A concanavalin A-like lectin domain in the CHS1/LYST protein, shared by members of the BEACH family

Mutations in RABE1C suppress the spirrig mutant phenotype

The plant BEACH-domain protein SPIRRIG (SPI) is involved in regulating cell morphogenesis and salt stress responses in Arabidopsis thaliana, Arabis alpina, and Marchantia polymorpha and was reported to function in the context of two unrelated cellular processes: vesicular trafficking and P-body mediated RNA metabolism. To further explore the molecular function of SPI, we isolated a second-site mutant, specifically rescuing the spi mutant trichome phenotype. The molecular analysis of the corresponding gene revealed a dominant negative mutation in RABE1C, a ras-related small GTP-binding protein that localizes to Golgi. Taken together, our data identified the genetic interaction between RABE1C and SPI, which is beneficial for further dissecting the function of SPI in vesicle trafficking-associated cell morphogenesis.

Lysosomal trafficking regulator restricts intracellular growth of Coxiella burnetii by inhibiting the expansion of Coxiella-containing vacuole and upregulating nos2 expression

Coxiella burnetii is an obligate intracellular bacterium that causes Q fever, a zoonotic disease typically manifests as a severe flu-illness. After invading into the host cells, C. burnetii delivers effectors to regulate the vesicle trafficking and fusion events to form a large and mature Coxiella-containing vacuole (CCV), providing sufficient space and nutrition for its intracellular growth and proliferation. Lysosomal trafficking regulator (LYST) is a member of the Beige and Chediak-Higashi syndrome (BEACH) family, which regulates the transport of vesicles to lysosomes and regulates TLR signaling pathway, but the effect of LYST on C. burnetii infection is unclear. In this study, a series of experiments has been conducted to investigate the influence of LYST on intracellular growth of C. burnetii. Our results showed that lyst transcription was up-regulated in the host cells after C. burnetii infection, but there is no significant change in lyst expression level after infection with the Dot/Icm type IV secretion system (T4SS) mutant strain, while CCVs expansion and significantly increasing load of C. burnetii appeared in the host cells with a silenced lyst gene, suggesting LYST inhibits the intracellular proliferation of C. burnetii by reducing CCVs size. Then, the size of CCVs and the load of C. burnetii in the HeLa cells pretreated with E-64d were significantly decreased. In addition, the level of iNOS was decreased significantly in LYST knockout THP-1 cells, which was conducive to the intracellular replication of C. burnetii. This data is consistent with the phenotype of L-NMMA-treated THP-1 cells infected with C. burnetii. Our results revealed that the upregulation of lyst transcription after infection is due to effector secretion of C. burnetii and LYST inhibit the intracellular replication of C. burnetii by reducing the size of CCVs and inducing nos2 expression.

Kratosvirus quantuckense: the history and novelty of an algal bloom disrupting virus and a model for giant virus research

Since the discovery of the first "giant virus," particular attention has been paid toward isolating and culturing these large DNA viruses through Acanthamoeba spp. bait systems. While this method has allowed for the discovery of plenty novel viruses in the Nucleocytoviricota, environmental -omics-based analyses have shown that there is a wealth of diversity among this phylum, particularly in marine datasets. The prevalence of these viruses in metatranscriptomes points toward their ecological importance in nutrient turnover in our oceans and as such, in depth study into non-amoebal Nucleocytoviricota should be considered a focal point in viral ecology. In this review, we report on Kratosvirus quantuckense (née Aureococcus anophagefferens Virus), an algae-infecting virus of the Imitervirales. Current systems for study in the Nucleocytoviricota differ significantly from this virus and its relatives, and a litany of trade-offs within physiology, coding potential, and ecology compared to these other viruses reveal the importance of K. quantuckense. Herein, we review the research that has been performed on this virus as well as its potential as a model system for algal-virus interactions.

The Tetrahymena bcd1 mutant implicates endosome trafficking in ciliate, cortical pattern formation

Ciliates, such as Tetrahymena thermophila, evolved complex mechanisms to determine both the location and dimensions of cortical organelles such as the oral apparatus (OA: involved in phagocytosis), cytoproct (Cyp: for eliminating wastes), and contractile vacuole pores (CVPs: involved in water expulsion). Mutations have been recovered in Tetrahymena that affect both the localization of such organelles along anterior-posterior and circumferential body axes and their dimensions. Here we describe BCD1, a ciliate pattern gene that encodes a conserved Beige-BEACH domain-containing protein a with possible protein kinase A (PKA)-anchoring activity. Similar proteins have been implicated in endosome trafficking and are linked to human Chediak-Higashi syndrome and autism. Mutations in the BCD1 gene broaden cortical organelle domains as they assemble during predivision development. The Bcd1 protein localizes to membrane pockets at the base of every cilium that are active in endocytosis. PKA activity has been shown to promote endocytosis in other organisms, so we blocked clathrin-mediated endocytosis (using "dynasore") and inhibited PKA (using H89). In both cases, treatment produced partial phenocopies of the bcd1 pattern mutant. This study supports a model in which the dimensions of diverse cortical organelle assembly-platforms may be determined by regulated balance between constitutive exocytic delivery and PKA-regulated endocytic retrieval of organelle materials and determinants.

