Phospholipase C delta-type consists of three isozymes: bovine PLCdelta2 is a homologue of human/mouse PLCdelta4

MiR-17-3p Facilitates Aggressive Cell Phenotypes in Colon Cancer by Targeting PLCD1 Through Affecting KIF14

Colon cancer (CC) is a common and lethal cancer to be further elucidated. Accumulating studies elaborated the crucial role of miRNAs differentially expressed in cancer cell growth. In the present study, differentially expressed miRNAs related to CC were screened by the bioinformatics methods on the strength of TCGA database. Highly expressed miR-17-3p was proved to notably influence CC cell proliferative, migratory, invasion, and apoptotic levels. By using TargetScan and miRTarBase databases, phospholipase C delta 1 (PLCD1) was predicted as a target downstream of miR-17-3p, and their binding site was predicted. Through TCGA database, low expression of PLCD1 and its significant negative correlation with miR-17-3p were identified in CC. Dual-luciferase reporter gene analysis ascertained the targeting relationship between miR-17-3p and PLCD1. Cell Counting Kit-8, colony formation, and transwell assays were introduced to detect CC cell malignant progression. Flow cytometry was applied to detect CC cell apoptosis. As result revealed, miR-17-3p was markedly highly expressed, and PLCD1, the target of miR-17-3p, was remarkably lowly expressed in CC cells. Forced expression of miR-17-3p facilitated CC cell proliferation, migration, invasion, and suppressed apoptosis. Biological roles of upregulating miR-17-3p in the colon cancer cells were markedly weakened by over-expressing PLCD1 simultaneously. MiR-17-3p regulated CC cell malignant progression, as well as apoptosis by targeting PLCD1. Moreover, KIF14 was extensively considered as an involved tumor-promoting gene that could be affected by miR-17-3p/PLCD1 axis based on BioGRID analysis and CO-IP assay. Concludingly, this study exhibited that miR-17-3p facilitated CC progression by PLCD1 downregulation.

Phospholipase C: underrated players in microbial infections

During bacterial infections, one or more virulence factors are required to support the survival, growth, and colonization of the pathogen within the host, leading to the symptomatic characteristic of the disease. The outcome of bacterial infections is determined by several factors from both host as well as pathogen origin. Proteins and enzymes involved in cellular signaling are important players in determining the outcome of host-pathogen interactions. phospholipase C (PLCs) participate in cellular signaling and regulation by virtue of their ability to hydrolyze membrane phospholipids into di-acyl-glycerol (DAG) and inositol triphosphate (IP3), which further causes the activation of other signaling pathways involved in various processes, including immune response. A total of 13 PLC isoforms are known so far, differing in their structure, regulation, and tissue-specific distribution. Different PLC isoforms have been implicated in various diseases, including cancer and infectious diseases; however, their roles in infectious diseases are not clearly understood. Many studies have suggested the prominent roles of both host and pathogen-derived PLCs during infections. PLCs have also been shown to contribute towards disease pathogenesis and the onset of disease symptoms. In this review, we have discussed the contribution of PLCs as a determinant of the outcome of host-pathogen interaction and pathogenesis during bacterial infections of human importance.

Phospholipase C families: Common themes and versatility in physiology and pathology

Phosphoinositide-specific phospholipase Cs (PLCs) are expressed in all mammalian cells and play critical roles in signal transduction. To obtain a comprehensive understanding of these enzymes in physiology and pathology, a detailed structural, biochemical, cell biological and genetic information is required. In this review, we cover all these aspects to summarize current knowledge of the entire superfamily. The families of PLCs have expanded from 13 enzymes to 16 with the identification of the atypical PLCs in the human genome. Recent structural insights highlight the common themes that cover not only the substrate catalysis but also the mechanisms of activation. This involves the release of autoinhibitory interactions that, in the absence of stimulation, maintain classical PLC enzymes in their inactive forms. Studies of individual PLCs provide a rich repertoire of PLC function in different physiologies. Furthermore, the genetic studies discovered numerous mutated and rare variants of PLC enzymes and their link to human disease development, greatly expanding our understanding of their roles in diverse pathologies. Notably, substantial evidence now supports involvement of different PLC isoforms in the development of specific cancer types, immune disorders and neurodegeneration. These advances will stimulate the generation of new drugs that target PLC enzymes, and will therefore open new possibilities for treatment of a number of diseases where current therapies remain ineffective.

Noteworthy prognostic value of phospholipase C delta genes in early stage pancreatic ductal adenocarcinoma patients after pancreaticoduodenectomy and potential molecular mechanisms

