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dc.contributor.advisor Suh, Byung Chang - Keum, Dong Il - 2017-05-10T08:52:00Z - 2016-08-18T00:00:00Z - 2016 -
dc.identifier.uri en_US
dc.identifier.uri -
dc.description.abstract After Luigi Galvani’s first observation in 1789, it has been found that bioelectricity plays crucial roles in biological systems. Most vital activities including sensory reception, decision making, learning, memory, cognition, motion, and generation of cardiac impulse are electrically mediated in precise and works of many ion channels and their regulators in concert. For instance, in excitable cells, external stimulations such as light, pressure, temperature, pH change, and ligand can activate ion channels and evoke membrane depolarization. If the stimulations are sufficiently strong to overcome threshold, action potential is generated and propagates by sequential activation of voltage-gated sodium channel (NaV) and voltage-gated potassium channel (KV). Then, the action potential activates voltage-gated calcium channels (CaV) in presynaptic terminal and triggers secretion of neuro-transmitter, resulting in synaptic transmission to post synaptic neuron. Regulators of ion channels precisely control shape and strength of the signal at each step.
Phosphoinositides (PIs) are phosphorylated isomers of phosphoinositol (PI), which has inositol head group and fatty acid tail group, and are named after phosphorylation at 3, 4, or 5 position of the inositol ring. They are minor (<1%) lipid in cell membranes and dynamically and accurately maintained by working of phosphoinositide kinases and phosphatases. Also, they regulates important cellular and physiological events such as cell differentiation, migration, cell-shaping, axon-regeneration, cell death / survival, tumorigenesis, protein regulation, fertilization and so on. Additionally, discovery and development of molecular probes attached with fluorescence proteins enables us to observe real-time concentration of PIs in live cells. Among these PIs, role of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is relatively well established. Not only as precursor of IP3 which induces release of Ca2+ from endoplasmic reticulum (ER), PI(4,5)P2 is known to directly regulate various ion channels including CaV channels, one of our study targets.
Recently cloned voltage-sensing phosphatases (VSPs) extend the concept of bioelectrical signal and their application. VSPs are transmembrane proteins that have voltage-sensing domain mimicking that of voltage-gated ion channels, and cytosolic catalytic domain homologous to phosphatase and tensin homolog (PTEN), a phosphoinositide PI(3,4)P2 and PI(3,4,5)P3 3-phosphatase. Thus, propagation of electricity can be transduced into catalytic activity. However, unlike PTEN, VSPs have a wider range of substrates, cleaving 3-phosphate from PI(3,4)P2 and probably PI(3,4,5)P3 and 5-phosphate from PI(4,5)P2, and PI(3,4,5)P3. Recent proposals say these reactions have differing voltage dependence. Using FRET probes specific for different phosphoinositides in living cells with zebrafish VSP, we quantitate both voltagedependent 5- and 3-phosphatase subreactions against endogenous substrates. These activities become apparent with different voltage thresholds, voltage sensitivities, and catalytic rates. As an analytical tool, we refine a kinetic model that includes the endogenous pools of phosphoinositides, endogenous phosphatase and kinase reactions connecting them, and four exogenous voltage-dependent 5- and 3- phosphatase subreactions of VSP. We show that apparent voltage threshold differences for seeing effects of the 5- and 3-phosphatase activities in cells are not due to different intrinsic voltage dependence of these reactions. Rather the