A trapper keeper for TRAPP, its structures and functions

Trappc1 intrinsically prevents ferroptosis of naive T cells to avoid spontaneous autoinflammatory disease in mice

T lymphocytes are pivotal in adaptive immunity. The role of the trafficking protein particle complex (TRAPPC) in regulating T-cell development and homeostasis is unknown. Using CD4cre -Trappc1flox/flox (Trappc1 cKO) mice, we found that Trappc1 deficiency in T cells significantly decreased cell number of naive T cells in the periphery, whereas thymic T-cell development in Trappc1 cKO mice was identical as WT mice. In the culture assays and mouse models with adoptive transfer of the sorted WT (CD45.1+ CD45.2+ ) and Trappc1 cKO naive T cells (CD45.2+ ) to CD45.1+ syngeneic mice, Trappc1-deficient naive T cells showed significantly reduced survival ability compared with WT cells. RNA-seq and molecular studies showed that Trappc1 deficiency in naive T cells reduced protein transport from the endoplasmic reticulum to the Golgi apparatus, enhanced unfolded protein responses, increased P53 transcription, intracellular Ca2+ , Atf4-CHOP, oxidative phosphorylation, and lipid peroxide accumulation, and subsequently led to ferroptosis. Trappc1 deficiency in naive T cells increased ferroptosis-related damage-associated molecular pattern molecules like high mobility group box 1 or lipid oxidation products like prostaglandin E2, leukotriene B4, leukotriene C4, and leukotriene D4. Functionally, the culture supernatant of Trappc1 cKO naive T cells significantly promoted neutrophils to express inflammatory cytokines like TNFα and IL-6, which was rescued by lipid peroxidation inhibitor Acetylcysteine. Importantly, Trappc1 cKO mice spontaneously developed severe autoinflammatory disease 4 weeks after birth. Thus, intrinsic expression of Trappc1 in naive T cells plays an integral role in maintaining T-cell homeostasis to avoid proinflammatory naive T-cell death-caused autoinflammatory syndrome in mice. This study highlights the importance of the TRAPPC in T-cell biology.

The P4-ATPase Drs2 interacts with and stabilizes the multisubunit tethering complex TRAPPIII in yeast

Multisubunit Tethering Complexes (MTCs) are a set of conserved protein complexes that tether vesicles at the acceptor membrane. Interactions with other components of the trafficking machinery regulate MTCs through mechanisms that are partially understood. Here, we systematically investigate the interactome that regulates MTCs. We report that P4-ATPases, a family of lipid flippases, interact with MTCs that participate in the anterograde and retrograde transport at the Golgi, such as TRAPPIII. We use the P4-ATPase Drs2 as a paradigm to investigate the mechanism and biological relevance of this interplay during transport of Atg9 vesicles. Binding of Trs85, the sole-specific subunit of TRAPPIII, to the N-terminal tail of Drs2 stabilizes TRAPPIII on membranes loaded with Atg9 and is required for Atg9 delivery during selective autophagy, a role that is independent of P4-ATPase canonical functions. This mechanism requires a conserved I(S/R)TTK motif that also mediates the interaction of the P4-ATPases Dnf1 and Dnf2 with MTCs, suggesting a broader role of P4-ATPases in MTC regulation.

Trappc1 deficiency impairs thymic epithelial cell development by breaking endoplasmic reticulum homeostasis

Thymic epithelial cells (TECs) are important for T cell development and immune tolerance establishment. Although comprehensive molecular regulation of TEC development has been studied, the role of transport protein particle complexes (Trappcs) in TECs is not clear. Using TEC-specific homozygous or heterozygous Trappc1 deleted mice model, we found that Trappc1 deficiency caused severe thymus atrophy with decreased cell number and blocked maturation of TECs. Mice with a TEC-specific Trappc1 deletion show poor thymic T cell output and have a greater percentage of activated/memory T cells, suffered from spontaneous autoimmune disorders. Our RNA-seq and molecular studies indicated that the decreased endoplasmic reticulum (ER) and Golgi apparatus, enhanced unfolded protein response (UPR) and subsequent Atf4-CHOP-mediated apoptosis, and reactive oxygen species (ROS)-mediated ferroptosis coordinately contributed to the reduction of Trappc1-deleted TECs. Additionally, reduced Aire⁺ mTECs accompanied by the decreased expression of Irf4, Irf8, and Tbx21 in Trappc1 deficiency mTECs, may further coordinately block the tissue-restricted antigen expression. In this study, we reveal that Trappc1 plays an indispensable role in TEC development and maturation and provide evidence for the importance of inter-organelle traffic and ER homeostasis in TEC development. This article is protected by copyright. All rights reserved.

