Novel Inositol 1,4,5-Trisphosphate Receptor Inhibitor Antagonizes Hepatic Stellate Cell Activation: A Potential Drug to Treat Liver Fibrosis.

Liver fibrosis, characterized by excessive extracellular matrix (ECM) deposition, can progress to cirrhosis and increases the risk of liver cancer. Hepatic stellate cells (HSCs) play a pivotal role in fibrosis progression, transitioning from a quiescent to activated state upon liver injury, wherein they proliferate, migrate, and produce ECM. Calcium signaling, involving the inositol 1,4,5-trisphosphate receptor (IP3R), regulates HSC activation. This study investigated the efficacy of a novel IP3R inhibitor, desmethylxestospongin B (dmXeB), in preventing HSC activation. Freshly isolated rat HSCs were activated in vitro in the presence of varying dmXeB concentrations. The dmXeB effectively inhibited HSC proliferation, migration, and expression of fibrosis markers without toxicity to the primary rat hepatocytes or human liver organoids. Furthermore, dmXeB preserved the quiescent phenotype of HSCs marked by retained vitamin A storage. Mechanistically, dmXeB suppressed mitochondrial respiration in activated HSCs while enhancing glycolytic activity. Notably, methyl pyruvate, dimethyl α-ketoglutarate, and nucleoside supplementation all individually restored HSC proliferation despite dmXeB treatment. Overall, dmXeB demonstrates promising anti-fibrotic effects by inhibiting HSC activation via IP3R antagonism without adverse effects on other liver cells. These findings highlight dmXeB as a potential therapeutic agent for liver fibrosis treatment, offering a targeted approach to mitigate liver fibrosis progression and its associated complications.

Agonist-Induced Ca2+ Signaling in HEK-293-Derived Cells Expressing a Single IP3 Receptor Isoform.

In mammals, three genes encode IP3 receptors (IP3Rs), which are involved in agonist-induced Ca2+ signaling in cells of apparently all types. Using the CRISPR/Cas9 approach for disruption of two out of three IP3R genes in HEK-293 cells, we generated three monoclonal cell lines, IP3R1-HEK, IP3R2-HEK, and IP3R3-HEK, with the single functional isoform, IP3R1, IP3R2, and IP3R3, respectively. All engineered cells responded to ACh with Ca2+ transients in an "all-or-nothing" manner, suggesting that each IP3R isotype was capable of mediating CICR. The sensitivity of cells to ACh strongly correlated with the affinity of IP3 binding to an IP3R isoform they expressed. Based on a mathematical model of intracellular Ca2+ signals induced by thapsigargin, a SERCA inhibitor, we developed an approach for estimating relative Ca2+ permeability of Ca2+ store and showed that all three IP3R isoforms contributed to Ca2+ leakage from ER. The relative Ca2+ permeabilities of Ca2+ stores in IP3R1-HEK, IP3R2-HEK, and IP3R3-HEK cells were evaluated as 1:1.75:0.45. Using the genetically encoded sensor R-CEPIA1er for monitoring Ca2+ signals in ER, engineered cells were ranged by resting levels of stored Ca2+ as IP3R3-HEK ≥ IP3R1-HEK > IP3R2-HEK. The developed cell lines could be helpful for further assaying activity, regulation, and pharmacology of individual IP3R isoforms.

The role of Ca2+ signalling and InsP3R in the pathogenesis of intrahepatic cholestasis of pregnancy.

BACKGROUND: In order to contribute new insights for future prevention and treatment of intrahepatic cholestasis of pregnancy (ICP), and to promote positive pregnancy outcomes, we evaluated serum Ca2+ levels and inositol 1,4,5-trisphosphate receptor (InsP3R) expression in the liver tissue of a rat ICP model. METHODS: After establishing the model by injection of oestradiol benzoate and progesterone into pregnant rats, animals were divided into normal control (n = 5) and ICP model groups (n = 5). The expression of InsP3R protein in the liver, and serum levels of Ca2+, glycocholic acid and bile acid were detected. RESULTS: InsP3R mRNA and protein were significantly lower in the ICP model group compared to the normal group, as determined by qPCR and immunohistochemistry, respectively. Serum enzyme-linked immunosorbent assay results revealed significantly higher levels of glycocholic acid and bile acid in the ICP model group compared to the normal group, while Ca2+ levels were significantly lower. The levers of Ca2+ were significantly and negatively correlated with the levels of glycocholic acid. The observed decrease in Ca2+ was associated with an increase in total bile acids, but there was no significant correlation. CONCLUSIONS: Our results revealed that the expression of InsP3R and serum Ca2+ levels was significantly decreased in the liver tissue of ICP model rats. Additionally, Ca2+ levels were found to be negatively correlated with the level of glycocholic acid.

