence of Munc13 and was not influenced by DOC2B mutations that abolish Munc13 binding. Purified DOC2B (expressed as a bacterial fusion protein) bound phospholipids in a Ca(2+)-dependent way, suggesting that the translocation is the result of a C2 domain activation mechanism. Ca(2+)-induced translocation was also observed in cultured neurons expressing DOC2B-enhanced green fluorescent protein. In this case, however, various degrees of membrane association occurred under resting conditions, suggesting that physiological Ca2+ concentrations modulate DOC2B localization. Depolarization of the neurons induced a complete translocation of DOC2B-enhanced green fluorescent protein to the target membrane within 5 s. We hypothesize that this novel Ca(2+)-induced activity of DOC2B functions synergistically with diacylglycerol-induced Munc13 binding to enhance exocytosis during episodes of high secretory activity.

The Drosophila synaptotagmin-like protein bitesize is required for growth and has mRNA localization sequences within its open reading frame

The vertebrate synaptotagmin-like protein granuphilin binds to the vesicle-trafficking proteins Rab27a and Munc18 and can modulate exocytosis of insulin-containing secretory granules in pancreatic beta cell lines. Here, we report the molecular and genetic characterization of bitesize, a granuphilin homolog and the only Drosophila synaptotagmin-like protein. Mutations that affect bitesize have reduced cell size and number, resulting in smaller animals that develop slowly. We also show that at least two classes of bitesize transcripts are localized to the apical plasma membrane in polarized epithelial cells. Whereas most cis-acting mRNA localization sequences map to 3' untranslated regions, bitesize contains a 2.2-kb sequence within its ORF that is necessary and sufficient for apical localization. Thus, we have found that bitesize is a metazoan example of a transcript for which all identifiable mRNA localization sequences are contained within the protein-coding region.

Novel putative nonprotein-coding RNA gene from 11q14 displays decreased expression in brains of patients with schizophrenia

A modified method of differential display was employed to identify a novel gene (named PSZA11q14), the expression of which was reduced in brains from patients with schizophrenia. Decreased expression of PSZA11q14 was identified initially in Brodmann's area (BA) 21 from a small group of patients with schizophrenia (n = 4) and normal controls (n = 6) and was confirmed subsequently using independent RT-PCR assay in BA 21, 22, and 9, and in hippocampus from a larger group of patients with schizophrenia (n = 36) and controls (n = 35). PSZA11q14 is located on chromosome 11q14, an area shown previously to co-segregate with schizophrenia and related disorders in several families. Decreased expression of PSZA11q14 in patients with schizophrenia and its location on 11q14 provide converging lines of evidence indicating that PSZA11q14 may be involved in at least some cases of schizophrenia. PSZA11q14 shows no significant homology with any known gene. It has no introns and produces two RNA transcripts of approximately 4.5 and approximately 7.0 kb. The largest open reading frame (ORF) in the PSZA11q14 transcripts may potentially encode for a short polypeptide of 71 amino acids. High frequency of rare codons, the short size of this ORF, and low homology with mouse sequences, however, indicate that PSZA11q14 may instead represent a novel member of a family of nonprotein-coding RNA genes that are not translated and that function at the RNA level. PSZA11q14 is located within the first intron of the DLG-2 gene and transcribed in the opposite direction to DLG-2. These results suggest that PSZA11q14 may be considered a candidate gene for schizophrenia acting as an antisense regulator of DLG-2, which controls assembling functional N-methyl-D-aspartate (NMDA) receptors.

Mucin secretion and PKC isoforms in SPOC1 goblet cells: differential activation by purinergic agonist and PMA

SPOC1 cells, which are a mucin-secreting model of rat airway goblet cells, possess a luminal P2Y2 purinoceptor through which UTP, ATP, and ATPgammaS stimulate secretion with EC50 values of approximately 3 microM. PMA elicits mucin secretion with high EC50 (75 nM) and saturation (300 nM) values. For the first time in airway mucin-secreting cells, the PKC isoforms expressed and activated by a secretagogue were determined using RT-PCR/restriction-enzyme mapping and Western blotting. Five isoforms were expressed: cPKCalpha, nPKCdelta and -eta, and aPKCzeta and -iota/lambda. PMA caused cPKCalpha and nPKCdelta to translocate to the membrane fraction of SPOC1 cells; only nPKCdelta so responded to ATPgammaS. Membrane-associated nPKCdelta and mucin secretion increased in parallel with ATPgammaS concentration and yielded EC50 values of 2-3 microM and maximum values of 100 microM. Effects of PMA to increase membrane-associated cPKCalpha and nPKCdelta saturated at 30 nM, whereas mucin secretion saturated at 300 nM, which suggests a significant PKC-independent effect of PMA on mucin secretion. A prime alternate phorbol ester-receptor candidate is the C1-domain protein MUNC13. RT-PCR revealed the expression of ubiquitous (ub)MUNC13-2 and its binding partner, DOC2-gamma. Hence, P2Y2 agonists activate nPKCdelta in SPOC1 cells. PMA activates cPKCalpha and nPKCdelta at high affinity and stimulates a lower affinity PKC-independent pathway that leads to mucin secretion.