TRAPPC13 Is a Novel Target of Mesorhizobium amorphae Type III Secretion System Effector NopP

Similar to pathogenic bacteria, rhizobia can inject effector proteins into host cells directly to promote infection via the type III secretion system (T3SS). Nodulation outer protein P (NopP), a specific T3SS effector of rhizobia, plays different roles in the establishment of multiple rhizobia-legume symbiotic systems. Mesorhizobium amorphae CCNWGS0123 (GS0123), which infects Robinia pseudoacacia specifically, secretes several T3SS effectors, including NopP. Here, we demonstrate that NopP is secreted through T3SS-I of GS0123 during the early stages of infection, and its deficiency decreases nodule nitrogenase activity of R. pseudoacacia nodules. A trafficking protein particle complex subunit 13-like protein (TRAPPC13) has been identified as a NopP target protein in R. pseudoacacia roots by screening a yeast two-hybrid library. The physical interaction between NopP and TRAPPC13 is verified by bimolecular fluorescence complementation and coimmunoprecipitation assays. In addition, subcellular localization analysis reveals that both NopP and its target, TRAPPC13, are colocalized on the plasma membrane. Compared with GS0123-inoculated R. pseudoacacia roots, some genes associated with cell wall remodeling and plant innate immunity down-regulated in ΔnopP-inoculated roots at 36 h postinoculation. The results suggest that NopP in M. amorphae CCNWGS0123 acts in multiple processes in R. pseudoacacia during the early stages of infection, and TRAPPC13 could participate in the process as a NopP target.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Deciphering the autophagy regulatory network via single-cell transcriptome analysis reveals a requirement for autophagy homeostasis in spermatogenesis

Background: Autophagy has been implicated as a crucial component in spermatogenesis, and autophagy dysfunction can lead to reproductive disorders in animal models, including yeast, C. elegans and mice. However, the sophisticated transcriptional networks of autophagic genes throughout human spermatogenesis and their biological significance remain largely uncharacterized. Methods: We profiled the transcriptional signatures of autophagy-related genes during human spermatogenesis by assessing specimens from nine fertile controls (including two normal persons and seven obstructive azoospermia (OA) patients) and one nonobstructive azoospermia (NOA) patient using single-cell RNA sequencing (scRNA-seq) analysis. Dysregulation of autophagy was confirmed in two additional NOA patients by immunofluorescence staining. Gene knockdown was used to identify the role of Cst3 in autophagy during spermatogenesis. Results: Our data uncovered a unique, global stage-specific enrichment of autophagy-related genes. Human-mouse comparison analysis revealed that the stage-specific expression pattern of autophagy-related genes was highly conserved in mammals. More importantly, dysregulation of some clusters of autophagy-related genes was observed in NOA patients, suggesting the association of autophagy with male infertility. Cst3, a human-mouse conserved and autophagy-related gene that is actively expressed in spermatogonia and early spermatocytes, was found to regulate spermatogonial stem cell (SSC) maintenance and subsequent male germ cell development. Knockdown of Cst3 increased autophagic activity in mouse SSCs and subsequently suppressed the transcription of SSC core factors such as Oct4, Id1, and Nanos3, which could be efficiently rescued by manipulating autophagic activity. Conclusions: Our study provides comprehensive insights into the global transcriptional signatures of autophagy-related genes and confirms the importance of autophagy homeostasis in SSC maintenance and normal spermatogenesis, opening new avenues for further dissecting the significance of the autophagy regulatory network in spermatogenesis as well as male infertility.