The evolving biology of cross-presentation

Cross-priming was first recognized in the context of in vivo cytotoxic T lymphocyte (CTL) responses generated against minor histocompatibility antigens induced by immunization with lymphoid cells. Even though the basis for T cell antigen recognition was still largely unclear at that time, these early studies recognized the implication that such minor histocompatibility antigens were derived from the immunizing cells and were obtained exogenously by the host's antigen presenting cells (APCs) that directly prime the CTL response. As antigen recognition by the T cell receptor became understood to involve peptides derived from antigens processed by the APCs and presented by major histocompatibility molecules, the "cross-priming" phenomenon was subsequently recast as "cross-presentation" and the scope considered for examining this process gradually broadened to include many different forms of antigens, including soluble proteins, and different types of APCs that may not be involved in in vivo CTL priming. Many studies of cross-presentation have relied on in vitro cell models that were recently found to differ from in vivo APCs in particular mechanistic details. A recent trend has focused on the APCs and pathways of cross-presentation used in vivo, especially the type 1 dendritic cells. Current efforts are also being directed towards validating the in vivo role of various putative pathways and gene candidates in cross-presentation garnered from various in vitro studies and to determine the relative contributions they make to CTL responses across various forms of antigens and immunologic settings. Thus, cross-presentation appears to be carried by different pathways in various types of cells for different forms under different physiologic settings, which remain to be evaluated in an in vivo physiologic setting.

The retinal pigmentation pathway in human albinism: Not so black and white

Albinism is a pigment disorder affecting eye, skin and/or hair. Patients usually have decreased melanin in affected tissues and suffer from severe visual abnormalities, including foveal hypoplasia and chiasmal misrouting. Combining our data with those of the literature, we propose a single functional genetic retinal signalling pathway that includes all 22 currently known human albinism disease genes. We hypothesise that defects affecting the genesis or function of different intra-cellular organelles, including melanosomes, cause syndromic forms of albinism (Hermansky-Pudlak (HPS) and Chediak-Higashi syndrome (CHS)). We put forward that specific melanosome impairments cause different forms of oculocutaneous albinism (OCA1-8). Further, we incorporate GPR143 that has been implicated in ocular albinism (OA1), characterised by a phenotype limited to the eye. Finally, we include the SLC38A8-associated disorder FHONDA that causes an even more restricted "albinism-related" ocular phenotype with foveal hypoplasia and chiasmal misrouting but without pigmentation defects. We propose the following retinal pigmentation pathway, with increasingly specific genetic and cellular defects causing an increasingly specific ocular phenotype: (HPS1-11/CHS: syndromic forms of albinism)-(OCA1-8: OCA)-(GPR143: OA1)-(SLC38A8: FHONDA). Beyond disease genes involvement, we also evaluate a range of (candidate) regulatory and signalling mechanisms affecting the activity of the pathway in retinal development, retinal pigmentation and albinism. We further suggest that the proposed pigmentation pathway is also involved in other retinal disorders, such as age-related macular degeneration. The hypotheses put forward in this report provide a framework for further systematic studies in albinism and melanin pigmentation disorders.

Anti-inflammatory and anti-necrotic effects of lectins from Canavalia ensiformis and Canavalia brasiliensis in experimental acute pancreatitis

Lectins isolated from Canavalia ensiformis (ConA) and Canavalia brasiliensis (ConBr) are promising molecules to prevent cell death. Acute pancreatitis, characterized by acinar cell necrosis and inflammation, presents significant morbidity and mortality. This study has investigated the effects of ConA and ConBr in experimental acute pancreatitis and pancreatic acinar cell death induced by bile acid. Pancreatitis was induced by retrograde pancreatic ductal injection of 3% sodium taurocholate (Na-TC) in male Swiss mice. ConA or ConBr (0.1, 1 or 10 mg/kg) were intravenously applied to mice 1 h and 12 h after induction. After 24 h, the severity of pancreatitis was evaluated by serum amylase and lipase, histopathological changes and myeloperoxidase assay. Pancreatic acinar cells were incubated with ConA (200 µg/ml) or ConBr (200 µg/ml) and taurolithocholic acid 3-sulfate (TLCS; 500 µM). Necrosis and changes in mitochondrial membrane potential (ΔѰm) were detected by fluorescence confocal microscopy. Treatment (post-insult) with ConA and ConBr decreased pancreatic damage caused by retrograde injection of Na-TC in mice, reducing pancreatic neutrophil infiltration, edema and necrosis. In addition, ConA and ConBr decreased pancreatic acinar cell necrosis and depolarization of ΔѰm caused by TLCS. The inhibition of necrosis was prevented by the lectin domain blockade. In conclusion, ConA and ConBr markedly inhibited in vitro and in vivo damage, effects partly dependent on the interaction with mannose residues on acinar cells. These data support the potential application of these proteins for treatment of acute pancreatitis.