The purpose of this investigation was to explore the prognostic value of phospholipase C delta (PLCD) genes in early stage pancreatic ductal adenocarcinoma (PDAC) and its potential molecular mechanisms. The prognostic value of PLCD genes in early stage PDAC was assessed using the Kaplan-Meier method and multivariate Cox proportional hazards regression model. Genome-wide correlation analysis was performed on PLCD3 to identify the highly correlated genes in the transcriptome. Then, PLCD3 and these correlated genes together underwent a bioinformatics analysis to elucidate the potential molecular biological functions of PLCD3 in PDAC. PLCD1 and PLCD3 are significantly overexpressed in PDAC. In PDAC patients, PLCD3 is overexpressed in certain groups of people with a history of alcoholism (P = .032). High expression of PLCD3 was found to be associated with lower overall survival (OS) of patients with early stage PDAC (P = .020; adjusted P = .016). A combination of PLCD3 and clinical variables was able to better predict the outcome of patients with early stage PDAC. These clinical variables are histological grade (P = .001; adjusted P = .001), targeted molecular therapy (P < .001; adjusted P < .001), radiation therapy (P = .002; adjusted P = .039), and residual resection (P = .001; adjusted P = .002). The bioinformatics analysis revealed that PLCD3 is associated with angiogenesis, intracellular signal transduction, and regulation of cell proliferation. In conclusion, PLCD3 may be a potential prognostic biomarker for early stage PDAC.

The phosphoinositide hydrolase phospholipase C delta1 inhibits epithelial-mesenchymal transition and is silenced in colorectal cancer

In this study, we found that the phospholipase C delta1 (PLCD1) protein expression is reduced in colorectal tumor tissues compared with paired surgical margin tissues. PLCD1-promoted CpG methylation was detected in 29/64 (45%) primary colorectal tumors, but not in nontumor tissues. The PLCD1 RNA expression was also reduced in three out of six cell lines, due to PLCD1 methylation. The ectopic expression of PLCD1 resulted in inhibited proliferation and attenuated migration of colorectal tumor cells, yet promoted colorectal tumor cell apoptosis in vitro. We also observed that PLCD1 suppressed proliferation and promoted apoptosis in vivo. In addition, PLCD1 induced G1/S phase cell cycle arrest. Furthermore, we found that PLCD1 led to the downregulation of several factors downstream of β-catenin, including c-Myc and cyclin D1, which are generally known to be promoters of tumorigenesis. This downregulation was caused by an upregulation of E-cadherin in colorectal tumor cells. Our findings provide insights into the role of PLCD1 as a tumor suppressor gene in colorectal cancer (CRC), and demonstrate that it plays significant roles in proliferation, migration, invasion, cell cycle progression, and epithelial-mesenchymal transition. On the basis of these results, tumor-specific methylation of PLCD1 could be used as a novel biomarker for early detection and prognostic prediction in CRC.

Phospholipase Cδ1 suppresses cell migration and invasion of breast cancer cells by modulating KIF3A-mediated ERK1/2/β- catenin/MMP7 signalling

Phospholipase C δ1 (PLCD1) encodes an enzyme involved in energy metabolism, calcium homeostasis and intracellular movement. It is located at 3p22 in a region that is frequently deleted in multiple cancers, and the PLCD1 enzyme is a potential tumour suppressor in breast cancer that inhibits matrix metalloprotease (MMP) 7, but the detailed mechanism remains elusive. In this study, we found that PLCD1 was downregulated in breast cancers, and the gain-or-loss functional assay revealed that PLCD1 inhibited cell migration and invasion in vitro via the ERK1/2/β-catenin/MMP7 signalling pathway. Furthermore, KIF3A was identified as a downstream mediator of PLCD1, and there was an inverse correlation between the expression of PLCD1 and KIF3A. Knockdown of KIF3A expression alone suppressed cell migration and invasion, and attenuated ERK1/2/β-catenin/MMP7 signalling that was reactivated by knocking down PLCD1 in vitro. Collectively, our findings suggest that PLCD1 acts as a tumour suppressor, by KIF3A-mediated suppression of ERK1/2/β-catenin/MMP7 signalling, at least in part, in breast cancer.

Methylation of PLCD1 and adenovirus-mediated PLCD1 overexpression elicits a gene therapy effect on human breast cancer

Our previous study showed that PLCD1 significantly decreases cell proliferation and affects cell cycle progression in breast cancer cells. In the present study, we aimed to investigate its functional and molecular mechanisms, and whether or not can become a new target for gene therapies. We found reduced PLCD1 protein expression in breast tumor tissues compared with paired surgical margin tissues. PLCD1 promoter CpG methylation was detected in 55 of 96 (57%) primary breast tumors, but not in surgical-margin tissues and normal breast tissues. Ectopic expression of PLCD1 inhibited breast tumor cell proliferation in vivo by inducing apoptosis and suppressed tumor cell migration by regulating cytoskeletal reorganization proteins including RhoA and phospho-cofilin. Furthermore, we found that PLCD1 induced p53 accumulation, increased p27 and p21 protein levels, and cleaved PARP. Finally, we constructed an adenoviral vector expressing PLCD1 (AdH5-PLCD1), which exhibited strong cytotoxicity in breast cancer cells. Our findings provide insights into the development of PLCD1 gene therapies for breast cancer and perhaps, other human cancers.