Emerging role of NIK/IKK2-binding protein (NIBP)/trafficking protein particle complex 9 (TRAPPC9) in nervous system diseases

NFκB signaling and protein trafficking network play important roles in various biological and pathological processes. NIK-and-IKK2-binding protein (NIBP), also known as trafficking protein particle complex 9 (TRAPPC9), is a prototype member of a novel protein family, and has been shown to regulate both NFκB signaling pathway and protein transport/trafficking. NIBP is extensively expressed in the nervous system and plays an important role in regulating neurogenesis and neuronal differentiation. NIBP/TRAPPC9 mutations have been linked to an autosomal recessive intellectual disability syndrome, called NIBP Syndrome, which is characterized by nonsyndromic autosomal recessive intellectual disability along with other symptoms such as obesity, microcephaly, and facial dysmorphia. As more cases of NIBP Syndrome are identified, new light is being shed on the role of NIBP/TRAPPC9 in the central nervous system developments and diseases. NIBP is also involved in the enteric nervous system. This review will highlight the importance of NIBP/TRAPPC9 in central and enteric nervous system diseases, and the established possible mechanisms for developing a potential therapeutic.

Distinct Roles of TRAPPC8 and TRAPPC12 in Ciliogenesis via Their Interactions With OFD1

The transport protein particle (TRAPP) complex was initially identified as a tethering factor for COPII vesicle. Subsequently, three forms (TRAPPI, II, and III) have been found and TRAPPIII has been reported to serve as a regulator in autophagy. This study investigates a new role of mammalian TRAPPIII in ciliogenesis. We found a ciliopathy protein, oral-facial-digital syndrome 1 (OFD1), interacting with the TRAPPIII-specific subunits TRAPPC8 and TRAPPC12. TRAPPC8 is necessary for the association of OFD1 with pericentriolar material 1 (PCM1). Its depletion reduces the extent of colocalized signals between OFD1 and PCM1, but does not compromise the structural integrity of centriolar satellites. The interaction between TRAPPC8 and OFD1 inhibits that between OFD1 and TRAPPC12, suggesting different roles of TRAPPIII-specific subunits in ciliogenesis and explaining the differences in cilium lengths in TRAPPC8-depleted and TRAPPC12-depleted hTERT-RPE1 cells. On the other hand, TRAPPC12 depletion causes increased ciliary length because TRAPPC12 is required for the disassembly of primary cilia. Overall, this study has revealed different roles of TRAPPC8 and TRAPPC12 in the assembly of centriolar satellites and demonstrated a possible tethering role of TRAPPIII during ciliogenesis.

TRAPPC9: Novel insights into its trafficking and signaling pathways in health and disease (Review)

Trafficking protein particle complex 9 (TRAPPC9) is a protein subunit of the transport protein particle II (TRAPPII), which has been reported to be important in the trafficking of cargo from the endoplasmic reticulum (ER) to the Golgi, and in intra‑Golgi and endosome‑to‑Golgi transport in yeast cells. In mammalian cells, TRAPPII has been shown to be important in Golgi vesicle tethering and intra‑Golgi transport. TRAPPC9 is considered to be a novel molecule capable of modulating the activation of nuclear factor‑κB (NF‑κB). Mutations in TRAPPC9 have been linked to a rare consanguineous hereditary form of mental retardation, as part of the NF‑κB pathways. In addition, TRAPPC9 has been reported to be involved in breast and colon cancer and liver diseases. The present review highlights the most recent publications on the structure, expression and function of TRAPPC9, and its association with various human diseases.

