Inositol 1,4,5-trisphosphate 3-kinases:functions and regulations

Inositol 1,4,5-trisphosphate 3-kinase (IP3 3-kinase/IP3K) plays an important role in signal transduction in animal cellsby phosphorylating inositol 1,4,5-trisphosphate (IP3) to inositol 1,3,4,5-tetrakisphosphate (IP4). Both IP3 and IP4 arecritical second messengers which regulate calcium (Ca2+) homeostasis. Mammalian IP3Ks are involved in many biologicalprocesses, including brain development, memory, learning and so on. It is widely reported that Ca2+ is a canonicalsecond messenger in higher plants. Therefore, plant IP3K should also play a crucial role in plant development. Recently,we reported the identification of plant IP3K gene (AtIpk2β/AtIP3K) from Arabidopsis thaliana and its characterization.Here, we summarize the molecular cloning, biochemical properties and biological functions of IP3Ks from animal, yeastand plant. This review also discusses potential functions of IP3Ks in signaling crosstalk, inositol phosphate metabolism,gene transcriptional control and so on.

白介素-6对NMDA损伤的小脑颗粒神经元NR1和IP3R1蛋白表达的影响

目的:观察白介素-6(IL-6)对N-甲基-D-天门冬氨酸(NMDA)损伤小脑颗粒神经元NMDA受体亚单位1(NR1)和三磷酸肌醇受体1(IP3R1)蛋白表达的影响。方法:取出生后8 d SD大鼠小脑进行小脑颗粒神经元(CGNs)体外培养。在培养液中加入IL-6(40或120 ng/mL),培养8 d后,用NMDA(100μmol/L)损伤神经元30 min,建立神经元损伤模型。Western Blot法检测NR1和IP3R1蛋白的表达。结果:IL-6下调NR1的蛋白表达,并抑制NMDA诱导的IP3R1的蛋白表达增高。结论:IL-6通过抑制NMDA受体和IP3受体实现神经保护作用。

ITPK1 is an InsP_(6)/ADP phosphotransferase that controls phosphate signaling in Arabidopsis.

In plants, phosphate (Pi) homeostasis is regulated by the interaction of PHR transcription factors with stand-alone SPX proteins, which act as sensors for inositol pyrophosphates. Here, we combined different methods to obtain a comprehensive picture of how inositol (pyro)phosphate metabolism is regulated by Pi and dependent on the inositol phosphate kinase ITPK1. We found that inositol pyrophosphates are more responsive to Pi than lower inositol phosphates, a response conserved across kingdoms. With CE-ESI-MS we could separate different InsP7 isomers in Arabidopsis and rice, and identify 4/6-InsP7 and a PP-InsP4 isomer hitherto not reported in plants. We found that the inositol pyrophosphates 1/3-InsP7, 5-InsP7 and InsP8 increase severalfold in shoots after Pi resupply and that tissue-specific accumulation of inositol pyrophosphates relies on ITPK1 activities and MRP5-dependent InsP6 compartmentalization. Notably, ITPK1 is critical for Pi-dependent 5-InsP7 and InsP8 synthesis in planta and its activity regulates Pi starvation responses in a PHR-dependent manner. Furthermore, we demonstrate that ITPK1-mediated conversion of InsP6 to 5-InsP7 requires high ATP concentrations and that Arabidopsis ITPK1 has an ADP phosphotransferase activity to dephosphorylate specifically 5-InsP7 under low ATP. Collectively, our study provides deeper insights into Pi-dependent changes in nutritional and energetic states with the synthesis of regulatory inositol pyrophosphates.

