Localization of a novel inositol 1,4,5-trisphosphate binding protein, p130 in rat brain

PLCL1 regulates fibroblast-like synoviocytes inflammation via NLRP3 inflammasomes in rheumatoid arthritis

Background

Phospholipase C-like 1 (PLCL1), a protein that lacks catalytic activity, has similar structures to the PLC family. The aim of this research was to find the function and underlying mechanisms of PLCL1 in fibroblast-like synoviocyte (FLS) of rheumatoid arthritis (RA).

Methods

In this study, we first analyzed the expression of PLCL1 in the synovial tissue of RA patients and K/BxN mice by immunohistochemical staining. Then silencing or overexpressing PLCL1 in FLS before stimulating by TNF-α. The levels of IL-6, IL-1β and CXCL8 in FLS and supernatants were detected by Western Blot (WB), Real-Time Quantitative PCR and Enzyme Linked Immunosorbent Assay. We used INF39 to specifically inhibit the activation of NLRP3 inflammasomes, and detected the expression of NLRP3, Cleaved Caspase-1, IL-6 and IL-1β in FLS by WB.

Result

When PLCL1 was silenced, the level of IL-6, IL-1β and CXCL8 were down-regulated. When PLCL1 was overexpressed, the level of IL-6, IL-1β and CXCL8 were unregulated. The previous results demonstrated that the mechanism of PLCL1 regulating inflammation in FLS was related to NLRP3 inflammasomes. INF39 could counteract the release of inflammatory cytokines caused by overexpression of PLCL1.

Conclusion

Result showed that the function of PLCL1 in RA FLS might be related to the NLRP3 inflammasomes. We finally confirmed our hypothesis with the NLRP3 inhibitor INF39. Our results suggested that PLCL1 might promote the inflammatory response of RA FLS by regulating the NLRP3 inflammasomes.

Tumor Cell "Slimming" Regulates Tumor Progression through PLCL1/UCP1-Mediated Lipid Browning

Emerging evidence has highlighted the important role of abnormal lipid accumulation in cancer development and progression, but the mechanism for this phenomenon remains unclear. Here, it is demonstrated that phospholipase C-like 1/uncoupling protein 1 (PLCL1)/(UCP1)-mediated lipid browning promotes tumor cell "slimming" and represses tumor progression. By screening three independent lipid metabolism-related gene sets in clear cell renal cell carcinoma (ccRCC) and analyzing the TCGA database, it is found that PLCL1 predicted a poor prognosis and was downregulated in ccRCC. Restoration of PLCL1 expression in ccRCC cells significantly represses tumor progression and reduces abnormal lipid accumulation. Additionally, a phenomenon called tumor cell "slimming," in which tumor cell volume is reduced and lipid droplets are transformed into tiny pieces, is observed. Further studies show that PLCL1 promotes tumor cell "slimming" and represses tumor progression through UCP1-mediated lipid browning, which consumes lipids without producing ATP energy. Mechanistic investigations demonstrate that PLCL1 improves the protein stability of UCP1 by influencing the level of protein ubiquitination. Collectively, the data indicate that lipid browning mediated by PLCL1/UCP1 promotes tumor cell "slimming" and consumes abnormal lipid accumulation, which represses the progression of ccRCC. Tumor cell "slimming" offers a promising new concept and treatment modality against tumor development and progression.

Propofol Anesthesia Is Reduced in Phospholipase C-Related Inactive Protein Type-1 Knockout Mice

The GABA type A receptor (GABA_A-R) is a major target of intravenous anesthetics. Phospholipase C-related inactive protein type-1 (PRIP-1) is important in GABA_A-R phosphorylation and membrane trafficking. In this study, we investigated the role of PRIP-1 in general anesthetic action. The anesthetic effects of propofol, etomidate, and pentobarbital were evaluated in wild-type and PRIP-1 knockout (PRIP-1 KO) mice by measuring the latency and duration of loss of righting reflex (LORR) and loss of tail-pinch withdrawal response (LTWR). The effect of pretreatment with okadaic acid (OA), a protein phosphatase 1/2A inhibitor, on propofol- and etomidate-induced LORR was also examined. PRIP-1 deficiency provided the reduction of LORR and LTWR induced by propofol but not by etomidate or pentobarbital, indicating that PRIP-1 could determine the potency of the anesthetic action of propofol. Pretreatment with OA recovered the anesthetic potency induced by propofol in PRIP-1 KO mice. OA injection enhanced phosphorylation of cortical the GABA_A-R β3 subunit in PRIP-1 KO mice. These results suggest that PRIP-1-mediated GABA_A-R β3 subunit phosphorylation might be involved in the general anesthetic action induced by propofol but not by etomidate or pentobarbital.