TRAPPC13 modulates autophagy and the response to Golgi stress

Tether complexes play important roles in endocytic and exocytic trafficking of lipids and proteins. In yeast, the multisubunit transport protein particle (TRAPP) tether regulates endoplasmic reticulum (ER)-to-Golgi and intra-Golgi transport and is also implicated in autophagy. In addition, the TRAPP complex acts as a guanine nucleotide exchange factor (GEF) for Ypt1, which is homologous to human Rab1a and Rab1b. Here, we show that human TRAPPC13 and other TRAPP subunits are critically involved in the survival response to several Golgi-disrupting agents. Loss of TRAPPC13 partially preserves the secretory pathway and viability in response to brefeldin A, in a manner that is dependent on ARF1 and the large GEF GBF1, and concomitant with reduced caspase activation and ER stress marker induction. TRAPPC13 depletion reduces Rab1a and Rab1b activity, impairs autophagy and leads to increased infectivity to the pathogenic bacterium Shigella flexneri in response to brefeldin A. Thus, our results lend support for the existence of a mammalian TRAPPIII complex containing TRAPPC13, which is important for autophagic flux under certain stress conditions.

Mammalian TRAPPIII Complex positively modulates the recruitment of Sec13/31 onto COPII vesicles

The Transport protein particle (TRAPP) complex is a tethering factor for COPII vesicle. Of three forms of TRAPP (TRAPPI, II and III) complexes identified so far, TRAPPIII has been largely considered to play a role in autophagy. While depletion of TRAPPIII specific subunits caused defects in the early secretory pathway and TRAPPIII might interact with components of the COPII vesicle coat, its exact role remains to be determined. In this study, we studied the function of TRAPPIII in early secretory pathway using a TRAPPIII-specific subunit, TRAPPC12, as starting point. We found that TRAPPC12 was localized to the ER exit sites and ERGIC. In cells deleted with TRAPPC12, ERGIC and to a lesser extent, the Golgi became dispersed. ER-to-Golgi transport was also delayed. TRAPPC12, but not TRAPPC8, bound to Sec13/Sec31A tetramer but each Sec protein alone could not interact with TRAPPC12. TRAPPIII positively modulated the assembly of COPII outer layer during COPII vesicle formation. These results identified a novel function of TRAPPIII as a positive modulator of the outer layer of the COPII coat.

COPI-TRAPPII activates Rab18 and regulates its lipid droplet association

The transport protein particle (TRAPP) was initially identified as a vesicle tethering factor in yeast and as a guanine nucleotide exchange factor (GEF) for Ypt1/Rab1. In mammals, structures and functions of various TRAPP complexes are beginning to be understood. We found that mammalian TRAPPII was a GEF for both Rab18 and Rab1. Inactivation of TRAPPII-specific subunits by various methods including siRNA depletion and CRISPR-Cas9-mediated deletion reduced lipolysis and resulted in aberrantly large lipid droplets. Recruitment of Rab18 onto lipid droplet (LD) surface was defective in TRAPPII-deleted cells, but the localization of Rab1 on Golgi was not affected. COPI regulates LD homeostasis. We found that the previously documented interaction between TRAPPII and COPI was also required for the recruitment of Rab18 to the LD We hypothesize that the interaction between COPI and TRAPPII helps bring TRAPPII onto LD surface, and TRAPPII, in turn, activates Rab18 and recruits it on the LD surface to facilitate its functions in LD homeostasis.

CATCHR, HOPS and CORVET tethering complexes share a similar architecture

We show that the Saccharomyces cerevisiae GARP complex and the Cog1-4 subcomplex of the COG complex, both members of the complexes associated with tethering containing helical rods (CATCHR) family of multisubunit tethering complexes, share the same subunit organization. We also show that the HOPS complex, a tethering complex acting in the endolysosomal pathway, shares a similar architecture, suggesting that multisubunit tethering complexes use related structural frameworks.

Multiple Types of Guanine Nucleotide Exchange Factors (GEFs) for Rab Small GTPases

Rab small GTPases are highly conserved master regulators of membrane traffic in all eukaryotes. The same as the activation and inactivation of other small GTPases, the activation and inactivation of Rabs are tightly controlled by specific GEFs (guanine nucleotide exchange factors) and GAPs (GTPase-activating proteins), respectively. Although almost all Rab-GAPs reported thus far have a TBC (Tre-2/Bub2/Cdc16)/Rab-GAP domain in common, recent accumulating evidence has indicated the existence of a number of structurally unrelated types of Rab-GEFs, including DENN proteins, VPS9 proteins, Sec2 proteins, TRAPP complexes, heterodimer GEFs (Mon1-Ccz1, HPS1-HPS4 (BLOC-3 complex), Ric1-Rgp1 and Rab3GAP1/2), and other GEFs (e.g., REI-1 and RPGR). In this review article we provide an up-to-date overview of the structures and functions of all putative Rab-GEFs in mammals, with a special focus on their substrate Rabs, interacting proteins, associations with genetic diseases, and intracellular localizations.