reactions have a common voltage dependence, and apparent differences arise only because each VSP subreaction has a different absolute catalytic rate that begins to surpass the respective endogenous enzyme activities at different voltages. For zebrafish VSP, our modeling also revealed clear 3-phosphatase activity against PI(3,4,5)P3, but it is 55-fold slower than 5-phosphatase activity against PI(4,5)P2, thus PI(4,5)P2, generated more slowly from dephosphorylating PI(3,4,5)P3, might never accumulate. When 5-phosphatase activity was counteracted by coexpression of a phosphatidylinositol 4- phosphate 5-kinase, there was accumulation of PI(4,5)P2 in parallel to PI(3,4,5)P3 dephosphorylation, demonstrating that VSPs also cleave the 3-phosphate of PI(3,4,5)P3. Using these catalytic properties of Dr-VSP, role of CaV β subunits on determining portion of two inhibition pathways by Gq-protein coupled receptor (GqPCR) activation was investigated. GPCRs signal through molecular messengers, such as Gβγ, Ca2+, and PI(4,5)P2, to modulate N-type CaV2.2 channels, playing a crucial role in regulating synaptic transmission. In our pervious studies, activation of Dr-VSP always showed weaker response than activation of M1 muscarinic receptor in CaV2.2 current inhibition (10% and 40%, respectively) although either are known as PI(4,5)P2 dependent pathways. In this study, we firstly identified that Gβγ dissociated from M1 GqPCR further inhibited CaV current beside PI(4,5)P2 depletion. We also report that the location of CaV β subunits is key to determining the voltage dependence of CaV2.2 channel modulation by GqPCRs. Application of the muscarinic agonist oxotremorine-M to tsA-201 cells expressing M1 receptors, together with CaV N-type α1B, α2δ1, and membrane-localized β2a subunits, shifted the current-voltage relationship for CaV2.2 activation 5 mV to the right and slowed current activation. Muscarinic suppression of CaV2.2 activity was relieved by strong depolarizing prepulses. Moreover, when the C terminus of β-adrenergic receptor kinase (which binds Gβγ) was coexpressed with N-type channels, inhibition of CaV2.2 current after M1 receptor activation was markedly reduced and delayed, whereas the delay between PIP2 hydrolysis and inhibition of CaV2.2 current was decreased. When the Gβγ-insensitive CaV2.2 α1C-1B chimera was expressed, voltage-dependent inhibition of calcium current was virtually abolished, suggesting that M1 receptors act through Gβγ to inhibit CaV2.2 channels bearing membranelocalized CaV β2a subunits. Expression of cytosolic β subunits such as β2b and β3, as well as the palmitoylationnegative mutant β2a(C3,4S), reduced the voltage dependence of M1 muscarinic inhibition of CaV2.2 channels, whereas it increased inhibition mediated by PIP2 depletion. Together, our results indicate that, with membrane-localized CaV β subunits, CaV2.2 channels are subject to Gβγ-mediated voltagedependent inhibition, whereas cytosol-localized β subunits confer more effective PIP2-mediated voltageindependent regulation. Thus, the voltage dependence of GqPCR regulation of calcium channels can be determined by the location of isotype-specific CaV β subunits.
These results suggest novel physiological roles of VSPs and CaV channels. Since VSPs also dephosphorylate 3-phosphate of PI(3,4,5)P3 as PTEN does, VSPs may participate in axon re-generation, spermato-genesis or stem cell differentiation which might even be triggered and regulated by electrochemical signals. VSPs also can compensate defect of PTEN activity in neural development or tumor suppression. Different temporal property of voltage-dependent and -independent inhibitions on CaV channels may be resposible for formation of M1R induced long term potentialtion and depression. ⓒ 2016 DGIST