The road to lysosome-related organelles: Insights from Hermansky-Pudlak syndrome and other rare diseases

Lysosome-related organelles (LROs) comprise a diverse group of cell type-specific, membrane-bound subcellular organelles that derive at least in part from the endolysosomal system but that have unique contents, morphologies and functions to support specific physiological roles. They include: melanosomes that provide pigment to our eyes and skin; alpha and dense granules in platelets, and lytic granules in cytotoxic T cells and natural killer cells, which release effectors to regulate hemostasis and immunity; and distinct classes of lamellar bodies in lung epithelial cells and keratinocytes that support lung plasticity and skin lubrication. The formation, maturation and/or secretion of subsets of LROs are dysfunctional or entirely absent in a number of hereditary syndromic disorders, including in particular the Hermansky-Pudlak syndromes. This review provides a comprehensive overview of LROs in humans and model organisms and presents our current understanding of how the products of genes that are defective in heritable diseases impact their formation, motility and ultimate secretion.

Puccinia triticina pathotypes THTT and THTS display complex transcript profiles on wheat cultivar Thatcher

BACKGROUND

Wheat leaf rust is an important disease worldwide. Understanding the pathogenic molecular mechanism of Puccinia triticina Eriks. (Pt) and the inconstant toxic region is critical for managing the disease. The present study aimed to analyze the pathogenic divergence between Pt isolates.

RESULTS

Total RNA was extracted from the wheat cultivar Thatcher infected by two Pt isolates, Tc361_1 (THTT) and Tc284_2 (THTS), at 144 h post inoculation (hpi). The mRNA was then sequenced, and a total of 2784 differentially expressed genes (DEGs) were detected. Forty-five genes were specifically expressed in THTT; these genes included transcription initiation factors and genes with transmembrane transporter activity and other genes. Twenty-six genes were specifically expressed in THTS, including genes with GTPase activity, ABC transporters and other genes. Fifty-four differentially expressed candidate effectors were screened from the two isolates. Two candidate effectors were chosen and validated on tobacco, and the results showed that they could inhibit necrosis induced by BAX. qRT-PCR of 12 significant DEGs was carried out to validate that the results are similar to those of RNA-seq at 144 hpi, to show the expression levels of these DEGs in the early stage and to elucidate the differences in expression between the two Pt pathotypes.

CONCLUSION

The results obtained in this study showed that although the two pathotypes of THTT and THTS contribute similar virulence to wheat, there are a large number of genes participate in the interaction with the susceptible wheat cultivar Thatcher, and revealed the pathogenicity of rust is very complicated.

Evolutionary Comparison of the Developmental/Physiological Phenotype and the Molecular Behavior of SPIRRIG Between Arabidopsis thaliana and Arabis alpina

Beige and Chediak Higashi (BEACH) domain proteins mediate membrane-dependent processes in eukaryotic cells. The plant BEACH domain protein SPIRRIG in A. thaliana (AtSPI) was shown to display a similar molecular behavior as its yeast and animal homologs, along with a range of cell morphological defects. In addition, AtSPI was shown to interact with the P-body component DCP1, to differentially effect RNA levels and to be involved in the regulation of RNA stability in the context of salt stress responses. To determine, whether the dual function of SPI in apparently unrelated molecular pathways and traits is evolutionary conserved, we analyzed three Aaspi alleles in Arabis alpina. We show that the molecular behavior of the SPI protein and the role in cell morphogenesis and salt stress response are similar in the two species, though we observed distinct deviations in the phenotypic spectrum.

CTLA4 Message Reflects Pathway Disruption in Monogenic Disorders and Under Therapeutic Blockade

CTLA-4 is essential for immune tolerance. Heterozygous CTLA4 mutations cause immune dysregulation evident in defective regulatory T cells with low levels of CTLA-4 expression. Biallelic mutations in LRBA also result in immune dysregulation with low levels of CTLA-4 and clinical presentation indistinguishable from CTLA-4 haploinsufficiency. CTLA-4 has become an immunotherapy target whereby its blockade with a monoclonal antibody has resulted in improved survival in advanced melanoma patients, amongst other malignancies. However, this therapeutic manipulation can result in autoimmune/inflammatory complications reminiscent of those seen in genetic defects affecting the CTLA-4 pathway. Despite efforts made to understand and establish disease genotype/phenotype correlations in CTLA-4-haploinsufficiency and LRBA-deficiency, such relationships remain elusive. There is currently no specific immunological marker to assess the degree of CTLA-4 pathway disruption or its relationship with clinical manifestations. Here we compare three different patient groups with disturbances in the CTLA-4 pathway—CTLA-4-haploinsufficiency, LRBA-deficiency, and ipilimumab-treated melanoma patients. Assessment of CTLA4 mRNA expression in these patient groups demonstrated an inverse correlation between the CTLA4 message and degree of CTLA-4 pathway disruption. CTLA4 mRNA levels from melanoma patients under therapeutic CTLA-4 blockade (ipilimumab) were increased compared to patients with either CTLA4 or LRBA mutations that were clinically stable with abatacept treatment. In summary, we show that increased CTLA4 mRNA levels correlate with the degree of CTLA-4 pathway disruption, suggesting that CTLA4 mRNA levels may be a quantifiable surrogate for altered CTLA-4 expression.

