Human inositol 1,4,5-trisphosphate type-1 receptor, InsP3R1: structure, function, regulation of expression and chromosomal localization

Phenotypical, genotypical and pathological characterization of the moonwalker mouse, a model of ataxia

We performed a comprehensive study of the morphological, functional, and genetic features of moonwalker (MWK) mice, a mouse model of spinocerebellar ataxia caused by a gain of function of the TRPC3 channel. These mice show numerous behavioral symptoms including tremor, altered gait, circling behavior, impaired motor coordination, impaired motor learning and decreased limb strength. Cerebellar pathology is characterized by early and almost complete loss of unipolar brush cells as well as slowly progressive, moderate loss of Purkinje cell (PCs). Structural damage also includes loss of synaptic contacts from parallel fibers, swollen ER structures, and degenerating axons. Interestingly, no obvious correlation was observed between PC loss and severity of the symptoms, as the phenotype stabilizes around 2 months of age, while the cerebellar pathology is progressive. This is probably due to the fact that PC function is severely impaired much earlier than the appearance of PC loss. Indeed, PC firing is already impaired in 3 weeks old mice. An interesting feature of the MWK pathology that still remains to be explained consists in a strong lobule selectivity of the PC loss, which is puzzling considering that TRPC is expressed in every PC. Intriguingly, genetic analysis of MWK cerebella shows, among other alterations, changes in the expression of both apoptosis inducing and resistance factors possibly suggesting that damaged PCs initiate specific cellular pathways that protect them from overt cell loss.

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.

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.

Inositol 1,4,5-trisphosphate receptor gene variants are related to the risk of breast cancer in a Chinese population

BACKGROUND

Mammalian inositol 1,4,5-trisphosphate receptor (ITPR) genes encode ubiquitously expressed endoplasmic reticulum Ca²⁺ channels that have recently been shown to be closely linked to the pathogenesis of several cancers. However, few studies to date have explored associations between ITPR gene family single nucleotide polymorphisms (SNPs) and breast cancer risk.

METHODS

In the present case-control study, 12 SNPs in the potential functional regions of the ITPR1, ITPR2, and ITPR3 genes were genotyped using an Illumina Infinium® Beadchip in 2095 Chinese women (1032 cases and 1063 controls).

RESULTS

Multivariate logistic regression analyses indicated that a missense SNP in the ITPR3 coding region (rs2229642) was significantly related to breast cancer risk when using an additive model in this study (rs2229642-adjusted odds ratio = 1.40, 95% confidence interval = 1.12-1.74, p = 2.97 × 10^-3 ). Expression quantitative trait loci analyses indicated that the SNP rs2229642 was associated with reduced ITPR3 expression levels (p = 3.2 × 10^-7 ) and with marked reductions in the expressions of several proximal genes, including BAK1, GRM4, HLA-DOB, and UQCC2 (p = 0.013, 0.018, 3.4 × 10^-3 , 3.8 × 10^-5 ), suggesting that it may further regulate other genes associated with oncogenic susceptibility. Kaplan-Meier analyses indicated that the patients with higher ITPR3 expression exhibited significantly poorer outcomes compared to the patients with lower expression of this gene (hazard ratio = 1.11, 95% confidence interval = 1-1.23, p = 0.046).

CONCLUSIONS

The results indicated that genetic variant in the coding region of ITPR3 gene may regulate the expressions of its host and some other cancer-related genes, as well as act as potential predictive biomarker for susceptibility to breast cancer in the Chinese population.

Astrocytic IP3Rs: Beyond IP3R2

Astrocytes are sensitive to ongoing neuronal/network activities and, accordingly, regulate neuronal functions (synaptic transmission, synaptic plasticity, behavior, etc.) by the context-dependent release of several gliotransmitters (e.g., glutamate, glycine, D-serine, ATP). To sense diverse input, astrocytes express a plethora of G-protein coupled receptors, which couple, via G_i/o and G_q, to the intracellular Ca²⁺ release channel IP₃-receptor (IP₃R). Indeed, manipulating astrocytic IP₃R-Ca²⁺ signaling is highly consequential at the network and behavioral level: Depleting IP₃R subtype 2 (IP₃R2) results in reduced GPCR-Ca²⁺ signaling and impaired synaptic plasticity; enhancing IP₃R-Ca²⁺ signaling affects cognitive functions such as learning and memory, sleep, and mood. However, as a result of discrepancies in the literature, the role of GPCR-IP₃R-Ca²⁺ signaling, especially under physiological conditions, remains inconclusive. One primary reason for this could be that IP₃R2 has been used to represent all astrocytic IP₃Rs, including IP₃R1 and IP₃R3. Indeed, IP₃R1 and IP₃R3 are unique Ca²⁺ channels in their own right; they have unique biophysical properties, often display distinct distribution, and are differentially regulated. As a result, they mediate different physiological roles to IP₃R2. Thus, these additional channels promise to enrich the diversity of spatiotemporal Ca²⁺ dynamics and provide unique opportunities for integrating neuronal input and modulating astrocyte–neuron communication. The current review weighs evidence supporting the existence of multiple astrocytic-IP₃R isoforms, summarizes distinct sub-type specific properties that shape spatiotemporal Ca²⁺ dynamics. We also discuss existing experimental tools and future refinements to better recapitulate the endogenous activities of each IP₃R isoform.

A novel de novo intronic variant in ITPR1 causes Gillespie syndrome

Gillespie syndrome (GLSP) is characterized by bilateral symmetric partial aplasia of the iris presenting as a fixed and large pupil, cerebellar hypoplasia with ataxia, congenital hypotonia, and varying levels of intellectual disability. GLSP is caused by either biallelic or heterozygous, dominant-negative, pathogenic variants in ITPR1. Here, we present a 5-year-old male with GLSP who was found to have a heterozygous, de novo intronic variant in ITPR1 (NM_001168272.1:c.5935-17G > A) through genome sequencing (GS). Sanger sequencing of cDNA from this individual's fibroblasts showed the retention of 15 nucleotides from intron 45, which is predicted to cause an in-frame insertion of five amino acids near the C-terminal transmembrane domain of ITPR1. In addition, qPCR and cDNA sequencing demonstrated reduced expression of both ITPR1 alleles in fibroblasts when compared to parental samples. Given the close proximity of the predicted in-frame amino acid insertion to the site of previously described heterozygous, de novo, dominant-negative, pathogenic variants in GLSP, we predict that this variant also has a dominant-negative effect on ITPR1 channel function. Overall, this is the first report of a de novo intronic variant causing GLSP, which emphasizes the utility of GS and cDNA studies for diagnosing patients with a clinical presentation of GLSP and negative clinical exome sequencing.

The ER-mitochondria Ca2+ signaling in cancer progression: Fueling the monster

Cancer is a leading cause of death worldwide. All major tumor suppressors and oncogenes are now recognized to have fundamental connections with metabolic pathways. A hallmark feature of cancer cells is a reprogramming of their metabolism even when nutrients are available. Increasing evidence indicates that most cancer cells rely on mitochondrial metabolism to sustain their energetic and biosynthetic demands. Mitochondria are functionally and physically coupled to the endoplasmic reticulum (ER), the major calcium (Ca²⁺) storage organelle in mammalian cells, through special domains known as mitochondria-ER contact sites (MERCS). In this domain, the release of Ca²⁺ from the ER is mainly regulated by inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs), a family of Ca²⁺ release channels activated by the ligand IP3. IP3R mediated Ca²⁺ release is transferred to mitochondria through the mitochondrial Ca²⁺ uniporter (MCU). Once in the mitochondrial matrix, Ca²⁺ activates several proteins that stimulate mitochondrial performance. The role of IP3R and MCU in cancer, as well as the other proteins that enable the Ca²⁺ communication between these two organelles is just beginning to be understood. Here, we describe the function of the main players of the ER mitochondrial Ca²⁺ communication and discuss how this particular signal may contribute to the rise and development of cancer traits.

