Takunari Yoneda

Presenilin-1 mutations downregulate the signalling pathway of the unfolded-protein response.

Missense mutations in the human presenilin-1 (PS1) gene, which is found on chromosome 14, cause early-onset familial Alzheimer’s disease (FAD). FAD-linked PS1 variants alter proteolytic processing of the amyloid precursor protein and cause an increase in vulnerability to apoptosis induced by various cell stresses. However, the mechanisms responsible for these phenomena are not clear. Here we report that mutations in PS1 affect the unfolded-protein response (UPR), which responds to the increased amount of unfolded proteins that accumulate in the endoplasmic reticulum (ER) under conditions that cause ER stress. PS1 mutations also lead to decreased expression of GRP78/Bip, a molecular chaperone, present in the ER, that can enable protein folding. Interestingly, GRP78 levels are reduced in the brains of Alzheimer’s disease patients. The downregulation of UPR signalling by PS1 mutations is caused by disturbed function of IRE1, which is the proximal sensor of conditions in the ER lumen. Overexpression of GRP78 in neuroblastoma cells bearing PS1 mutants almost completely restores resistance to ER stress to the level of cells expressing wild-type PS1. These results show that mutations in PS1 may increase vulnerability to ER stress by altering the UPR signalling pathway.

Two cis-acting elements in the 3′ untranslated region of α-CaMKIIregulate its dendritic targeting

Dendritic localization of the α subunit of Ca2+/calmodulin-dependent protein kinase II (αCaMKII) mRNA in CNS neurons requires its 3′ untranslated region (3′UTR). We investigated this targeting mechanism by identifying two cis-acting elements in the 3′UTR. One is a 30-nucleotide element that mediated dendritic translocation. A homologous sequence in the 3′UTR of neurogranin, transcripts of which also reside in dendrites, also funtioned in cis to promote its dendritic transport. Other putative elements in the αCaMKII mRNA inhibit its transport in a resting state. This inhibition was removed in depolarized neurons, and such activity-dependent derepression was a primary requirement for their dendritic targeting.

Disturbed activation of endoplasmic reticulum stress transducers by familial Alzheimer's disease-linked presenilin-1 mutations.

Recent studies have shown independently that presenilin-1 (PS1) null mutants and familial Alzheimers disease (FAD)-linked mutants should both down-regulate signaling of the unfolded protein response (UPR). However, it is difficult to accept that both mutants possess the same effects on the UPR. Furthermore, contrary to these observations, neither loss of PS1 and PS2 function nor expression of FAD-linked PS1 mutants were reported to have a discernable impact on the UPR. Therefore, re-examination and detailed analyses are needed to clarify the relationship between PS1 function and UPR signaling. Here, we report that PS1/PS2 null and dominant negative PS1 mutants, which are mutated at aspartate residue 257 or 385, did not affect signaling of the UPR. In contrast, FAD-linked PS1 mutants were confirmed to disturb UPR signaling by inhibiting activation of both Ire1α and ATF6, both of which are endoplasmic reticulum (ER) stress transducers in the UPR. Furthermore, PS1 mutants also disturbed activation of PERK (PKR-like ER kinase), which plays a crucial role in inhibiting translation during ER stress. Taken together, these observations suggested that PS1 mutations could affect signaling pathways controlled by each of the respective ER-stress transducers, possibly through a gain-of-function.

Filamin A-interacting protein (FILIP) regulates cortical cell migration out of the ventricular zone

Precisely regulated radial migration out of the ventricular zone is essential for corticogenesis. Here, we identify a mechanism that can tether ventricular zone cells in situ. FILIP interacts with Filamin A, an indispensable actin-binding protein that is required for cell motility, and induces its degradation in COS-7 cells. Degradation of Filamin A is identified in the cortical ventricular zone, where filip mRNA is localized. Furthermore, most ventricular zone cells that overexpress FILIP fail to migrate in explants. These results demonstrate that FILIP functions through a Filamin A–F-actin axis to control the start of neocortical cell migration from the ventricular zone.

