PLC- : A Shared Effector Protein in Ras-, Rho-, and G -Mediated Signaling

Lysophospholipid receptor activation of RhoA and lipid signaling pathways

The lysophospholipids sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) signal through G-protein coupled receptors (GPCRs) which couple to multiple G-proteins and their effectors. These GPCRs are quite efficacious in coupling to the Gα(12/13) family of G-proteins, which stimulate guanine nucleotide exchange factors (GEFs) for RhoA. Activated RhoA subsequently regulates downstream enzymes that transduce signals which affect the actin cytoskeleton, gene expression, cell proliferation and cell survival. Remarkably many of the enzymes regulated downstream of RhoA either use phospholipids as substrates (e.g. phospholipase D, phospholipase C-epsilon, PTEN, PI3 kinase) or are regulated by phospholipid products (e.g. protein kinase D, Akt). Thus lysophospholipids signal from outside of the cell and control phospholipid signaling processes within the cell that they target. Here we review evidence suggesting an integrative role for RhoA in responding to lysophospholipids upregulated in the pathophysiological environment, and in transducing this signal to cellular responses through effects on phospholipid regulatory or phospholipid regulated enzymes. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Replication study of PLCE1 and C20orf54 polymorphism and risk of esophageal cancer in a Chinese population

Esophageal cancer is one of the most aggressive cancers in the world. Recent large-scale genome-wide association studies (GWAS) reported that functional genetic variations in the phospholipase C epsilon gene (PLCE1) were strongly associated with risk of esophageal squamous cell carcinoma (ESCC) and gastric cardia adenocarcinoma (GCA) in Chinese population. For C20orf54 rs13042395 genotype and risk of esophageal cancer, the results were inconsistent. We conducted a replication case-control study to evaluate the genetic effects of these two functional single nucleotide polymorphisms (SNPs) on the development of esophageal cancer. A total of 380 cases and 380 controls were recruited for this study. The genotypes were determined by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS). The variant alleles of the functional polymorphism, PLCE1 rs2274223 SNP was associated with the increased risk of esophageal cancer [adjusted odds ratio (OR) = 1.95, 95 % confidence interval (CI) = 1.05-3.59 for PLCE1 rs2274223 GG vs. AA]. However, there was no significant association between the C20orf54 rs13042395 genotype and esophageal cancer risk (adjusted OR = 0.99, 95 % CI = 0.63-1.57 for C20orf54 rs13042395 TT vs. CC). Stratified analyses indicated a significantly increased risk of esophageal cancer associated with the PLCE1 rs2274223 AG genotype was more evident among females, younger patients and never drinkers, compared with the PLCE1 rs2274223 AA genotypes. Stratified analyses also indicated a significantly increased risk of esophageal cancer associated with the PLCE1 rs2274223 GG genotype was more evident among never smokers and never drinkers compared with the PLCE1 rs2274223 AA genotypes. These findings indicated that functional polymorphisms PLCE1 rs2274223 might contribute to esophageal cancer susceptibility.

Association of 10q23 with colorectal cancer in a Chinese population

Recently, a genome-wide association study of gastric cancer (GC) reported the significant association of seven genetic variants (rs4072037 and rs4460629 on 1q22; rs753724, rs11187842, rs3765524, rs2274223, and rs3781264 on 10q23) with GC in a Chinese population. These findings were confirmed in a subsequent independent study. However, it remains unknown whether these loci are associated with an increased risk of colorectal cancer (CRC). This study was to test whether the seven single nucleotide polymorphisms (SNPs) associated with GC were also associated with CRC in a Chinese population. The seven SNPs were genotyped using MassARRAY system. Allelic, genotypic, and haplotypic associations of the SNPs with CRC were investigated using χ(2) tests and logistic regression analysis. The SNPs rs3765524 and rs2274223, located on 10q23, were found to have significant protective effects against CRC, with equal odds ratios per allele. The two SNPs located on 1q22 (rs4072037 and rs4460629) showed a weak association with CRC. No significant association was identified with CRC for the remaining three SNPs located on 10q23 (rs753724, rs11187842, and rs3781264). These results suggest that rs3765524 and rs2274223 on 10q23 are associated with a protective effect against CRC in a Chinese population.

Behavioral plasticity in honey bees is associated with differences in brain microRNA transcriptome

Small, non-coding microRNAs (miRNAs) have been implicated in many biological processes, including the development of the nervous system. However, the roles of miRNAs in natural behavioral and neuronal plasticity are not well understood. To help address this we characterized the microRNA transcriptome in the adult worker honey bee head and investigated whether changes in microRNA expression levels in the brain are associated with division of labor among honey bees, a well-established model for socially regulated behavior. We determined that several miRNAs were downregulated in bees that specialize on brood care (nurses) relative to foragers. Additional experiments showed that this downregulation is dependent upon social context; it only occurred when nurse bees were in colonies that also contained foragers. Analyses of conservation patterns of brain-expressed miRNAs across Hymenoptera suggest a role for certain miRNAs in the evolution of the Aculeata, which includes all the eusocial hymenopteran species. Our results support the intriguing hypothesis that miRNAs are important regulators of social behavior at both developmental and evolutionary time scales.

Involvement of the PLCε/PKCα pathway in human BIU-87 bladder cancer cell proliferation

PLCε (phospholipase Cε), one of effectors belonging to the small GTPase superfamily, has been suggested to play a crucial role in carcinogenesis. However, its bio-function in bladder cancer has never been demonstrated. In our previous study, we found that PLCε mRNA was highly expressed in bladder cancer tissues. In the present study, we silenced the PLCε gene by shRNA (small-hairpin RNA) in the bladder cancer cell line BIU-87. The results showed that it significantly inhibited cell proliferation and arrested the cell cycle at G0/G1-phase. The regulation of cell characteristics has been related to PKCα (protein kinase Cα) activity. Further study showed that knockdown of the PLCε gene down-regulated oncogenes c-fos and c-jun. These results indicate that PLCε plays a crucial role in bladder cancer, and PLCε may be a key molecule regulating the signal pathway of bladder cancer proliferation.