Involvement of PRIP (Phospholipase C-Related But Catalytically Inactive Protein) in BMP-Induced Smad Signaling in Osteoblast Differentiation

Phospholipase C-related but catalytically inactive protein (PRIP) was first isolated as an inositol 1,4,5-trisphosphate binding protein. We generated PRIP gene-deficient mice which exhibited the increased bone mineral density and trabecular bone volume, indicating that PRIP is implicated in the regulation of bone properties. In this study, we investigated the possible mechanisms by which PRIP plays a role in bone morphogenetic protein (BMP) signaling, by analyzing the culture of primary cells isolated from calvaria of two genotypes, the wild type and a mutant. In the mutant culture, enhanced osteoblast differentiation was observed by measuring alkaline phosphatase staining and activity. The promoter activity of Id1 gene, responding immediately to BMP, was also more increased. Smad1/5 phosphorylation in response to BMP showed an enhanced peak and was more persistent in mutant cells, but the dephosphorylation process was not different between the two genotypes. The luciferase assay using calvaria cells transfected with the Smad1 mutated as a constitutive active form showed increased transcriptional activity at similar levels between the genotypes. The expression of BMP receptors was not different between the genotypes. BMP-induced phosphorylation of Smad1/5 was robustly decreased in wild type cells, but not in mutant cells, by pretreatment with DB867, an inhibitor of methyltransferase of inhibitory Smad6. Furthermore, BMP-induced translocation of Smad6 from nucleus to cytosol was not much observed in PRIP-deficient cells. These results indicate that PRIP is implicated in BMP-induced osteoblast differentiation by the negative regulation of Smad phosphorylation, through the methylation of inhibitory Smad6.

Progesterone-Dependent Induction of Phospholipase C-Related Catalytically Inactive Protein 1 (PRIP-1) in Decidualizing Human Endometrial Stromal Cells

Decidualization denotes the transformation of endometrial stromal cells into specialized decidual cells. In pregnancy, decidual cells form a protective matrix around the implanting embryo, enabling coordinated trophoblast invasion and formation of a functional placenta. Continuous progesterone (P4) signaling renders decidual cells resistant to various environmental stressors, whereas withdrawal inevitably triggers tissue breakdown and menstruation or miscarriage. Here, we show that PLCL1, coding phospholipase C (PLC)-related catalytically inactive protein 1 (PRIP-1), is highly induced in response to P4 signaling in decidualizing human endometrial stromal cells (HESCs). Knockdown experiments in undifferentiated HESCs revealed that PRIP-1 maintains basal phosphoinositide 3-kinase/Protein kinase B activity, which in turn prevents illicit nuclear translocation of the transcription factor forkhead box protein O1 and induction of the apoptotic activator BIM. By contrast, loss of this scaffold protein did not compromise survival of decidual cells. PRIP-1 knockdown did also not interfere with the responsiveness of HESCs to deciduogenic cues, although the overall expression of differentiation markers, such as PRL, IGFBP1, and WNT4, was blunted. Finally, we show that PRIP-1 in decidual cells uncouples PLC activation from intracellular Ca(2+) release by attenuating inositol 1,4,5-trisphosphate signaling. In summary, PRIP-1 is a multifaceted P4-inducible scaffold protein that gates the activity of major signal transduction pathways in the endometrium. It prevents apoptosis of proliferating stromal cells and contributes to the relative autonomy of decidual cells by silencing PLC signaling downstream of Gq protein-coupled receptors.