This study investigated the relationship between serum Ca²⁺ levels, inositol 1,4,5-trisphosphate receptor (InsP3R) expression and intrahepatic cholestasis of pregnancy (ICP) in a rat model. The results indicated a significant decrease in InsP3R expression and Ca²⁺ in the disease group compared to the control group, alongside elevated levels of glycocholic acid and bile acid. The levels of Ca²⁺ exhibited a negative correlation with the levels of glycocholic acid. These findings indicated that the decrease of InsP3R expression and Ca²⁺ levels may be related to the pathogenesis of ICP. The study provides further insight into the treatment of this disease.

A structure-based computational model of IP3R1 incorporating Ca and IP3 regulation.

The inositol 1,4,5-triphosphate receptor (IP3R) mediates Ca release in many cell types and is pivotal to a wide range of cellular processes. High-resolution cryoelectron microscopy studies have provided new structural details of IP3R type 1 (IP3R1), showing that channel function is determined by the movement of various domains within and between each of its four subunits. Channel properties are regulated by ligands, such as Ca and IP3, which bind at specific sites and control the interactions between these domains. However, it is not known how the various ligand-binding sites on IP3R1 interact to control the opening of the channel. In this study, we present a coarse-grained model of IP3R1 that accounts for the channel architecture and the location of specific Ca- and IP3-binding sites. This computational model accounts for the domain-domain interactions within and between the four subunits that form IP3R1, and it also describes how ligand binding regulates these interactions. Using a kinetic model, we explore how two Ca-binding sites on the cytosolic side of the channel interact with the IP3-binding site to regulate the channel open probability. Our primary finding is that the bell-shaped open probability of IP3R1 provides constraints on the relative strength of these regulatory binding sites. In particular, we argue that a specific Ca-binding site, whose function has not yet been established, is very likely a channel antagonist. Additionally, we apply our model to show that domain-domain interactions between neighboring subunits exert control over channel cooperativity and dictate the nonlinear response of the channel to Ca concentration. This suggests that specific domain-domain interactions play a pivotal role in maintaining the channel's stability, and a disruption of these interactions may underlie disease states associated with Ca dysregulation.

Voltage-induced calcium release in Caenorhabditis elegans body muscles.

Type 1 voltage-activated calcium channels (CaV1) in the plasma membrane trigger calcium release from the sarcoplasmic reticulum (SR) by two mechanisms. In voltage-induced calcium release (VICR), CaV1 voltage sensing domains are directly coupled to ryanodine receptors (RYRs), an SR calcium channel. In calcium-induced calcium release (CICR), calcium ions flowing through activated CaV1 channels bind and activate RYR channels. VICR is thought to occur exclusively in vertebrate skeletal muscle while CICR occurs in all other muscles (including all invertebrate muscles). Here, we use calcium-activated SLO-2 potassium channels to analyze CaV1-SR coupling in Caenorhabditis elegans body muscles. SLO-2 channels were activated by both VICR and external calcium. VICR-mediated SLO-2 activation requires two SR calcium channels (RYRs and IP3 Receptors), JPH-1/Junctophilin, a PDZ (PSD95, Dlg1, ZO-1 domain) binding domain (PBD) at EGL-19/CaV1's carboxy-terminus, and SHN-1/Shank (a scaffolding protein that binds EGL-19's PBD). Thus, VICR occurs in invertebrate muscles.

IP3R1 dysregulation via mir-200c-3p/SSFA2 axis contributes to taxol resistance in head and neck cancer.