Expression analysis and enzymatic characterization of phospholipase Cδ4 from olive flounder (Paralichthys olivaceus)

Phospholipase Cδ4 (PLCδ4) plays a significant role in cell proliferation, tumorigenesis, and in an early stage of fertilization. Despite the characterization of the mammalian PLCδ4, extensive study in aquatic organisms has not been carried out so far. Here, we performed the molecular and biochemical characterization of flatfish Paralichthys olivaceus PLCδ4 (PoPLCδ4) to understand its enzymatic properties and physiological functions. The olive flounder PLCδ4 cDNA has an open reading frame (ORF) of 2,268 bp, and encodes a 755 amino acid polypeptide with a predicted molecular weight of 86 kDa. All the characteristic domains found in mammalian PLCδ isoforms (PH domain, EF hands, an X-Y catalytic region, and a C2 domain) were found to be present in PoPLCδ4. The mRNA expression analysis of PoPLCδ4 showed that PoPLCδ4 is predominantly expressed in the brain, eye and heart tissues. Like other mammalian PLCδ proteins, the enzyme activity of recombinant PoPLCδ4 to phosphatidylinositol-4,5-bis-phosphate (PIP2) was noted to be concentration- and Ca(2+)-dependent. The structural features and biochemical characteristics of PoPLCδ4 were found to be similar to those of mammalian PLCδ4. This is the first demonstration of the expression analysis and enzymatic characterization of piscine PLCδ4.

Physiological functions of phospholipase Cδ1 and phospholipase Cδ3

Phospholipase C (PLC) is a key enzyme in phosphoinositide turnover, and in the regulation of various cellular events. Among the 13 PLC isozymes, PLCδ1 and PLCδ3 share a high sequence homology, and similar tissue distribution. Recent studies with genetically manipulated mice have clarified the importance of these PLC isozymes in a number of tissues. PLCδ1 is required for maintenance of homeostasis in skin and metabolic tissues, while PLCδ3 regulates microvilli formation in enterocytes and the radial migration of neurons in the cerebral cortex of the developing brain. Furthermore, simultaneous loss of PLCδ1 and PLCδ3 in mice causes placental vascular defects, leading to embryonic lethality. Taken together, PLCδ1 and PLCδ3 have unique and redundant roles in various tissues.

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.

Functional analysis of duplicated genes and N-terminal splice variant of phospholipase C-δ1 in Paralichthys olivaceus

Phosphoinositide-specific phospholipase C δ (PLC δ) plays an important role in many cellular responses and is involved in the production of second messenger. Here, we describe the presence of novel N-terminal extended alternative splice form of PLC-δ1B in Paralichthys olivaceus, which differs from the reported mammalian PLC-δ1 isoform. The two variants PoPLC-δ1B-Lf and PoPLC-δ1B-Sf share exon 3 (including the PH domain) to exon 16, but differ at the exon 1 (Short form: Sf) and novel exon 2 (Long form: Lf) of the transcript. For the characterization of the novel duplicated gene variant of PLC-δ1B in P. olivaceus, tissue-specific expression with RT-PCR and real-time PCR, and purification and enzymatic characterization of native and recombinant proteins of all the three-types of PLC-δ1 isoforms (PoPLC-δ1A, PoPLC-δ1B-Lf and PoPLC-δ1B-Sf) of P. olivaceus were studied. The PoPLC-δ1A was ubiquitously distributed in gill, kidney and spleen. The PoPLC-δ1B-Lf gene was widely detected in various tissues, especially in the digestive system, while PoPLC-δ1B-Sf was highly expressed in the stomach. The recombinant PoPLC-δ1A, PoPLC-δ1B-Lf and PoPLC-δ1B-Sf proteins were expressed as a histidine-tagged fusion protein in Escherichia coli. The PLC activity of the PoPLC-δ1 isoform proteins showed a concentration-dependent activity to phosphatidylinositol (PI) and phosphatidylinositol 4,5-bisphosphate (PIP(2)). In addition, U73122, the PLC inhibitor, effectively inhibited PLC activities of PoPLC-δ1A, PoPLC-δ1B-Lf and PoPLC-δ1B-Sf proteins. However, PoPLC-δ1A and PoPLC-δ1B-Lf were sensitive at pH 7.5, while PoPLC-δ1B-Sf was relatively sensitive at pH 7. These results might be useful for the study of phospholipase C-mediated signal transduction in fish.

Phosphoinositide pathway and the signal transduction network in neural development

The development of the nervous system is under the strict control of a number of signal transduction pathways, often interconnected. Among them, the phosphoinositide (PI) pathway and the related phospholipase C (PI-PLC) family of enzymes have been attracting much attention. Besides their well-known role in the regulation of intracellular calcium levels, PI-PLC enzymes interact with a number of molecules belonging to further signal transduction pathways, contributing to a specific and complex network in the developing nervous system. In this review, the connections of PI signalling with further transduction pathways acting during neural development are discussed, with special regard to the role of the PI-PLC family of enzymes.

Alopecia in a viable phospholipase C delta 1 and phospholipase C delta 3 double mutant

BACKGROUND

Inositol 1,4,5trisphosphate (IP(3)) and diacylglycerol (DAG) are important intracellular signalling molecules in various tissues. They are generated by the phospholipase C family of enzymes, of which phospholipase C delta (PLCD) forms one class. Studies with functional inactivation of Plcd isozyme encoding genes in mice have revealed that loss of both Plcd1 and Plcd3 causes early embryonic death. Inactivation of Plcd1 alone causes loss of hair (alopecia), whereas inactivation of Plcd3 alone has no apparent phenotypic effect. To investigate a possible synergy of Plcd1 and Plcd3 in postnatal mice, novel mutations of these genes compatible with life after birth need to be found.