LRBA in the endomembrane system

Bi-allelic mutations in LRBA (from Lipopolysaccharide-responsive and beige-like anchor protein) result in a primary immunodeficiency with clinical features ranging from hypogammaglobulinemia and lymphoproliferative syndrome to inflammatory bowel disease and heterogeneous autoimmune manifestations. LRBA deficiency has been shown to affect vesicular trafficking, autophagy and apoptosis, which may lead to alterations of several molecules and processes that play key roles for immunity.

In this review, we will discuss the relationship of LRBA with the endovesicular system in the context of receptor trafficking, autophagy and apoptosis. Since these mechanisms of homeostasis are inherent to all living cells and not only limited to the immune system and also, because they are involved in physiological as well as pathological processes such as embryogenesis or tumoral transformation, we envisage advancing in the identification of potential pharmacological agents to manipulate these processes.

Molecular Dissection of Neurobeachin Function at Excitatory Synapses

Spines are small protrusions from dendrites where most excitatory synapses reside. Changes in number, shape, and size of dendritic spines often reflect changes of neural activity in entire circuits or at individual synapses, making spines key structures of synaptic plasticity. Neurobeachin is a multidomain protein with roles in spine formation, postsynaptic neurotransmitter receptor targeting and actin distribution. However, the contributions of individual domains of Neurobeachin to these functions is poorly understood. Here, we used mostly live cell imaging and patch-clamp electrophysiology to monitor morphology and function of spinous synapses in primary hippocampal neurons. We demonstrate that a recombinant full-length Neurobeachin from humans can restore mushroom spine density and excitatory postsynaptic currents in neurons of Neurobeachin-deficient mice. We then probed the role of individual domains of Neurobeachin by comparing them to the full-length molecule in rescue experiments of knockout neurons. We show that the combined PH-BEACH domain complex is highly localized in spine heads, and that it is sufficient to restore normal spine density and surface targeting of postsynaptic AMPA receptors. In addition, we report that the Armadillo domain facilitates the formation of filopodia, long dendritic protrusions which often precede the development of mature spines, whereas the PKA-binding site appears as a negative regulator of filopodial extension. Thus, our results indicate that individual domains of Neurobeachin sustain important and specific roles in the regulation of spinous synapses. Since heterozygous mutations in Neurobeachin occur in autistic patients, the results will also improve our understanding of pathomechanism in neuropsychiatric disorders associated with impairments of spine function.

Potential for therapeutic targeting of AKAP signaling complexes in nervous system disorders

A common feature of neurological and neuropsychiatric disorders is a breakdown in the integrity of intracellular signal transduction pathways. Dysregulation of ion channels and receptors in the cell membrane and the enzymatic mediators that link them to intracellular effectors can lead to synaptic dysfunction and neuronal death. However, therapeutic targeting of these ubiquitous signaling elements can lead to off-target side effects due to their widespread expression in multiple systems of the body. A-kinase anchoring proteins (AKAPs) are multivalent scaffolding proteins that compartmentalize a diverse range of receptor and effector proteins to streamline signaling within nanodomain signalosomes. A number of essential neurological processes are known to critically depend on AKAP-directed signaling and an understanding of the role AKAPs play in nervous system disorders has emerged in recent years. Selective targeting of AKAP protein-protein interactions may be a means to uncouple pathologically active signaling pathways in neurological disorders with a greater degree of specificity. In this review we will discuss the role of AKAPs in both regulating normal nervous system function and dysfunction associated with disease, and the potential for therapeutic targeting of AKAP signaling complexes.

The Neurobeachin-like 2 Protein Regulates Mast Cell Homeostasis

The neurobeachin-like 2 protein (Nbeal2) belongs to the family of beige and Chediak-Higashi (BEACH) domain proteins. Loss-of-function mutations in the human NBEAL2 gene or Nbeal2 deficiency in mice cause gray platelet syndrome, a bleeding disorder characterized by macrothrombocytopenia, splenomegaly, and paucity of α-granules in megakaryocytes and platelets. We found that in mast cells, Nbeal2 regulates the activation of the Shp1-STAT5 signaling axis and the composition of the c-Kit/STAT signalosome. Furthermore, Nbeal2 mediates granule formation and restricts the expression of the transcription factors, IRF8, GATA2, and MITF as well as of the cell-cycle inhibitor p27, which are essential for mast cell differentiation, proliferation, and cytokine production. These data demonstrate the relevance of Nbeal2 in mast cells above and beyond granule biosynthesis.

Dawning of the age of genomics for platelet granule disorders: improving insight, diagnosis and management

Inherited disorders of platelet granules are clinically heterogeneous and their prevalence is underestimated because most patients do not undergo a complete diagnostic work-up. The lack of a genetic diagnosis limits the ability to tailor management, screen family members, aid with family planning, predict clinical progression and detect serious consequences, such as myelofibrosis, lung fibrosis and malignancy, in a timely manner. This is set to change with the introduction of high throughput sequencing (HTS) as a routine clinical diagnostic test. HTS diagnostic tests are now available, affordable and allow parallel screening of DNA samples for variants in all of the 80 known bleeding, thrombotic and platelet genes. Increased genetic diagnosis and curation of variants is, in turn, improving our understanding of the pathobiology and clinical course of inherited platelet disorders. Our understanding of the genetic causes of platelet granule disorders and the regulation of granule biogenesis is a work in progress and has been significantly enhanced by recent genomic discoveries from high-powered genome-wide association studies and genome sequencing projects. In the era of whole genome and epigenome sequencing, new strategies are required to integrate multiple sources of big data in the search for elusive, novel genes underlying granule disorders.