Phospholipase C-related catalytically inactive protein can regulate obesity, a state of peripheral inflammation

Obesity is defined as abnormal or excessive fat accumulation. Chronic inflammation in fat influences the development of obesity-related diseases. Many reports state that obesity increases the risk of morbidity in many diseases, including hypertension, dyslipidemia, type 2 diabetes, coronary heart disease, stroke, sleep apnea, and breast, prostate and colon cancers, leading to increased mortality. Obesity is also associated with chronic neuropathologic conditions such as depression and Alzheimer's disease. However, there is strong evidence that weight loss reduces these risks, by limiting blood pressure and improving levels of serum triglycerides, total cholesterol, low-density lipoprotein (LDL)-cholesterol, and high-density lipoprotein (HDL)-cholesterol. Prevention and control of obesity is complex, and requires a multifaceted approach. The elucidation of molecular mechanisms driving fat metabolism (adipogenesis and lipolysis) aims at developing clinical treatments to control obesity. We recently reported a new regulatory mechanism in fat metabolism: a protein phosphatase binding protein, phospholipase C-related catalytically inactive protein (PRIP), regulates lipolysis in white adipocytes and heat production in brown adipocytes via phosphoregulation. Deficiency of PRIP in mice led to reduced fat accumulation and increased energy expenditure, resulting in a lean phenotype. Here, we evaluate PRIP as a new therapeutic target for the control of obesity.

Phosphoinositides: tiny lipids with giant impact on cell regulation

Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.

Phenotypes of pain behavior in phospholipase C-related but catalytically inactive protein type 1 knockout mice

Phospholipase C-related inactive protein (PRIP) plays important roles in trafficking to the plasma membrane of GABA(A) receptor, which is involved in the dominant inhibitory neurotransmission in the spinal cord and plays an important role in nociceptive transmission. However, the role of PRIP in pain sensation remains unknown. In this study, we investigated the phenotypes of pain behaviors in PRIP type 1 knockout (PRIP-1 (-/-)) mice. The mutant mice showed hyperalgesic responses in the second phase of the formalin test and the von Frey test as compared with those in wild-type mice. In situ hybridization studies of GABA(A) receptors revealed significantly decreased expression of γ2 subunit mRNA in the dorsal and ventral horns of the spinal cord in PRIP-1 (-/-) mice, but no difference in α1 subunit mRNA expression. β2 subunit mRNA expression was significantly higher in PRIP-1 (-/-) mice than in wild-type mice in all areas of the spinal cord. On the other hand, the slow decay time constant for the spontaneous inhibitory current was significantly increased by treatment with diazepam in wild-type mice, but not in PRIP-1 (-/-) mice. These results suggest that PRIP-1 (-/-) mice exhibit the changes of the function and subunits expression of GABA(A) receptor in the spinal cord, which may be responsible for abnormal pain sensation in these mice.

Involvement of PRIP, phospholipase C-related, but catalytically inactive protein, in bone formation

PRIP (phospholipase C-related, but catalytically inactive protein) is a novel protein isolated in this laboratory. PRIP-deficient mice showed increased serum gonadotropins, but decreased gonadal steroid hormones. This imbalance was similar to that for the cause of bone disease, such as osteoporosis. In the present study, therefore, we analyzed mutant mice with special reference to the bone property. We first performed three-dimensional analysis of the femur of female mice. The bone mineral density and trabecular bone volume were higher in mutant mice. We further performed histomorphometrical assay of bone formation parameters: bone formation rate, mineral apposition rate, osteoid thickness, and osteoblast number were up-regulated in the mutant, indicating that increased bone mass is caused by the enhancement of bone formation ability. We then cultured primary cells isolated from calvaria prepared from both genotypes. In mutant mice, osteoblast differentiation, as assessed by alkaline phosphatase activity and the expression of osteoblast differentiation marker genes, was enhanced. Moreover, we analyzed the phosphorylation of Smad1/5/8 in response to bone morphogenetic protein, with longer phosphorylation in the mutant. These results indicate that PRIP is implicated in the negative regulation of bone formation.