Tethering Complexes in the Arabidopsis Endomembrane System

Targeting of endomembrane transport containers is of the utmost importance for proper land plant growth and development. Given the immobility of plant cells, localized membrane vesicle secretion and recycling are amongst the main processes guiding proper cell, tissue and whole plant morphogenesis. Cell wall biogenesis and modification are dependent on vectorial membrane traffic, not only during normal development, but also in stress responses and in plant defense against pathogens and/or symbiosis. It is surprising how little we know about these processes in plants, from small GTPase regulation to the tethering complexes that act as their effectors. Tethering factors are single proteins or protein complexes mediating first contact between the target membrane and arriving membrane vesicles. In this review we focus on the tethering complexes of the best-studied plant model—Arabidopsis thaliana. Genome-based predictions indicate the presence of all major tethering complexes in plants that are known from a hypothetical last eukaryotic common ancestor (LECA). The evolutionary multiplication of paralogs of plant tethering complex subunits has produced the massively expanded EXO70 family, indicating a subfunctionalization of the terminal exocytosis machinery in land plants. Interpretation of loss of function (LOF) mutant phenotypes has to consider that related, yet clearly functionally-specific complexes often share some common core subunits. It is therefore impossible to conclude with clarity which version of the complex is responsible for the phenotypic deviations observed. Experimental interest in the analysis of plant tethering complexes is growing and we hope to contribute with this review by attracting even more attention to this fascinating field of plant cell biology.

The HOPS/class C Vps complex tethers membranes by binding to one Rab GTPase in each apposed membrane

Many Rab GTPase effectors are membrane-tethering factors, that is, they physically link two apposed membranes before intracellular membrane fusion. In this study, we investigate the distinct binding factors needed on apposed membranes for Rab effector-dependent tethering. We show that the homotypic fusion and protein-sorting/class C vacuole protein-sorting (HOPS/class C Vps) complex can tether low-curvature membranes, that is, liposomes with a diameter of ∼100 nm, only when the yeast vacuolar Rab GTPase Ypt7p is present in both tethered membranes. When HOPS is phosphorylated by the vacuolar casein kinase I, Yck3p, tethering only takes place when GTP-bound Ypt7p is present in both tethered membranes. When HOPS is not phosphorylated, however, its tethering activity shows little specificity for the nucleotide-binding state of Ypt7p. These results suggest a model for HOPS-mediated tethering in which HOPS tethers membranes by binding to Ypt7p in each of the two tethered membranes. Moreover, because vacuole-associated HOPS is presumably phosphorylated by Yck3p, our results suggest that nucleotide exchange of Ypt7p on multivesicular bodies (MVBs)/late endosomes must take place before HOPS can mediate tethering at vacuoles.

Bet3 participates in autophagy through GTPase Ypt1 in Saccharomyces cerevisiae

Three TRAPP (transport protein particle) complexes have been identified in Saccharomyces cerevisiae. GTPases Ypt1 and Ypt31/32 suppress autophagic defects in the mutants of TRAPPIII-specific subunit (Trs85) and TRAPPII-specific subunits (Trs130 and Trs120), respectively. However, the roles of the common TRAPP subunits (which also form the TRAPPI complex) in autophagy and their relationship to Rab GTPases in autophagy remain unclear. As Bet3 (a common TRAPP subunit) cannot be mutated together with either Trs85 or Trs130, we examined starvation-induced autophagy and the cytoplasm-to-vacuole targeting (Cvt) pathway in bet3ts cells. The results demonstrated that GFP-Atg8 was dispersed in the cytoplasm and Ape1 accumulated as a unique dot on the vacuolar membrane in bet3ts cells. Further analysis revealed that Ape1 maturation and GFP-Atg8 processing are defective in these cells. However, prApe1 (precursor form of Ape1) and GFP-Atg8 are protease-accessible in bet3ts cells under starvation, which indicates that Bet3 functions before autophagosome closure. Furthermore, active Ypt1, but not Ypt31, partly rescued the autophagic defects of bet3ts cells. We conclude that Bet3 is involved in autophagy and propose that it participates in autophagy through TRAPP complexes mostly via Ypt1 in yeast.