METHODOLOGY/PRINCIPAL FINDINGS

We characterise a novel mouse mutant with a spontaneously arisen mutation in Plcd3 (Plcd3(mNab)) that resulted from the insertion of an intracisternal A particle (IAP) into intron 2 of the Plcd3 gene. This mutation leads to the predominant expression of a truncated PLCD3 protein lacking the N-terminal PH domain. C3H mice that carry one or two mutant Plcd3(mNab) alleles are phenotypically normal. However, the presence of one Plcd3(mNab) allele exacerbates the alopecia caused by the loss of functional Plcd1 in Del(9)olt1Pas mutant mice with respect to the number of hair follicles affected and the body region involved. Mice double homozygous for both the Del(9)olt1Pas and the Plcd3(mNab) mutations survive for several weeks and exhibit total alopecia associated with fragile hair shafts showing altered expression of some structural genes and shortened phases of proliferation in hair follicle matrix cells.

CONCLUSIONS/SIGNIFICANCE

The Plcd3(mNab) mutation is a novel hypomorphic mutation of Plcd3. Our investigations suggest that Plcd1 and Plcd3 have synergistic effects on the murine hair follicle in specific regions of the body surface.

Phospholipase C

Phospholipase C (PLC) family members constitute a family of diverse enzymes. Thirteen different family members have been cloned. These family members have unique structures that mediate diverse functions. Although PLC family members all appear to signal through the bi-products of cleaving phospholipids, it is clear that each family member, and at times each isoform, contributes to unique cellular functions. This chapter provides a review of the current literature. In addition, references have been provided for more in depth information regarding areas that are discussed. Ultimately, understanding the roles of the individual PLC enzymes, and their distinct cellular functions, will lead to a better understanding of the development of diseases and the maintenance of homeostasis.

The phospholipase C isozymes and their regulation

The physiological effects of many extracellular neurotransmitters, hormones, growth factors, and other stimuli are mediated by receptor-promoted activation of phospholipase C (PLC) and consequential activation of inositol lipid signaling pathways. These signaling responses include the classically described conversion of phosphatidylinositol(4,5)P(2) to the Ca(2+)-mobilizing second messenger inositol(1,4,5)P(3) and the protein kinase C-activating second messenger diacylglycerol as well as alterations in membrane association or activity of many proteins that harbor phosphoinositide binding domains. The 13 mammalian PLCs elaborate a minimal catalytic core typified by PLC-d to confer multiple modes of regulation of lipase activity. PLC-b isozymes are activated by Gaq- and Gbg-subunits of heterotrimeric G proteins, and activation of PLC-g isozymes occurs through phosphorylation promoted by receptor and non-receptor tyrosine kinases. PLC-e and certain members of the PLC-b and PLC-g subclasses of isozymes are activated by direct binding of small G proteins of the Ras, Rho, and Rac subfamilies of GTPases. Recent high resolution three dimensional structures together with biochemical studies have illustrated that the X/Y linker region of the catalytic core mediates autoinhibition of most if not all PLC isozymes. Activation occurs as a consequence of removal of this autoinhibition.

Phospholipase Cdelta3 regulates RhoA/Rho kinase signaling and neurite outgrowth

Phospholipase Cδ3 (PLCδ3) is a key enzyme regulating phosphoinositide metabolism; however, its physiological function remains unknown. Because PLCδ3 is highly enriched in the cerebellum and cerebral cortex, we examined the role of PLCδ3 in neuronal migration and outgrowth. PLCδ3 knockdown (KD) inhibits neurite formation of cerebellar granule cells, and application of PLCδ3KD using in utero electroporation in the developing brain results in the retardation of the radial migration of neurons in the cerebral cortex. In addition, PLCδ3KD inhibits axon and dendrite outgrowth in primary cortical neurons. PLCδ3KD also suppresses neurite formation of Neuro2a neuroblastoma cells induced by serum withdrawal or treatment with retinoic acid. This inhibition is released by the reintroduction of wild-type PLCδ3. Interestingly, the H393A mutant lacking phosphatidylinositol 4,5-bisphosphate hydrolyzing activity generates supernumerary protrusions, and a constitutively active mutant promotes extensive neurite outgrowth, indicating that PLC activity is important for normal neurite outgrowth. The introduction of dominant negative RhoA (RhoA-DN) or treatment with Y-27632, a Rho kinase-specific inhibitor, rescues the neurite extension in PLCδ3KD Neuro2a cells. Similar effects were also detected in primary cortical neurons. Furthermore, the RhoA expression level was significantly decreased by serum withdrawal or retinoic acid in control cells, although this decrease was not observed in PLCδ3KD cells. We also found that exogenous expression of PLCδ3 down-regulated RhoA protein, and constitutively active PLCδ3 promotes the RhoA down-regulation more significantly than PLCδ3 upon differentiation. These results indicate that PLCδ3 negatively regulates RhoA expression, inhibits RhoA/Rho kinase signaling, and thereby promotes neurite extension.

