γ-Secretase-Regulated Mechanisms Similar to Notch Signaling May Play a Role in Signaling Events, Including APP Signaling, Which Leads to Alzheimer's Disease

Although gamma-secretase was first identified as a protease that cleaves amyloid precursor protein (APP) within the transmembrane domain, thus producing A beta peptides that are thought to be pathogenic in Alzheimer's disease (AD), its physiological functions have not been fully elucidated. In the canonical Notch signaling pathway, intramembrane cleavage by gamma-secretase serves to release an intracellular domain of Notch that shows activity in the nucleus through binding to transcription factors. Many type 1 transmembrane proteins, including Notch, Delta, and APP, have recently been shown to be substrates for gamma-secretase, and their intracellular domains are released from the cell membrane following cleavage by gamma-secretase. The common enzyme gamma-secretase modulates proteolysis and the turnover of possible signaling molecules, which has led to the attractive hypothesis that mechanisms similar to Notch signaling contribute widely to proteolysis-regulated signaling pathways. APP is also likely to have a signaling mechanism, although the physiological functions of APP have not been elucidated. Indeed, we have shown that the intracellular domain of APP alters gene expression and induces neuron-specific apoptosis. These results suggest that APP signaling responds to the onset of AD. Here, we review the possibility of gamma-secretase-regulated signaling, including APP signaling, which leads to AD.ArticleCELLULAR AND MOLECULAR NEUROBIOLOGY. 31(6):887-900 (2011)journal articl

The Delta intracellular domain mediates TGF-β/Activin signaling through binding to Smads and has an important bi-directional function in the Notch–Delta signaling pathway

Delta is a major transmembrane ligand for Notch receptor that mediates numerous cell fate decisions. The Notch signaling pathway has long been thought to be mono-directional, because ligands for Notch were generally believed to be unable to transmit signals into the cells expressing them. However, we showed here that Notch also supplies signals to neighboring mouse neural stem cells (NSCs). To investigate the Notch–Delta signaling pathway in a bi-directional manner, we analyzed functional roles of the intracellular domain of mouse Delta like protein 1 (Dll1IC). In developing mouse NSCs, Dll1IC, which is released from cell membrane by proteolysis, is present in the nucleus. Furthermore, we screened for transcription factors that bind to Dll1IC and demonstrated that Dll1IC binds specifically to transcription factors involved in TGF-β/Activin signaling—Smad2, Smad3 and Smad4—and enhances Smad-dependent transcription. In addition, the results of the present study indicated that over-expression of Dll1IC in embryonic carcinoma P19 cells induced neurons, and this induction was blocked by SB431542, which is a specific inhibitor of TGF-β/Activin signaling. These observations strongly suggested that Dll1IC mediates TGF-β/Activin signaling through binding to Smads and plays an important role for bi-directional Notch–Delta signaling pathway

妊娠中のウイルス感染モデルを用いた神経発達の研究

application/pdf近年、発症率が増加している自閉症の危険因子として妊娠中のウイルス感染が報告されているが、どの時期にウイルス感染が起こると産まれてきた児が自閉症になるリスクが高いのかに関してはあまりわかっていない。そのため研究代表者は、産まれてきた児が自閉症になる可能性が高いウイルス感染時期（臨界期）を調べるために、ウイルス感染モデルラットを用いて、自閉症への関与が疑われるセロトニン神経系の異常を指標に臨界期の同定を行った。その結果、産まれてきた仔のセロトニン神経系に異常を引き起こすウイルス感染時期が少なくとも２つあることを明らかにした。Recently, the prevalence of autism spectrum disorder (ASD) is increased. It is reported that viral infection during pregnancy is one of the risk factors of ASD. However, little is known about critical period to viral infection during pregnancy that cause ASD. To examine the critical period to viral infection during pregnancy that cause ASD, I made viral infection model during pregnancy and examined the critical period. I revealed that there are at least two critical periods to viral infection during pregnancy that induce abnormality to serotonergic system of offspring.2014年度～2016年度科学研究費補助金(基盤研究(C))研究成果報告書2646025

A novel basic helix-loop-helix (bHLH) transcriptional repressor, NeuroAB,expressed in bipolar and amacrine cells in the retina.

