細胞外サイクリックADPリボースのセンサー機構

金沢大学医薬保健研究域医学系サイクリックADPリボース(cADPR)は、CD38分子により細胞外でβ-NAD^+から作られるセカンドメッセンジャーであり、温度感受性センサーであるTRPM2チャネルを活性化することがわかってきた(Togashi, Tominagaet al. ; 2006, 2008)。今回、(1) 神経細胞において細胞外に投与したcADPRがTRPM2を活性化し細胞内Ca^濃度上昇をおこすか?(2) CD38にどのような周辺蛋白が結合し、酵素活性を調節するのか(3) 安定かつ細胞外から投与できるcADPRアナログの開発、の3点を調査した。本年度の成果として、まず上記(1) に関して、視床下部の一次培養神経・NG108-15培養神経細胞共に、温度を37Cに上昇させると、細胞外cADPR存在下で顕著な細胞内Ca^濃度上昇が起こることを見出した。この現象は細胞外β-NAD^+もしくはADPR投与でも出現し、さらに視床下部・NG108-15細胞共にTRPM2のmRNAが発現していることがわかり、神経細胞においてもcADPRがTRPM2チャネルを活性化しCa^流入を起こすことが予想された。次に上記(2) については、HEK293T細胞にhCD38-HA融合蛋白を発現させ、HA抗体ビーズで免疫沈降、結合蛋白を回収し、2次元電気泳動で分離した。hCD38発現細胞にのみにみられるスポットを切り出し、MALDI-TOF/MS質量分析を行った結果、ATP synthaseなどの3種の酵素が得られた。次に上記(3) に関しては、カーボ型の合成cADPRアナログ(cADPcR : cyclic ADP-carbocyclic ribose)を用いてNG108-15細胞への細胞外投与の効果を調べ、暖温下でやはり細胞内Ca^濃度上昇を引き起こすことを見出した。研究課題/領域番号:19045011, 研究期間(年度):2007 – 2008出典：「細胞外サイクリックADPリボースのセンサー機構」研究成果報告書　課題番号19045011（KAKEN：科学研究費助成事業データベース（国立情報学研究所））（https://kaken.nii.ac.jp/ja/grant/KAKENHI-PROJECT-19045011/)を加工して作

ラスがん遺伝子とイノシトール四リン酸で駆動されるCa^<2+>流入チャネルとの機能相関

私たちは、がん化した変異ラスにより異常活性化される受動体作動性Ca^流入経路を、特にイノシトール4リン酸(InsP4)受容体にターゲットをあて、具体的に調査している。最近になりラス特異的GTPase活性化タンパク質、RasGAPがInsP4受容体としての機能を有することがわかり、RasとInsP4受容体の関連性について、調査をすすめてきた。前年度までに、マウスラスがん細胞(DT)へのAntisense RasGAP1(-1mおよび-3)cDNAステーブル導入による、InsP4受容体ノックダウンを行い、カルシウムオシレーションの消失、InsP4依存性Ca^流入の阻害、形態変化(親株のNIH/3T3細胞に似たような形に戻る)を明らかにした。本年度は、上記RasGAP1をそれぞれノックダウンしたステーブル株において、内在性のv-Ki-ras(がん化ラス)レベルがコントロールDT細胞と差がないことをSYBR greenを用いたリアルタイムPCRにより確認すると共に、RasGAP1ノックダウン率の定量をノーザンブロットおよびリアルタイムPCRにより行った。その結果、まずRas GAP1ノックダウン細胞において、内在性のがん化v-Ki-rasレベルはコントロールDT細胞と全く差が認めなかった。ついでRas GAP1 mRNA発現レベルの検討では、ノーザンブロットでは30%に、リアルタイムPCRでは50%にRasGAP1のmRNA発現が低下していることがわかった。The final step is that GTP hydrolysis facilitated by GAP1 InsP_4 on c-Ras, but not on v-Ras, could lead to closing the channels. Such a molecular switch between activated and inactivated c-Ras may be a key to controling the Ca^ influx channels in non-transformed fibroblast cells and this might be true in many other cells. In sharp contrast this regulation capacity for closing channels is lost in ras-transformed cells, so that v-Ras may cause Ca^ influx channels to lock in the open state.It is now generally accepted that GAP1 as an InsP_4-binding protein and Ras exchanger Sos activated by tyrosine kinases interact with Ras. Circumstantial evidence suggests that molecular association of these proteins seems to be involved in the opening and closing putative Ca^ influx channels. Thus, Ca^ influx machinery seems to be effectively controlled by two branches of signal transduction for tyrosine kinase activation and InsP_4 formation downstream of phospholipase C-coupled bradykinin receptors. This c-Ras-dependent Ca^ influx in nontransformed cells provides a hint for identifying the action site of v-Ras, whose activation elicits repetitive [Ca^]i increases, called Ca^ oscillations, in transformed cells. Our hypothesis may hold interest for the future design of anticancer drugs, because Ca^ influx channels associated with Sos-GAP1-Ras could be a new target. Further validation is necessary to confirm our hypothesis by means of a technique which can functionally null each component in the Ca^ influx process.研究課題/領域番号:10670038, 研究期間(年度):1998-2000出典：「ラスがん遺伝子とイノシトール四リン酸で駆動されるCa^流入チャネルとの機能相関」研究成果報告書　課題番号10670038 (KAKEN：科学研究費助成事業データベース（国立情報学研究所）)　　　本文データは著者版報告書より作