GABA(A) receptor subunit alteration-dependent diazepam insensitivity in the cerebellum of phospholipase C-related inactive protein knockout mice

The GABA(A) receptor, a pentamer composed predominantly of alpha, beta, and gamma subunits, mediates fast inhibitory synaptic transmission. We have previously reported that phospholipase C-related inactive protein (PRIP) is a modulator of GABA(A) receptor trafficking and that knockout (KO) mice exhibit a diazepam-insensitive phenotype in the hippocampus. The alpha subunit affects diazepam sensitivity; alpha1, 2, 3, and 5 subunits assemble with any form of beta and the gamma2 subunits to produce diazepam-sensitive receptors, whereas alpha4 or alpha6/beta/gamma2 receptors are diazepam-insensitive. Here, we investigated how PRIP is implicated in the diazepam-insensitive phenotype using cerebellar granule cells in animals expressing predominantly the alpha6 subunit. The expression of alpha1/beta/gamma2 diazepam-sensitive receptors was decreased in the PRIP-1 and 2 double KO cerebellum without any change in the total number of benzodiazepine-binding sites as assessed by radioligand-binding assay. Since levels of the alpha6 subunit were increased, the alpha1/beta/gamma2 receptors might be replaced with alpha6 subunit-containing receptors. Then, we further performed autoradiographic and electrophysiologic analyses. These results suggest that the expression of alpha6/delta receptors was decreased in cerebellar granule neurons, while that of alpha6/gamma2 receptors was increased. PRIP-1 and 2 double KO mice exhibit a diazepam-insensitive phenotype because of a decrease in diazepam-sensitive (alpha1/gamma2) and increase in diazepam-insensitive (alpha6/gamma2) GABA(A) receptors in the cerebellar granule cells.

Phospholipase C-related but catalytically inactive protein is required for insulin-induced cell surface expression of gamma-aminobutyric acid type A receptors

The gamma-aminobutyric acid type A (GABA(A)) receptors play a pivotal role in fast synaptic inhibition in the central nervous system. One of the key factors for determining synaptic strength is the number of receptors on the postsynaptic membrane, which is maintained by the balance between cell surface insertion and endocytosis of the receptors. In this study, we investigated whether phospholipase C-related but catalytically inactive protein (PRIP) is involved in insulin-induced GABA(A) receptor insertion. Insulin potentiated the GABA-induced Cl(-) current (I(GABA)) by about 30% in wild-type neurons, but not in PRIP1 and PRIP2 double-knock-out (DKO) neurons, suggesting that PRIP is involved in insulin-induced potentiation. The phosphorylation level of the GABA(A) receptor beta-subunit was increased by about 30% in the wild-type neurons but not in the mutant neurons, which were similar to the changes observed in I(GABA). We also revealed that PRIP recruited active Akt to the GABA(A) receptors by forming a ternary complex under insulin stimulation. The disruption of the binding between PRIP and the GABA(A) receptor beta-subunit by PRIP interference peptide attenuated the insulin potentiation of I(GABA). Taken together, these results suggest that PRIP is involved in insulin-induced GABA(A) receptor insertion by recruiting active Akt to the receptor complex.

Phospholipase C-related inactive protein is involved in trafficking of gamma2 subunit-containing GABA(A) receptors to the cell surface

The subunit composition of GABA(A) receptors is known to be associated with distinct physiological and pharmacological properties. Previous studies that used phospholipase C-related inactive protein type 1 knock-out (PRIP-1 KO) mice revealed that PRIP-1 is involved in the assembly and/or the trafficking of gamma2 subunit-containing GABA(A) receptors. There are two PRIP genes in mammals; thus the roles of PRIP-1 might be compensated partly by those of PRIP-2 in PRIP-1 KO mice. Here we used PRIP-1 and PRIP-2 double knock-out (PRIP-DKO) mice and examined the roles for PRIP in regulating the trafficking of GABA(A) receptors. Consistent with previous results, sensitivity to diazepam was reduced in electrophysiological and behavioral analyses of PRIP-DKO mice, suggesting an alteration of gamma2 subunit-containing GABA(A) receptors. The surface numbers of diazepam binding sites (alpha/gamma2 subunits) assessed by [3H]flumazenil binding were reduced in the PRIP-DKO mice as compared with those of wild-type mice, whereas the cell surface GABA binding sites (alpha/beta subunits, assessed by [3H]muscimol binding) were increased in PRIP-DKO mice. The association between GABA(A) receptors and GABA(A) receptor-associated protein (GABARAP) was reduced significantly in PRIP-DKO neurons. Disruption of the direct interaction between PRIP and GABA(A) receptor beta subunits via the use of a peptide corresponding to the PRIP-1 binding site reduced the cell surface expression of gamma2 subunit-containing GABA(A) receptors in cultured cell lines and neurons. These results suggest that PRIP is implicated in the trafficking of gamma2 subunit-containing GABA(A) receptors to the cell surface, probably by acting as a bridging molecule between GABARAP and the receptors.