Fractionation profiling: a fast and versatile approach for mapping vesicle proteomes and protein-protein interactions

We developed "fractionation profiling," a method for rapid proteomic analysis of membrane vesicles and protein particles. The approach combines quantitative proteomics with subcellular fractionation to generate signature protein abundance distribution profiles. Functionally associated groups of proteins are revealed through cluster analysis. To validate the method, we first profiled >3500 proteins from HeLa cells and identified known clathrin-coated vesicle proteins with >90% accuracy. We then profiled >2400 proteins from Drosophila S2 cells, and we report the first comprehensive insect clathrin-coated vesicle proteome. Of importance, the cluster analysis extends to all profiled proteins and thus identifies a diverse range of known and novel cytosolic and membrane-associated protein complexes. We show that it also allows the detailed compositional characterization of complexes, including the delineation of subcomplexes and subunit stoichiometry. Our predictions are presented in an interactive database. Fractionation profiling is a universal method for defining the clathrin-coated vesicle proteome and may be adapted for the analysis of other types of vesicles and particles. In addition, it provides a versatile tool for the rapid generation of large-scale protein interaction maps.

Crystal structure of the yeast TRAPP-associated protein Tca17

The transport protein particle (TRAPP) is a hetero-multimeric complex involved in the trafficking of COP II (coat protein complex II) vesicles. TRAPP is present in different eukaryotes from yeast to vertebrates and occurs in three distinct modifications with function in different intracellular transport steps. All forms contain a core of five essential subunits, and the different species of TRAPP are formed by the addition of various subunits. A recently identified TRAPP-associated protein, Tca17, is supposed to be involved in the regulation of the transport complex. We have determined the three-dimensional structure of yeast Tca17 by X-ray crystallography at a resolution of 1.8 Å. It adopts the longin fold characteristic for the Bet5 family of TRAPP subunits, and it also shares a binding motif of these for the interaction with other members of the complex. Two alternative models of the localization of Tca17 within TRAPP as well as its potential role in the regulation of TRAPP function by transient integration into the complex are discussed.

DATABASE

Structural data are available in the Protein Databank under accession number 3PR6.

Identification of conserved, centrosome-targeting ASH domains in TRAPPII complex subunits and TRAPPC8

BACKGROUND

Assembly of primary cilia relies on vesicular trafficking towards the cilium base and intraflagellar transport (IFT) between the base and distal tip of the cilium. Recent studies have identified several key regulators of these processes, including Rab GTPases such as Rab8 and Rab11, the Rab8 guanine nucleotide exchange factor Rabin8, and the transport protein particle (TRAPP) components TRAPPC3, -C9, and -C10, which physically interact with each other and function together with Bardet Biedl syndrome (BBS) proteins in ciliary membrane biogenesis. However, despite recent advances, the exact molecular mechanisms by which these proteins interact and target to the basal body to promote ciliogenesis are not fully understood.

RESULTS

We surveyed the human proteome for novel ASPM, SPD-2, Hydin (ASH) domain-containing proteins. We identified the TRAPP complex subunits TRAPPC8, -9, -10, -11, and -13 as novel ASH domain-containing proteins. In addition to a C-terminal ASH domain region, we predict that the N-terminus of TRAPPC8, -9, -10, and -11, as well as their yeast counterparts, consists of an α-solenoid bearing stretches of multiple tetratricopeptide (TPR) repeats. Immunofluorescence microscopy analysis of cultured mammalian cells revealed that exogenously expressed ASH domains, as well as endogenous TRAPPC8, localize to the centrosome/basal body. Further, depletion of TRAPPC8 impaired ciliogenesis and GFP-Rabin8 centrosome targeting.