Mechanism of calcium-independent synaptotagmin binding to target SNAREs

Synaptic vesicle exocytosis requires three SNARE (soluble N-ethylmaleimide-sensitive-factor attachment protein receptor) proteins: syntaxin and SNAP-25 on the plasma membrane (t-SNAREs) and synaptobrevin/VAMP on the synaptic vesicles (v-SNARE). Vesicular synaptotagmin 1 is essential for fast synchronous SNARE-mediated exocytosis and interacts with the SNAREs in brain material. To uncover the step at which synaptotagmin becomes linked to the three SNAREs, we purified all four proteins from brain membranes and analyzed their interactions. Our study reveals that, in the absence of calcium, native synaptotagmin 1 binds the t-SNARE heterodimer, formed from syntaxin and SNAP-25. This interaction is both stoichiometric and of high affinity. Synaptotagmin contains two divergent but conserved C2 domains that can act independently in calcium-triggered phospholipid binding. We now show that both C2 domains are strictly required for the calcium-independent interaction with the t-SNARE heterodimer, indicating that the double C2 domain structure of synaptotagmin may have evolved to acquire a function beyond calcium/phospholipid binding.

Accumulation of 7S SNARE complexes in hippocampal synaptosomes from chronically kindled rats

Kindling is a model of complex partial epilepsy wherein periodic application of an initially subconvulsive stimulus leads to first limbic and then generalized tonic-clonic seizures. Several laboratories have reported that augmented neurotransmitter release of l-glutamate is associated with the chronically kindled state. Neurotransmitter release requires membrane proteins called SNAREs, which form transmembrane complexes that participate in vesicle docking and are required for membrane fusion. We show here that kindling by entorhinal stimulation is associated with an accumulation of 7S SNARE complexes in the ipsilateral hippocampus. This increase of 7S SNARE complexes appears to begin early in the kindling process, achieves a peak with full kindling, and remains at this level for at least a month following cessation of further kindling stimuli. The increase is focal and permanently limited to the ipsilateral hippocampus despite progression to generalized electrographic and behavioral seizures. It is not seen in animals that receive electroconvulsive seizures, suggesting it is related to the kindling process itself. The duration and focality of increased 7S SNARE complexes with entorhinal kindling suggest that this is an altered molecular process associated with epileptogenesis.

Synaptotagmin-like protein 5: a novel Rab27A effector with C-terminal tandem C2 domains

Synaptotagmin-like proteins 1-4 (Slp1-4) are new members of the carboxyl-terminal-type (C-type) tandem C2 proteins and are classified as a subfamily distinct from the synaptotagmin and the Doc2 families, because the Slp family contains a unique homology domain at the amino terminus, referred to as the Slp homology domain (SHD). We previously showed that the SHD functions as a binding site for Rab27A, which is associated with human hemophagocytic syndrome (Griscelli syndrome) [J. Biol. Chem. 277 (2002) 9212; J. Biol. Chem. 277 (2002) 12432]. In the present study, we identified a novel member of the Slp family, Slp5. The same as other Slp family members, the SHD of Slp5 preferentially interacted with the GTP-bound form of Rab27A and marginally with Rab3A and Rab6A, both in vitro and in intact cells, but not with other Rabs tested (Rab1, Rab2, Rab4A, Rab5A, Rab7, Rab8, Rab9, Rab10, Rab11A, Rab17, Rab18, Rab20, Rab22, Rab23, Rab25, Rab28, and Rab37). However, unlike other members of the Slp family, expression of Slp5 mRNA was highly restricted to human placenta and liver. Expression of Slp5 protein and in vivo association of Slp5 with Rab27A in the mouse liver were further confirmed by immunoprecipitation. The results suggest that Slp5 might be involved in Rab27A-dependent membrane trafficking in specific tissues.