Head and neck cancer (HNC) is the sixth most common malignancy worldwide. Although current modalities offer a wide variety of therapy choices, head and neck carcinoma has poor prognosis due to its diagnosis at later stages and development of resistance to current therapeutic tools. In the current study, we aimed at exploring the roles of miR-200c-3p during head and neck carcinogenesis and acquisition of taxol resistance. We analyzed miR-200c-3p levels in HNC clinical samples and cell lines using quantitative real-time polymerase chain reaction and evaluated the effects of differential miR-200c-3p expression on cancer-related cellular phenotypes using in-vitro tools. We identified and characterized a direct target of miR-200c-3p using in-silico tools, luciferase and various in-vitro assays. We investigated potential involvement of miR-200c-3p/SSFA2 axis in taxol resistance in-vitro. We found miR-200c-3p expression as significantly downregulated in both HNC tissues and cells compared to corresponding controls. Ectopic miR-200c-3p expression in HNC cells significantly inhibited cancer-related phenotypes such as viability, clonogenicity, migration, and invasion. We, then, identified SSFA2 as a direct target of miR-200c-3p and demonstrated that overexpression of SSFA2 induced malignant phenotypes in HNC cells. Furthermore, we found reduced miR-200c-3p expression in parallel with overexpression of SSFA2 in taxol resistant HNC cells compared to parental sensitive cells. Both involved in intracellular cytoskeleton remodeling, we found that SSFA2 works collaboratively with IP3R1 to modulate resistance to taxol in HNC cells. When considered collectively, our results showed that miR-200c-3p acts as a tumor suppressor microRNA and targets SSFA2/IP3R1 axis to sensitize HNC cells to taxol.

Neighbourhood Watch: Two-pore-2 channels talking to IP3 receptors.

The recent elegant study by Y. Yuan and colleagues examined functional relationships between the lysosomal two-pore channels 2 (TPC2) and IP3 receptors (IP3Rs) located in the endoplasmic reticulum [1]. The findings of this study suggest functional coupling of these channels and receptors. The study also describes interesting novel phenomena, which may indicate an additional coupling mechanism.

Cyfluthrin exposure during pregnancy causes neurotoxicity in offspring-Ca2+ overload via IP3R-GRP75-VDAC1 pathway.

Cyfluthrin (Cy) is a widely used pyrethroid insecticide. There is growing evidence that Cy can cause damage to the nervous, reproductive, and immune systems, but there is limited evidence on the potential effects of maternal Cy exposure on offspring. A model of maternal Cy exposure was used to assess its neurobehavioral effects on young-adult offspring. We found that gestational Cy exposure affected pregnancy outcomes and fetal development, and that offspring showed impairments in anxiety as well as learning and memory, accompanied by impairments in hippocampal synaptic ultrastructure and synaptic plasticity. In addition, the IP3R-GRP75-VDAC1 apoptogenic pathway was also upregulated, and in vitro models showed that inhibition of this pathway alleviated neuronal apoptosis as well as synaptic plasticity damage. In conclusion, maternal Cy exposure during pregnancy can cause neurobehavioral abnormalities and synaptic damage in offspring, which may be related to neuronal apoptosis induced by activation of the IP3R-GRP75-VDAC1 pathway in the hippocampus of offspring. Our findings provide clues to understand the neurotoxicity mechanism of maternal Cy exposure to offspring during pregnancy.

Crosstalk between TPC2 and IP3R regulates Ca2+ signals.

Calcium (Ca2+) plays a pivotal role in cellular signal transmission by triggering downstream signaling in response to an increase in the cytosolic Ca2+ concentration. Intracellular organelles serve as Ca2+ stores that induce differently shaped Ca2+ signals. We discuss a study by Yuan et al. that investigated the interplay between the lysosomal two-pore channel 2 (TPC2) and endoplasmic reticulum (ER)-localized inositol 1,4,5-trisphosphate receptors (IP3Rs).

Substrate promiscuity of inositol 1,4,5-trisphosphate kinase driven by structurally-modified ligands and active site plasticity.