CONCLUSIONS

Our results suggest that ASH domains confer targeting to the centrosome and cilia, and that TRAPPC8 has cilia-related functions. Further, we propose that the yeast TRAPPII complex and its mammalian counterpart are evolutionarily related to the bacterial periplasmic trafficking chaperone PapD of the usher pili assembly machinery.

Plant cytokinesis is orchestrated by the sequential action of the TRAPPII and exocyst tethering complexes

Plant cytokinesis is initiated in a transient membrane compartment, the cell plate, and completed by a process of maturation during which the cell plate becomes a cross wall. How the transition from juvenile to adult stages occurs is poorly understood. In this study, we monitor the Arabidopsis transport protein particle II (TRAPPII) and exocyst tethering complexes throughout cytokinesis. We show that their appearance is predominantly sequential, with brief overlap at the onset and end of cytokinesis. The TRAPPII complex is required for cell plate biogenesis, and the exocyst is required for cell plate maturation. The TRAPPII complex sorts plasma membrane proteins, including exocyst subunits, at the cell plate throughout cytokinesis. We show that the two tethering complexes physically interact and propose that their coordinated action may orchestrate not only plant but also animal cytokinesis.

Synbindin in extracellular signal-regulated protein kinase spatial regulation and gastric cancer aggressiveness

BACKGROUND

The molecular mechanisms that control the aggressiveness of gastric cancer (GC) remain poorly defined. Here we show that synbindin contributes to the aggressiveness of GC by activating extracellular signal-regulated protein kinase (ERK) signaling on the Golgi apparatus.

METHODS

Expression of synbindin was examined in normal gastric mucosa (n = 44), intestinal metaplastic gastric mucosa (n = 66), and GC tissues (n=52), and the biological effects of synbindin on tumor growth and ERK signaling were detected in cultured cells, nude mice, and human tissue samples. The interaction between synbindin and mitogen-activated protein kinase kinase (MEK1)/ERK was determined by immunofluorescence and fluorescence resonance energy transfer assays. The transactivation of synbindin by nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) was detected using luciferase reporter assay and chromatin immunoprecipitation.

RESULTS

High expression of synbindin was associated with larger tumor size (120.8 vs 44.8 cm(3); P = .01), advanced tumor node metastasis (TNM) stage (P = .003), and shorter patient survival (hazard ratio = 1.51; 95% confidence interval [CI] = 1.01 to 2.27; P = .046). Synbindin promotes cell proliferation and invasion by activating ERK2 on the Golgi apparatus, and synbindin is directly transactivated by NF-κB. Synbindin expression level was statistically significantly higher in human GCs with activated ERK2 than those with low ERK2 activity (intensity score of 11.5, 95% CI = 10.4 to 12.4 vs intensity score of 4.6, 95% CI 3.9 to 5.3; P < .001). Targeting synbindin in xenograft tumors decreased ERK2 phosphorylation and statistically significantly reduced tumor volume (451.2mm(3), 95% CI = 328.3 to 574.1 vs 726.1mm(3), 95% CI = 544.2 to 908.2; P = .01).

CONCLUSIONS

Synbindin contributes to malignant phenotypes of GC by activating ERK on the Golgi, and synbindin is a potential biomarker and therapeutic target for GC.

Comparative genomic analysis of multi-subunit tethering complexes demonstrates an ancient pan-eukaryotic complement and sculpting in Apicomplexa

