Study of IP3 receptor/Ca^<2+> signaling in neural plasticity and brain development and differentiation

IP_3是从内部存储中释放钙的第二个信使。我们发现浦肯野神经元变性突变体中缺失的P400是IP_3受体(IP_3R)。IP_3R/P400定位于内质网。纯化的IP_3受体(IP_3R)起钙释放通道和钙振荡器的作用。IP_3R的功能受磷酸化(受PKC、CaMK II、PKG)的调节，提示IP_3R在Ca~(2+)、Ca~(2+)、P~(2+)信号和磷酸化之间起着交叉站的作用。IP_3R具有独特的性质：1)IP_3R是功能性的，即使被酶切成几个片段；2)IP_3R可逆地变构和动态地改变其形态；_3)低温EM研究表明IP_3R含有多个空腔；4)内质网形成网状结构，含有IP_3R的泡状ER在动蛋白马达的作用下沿着微管快速移动。我们成功地结晶了IP_3结合核心和抑制序列。它们表现出独特的结构，并相互作用以重新…对IP_3R在发育过程中的作用的研究表明，IP_3R参与受精，对决定背腹轴的形成是必不可少的。IP_3R参与神经元的可塑性。IP_3R2和IP_3R_3双纯合子突变体表现为外分泌缺陷。ERp44在内质网中作为氧化还原感受器，调节IP_3R1的活性。我们利用IP_3结合核开发了IP_3指示器(简称IRIS)。我们发现，IP_3不仅能释放Ca~(2+)，还能释放Irbit。Irbit与IP_3结合在同一个位点上。Irbit只有在被磷酸化时才起作用。它调节IP_3R产生的钙振荡的频率和幅度。此外，磷酸化的Irbit与胰脏Na，HCO3+共转运蛋白1(NBC1)结合，并作为第三信使增强NBC1，调节细胞内的pH。因此，信号转导途径可能被修饰为：[细胞外信号→IP_3→IP_3R→钙离子释放，Irbit释放→Nbc1激活，钙离子振荡修饰]。较少

IP_3 is a second messenger to release Ca^<2+> from internal stores. We discovered that P400 which is deficient in Purkinje-neuron-degenerating mutant is IP_3 receptor (IP_3R). IP_3R /P400 is found to be localized on endoplasmic reticulum (ER). Purified IP_3 receptor (IP_3R) works as Ca^<2+> release channel and works as Ca^<2+> oscillator. IP_3R function is regulated by phosphorylation (by PKC, CaMK II, PKG) suggesting that IP_3R works as a cross-talk station between Ca^<2+> signaling and phosphorylation. IP_3R has unique properties: 1) IP_3R is functional even though it is fragmented by proteases into several pieces; 2) IP_3R allosterically and dynamically changes its form reversibly; _3) CryoEM study shows that IP_3R contains multiple cavities; 4) ER forms a meshwork and vesicular ER containing IP_3R moves rapidly along microtubles using kinesin motor. We succeeded in crystallization of IP_3 binding core and suppressor sequence. They show unique structure and interact each other to re … More cognize IP_3. Studies on the role of IP_3R during development show that IP_3R is involved in fertilization and is essential for determination of dorsoventral axis formation. IP_3R is involved in neuronal plasticity. Double homozygous mutant of IP_3R2 and IP_3R_3 shows deficit of exocrine secretion. ERp44 works as a redox sensor in the ER and regulates IP_3R1 activity. We developed IP_3 indicator (named as IRIS) using the IP_3 binding core. We discovered that IP_3 not only releases Ca^<2+>, but also releases IRBIT. IRBIT binds to the same site as IP_3. IRBIT works only when it is phosphorylated. It regulates frequency and amplitude of Ca^<2+> oscillation generated by IP_3R. In addition, phosphorylated IRBIT binds to pancreas type Na, Bicarbonate co-transporter 1 (NBC1) and works as a third messenger to enhance NBC1 which regulates pH inside cells. Therefore, signaling pathway may be modified to be as follows: [ extracellular signal →IP_3→IP_3R→Ca^<2+> release, and IRBIT release→NBC1 activation, and Ca^<2+> oscillation modification ]. Less