Nuclear Localization of the Autism Candidate Gene Neurobeachin and Functional Interaction with the NOTCH1 Intracellular Domain Indicate a Role in Regulating Transcription

BACKGROUND

Neurobeachin (NBEA) is an autism spectrum disorders (ASD) candidate gene. NBEA deficiency affects regulated secretion, receptor trafficking, synaptic architecture and protein kinase A (PKA)-mediated phosphorylation. NBEA is a large multidomain scaffolding protein. From N- to C-terminus, NBEA has a concanavalin A-like lectin domain flanked by armadillo repeats (ACA), an A-kinase anchoring protein domain that can bind to PKA, a domain of unknown function (DUF1088) and a BEACH domain, preceded by a pleckstrin homology-like domain and followed by WD40 repeats (PBW). Although most of these domains mediate protein-protein interactions, no interaction screen has yet been performed.

METHODS

Yeast two-hybrid screens with the ACA and PBW domain modules of NBEA gave a list of interaction partners, which were analyzed for Gene Ontology (GO) enrichment. Neuro-2a cells were used for confocal microscopy and nuclear extraction analysis. NOTCH-mediated transcription was studied with luciferase reporter assays and qRT-PCR, combined with NBEA knockdown or overexpression.

RESULTS

Both domain modules showed a GO enrichment for the nucleus. PBW almost exclusively interacted with transcription regulators, while ACA interacted with a number of PKA substrates. NBEA was partially localized in the nucleus of Neuro-2a cells, albeit much less than in the cytoplasm. A nuclear localization signal was found in the DUF1088 domain, which was shown to contribute to the nuclear localization of an EGFP-DPBW fusion protein. Yeast two-hybrid identified the Notch1 intracellular domain as a physical interactor of the PBW domain and a role for NBEA as a negative regulator in Notch-mediated transcription was demonstrated.

CONCLUSION

Defining novel interaction partners of conserved NBEA domain modules identified a role for NBEA as transcriptional regulator in the nucleus. The physical interaction of NBEA with NOTCH1 is most relevant for ASD pathogenesis because NOTCH signaling is essential for neural development.

The BEACH Domain Protein SPIRRIG Is Essential for Arabidopsis Salt Stress Tolerance and Functions as a Regulator of Transcript Stabilization and Localization

Members of the highly conserved class of BEACH domain containing proteins (BDCPs) have been established as broad facilitators of protein-protein interactions and membrane dynamics in the context of human diseases like albinism, bleeding diathesis, impaired cellular immunity, cancer predisposition, and neurological dysfunctions. Also, the Arabidopsis thaliana BDCP SPIRRIG (SPI) is important for membrane integrity, as spi mutants exhibit split vacuoles. In this work, we report a novel molecular function of the BDCP SPI in ribonucleoprotein particle formation. We show that SPI interacts with the P-body core component DECAPPING PROTEIN 1 (DCP1), associates to mRNA processing bodies (P-bodies), and regulates their assembly upon salt stress. The finding that spi mutants exhibit salt hypersensitivity suggests that the local function of SPI at P-bodies is of biological relevance. Transcriptome-wide analysis revealed qualitative differences in the salt stress-regulated transcriptional response of Col-0 and spi. We show that SPI regulates the salt stress-dependent post-transcriptional stabilization, cytoplasmic agglomeration, and localization to P-bodies of a subset of salt stress-regulated mRNAs. Finally, we show that the PH-BEACH domains of SPI and its human homolog FAN (Factor Associated with Neutral sphingomyelinase activation) interact with DCP1 isoforms from plants, mammals, and yeast, suggesting the evolutionary conservation of an association of BDCPs and P-bodies.

LYST controls the biogenesis of the endosomal compartment required for secretory lysosome function

Chediak-Higashi syndrome (CHS) is caused by mutations in the gene encoding LYST protein, the function of which remains poorly understood. Prominent features of CHS include defective secretory lysosome exocytosis and the presence of enlarged, lysosome-like organelles in several cell types. In order to get further insight into the role of LYST in the biogenesis and exocytosis of cytotoxic granules, we analyzed cytotoxic T lymphocytes (CTLs) from patients with CHS. Using confocal microscopy and correlative light electron microscopy, we showed that the enlarged organelle in CTLs is a hybrid compartment that contains proteins components from recycling-late endosomes and lysosomes. Enlargement of cytotoxic granules results from the progressive clustering and then fusion of normal-sized endolysosomal organelles. At the immunological synapse (IS) in CHS CTLs, cytotoxic granules have limited motility and appear docked while nevertheless unable to degranulate. By increasing the expression of effectors of lytic granule exocytosis, such as Munc13-4, Rab27a and Slp3, in CHS CTLs, we were able to restore the dynamics and the secretory ability of cytotoxic granules at the IS. Our results indicate that LYST is involved in the trafficking of the effectors involved in exocytosis required for the terminal maturation of perforin-containing vesicles into secretory cytotoxic granules.