dc.description.tableofcontents 1. INTRODUCTION 1--
1.1 Voltage-sensing phosphatase (VSP) is a unique voltage-activated enzyme 1--
1.2 Structure of VSP 4--
1.3 Phosphoinositide phosphatase activity of VSP 6--
1.4 G-protein coupled receptor (GPCR) regulation on N-type voltage-gated Ca2+ (CaV) channels 8--
2.1 Cell Culture and transfection 12--
2.2 Electrophysiology 13--
2.3 Förster Resonance Energy Transfer (FRET) 15--
2.4 Normalization and fitting of traces 16--
2.5 Confocal microscopy 17--
2.6 Mathematical modeling 17--
2.7 Analysis and statistics 18--
2.8 Materials 19--
3.1 Voltage-dependet PI 3- and 5-phosphatase activities 20--
3.2 Perturbations with wortmannin 31--
3.3 Voltage-dependent PI(3,4,5)P3 3-phosphatase activity of Ci-VSPTEN 34--
3.4 Phosphatidylinositol 4-phosphate 5-kinase type Iγ (PIPKIγ) nullifies 5-phosphatase effects of Dr-VSP 37--
3.5 tep response of Dr-VSP in PIPKIγ co-expressing cells 43--
4.1 Activation of Dr-VSP inhibits CaV2.2 current 45--
4.2 M1 muscarinic recptors may suppress N-type CaV2.2 through two pathways 47--
4.3 Gβγ scavenger attenuates M1 muscarinic receptor-inducuced CaV2.2. current inhibition 50--
4.4 Single-cell assay reveals separation of fast and slow pathways in M1R-induced current modulation 54--
4.5 Gβγ-dependent, but not PIP2-dependent, modulation is absent in a chimeric N-type channel 58--
dc.format.extent 91 -
dc.language eng -
dc.publisher DGIST -
dc.subject bioelectricity -
dc.subject voltage-gated calcium channel -
dc.subject voltage-sensing phosphatase -
dc.subject phosphoinositides -
dc.subject PTEN -
dc.title Characterization of voltage-sensing phosphatase regulation on membrane phosphoinositides and voltage-gated calcium channels -
dc.title.alternative 이노시톨 인지질과 전압개패 칼슘채널에 대한 전압감응 탈인산화효소의 조절작용의 특징 파악 -
dc.type Thesis -
dc.identifier.doi 10.22677/thesis.2296773 -
dc.description.alternativeAbstract 이 논문은 비교적 최근 발견된 전압감응 탈인산화효소(voltage-sensing phosphatase, VSP)가 세포막 인지질의 일종인 이노시톨인지질을 탈인산화 하는 생물물리학적 특징에 관한 내용을 다루고 있다. VSP는 종양억제 효소로 알려진 PTEN의 상동체이다. PTEN이 PI(3,4)P2와 PI(3,4,5)P3의 3번 인산기를 탈인산화 시키는 것과는 달리 VSP는 PI(3,4)P2, PI(4,5)P2 및 PI(3,4,5)P3의 3번과 5번 인산기를 탈인산화 하는 것으로 알려져 있으나PIP3의 3번 인산기에 대한 탈인산화 작용에 대해서는 이견이 있었다. 또한, 최근 연구에서는 VSP가 여러 기질에 대해 각각 다른 전압의존성을 가지고 있다는 결과를 발표했다.
본 연구에서 우리는 여러 종류의 이노시톨인지질에 대한 Förster Resonance Energy Transfer(FRET) 표지를 이용해 살아있는 세포에서 전압 변화에 따른 각각의 기질에 대한 VSP의 3번과 5번 포스파타아제 작용의 특성을 측정했다. 먼저, PI 4 monophosphate 5-kinase type Iγ (PIPKIγ)가 VSP의 5번 포스파타아제 작용에 대해 선택적으로 길항작용을 한다는 것을 발견했고, 이 현상을 이용해 VSP가 PI(3,4,5)P3의 3번 인산기를 탈인산화 시켜 PI(4,5)P2를 생성함을 실험적으로 증명했다. 또한, VSP의 작용으로 알려진 PI(3,4,5)P3→PI(4,5)P2, PI(3,4,5)P3→PI(3,4)P2, PI(4,5)P2→PI(4)P, PI(3,4)P2→PI(4)P 반응들에 대한 전압의존성을 정량화하고 모델링 하는 데에 성공했다.
이 반응들은 VSP의 기질선호도와 이노시톨 인지질들의 내생적인 농도로 인하여 각각 다른 막전위에서 반응이 시작되는 것처럼 보였으나, 명백하게 하나의 전압의존성을 가지고 있는 것으로 판명됐다. 우리가 수립한 모델에 의하면 zebrafish VSP에서 PI(4,5)P2의 5번 인산기에 대한 탈인산화 효과가 PI(3,4,5)P3의 3번 인산기에 대한 탈인산화 효과에 비해 55배 크기 때문에 VSP에 의해 PI(3,4,5)P3의 3번 인산기가 탈인산화 되어 PI(4,5)P2가 생성되더라도 PI(4)P로 바로 바뀌기 때문에 지금까지 살아있는 세포에서 VSP의 PI(3,4,5)P3에 대한 3번 인산기의 탈인산화를 관찰하지 못한 것으로 드러났다.
또한 이러한 VSP의 특성을 실험적으로 응용하여q타입의 G 단백질 연결 수용체 (GqPCR)이 이노시톨인지질 중 하나인 PI(4,5)P2의 고갈과 G단백질 연결 수용체의 βγ 아단위체의 직접적인 부착의 두 가지 경로를 통하여 전압감응 칼슘채널 (CaV channel)의 활성화를 억제하는 것과 이러한 양 갈래 억제의 비율이 CaV채널의 β아단위체의 세포 내 위치에 의해 조절됨을 보여주었다. ⓒ 2016 DGIST
- Doctor -
dc.contributor.department Brain and Cognitive Sciences -
dc.contributor.coadvisor Jang, Deok Jin - 2016. 8 -
dc.publisher.location Daegu -
dc.description.database dCollection - 2016-08-18 -
dc.contributor.alternativeDepartment 대학원 뇌인지과학전공 -
dc.contributor.affiliatedAuthor Keum, Dong Il -
dc.contributor.affiliatedAuthor Suh, Byung Chang -
dc.contributor.alternativeName 금동일 -
dc.contributor.alternativeName 서병창 -
dc.contributor.alternativeName 장덕진 -
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