Contribution of the long form of syntaxin 5 to the organization of the endoplasmic reticulum.

The SNARE protein syntaxin 5 exists as long (42 kDa) and short (35 kDa) isoforms. The short form is principally localized in the Golgi complex, whereas the long form resides not only in the Golgi but also in the endoplasmic reticulum (ER). Although the Golgi-localized short form has been extensively investigated, little is known about the long form. In the present study, we demonstrate that the long form of syntaxin 5 functions to shape the ER. We found that overexpression of the long form of syntaxin 5 induces rearrangement and co-alignment of the ER membrane with microtubules, the pattern of which is quite similar to that observed in cells overexpressing CLIMP-63, a linker between the ER membrane and microtubules. The ability of syntaxin 5 to induce ER-microtubule rearrangement is not related to its SNARE function, but correlates with its binding affinities for CLIMP-63, and CLIMP-63 is essential for the induction of this rearrangement. Microtubule co-sedimentation assays demonstrated that the long form of syntaxin 5 has a substantial microtubule-binding activity. These results suggest that the long form of syntaxin 5 contributes to the regulation of ER structure by interacting with both CLIMP-63 and microtubules. Indeed, depletion of syntaxin 5 caused the spreading of the ER to the cell periphery, similar to the phenotype observed in cells treated with the microtubule-depolymerizing reagent nocodazole. Our results disclose a previously undescribed function of the long form of syntaxin 5 that is not related to its function as a SNARE.

Sec16B is involved in the endoplasmic reticulum export of the peroxisomal membrane biogenesis factor peroxin 16 (Pex16) in mammalian cells.

Sec16 plays a key role in the formation of coat protein II vesicles, which mediate protein transport from the endoplasmic reticulum (ER) to the Golgi apparatus. Mammals have two Sec16 isoforms: Sec16A, which is a longer primary ortholog of yeast Sec16, and Sec16B, which is a shorter distant ortholog. Previous studies have shown that Sec16B, as well as Sec16A, defines ER exit sites, where coat protein II vesicles are formed in mammalian cells. Here, we reveal an unexpected role of Sec16B in the biogenesis of mammalian peroxisomes. When overexpressed, Sec16B was targeted to the entire ER, whereas Sec16A was mostly cytosolic. Concomitant with the overexpression of Sec16B, peroxisomal membrane biogenesis factors peroxin 3 (Pex3) and Pex16 were redistributed from peroxisomes to Sec16B-positive ER membranes. Knockdown of Sec16B but not Sec16A by RNAi affected the morphology of peroxisomes, inhibited the transport of Pex16 from the ER to peroxisomes, and suppressed expression of Pex3. These phenotypes were significantly reversed by the expression of RNAi-resistant Sec16B. Together, our results support the view that peroxisomes are formed, at least partly, from the ER and identify a factor responsible for this process.

Neuronal Excitation Induces Tau Protein Dephosphorylation via Protein Phosphatase 1 Activation to Promote Its Binding with Stable Microtubules.

The tau protein is a microtubule-associated protein that promotes microtubule stabilization. The phosphorylation of the tau protein has been linked to its dissociation from microtubules. Here, we examined the relationship between neuronal depolarization activity and tau protein phosphorylation by employing model systems in culture as well as in vivo. The KCl-evoked depolarization of cultured neurons has often been used to investigate the effects of neuronal activity. We found dephosphorylation at AT8 sites (S202, T205), T212, AT180 sites (T231, S235), and S396 in KCl-simulated cultured neurons. We also found that the KCl-induced tau protein dephosphorylation increases the level of the tau protein fractionated with stable microtubules. In an in vivo experiment, we demonstrated that the exposure of mice to a new environment activates protein phosphatase 1 in the mouse hippocampus and induces tau protein dephosphorylation. We also found an increased amount of the tau protein in a stable microtubule fraction, suggesting that the dephosphorylation of the tau protein may lead to its increased microtubule association in vivo. These results suggest that the association of microtubules with tau proteins may be regulated by the tau protein phosphorylation status affected by neuronal electrical activity.

Transient sleep apnea results in long-lasting increase in ß-amyloid generation and tau hyperphosphorylation.