Expression pattern and sub-cellular distribution of phosphoinositide specific phospholipase C enzymes after treatment with U-73122 in rat astrocytoma cells

Phosphoinositide specific phospholipase C (PI-PLC) enzymes interfere with the metabolism of inositol phospholipids (PI), molecules involved in signal transduction, a complex process depending on various components. Many evidences support the hypothesis that, in the glia, isoforms of PI-PLC family display different expression and/or sub cellular distribution under non-physiological conditions such as the rat astrocytes activation during neurodegeneration, the tumoural progression of some neoplasms and the inflammatory cascade activation after lipopolysaccharide administration, even if their role remains not completely elucidated. Treatment of a cultured established glioma cell line (C6 rat astrocytoma cell line) induces a modification in the pattern of expression and of sub cellular distribution of PI-PLCs compared to untreated cells. Special attention require PI-PLC beta3 and PI-PLC gamma2 isoforms, whose expression and sub cellular localization significantly differ after U-73122 treatment. The meaning of these modifications is unclear, also because the use of this N-aminosteroid compound remains controversial, inasmuch it has further actions which might contribute to the global effect recorded on the treated cells.

Expression of phosphoinositide-specific phospholipase C isoenzymes in cultured astrocytes activated after stimulation with lipopolysaccharide

Signal transduction pathways, involved in cell cycle and activities, depend on various components including lipid signalling molecules, such as phosphoinositides and related enzymes. Many evidences support the hypothesis that inositol lipid cycle is involved in astrocytes activation during neurodegeneration. Previous studies investigated the pattern of expression of phosphoinositide-specific phospholipase C (PI-PLC) family isoforms in astrocytes, individuating in cultured neonatal rat astrocytes, supposed to be quiescent cells, the absence of some isoforms, accordingly to their well known tissue specificity. The same study was conducted in cultured rat astrocytoma C6 cells and designed a different pattern of expression of PI-PLCs in the neoplastic counterpart, accordingly to literature suggesting a PI signalling involvement in tumour progression. It is not clear the role of PI-PLC isoforms in inflammation; recent data demonstrate they are involved in cytokines production, with special regard to IL-6. PI-PLCs expression in LPS treated neonatal rat astrocytes performed by using RT-PCR, observed at 3, 6, 18 and 24 h intervals, expressed: PI-PLC beta1, beta4 and gamma1 in all intervals analysed; PI-PLC delta1 at 6, 18 and 24 h; PI-PLC delta3 at 6 h after treatment. PI-PLC beta3, delta4 and epsilon, present in untreated astrocytes, were not detected after LPS treatment. Immunocytochemical analysis, performed to visualize the sub-cellular distribution of the expressed isoforms, demonstrated different patterns of localisation at different times of exposure. These observations suggest that PI-PLCs expression and distribution may play a role in ongoing inflammation process of CNS.

Phosphorylation of phospholipase C-delta 1 regulates its enzymatic activity

Phosphorylation of phospholipase C-delta(1) (PLC-delta(1)) in vitro and in vivo was investigated. Of the serine/threonine kinases tested, protein kinase C (PKC) phosphorylated the serine residue(s) of bacterially expressed PLC-delta(1) most potently. It was also demonstrated that PLC-delta(1) directly bound PKC-alpha via its pleckstrin homology (PH) domain. Using deletion mutants of PLC-delta(1) and synthetic peptides, Ser35 in the PH domain was defined as the PKC mediated in vitro phosphorylation site of PLC-delta(1). In vitro phosphorylation of PLC-delta(1) by PKC stimulated [(3)H]PtdIns(4,5)P(2) hydrolyzing activity and [(3)H]Ins(1,4,5)P(3)-binding of the PLC-delta(1). On the other hand, endogenous PLC-delta(1) was constitutively phosphorylated and phosphoamino acid analysis revealed that major phosphorylation sites were threonine residues in quiescent cells. The phosphorylation level and the species of phosphoamino acid were not changed by various stimuli such as PMA, EGF, NGF, and forskolin. Using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, we determined that Thr209 of PLC-delta(1) is one of the constitutively phosphorylated sites in quiescent cells. The PLC activity was potentiated when constitutively phosphorylated PLC-delta(1) was dephosphorylated by endogenous phosphatase(s) in vitro. Additionally, coexpression with PKC-alpha reduced serine phosphorylation of PLC-delta(1) detected by an anti-phosphoserine antibody and PLC-delta(1)-dependent basal production of inositol phosphates in NIH-3T3 cells, suggesting PKC-alpha activates phosphatase or inactivates another kinase involved in PLC-delta(1) serine phosphorylation to modulate the PLC-delta(1) activity in vivo. Taken together, these results suggest that PLC-delta(1) has multiple phosphorylation sites and phosphorylation status of PLC-delta(1) regulates its activity positively or negatively depends on the phosphorylation sites.