Autosomal-recessive complicated spastic paraplegia with a novel lysosomal trafficking regulator gene mutation

BACKGROUND

Autosomal-recessive hereditary spastic paraplegias (AR-HSP) consist of a genetically diverse group of neurodegenerative diseases characterised by pyramidal tracts dysfunction. The causative genes for many types of AR-HSP remain elusive. We tried to identify the gene mutation for AR-HSP with cerebellar ataxia and neuropathy.

METHODS

This study included two patients in a Japanese family with their parents who are first cousins. Neurological examination and gene analysis were conducted in the two patients and two normal family members. We undertook genome-wide linkage analysis employing single nucleotide polymorphism arrays using the two patients' DNAs and exome sequencing using one patient's sample.

RESULTS

We detected a homozygous missense mutation (c.4189T>G, p.F1397V) in the lysosomal trafficking regulator (LYST) gene, which is described as the causative gene for Chédiak-Higashi syndrome (CHS). CHS is a rare autosomal-recessive syndrome characterised by hypopigmentation, severe immune deficiency, a bleeding tendency and progressive neurological dysfunction. This mutation was co-segregated with the disease in the family and was located at well-conserved amino acid. This LYST mutation was not found in 200 Japanese control DNAs. Microscopic observation of peripheral blood in the two patients disclosed large peroxidase-positive granules in both patients' granulocytes, although they had no symptoms of immune deficiency or bleeding tendency.

CONCLUSIONS

We diagnosed these patients as having adult CHS presenting spastic paraplegia with cerebellar ataxia and neuropathy. The clinical spectrum of CHS is broader than previously recognised. Adult CHS must be considered in the differential diagnosis of AR-HSP.

Platelets of mice heterozygous for neurobeachin, a candidate gene for autism spectrum disorder, display protein changes related to aberrant protein kinase A activity

BACKGROUND

Neurobeachin (NBEA) has been identified as a candidate gene for autism spectrum disorders (ASD) in several unrelated patients with alterations in the NBEA gene. The exact function of NBEA, a multidomain scaffolding protein, is currently unknown. It contains an A-kinase anchoring protein (AKAP) domain which binds the regulatory subunit of protein kinase A (PKA) thereby confining its activity to specific subcellular regions. NBEA has been implicated in post-Golgi membrane trafficking and in regulated secretion. The mechanism of regulated secretion is largely conserved between neurons and platelets, and the morphology of platelet dense granules was found to be abnormal in several ASD patients, including one with NBEA haploinsufficiency. Platelet dense granules are secreted upon vascular injury when platelets are exposed to for instance collagen. Dense granules contain serotonin, ATP and ADP, which are necessary for platelet plug formation and vascular contraction.

METHODS

To further investigate possible roles for NBEA in secretion or dense granule morphology, platelets from Nbea+/- mice were analyzed morphometrically, functionally and biochemically. A differential proteomics and peptidomics screen was performed between Nbea+/- and Nbea+/+ mice, in which altered Talin-1 cleavage was further investigated and validated in brain samples. Finally, the phosphorylation pattern of PKA substrates was analyzed.

RESULTS

Platelet dense granules of Nbea+/- mice had a reduced surface area and abnormal dense-core halo, but normal serotonin-content. Nbea haploinsufficiency did not affect platelet aggregation and ATP secretion after collagen stimulation, although the platelet shape change was more pronounced. Furthermore, peptidomics revealed that Nbea+/- platelets contain significantly reduced levels of several actin-interacting peptides. Decreased levels were detected of the actin-binding head and rod domain of Talin-1, which are cleavage products of Calpain-2. This is most likely due to increased PKA-mediated phosphorylation of Calpain-2, which renders the enzyme less active. Analysis of other PKA substrates revealed both increased and reduced phosphorylation.

CONCLUSION

Our results show the pleiotropic effects of alterations in PKA activity due to Nbea haploinsufficiency, highlighting the important function of the AKAP domain in Nbea in regulating and confining PKA activity. Furthermore, these results suggest a role for Nbea in remodeling the actin cytoskeleton of platelets.

The Nbeal2(-/-) mouse as a model for the gray platelet syndrome

The gray platelet syndrome (GPS) is a rare, autosomal-recessive platelet disorder characterized by thrombocytopenia, large platelets lacking α-granules, and variable bleeding. GPS has been linked to mutations in the neurobeachin-like 2 gene (NBEAL2). We have recently characterized Nbeal2-deficient mice and shown that the absence of Nbeal2 results in defective protein sorting in megakaryocytes (MKs) and impaired α-granule biogenesis, a finding also seen for human MKs. In the mice, the lack of α-granules results in impaired aggregation, defective platelet adhesion to collagen under flow and reduced pro-coagulant activity; findings that translate into defective hemostasis and thrombosis in vivo indicating that α-granule secretion is critical for platelet plug stability. Furthermore, we revealed a role of α-granule proteins in ischemic stroke and wound healing. Thus, Nbeal2-deficient mice recapitulate the hallmarks of human GPS without showing its phenotypic heterogeneity and are a promising model to investigate the (patho-)physiological relevancy of α-granules.