Sleep apnea is regarded as an important risk factor in the pathogenesis of Alzheimer disease (AD). Chronic intermittent hypoxia treatment (IHT) given during the sleep period of the circadian cycle in experimental animals is a well-established sleep apnea model. Here we report that transient IHT for 4 days on AD model mice causes Aß overproduction 2 months after IHT presumably via upregulation of synaptic BACE1, side-by-side with tau hyperphosphorylation. These results suggest that even transient IHT may be sufficient to cause long-lasting changes in the molecules measured as AD biomarkers in the brain.

Validity of the source term for the Fukushima Dai-ichi Nuclear Power Station accident estimated using local-scale atmospheric dispersion simulations to reproduce the large-scale atmospheric dispersion of 137Cs.

The source term of 137Cs from the Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident was estimated from the results of local-scale atmospheric dispersion simulations and measurements. To confirm the source term's validity for reproducing the large-scale atmospheric dispersion of 137Cs, this study conducted hemispheric-scale atmospheric and oceanic dispersion simulations. In the dispersion simulations, the atmospheric-dispersion database system Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI)-DB and oceanic dispersion model SEA-GEARN-FDM that were developed by the Japan Atomic Energy Agency were used. Compared with the air concentrations of 137Cs measured by the Comprehensive Nuclear-Test-Ban Treaty Organization, overall, the WSPEEDI-DB simulations well reproduced the measurements, whereas the simulation results partly overestimated some measurements. Furthermore, the validity of the deposition of 137Cs by WSPEEDI-DB was investigated using SEA-GEARN-FDM and concentrations of 137Cs in seawater sampled from the North Pacific. Seawater concentrations of 137Cs by the oceanic dispersion simulation, in which the deposition flux of 137Cs by WSPEEDI-DB was used as input from the atmosphere to oceans, were statistically consistent to the measurement. However, the simulated seawater concentrations of 137Cs were underestimated regionally in the North Pacific. Both the overestimation of air concentrations and underestimation of seawater concentrations could be attributed to the less amounts of 137Cs deposition by less precipitation over the North Pacific. The overestimation and underestimation could be improved without contradiction between the air and seawater concentrations of 137Cs using more realistic precipitation in atmospheric dispersion simulations. This shows that the source term validated in this study could reproduce the spatiotemporal distribution of 137Cs from the FDNPS accident in both local and large-scale atmospheric dispersion simulations.

Refinement of source term and atmospheric dispersion simulations of radionuclides during the Fukushima Daiichi Nuclear Power Station accident.

To assess the radiological dose to the public resulting from the Fukushima Daiichi Nuclear Power Station (FDNPS) accident in Japan, especially for the early phase of the accident when no measured data are available for that purpose, the spatial and temporal distributions of radioactive materials in the environment need to be reconstructed through computer simulations using the atmospheric transport, dispersion, and deposition model (ATDM). For the ATDM simulation, the source term of radioactive materials discharged into the atmosphere is essential and has been estimated in many studies. In the present study, we further refined the source term estimated in our previous study and improved the ATDM simulation with an optimization method based on Bayesian inference, which used various measurements such as air concentration, surface deposition, fallout, and newly released hourly air concentrations of 137Cs derived by analyzing suspended particulate matter (SPM) collected at air pollution monitoring stations. This optimization improved not only the source term but also the wind field in meteorological calculation, which led to the reduction of discrepancies in plume passage time at monitoring points to less than 3 h between calculations and measurements, by feeding back comparison results between the dispersion calculations and measurements of radionuclides. As a result, the total amounts of 137Cs and 131I by the present study became 1.0 × 1016 and 1.2 × 1017 Bq, respectively, and decreased by 29% and 20%, respectively, in comparison with those by previous study. The ATDM simulation successfully reproduced both the air concentrations at SPM monitoring points and surface depositions by airborne monitoring. FA10 for total samples of air concentrations of 137Cs at SPM monitoring points increased from 35.9% by the previous study to 47.3%. The deposition amount on the land decreased from 3.7 × 1015 Bq by the previous study to 2.1 × 1015 Bq, which was close to the measured amount of 2.4 × 1015 Bq. We also constructed the spatiotemporal distribution of some major radionuclides in the air and on the surface (optimized dispersion database) by using the optimized release rates and ATDM simulations. The optimized dispersion database can be used for comprehensive dose assessment in tandem with behavioral patterns of evacuees from the FDNPS accident by collaborating research group in the Japanese dose assessment project. The improvements in the present study lead to the refinement of the dose estimation.