Phospholipase C delta 1 is a novel 3p22.3 tumor suppressor involved in cytoskeleton organization, with its epigenetic silencing correlated with high-stage gastric cancer

Located at the important tumor suppressor locus, 3p22, PLCD1 encodes an enzyme that mediates regulatory signaling of energy metabolism, calcium homeostasis and intracellular movements. We identified PLCD1 as a downregulated gene in aerodigestive carcinomas through expression profiling and epigenetic characterization. We found that PLCD1 was expressed in all normal adult tissues but low or silenced in 84% (16/19) gastric cancer cell lines, well correlated with its CpG island (CGI) methylation status. Methylation was further detected in 62% (61/98) gastric primary tumors, but none of normal gastric mucosa tissues. PLCD1 methylation was significantly correlated with tumor high stage. Detailed methylation analysis of 37 CpG sites at the PLCD1 CGI by bisulfite genomic sequencing confirmed its methylation. PLCD1 silencing could be reversed by pharmacological demethylation with 5-aza-2'-deoxycytidine, indicating a direct epigenetic silencing. Ectopic expression of PLCD1 in silenced gastric tumor cells dramatically inhibited their clonogenicity and migration, possibly through downregulating MMP7 expression and hampering the reorganization of cytoskeleton through cofilin inactivation by phosphorylation. Thus, epigenetic inactivation of PLCD1 is common and tumor-specific in gastric cancer, and PLCD1 acts as a functional tumor suppressor involved in gastric carcinogenesis.

Phospholipase C-delta1 modulates sustained contraction of rat mesenteric small arteries in response to noradrenaline, but not endothelin-1

Vasoconstrictors activate phospholipase C (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP(2)), leading to calcium mobilization, protein kinase C activation, and contraction. Our aim was to investigate whether PLC-delta(1), a PLC isoform implicated in alpha(1)-adrenoreceptor signaling and the pathogenesis of hypertension, is involved in noradrenaline (NA) or endothelin (ET-1)-induced PIP(2) hydrolysis and contraction. Rat mesenteric small arteries were studied. Contractility was measured by pressure myography, phospholipids or inositol phosphates were measured by radiolabeling with (33)Pi or myo-[(3)H]inositol, and caveolae/rafts were prepared by discontinuous sucrose density centrifugation. PLC-delta(1) was localized by immunoblot analysis and neutralized by delivery of PLC-delta(1) antibody. The PLC inhibitor U73122, but not the negative control U-73342, markedly inhibited NA and ET-1 contraction but had no effect on potassium or phorbol ester contraction, implicating PLC activity in receptor-mediated smooth muscle contraction. PLC-delta(1) was present in caveolae/rafts, and NA, but not ET-1, stimulated a rapid twofold increase in PLC-delta(1) levels in these domains. PLC-delta(1) is calcium dependent, and removal of extracellular calcium prevented its association with caveolae/rafts in response to NA, concomitantly reducing NA-induced [(33)P]PIP(2) hydrolysis and [(3)H]inositol phosphate formation but with no effect on ET-1-induced [(33)P]PIP(2) hydrolysis. Neutralization of PLC-delta(1) by PLC-delta(1) antibody prevented its caveolae/raft association and attenuated the sustained contractile response to NA compared with control antibodies. In contrast, ET-1-induced contraction was not affected by PLC-delta(1) antibody. These results indicate the novel and selective role of caveolae/raft localized PLC-delta(1) in NA-induced PIP(2) hydrolysis and sustained contraction in intact vascular tissue.

Phospholipase C mediated modulation of TRPV1 channels

The transient receptor potential vanilloid type 1 (TRPV1) channels are involved in both thermosensation and nociception. They are activated by heat, protons, and capsaicin and modulated by a plethora of other agents. This review will focus on the consequences of phospholipase C (PLC) activation, with special emphasis on the effects of phosphatidylinositol 4,5-bisphosphate (PIP2) on these channels. Two opposing effects of PIP2 have been reported on TRPV1. PIP2 has been proposed to inhibit TRPV1, and relief from this inhibition was suggested to be involved in sensitization of these channels by pro-inflammatory agents. In excised patches, however, PIP2 was shown to activate TRPV1. Calcium flowing through TRPV1 activates PLC and the resulting depletion of PIP2 was proposed to play a role in capsaicin-induced desensitization of these channels. We will describe the data indicating involvement of PLC and PIP2 in sensitization and desensitization of TRPV1 and will also discuss other pathways potentially contributing to these two phenomena. We attempt to resolve the seemingly contradictory data by proposing that PIP2 can both activate and inhibit TRPV1 depending on the experimental conditions, more specifically on the level of stimulation of these channels. Finally, we also discuss data in the literature indicating that other TRP channels, TRPA1 and some members of the TRPC subfamily, may also be under a similar dual control by PIP2.