　　　All retinal neurons develop from a common retinal progenitor, cell fate becoming irreversible during the final mitosis. Different cell types are produced in an ordered manner: The most likely order in chick is retinal ganglion cells, cone photoreceptors, amacrine cells and horizontal cells, followed by rod photoreceptors, bipolar cells, and finally Müller glia, with significant overlap in the appearance of these different cell types. This order is largely conserved among the vertebrates, which suggests conserved regulatory mechanisms underlying the onset of specification of each cell type.　　　A variety of extrinsic and intrinsic factors have been demonstrated to regulate retinogenesis. Extrinsic factors including secreted factors have been suggested to influence intrinsic factors. It is known that the basic helix-loop-helix (bHLH) transcription factors play an important role as intrinsic factors in the cell fate determination of retinal cell types. Based on sequence similarity, neuronal bHLH proteins can be largely divided into two families: Achaete-Scute complex (AS-C) related proteins and Atonal-related protein (ARPs). Furthermore, based on phylogenetic tree analysis, four subgroups have been proposed in the ARP family: the Neurogenin, NeuroD, ATO, and BETA3 groups.　　　He identified a novel chick bHLH transcription factor, NeuroAB. A phylogenetic tree prepared from bHLH sequences suggests that NeuroAB is a member of the BETA3 group, which consists of BETA3, BHLHB4, and Olig1-3. In situ hybridization and immunostaining indicated that NeuroAB is expressed predominantly in postmitotic bipolar cells and GABAergic amacrine cells in the retina. These findings suggest that NeuroAB is involved in the maturation and maintenance of bipolar cells and GABAergic amacrine cells.　　　The bHLH transcription factors bind to DNA as dimmers and recognize the consensus sequence CANNTG, called the E-box. A DNA pull down assay indicated that the NeuroAB protein binds to the E-box sequence. bHLH proteins function as a transcriptional activator or repressor in many developmental events. To investigate the transcriptional properties of NeuroAB, he preformed reporter assays using the minimal helpes simplex virus thymidine kinase (TK) promoter with five copies of the E-box sequences and the native GAP-43 promoter containing E-box motifs. The results obtained from the two promoters suggested that NeuroAB functions as a transcriptional repressor.　　　Protein phosphorylation represents a mechanism that is frequently employed by cells to regulate functions of a variety of molecules including transcription factors. Recently, some transcription factors have been demonstrated to be regulated by phosphorylation at a specific serine residue by GSK3β that is a serine/threonine kinase known to play important roles in a variety of developmental events. He found a consensus phosphorylation site for GSK3β in NeuroAB at serine 56. A series of reporter assay showed that the repressive activity of NeuroAB is inhibited by phosphorylation at a specific serine residue in the consensus phosphorylation site for GSK3β. Similar phosphorylation sites are observed in other BETA3 group members: BETA3, BHLHB4, Olig1, and Olig2. This finding suggests that the activities of BETA3 group members are commonly regulated by GSK3β or other kinases sharing the same substrate specificity such as GSK3α. It is conceivable that protein phosphorylation regulates transcription factor activity by modulating cellular localization, protein stability, protein-protein interactions or DNA binding. The results of the DNA binding assays suggested that phosphorylation of NeuroAB by GSK3β leads to reduction of the DNA-binding activity.　　　As the expression profile of GSK3β in the developing retina had yet to be elucidated, he performed in situ hybridization to examine whether the expression of GSK3β is spatially and temporally regulated in the developing retina. Its strong expression was observed in ganglion cells from E8 and a subset of amacrine cells from E12. These findings suggest that NeuroAB is involved in the maturation and maintenance of bipolar cells and GABAergic amacrine cells and regulation by GSK3β plays an important role in retinogenesis

Factors associated with the overall survival of elderly patients with hepatocellular carcinoma

AIM: To identify the factors associated with overall survival of elderly patients with hepatocellular carcinoma (HCC)

The Delta

intracellular domain mediates TGF-b/Activin signaling through binding to Smads and has an important bi-directional function in the Notch–Delta signaling pathwa