JAB1 participates in unfolded protein responses by association and dissociation with IRE1

Recent papers have reported that neuronal death in patients with Alzheimers disease, Parkinsons disease, and cerebral ischemia has its origin in the endoplasmic reticulum (ER). IRE1alpha is one of the ER stress transducers that detect the accumulation of unfolded proteins in the ER. IRE1alpha mediates two major cellular responses, which are the unfolded protein response (UPR), a defensive response, and apoptosis that leads to cell death. However, little is known about the regulatory mechanisms that select between the UPR and apoptosis. We identified Jun activation domain-binding protein-1 (JAB1) as a molecule that interacts with IRE1alpha using a yeast two-hybrid system. We demonstrated that JAB1 binds to IRE1alpha in the absence of stress, but that binding is decreased by ER stress inducers. Moreover, mutant JAB1 down-regulates the UPR signaling pathway through tight binding with IRE1alpha. These results suggested that JAB1 may act as a key molecule in selecting the UPR or cell death by association and dissociation with IRE1alpha.

Identification of a novel adenylate kinase system in the brain: cloning of the fourth adenylate kinase.

We identify a novel subtype of adenylate kinase, which is the 4th adenylate kinase (AK4), in the vertebrate. AK4 mRNA is expressed in the mammalian central nervous system in a region-specific manner from the middle stage of embryogenesis to the adulthood in the rodent. The presence of three isozymes of adenylate kinase (AK1, AK2 and AK3) that maintains the homeostasis of adenine and guanine nucleotide composition has been reported in the vertebrate. Obtained mouse AK4 cDNA is 3667 bp in size. The predicted open reading frame consists of 223 amino acid residues. Rat AK4 cDNA is also obtained, and the predicted open reading frame is the same length as that of the mouse. The predicted rat AK4 molecule shows 97.8% homology with mouse AK4. Rat AK4 protein is distinct from rat AK3, 53.8% homologous with rat AK3, although the adenylate kinase signature and the mitochondrial energy transfer protein signature are found in both sequences. Interestingly, rat AK4 is 89.2% homologous with the human AK3 over 223 amino acid residues and rat AK3 is 53.7% homologous with the human AK3 indicating that the reported human AK3 actually belongs to the AK4 group (therefore, it should be referred to as human AK4). Although the sequence of AK4 is most similar to that of AK3 among the AK isozymes, its in vivo expression is completely different from AK3; AK4 mRNA is expressed in the pyramidal cells in the hippocampus (mainly in the subfield CA3), the granular cells in the cerebellum, nasal neuroepithelium and the liver while AK3 mRNA is expressed ubiquitously in the body. It is probable that AK4 acts on the specific mechanism of energy metabolism rather than control of the homeostasis of the ADP pool ubiquitously.

Vlgr1 knockout mice show audiogenic seizure susceptibility

Susceptibility to audiogenic seizures, which are reflex seizures provoked by loud noise, can be induced in rodents by acoustic priming (exposing animals to strong auditory stimuli at an early developmental stage). Some strains of mice and rats are susceptible to audiogenic seizures without priming and these have been used as good experimental models with which to study epilepsies. Here we identified Vlgr1d and Vlgr1e, novel alternatively‐spliced variants of Vlgr1b/MGR1, which, upon sequence analysis, were shown to be transcripts from a locus previously characterized as mass1. Vlgr1 (Vlgr1b, Vlgr1d and Vlgr1e) mRNA is expressed predominantly in the neuroepithelium of the developing mouse brain. Our protein‐tagged experiment suggested that Vlgr1d and Vlgr1e are secretory molecules, while Vlgr1b is a receptor. Knockout mice lacking exons 2–4 of Vlgr1 were susceptible to audiogenic seizures without priming, although there were no apparent histological abnormalities in their brains. Ninety‐five percent of these knockout mice exhibited wild running, a feature typical of the preconvulsive phase of audiogenic seizures triggered by loud noise (11 kHz, 105 dB), and 68% exhibited tonic convulsions at 3 weeks after birth. Our monogenic mice, which have a unique genetic background, serve as a useful tool for further studies on seizures.