LW-213 induces cell apoptosis in human cutaneous T-cell lymphomas by activating PERK-eIF2α-ATF4-CHOP axis

Cutaneous T-cell lymphoma (CTCL) is characterized by a heterogeneous group of extranodal non-Hodgkin lymphomas, in which monoclonal T lymphocytes infiltrate the skin. LW-213, a derivative of wogonin, was found to induce cell apoptosis in chronic myeloid leukemia (CML). In this study, we investigated the effects of LW-213 on CTCL cells and the underlying mechanisms. We showed that LW-213 (1-25 μM) dose-dependently inhibited human CTCL cell lines (Hut-102, Hut-78, MyLa, and HH) with IC₅₀ values of around 10 μM, meanwhile it potently inhibited primary leukemia cells derived from peripheral blood of T-cell lymphoma patients. We revealed that LW-213-induced apoptosis was accompanied by ROS formation and the release of calcium from endoplasmic reticulum (ER) through IP₃R-1channel. LW-213 selectively activated CHOP and induced apoptosis in Hut-102 cells via activating PERK-eIF2α-ATF4 pathway. Interestingly, the degree of apoptosis and expression of ER stress-related proteins were alleviated in the presence of either N-acetyl cysteine (NAC), an ROS scavenger, or 2-aminoethyl diphenylborinate (2-APB), an IP₃R-1 inhibitor, implicating ROS/calcium-dependent ER stress in LW-213-induced apoptosis. In NOD/SCID mice bearing Hut-102 cell line xenografts, administration of LW-213 (10 mg/kg, ip, every other day for 4 weeks) markedly inhibited the growth of Hut-102 derived xenografts and prolonged survival. In conclusion, our study provides a new insight into the mechanism of LW-213-induced apoptosis, suggesting the potential of LW-213 as a promising agent against CTCL.

Disrupted Calcium Signaling in Animal Models of Human Spinocerebellar Ataxia (SCA)

Spinocerebellar ataxias (SCAs) constitute a heterogeneous group of more than 40 autosomal-dominant genetic and neurodegenerative diseases characterized by loss of balance and motor coordination due to dysfunction of the cerebellum and its efferent connections. Despite a well-described clinical and pathological phenotype, the molecular and cellular events that underlie neurodegeneration are still poorly undaerstood. Emerging research suggests that mutations in SCA genes cause disruptions in multiple cellular pathways but the characteristic SCA pathogenesis does not begin until calcium signaling pathways are disrupted in cerebellar Purkinje cells. Ca²⁺ signaling in Purkinje cells is important for normal cellular function as these neurons express a variety of Ca²⁺ channels, Ca²⁺-dependent kinases and phosphatases, and Ca²⁺-binding proteins to tightly maintain Ca²⁺ homeostasis and regulate physiological Ca²⁺-dependent processes. Abnormal Ca²⁺ levels can activate toxic cascades leading to characteristic death of Purkinje cells, cerebellar atrophy, and ataxia that occur in many SCAs. The output of the cerebellar cortex is conveyed to the deep cerebellar nuclei (DCN) by Purkinje cells via inhibitory signals; thus, Purkinje cell dysfunction or degeneration would partially or completely impair the cerebellar output in SCAs. In the absence of the inhibitory signal emanating from Purkinje cells, DCN will become more excitable, thereby affecting the motor areas receiving DCN input and resulting in uncoordinated movements. An outstanding advantage in studying the pathogenesis of SCAs is represented by the availability of a large number of animal models which mimic the phenotype observed in humans. By mainly focusing on mouse models displaying mutations or deletions in genes which encode for Ca²⁺ signaling-related proteins, in this review we will discuss the several pathogenic mechanisms related to deranged Ca²⁺ homeostasis that leads to significant Purkinje cell degeneration and dysfunction.

IP3 Receptor Plasticity Underlying Diverse Functions

In the body, extracellular stimuli produce inositol 1,4,5-trisphosphate (IP₃), an intracellular chemical signal that binds to the IP₃ receptor (IP₃R) to release calcium ions (Ca²⁺) from the endoplasmic reticulum. In the past 40 years, the wide-ranging functions mediated by IP₃R and its genetic defects causing a variety of disorders have been unveiled. Recent cryo-electron microscopy and X-ray crystallography have resolved IP₃R structures and begun to integrate with concurrent functional studies, which can explicate IP₃-dependent opening of Ca²⁺-conducting gates placed ∼90 Å away from IP₃-binding sites and its regulation by Ca²⁺. This review highlights recent research progress on the IP₃R structure and function. We also propose how protein plasticity within IP₃R, which involves allosteric gating and assembly transformations accompanied by rapid and chronic structural changes, would enable it to regulate diverse functions at cellular microdomains in pathophysiological states.

Consensus report of the 8 and 9th Weinman Symposia on Gene x Environment Interaction in carcinogenesis: novel opportunities for precision medicine

The relative contribution of intrinsic genetic factors and extrinsic environmental ones to cancer aetiology and natural history is a lengthy and debated issue. Gene-environment interactions (G x E) arise when the combined presence of both a germline genetic variant and a known environmental factor modulates the risk of disease more than either one alone. A panel of experts discussed our current understanding of cancer aetiology, known examples of G × E interactions in cancer, and the expanded concept of G × E interactions to include somatic cancer mutations and iatrogenic environmental factors such as anti-cancer treatment. Specific genetic polymorphisms and genetic mutations increase susceptibility to certain carcinogens and may be targeted in the near future for prevention and treatment of cancer patients with novel molecularly based therapies. There was general consensus that a better understanding of the complexity and numerosity of G × E interactions, supported by adequate technological, epidemiological, modelling and statistical resources, will further promote our understanding of cancer and lead to novel preventive and therapeutic approaches.

Calcium Signaling, PKC Gamma, IP3R1 and CAR8 Link Spinocerebellar Ataxias and Purkinje Cell Dendritic Development

Background

Spinocerebellar ataxias (SCAs) are a group of cerebellar diseases characterized by progressive ataxia and cerebellar atrophy. Several forms of SCAs are caused by missense mutations or deletions in genes related to calcium signaling in Purkinje cells. Among them, spinocerebellar ataxia type 14 (SCA14) is caused by missense mutations in PRKCG gene which encodes protein kinase C gamma (PKCγ). It is remarkable that in several cases in which SCA is caused by point mutations in an individual gene, the affected genes are involved in the PKCγ signaling pathway and calcium signaling which is not only crucial for proper Purkinje cell function but is also involved in the control of Purkinje cell dendritic development. In this review, we will focus on the PKCγ signaling related genes and calcium signaling related genes then discuss their role for both Purkinje cell dendritic development and cerebellar ataxia.

Methods

Research related to SCAs and Purkinje cell dendritic development is reviewed.

Results

PKCγ dysregulation causes abnormal Purkinje cell dendritic development and SCA14. Carbonic anhydrase related protein 8 (Car8) encoding CAR8 and Itpr1 encoding IP3R1were identified as upregulated genes in one of SCA14 mouse model. IP3R1, CAR8 and PKCγ proteins are strongly and specifically expressed in Purkinje cells. The common function among them is that they are involved in the regulation of calcium homeostasis in Purkinje cells and their dysfunction causes ataxia in mouse and human. Furthermore, disruption of intracellular calcium homeostasis caused by mutations in some calcium channels in Purkinje cells links to abnormal Purkinje cell dendritic development and the pathogenesis of several SCAs.

Conclusion

Once PKCγ signaling related genes and calcium signaling related genes are disturbed, the normal dendritic development of Purkinje cells is impaired as well as the integration of signals from other neurons, resulting in abnormal development, cerebellar dysfunction and eventually Purkinje cell loss.

Unravelling the GSK3β-related genotypic interaction network influencing hippocampal volume in recurrent major depressive disorder

OBJECTIVE

Glycogen synthase kinase 3β (GSK3β) has been implicated in mood disorders. We previously reported associations between a GSK3β polymorphism and hippocampal volume in major depressive disorder (MDD). We then reported similar associations for a subset of GSK3β-regulated genes. We now investigate an algorithm-derived comprehensive list of genes encoding proteins that directly interact with GSK3β to identify a genotypic network influencing hippocampal volume in MDD.

PARTICIPANTS AND METHODS

We used discovery (N=141) and replication (N=77) recurrent MDD samples. Our gene list was generated from the NetworKIN database. Hippocampal measures were derived using an optimized Freesurfer protocol. We identified interacting single nucleotide polymorphisms using the machine learning algorithm Random Forest and verified interactions using likelihood ratio tests between nested linear regression models.

RESULTS

The discovery sample showed multiple two-single nucleotide polymorphism interactions with hippocampal volume. The replication sample showed a replicable interaction (likelihood ratio test: P=0.0088, replication sample; P=0.017, discovery sample; Stouffer's combined P=0.0007) between genes associated previously with endoplasmic reticulum stress, calcium regulation and histone modifications.

CONCLUSION

Our results provide genetic evidence supporting associations between hippocampal volume and MDD, which may reflect underlying cellular stress responses. Our study provides evidence of biological mechanisms that should be further explored in the search for disease-modifying therapeutic targets for depression.