D-myo-inositol 1,4,5-trisphosphate (InsP3) is a fundamental second messenger in cellular Ca2+ mobilization. InsP3 3-kinase, a highly specific enzyme binding InsP3 in just one mode, phosphorylates InsP3 specifically at its secondary 3-hydroxyl group to generate a tetrakisphosphate. Using a chemical biology approach with both synthetised and established ligands, combining synthesis, crystallography, computational docking, HPLC and fluorescence polarization binding assays using fluorescently-tagged InsP3, we have surveyed the limits of InsP3 3-kinase ligand specificity and uncovered surprisingly unforeseen biosynthetic capacity. Structurally-modified ligands exploit active site plasticity generating a helix-tilt. These facilitated uncovering of unexpected substrates phosphorylated at a surrogate extended primary hydroxyl at the inositol pseudo 3-position, applicable even to carbohydrate-based substrates. Crystallization experiments designed to allow reactions to proceed in situ facilitated unequivocal characterization of the atypical tetrakisphosphate products. In summary, we define features of InsP3 3-kinase plasticity and substrate tolerance that may be more widely exploitable.

Structural and functional insight into a new emerging target IP3R in cancer.

Calcium signaling has been identified as an important phenomenon in a plethora of cellular processes. Inositol 1,4,5-trisphosphate receptors (IP3Rs) are ER-residing intracellular calcium (Ca2+) release channels responsible for cell bioenergetics by transferring calcium from the ER to the mitochondria. The recent availability of full-length IP3R channel structure has enabled the researchers to design the IP3 competitive ligands and reveal the channel gating mechanism by elucidating the conformational changes induced by ligands. However, limited knowledge is available for IP3R antagonists and the exact mechanism of action of these antagonists within a tumorigenic environment of a cell. Here in this review a summarized information about the role of IP3R in cell proliferation and apoptosis has been discussed. Moreover, structure and gating mechanism of IP3R in the presence of antagonists have been provided in this review. Additionally, compelling information about ligand-based studies (both agonists and antagonists) has been discussed. The shortcomings of these studies and the challenges toward the design of potent IP3R modulators have also been provided in this review. However, the conformational changes induced by antagonists for channel gating mechanism still display some major drawbacks that need to be addressed. However, the design, synthesis and availability of isoform-specific antagonists is a rather challenging one due to intra-structural similarity within the binding domain of each isoform. HighlightsThe intricate complexity of IP3R's in cellular processes declares them an important target whereby, the recently solved structure depicts the receptor's potential involvement in a complex network of processes spanning from cell proliferation to cell death.Pharmacological inhibition of IP3R attenuates the proliferation or invasiveness of cancers, thus inducing necrotic cell death.Despite significant advancements, there is a tremendous need to design new potential hits to target IP3R, based upon 3D structural features and pharmacophoric patterns.Communicated by Ramaswamy H. Sarma.

Detailed Analysis of ITPR1 Missense Variants Guides Diagnostics and Therapeutic Design.

BACKGROUND: The ITPR1 gene encodes the inositol 1,4,5-trisphosphate (IP3 ) receptor type 1 (IP3 R1), a critical player in cerebellar intracellular calcium signaling. Pathogenic missense variants in ITPR1 cause congenital spinocerebellar ataxia type 29 (SCA29), Gillespie syndrome (GLSP), and severe pontine/cerebellar hypoplasia. The pathophysiological basis of the different phenotypes is poorly understood. OBJECTIVES: We aimed to identify novel SCA29 and GLSP cases to define core phenotypes, describe the spectrum of missense variation across ITPR1, standardize the ITPR1 variant nomenclature, and investigate disease progression in relation to cerebellar atrophy. METHODS: Cases were identified using next-generation sequencing through the Deciphering Developmental Disorders study, the 100,000 Genomes project, and clinical collaborations. ITPR1 alternative splicing in the human cerebellum was investigated by quantitative polymerase chain reaction. RESULTS: We report the largest, multinational case series of 46 patients with 28 unique ITPR1 missense variants. Variants clustered in functional domains of the protein, especially in the N-terminal IP3 -binding domain, the carbonic anhydrase 8 (CA8)-binding region, and the C-terminal transmembrane channel domain. Variants outside these domains were of questionable clinical significance. Standardized transcript annotation, based on our ITPR1 transcript expression data, greatly facilitated analysis. Genotype-phenotype associations were highly variable. Importantly, while cerebellar atrophy was common, cerebellar volume loss did not correlate with symptom progression. CONCLUSIONS: This dataset represents the largest cohort of patients with ITPR1 missense variants, expanding the clinical spectrum of SCA29 and GLSP. Standardized transcript annotation is essential for future reporting. Our findings will aid in diagnostic interpretation in the clinic and guide selection of variants for preclinical studies. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The interplay between associated proteins, redox state and Ca2+ in the intraluminal ER compartment regulates the IP3 receptor.