Oceanic dispersion of Fukushima-derived Cs-137 simulated by multiple oceanic general circulation models.

To understand the concentration and amount of Fukushima-derived Cs-137 in the ocean, this study simulated the oceanic dispersion of Cs-137 by atmospheric and oceanic dispersion simulations. The oceanic dispersion simulations were carried out with an oceanic dispersion model and multiple oceanic general circulation models. The Cs-137 concentrations were sensitive to ocean currents in the coastal, offshore, and open oceans. The mean Cs-137 concentrations of the multiple models relatively well agreed with the observed concentrations in the coastal and offshore oceans during the first few months after the Fukushima disaster, and in the open ocean during the first year after the disaster. The Cs-137 amounts were quantified in the coastal, offshore, and open oceans during the first year after the disaster. It was suggested that Cs-137 actively dispersed from the coastal and offshore oceans to the open ocean, and from the surface layer to the deeper layers in the North Pacific.

Visualization of the post-Golgi trafficking of multiphoton photoactivated transferrin receptors.

Newly synthesized membrane proteins are sorted in the trans-Golgi network (TGN) on the basis of sorting signals carried in their cytoplasmic domains and delivered to their final destinations in the secretory and endocytic pathways. Although previous studies have suggested the involvement of early endosomes in the biosynthetic pathway of transmembrane proteins, the precise trafficking routes followed by the newly synthesized plasma membrane proteins, such as transferrin receptors (TfRs), after exit from the TGN remain unclear. In this report, first, we demonstrated the advantages of photoactivating PA-GFP, a variant of the Aequorea victoria green fluorescent protein (GFP), with multiphoton laser light rather than single-photon laser light, in terms of photoactivation efficiency and spatial resolution. We then applied the multiphoton photoactivation technique to selectively photoactivate the TfR tagged with PA-GFP (PA-GFP-TfR) at the TGN, and monitored the movement of the photoactivated PA-GFP-TfR in live cells. We observed that the PA-GFP-TfR photoactivated at the TGN are transported to the Tfn(+)EEA1(+) endosomal compartments after exiting the TGN. These data support the notion that early endosomes can serve as a sorting station for not only internalized plasma membrane proteins in the endocytic pathway but also newly synthesized membrane proteins in the post-Golgi secretory pathway.

Oxidative stress-dependent phosphorylation activates ZNRF1 to induce neuronal/axonal degeneration.

Oxidative stress is a well-known inducer of neuronal apoptosis and axonal degeneration. We previously showed that the E3 ubiquitin ligase ZNRF1 promotes Wallerian degeneration by degrading AKT to induce GSK3B activation. We now demonstrate that oxidative stress serves as an activator of the ubiquitin ligase activity of ZNRF1 by inducing epidermal growth factor receptor (EGFR)-mediated phosphorylation at the 103rd tyrosine residue and that the up-regulation of ZNRF1 activity by oxidative stress leads to neuronal apoptosis and Wallerian degeneration. We also show that nicotinamide adenine dinucleotide phosphate-reduced oxidase activity is required for the EGFR-dependent phosphorylation-induced activation of ZNRF1 and resultant AKT degradation via the ubiquitin proteasome system to induce Wallerian degeneration. These results indicate the pathophysiological significance of the EGFR-ZNRF1 pathway induced by oxidative stress in the regulation of neuronal apoptosis and Wallerian degeneration. A deeper understanding of the regulatory mechanism for ZNRF1 catalytic activity via phosphorylation will provide a potential therapeutic avenue for neurodegeneration.

A role for the ancient SNARE syntaxin 17 in regulating mitochondrial division.