The BEACH is hot: a LYST of emerging roles for BEACH-domain containing proteins in human disease

BEACH (named after 'Beige and Chediak-Higashi') is a conserved ∼280 residue domain, present in nine human BEACH domain containing proteins (BDCPs). Most BDCPs are large, containing a PH-like domain for membrane association preceding their BEACH domain, and containing WD40 and other domains for ligand binding. Recent studies found that mutations in individual BDCPs cause several human diseases. BDCP alterations affect lysosome size (LYST and NSMAF), apoptosis (NSMAF), autophagy (LYST, WDFY3, LRBA), granule size (LYST, NBEAL2, NBEA) or synapse formation (NBEA). However, the roles of each BDCP in these membrane events remain controversial. After reviewing studies on individual BDCPs, we propose a unifying hypothesis that BDCPs act as scaffolding proteins that facilitate membrane events, including both fission and fusion, determined by their binding partners. BDCPs may also bind each other, enabling fusion or fission of vesicles that are not necessarily of the same type. Such mechanisms explain why different BDCPs may have roles in autophagy; each BDCP is specific for the cell type or the cargo, but not necessarily specific for attaching to the autophagosome. Further elucidation of these mechanisms, preferably carrying out the same experiment on multiple BDCPs, and possibly using patients' cells, may identify potential targets for therapy.

Drosophila rugose is a functional homolog of mammalian Neurobeachin and affects synaptic architecture, brain morphology, and associative learning

Neurobeachin (Nbea) is implicated in vesicle trafficking in the regulatory secretory pathway, but details on its molecular function are currently unknown. We have used Drosophila melanogaster mutants for rugose (rg), the Drosophila homolog of Nbea, to further elucidate the function of this multidomain protein. Rg is expressed in a granular pattern reminiscent of the Golgi network in neuronal cell bodies and colocalizes with transgenic Nbea, suggesting a function in secretory regulation. In contrast to Nbea(-/-) mice, rg null mutants are viable and fertile and exhibit aberrant associative odor learning, changes in gross brain morphology, and synaptic architecture as determined at the larval neuromuscular junction. At the same time, basal synaptic transmission is essentially unaffected, suggesting that structural and functional aspects are separable. Rg phenotypes can be rescued by a Drosophila rg+ transgene, whereas a mouse Nbea transgene rescues aversive odor learning and synaptic architecture; it fails to rescue brain morphology and appetitive odor learning. This dissociation between the functional redundancy of either the mouse or the fly transgene suggests that their complex composition of numerous functional and highly conserved domains support independent functions. We propose that the detailed compendium of phenotypes exhibited by the Drosophila rg null mutant provided here will serve as a test bed for dissecting the different functional domains of BEACH (for beige and human Chediak-Higashi syndrome) proteins, such as Rugose, mouse Nbea, or Nbea orthologs in other species, such as human.

Haploinsufficiency of the autism candidate gene Neurobeachin induces autism-like behaviors and affects cellular and molecular processes of synaptic plasticity in mice

Neurobeachin (NBEA), a brain-enriched multidomain scaffolding protein involved in neurotransmitter release and synaptic functioning, has been identified as a candidate gene for autism spectrum disorder (ASD) in four unrelated patients haploinsufficient for NBEA. The aim of this study was to map the behavioral phenotype of Nbea(+/-) mice in order to understand its contribution to the pathogenesis of ASD. ASD-like behavioral variables of Nbea(+/-) mice were related to basal neuronal activity in different brain regions by in situ hybridizations and extracellular field recordings of synaptic plasticity in hippocampal cornu ammonis 1 (CA1) region. Levels of BDNF and phosphorylated cAMP response element-binding protein (CREB) were measured in an attempt to investigate putatively underlying changes in these neuromolecules. Nbea(+/-) mice exhibit several ASD-like features, including changes in self-grooming behavior, social behaviors, conditioned fear responses, and spatial learning and memory, which coincided with enhanced long-term potentiation (LTP) in their CA1 region. The observed alterations in learning and memory and hippocampal LTP are concomitant with decreased expression of the immediate early gene zif268 in dorsomedial striatum and hippocampal CA1 region, increased CREB phosphorylation, and increased hippocampal BDNF expression. These findings indicate that Nbea haploinsufficiency leads to various molecular and cellular changes that affect neuroplasticity and behavioral functions in mice, and could thus underlie the ASD symptomatology in NBEA deficient humans.