Phospholipase C-related inactive protein is implicated in the constitutive internalization of GABAA receptors mediated by clathrin and AP2 adaptor complex

A mechanism for regulating the strength of synaptic inhibition is enabled by altering the number of GABA(A) receptors available at the cell surface. Clathrin and adaptor protein 2 (AP2) complex-mediated endocytosis is known to play a fundamental role in regulating cell surface GABA(A) receptor numbers. Very recently, we have elucidated that phospholipase C-related catalytically inactive protein (PRIP) molecules are involved in the phosphorylation-dependent regulation of the internalization of GABA(A) receptors through association with receptor beta subunits and protein phosphatases. In this study, we examined the implications of PRIP molecules in clathrin-mediated constitutive GABA(A) receptor endocytosis, independent of phospho-regulation. We performed a constitutive receptor internalization assay using human embryonic kidney 293 (HEK293) cells transiently expressed with GABA(A) receptor alpha/beta/gamma subunits and PRIP. PRIP was internalized together with GABA(A) receptors, and the process was inhibited by PRIP-binding peptide which blocks PRIP binding to beta subunits. The clathrin heavy chain, mu2 and beta2 subunits of AP2 and PRIP-1, were complexed with GABA(A) receptor in brain extract as analyzed by co-immunoprecipitation assay using anti-PRIP-1 and anti-beta2/3 GABA(A) receptor antibody or by pull-down assay using beta subunits of GABA(A) receptor. These results indicate that PRIP is primarily implicated in the constitutive internalization of GABA(A) receptor that requires clathrin and AP2 protein complex.

Modulation of GABAA Receptor Phosphorylation and Membrane Trafficking by Phospholipase C-related Inactive Protein/Protein Phosphatase 1 and 2A Signaling Complex Underlying Brain-derived Neurotrophic Factor-dependent Regulation of GABAergic Inhibition

Brain-derived neurotrophic factor (BDNF) modulates several distinct aspects of synaptic transmission, including GABAergic transmission. Exposure to BDNF alters properties of GABA(A) receptors and induces changes in the expression level at the cell surface. Although phospholipase C-related inactive protein-1 (PRIP-1) plays an important role in GABA(A) receptor trafficking and function, its role in BDNF-dependent modulation of these receptors, together with the role of PRIP-2, was investigated using neurons cultured from PRIP double knock-out mice. The BDNF-dependent inhibition of whole cell GABA-evoked currents observed in wild type neurons was not detected in neurons cultured from knock-out mice. Instead, a gradual increase in GABA-evoked currents in these neurons correlated with a gradual increase in phosphorylation of GABA(A) receptor beta3 subunit in response to BDNF. To characterize the specific role(s) that PRIP plays as components of underlying molecular machinery, we examined the recruitment of protein phosphatase(s) to GABA(A) receptors. We demonstrate that PRIP associates with phosphatases as well as with beta subunits. PRIP was found to colocalize with GABA(A) receptor clusters in cultured neurons and with recombinant GABA(A) receptors when co-expressed in HEK293 cells. Importantly, a peptide mimicking a domain of PRIP involved in binding to beta subunits disrupted the co-localization of these proteins in HEK293 cells and potently inhibited the BDNF-mediated attenuation of GABA(A) receptor currents in wild type neurons. Together, the results suggest that PRIP plays an important role in BDNF-dependent regulation of GABA(A) receptors by mediating the specific association between beta subunits of these receptors with protein phosphatases.