Potentially functional variants of PLCE1 identified by GWASs contribute to gastric adenocarcinoma susceptibility in an eastern Chinese population

BACKGROUND

Recent genome-wide association studies (GWAS) have found a single nucleotide polymorphism (SNP, rs2274223 A>G) in PLCE1 to be associated with risk of gastric adenocarcinoma. In the present study, we validated this finding and also explored the risk associated with another unreported potentially functional SNP (rs11187870 G>C) of PLCE1 in a hospital-based case-control study of 1059 patients with pathologically confirmed gastric adenocarcinoma and 1240 frequency-matched healthy controls.

METHODOLOGY/PRINCIPAL FINDINGS

We determined genotypes of these two SNPs by the Taqman assay and used logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (95% CI). We found that a significant higher gastric adenocarcinoma risk was associated with rs2274223 variant G allele (adjusted OR = 1.35, 95% CI = 1.14-1.60 for AG+GG vs. AA) and rs11187870 variant C allele (adjusted OR = 1.26, 95% CI = 1.05-1.50 for CG+CC vs. GG). We also found that the number of combined risk alleles (i.e., rs2274223G and rs11187870C) was associated with risk of gastric adenocarcinoma in an allele-dose effect manner (P(trend) = 0.0002). Stratification analysis indicated that the combined effect of rs2274223G and rs11187870C variant alleles was more evident in subgroups of males, non-smokers, non-drinkers and patients with gastric cardia adenocarcinoma. Further real-time PCR results showed that expression levels of PLCE1 mRNA were significantly lower in tumors than in adjacent noncancerous tissues (0.019±0.002 vs. 0.008±0.001, P<0.05).

CONCLUSIONS/SIGNIFICANCES

Our results further confirmed that genetic variations in PLCE1 may contribute to gastric adenocarcinoma risk in an eastern Chinese population.

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.

Putatively functional PLCE1 variants and susceptibility to esophageal squamous cell carcinoma (ESCC): a case-control study in eastern Chinese populations

BACKGROUND

A novel variant rs2274223 located in the phospholipase C epsilon 1 (PLCE1) gene was found to be associated with risk of esophageal squamous cell carcinoma (ESCC) by 2 large-scale genome-wide association studies (GWASs) in Chinese populations. In this study, we aimed to assess such an association in an eastern Chinese population and to address its possibly functional role in the etiology of ESCC.

METHODS

A total of 1061 ESCC cases and 1211 controls were recruited and successfully genotyped for 2 single nucleotide polymorphisms (SNPs) (rs2274223 and rs11187870) of the PLCE1 gene by the TaqMan assay. Real-time PCR and immunohistochemical (IHC) analysis were applied to assess mRNA and protein expression levels, respectively, in a subset of tumor samples.

RESULTS

SNP rs2274223 was independently associated with risk of ESCC (adjusted odds ratio [OR], 1.49; 95% confidence interval [95% CI], 1.03-2.17 for GG vs AA), and SNP rs11187870 was also found to be associated with risk of ESCC assuming a dominant model (adjusted OR, 1.20; 95% CI, 1.00-1.44 for CG/CC vs GG). The Grs2274223Crs11187870 haplotype increased the risk for ESCC by 1.22-fold (95% CI, 1.04-1.42). Further experiments showed that overall PLCE1 mRNA expression was lower in tumor than in paired normal tissues (0.067±0.016 vs 0.264±0.067, P<.05), and the IHC analysis showed the normal tissues of rs2274223 GG genotype had a lower PLCE1 staining score than that of the AG genotype (0.40±0.22 vs 1.33±0.32, P<.05).

CONCLUSIONS

PLCE1 SNP rs2274223 A>G change may reduce gene expression, and the variant G genotypes might contribute to risk of ESCC.

Genetic variation in PLCE1 is associated with gastric cancer survival in a Chinese population

BACKGROUND

Two genome-wide association studies on gastric cancer showed a previously unknown gastric cancer susceptible locus in PLCE1 at 10q23. We hypothesized that the single nucleotide polymorphism (SNP) rs2274223 A/G is associated with the survival rate of gastric cancer.

METHODS

We genotyped the above SNP in 940 gastric cancer patients to investigate the association between the polymorphism and gastric cancer survival by the TaqMan method.

RESULTS

We found that patients carrying PLCE1 rs2274223 AA genotype survived for a significantly shorter time than those carrying the AG and GG genotypes (log-rank P = 0.046). This significance was enhanced in the dominant model (AA vs. AG/GG, log-rank P = 0.014). Multivariate Cox regression analyses showed that the AG/GG genotypes were associated with a significantly decreased risk of death from gastric cancer [adjusted hazard ratio (HR) = 0.79, 95% confidence interval (CI) = 0.65-0.95]. Most of stratification analysis did not find an enhanced association between the same genotype and prognosis, except for patients with TNM stage III disease (HR = 0.63, 95% CI = 0.48-0.83).

CONCLUSION

Our findings showed that the PLCE1 SNP rs2274223 was associated with significantly improved gastric cancer survival in a Chinese population. Further functional studies are needed to validate our results.