Nonprogressive congenital ataxias

The terminology of nonprogressive congenital ataxia (NPCA) refers to a clinically and genetically heterogeneous group of disorders characterized by congenital or early-onset ataxia, but no progression or even improvement on follow-up. Ataxia is preceded by muscular hypotonia and delayed motor (and usually language) milestones. We exclude children with prenatal, perinatal, and postnatal acquired diseases, malformations other than cerebellar hypoplasia, and defined syndromic disorders. Patients with NPCA have a high prevalence of cognitive and language impairments, in addition to increased occurrence of seizures, ocular signs (nystagmus, strabismus), behavior changes, and microcephaly. Neuroimaging is variable, ranging from normal cerebellar anatomy to reduced cerebellar volume (hypoplasia in the proper sense), and enlarged interfolial spaces, potentially mimicking atrophy. The latter appearance is often called "hypoplasia" as well, in view of the static clinical course. Some patients had progressive enlargement of cerebellar fissures, but a nonprogressive course. There is no imaging-clinical-genetic correlation. Dominant, recessive, and X-linked inheritance is documented for NPCA. Here, we focus on the still rather short list of dominant and recessive genes associated with NPCA, identified in the last few years. With future advances in genetics, we expect a rapid expansion of knowledge in this field.

Remodeling of Ca2+ signaling in cancer: Regulation of inositol 1,4,5-trisphosphate receptors through oncogenes and tumor suppressors

The calcium ion (Ca²⁺) is a ubiquitous intracellular signaling molecule that regulates diverse physiological and pathological processes, including cancer. Increasing evidence indicates that oncogenes and tumor suppressors regulate the Ca²⁺ transport systems. Inositol 1,4,5-trisphosphate (IP₃) receptors (IP₃Rs) are IP₃-activated Ca²⁺ release channels located on the endoplasmic reticulum (ER). They play pivotal roles in the regulation of cell death and survival by controlling Ca²⁺ transfer from the ER to mitochondria through mitochondria-associated ER membranes (MAMs). Optimal levels of Ca²⁺ mobilization to mitochondria are necessary for mitochondrial bioenergetics, whereas excessive Ca²⁺ flux into mitochondria causes loss of mitochondrial membrane integrity and apoptotic cell death. In addition to well-known functions on outer mitochondrial membranes, B-cell lymphoma 2 (Bcl-2) family proteins are localized on the ER and regulate IP₃Rs to control Ca²⁺ transfer into mitochondria. Another regulatory protein of IP₃R, IP₃R-binding protein released with IP₃ (IRBIT), cooperates with or counteracts the Bcl-2 family member depending on cellular states. Furthermore, several oncogenes and tumor suppressors, including Akt, K-Ras, phosphatase and tensin homolog (PTEN), promyelocytic leukemia protein (PML), BRCA1, and BRCA1 associated protein 1 (BAP1), are localized on the ER or at MAMs and negatively or positively regulate apoptotic cell death through interactions with IP₃Rs and regulation of Ca²⁺ dynamics. The remodeling of Ca²⁺ signaling by oncogenes and tumor suppressors that interact with IP₃Rs has fundamental roles in the pathology of cancers.

Mutational analysis of ITPR1 in a Taiwanese cohort with cerebellar ataxias

Background

The inositol 1,4,5-triphosphate (IP3) receptor type 1 gene (ITPR1) encodes the IP3 receptor type 1 (IP3R1), which modulates intracellular calcium homeostasis and signaling. Mutations in ITPR1 have been implicated in inherited cerebellar ataxias. The aim of this study was to investigate the role of ITPR1 mutations, including both large segmental deletion and single nucleotide mutations, in a Han Chinese cohort with inherited cerebellar ataxias in Taiwan.

Methodology and principal findings

Ninety-three unrelated individuals with molecularly unassigned spinocerebellar ataxia selected from 585 pedigrees with autosomal dominant cerebellar ataxias, were recruited into the study with elaborate clinical evaluations. The quantitative PCR technique was used to survey large segmental deletion of ITPR1 and a targeted sequencing approach was applied to sequence all of the 61 exons and the flanking regions of ITPR1. A novel ITPR1 mutation, c.7721T>C (p.V2574A), was identified in a family with dominantly inherited cerebellar ataxia. The proband has an adult-onset non-progressive pure cerebellar ataxia and her daughter is afflicted with a childhood onset cerebellar ataxia with intellectual sub-normalities.

Conclusion

ITPR1 mutation is an uncommon cause of inherited cerebellar ataxia, accounting for 0.2% (1/585) of patients with dominantly inherited cerebellar ataxias in Taiwan. This study broadens the mutational spectrum of ITPR1 and also emphasizes the importance of considering ITPR1 mutations as a potential cause of inherited cerebellar ataxias.

PLSCR1/IP3R1/Ca2+ axis contributes to differentiation of primary AML cells induced by wogonoside

Multiple lines of evidence have demonstrated that increased expression of phospholipid scramblase 1 (PLSCR1) is involved in the differentiation of acute myeloid leukemia (AML) cells by several differentiation-inducing agents including ATRA and phorbol 12-myristate 13-acetate. However, none of these agents can achieve nonhomogenous subcellular distribution of PLSCR1. We have demonstrated that wogonoside possesses differentiation and anti-leukemic effects in AML cell lines by promoting PLSCR1 trafficking into nucleus. Here we report that wogonoside promotes the expression of PLSCR1 and enhances its nuclear translocation and binding to the 1, 4, 5-trisphosphate receptor 1 (IP3R1) promoter in AML patient-derived primary cells. Wogonoside activates IP3R1, in turn, promotes release of Ca²⁺ from endoplasmic reticulum, and eventually leads to cell differentiation. Our in vivo study further confirms that wogonoside can promote PLSCR1 and IP3R1 expression in primary AML cells and reduce the AML cell counts in engrafted nonobese diabetic/severe combined immunodeficient mice. Taken together, our findings provide new insight into the mechanism of wogonoside-induced differentiation and anti-leukemic effect on primary AML cells, suggesting the therapeutic potential of wogonoside for AML, especially for non-APL AML.

Mutations in the IRBIT domain of ITPR1 are a frequent cause of autosomal dominant nonprogressive congenital ataxia

Congenital ataxias are nonprogressive neurological disorders characterized by neonatal hypotonia, developmental delay and ataxia, variably associated with intellectual disability and other neurological or extraneurological features. We performed trio-based whole-exome sequencing of 12 families with congenital cerebellar and/or vermis atrophy in parallel with targeted next-generation sequencing of known ataxia genes (CACNA1A, ITPR1, KCNC3, ATP2B3 and GRM1) in 12 additional patients with a similar phenotype. Novel pathological mutations of ITPR1 (inositol 1,4,5-trisphosphate receptor, type 1) were found in seven patients from four families (4/24, ∼16.8%) all localized in the IRBIT (inositol triphosphate receptor binding protein) domain which plays an essential role in the regulation of neuronal plasticity and development. Our study expands the mutational spectrum of ITPR1-related congenital ataxia and indicates that ITPR1 gene screening should be implemented in this subgroup of ataxias.

Protection by dietary restriction in the YAC128 mouse model of Huntington's disease: Relation to genes regulating histone acetylation and HTT

Huntington's disease (HD) is a fatal neurodegenerative disease characterized by metabolic, cognitive, and motor deficits. HD is caused by an expanded CAG repeat in the first exon of the HTT gene, resulting in an expanded polyglutamine section. Dietary restriction (DR) increases lifespan and ameliorates age-related pathologies, including in a model of HD, but the mechanisms mediating these protective effects are unknown. We report metabolic and behavioral effects of DR in the full-length YAC128 HD mouse model, and associated transcriptional changes in hypothalamus and striatum. DR corrected many effects of the transgene including increased body weight, decreased blood glucose, and impaired motor function. These changes were associated with reduced striatal human (but not mouse) HTT expression, as well as alteration in gene expression regulating histone acetylation modifications, particularly Hdac2. Other mRNAs related to Huntington's pathology in striatal tissue showed significant modulation by the transgene, dietary restriction or both. These results establish a protective role of DR in a transgenic model that contains the complete human HTT gene and for the first time suggest a role for DR in lowering HTT level, which correlates with severity of symptoms.