Characterization of the human PRIP-1 gene structure and transcriptional regulation

The PRIP [phospholipase C related, but catalytically inactive protein] family has been isolated as a novel inositol 1,4,5-trisphosphate binding protein with a domain organization similar to phospholipase C-delta but lacking the enzyme activity, comprising PRIP-1 and PRIP-2. The PRIP-1 gene is expressed predominantly in the brain, while PRIP-2 exhibits a relatively ubiquitous expression in rats and mice. We also found that PRIP-1 plays an important role in type A receptor signaling for gamma-aminobutyric acid in the brain. In this study, we investigated PRIP-1 gene structure and the possible mechanisms involved in the expression. The tissue distribution pattern of PRIP gene expression in humans was similar to that in rodents. 5'RACE (rapid amplification of cDNA ends) analysis using PRIP-1 gene specific primers with human brain mRNA revealed the presence of three new exons, indicating that the PRIP-1 gene is organized into 8 exons intervened by 7 introns. Although three transcripts resulting from the alternative splicing of exon 2 and/or 3 were detected, a transcript lacking exons 2 and 3 was predominantly expressed in humans, suggesting that the translation start codon of human PRIP-1 exists in exon 1. To characterize the human PRIP-1 promoter, transient luciferase assay was carried out with luciferase constructs including various lengths of the 5' flanking region of the PRIP-1 gene. The results indicated that the positive regulatory region is located -237 to -108 bp upstream from the transcription start site. Gel shift assay revealed the specific binding of some nuclear proteins to this region, suggesting that the existence of transcription factors contributes to the positive regulation of PRIP-1 gene expression. Mutation analyses revealed that the binding of a transcription factor, MAZ to the regulatory site leads to the promoter activity, indicating that MAZ is involved in the expression regulation of the human PRIP-1 gene.

Hypersensitivity to pentylenetetrazol-induced convulsion in mice lacking the PLC-related inactive protein-1

In the present study, we investigated the effects of pentylenetetrazol (PTZ), a chemical convulsant that interacts with the GABA(A) receptor, in mice lacking the phospholipase C (PLC)-related inactive protein-1 (PRIP-1). PRIP-1 knockout mice did not develop spontaneous behavioral seizure. PRIP-1 knockout mice had markedly shorter latencies until the first clonic convulsion (CL) and tonic extensor (TE) following PTZ administration and increased incidence of convulsion compared to those in wild-type mice. Furthermore, the mortality rate by PTZ in mice lacking the PRIP-1 was also significantly increased in comparison with that in wild-type mice. These findings suggested that mice lacking the PRIP-1 were hypersensitive to PTZ-induced convulsion, and PRIP-1 might play roles in suppressing excessive excitability via interactions with the GABA(A) receptor.

[The life cycle of the GABA(A) receptor and its regulating molecules]

Gamma-aminobutyric acid(A) (GABA(A)) receptors mediate most of the fast inhibitory neurotransmission in the central nervous system. These ligand-gated ion channels are crucial in the control of cell and network activity. Therefore, modulating their function or cell surface stability will have major consequences for neuronal excitation. This review highlights recent findings on the regulation of GABA(A)-receptor expression and function, focusing on the mechanisms of sorting, targeting, synaptic clustering, and endocytic events of GABA(A) receptors, all which are regulated by their associated proteins. Now these topics are an area of active interest in studies on inhibitory neurotransmission.