Effects of progesterone treatment on expression of genes involved in uterine quiescence

An important action of progesterone during pregnancy is to maintain the uterus in a quiescent state and thereby prevent preterm labor. The causes of preterm labor are not well understood, so progesterone action on the myometrium can provide clues about the processes that keep the uterus from contracting prematurely. Accordingly, we have carried out Affymetrix GeneChip analysis of progesterone effects on gene expression in immortalized human myometrial cells cultured from a patient near the end of pregnancy. Progesterone appears to inhibit uterine excitability by a number of mechanisms, including increased expression of calcium and voltage-operated K(+) channels, which dampens the electrical activity of the myometrial cell, downregulation of agents, and receptors involved in myometrial contraction, reduction in cell signal components that lead to increased intracellular Ca(2+) concentrations in response to contractile stimuli, and downregulation of proteins involved in the cross-linking of actin and myosin filaments to produce uterine contractions.

Pathogenesis and therapy of focal segmental glomerulosclerosis: an update

Focal and segmental glomerulosclerosis (FSGS) is an important cause of steroid-resistant nephrotic syndrome in adults and children. It is responsible for 5-20% of all cases of end-stage kidney disease (ESKD) in the United States. The pathogenesis of FSGS has not been fully elucidated; however, data from molecular studies of familial cases in the last two decades suggest that FSGS is a defect of the podocyte. The therapeutic agents available for treatment of FSGS are not very effective and only a small percentage of affected individuals will achieve complete remission. Recent data from molecular biology and molecular genetics has provided insight into the mechanisms of action of old agents and also identification of other novel therapeutic targets. This review focuses on recent advances in the molecular pathogenesis of FSGS and currently available therapeutic agents as well as potential novel therapies.

Inhibition of MLC phosphorylation restricts replication of influenza virus--a mechanism of action for anti-influenza agents

Influenza A viruses are a severe threat worldwide, causing large epidemics that kill thousands every year. Prevention of influenza infection is complicated by continuous viral antigenic changes. Newer anti-influenza agents include MEK/ERK and protein kinase C inhibitors; however, the downstream effectors of these pathways have not been determined. In this study, we identified a common mechanism for the inhibitory effects of a significant group of anti-influenza agents. Our studies showed that influenza infection activates a series of signaling pathways that converge to induce myosin light chain (MLC) phosphorylation and remodeling of the actin cytoskeleton. Inhibiting MLC phosphorylation by blocking RhoA/Rho kinase, phospholipase C/protein kinase C, and HRas/Raf/MEK/ERK pathways with the use of genetic or chemical manipulation leads to the inhibition of influenza proliferation. In contrast, the induction of MLC phosphorylation enhances influenza proliferation, as does activation of the HRas/Raf/MEK/ERK signaling pathway. This effect is attenuated by inhibiting MLC phosphorylation. Additionally, in intracellular trafficking studies, we found that the nuclear export of influenza ribonucleoprotein depends on MLC phosphorylation. Our studies provide evidence that modulation of MLC phosphorylation is an underlying mechanism for the inhibitory effects of many anti-influenza compounds.

Association between novel PLCE1 variants identified in published esophageal cancer genome-wide association studies and risk of squamous cell carcinoma of the head and neck

BACKGROUND

Phospholipase C epsilon 1 (PLCE1) (an effector of Ras) belonging to the phospholipase family plays crucial roles in carcinogenesis and progression of several cancers, including squamous cell carcinoma of the head and neck (SCCHN). A single nucleotide polymorphism (SNP, rs2274223) in PLCE1 has been identified as a novel susceptibility locus in genome-wide association studies (GWAS) of esophageal squamous cell carcinoma (ESCC) and gastric cardia adenocarcinoma (GCA) that share similar risk factors with SCCHN. Therefore, we investigated the association between potentially functional SNPs in PLCE1 and susceptibility to SCCHN.

METHODS

We genotyped three potentially functional SNPs (rs2274223A/G, rs3203713A/G and rs11599672T/G) of PLCE1 in 1,098 SCCHN patients and 1,090 controls matched by age and sex in a non-Hispanic white population.

RESULTS

Although none of three SNPs was alone significantly associated with overall risk of SCCHN, their combined effects of risk alleles (rs2274223G, rs3203713G and rs11599672G) were found to be associated with risk of SCCHN in a locus-dose effect manner (Ptrend=0.046), particularly for non-oropharyngeal tumors (Ptrend=0.017); specifically, rs2274223 was associated with a significantly increased risk (AG vs. AA: adjusted OR=1.29, 95% CI=1.01-1.64; AG/GG vs. AA: adjusted OR=1.30, 95% CI=1.03-1.64), while rs11599672 was associated with a significantly decreased risk (GG vs. TT: adjusted OR=0.54, 95% CI=0.34-0.86; TG/GG vs. TT: adjusted OR=0.76, 95% CI=0.61-0.95).

CONCLUSIONS

Our findings suggest that PLCE1 variants may have an effect on risk of SCCHN associated with tobacco and alcohol exposure, particularly for those tumors arising at non-oropharyngeal sites. These findings, although need to be validated by larger studies, are consistent with those in esophageal and gastric cancers.

Novel mutations in steroid-resistant nephrotic syndrome diagnosed in Tunisian children

Steroid-resistant nephrotic syndrome (NS) remains one of the most intractable causes of end-stage renal disease in the first two decades of life. Several genes have been involved including NPHS1, NPHS2, WT1, PLCE1, and LAMB2. Our aim was to identify causative mutations in these genes, in 24 children belonging to 13 families with NS manifesting with various ages of onset. We performed haplotype analysis and direct exon sequencing of NPHS1, NPHS2, PLCE1, LAMB2, and the relevant exons 8 and 9 of WT1. Ten different pathogenic mutations were detected in seven families concerning four genes (NPHS1 (3/7), LAMB2 (2/7), NPHS2 (1/7), and WT1 (1/7)). Five of the detected mutations were novel; IVS9+2 T>C and p.D616G in NPHS1; p.E371fsX16 in NPHS2, and p.E705X and p.D1151fsX23 in LAMB2. Nine of 24 patients failed to be categorized by mutational analysis. Our study extends the spectrum of abnormalities underlying NS, by reporting novel mutations in the NPHS1 and NPHS2 genes and the first cases of LAMB2 mutations in Tunisia. Congenital and infantile NS can be explained by mutations in NPHS1, NPHS2, WT1, or LAMB2 genes. The identification of additional genes mutated in NS can be anticipated.