Genome-Wide Association and Trans-ethnic Meta-Analysis for Advanced Diabetic Kidney Disease: Family Investigation of Nephropathy and Diabetes (FIND)

Diabetic kidney disease (DKD) is the most common etiology of chronic kidney disease (CKD) in the industrialized world and accounts for much of the excess mortality in patients with diabetes mellitus. Approximately 45% of U.S. patients with incident end-stage kidney disease (ESKD) have DKD. Independent of glycemic control, DKD aggregates in families and has higher incidence rates in African, Mexican, and American Indian ancestral groups relative to European populations. The Family Investigation of Nephropathy and Diabetes (FIND) performed a genome-wide association study (GWAS) contrasting 6,197 unrelated individuals with advanced DKD with healthy and diabetic individuals lacking nephropathy of European American, African American, Mexican American, or American Indian ancestry. A large-scale replication and trans-ethnic meta-analysis included 7,539 additional European American, African American and American Indian DKD cases and non-nephropathy controls. Within ethnic group meta-analysis of discovery GWAS and replication set results identified genome-wide significant evidence for association between DKD and rs12523822 on chromosome 6q25.2 in American Indians (P = 5.74x10^-9). The strongest signal of association in the trans-ethnic meta-analysis was with a SNP in strong linkage disequilibrium with rs12523822 (rs955333; P = 1.31x10^-8), with directionally consistent results across ethnic groups. These 6q25.2 SNPs are located between the SCAF8 and CNKSR3 genes, a region with DKD relevant changes in gene expression and an eQTL with IPCEF1, a gene co-translated with CNKSR3. Several other SNPs demonstrated suggestive evidence of association with DKD, within and across populations. These data identify a novel DKD susceptibility locus with consistent directions of effect across diverse ancestral groups and provide insight into the genetic architecture of DKD.

Type 2 diabetes is the most common cause of severe kidney disease worldwide and diabetic kidney disease (DKD) associates with premature death. Individuals of non-European ancestry have the highest burden of type 2 DKD; hence understanding the causes of DKD remains critical to reducing health disparities. Family studies demonstrate that genes regulate the onset and progression of DKD; however, identifying these genes has proven to be challenging. The Family Investigation of Diabetes and Nephropathy consortium (FIND) recruited a large multi-ethnic collection of individuals with type 2 diabetes with and without kidney disease in order to detect genes associated with DKD. FIND discovered and replicated a DKD-associated genetic locus on human chromosome 6q25.2 (rs955333) between the SCAF8 and CNKSR genes. Findings were supported by significantly different expression of genes in this region from kidney tissue of subjects with, versus without DKD. The present findings identify a novel kidney disease susceptibility locus in individuals with type 2 diabetes which is consistent across subjects of differing ancestries. In addition, FIND results provide a rich catalogue of genetic variation in DKD patients for future research on the genetic architecture regulating this common and devastating disease.

Role of IP3 receptor signaling in cell functions and diseases

IP3 receptor (IP3R) was found to release Ca(2+) from non-mitochondrial store but the exact localization and the mode of action of IP3 remained a mystery. IP3R was identified to be P400 protein, a protein, which was missing in the cerebellum of ataxic mutant mice lacking Ca(2+) spikes in Pukinje cells. IP3R was an IP3 binding protein and was a Ca(2+) channel localized on the endoplasmic reticulum. Full-length cDNA of IP3R type 1 was initially cloned and later two other isoforms of IP3R (IP3R type 2 and type 3) were cloned in vertebrates. Interestingly, the phosphorylation sites, splicing sites, associated molecules, IP3 binding affinity and 5' promoter sequences of each isoform were different. Thus each isoform of IP3 receptor plays a role as a signaling hub offering a unique platform for matching various functional molecules that determines different trajectories of cell signaling. Because of this distinct role of each isoform of IP3R, the dysregulation of IP3 receptor causes various kinds of diseases in human and rodents such as ataxia, vulnerability to neuronal degeneration, heart disease, exocrine secretion deficit, taste perception deficit. Moreover, IP3 was found not only to release Ca(2+), but also to release IRBIT (IP3receptor binding protein released with inositol trisphosphate) essential for the regulation of acid-base balance, RNA synthesis and ribonucleotide reductase.

Inositol trisphosphate receptors in smooth muscle cells

Inositol 1,4,5-trisphosphate receptors (IP(3)Rs) are a family of tetrameric intracellular calcium (Ca(2+)) release channels that are located on the sarcoplasmic reticulum (SR) membrane of virtually all mammalian cell types, including smooth muscle cells (SMC). Here, we have reviewed literature investigating IP(3)R expression, cellular localization, tissue distribution, activity regulation, communication with ion channels and organelles, generation of Ca(2+) signals, modulation of physiological functions, and alterations in pathologies in SMCs. Three IP(3)R isoforms have been identified, with relative expression and cellular localization of each contributing to signaling differences in diverse SMC types. Several endogenous ligands, kinases, proteins, and other modulators control SMC IP(3)R channel activity. SMC IP(3)Rs communicate with nearby ryanodine-sensitive Ca(2+) channels and mitochondria to influence SR Ca(2+) release and reactive oxygen species generation. IP(3)R-mediated Ca(2+) release can stimulate plasma membrane-localized channels, including transient receptor potential (TRP) channels and store-operated Ca(2+) channels. SMC IP(3)Rs also signal to other proteins via SR Ca(2+) release-independent mechanisms through physical coupling to TRP channels and local communication with large-conductance Ca(2+)-activated potassium channels. IP(3)R-mediated Ca(2+) release generates a wide variety of intracellular Ca(2+) signals, which vary with respect to frequency, amplitude, spatial, and temporal properties. IP(3)R signaling controls multiple SMC functions, including contraction, gene expression, migration, and proliferation. IP(3)R expression and cellular signaling are altered in several SMC diseases, notably asthma, atherosclerosis, diabetes, and hypertension. In summary, IP(3)R-mediated pathways control diverse SMC physiological functions, with pathological alterations in IP(3)R signaling contributing to disease.

Functional characterization of the P1059L mutation in the inositol 1,4,5-trisphosphate receptor type 1 identified in a Japanese SCA15 family

Spinocerebellar ataxia type 15 (SCA15) is a group of human neurodegenerative disorders characterized by a slowly progressing pure cerebellar ataxia. The inositol 1,4,5-trisphosphate (IP(3)) receptor type 1 (IP(3)R1) is an intracellular IP(3)-induced Ca(2+) release channel that was recently identified as a causative gene for SCA15. In most case studies, a heterozygous deletion of the IP(3)R1 gene was identified. However, one Japanese SCA15 family was found to have a Pro to Leu (P1059L) substitution in IP(3)R1. To investigate the effect of the P1059L mutation, we analyzed the channel properties of the mutant human IP(3)R1 by expressing it in an IP(3)R-deficient B lymphocyte cell line. The P1059L mutant was a functional Ca(2+) release channel with a twofold higher IP(3) binding affinity compared to wild-type IP(3)R1. The cooperative dependence of the Ca(2+) release activity of the mutant on IP(3) concentration was reduced, but both wild-type and mutant receptors produced similar B cell receptor-induced Ca(2+) signals. These results demonstrate that the Ca(2+) release properties of IP(3)R1 are largely unaffected by the P1059L mutation.

Global analysis of transcriptional regulation by poly(ADP-ribose) polymerase-1 and poly(ADP-ribose) glycohydrolase in MCF-7 human breast cancer cells

Poly(ADP-ribose) polymerase-1 (PARP-1) and poly(ADP-ribose) glycohydrolase (PARG) are enzymes that modify target proteins by the addition and removal, respectively, of ADP-ribose polymers. Although a role for PARP-1 in gene regulation has been well established, the role of PARG is less clear. To investigate how PARP-1 and PARG coordinately regulate global patterns of gene expression, we used short hairpin RNAs to stably knock down PARP-1 or PARG in MCF-7 cells followed by expression microarray analyses. Correlation analyses showed that the majority of genes affected by the knockdown of one factor were similarly affected by the knockdown of the other factor. The most robustly regulated common genes were enriched for stress-response and metabolic functions. In chromatin immunoprecipitation assays, PARP-1 and PARG localized to the promoters of positively and negatively regulated target genes. The levels of chromatin-bound PARG at a given promoter generally correlated with the levels of PARP-1 across the subset of promoters tested. For about half of the genes tested, the binding of PARP-1 at the promoter was dependent on the binding of PARG. Experiments using stable re-expression of short hairpin RNA-resistant catalytic mutants showed that PARP-1 and PARG enzymatic activities are required for some, but not all, target genes. Collectively, our results indicate that PARP-1 and PARG, nuclear enzymes with opposing enzymatic activities, localize to target promoters and act in a similar, rather than antagonistic, manner to regulate gene expression.