Oxytocin-induced elevation of ADP-ribosyl cyclase activity, cyclic ADP-riboseor Ca2+ concentrations is involved in autoregulation of oxytocin secretionin the hypothalamus and posterior pituitary in male mice

金沢大学医薬保健研究域医学系Locally released oxytocin (OT) activates OT receptors (2.1:OXY:1:OT:) in neighboring neurons in the hypothalamus and their terminals in the posterior pituitary, resulting in further OT release, best known in autoregulation occurring during labor or milk ejection in reproductive females. OT also plays a critical role in social behavior of non-reproductive females and even in males in mammals from rodents to humans. Social behavior is disrupted when elevation of free intracellular Ca2+ concentration ([Ca2+]i) and OT secretion are reduced in male and female CD38 knockout mice. Therefore, it is interesting to investigate whether ADP-ribosyl cyclase-dependent signaling is involved in OT-induced OT release for social recognition in males, independent from female reproduction, and to determine its molecular mechanism. Here, we report that ADP-ribosyl cyclase activity was increased by OT in crude membrane preparations of the hypothalamus and posterior pituitary in male mice, and that OT elicited an increase in [Ca2+]i in the isolated terminals over a period of 5 min. The increases in cyclase and [Ca2+]i were partially inhibited by nonspecific protein kinase inhibitors and a protein kinase C specific inhibitor, calphostin C. Subsequently, OT-induced OT release was also inhibited by calphostin C to levels inhibited by vasotocin, an OT receptor antagonist, and 8-bromo-cADP-ribose. These results demonstrate that OT receptors are functionally coupled to membrane-bound ADP-ribosyl cyclase and/or CD38 and suggest that cADPR-mediated intracellular calcium signaling is involved in autoregulation of OT release, which is sensitive to protein kinase C, in the hypothalamus and neurohypophysis in male mice. © 2009 Elsevier Ltd. All rights reserved

Amplification of depolarization-induced and ryanodine-sensitive cytosolic Ca2+ elevation by synthetic carbocyclic analogs of cyclic ADP-ribose and their antagonistic effects in NG108-15 neuronal cells

金沢大学大学院医学系研究科We synthesized analogs modified in the ribose unit (ribose linked to N1 of adenine) of cyclic ADP-ribose (cADPR), a Ca2+-mobilizing second messenger. The biological activities of these analogs were determined in NG108-15 neuroblastoma × glioma hybrid cells that were pre-loaded with fura-2 acetoxymethylester and subjected to whole-cell patch-clamp. Application of the hydrolysis-resistant cyclic ADP-carbocyclicribose (cADPcR) through patch pipettes potentiated elevation of the cytoplasmic free Ca2+ concentration ([Ca2+]i) at the depolarized membrane potential. The increase in [Ca2+]i evoked upon sustained membrane depolarization was significantly larger in cADPcR-infused cells than in non-infused cells and its degree was equivalent to or significantly greater than that induced by cADPR or β-NAD+. 8-chloro-cADPcR and two inosine congeners (cyclic IDP-carbocyclic-ribose and 8-bromo-cyclic IDP-carbocyclic-ribose) did not induce effects similar to those of cADPcR or cADPR. Instead, 8-chloro-cADPcR together with cADPR or cADPcR caused inhibition of the depolarization-induced [Ca2+]i increase as compared with either cADPR or cADPcR alone. These results demonstrated that our cADPR analogs have agonistic or antagonistic effects on the depolarization-induced [Ca2+]i increase and suggested the presence of functional reciprocal coupling between ryanodine receptors and voltage-activated Ca 2+ channels via cADPR in mammalian neuronal cells. © 2005 International Society for Neurochemistry