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.

Hereditary kidney diseases: highlighting the importance of classical Mendelian phenotypes

A Mendelian inheritance underlies a nonnegligible proportion of hereditary kidney diseases, suggesting that the encoded proteins are essential for maintenance of the renal function. The identification of genes involved in congenital anomalies of the kidney and in familial forms of nephrotic syndrome significantly increased our understanding of the renal development and kidney filtration barrier physiology. This review will focus on the classical phenotype and clinical heterogeneity observed in the monogenic forms of these disorders. In addition, the role of susceptibility genes in kidney diseases with a complex inheritance will also be discussed.

Hereditary nephrotic syndrome: a systematic approach for genetic testing and a review of associated podocyte gene mutations

Several genes have been implicated in genetic forms of nephrotic syndrome occurring in children. It is now known that the phenotypes associated with mutations in these genes display significant variability, rendering genetic testing and counselling a more complex task. This review will focus on the recent clinical findings associated with those genes known to be involved in isolated steroid-resistant nephrotic syndrome in children and, thereby, propose an approach for appropriate mutational screening. The recurrence of proteinuria after transplantation in patients with hereditary forms of nephrotic syndrome will also be discussed.

RNA interference suppressing PLCE1 gene expression decreases invasive power of human bladder cancer T24 cell line

Mutational activation of the ras proto-oncogenes is frequently found in cancers. The phospholipase C epsilon gene (PLCE1) encodes a novel ras-related protein (R-Ras) effector mediating the effects of R-Ras on the actin cytoskeleton and membrane protrusion, because R-Ras is coprecipitated with the PLCE1 protein and can increase its activity. The nature of downstream signaling pathways from Ras involved in bladder cancer remains poorly understood. We aimed to construct a small hairpin RNA (shRNA) expression plasmid against the PLCE1 gene and to observe the inhibition of human bladder carcinoma cell T24 migration by RNA interference suppressing the expression of PLCE1. Two PLCE1 plasmids (P1 and P2) were constructed and inserted into T24 cells. Reverse transcriptase-polymerase chain reaction and Western blot analyses were performed to investigate inhibition of PLCE1 expression after plasmid transfection. Invasive power of the T24 cell line was measured before and after transfection by a membrane invasion culture system (transwell chamber), gelatin enzymography, and immunocytochemistry of cells. The RT-PCR analysis of BCL2 mRNA levels among different groups of T24 cell line indicated that expression of BCL2 mRNA was lower in the two positive plasmid-transfected cell groups than in the blank control or HK-A groups. Silencing of PLCE1 might downregulate the level of MMP and BCL2 gene expression, decreasing the invasive power of bladder cancer T24 cells and thus inhibiting tumor development.

Revisited and revised: is RhoA always a villain in cardiac pathophysiology?

The neonatal rat ventricular myocyte model of hypertrophy has provided tremendous insight with regard to signaling pathways regulating cardiac growth and gene expression. Many mediators thus discovered have been successfully extrapolated to the in vivo setting, as assessed using genetically engineered mice and physiological interventions. Studies in neonatal rat ventricular myocytes demonstrated a role for the small G-protein RhoA and its downstream effector kinase, Rho-associated coiled-coil containing protein kinase (ROCK), in agonist-mediated hypertrophy. Transgenic expression of RhoA in the heart does not phenocopy this response, however, nor does genetic deletion of ROCK prevent hypertrophy. Pharmacologic inhibition of ROCK has effects most consistent with roles for RhoA signaling in the development of heart failure or responses to ischemic damage. Whether signals elicited downstream of RhoA promote cell death or survival and are deleterious or salutary is, however, context and cell-type dependent. The concepts discussed above are reviewed, and the hypothesis that RhoA might protect cardiomyocytes from ischemia and other insults is presented. Novel RhoA targets including phospholipid regulated and regulating enzymes (Akt, PI kinases, phospholipase C, protein kinases C and D) and serum response element-mediated transcriptional responses are considered as possible pathways through which RhoA could affect cardiomyocyte survival.

Clostridium difficile toxin B differentially affects GPCR-stimulated Ca2+ responses in macrophages: independent roles for Rho and PLA2

Clostridium difficile toxins cause acute colitis by disrupting the enterocyte barrier and promoting inflammation. ToxB from C. difficile inactivates Rho family GTPases and causes release of cytokines and eicosanoids by macrophages. We studied the effects of ToxB on GPCR signaling in murine RAW264.7 macrophages and found that ToxB elevated Ca(2+) responses to Galphai-linked receptors, including the C5aR, but reduced responses to Galphaq-linked receptors, including the UDP receptors. Other Rho inhibitors also reduced UDP Ca(2+) responses, but they did not affect C5a responses, suggesting that ToxB inhibited UDP responses by inhibiting Rho but enhanced C5a responses by other mechanisms. By using PLCbeta isoform-deficient BMDM, we found that ToxB inhibited Ca(2+) signaling through PLCbeta4 but enhanced signaling through PLCbeta3. Effects of ToxB on GPCR Ca(2+) responses correlated with GPCR use of PLCbeta3 versus PLCbeta4. ToxB inhibited UDP Ca(2+) signaling without reducing InsP3 production or the sensitivity of cellular Ca(2+) stores to exogenous InsP3, suggesting that ToxB impairs UDP signaling at the level of InsP3/Ca(2+)coupling. In contrast, ToxB elevated InsP3 production by C5a, and the enhancement of Ca(2+) signaling by C5a was prevented by inhibition of PLA(2) or 5-LOX but not COX, implicating LTs but not prostanoids in the mechanism. In sum, ToxB has opposing, independently regulated effects on Ca(2+) signaling by different GPCR-linked PLCbeta isoforms in macrophages.