Insulin promotes the association of heat shock protein 90 with the inositol 1,4,5-trisphosphate receptor to dampen its Ca2+ release activity

The inositol 1,4,5-trisphosphate receptor (IP(3)R) is a Ca(2+) release channel that plays a pivotal role in regulating intracellular Ca(2+) levels in resting cells. Three isoforms of IP(3)Rs have been identified, and they all possess a large regulatory domain that covers about 60% of the protein. This regulation is accomplished by interaction with small molecules, posttranslational modifications, and mostly protein-protein interactions. In our search for new binding partners of the IP(3)R, we found that 90-kDa heat-shock protein (Hsp90) binds to the IP(3)R. This interaction increased on stimulation of HEK293T6.11 cells with insulin but not with G(q) protein-coupled receptor (G(q)PCR) agonists. Moreover, the Hsp90 inhibitor geldanamycin (GA) disrupted the interaction between Hsp90 and the IP(3)R. Pretreatment of HEK293T6.11 cells with GA greatly increased the intracellular Ca(2+) release induced by a G(q)PCR agonist. Insulin alone did not induce any intracellular Ca(2+) release. However, insulin diminished the intracellular Ca(2+) release induced by a G(q)PCR agonist. Interestingly, GA abolished the inhibitory effect of insulin on G(q)PCR-induced intracellular Ca(2+) release. Furthermore, in our search for a mechanistic explanation to this phenomenon, we found that inhibition of kinases activated downstream of the insulin receptor greatly increased the interaction between Hsp90 and the IP(3)R. Of greater interest, we found that the simultaneous inhibition of mammalian target of rapamycin and the Src kinase almost completely disrupted the interaction between Hsp90 and the IP(3)R. These results demonstrate that insulin promotes the interaction of Hsp90 with the IP(3)R to dampen its Ca(2+) release activity by a complex mechanism involving mammalian target of rapamycin and the Src kinase.

IP3 receptor/Ca2+ channel: from discovery to new signaling concepts

Inositol 1,4,5-trisphosphate (IP(3)) is a second messenger that induces the release of Ca(2+) from the endoplasmic reticulum (ER). The IP(3) receptor (IP(3)R) was discovered as a developmentally regulated glyco-phosphoprotein, P400, that was missing in strains of mutant mice. IP(3)R can allosterically and dynamically change its form in a reversible manner. The crystal structures of the IP(3)-binding core and N-terminal suppressor sequence of IP(3)R have been identified. An IP(3) indicator (known as IP(3)R-based IP(3) sensor) was developed from the IP(3)-binding core. The IP(3)-binding core's affinity to IP(3) is very similar among the three isoforms of IP(3)R; instead, the N-terminal IP(3) binding suppressor region is responsible for isoform-specific IP(3)-binding affinity tuning. Various pathways for the trafficking of IP(3)R have been identified; for example, the ER forms a meshwork upon which IP(3)R moves by lateral diffusion, and vesicular ER subcompartments containing IP(3)R move rapidly along microtubles using a kinesin motor. Furthermore, IP(3)R mRNA within mRNA granules also moves along microtubules. IP(3)Rs are involved in exocrine secretion. ERp44 works as a redox sensor in the ER and regulates IP(3)R1 activity. IP(3) has been found to release Ca(2+), but it also releases IRBIT (IP(3)R-binding protein released with IP(3)). IRBIT is a pseudo-ligand for IP(3) that regulates the frequency and amplitude of Ca(2+) oscillations through IP(3)R. IRBIT binds to pancreas-type Na, bicarbonate co-transporter 1, which is important for acid-base balance. The presence of many kinds of binding partners, like homer, protein 4.1N, huntingtin-associated protein-1A, protein phosphatases (PPI and PP2A), RACK1, ankyrin, chromogranin, carbonic anhydrase-related protein, IRBIT, Na,K-ATPase, and ERp44, suggest that IP(3)Rs form a macro signal complex and function as a center for signaling cascades. The structure of IP(3)R1, as revealed by cryoelectron microscopy, fits closely with these molecules.

Phospholipid scramblases: An overview

Phospholipid scramblases are a group of homologous proteins that are conserved in all eukaryotic organisms. They are believed to be involved in destroying plasma membrane phospholipid asymmetry at critical cellular events like cell activation, injury and apoptosis. However, a detailed mechanism of phospholipid scrambling still awaits a proper understanding. The most studied member of this family, phospholipid scramblase 1 (PLSCR1) (a 37kDa protein), is involved in rapid Ca2+ dependent transbilayer redistribution of plasma membrane phospholipids. Recently the function of PLSCR1 as a phospholipids translocator has been challenged and evidences suggest that PLSCR1 acts as signaling molecule. It has been shown to be involved in protein phosphorylation and as a potential activator of genes in response to interferon and other cytokines. Interferon induced rapid biosynthesis of PLSCR1 targets some of the protein into the nucleus, where it binds to the promoter region of inositol 1,4,5-triphosphate (IP3) receptor type 1 (IP3R1) gene and induces its expression. Palmitoylation of PLSCR1 acts as a switch, controlling its localization either to the PM or inside the nucleus. In the present review, we discuss the current understanding of PLSCR1 in relation to its trafficking, localization and signaling functions.

Calcium signalling in the endothelium

Elevations in cytosolic Ca2+ concentration are the usual initial response of endothelial cells to hormonal and chemical transmitters and to changes in physical parameters, and many endothelial functions are dependent upon changes in Ca2+ signals produced. Endothelial cell Ca2+ signalling shares similar features with other electrically non-excitable cell types, but has features unique to endothelial cells. This chapter discusses the major components of endothelial cell Ca2+ signalling.

The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology

Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.

The type III inositol 1,4,5-trisphosphate receptor is phosphorylated by cAMP-dependent protein kinase at three sites

IP3 (inositol 1,4,5-trisphosphate) receptors form tetrameric, IP3-gated Ca2+ channels in endoplasmic reticulum membranes, and are substrates for several kinases, including PKA (cAMP-dependent protein kinase). Activation of PKA has been reported to either enhance or inhibit type III IP3 receptor Ca2+-channel activity, but, as yet, the sites of phosphorylation remain unknown. Here, we reveal that PKA phosphorylates the type III IP3 receptor at Ser916, Ser934 and Ser1832, and that, intriguingly, each site is located close to a putative surface-exposed peptide loop. Furthermore, we demonstrate that Ser934 is considerably more susceptible to PKA-dependent phoshorylation than either Ser916 or Ser1832. These findings define the sites at which the type III IP3 receptor is phosphorylated by PKA, and provide the basis for exploring the functional consequences of this regulatory event.

Phospholipid Scramblase 1 Binds to the Promoter Region of the Inositol 1,4,5-Triphosphate Receptor Type 1 Gene to Enhance Its Expression

Phospholipid scramblase 1 (PLSCR1) is a multiply palmitoylated, endofacial membrane protein originally identified based on its capacity to promote accelerated transbilayer phospholipid movement in response to Ca(2+). Recent evidence suggests that this protein also participates in cell response to various growth factors and cytokines, influencing myeloid differentiation, tumor growth, and the antiviral activity of interferon. Whereas plasma membrane PLSCR1 was shown to be required for normal recruitment and activation of Src kinase by stimulated cell surface growth factor receptors, PLSCR1 was also found to traffic into the nucleus and to tightly bind to genomic DNA, suggesting a possible additional nuclear function. We now report evidence that PLSCR1 directly binds to the 5'-promoter region of the inositol 1,4,5-triphosphate receptor type 1 gene (IP3R1) to enhance expression of the receptor. Probing a CpG island genomic library with PLSCR1 as bait identified four clones with avidity for PLSCR1, including a 191-bp fragment of the IP3R1 promoter. Using electrophoretic mobility shift and transcription reporter assays, the PLSCR1-binding site in IP3R1 was mapped to residues (-101)GTAACCATGTGGA(-89), and the segment spanning Met(86)-Glu(118) in PLSCR1 was identified to mediate its transcriptional activity. The significance of this interaction between PLSCR1 and IP3R1 in situ was confirmed by comparing levels of IP3R1 mRNA and protein in matched cells that either expressed or were deficient in PLSCR1. These data suggest that in addition to its role at the plasma membrane, effects of PLSCR1 on cell proliferative and maturational responses may also relate to alterations in expression of cellular IP3 receptors.