Non-synonymous single-nucleotide variations of the human oxytocin receptor gene and autism spectrum disorders: a case-control study in a Japanese population and functional analysis.

Background: The human oxytocin receptor (hOXTR) is implicated in the etiology of autism spectrum disorders (ASDs) and is a potential target for therapeutic intervention. Several studies have reported single-nucleotide polymorphisms (SNPs) of the OXTR gene associated with ASDs. These SNPs, however, reside outside the protein-coding region. Not much is known about genetic variations that cause amino acid substitutions that alter receptor functions. Methods. Variations in the OXTR gene were analyzed in 132 ASD patients at Kanazawa University Hospital in Japan and 248 unrelated healthy Japanese volunteers by re-sequencing and real-time polymerase chain reaction-based genotyping. Functional changes in variant OXTRs were assessed by radioligand binding assay and measurements of intracellular free calcium concentrations ([Ca§ssup§2+§esup§]§ssub§i§esub§) and inositol 1,4,5-trisphosphate (IP§ssub§3§esub§) levels. Results: Six subjects (4.5%) in the ASD group and two in the control group (0.8%) were identified as heterozygotes carrying the R376G variation (rs35062132; c.1126C>G); one individual from the ASD group (0.8%) and three members of the control group (1.2%) were found to be carrying R376C (c.1126C>T). The C/G genotype significantly correlated with an increased risk of ASDs (odds ratio (OR) = 5.83; 95% confidence interval (CI) = 1.16 to 29.33; P = 0.024, Fisher\u27s exact test). Consistently, the G allele showed a correlation with an increased likelihood of ASDs (OR = 5.73; 95% CI = 1.15 to 28.61; P = 0.024, Fisher\u27s exact test). The frequencies of the C/T genotype and the T allele in the ASD and control groups did not differ significantly. We also examined changes in agonist-induced cellular responses mediated by the variant receptors hOXTR-376G and hOXTR-376C. OXT-induced receptor internalization and recycling were faster in hOXTR-376G-expressing HEK-293 cells than in cells expressing hOXTR-376R or hOXTR-376C. In addition, the elevation in [Ca§ssup§2+§esup§]§ssub§i§esub§ and IP§ssub§3§esub§ formation decreased in the cells expressing hOXTR-376G and hOXTR-376C tagged with enhanced green fluorescent protein (EGFP), in comparison with the cells expressing the common-type hOXTR-376R tagged with EGFP. Conclusions: These results suggest that the rare genetic variation rs35062132 might contribute to the pathogenesis of ASDs, and could provide a molecular basis of individual differences in OXTR-mediated modulation of social behavior. © 2013 Ma et al.; licensee BioMed Central Ltd

Bradykinin activates ADP-ribosyl cyclase in neuroblastoma cells: Intracellular concentration decrease in NAD and increase in cyclic ADP-ribose

金沢大学大学院医学系研究科脳細胞分子学ADP-ribosyl cyclase activity in the crude membrane fraction of neuroblastoma × glioma NGPM1-27 hybrid cells was measured by monitoring [3H] cyclic ADP-ribose (cADPR) formation from [3H] NAD+. Bradykinin (BK) at 100 nM increased ADP-ribosyl cyclase activity by about 2.5-fold. Application of 300 nM BK to living NGPM1-27 cells decreased NAD+ to 78% of the prestimulation level at 30 s. In contrast, intracellular cADPR concentrations were increased by 2-3-fold during the period from 30 to 120 s after the same treatment. Our results suggest that cADPR is one of the second messengers downstream of B2 BK receptors. © 2006 Federation of European Biochemical Societies