There have been in the last three decades repeated publications indicating that the inositol 1,4,5-trisphosphate receptor (IP3R) is regulated not only by cytosolic Ca2+ but also by intraluminal Ca2+. Although most studies indicated that a decreasing intraluminal Ca2+ level led to an inhibition of the IP3R, a number of publications reported exactly the opposite effect, i.e. an inhibition of the IP3R by high intraluminal Ca2+ levels. Although intraluminal Ca2+-binding sites on the IP3Rs were reported, a regulatory role for them was not demonstrated. It is also well known that the IP3R is regulated by a vast array of associated proteins, but only relatively recently proteins were identified that can be linked to the regulation of the IP3R by intraluminal Ca2+. The first to be reported was annexin A1 that is proposed to associate with the second intraluminal loop of the IP3R at high intraluminal Ca2+ levels and to inhibit the IP3R. More recently, ERdj5/PDIA19 reductase was described to reduce an intraluminal disulfide bridge of IP3R1 only at low intraluminal Ca2+ levels and thereby to inhibit the IP3R. Annexin A1 and ERdj5/PDIA19 can therefore explain most of the experimental results on the regulation of the IP3R by intraluminal Ca2+. Further studies are needed to provide a fuller understanding of the regulation of the IP3R from the intraluminal side. These findings underscore the importance of the state of the endoplasmic reticulum in the control of IP3R activity.

HERPUD1 governs tumor cell mitochondrial function via inositol 1,4,5-trisphosphate receptor-mediated calcium signaling.

The intricate relationship between calcium (Ca2+) homeostasis and mitochondrial function is crucial for cellular metabolic adaptation in tumor cells. Ca2+-initiated signaling maintains mitochondrial respiratory capacity and ATP synthesis, influencing critical cellular processes in cancer development. Previous studies by our group have shown that the homocysteine-inducible ER Protein with Ubiquitin-Like Domain 1 (HERPUD1) regulates inositol 1,4,5-trisphosphate receptor (ITPR3) levels and intracellular Ca2+ signals in tumor cells. This study explores the role of HERPUD1 in regulating mitochondrial function and tumor cell migration by controlling ITPR3-dependent Ca2+ signals. We found HERPUD1 levels correlated with mitochondrial function in tumor cells, with HERPUD1 deficiency leading to enhanced mitochondrial activity. HERPUD1 knockdown increased intracellular Ca2+ release and mitochondrial Ca2+ influx, which was prevented using the ITPR3 antagonist xestospongin C or the Ca2+ chelator BAPTA-AM. Furthermore, HERPUD1 expression reduced tumor cell migration by controlling ITPR3-mediated Ca2+ signals. HERPUD1-deficient cells exhibited increased migratory capacity, which was attenuated by treatment with xestospongin C or BAPTA-AM. Additionally, HERPUD1 deficiency led to reactive oxygen species-dependent activation of paxillin and FAK proteins, which are associated with enhanced cell migration. Our findings highlight the pivotal role of HERPUD1 in regulating mitochondrial function and cell migration by controlling intracellular Ca2+ signals mediated by ITPR3. Understanding the interplay between HERPUD1 and mitochondrial Ca2+ regulation provides insights into potential therapeutic targets for cancer treatment and other pathologies involving altered energy metabolism.

Deoxynivalenol induced intestinal barrier injury, mitochondrial dysfunction and calcium overload by inositol 1,4,5-triphosphate receptors (IP3Rs)-mitochondrial calcium uniporter (MCU) calcium axis.