Phospholipase C as a potential target for cardioprotection during oxidative stressThis review is one of a selection of papers published in a Special Issue on Oxidative Stress in Health and Disease

Cardiac dysfunction due to ischemia–reperfusion (I/R) is associated with marked changes in membrane function and subsequent Ca2+-handling abnormalities in cardiomyocytes. The membrane abnormalities in hearts subjected to I/R arise primarily from oxidative stress as a consequence of increased formation of reactive oxygen species and other oxidants, as well as reduced antioxidant defenses. Little is known, however, about the nature and mechanisms of the sarcolemmal membrane changes with respect to phospholipase C (PLC)-related signaling events. In addition, the mechanisms involved in protection of the postischemic myocardium and in ischemic preconditioning with respect to PLC function need to be established. Accordingly, this article reviews the historical and current information on PLC-mediated signal transduction mechanisms in I/R, as well as outlining future directions that should be addressed. Such information will extend our knowledge of ischemic heart disease and help improve its therapy.

Genetics of nephrotic syndrome: connecting molecular genetics to podocyte physiology

Urinary losses of macromolecules in nephrotic syndrome (NS) reflect a dysfunction of the highly permselective glomerular filtration barrier. Genetic studies of hereditary forms of NS have led to the identification of proteins playing a crucial role in slit-diaphragm signalling, regulation of actin cytoskeleton dynamics, maintenance of podocyte integrity and cell-matrix interactions. This review will focus on recent molecular and clinical findings in the field of genetics of NS, thereby providing a better understanding of the complex glomerular filtration barrier physiology.

Roles of Phospholipase C Isozymes in Organogenesis and Embryonic Development

Phosphoinositide metabolism is an important intracellular signaling system that regulates a variety of cellular functions. Phospholipase C (PLC) is a key enzyme in this system. Recent studies on genetically manipulated mice have clarified the functions of PLC in vivo. This review focuses on the roles of PLC in organogenesis and embryonic development.

Genetics of nephrotic syndrome: new insights into molecules acting at the glomerular filtration barrier

Nephrotic syndrome is caused by increased permeability of the glomerular filtration barrier for macromolecules. The identification of mutations of various podocyte-expressed proteins as causes of familial nephrotic syndrome has significantly contributed to shedding light into the molecular pathogenesis of nephrotic proteinuria and into the physiology of the glomerular sieve. More recent findings have changed our conception of the glomerular filtration barrier from a relatively static structure to a highly dynamic one. Both the multiprotein slit diaphragm complex around nephrin and the integrin receptor complex that mediates binding of the podocyte to the glomerular basement membrane, may translate outside-inside signaling and lead to podocyte actin cytoskeleton rearrangement. This may enable the podocyte network to adapt to environmental changes and respond to injury. Disturbance in these processes may not only be involved in the pathogenesis of hereditary nephrotic syndrome but also in that of more common acquired proteinuric diseases. Elucidation of the molecular mechanisms involved will possibly open the way to new therapeutic approaches.

Molecular cloning and expression of phospholipase C epsilon 1 in zebrafish

Phospholipase C (PLC) is a key enzyme that generates inositol 1,4,5-triphosphate (IP(3)) and diacylglycerol (DAG), two second messengers in signal transduction. Phospholipase Cepsilon (PLCE1) is a unique member of the PLC family in that it carries both RasGEF and Ras-associating (RA) domains and may serve as an activator and an effector of small GTPases. Recently, mutations in PLCE1 have been associated with early-onset nephrotic syndrome. We have identified the zebrafish ortholog of PLCE1 and characterized its expression pattern in zebrafish embryos by in situ hybridization. Zebrafish plce1 gene encodes a protein of 2248 amino acids that shares 56% identity with mammalian PLCepsilon. During zebrafish embryonic development, plce1 is expressed in a dynamic pattern in a variety of organs, such as brain, muscle, liver, and pronephric glomeruli. Our results suggest that zebrafish may be used as a model organism to address the function of PLCepsilon during the development of these organs.

Exclusion of homozygous PLCE1 (NPHS3) mutations in 69 families with idiopathic and hereditary FSGS

Focal and segmental glomerulosclerosis (FSGS) is the most common glomerular cause of end-stage kidney disease (ESKD). Although the etiology of FSGS has not been fully elucidated, recent results from the positional cloning of genes mutated in nephrotic syndromes are now beginning to provide insight into the pathogenesis of these diseases. Mutations in PLCE1/NPHS3 have recently been reported as a cause of nephrotic syndrome characterized by diffuse mesangial sclerosis (DMS) histology. One single family with a missense mutation had late onset of the disease that was characterized by FSGS. To further define the role of PLCE1 mutations in the etiology of FSGS, we performed mutational analysis in 69 families with FSGS. A total of 69 families with 231 affected individuals were examined. The median age of disease onset was 26 years (range 1-66 years). Onset of ESKD was at a median age of 35.5 years. Seven variants leading to non-synonymous changes were found, of which only two are new variants (exon 4 c.1682 G>A R561Q, exon 31 c.6518A>G K2173R). No known disease-causing mutations were identified in the families screened. PLCE1/NPHS3 mutations are not a cause of FSGS in this cohort. The absence of mutations in PLCE1/NPHS3 in this study indicates that there are additional genetic causes of FSGS and that hereditary FSGS is a heterogeneous disease. Kindreds appropriate for genome-wide screening are currently being subjected to analysis with the aim of identifying other genetic causes of FSGS.