retinoic acid, bromodeoxyuridine, and the Delta 205 mutant polyoma virus middle T antigen regulate expression levels of a common ensemble of proteins associated with early stages of inducing HL-60 leukemic cell differentiation

Retinoic acid (RA), bromodeoxyuridine (BrdU), and the Delta 205 mutant polyoma middle T antigen affect the expression of a common ensemble of proteins in HL-60 human myeloblastic leukemia cells. Each of these agents is known to be able to prime HL-60 cells and accelerate subsequently induced myeloid or monocytic differentiation and G0 cell cycle arrest, suggesting that they have equal or identical cellular targets relevant to the early stages of inducing cell differentiation and G0 arrest. As a test of this possibility, a survey of protein expression changes induced by RA, BrdU, or Delta 205 transfection was performed. Retinoic acid induced numerous changes within h. Bromodeoxyuridine caused larger numbers of changes, whereas Delta 205 caused a more limited number. Among the hundreds of affected proteins detected, there were comparable numbers of up- or downregulated proteins. A small number changed between undetectable and detectable expression. The affected proteins were not restricted to a single functional class and included transcription factors, receptors, signaling molecules, cytoskeletal molecules, and effectors of various cellular processes such as deoxyribonucleic acid replication, transcription, and translation. The intersect of the sets of proteins affected by RA, BrdU, and Delta 205 was identified to determine if these agents regulated a common subset of proteins. This ensemble contained the commonly upregulated proteins AF6, ABP-280, ENC-1, ESE 1, MAP2B, NTF2, casein kinase, IRF1, SRPK2, Rb2, RhoGDI, P47phox, CD45, PKR, and SIIIp15. The commonly downregulated proteins were SHC, katanin, flotillin-2/ESA, EB 1, p43/EMAPIIprecursor, Jab1, FNK. The composition of the ensemble suggested three apparent themes for cellular processes that were affected early. The themes reflected the ultimate fate of the treated precursor cells as a mature myeloid cell, namely a cell whose hallmarks are (1) motility to migrate to a target and phagocytize it, (2) inducible oxidative metabolism to reduce the target with superoxide from a respiratory burst, and (3) biosynthetic slow down consistent with conversion from cell proliferation to quiescence. Interestingly, RA appears to induce aspects of an interferon-like response of potential significance as part of a biosynthetic slow down leading to cell cycle arrest. In conclusion, three biologically disparate ways to prime cells to differentiate were used to filter out a small ensemble of commonly regulated proteins that group as either microtubule associated, oxidative metabolism machinery, or effectors of cellular responses to interferon.

Molecular Cloning of Mouse Type 2 and Type 3 Inositol 1,4,5-Trisphosphate Receptors and Identification of a Novel Type 2 Receptor Splice Variant

We isolated cDNAs encoding type 2 and type 3 inositol 1,4,5-trisphosphate (IP(3)) receptors (IP(3)R2 and IP(3)R3, respectively) from mouse lung and found a novel alternative splicing segment, SI(m2), at 176-208 of IP(3)R2. The long form (IP(3)R2 SI(m2)(+)) was dominant, but the short form (IP(3)R2 SI(m2)(-)) was detected in all tissues examined. IP(3)R2 SI(m2)(-) has neither IP(3) binding activity nor Ca(2+) releasing activity. In addition to its reticular distribution, IP(3)R2 SI(m2)(+) is present in the form of clusters in the endoplasmic reticulum of resting COS-7 cells, and after ATP or Ca(2+) ionophore stimulation, most of the IP(3)R2 SI(m2)(+) is in clusters. IP(3)R3 is localized uniformly on the endoplasmic reticulum of resting cells and forms clusters after ATP or Ca(2+) ionophore stimulation. IP(3)R2 SI(m2)(-) does not form clusters in either resting or stimulated cells. IP(3) binding-deficient site-directed mutants of IP(3)R2 SI(m2)(+) and IP(3)R3 fail to form clusters, indicating that IP(3) binding is involved in the cluster formation by these isoforms. Coexpression of IP(3)R2 SI(m2)(-) prevents stimulus-induced IP(3)R clustering, suggesting that IP(3)R2 SI(m2)(-) functions as a negative coordinator of stimulus-induced IP(3)R clustering. Expression of IP(3)R2 SI(m2)(-) in CHO-K1 cells significantly reduced ATP-induced Ca(2+) entry, but not Ca(2+) release, suggesting that the novel splice variant of IP(3)R2 specifically influences the dynamics of the sustained phase of Ca(2+) signals.

The effect of higher order RNA processes on changing patterns of protein domain selection: A developmentally regulated transcriptome of type 1 inositol 1,4,5-trisphosphate receptors

The domain structure of proteins synthesized from a single gene can be remodeled during tissue development by activities at the RNA level of gene expression. The impact of higher order RNA processing on changing patterns of protein domain selection may be explored by systematically profiling single-gene transcriptomes. itpr1 is one of three mammalian genes encoding receptors for the second messenger inositol 1,4,5-trisphosphate (InsP3). Some phenotypic variations of InsP3 receptors have been attributed to hetero-oligomers of subunit isoforms from itpr1, itpr2, and itpr3. However, itpr1 itself is subject to alternative RNA splicing, with 7 sites of transcript variation, 6 within the ORF. We have identified 17 itpr1 subunit species expressed in mammalian brain in ensembles that change with tissue differentiation. Statistical analyses of populations comprising >1,300 full-length clones suggest that subunit variation arises from a variably biased stochastic splicing mechanism. Surprisingly, the protein domains of this highly allosteric receptor appear to be assembled in a partially randomized way, yielding stochastic arrays of subunit species that form tetrameric complexes in single cells. Nevertheless, functional expression studies of selected subunits confirm that splicing regulation is connected to phenotypic variation. The potential for itpr1 subunits to form hetero-tetramers in single cells suggests the expression of a developmentally regulated continuum of molecular forms that could display diverse properties, including incremental sensitivities to agonist activation and varying patterns of Ca2+ mobilization. These studies illuminate the extent to which itpr1 molecular phenotype is induced by higher order RNA processing.

Pressor responses to platelet-activating factor and thromboxane are mediated by Rho-kinase

Platelet-activating factor (PAF) contracts smooth muscle of airways and vessels primarily via release of thromboxane. Contraction of smooth muscle is thought to be mediated either by calcium and inositol trisphosphate (IP(3))-dependent activation of the myosin light chain kinase or, alternatively, via the recently discovered Rho-kinase pathway. Here we investigated the contribution of these two pathways to PAF and thromboxane receptor-mediated broncho- and vasoconstriction in two different rat models: the isolated perfused lung (IPL) and precision-cut lung slices. Inhibition of the IP(3) receptor (1-10 microM xestospongin C) or inhibition of phosphatidylinositol-specific PLC (30 microM L-108) did not affect bronchoconstriction but attenuated the sustained vasoconstriction by PAF. Inhibition of myosin light chain kinase (35 microM ML-7) or of calmodulin kinase kinase (26 microM STO609), which regulates the phosphorylation of the myosin light chain, had only a small effect on PAF- or thromboxane-induced pressor responses. Similarly, calmidazolium (10 microM), which inhibits calmodulin-dependent proteins, only weakly reduced the airway responses. In contrast, Y-27632 (10 microM), a Rho-kinase inhibitor, attenuated the thromboxane release triggered by PAF and provided partial or complete inhibition against PAF- and thromboxane-induced pressor responses, respectively. Together, our data indicate that PAF- and thus thromboxane receptor-mediated smooth muscle contraction depends largely on the Rho-kinase pathway.

Spinocerebellar ataxia type 15 (sca15) maps to 3p24.2-3pter: exclusion of the ITPR1 gene, the human orthologue of an ataxic mouse mutant

We have studied a large Australian kindred with a dominantly inherited pure cerebellar ataxia, SCA15. The disease is characterised by a very slow rate of progression in some family members, and atrophy predominantly of the superior vermis, and to a lesser extent the cerebellar hemispheres. Repeat expansion detection failed to identify either a CAG/CTG or ATTCT/AGAAT repeat expansions segregating with the disease in this family. A genome-wide scan revealed significant evidence for linkage to the short arm of chromosome 3. The highest two-point LOD score was obtained with D3S3706 (Z = 3.4, theta = 0.0). Haplotype analysis identified recombinants that placed the SCA15 locus within an 11.6-cM region flanked by the markers D3S3630 and D3S1304. The mouse syntenic region contains two ataxic mutants, itpr1-/- and opt, affecting the inositol 1,4,5-triphosphate type 1 receptor, ITPR1 gene. ITPR1 is predominantly expressed in the cerebellar Purkinje cells. Mutation analysis from two representative affected family members excluded the coding region of the ITPR1 gene from being involved in the pathogenesis of SCA15. Thus, the itpr1-/- and opt ITPR1 mouse mutants, which each result in ataxia, are not allelic to the human SCA15 locus.