Pharmacological evidence for the involvement of diacylglycerol lipase in depolarization-induced endocanabinoid release

Depolarization-induced suppression of inhibition (DSI) or excitation (DSE) is a well-known form of endocannabinoid-mediated short-term plasticity that is induced by postsynaptic depolarization. It is generally accepted that DSI/DSE is triggered by Ca(2+) influx through voltage-gated Ca(2+) channels. It is also demonstrated that DSI/DSE is mediated by 2-arachidonoylglycerol (2-AG). However, how Ca(2+) induces 2-AG production is still unclear. In the present study, we investigated molecular mechanisms underlying the Ca(2+)-driven 2-AG production. Using cannabinoid-sensitive inhibitory synapses of cultured hippocampal neurons, we tested several inhibitors for enzymes that are supposed to be involved in 2-AG metabolism. The chemicals we tested include inhibitors for phospholipase C (U73122 and ET-18), diacylglycerol kinase (DGK inhibitor 1), phosphatidic acid phosphohydrolase (propranolol), and diacylglycerol lipase (DGL; RHC-80267 and tetrahydrolipstatin (THL)). However, unfavorable side effects were observed with these inhibitors, except for THL. Furthermore, we found that RHC-80267 hardly inhibited the endocannabinoid release driven by G(q/11)-coupled receptors, which is thought to be DGL-dependent. By contrast, THL exhibited no side effects as long as we tested, and was confirmed to inhibit the DGL-dependent process. Using THL as a DGL inhibitor, we demonstrated that DGL is involved in both hippocampal DSI and cerebellar DSE. To test a possible involvement of PLCdelta in DSI, we examined hippocampal DSI in PLCdelta1, delta3 and delta4-knockout mice. However, there was no significant difference in the DSI magnitude between these knockout mice and wild-type mice. The present study clearly shows that DGL is a prerequisite for DSI/DSE. The enzymes yielding DG remain to be determined.

Lack of phospholipase C-δ1 induces skin inflammation

Phospholipase C (PLC) is a key enzyme in phosphoinositide signaling. We previously generated PLC-delta1 knockout (KO) mice and found that these mice showed remarkable hair loss caused by abnormalities in hair follicle structures. Here we show that the skin of PLC-delta1 KO mice displays typical inflammatory phenotypes, including increased dermal cellularity, leukocyte infiltration, and expression of pro-inflammatory cytokines. In addition, exogenously expressed PLC-delta1 attenuates lipopolysaccharide-induced expression of IL-1beta, a pro-inflammatory cytokine, in an enzymatic activity-dependent manner. Furthermore, suppression of skin inflammation by anti-inflammatory reagents cured the epidermal hyperplasia in PLC-delta1 KO mice. Taken together, these results indicate that lack of PLC-delta1 induces skin inflammation and that the epidermal hyperplasia in PLC-delta1 KO mice is caused by skin inflammation. Our results also suggest that PLC-delta1 regulates homeostasis of the immune system in skin.

Expression of phosphoinositide-specific phospholipase C isoenzymes in cultured astrocytes

Signal transduction from plasma membrane to cell nucleus is a complex process depending on various components including lipid signaling molecules, in particular phosphoinositides and their related enzymes, which act at cell periphery and/or plasma membrane as well as at nuclear level. As far as the nervous system may concern the inositol lipid cycle has been hypothesized to be involved in numerous neural as well as glial functions. In this context, however, a precise panel of glial PLC isoforms has not been determined yet. In the present experiments we investigated astrocytic PLC isoforms in astrocytes obtained from foetal primary cultures of rat brain and from an established cultured (C6) rat astrocytoma cell line, two well known cell models for experimental studies on glia. Identification of PLC isoforms was achieved by using a combination of RT-PCR and immunocytochemistry experiments. While in both cell models the most represented PI-PLC isoforms were beta4, gamma1, delta4, and epsilon, isoforms PI-PLC beta2 and delta3 were not detected. Moreover, in primary astrocyte cultures PI-PLC delta3 resulted well expressed in C6 cells but was absent in astrocytes. Immunocytochemistry performed with antibodies against specific PLC isoforms substantially confirmed this pattern of expression both in astrocytes and C6 glioma cells. In particular while some isoenzymes (namely isoforms beta3 and beta4) resulted mainly nuclear, others (isoforms delta4 and epsilon) were preferentially localized at cytoplasmic and plasma membrane level.

Coordinated intracellular translocation of phosphoinositide-specific phospholipase C-δ with the cell cycle

The delta family phosphoinositide (PI)-specific phospholipase C (PLC) are most fundamental forms of eukaryotic PI-PLCs. Despite the presence of lipid targeting domains such as the PH domain and C2 domain, the isoforms are also found in the cytoplasm and nucleus as well as at the plasma membrane. The isoforms have sequences or regions that can serve as a nuclear localization signal (NLS) and a nuclear export signal (NES). Their intracellular localization differs from one isoform to another, presumably due to the difference in the transport equilibrium balanced by the strength of the two signals of each isoform. Even for a particular isoform, its intracellular localization seems to vary during the cell cycle. As an example, PLCdelta(1), which is generally found at the plasma membrane and in the cytoplasm of quiescent cells, localizes to discrete nuclear structures in the G(1)/S boundary of the cell cycle. This may be at least partly due to an increase in intracellular Ca(2+), since Ca(2+) facilitates the formation of a nuclear transport complex comprised of PLCdelta(1) and importin beta1, a carrier molecule for the nuclear import. PLCdelta(1) as well as PLCdelta(4) may play a pivotal role in controlling the initiation of DNA synthesis in S phase. Spatio-temporal changes in the levels of PtdIns(4,5)P(2) seem to be another major determinant for the localization and regulation of the delta isoforms. High nuclear PtdIns(4,5)P(2) levels are associated with the G(1)/S phases. After entering M phase, PtdIns(4,5)P(2) synthesis at sites of cell division occurs and PLCs seem to localize to the cleavage furrow during cytokinesis. Coordinated translocation of PLCs with the cell cycle or with stress responses may result in changes in intra-nuclear environments and local membrane architectures that modulate proliferation and differentiation. In this review, recent findings regarding the molecular machineries and mechanisms of the nucleocytoplasmic shuttling as well as roles in the cell cycle progression of the delta isoforms of PLC will be discussed.