Molecules interacting with PRIP-2, a novel Ins(1,4,5)P3 binding protein type 2: Comparison with PRIP-1

A family of phospholipase C-related, catalytically inactive proteins (designated PRIP) have been identified as a group of novel inositol 1,4,5-trisphosphate binding proteins with a domain organization similar to phospholipase C-delta but lacking the enzymatic activity. The PRIP family consists of at least two types of proteins (PRIP-1 and PRIP-2 subfamilies). In the present study, we examined the tissue distribution of PRIP-2, its expression in rat brain at the mRNA level, and the characteristics of its binding to inositol compounds, protein phosphatase 1, and gamma-amino butyric acid receptor associated protein. We also compared these characteristics with those of PRIP-1. Northern blot analysis and reverse-transcription polymerase chain reaction showed that PRIP-1 was present mainly in the brain, whereas PRIP-2 was expressed ubiquitously. In situ hybridization studies using rat brain revealed that the mRNA for both PRIP-1 and PRIP-2 was similarly expressed; it was detected in the granular cell and Purkinje cell layers in the cerebellum, and in the hippocampal pyramidal cells, dentate granule cells, and pyramidal and/or granule cells of the cerebral cortex in the cerebrum. PRIP-2 bound inositol 1,4,5-trisphosphate and its parent lipid, phosphatidylinositol 4,5-bisphosphate, with a similar affinity, while PRIP-1 preferentially bound the former ligand by about 10-fold. PRIP-1 and PRIP-2 interacted with protein phosphatase 1 and gamma-amino butyric acid receptor associated protein in a similar manner. These results indicate that, similar to PRIP-1, PRIP-2 may be involved in both inositol 1,4,5-trisphosphate-mediated and gamma-amino butyric acid-related signaling.

Role of the PLC-related, catalytically inactive protein p130 in GABA(A) receptor function

The protein p130 was isolated from rat brain as an inositol 1,4,5-trisphosphate-binding protein with a domain organization similar to that of phospholipase C-delta1 but lacking PLC activity. We show that p130 plays an important role in signaling by the type A receptor for gamma-aminobutyric acid (GABA). Yeast twohybrid screening identified GABARAP (GABA(A) receptor-associated protein), which is proposed to contribute to the sorting, targeting or clustering of GABA(A) receptors, as a protein that interacts with p130. Furthermore, p130 competitively inhibited the binding of the gamma2 subunit of the GABA(A) receptor to GABARAP in vitro. Electrophysiological analysis revealed that the modulation of GABA-induced Cl- current by Zn2+ or diazepam, both of which act at GABA(A) receptors containing gamma subunits, is impaired in hippocampal neurons of p130 knockout mice. Moreover, behavioral analysis revealed that motor coordination was impaired and the intraperitoneal injection of diazepam induced markedly reduced sedative and antianxiety effects in the mutant mice. These results indicate that p130 is essential for the function of GABA(A) receptors, especially in response to the agents acting on a gamma2 subunit.

Inhibition of Ca(2+) signalling by p130, a phospholipase-C-related catalytically inactive protein: critical role of the p130 pleckstrin homology domain

p130 was originally identified as an Ins(1,4,5)P(3)-binding protein similar to phospholipase C-delta but lacking any phospholipase activity. In the present study we have further analysed the interactions of p130 with inositol compounds in vitro. To determine which of the potential ligands interacts with p130 in cells, we performed an analysis of the cellular localization of this protein, the isolation of a protein-ligand complex from cell lysates and studied the effects of p130 on Ins(1,4,5)P(3)-mediated Ca(2+) signalling by using permeabilized and transiently or stably transfected COS-1 cells (COS-1(p130)). In vitro, p130 bound Ins(1,4,5)P(3) with a higher affinity than that for phosphoinositides. When the protein was isolated from COS-1(p130) cells by immunoprecipitation, it was found to be associated with Ins(1,4,5)P(3). Localization studies demonstrated the presence of the full-length p130 in the cytoplasm of living cells, not at the plasma membrane. In cell-based assays, p130 had an inhibitory effect on Ca(2+) signalling. When fura-2-loaded COS-1(p130) cells were stimulated with bradykinin, epidermal growth factor or ATP, it was found that the agonist-induced increase in free Ca(2+) concentration, observed in control cells, was inhibited in COS-1(p130). This inhibition was not accompanied by the decreased production of Ins(1,4,5)P(3); the intact p130 pleckstrin homology domain, known to be the ligand-binding site in vitro, was required for this effect in cells. These results suggest that Ins(1,4,5)P(3) could be the main p130 ligand in cells and that this binding has the potential to inhibit Ins(1,4,5)P(3)-mediated Ca(2+) signalling.