Regulation of calreticulin expression during induction of differentiation in human myeloid cells. Evidence for remodeling of the endoplasmic reticulum

Induction of differentiation of HL-60 human myeloid cells profoundly affected expression of calreticulin, a Ca(2+)-binding endoplasmic reticulum chaperone. Induction with Me(2)SO or retinoic acid reduced levels of calreticulin protein by approximately 60% within 4 days. Pulse-chase studies indicated that labeled calreticulin decayed at similar rates in differentiated and undifferentiated cells (t(12) approximately 4.6 days), but the biosynthetic rate was <10% of control after 4 days. Differentiation also induced a rapid decline in calreticulin mRNA levels (90% reduction after 1 day) without a decrease in transcript stability (t(12) approximately 5 h). Nuclear run-on analysis demonstrated rapid down-regulation of gene transcription (21% of control at 2 h). Differentiation also greatly reduced the Ca(2+) content of the cells (25% of control), although residual Ca(2+) pools remained sensitive to thapsigargin, ionomycin, and inositol trisphosphate. Progressive decreases were also observed in levels of calnexin and ERp57, whereas BiP/GRP78 and protein disulfide isomerase were only modestly affected. Ultrastructural studies showed a substantial reduction in endoplasmic reticulum content of the cells. Thus, terminal differentiation of myeloid cells was associated with decreased endoplasmic reticulum content, selective reductions in molecular chaperones, and diminished intracellular Ca(2+) stores, perhaps reflecting an endoplasmic reticulum remodeling program as a prominent feature of granulocytic differentiation.

Molecular cytogenetic characterization of a subtle interstitial del(3)(p25.3p26.2) in a patient with deletion 3p syndrome

Deletion 3p syndrome is associated with characteristic facial features, growth failure, and mental retardation. Typically, individuals with deletion 3p syndrome have terminal deletions that result in loss of material from 3p25 to 3pter. We present a child with a clinical phenotype consistent with deletion 3p syndrome (ptosis, microcephaly, growth retardation, and developmental delay) and a subtle interstitial deletion in the distal portion of the short arm of chromosome 3, del(3)(p25.3p26.2). Fluorescence in situ hybridization (FISH) studies using 3p subtelomeric probes confirmed the terminal region of chromosome 3 was present. Sequence tagged sites (STS)-linked BAC clones mapping to chromosomal region 3p25-p26 were used to characterize the interstitial deletion by FISH. The results indicate the deletion is within a region of approximately 4.5 Mb between STS markers D3S3630 and D3S1304. This interstitial deletion lies within all previously reported terminal deletions in deletion 3p syndrome individuals, and represents the smallest reported deletion associated with deletion 3p syndrome. Characterization of the deletion may help identify genes important to growth and development that contribute to the deletion 3p syndrome phenotype when present in a hemizygous state.

Molecular characterization of the starfish inositol 1,4,5-trisphosphate receptor and its role during oocyte maturation and fertilization

The release of calcium ions (Ca(2+)) from their intracellular stores is essential for the fertilization of oocytes of various species. The calcium pools can be induced to release Ca(2+) via two main types of calcium channel receptor: the inositol 1,4,5-trisphosphate receptor (IP(3)R) and the ryanodine receptor. Starfish oocytes have often been used to study intracellular calcium mobilization during oocyte maturation and fertilization, but how the intracellular calcium channels contribute to intracellular calcium mobilization has never been understood fully, because these molecules have not been identified and no specific inhibitors of these channels have ever been found. In this study, we utilized a novel IP(3)R antagonist, the "IP(3) sponge," to investigate the role of IP(3) during fertilization of the starfish oocyte. The IP(3) sponge strongly and specifically competed with endogenous IP(3)R for binding to IP(3). By injecting IP(3) sponge into starfish oocyte, the increase in intracellular calcium and formation of the fertilization envelope were both dramatically blocked, although oocyte maturation was not blocked. To investigate the role of IP(3)R in the starfish oocyte more precisely, we cloned IP(3)R from the ovary of starfish, and the predicted amino acid sequence indicated that the starfish IP(3)R has 58-68% identity to mammalian IP(3)R types 1, 2, and 3. We then raised antibodies that recognize starfish IP(3)R, and use of the antibodies to perform immunoblot analysis revealed that the level of expression of IP(3)R remained unchanged throughout oocyte maturation. An immunocytochemical study, however, revealed that the distribution of starfish IP(3)R changes during oocyte maturation.

Nucleotide sequence analysis of the binding site on the inositol 1,4,5-trisphosphate type-1 receptor in bipolar disorder -- a negative study

Pharmacological studies of bipolar disorder suggest that dysfunction of calcium mobilization via phosphatidylinositol-mediated transduction may be involved in its pathogenesis. The present study tests the hypothesis that dysfunction of calcium mobilization in bipolar disorder is due to the mutation of the nucleotide sequence in the FKBP12 binding site on the inositol 1,4,5-trisphosphate type-1 receptor (IP(3)R1). Nucleotide sequence analysis of the FKBP12 binding site on IP(3)R1 was performed using reverse transcription-polymerase chain reaction and DNA sequencing. The nucleotide sequence in this region was preserved in all subjects. This finding suggests that IP(3)R1 dysfunction through the FKBP12 binding site is not involved in the pathogenesis of bipolar disorder.

Differential neuronal localizations and dynamics of phosphorylated and unphosphorylated type 1 inositol 1,4,5-trisphosphate receptors

Type 1 inositol 1,4,5-trisphosphate receptors are phosphorylated by cyclic-AMP-dependent protein kinase A at serines 1589 and 1755, with serine 1755 phosphorylation greatly predominating in the brain. Inositol 1,4,5-trisphosphate receptor protein kinase A phosphorylation augments Ca(2+) release. To assess type 1 protein kinase A phosphorylation dynamics in the intact organism, we developed antibodies selective for either serine 1755 phosphorylated or unphosphorylated species. Immunohistochemical studies reveal marked variation in localization. For example, in the hippocampus the phosphorylated type 1 inositol 1,4,5-trisphosphate receptor is restricted to CA1, while the unphosphorylated receptor occurs ubiquitously in CA1-CA3 and dentate gyrus granule cells. Throughout the brain the phosphorylated type 1 inositol 1,4,5-trisphosphate receptor is selectively enriched in dendrites, while the unphosphorylated receptor predominates in cell bodies. Focal cerebral ischemia in rats and humans is associated with dephosphorylation of type 1 inositol 1,4,5-trisphosphate receptors, and glutamatergic excitation of cerebellar Purkinje cells mediated by ibogaine elicits dephosphorylation of type 1 inositol 1,4,5-trisphosphate receptors that precedes evidence of excitotoxic neuronal degeneration. We have demonstrated striking variations in regional and subcellular distribution of inositol 1,4,5-trisphosphate receptor phosphorylation that may influence normal physiological intracellular Ca(2+) signaling in rat and human brain. We have further shown that the subcellular distribution of inositol 1,4,5-trisphosphate receptor phosphorylation in neurons is regulated by excitatory neurotransmission, as well as excitotoxic insult and neuronal ischemia-reperfusion. Phosphorylation dynamics of type 1 inositol 1,4,5-trisphosphate receptors may modulate intracellular Ca(2+) release and influence the cellular response to neurotoxic insults.