Deoxynivalenol (DON) contamination is widespread in crops and could easily cause intestinal injury, which brings hazards to animals. Mitochondria are considered as an important target of DON, nevertheless, the mechanism is still unclear. Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) have gained arousing interest and are recognized as critical signaling hubs that control calcium signaling transduction between ER and mitochondria. This study aims to investigate the effects of DON on intestinal barrier, mitochondria, MAMs and inositol 1,4,5-triphosphate receptors (IP3Rs)-mitochondrial calcium uniporter (MCU) calcium axis in piglets and porcine intestinal epithelial cells (IPEC-J2). Furthermore, inhibition of IP3Rs or MCU was used to explore whether IP3Rs-MCU axis of MAMs was involved in the mitochondria dysfunction and intestinal epithelium barrier injury induced by DON in IPEC-J2. The data showed that DON induced intestinal barrier injury, mitochondrial dysfunction and ERS in piglets' jejunum and IPEC-J2. Moreover, DON increased MAMs by upregulating the protein level of Mitofusin 2 (Mfn2), increasing the percentage of mitochondria with MAMs/total mitochondria and the ratio of MAMs length/mitochondrial perimeter and shortening the distance between mitochondria and ER of MAMs. Importantly, DON influenced IP3Rs-glucose-regulated protein 75 (GRP75)-voltage-dependent anion channel 1 (VDAC1)-MCU calcium axis by increasing the protein levels of GRP75 and MCU and the interaction of VDAC1-GRP75-IP3Rs complex, which in turn induced mitochondrial calcium overload. Furthermore, inhibition of IP3Rs or MCU alleviated DON-induced intestinal epithelium barrier injury, mitochondrial dysfunction and mitochondrial calcium overload of IPEC-J2. The current investigation proposed that DON induced intestinal injury, mitochondrial dysfunction and calcium overload via IP3Rs-GRP75-VDAC1-MCU calcium axis.

Two-pore channel-2 and inositol trisphosphate receptors coordinate Ca2+ signals between lysosomes and the endoplasmic reticulum.

Lysosomes and the endoplasmic reticulum (ER) are Ca2+ stores mobilized by the second messengers NAADP and IP3, respectively. Here, we establish Ca2+ signals between the two sources as fundamental building blocks that couple local release to global changes in Ca2+. Cell-wide Ca2+ signals evoked by activation of endogenous NAADP-sensitive channels on lysosomes comprise both local and global components and exhibit a major dependence on ER Ca2+ despite their lysosomal origin. Knockout of ER IP3 receptor channels delays these signals, whereas expression of lysosomal TPC2 channels accelerates them. High-resolution Ca2+ imaging reveals elementary events upon TPC2 opening and signals coupled to IP3 receptors. Biasing TPC2 activation to a Ca2+-permeable state sensitizes local Ca2+ signals to IP3. This increases the potency of a physiological agonist to evoke global Ca2+ signals and activate a downstream target. Our data provide a conceptual framework to understand how Ca2+ release from physically separated stores is coordinated.

Host IP3R channels are dispensable for rotavirus Ca2+ signaling but critical for intercellular Ca2+ waves that prime uninfected cells for rapid virus spread.

IMPORTANCE: Many viruses exploit host Ca2+ signaling to facilitate their replication; however, little is known about how Ca2+ signals from different host and viral channels contribute to the overall dysregulation of Ca2+ signaling or promote virus replication. Using cells lacking IP3R, a host ER Ca2+ channel, we delineated intracellular Ca2+ signals within virus-infected cells and intercellular Ca2+ waves (ICWs), which increased Ca2+ signaling in neighboring, uninfected cells. In infected cells, IP3R was dispensable for rotavirus-induced Ca2+ signaling and replication, suggesting the rotavirus NSP4 viroporin supplies these signals. However, IP3R-mediated ICWs increase rotavirus replication kinetics and spread, indicating that the Ca2+ signals from the ICWs may prime nearby uninfected cells to better support virus replication upon eventual infection. This "pre-emptive priming" of uninfected cells by exploiting host intercellular pathways in the vicinity of virus-infected cells represents a novel mechanism for viral reprogramming of the host to gain a replication advantage.

Steady-state regulation of COPII-dependent secretory cargo sorting by inositol trisphosphate receptors, calcium, and penta EF hand proteins.