Application of an Epac activator enhances neurotransmitter release at excitatory central synapses

cAMP regulates secretory processes through both PKA-independent and PKA-dependent signaling pathways. Their relative contributions to fast neurotransmission are unclear at present, although forskolin, which is generally believed to enhance intracellular cAMP levels by stimulation of adenylyl cyclase activity, was shown to increase vesicular release probability (p) and the number of releasable vesicles (N) in various neuronal preparations. Using low-frequency (0.2 Hz) electrophysiological recordings in the presence of the Epac-selective cAMP analog 8-pCPT-2'-O-Me-cAMP (ESCA(1)), we find that Epac activation by this analog accounts on average for 38% of the forskolin-induced increase in evoked EPSC amplitudes and for 100% of the forskolin-induced increase in miniature EPSC (mEPSC) frequency in dissociated autaptic neuronal cultures from mouse hippocampus. From paired-pulse facilitation experiments, and considering the enhancement of mEPSC frequency, we conclude that ESCA(1)-induced Epac activity is presynaptic in origin and increases p. In addition, preapplication of ESCA(1) augmented a subsequent enhancement of evoked EPSC amplitudes by phorbol ester (PDBu). This effect was maximal when ESCA(1) application preceded the PDBu application by 3 min. Because the PDBu response was abolished after downregulation of intracellular PKC activity, we conclude that ESCA(1)-induced Epac activation leads to presynaptic changes involving Epac-to-PKC signaling.

Phospholipid-mediated signaling and heart disease

Cardiac hypertrophy, congestive heart failure, diabetic cardiomyopathy and myocardial ischemia-reperfusion injury are associated with a disturbance in cardiac sarcolemmal membrane phospholipid homeostasis. The contribution of the different phospholipases and their related signaling mechanisms to altered function of the diseased myocardium is not completely understood. Resolution of this issue is essential for both the understanding of the pathophysiology of heart disease and for determining if components of the phospholipid signaling pathways could serve as appropriate therapeutic targets. This review provides an outline of the role of phospholipase A2, C and D and subsequent signal transduction mechanisms in different cardiac pathologies with a discussion of their potential as targets for drug development for the prevention/treatment of heart disease.

Modulation of enzymatic activities by n-3 polyunsaturated fatty acids to support cardiovascular health

Epidemiological evidence from Greenland Eskimos and Japanese fishing villages suggests that eating fish oil and marine animals can prevent coronary heart disease. Dietary studies from various laboratories have similarly indicated that regular fish oil intake affects several humoral and cellular factors involved in atherogenesis and may prevent atherosclerosis, arrhythmia, thrombosis, cardiac hypertrophy and sudden cardiac death. The beneficial effects of fish oil are attributed to their n-3 polyunsaturated fatty acid (PUFA; also known as omega-3 fatty acids) content, particularly eicosapentaenoic acid (EPA; 20:5, n-3) and docosahexaenoic acid (DHA; 22:6, n-3). Dietary supplementation of DHA and EPA influences the fatty acid composition of plasma phospholipids that, in turn, may affect cardiac cell functions in vivo. Recent studies have demonstrated that long-chain omega-3 fatty acids may exert beneficial effects by affecting a wide variety of cellular signaling mechanisms. Pathways involved in calcium homeostasis in the heart may be of particular importance. L-type calcium channels, the Na+-Ca2+ exchanger and mobilization of calcium from intracellular stores are the most obvious key signaling pathways affecting the cardiovascular system; however, recent studies now suggest that other signaling pathways involving activation of phospholipases, synthesis of eicosanoids, regulation of receptor-associated enzymes and protein kinases also play very important roles in mediating n-3 PUFA effects on cardiovascular health. This review is therefore focused on the molecular targets and signaling pathways that are regulated by n-3 PUFAs in relation to their cardioprotective effects.

Identification of BRAF as a new interactor of PLCε1, the protein mutated in nephrotic syndrome type 3

Steroid-resistant nephrotic syndrome is a malfunction of the kidney glomerular filter that leads to proteinuria, hypoalbuminemia, edema, and renal failure. Recently, we identified recessive mutations in the phospholipase C epsilon 1 gene ( PLCE1) as a new cause of early-onset nephrotic syndrome and demonstrated interaction of PLCε1 with IQGAP1. To further elucidate the mechanism by which PLCE1 mutations cause nephrotic syndrome, we sought to identify new protein interaction partners of PLCε1. We utilized information from the genetic interaction network of C. elegans. It relates the PLCE1 ortholog ( plc-1) to the C. elegans ortholog ( lin-45) of human BRAF ( v-raf murine sarcoma viral oncogene homolog B1). We hypothesized that this may indicate a functional protein-protein interaction. Using GST pull down of HEK293T cell lysates in vitro and coimmunoprecipation of mouse kidney lysates in vivo, we show that BRAF interacts with PLCε1. By immunohistochemistry in rat kidney, we demonstrate that both proteins are coexpressed and colocalize in developing and mature glomerular podocytes, reporting for the first time the expression of BRAF in the glomerular podocyte.