Recent evidence suggests that endoplasmic reticulum (ER) tubules mark the sites where the GTPase Drp1 promotes mitochondrial fission via a largely unknown mechanism. Here, we show that the SNARE protein syntaxin 17 (Syn17) is present on raft-like structures of ER-mitochondria contact sites and promotes mitochondrial fission by determining Drp1 localization and activity. The hairpin-like C-terminal hydrophobic domain, including Lys-254, but not the SNARE domain, is important for this regulation. Syn17 also regulates ER Ca(2+) homeostasis and interferes with Rab32-mediated regulation of mitochondrial dynamics. Starvation disrupts the Syn17-Drp1 interaction, thus favoring mitochondrial elongation during autophagy. Because we also demonstrate that Syn17 is an ancient SNARE, our findings suggest that Syn17 is one of the original key regulators for ER-mitochondria contact sites present in the last eukaryotic common ancestor. As such, Syn17 acts as a switch that responds to nutrient conditions and integrates functions for the ER and autophagosomes with mitochondrial dynamics.

Numerical simulation on the long-term variation of radioactive cesium concentration in the North Pacific due to the Fukushima disaster.

Numerical simulations on oceanic (134)Cs and (137)Cs dispersions were intensively conducted in order to assess an effect of the radioactive cesium on the North Pacific environment with a focus on the long-term variation of the radioactive cesium concentration after the Fukushima disaster that occurred in March 2011. The amounts of (134)Cs and (137)Cs released into the ocean were estimated using oceanic monitoring data, whereas the atmospheric deposition was calculated through atmospheric dispersion simulations. The highly accurate ocean current reanalyzed through a three-dimensional variational data assimilation enabled us to clarify the time series of the (134)Cs and (137)Cs concentrations in the North Pacific. It was suggested that the main radioactive cesium cloud due to the direct oceanic release reached the central part of the North Pacific, crossing 170°W one year after the Fukushima disaster. The radioactive cesium was efficiently diluted by meso-scale eddies in the Kuroshio Extension region and its concentration in the surface, intermediate, and deep layers had already been reduced to the pre-Fukushima background value in the wide area within the North Pacific 2.5 years after the Fukushima disaster.

Na+/H+ exchangers induce autophagy in neurons and inhibit polyglutamine-induced aggregate formation.

In polyglutamine diseases, an abnormally elongated polyglutamine results in protein misfolding and accumulation of intracellular aggregates. Autophagy is a major cellular degradative pathway responsible for eliminating unnecessary proteins, including polyglutamine aggregates. Basal autophagy constitutively occurs at low levels in cells for the performance of homeostatic function, but the regulatory mechanism for basal autophagy remains elusive. Here we show that the Na(+)/H(+) exchanger (NHE) family of ion transporters affect autophagy in a neuron-like cell line (Neuro-2a cells). We showed that expression of NHE1 and NHE5 is correlated to polyglutamine accumulation levels in a cellular model of Huntington's disease, a fatal neurodegenerative disorder characterized by accumulation of polyglutamine-containing aggregate formation in the brain. Furthermore, we showed that loss of NHE5 results in increased polyglutamine accumulation in an animal model of Huntington's disease. Our data suggest that cellular pH regulation by NHE1 and NHE5 plays a role in regulating basal autophagy and thereby promotes autophagy-mediated degradation of proteins including polyglutamine aggregates.

A new role for RINT-1 in SNARE complex assembly at the trans-Golgi network in coordination with the COG complex.

Docking and fusion of transport vesicles/carriers with the target membrane involve a tethering factor-mediated initial contact followed by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-catalyzed membrane fusion. The multisubunit tethering CATCHR family complexes (Dsl1, COG, exocyst, and GARP complexes) share very low sequence homology among subunits despite likely evolving from a common ancestor and participate in fundamentally different membrane trafficking pathways. Yeast Tip20, as a subunit of the Dsl1 complex, has been implicated in retrograde transport from the Golgi apparatus to the endoplasmic reticulum. Our previous study showed that RINT-1, the mammalian counterpart of yeast Tip20, mediates the association of ZW10 (mammalian Dsl1) with endoplasmic reticulum-localized SNARE proteins. In the present study, we show that RINT-1 is also required for endosome-to-trans-Golgi network trafficking. RINT-1 uncomplexed with ZW10 interacts with the COG complex, another member of the CATCHR family complex, and regulates SNARE complex assembly at the trans-Golgi network. This additional role for RINT-1 may in part reflect adaptation to the demand for more diverse transport routes from endosomes to the trans-Golgi network in mammals compared with those in a unicellular organism, yeast. The present findings highlight a new role of RINT-1 in coordination with the COG complex.