ATP regulation of recombinant type 3 inositol 1,4,5-trisphosphate receptor gating

A family of inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R) Ca2+ release channels plays a central role in Ca2+ signaling in most cells, but functional correlates of isoform diversity are unclear. Patch-clamp electrophysiology of endogenous type 1 (X-InsP3R-1) and recombinant rat type 3 InsP3R (r-InsP3R-3) channels in the outer membrane of isolated Xenopus oocyte nuclei indicated that enhanced affinity and reduced cooperativity of Ca2+ activation sites of the InsP3-liganded type 3 channel distinguished the two isoforms. Because Ca2+ activation of type 1 channel was the target of regulation by cytoplasmic ATP free acid concentration ([ATP](i)), here we studied the effects of [ATP]i on the dependence of r-InsP(3)R-3 gating on cytoplasmic free Ca2+ concentration ([Ca2+]i. As [ATP]i was increased from 0 to 0.5 mM, maximum r-InsP3R-3 channel open probability (Po) remained unchanged, whereas the half-maximal activating [Ca2+]i and activation Hill coefficient both decreased continuously, from 800 to 77 nM and from 1.6 to 1, respectively, and the half-maximal inhibitory [Ca2+]i was reduced from 115 to 39 microM. These effects were largely due to effects of ATP on the mean closed channel duration. Whereas the r-InsP3R-3 had a substantially higher Po than X-InsP3R-1 in activating [Ca2+]i (< 1 microM) and 0.5 mM ATP, the Ca2+ dependencies of channel gating of the two isoforms became remarkably similar in the absence of ATP. Our results suggest that ATP binding is responsible for conferring distinct gating properties on the two InsP3R channel isoforms. Possible molecular models to account for the distinct regulation by ATP of the Ca2+ activation properties of the two channel isoforms and the physiological implications of these results are discussed. Complex regulation by ATP of the types 1 and 3 InsP3R channel activities may enable cells to generate sophisticated patterns of Ca2+ signals with cytoplasmic ATP as one of the second messengers.

Up-regulation of inositol 1,4,5 trisphosphate receptor expression in atrial tissue in patients with chronic atrial fibrillation

OBJECTIVES

We examined whether patients with atrial fibrillation (AF) have alterations in atrial inositol 1,4,5 trisphosphate receptors (IP3 receptors).

BACKGROUND

Abnormal intracellular Ca2+ homeostasis occurs in chronic AF. The intracellular Ca2+ concentration is regulated by ryanodine and IP3 receptors. We recently reported alterations in ryanodine receptors in atrial tissue from patients in chronic AF.

METHODS

We analyzed IP3 receptor expression in the right atrial myocardium from 13 patients with mitral valvular disease (MVD) with AF (MVD/AF), five patients with MVD who had normal sinus rhythm (MVD/NSR) and eight control patients with NSR (tissue obtained during coronary artery bypass surgery). Hemodynamic and echocardiographic data were obtained preoperatively, and an immunohistochemical study was performed on atrial tissue.

RESULTS

The relative expression level of IP3 receptor protein was significantly greater in MVD/AF (0.75 +/- 0.26) than it was in MVD/NSR (0.42 +/- 0.13, p < 0.01), and both were significantly above control (0.14 +/- 0.08). The relative expression level of IP3 receptor messenger RNA was significantly greater in the MVD/AF group (0.028 +/- 0.008) than it was in the control group (0.015 +/- 0.004, p < 0.01), but patients with MVD/AF did not differ from patients with MVD/NSR (0.020 +/- 0.006). The relative expression levels of IP3 receptor protein and messenger RNA were higher in patients with left atrial dimension > or = 40 mm, pulmonary capillary wedge pressure > or = 10 mm Hg and right atrial pressure > or = 5 mm Hg. Inositol 1,4,5 trisphosphate receptors were over-expressed in the cytosol and at the nuclear envelope of atrial myocytes in MVD.

CONCLUSIONS

Since chronic mechanical overload of the atrial myocardium increased IP3 receptor expression, especially in patients with chronic AF, up-regulation of IP3 receptors may be important in modulating intracellular Ca2+ homeostasis and initiating or perpetuating AF.

Interaction of chromogranin B and the near N-terminal region of chromogranin B with an intraluminal loop peptide of the inositol 1,4, 5-trisphosphate receptor

Given the interaction of the inositol 1,4,5-trisphosphate receptor (IP(3)R) with chromogranins A (CGA) and B (CGB), two major Ca(2+) storage proteins of secretory granules that have been shown to be IP(3)-sensitive intracellular Ca(2+) store of neuroendocrine cells, we have investigated the potential interaction of the intraluminal loop regions of the IP(3)R with both intact CGB and the conserved near N-terminal region of CGB. The interaction studies carried out with CGB and glutathione S-transferase fusion proteins of intraluminal loop regions of bovine type 1 IP(3)R showed that CGB interacts with intraluminal loop 3-2 (the second loop formed between transmembrane regions 5 and 6) of the IP(3)R at both pH 5.5 and 7.5. Analytical ultracentrifugation studies also indicated that CGB interacts with the same intraluminal loop region of the IP(3)R and the interaction was much stronger than that between CGA and the loop. Moreover, the conserved near N-terminal region of CGB also interacted with the intraluminal loop region of the IP(3)R. The CGB interaction with the IP(3)R intraluminal loop peptide at pH 7.5 showed a DeltaG(0) value of -8.1 kcal/mol at 37 degrees C for a 1:1 stoichiometry, indicating a K(d) of approximately 1.9 micrometer. These results give insight into the molecular organization of the IP(3)-sensitive Ca(2+) store.

Biogenesis of endoplasmic reticulum proteins involved in Ca2+ signalling during megakaryocytic differentiation: an in vitro study

The endoplasmic reticulum (ER) plays a key role in Ca(2+) signalling through Ca(2+) release via inositol 1,4,5-trisphosphate receptors (InsP(3)-Rs) and Ca(2+) uptake by sarco/endoplasmic reticulum Ca(2+)-ATPases (SERCAs). Here, we investigated the organization of platelet ER and its biogenesis during megakaryocytopoiesis. First, erythro/megakaryoblastic MEG 01, UT7, M-O7e and CHRF 288-11 cell lines, platelets and thrombopoietin-induced UT7-Mpl cells were selected for the study of SERCA2b and SERCA3 proteins by Western blotting using the antibodies IID8 and PL/IM430, respectively. As judged by platelet glycoprotein IIIa (GPIIIa) expression, an increase in SERCA3 proteins was observed while that of SERCA2b remained unchanged throughout maturation. Second, these studies were extended to the newly described alternatively spliced SERCA3a-c RNAs and InsP(3)-Rs using the in vitro model of PMA-induced differentiation of MEG 01 cells. Time-course and dose-response studies showed a maximal approx. 4-fold up-regulation of SERCA3 proteins using 10(-8) M PMA for 3 days, which paralleled induction of GPIIIa expression. SERCA3 induction was found to occur at the level of mRNA. The modulation of the different SERCA3 species (i.e. 3a, 3b and 3c) was isoform-specific: while SERCA3a was slightly increased, an approx. 3-fold induction of SERCA3b, and a 4-fold induction of SERCA3c, was observed after 24 h of PMA treatment. Isoform-specific Western blotting and/or reverse transcriptase PCR studies showed that InsP(3)-R types I, II and III are expressed in MEG 01 cells, as well as in platelets. Study of the expression of these InsP(3)-R types in PMA-induced MEG 01 cells revealed that: (i) InsP(3)-RI protein and mRNA showed no changes; (ii) InsP(3)-RII mRNA was up-regulated and peaked at hour 48 and (iii) InsP(3)-RIII mRNA and protein showed a transitory maximal 3- and 2.3-fold increase at hours 6 and 30, respectively. Upon PMA treatment of CHRF 288-11 cells, in which GPIIIa is not induced upon treatment, a similar pattern of regulation of InsP(3)-R types II and III was seen, but a distinct pattern of SERCA3 regulation was observed. These results suggest a profound reorganization of ER-protein patterns during megakaryocytopoiesis and underline the role of SERCA3 gene regulation in the control of Ca(2+)-dependent platelet functions.

Ca(2+) signalling is not required for chemotaxis in Dictyostelium

Dictyostelium cells can move rapidly towards a source of cyclic-AMP (cAMP). This chemoattractant is detected by G-protein-linked receptors, which trigger a signalling cascade including a rapid influx of Ca(2+). We have disrupted an inositol 1,4,5-trisphosphate (InsP(3)) receptor-like gene, iplA, to produce null cells in which Ca(2+) entry in response to chemoattractants is abolished, as is the normal increase in free cytosolic Ca(2+) ([Ca(2+)](c)) that follows chemotactic stimulation. However, the resting [Ca(2+)](c) is similar to wild type. This mutant provides a test for the role of Ca(2+) influx in both chemotaxis and the signalling cascade that controls it. The production of cyclic-GMP and cAMP, and the activation of the MAP kinase, DdERK2, triggered from the cAMP receptor, are little perturbed in the mutant; mobilization of actin into the cytoskeleton also follows similar kinetics to wild type. Mutant cells chemotax efficiently towards cAMP or folic acid and their sensitivity to cAMP is similar to wild type. Finally, they move at similar speeds to wild-type cells, with or without chemoattractant. We conclude that Ca(2+) signalling is not necessary for chemotaxis to cAMP.