Drosophila mauve mutants reveal a role of LYST homologs late in the maturation of phagosomes and autophagosomes

Chediak-Higashi syndrome (CHS) is a lethal disease caused by mutations that inactivate the lysosomal trafficking regulator protein (LYST). Patients suffer from diverse symptoms including oculocutaneous albinism, recurrent infections, neutropenia and progressive neurodegeneration. These defects have been traced back to over-sized lysosomes and lysosome-related organelles (LROs) in different cell types. Here, we explore mutants in the Drosophila mauve gene as a new model system for CHS. The mauve gene (CG42863) encodes a large BEACH domain protein of 3535 amino acids similar to LYST. This reflects a functional homology between these proteins as mauve mutants also display enlarged LROs, such as pigment granules. This Drosophila model also replicates the enhanced susceptibility to infections and we show a defect in the cellular immune response. Early stages of phagocytosis proceed normally in mauve mutant hemocytes but, unlike in wild type, late phagosomes fuse and generate large vacuoles containing many bacteria. Autophagy is similarly affected in mauve fat bodies as starvation-induced autophagosomes grow beyond their normal size. Together these data suggest a model in which Mauve functions to restrict homotypic fusion of different pre-lysosomal organelles and LROs.

Synapse associated protein 102 (SAP102) binds the C-terminal part of the scaffolding protein neurobeachin

Neurobeachin (Nbea) is a multidomain scaffold protein abundant in the brain, where it is highly expressed during development. Nbea-null mice have severe defects in neuromuscular synaptic transmission resulting in lethal paralysis of the newborns. Recently, it became clear that Nbea is important also for the functioning of central synapses, where it is suggested to play a role in trafficking membrane proteins to both, the pre- and post-synaptic sites. So far, only few binding partners of Nbea have been found and the precise mechanism of their trafficking remains unclear. Here, we used mass spectrometry to identify SAP102, a MAGUK protein implicated in trafficking of the ionotropic glutamate AMPA- and NMDA-type receptors during synaptogenesis, as a novel Nbea interacting protein in mouse brain. Experiments in heterologous cells confirmed this interaction and revealed that SAP102 binds to the C-terminal part of Nbea that contains the DUF, PH, BEACH and WD40 domains. Furthermore, we discovered that introducing a mutation in Nbea's PH domain, which disrupts its interaction with the BEACH domain, abolishes this binding, thereby creating an excellent starting point to further investigate Nbea-SAP102 function in the central nervous system.

Mutations in NBEAL2, encoding a BEACH protein, cause gray platelet syndrome

Next-generation RNA sequence analysis of platelets from an individual with autosomal recessive gray platelet syndrome (GPS, MIM139090) detected abnormal transcript reads, including intron retention, mapping to NBEAL2 (encoding neurobeachin-like 2). Genomic DNA sequencing confirmed mutations in NBEAL2 as the genetic cause of GPS. NBEAL2 encodes a protein containing a BEACH domain that is predicted to be involved in vesicular trafficking and may be critical for the development of platelet α-granules.

Lysosomal Ca(2+) homeostasis: role in pathogenesis of lysosomal storage diseases

Disrupted cellular Ca(2+) signaling is believed to play a role in a number of human diseases including lysosomal storage diseases (LSD). LSDs are a group of ∼50 diseases caused predominantly by mutations in lysosomal proteins that result in accumulation of macromolecules within the lysosome. We recently reported that Niemann-Pick type C (NPC) is the first human disease to be associated with defective lysosomal Ca(2+) uptake and defective NAADP-mediated lysosomal Ca(2+) release. These defects in NPC cells leads to the disruption in endocytosis and subsequent lipid storage that is a feature of this disease. In contrast, Chediak-Higashi Syndrome cells have been reported to have enhanced lysosomal Ca(2+) uptake whilst the TRPML1 protein defective in mucolipidosis type IV is believed to function as a Ca(2+) channel. In this review we provide a summary of the current knowledge on the role of lysosomal Ca(2+) signaling in the pathogenesis of this group of diseases.

Inherited defects in lymphocyte cytotoxic activity

The granule-dependent cytotoxic activity of lymphocytes plays a critical role in the defense against virally infected cells and tumor cells. The importance of this cytotoxic pathway in immune regulation is evidenced by the severe and often fatal condition, known as hemophagocytic lymphohistiocytic syndrome (HLH) that occurs in mice and humans with genetically determined impaired lymphocyte cytotoxic function. HLH manifests as the occurrence of uncontrolled activation of T lymphocytes and macrophages infiltrating multiple organs. In this review, we focus on recent advances in the characterization of effectors regulating the release of cytotoxic granules, and on the role of this cytotoxic pathway in lymphocyte homeostasis and immune surveillance. Analysis of the mechanisms leading to the occurrence of hemophagocytic syndrome designates gamma-interferon as an attractive therapeutic target to downregulate uncontrolled macrophage activation, which sustains clinical and biological features of HLH.

Molecular mechanisms of biogenesis and exocytosis of cytotoxic granules

Cytotoxic T cells and natural killer cells are crucial for immune surveillance against virus-infected cells and tumour cells. Molecular studies of individuals with inherited defects that impair lymphocyte cytotoxic function have also highlighted the importance of cytotoxicity in the regulation and termination of immune responses. As discussed in this Review, characterization of these defects has contributed to our understanding of the key steps that are required for the maturation of cytotoxic granules and the secretion of their contents at the immunological synapse during target cell killing. This has revealed a marked similarity between cytotoxic granule exocytosis at the immunological synapse and synaptic vesicle exocytosis at the neurological synapse. We explore the possibility that comparison of these two kinetically and spatially regulated secretory pathways will provide clues to uncover additional effectors that regulate the cytotoxic function of lymphocytes.