Cloning and functional expression of ASIC-β2, a splice variant of ASIC-β

We have isolated a cDNA encoding a splice variant of ASIC (acid-sensing ion channel)-β from the rat trigeminal ganglion. This clone, designated ASIC-β2, showed a 342 base deletion just after the first transmembrane domain in ASIC-β. RT–PCR experiments revealed that ASIC-β2 was expressed exclusively in the trigeminal ganglion and dorsal root ganglion. In situ hybridization showed that ASIC-β2 mRNA was concentrated in both small diameter and large diameter neurons and co-localized with ASIC-β mRNA within single sensory neurons in the trigeminal ganglion. When expressed in Xenopus oocytes, ASIC-β2 was inactive by itself. However, it associated with ASIC-β to form heteromers, which display lower affinity for protons than ASIC-β alone.

Interchangeable binding of Bcl10 to TRAF2 and cIAPs regulates apoptosis signaling.

Bcl10 was identified as a candidate gene responsible for low grade B cell lymphomas of mucosa-associated lymphoid tissue. Overexpression of Bcl10 in cultured cells was reported to promote apoptosis, however, the mechanism of regulation of apoptosis mediated by Bcl10 has not been demonstrated. In the present study, we analysed the apoptosis signaling pathway mediated by Bcl10, focusing on phosphorylation of Bcl10 and the dynamic interaction with its binding partners during apoptosis. Previously, we have demonstrated that Bcl10 potentially interacts with the other apoptosis regulator, TNF receptor associated factor-2 (TRAF2) and inhibitor of apoptosis proteins (cIAPs). The present results showed that the complex formation of these molecules was regulated by phosphorylation of Bcl10, that is, phosphorylation of Bcl10 resulted in binding of Bcl10 to cIAPs and the dissociation of it from TRAF2. Moreover, hyperphosphorylation of Bcl10 enhanced apoptosis, suggesting that changes in the binding partners of Bcl10 were correlated to the promotion of apoptosis as mediated by Bcl10. Indeed, the mutant which was deleted from the binding site of Bcl10 for cIAPs, could not induce apoptosis. These findings indicate that Bcl10 is a mediator of apoptosis signaling, by switching over binding to cIAPs from TRAF2 through the events of Bcl10 phosphorylation.

Expression of secretory leukocyte protease inhibitor in women with endometriosis

OBJECTIVE To explore endometriosis-related molecules in patients with use of differential display analysis. DESIGN Prospective study. SETTING Nagoya City University Medical School, Nagoya, Japan. PATIENT(S) Women with endometriosis (n = 27) and without endometriosis (n = 21). INTERVENTION(S) Surgery was scheduled in the proliferative or secretory phase of the menstrual cycle. MAIN OUTCOME MEASURE(S) Differentially expressed products of endometrioma samples were sequenced at nucleotides. One of the candidate genes, secretory leukocyte protease inhibitor (SLPI) gene, was analyzed with use of in situ hybridization and Northern blot analyses. Distribution of SLPI was determined by immunohistochemistry, and the amount of SLPI in the peritoneal fluid and serum was measured by ELISA. RESULT(S) Distinct expression of SLPI messenger RNA could be detected in the endometrial-type epithelium of extrauterine endometriotic tissues and in the eutopic endometrium of women with endometriosis. SLPI was localized in the endometrial-type epithelium of endometriomas immunohistochemically. The amount of SLPI in the peritoneal fluid was markedly elevated in the endometriosis group (91.6+/-6.6 ng/mL compared with 68.4+/-5.3 ng/mL in the controls). CONCLUSION(S) Secretory leukocyte protease inhibitor may be involved in the pathogenesis of endometriosis.