Phospholipase Cepsilon is a nexus for Rho and Rap-mediated G protein-coupled receptor-induced astrocyte proliferation

Phospholipase Cepsilon (PLCepsilon) has been suggested to transduce signals from small GTPases, but its biological function has not yet been clarified. Using astrocytes from PLCepsilon-deficient mice, we demonstrate that endogenous G protein-coupled receptors (GPCRs) for lysophosphatidic acid, sphingosine 1-phosphate, and thrombin regulate phosphoinositide hydrolysis primarily through PLCepsilon. Stimulation by lysophospholipids occurs through G(i), whereas thrombin activates PLC through Rho. Further studies reveal that PLCepsilon is required for thrombin- but not LPA-induced sustained ERK activation and DNA synthesis, providing a novel mechanism for GPCR and Rho signaling to cell proliferation. The requirement for PLCepsilon in this pathway can be explained by its role as a guanine nucleotide exchange factor for Rap1. Thus, PLCepsilon serves to transduce mitogenic signals through a mechanism distinct from its role in generation of PLC-derived second messengers.

A highly polymorphic meiotic recombination mouse hot spot exhibits incomplete repair

The recent mapping of recombination hot spots in the human genome has demonstrated that crossover is a nonrandom process that occurs at well-defined positions along chromosomes. However, the mechanisms that direct hot-spot turnover in complex mammalian genomes are poorly understood. Analyses of the human genome are impaired by the inability to genetically dissect and molecularly manipulate recombinogenic regions to test their roles in regulating hot spots. Here, using the BXD recombinant inbred strains as a crossover library, three new recombination hot spots have been identified on mouse chromosome 19. Analyses of a highly polymorphic recombination hot spot (HS22) revealed that approximately 4% of recombinant molecules display complex and incomplete repair with discontinuous conversion tracts, as well as persistent heteroduplex DNA at crossover sites in mature spermatozoa. Also, sequence analysis of the wild house mouse revealed instability at the center of this hot spot. This suggests that complete repair is not required for completion of mammalian meiosis, a scenario that leaves duplex DNA containing mismatches at crossover sites.

Phospholipid-mediated signaling systems as novel targets for treatment of heart disease

The phospholipases associated with the cardiac sarcolemmal (SL) membrane hydrolyze specific membrane phospholipids to generate important lipid signaling molecules, which are known to influence normal cardiac function. However, impairment of the phospholipases and their related signaling events may be contributory factors in altering cardiac function of the diseased myocardium. The identification of the changes in such signaling systems as well as understanding the contribution of phospholipid-signaling pathways to the pathophysiology of heart disease are rapidly emerging areas of research in this field. In this paper, I provide an overview of the role of phospholipid-mediated signal transduction processes in cardiac hypertrophy and congestive heart failure, diabetic cardiomyopathy, as well as in ischemia-reperfusion. From the cumulative evidence presented, it is suggested that phospholipid-mediated signal transduction processes could serve as novel targets for the treatment of the different types of heart disease.

Phospholipase C-β2 promotes mitosis and migration of human breast cancer-derived cells

Like most human neoplasm, breast cancer has aberrations in signal transduction elements that can lead to increased proliferative potential, apoptosis inhibition, tissue invasion and metastasis. Due to the high heterogeneity of this tumor, currently, no markers are clearly associated with the insurgence of breast cancer, as well as with its progression from in situ lesion to invasive carcinoma. We have recently demonstrated an altered expression of the beta2 isoform of the phosphoinositide-dependent phospholipase C (PLC) in invasive breast tumors with different histopathological features. In primary breast tumor cells, elevated amounts of this protein are closely correlated with a poor prognosis of patients with mammary carcinoma, suggesting that PLC-beta2 may be involved in the development and worsening of the malignant phenotype. Here we demonstrate that PLC-beta2 may improve some malignant characteristics of tumor cells, like motility and invasion capability, but it fails to induce tumorigenesis in non-transformed breast-derived cells. We also report that, compared with the G(0)/G(1) phases of the cell cycle, the cells in S/G(2)/M phases show high PLC-beta2 expressions that reach the greatest levels during the late mitotic stages. In addition, even if unable to modify the proliferation rate and the expression of cell cycle-related enzymes of malignant cells, PLC-beta2 may promote the G(2)/M progression, a critical event in cancer evolution. Since phosphoinositides, substrates of PLC, are involved in regulating cytoskeleton architecture, PLC-beta2 in breast tumor cells may mediate the modification of cell shape that characterizes cell division, motility and invasion. On the basis of these data, PLC-beta2 may constitute a molecular marker of breast tumor cells able to monitor the progression to invasive cancers and a target for novel therapeutic breast cancer strategies.

Phospholipase Cbeta 3 mediates the scratching response activated by the histamine H1 receptor on C-fiber nociceptive neurons

Phospholipase Cbeta (PLCbeta) isozymes represent a family of molecules that link G protein-coupled receptors (GPCRs) to an intracellular signaling network. Here, we investigated the function of PLCbeta isozymes in sensory neurons by using mutant mice deficient for specific PLCbeta family members. Expression analysis indicated that PLCbeta3, one of the four isoforms, is predominantly expressed in a subpopulation of C-fiber nociceptors. A subset of these neurons expressed the histamine H1 receptor. Ca(2+) imaging studies revealed that PLCbeta3 specifically mediates histamine-induced calcium responses through the histamine H1 receptor in cultured sensory neurons. In line with this, we found that PLCbeta3(-/-) mice showed significant defects in scratching behavior induced by histamine; histamine-trifluoromethyl-toluidine (HTMT), a selective H1 agonist; and compound 48/80, a mast cell activator. These results demonstrate that PLCbeta3 is required to mediate "itch" sensation in response to histamine acting on the histamine H1 receptor in C-fiber nociceptive neurons.

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.