Apicomplexa are obligate intracellular parasites that cause tremendous disease burden world-wide. They utilize a set of specialized secretory organelles in their invasive process that require delivery of components for their biogenesis and function, yet the precise mechanisms underpinning such processes remain unclear. One set of potentially important components is the multi-subunit tethering complexes (MTCs), factors increasingly implicated in all aspects of vesicle-target interactions. Prompted by the results of previous studies indicating a loss of membrane trafficking factors in Apicomplexa, we undertook a bioinformatic analysis of MTC conservation. Building on knowledge of the ancient presence of most MTC proteins, we demonstrate the near complete retention of MTCs in the newly available genomes for Guillardiatheta and Bigelowiellanatans. The latter is a key taxonomic sampling point as a basal sister taxa to the group including Apicomplexa. We also demonstrate an ancient origin of the CORVET complex subunits Vps8 and Vps3, as well as the TRAPPII subunit Tca17. Having established that the lineage leading to Apicomplexa did at one point possess the complete eukaryotic complement of MTC components, we undertook a deeper taxonomic investigation in twelve apicomplexan genomes. We observed excellent conservation of the VpsC core of the HOPS and CORVET complexes, as well as the core TRAPP subunits, but sparse conservation of TRAPPII, COG, Dsl1, and HOPS/CORVET-specific subunits. However, those subunits that we did identify appear to be expressed with similar patterns to the fully conserved MTC proteins, suggesting that they may function as minimal complexes or with analogous partners. Strikingly, we failed to identify any subunits of the exocyst complex in all twelve apicomplexan genomes, as well as the dinoflagellate Perkinsus marinus. Overall, we demonstrate reduction of MTCs in Apicomplexa and their ancestors, consistent with modification during, and possibly pre-dating, the move from free-living marine algae to deadly human parasites.

Morpho-functional architecture of the Golgi complex of neuroendocrine cells

In neuroendocrine cells, prohormones move from the endoplasmic reticulum to the Golgi complex (GC), where they are sorted and packed into secretory granules. The GC is considered the central station of the secretory pathway of proteins and lipids en route to their final destination. In most mammalian cells, it is formed by several stacks of cisternae connected by tubules, forming a continuous ribbon. This organelle shows an extraordinary structural and functional complexity, which is exacerbated by the fact that its architecture is cell type specific and also tuned by the functional status of the cell. It is, indeed, one the most beautiful cellular organelles and, for that reason, perhaps the most extensively photographed by electron microscopists. In recent decades, an exhaustive dissection of the molecular machinery involved in membrane traffic and other Golgi functions has been carried out. Concomitantly, detailed morphological studies have been performed, including 3D analysis by electron tomography, and the precise location of key proteins has been identified by immunoelectron microscopy. Despite all this effort, some basic aspects of Golgi functioning remain unsolved. For instance, the mode of intra-Golgi transport is not known, and two opposing theories (vesicular transport and cisternal maturation models) have polarized the field for many years. Neither of these theories explains all the experimental data so that new theories and combinations thereof have recently been proposed. Moreover, the specific role of the small vesicles and tubules which surround the stacks needs to be clarified. In this review, we summarize our current knowledge of the Golgi architecture in relation with its function and the mechanisms of intra-Golgi transport. Within the same framework, the characteristics of the GC of neuroendocrine cells are analyzed.

Trs130 participates in autophagy through GTPases Ypt31/32 in Saccharomyces cerevisiae

Trs130 is a specific component of the transport protein particle II complex, which functions as a guanine nucleotide exchange factor (GEF) for Rab GTPases Ypt31/32. Ypt31/32 is known to be involved in autophagy, although the precise mechanism has not been thoroughly studied. In this study, we investigated the potential involvement of Trs130 in autophagy and found that both the cytoplasm-to-vacuole targeting (Cvt) pathway and starvation-induced autophagy were defective in a trs130ts (trs130 temperature-sensitive) mutant. Mutant cells could not transport Atg8 and Atg9 to the pre-autophagosomal structure/phagophore assembly site (PAS) properly, resulting in multiple Atg8 dots and Atg9 dots dispersed in the cytoplasm. Some dots were trapped in the trans-Golgi. Genetic studies showed that the effect of the Trs130 mutation was downstream of Atg5 and upstream of Atg1, Atg13, Atg9 and Atg14 on the autophagic pathway. Furthermore, overexpression of Ypt31 or Ypt32, but not of Ypt1, rescued autophagy defects in trs130ts and trs65ts (Trs130-HA Trs120-myc trs65Δ) mutants. Our data provide mechanistic insight into how Trs130 participates in autophagy and suggest that vesicular trafficking regulated by GTPases/GEFs is important in the transport of autophagy proteins from the trans-Golgi to the PAS.