Short-term synaptic plasticity

Synaptic transmission is a dynamic process. Postsynaptic responses wax and wane as presynaptic activity evolves. This prominent characteristic of chemical synaptic transmission is a crucial determinant of the response properties of synapses and, in turn, of the stimulus properties selected by neural networks and of the patterns of activity generated by those networks. This review focuses on synaptic changes that result from prior activity in the synapse under study, and is restricted to short-term effects that last for at most a few minutes. Forms of synaptic enhancement, such as facilitation, augmentation, and post-tetanic potentiation, are usually attributed to effects of a residual elevation in presynaptic [Ca(2+)]i, acting on one or more molecular targets that appear to be distinct from the secretory trigger responsible for fast exocytosis and phasic release of transmitter to single action potentials. We discuss the evidence for this hypothesis, and the origins of the different kinetic phases of synaptic enhancement, as well as the interpretation of statistical changes in transmitter release and roles played by other factors such as alterations in presynaptic Ca(2+) influx or postsynaptic levels of [Ca(2+)]i. Synaptic depression dominates enhancement at many synapses. Depression is usually attributed to depletion of some pool of readily releasable vesicles, and various forms of the depletion model are discussed. Depression can also arise from feedback activation of presynaptic receptors and from postsynaptic processes such as receptor desensitization. In addition, glial-neuronal interactions can contribute to short-term synaptic plasticity. Finally, we summarize the recent literature on putative molecular players in synaptic plasticity and the effects of genetic manipulations and other modulatory influences.

Slac2-a/melanophilin, the missing link between Rab27 and myosin Va: implications of a tripartite protein complex for melanosome transport

Myosin Va is a member of the unconventional class V myosin family, and a mutation in the myosin Va gene causes pigment granule transport defects in human Griscelli syndrome and dilute mice. How myosin Va recognizes its cargo (i.e. melanosomes), however, has remained undetermined over the past decade. In this study, we discovered Slac2-a/melanophilin to be the "missing link" between myosin Va and GTP-Rab27A present in the melanosome. Deletion analysis and site-directed mutagenesis showed that the N-terminal Slp (synaptotagmin-like protein) homology domain of Slac2-a specifically binds Rab27A/B isoforms and that the C-terminal half directly binds the globular tail of myosin Va. The tripartite protein complex (Rab27A.Slac2-a.myosin Va) in melanoma cells was further confirmed by immunoprecipitation. The discovery that myosin Va indirectly recognizes its cargo through Slac2-a, a novel Rab27A/B effector, should shed light on molecular recognition of its specific cargo by class V myosin.

The C2A domain of double C2 protein gamma contains a functional nuclear localization signal

The C2 domain was originally defined as a homologous domain to the C2 regulatory region of Ca2+ -dependent protein kinase C and has been identified in more than 50 different signaling molecules. The original C2 domain of protein kinase Calpha functions as a Ca2+ binding module, and the Ca2+ binding to the C2 domain allows translocation of proteins to phospholipid membranes. By contrast, however, some C2 domains do not exhibit Ca2+ binding activity because of amino acid substitutions at Ca2+ -binding sites, and their physiological meanings remain largely unknown. In this study, we discovered an unexpected function of the Ca2+ -independent C2A domain of double C2 protein gamma (Doc2gamma) in nuclear localization. Deletion and mutation analyses revealed that the putative Ca2+ binding loop 3 of Doc2gamma contains six Arg residues ((177)RLRRRRR(183)) and that this basic cluster is both necessary and sufficient for nuclear localization of Doc2gamma. Because of the presence of the basic cluster, the C2A domain of Doc2gamma did not show Ca2+ -dependent phospholipid binding activity. Our findings indicate that by changing the nature of the putative Ca2+ binding loops the C2 domain has more diversified function in cellular signaling than a simple Ca2+ binding motif.

Synaptic vesicle endocytosis: calcium works overtime in the nerve terminal

The functions of Ca2+ are many and varied within cells, but in the nerve terminals of neurons it has had a very defined role. That is, the influx of extracellular Ca2+ through voltage-dependent Ca2+ channels stimulates neurotransmitter release by exocytosis. For years this was assumed to be the main role for Ca2+ in this specialized subcellular region. However recent studies have shown that Ca2+ also has multiple roles in synaptic-vesicle endocytosis. This review will present evidence for three Ca2+-dependent and -independent steps; a high-affinity Ca2+-dependent triggering step, a Ca2+-independent maintenance phase, and a low-affinity Ca2+-dependent inhibition step. How the control of endocytosis by Ca2+ might impact on different neuronal functions such as synaptic transmission, the nucleation of SV endocytosis, and the repair of damaged membrane is then discussed.