Up-regulation of ras-GAP genes is reversed by a MEK inhibitor and doxorubicin in v-Ki-ras-transformed NIH/3T3 fibroblasts

金沢大学大学院医学系研究科脳細胞分子学金沢大学薬学部Ras-GTPase-activating proteins (Ras-GAPs) have been implicated both as suppressors of Ras and as effectors in regulating cellular activities. To study whether Ras-GAPs have roles in tumor cell survival or not, mRNA levels of ras-related genes were measured in v-Ki-ras-transformed (DT) and the parental NIH/3T3 cells, using real-time PCR. mRNA levels of p120-Gap, Gap1m, and PIK3CA were increased in DT cells compared with NIH/3T3 cells. p120-Gap and PIK3CA genes were induced by addition of serum or epidermal growth factor to serum-starved DT cells. Three anti-cancer drugs, an ERK kinase (MEK) inhibitor PD98059, a topoisomerase II poison doxorubicin (adriamycin), and a histone deacetylase inhibitor trichostatin A, selectively blocked the overexpression of p120-Gap and Gap1m genes in DT cells. These drugs also caused reversion of DT cells to the adherent shape associated with growth arrest. Our results suggest that p120-Gap and Gap1m genes provide important biomarkers for cancer therapies. © 2007 Elsevier Inc. All rights reserved

Dopamine release via the vacuolar ATPase V0 sector c-subunit, confirmed in N18 neuroblastoma cells, results in behavioral recovery in hemiparkinsonian mice

A 16-kDa proteolipid, mediatophore, in Torpedo electric organs mediates Ca 2+-dependent acetylcholine release. Mediatophore is identical to the pore-forming stalk c-subunit of the V0 sector of vacuolar proton ATPase (ATP6V0C). The function of ATP6V0C in the mammalian central nervous system is not clear. Here, we report transfection of adeno-associated viral vectors harboring rat ATP6V0C into the mouse substantia nigra, in which high potassium stimulation increased overflow of endogenous dopamine (DA) measured in the striatum by in vivo microdialysis. Next, in the striatum of 6-hydroxydopamine- lesioned mice, a model of Parkinson\u27s disease (PD), human tyrosine hydroxylase, aromatic l-amino-acid decarboxylase and guanosine triphosphate cyclohydrolase 1, together with or without ATP6V0C, were expressed in the caudoputamen for rescue. Motor performance on the accelerating rotarod test and amphetamine-induced ipsilateral rotation were improved in the rescued mice coexpressing ATP6V0C. [ 3H]DA, taken up into cultured N18 neuronal tumor cells transformed to express ATP6V0C, was released by potassium stimulation. These results indicated that ATP6V0C mediates DA release from nerve terminals in the striatum of DA neurons of normal mice and from gene-transferred striatal cells of parkinsonian mice. The results suggested that ATP6V0C may be useful as a rescue molecule in addition to DA-synthetic enzymes in the gene therapy of PD. © 2011 Elsevier Ltd. All rights reserved

Cyclic ADP-ribose as a universal calcium signal molecule in the nervous system

金沢大学大学院医学系研究科脳細胞分子学β-NAD+ is as abundant as ATP in neuronal cells. β-NAD+ functions not only as a coenzyme but also as a substrate. β-NAD+-utilizing enzymes are involved in signal transduction. We focus on ADP-ribosyl cyclase/CD38 which synthesizes cyclic ADP-ribose (cADPR), a universal Ca2+ mobilizer from intracellular stores, from β-NAD+. cADPR acts through activation/modulation of ryanodine receptor Ca2+ releasing Ca2+ channels. cADPR synthesis in neuronal cells is stimulated or modulated via different pathways and various factors. Subtype-specific coupling of various neurotransmitter receptors with ADP-ribosyl cyclase confirms the involvement of the enzyme in signal transduction in neurons and glial cells. Moreover, cADPR/CD38 is critical in oxytocin release from the hypothalamic cell dendrites and nerve terminals in the posterior pituitary. Therefore, it is possible that pharmacological manipulation of intracellular cADPR levels through ADP-ribosyl cyclase activity or synthetic cADPR analogues may provide new therapeutic opportunities for treatment of neurodevelopmental disorders. © 2007