Positional cloning uncovers mutations in PLCE1 responsible for a nephrotic syndrome variant that may be reversible

Nephrotic syndrome, a malfunction of the kidney glomerular filter, leads to proteinuria, edema and, in steroid-resistant nephrotic syndrome, end-stage kidney disease. Using positional cloning, we identified mutations in the phospholipase C epsilon gene (PLCE1) as causing early-onset nephrotic syndrome with end-stage kidney disease. Kidney histology of affected individuals showed diffuse mesangial sclerosis (DMS). Using immunofluorescence, we found PLCepsilon1 expression in developing and mature glomerular podocytes and showed that DMS represents an arrest of normal glomerular development. We identified IQ motif-containing GTPase-activating protein 1 as a new interaction partner of PLCepsilon1. Two siblings with a missense mutation in an exon encoding the PLCepsilon1 catalytic domain showed histology characteristic of focal segmental glomerulosclerosis. Notably, two other affected individuals responded to therapy, making this the first report of a molecular cause of nephrotic syndrome that may resolve after therapy. These findings, together with the zebrafish model of human nephrotic syndrome generated by plce1 knockdown, open new inroads into pathophysiology and treatment mechanisms of nephrotic syndrome.

Structural and mechanistic insights into ras association domains of phospholipase C epsilon

Ras proteins signal to a number of distinct pathways by interacting with diverse effectors. Studies of ras/effector interactions have focused on three classes, Raf kinases, ral guanylnucleotide-exchange factors, and phosphatidylinositol-3-kinases. Here we describe ras interactions with another effector, the recently identified phospholipase C epsilon (PLCepsilon). We solved structures of PLCepsilon RA domains (RA1 and RA2) by NMR and the structure of the RA2/ras complex by X-ray crystallography. Although the similarity between ubiquitin-like folds of RA1 and RA2 proves that they are homologs, only RA2 can bind ras. Some of the features of the RA2/ras interface are unique to PLCepsilon, while the ability to make contacts with both switch I and II regions of ras is shared only with phosphatidylinositol-3-kinase. Studies of PLCepsilon regulation suggest that, in a cellular context, the RA2 domain, in a mode specific to PLCepsilon, has a role in membrane targeting with further regulatory impact on PLC activity.

Isozyme-specific stimulation of phospholipase C-gamma2 by Rac GTPases

The regulation of the two isoforms of phospholipase C-gamma, PLCgamma(1) and PLCgamma(2), by cell surface receptors involves protein tyrosine phosphorylation as well as interaction with adapter proteins and phosphatidylinositol 3,4,5-trisphosphate (PtdInsP(3)) generated by inositol phospholipid 3-kinases (PI3Ks). All three processes may lead to recruitment of the PLCgamma isozymes to the plasma membrane and/or stimulation of their catalytic activity. Recent evidence suggests that PLCgamma may also be regulated by Rho GTPases. In this study, PLCgamma(1) and PLCgamma(2) were reconstituted in intact cells and in a cell-free system with Rho GTPases to examine their influence on PLCgamma activity. PLCgamma(2), but not PLCgamma(1), was markedly activated in intact cells by constitutively active Rac1(G12V), Rac2(G12V), and Rac3(G12V) but not by Cdc42(G12V) and RhoA(G14V). The mechanism of PLCgamma(2) activation was apparently independent of phosphorylation of tyrosine residues known to be modified by PLCgamma(2)-activating protein-tyrosine kinases. Activation of PLCgamma(2) by Rac2(G12V) in intact cells coincided with a translocation of PLCgamma(2) from the soluble to the particulate fraction. PLCgamma isozyme-specific activation of PLCgamma(2) by Rac GTPases (Rac1 approximately Rac2 > Rac3), but not by Cdc42 or RhoA, was also observed in a cell-free system. Herein, activation of wild-type Rac GTPases with guanosine 5'-(3-O-thio)triphosphate caused a marked stimulation of PLCgamma(2) but had no effect on the activity of PLCgamma(1). PLCgamma(1) and PLCgamma(2) have previously been shown to be indiscriminately activated by PtdInsP(3) in vitro. Thus, the results suggest a novel mechanism of PLCgamma(2) activation by Rac GTPases involving neither protein tyrosine phosphorylation nor PI3K-mediated generation of PtdInsP(3).

New insights into the families of PLC enzymes: looking back and going forward

A study in this issue of the Biochemical Journal by Harden and colleagues, in association with one published in the Biochemical Journal very recently [Hwang, Oh, Shin, Kim, Ryu and Suh (2005) Biochem. J. 389, 181-186], have defined a new member of the superfamily of PLC (phosphoinositide-specific phospholipase C) enzymes, PLCeta. Two isoforms, PLCeta1 and PLCeta2, and their splice variants add to the molecular diversity of PLC enzymes. The studies of PLCeta regulation suggest that at least some splice variants of PLCeta2 could be regulated by the G-protein subunits Gbetagamma. As two other families, PLCbeta and PLC, are also regulated through heterotrimeric G-proteins, this finding reveals further complexity and possible interplay between different PLC families and their regulatory networks. At this point, when it is likely that the PLCeta family completes the effort of identifying new members of this related group of PLC enzymes, I also discuss some more general concepts of PLC regulation and catalysis, and challenges awaiting their further studies.

Signaling interplay in Ras superfamily function

Ras proteins function as signaling hubs that are activated by convergent signaling pathways initiated by extracellular stimuli. Activated Ras in turn regulates a diversity of downstream cytoplasmic signaling cascades. Ras proteins are founding members of a large superfamily of small GTPases that have significant sequence and biochemical similarities. Recent observations have established a complex signaling interplay between Ras and other members of the family. A key biochemical mechanism facilitating this crosstalk involves guanine nucleotide exchange factors (GEFs), which serve as regulators and effectors, as well as signaling integrators, of Ras signaling.