Phospholipase Cdelta4 associates with glutamate receptor interacting protein 1 in testis

We reported previously that phospholipase C (PLC) delta4 is required for calcium mobilization in the zona pellucida-induced acrosome reaction in sperm. Here we focused on the function of the C2 domain of PLCdelta4 and report that glutamate receptor-interacting protein1 (GRIP1) was identified as a binding protein of the PLCdelta4-C2 domain on yeast two-hybrid screening. Physiological interaction of GRIP1 with PLCdelta4 in mouse testis was confirmed by immunoprecipitation with anti-PLCdelta4 antibodies and the association seemed to correlate with the maturation stage of sperm. We also determined that a PDZ-binding motif at the C-terminus of the PLCdelta4-C2 domain is responsible for GRIP1 binding, whereas the sixth or seventh PDZ domain of GRIP1 is essential and sufficient for association with the PLCdelta4-C2 domain. These results indicate that PLCdelta4 binds via its C2 domain to the PDZ6 or PDZ7 domain of GRIP1, and that this association may play a role in spermatogenesis.

Phospholipase C-delta1 and -delta3 are essential in the trophoblast for placental development

Phosphoinositide-specific phospholipase C (PLC) is a key enzyme in phosphoinositide turnover and is involved in a variety of physiological functions. We analyzed PLCdelta1 knockout mice and found that PLCdelta1 is required for the maintenance of skin homeostasis. However, there were no remarkable abnormalities except hair loss and runting in PLCdelta1 knockout mice, even though PLCdelta1 is broadly distributed. Here, we report that mice lacking both PLCdelta1 and PLCdelta3 died at embryonic day 11.5 (E11.5) to E13.5. PLCdelta1/PLCdelta3 double-knockout mice exhibited severe disruption of the normal labyrinth architecture in the placenta and decreased placental vascularization, as well as abnormal proliferation and apoptosis of trophoblasts in the labyrinth area. Furthermore, PLCdelta1/PLCdelta3 double-knockout embryos supplied with a normal placenta by the tetraploid aggregation method survived beyond E14.5, clearly indicating that the embryonic lethality is caused by a defect in trophoblasts. On the basis of these results, we conclude that PLCdelta1 and PLCdelta3 are essential in trophoblasts for placental development.

The latest phospholipase C, PLCeta, is implicated in neuronal function

Members of the phosphoinositide-specific phospholipase C (PLC) family have key roles in cell signalling. In response to many extracellular stimuli, such as hormones, neurotransmitters, antigens and growth factors, PLCs catalyse the hydrolysis of phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P(2)], thereby generating two well-established second messengers, inositol (1,4,5)-trisphosphate and diacylglycerol. Eleven PLC isozymes encoded by different genes have been identified in mammals and, on the basis of their structure and sequence relationships, have been classified into five families designated PLCbeta (1-4), PLCgamma (1 and 2), PLCdelta (1, 3 and 4), PLCepsilon (1) and PLCzeta (1). All PLCs contain the catalytic X and Y domain, in addition to other regulatory domains including the C2 domain and the EF-hand domain. In 2005, four groups independently identified an entirely new family of PLCs--eta1 and eta2--using data mining of mammalian genomes. The properties of the PLCeta enzyme suggest that it might act as a Ca(2+) sensor, in particular, functioning during formation and maintenance of the neuronal network in the postnatal brain.

Molecular cloning and expression analysis of phospholipase Cδ from mud loach, Misgurnus mizolepis

A gene encoding phosphoinositide-specific phospholipase C (PLC), designated ML-PLCdelta, was cloned from mud loach (Misgurnus mizolepis) liver. A complete cDNA encoding ML-PLCdelta was isolated by screening the cDNA library of mud loach liver and using the 5'-rapid amplification of cDNA ends (RACE) method. The full-length ML-PLCdelta gene contains an open reading frame of 2325 base pairs encoding a 774 amino acid protein with a molecular mass of 88,072 Da; this corresponds to the size of the protein expressed in Escherichia coli BL21 (DE3) using pET28a vector. It contains all of the characteristic domains found in mammalian PLCdelta isozymes (PH domain, EF-hands, X-Y catalytic region, and a C2 domain). A homology search revealed that ML-PLCdelta shares relatively high sequence identity with mammalian PLCdelta1 (51-52%) and catfish PLCdelta (64%). The recombinant ML-PLCdelta protein expressed as a histidine-tagged fusion protein in E. coli was purified to apparent homogeneity by Ni(2+)-NTA affinity chromatography. The recombinant ML-PLCdelta showed a concentration-dependent PLC activity to phosphatidylinositol 4,5-bis-phosphate (PIP(2)) and its activity was Ca(2+)-dependent, which was similar to mammalian PLCdelta isozymes.