Recently, we demonstrated that agonist-stimulated Ca2+ signaling involving IP3 receptors modulates ER export rates through activation of the penta-EF Hand proteins apoptosis-linked gene-2 (ALG-2) and peflin. It is unknown, however, whether IP3Rs and penta-EF proteins regulate ER export rates at steady state. Here we tested this idea in normal rat kidney epithelial cells by manipulation of IP3R isoform expression. Under standard growth conditions, spontaneous cytosolic Ca2+ oscillations occurred simultaneously in successive groups of contiguous cells, generating intercellular Ca2+ waves that moved across the monolayer periodically. Depletion of IP3R-3, typically the least promiscuous IP3R isoform, caused increased cell participation in intercellular Ca2+ waves in unstimulated cells. The increased spontaneous signaling was sufficient to cause increased ALG-2 and COPII coat subunit Sec31A and decreased peflin localization at ER exit sites, resulting in increased ER-to-Golgi transport of the COPII client cargo VSV-G. The elevated ER-to-Golgi transport caused greater concentration of VSV-G at ER exit sites and had reciprocal effects on transport of VSV-G and a bulk-flow cargo, though both cargos equally required Sec31A. Inactivation of client cargo sorting using 4-phenylbutyrate had opposing reciprocal effects on client and bulk-flow cargo and neutralized any effect of ALG-2 activation on transport. This work extends our knowledge of ALG-2 mechanisms and indicates that in normal rat kidney cells, IP3R isoforms regulate homeostatic Ca2+ signaling that helps determine the basal secretion rate and stringency of COPII-dependent cargo sorting.

Type 3 IP3 receptor: Its structure, functions, and related disease implications.

Cell-fate decisions depend on the precise and strict regulation of multiple signaling molecules and transcription factors, especially intracellular Ca2+ homeostasis and dynamics. Type 3 inositol 1,4,5-triphosphate receptor (IP3R3) is an a tetrameric channel that can mediate the release of Ca2+ from the endoplasmic reticulum (ER) in response to extracellular stimuli. The gating of IP3R3 is regulated not only by ligands but also by other interacting proteins. To date, extensive research conducted on the basic structure of IP3R3, as well as its regulation by ligands and interacting proteins, has provided novel perspectives on its biological functions and pathogenic mechanisms. This review aims to discuss recent advancements in the study of IP3R3 and provides a comprehensive overview of the relevant literature pertaining to its structure, biological functions, and pathogenic mechanisms.

In Cerebellar Atrophy of 12-Month-Old ATM-Null Mice, Transcriptome Upregulations Concern Most Neurotransmission and Neuropeptide Pathways, While Downregulations Affect Prominently Itpr1, Usp2 and Non-Coding RNA.

The autosomal recessive disorder Ataxia-Telangiectasia is caused by a dysfunction of the stress response protein, ATM. In the nucleus of proliferating cells, ATM senses DNA double-strand breaks and coordinates their repair. This role explains T-cell dysfunction and tumour risk. However, it remains unclear whether this function is relevant for postmitotic neurons and underlies cerebellar atrophy, since ATM is cytoplasmic in postmitotic neurons. Here, we used ATM-null mice that survived early immune deficits via bone-marrow transplantation, and that reached initial neurodegeneration stages at 12 months of age. Global cerebellar transcriptomics demonstrated that ATM depletion triggered upregulations in most neurotransmission and neuropeptide systems. Downregulated transcripts were found for the ATM interactome component Usp2, many non-coding RNAs, ataxia genes Itpr1, Grid2, immediate early genes and immunity factors. Allelic splice changes affected prominently the neuropeptide machinery, e.g., Oprm1. Validation experiments with stressors were performed in human neuroblastoma cells, where ATM was localised only to cytoplasm, similar to the brain. Effect confirmation in SH-SY5Y cells occurred after ATM depletion and osmotic stress better than nutrient/oxidative stress, but not after ATM kinase inhibition or DNA stressor bleomycin. Overall, we provide pioneer observations from a faithful A-T mouse model, which suggest general changes in synaptic and dense-core vesicle stress adaptation.