NMDA受体和IP3受体介导NMDA诱导的小脑颗粒神经元内Ca^(2+)超载

目的探讨N-甲基-D-天门冬氨酸(NMDA)诱导的小脑颗粒神经元(CGNs)钙超载与NMDA受体(NMDAR)及细胞内钙库受体三磷酸肌醇受体(IP3R)和兰尼定受体(RyR)之间的关系。方法取出生后8 d SD大鼠小脑进行颗粒神经元体外培养。用NMDA(100μmol/L)急性损伤神经元,在激光扫描共聚焦显微镜(LSCM)扫描开始前30 min,或扫描开始后4,9,14 min分别加入NMDAR、IP3R、RyR拮抗剂MK-801、2-APB和DAN,检测神经元内Ca2+浓度的动态变化。结果 MK-801预孵育神经元经NMDA急性刺激后,神经元内Ca2+的荧光强度不再升高,NMDA刺激后加入MK-801,上升的Ca2+水平立即下降,最终下降至基线水平;NMDA急性刺激2-APB预孵育神经元,神经元内Ca2+的荧光强度升高,但升高幅度明显低于未经NMDA刺激组,NMDA刺激后加入2-APB,细胞内升高的Ca2+水平急剧下降,最终下降至接近基线水平;DAN预孵育的神经元经NMDA急性刺激后,胞内Ca2+的荧光强度急剧升高,达到NMDA刺激组水平,NMDA刺激后加入DAN,神经元内Ca2+水平无明显下降。结论 NMDA诱导的神经元Ca2+超载,主要由细胞膜钙通道NMDAR和细胞内钙释放通道IP3R介导,而细胞内钙释放通道RyR不起主导作用。

The role of TRPP2 in agonist-induced gallbladder smooth muscle contraction

TRPP2 channel protein belongs to the superfamily of transient receptor potential(TRP) channels and is widely expressed in various tissues, including smooth muscle in digestive gut. Accumulating evidence has demonstrated that TRPP2 can mediate Ca^(2+) release from Ca^(2+) stores. However, the functional role of TRPP2 in gallbladder smooth muscle contraction still remains unclear. In this study, we used Ca^(2+) imaging and tension measurements to test agonist-induced intracellular Ca^(2+) concentration increase and smooth muscle contraction of guinea pig gallbladder, respectively. When TRPP2 protein was knocked down in gallbladder muscle strips from guinea pig, carbachol(CCh)-evoked Ca^(2+) release and extracellular Ca^(2+) influx were reduced significantly, and gallbladder contractions induced by endothelin 1 and cholecystokinin were suppressed markedly as well. CCh-induced gallbladder contraction was markedly suppressed by pretreatment with U73122, which inhibits phospholipase C to terminate inositol 1,4,5-trisphosphate receptor(IP3) production, and 2-aminoethoxydiphenyl borate(2APB), which inhibits IP3 recepor(IP3R) to abolish IP3R-mediated Ca^(2+) release. To confirm the role of Ca^(2+) release in CCh-induced gallbladder contraction, we used thapsigargin(TG)-to deplete Ca^(2+) stores via inhibiting sarco/endoplasmic reticulum Ca^(2+)-ATPase and eliminate the role of store-operated Ca^(2+) entry on the CCh-induced gallbladder contraction. Preincubation with 2 μmol L^(-1) TG significantly decreased the CCh-induced gallbladder contraction. In addition, pretreatments with U73122, 2APB or TG abolished the difference of the CCh-induced gallbladder contraction between TRPP2 knockdown and control groups. We conclude that TRPP2 mediates Ca^(2+) release from intracellular Ca^(2+) stores, and has an essential role in agonist-induced gallbladder muscle contraction.

ERp44 C160S/C212S mutants regulate IP_(3)R_(1) channel activity

Previous studies have indicated that ERp44 inhibits inositol 1,4,5-trisphosphate(IP3)-induced Ca2+release(IICR)via IP3R1,but the mechanism remains largely unexplored.Using extracellular ATP to induce intracellular calcium transient as an IICR model,Ca2+image,pull down assay,and Western blotting experiments were carried out in the present study.We found that extracellular ATP induced calcium transient via IP3Rs(IICR)and the IICR were markedly decreased in ERp44 overexpressed Hela cells.The inhibitory effect of C160S/C212S but not C29S/T396A/ΔT(331–377)mutants of ERp44 on IICR were significantly decreased compared with ERp44.However,the binding capacity of ERp44 to L3V domain of IP3R1(1L3V)was enhanced by ERp44 C160S/C212S mutation.Taken together,these results suggest that the mutants of ERp44,C160/C212,can more tightly bind to IP3R1 but exhibit a weak inhibition of IP3R1 channel activity in Hela cells.