Identification of PLC210, a Caenorhabditis elegans phospholipase C, as a putative effector of Ras

Untangling the role of RhoA in the heart: protective effect and mechanism

RhoA (ras homolog family member A) is a small G-protein that transduces intracellular signaling to regulate a broad range of cellular functions such as cell growth, proliferation, migration, and survival. RhoA serves as a proximal downstream effector of numerous G protein-coupled receptors (GPCRs) and is also responsive to various stresses in the heart. Upon its activation, RhoA engages multiple downstream signaling pathways. Rho-associated coiled-coil-containing protein kinase (ROCK) is the first discovered and best characterized effector or RhoA, playing a major role in cytoskeletal arrangement. Many other RhoA effectors have been identified, including myocardin-related transcription factor A (MRTF-A), Yes-associated Protein (YAP) and phospholipase Cε (PLCε) to regulate transcriptional and post-transcriptional processes. The role of RhoA signaling in the heart has been increasingly studied in last decades. It was initially suggested that RhoA signaling pathway is maladaptive in the heart, but more recent studies using cardiac-specific expression or deletion of RhoA have revealed that RhoA activation provides cardioprotection against stress through various mechanisms including the novel role of RhoA in mitochondrial quality control. This review summarizes recent advances in understanding the role of RhoA in the heart and its signaling pathways to prevent progression of heart disease.

Functional and structural insights into RAS effector proteins

RAS proteins are conserved guanosine triphosphate (GTP) hydrolases (GTPases) that act as molecular binary switches and play vital roles in numerous cellular processes. Upon GTP binding, RAS GTPases adopt an active conformation and interact with specific proteins termed RAS effectors that contain a conserved ubiquitin-like domain, thereby facilitating downstream signaling. Over 50 effector proteins have been identified in the human proteome, and many have been studied as potential mediators of RAS-dependent signaling pathways. Biochemical and structural analyses have provided mechanistic insights into these effectors, and studies using model organisms have complemented our understanding of their role in physiology and disease. Yet, many critical aspects regarding the dynamics and biological function of RAS-effector complexes remain to be elucidated. In this review, we discuss the mechanisms and functions of known RAS effector proteins, provide structural perspectives on RAS-effector interactions, evaluate their significance in RAS-mediated signaling, and explore their potential as therapeutic targets.

MicroRNA-34 and gastrointestinal cancers: a player with big functions

It is commonly assumed that gastrointestinal cancer is the most common form of cancer across the globe and is the leading contributor to cancer-related death. The intricate mechanisms underlying the growth of GI cancers have been identified. It is worth mentioning that both non-coding RNAs (ncRNAs) and certain types of RNA, such as circular RNAs (circRNAs), long non-coding RNAs (lncRNAs), and microRNAs (miRNAs), can have considerable impact on the development of gastrointestinal (GI) cancers. As a tumour suppressor, in the group of short non-coding regulatory RNAs is miR-34a. miR-34a silences multiple proto-oncogenes at the post-transcriptional stage by targeting them, which inhibits all physiologically relevant cell proliferation pathways. However, it has been discovered that deregulation of miR-34a plays important roles in the growth of tumors and the development of cancer, including invasion, metastasis, and the tumor-associated epithelial-mesenchymal transition (EMT). Further understanding of miR-34a's molecular pathways in cancer is also necessary for the development of precise diagnoses and effective treatments. We outlined the most recent research on miR-34a functions in GI cancers in this review. Additionally, we emphasize the significance of exosomal miR-34 in gastrointestinal cancers.

Defining bone fide effectors of RAS GTPases

RAS GTPases play essential roles in normal development and are direct drivers of human cancers. Three decades of study have failed to wholly characterize pathways stimulated by activated RAS, driven by engagement with 'effector' proteins that have RAS binding domains (RBDs). Bone fide effectors must bind directly to RAS GTPases in a nucleotide-dependent manner, and this interaction must impart a clear change in effector activity. Despite this, for most proteins currently deemed effectors there is little mechanistic understanding of how binding to the GTPase alters protein function. There has also been limited effort to comprehensively resolve the specificity of effector binding to the full array of RAS superfamily GTPase proteins. This review will summarize what is known about RAS-driven activation for an array of potential effector proteins, focusing on structural and mechanistic effects and highlighting how little is still known regarding this key paradigm of cellular signal transduction.

Targeting small GTPases: emerging grasps on previously untamable targets, pioneered by KRAS

Small GTPases including Ras, Rho, Rab, Arf, and Ran are omnipresent molecular switches in regulating key cellular functions. Their dysregulation is a therapeutic target for tumors, neurodegeneration, cardiomyopathies, and infection. However, small GTPases have been historically recognized as "undruggable". Targeting KRAS, one of the most frequently mutated oncogenes, has only come into reality in the last decade due to the development of breakthrough strategies such as fragment-based screening, covalent ligands, macromolecule inhibitors, and PROTACs. Two KRAS^G12C covalent inhibitors have obtained accelerated approval for treating KRAS^G12C mutant lung cancer, and allele-specific hotspot mutations on G12D/S/R have been demonstrated as viable targets. New methods of targeting KRAS are quickly evolving, including transcription, immunogenic neoepitopes, and combinatory targeting with immunotherapy. Nevertheless, the vast majority of small GTPases and hotspot mutations remain elusive, and clinical resistance to G12C inhibitors poses new challenges. In this article, we summarize diversified biological functions, shared structural properties, and complex regulatory mechanisms of small GTPases and their relationships with human diseases. Furthermore, we review the status of drug discovery for targeting small GTPases and the most recent strategic progress focused on targeting KRAS. The discovery of new regulatory mechanisms and development of targeting approaches will together promote drug discovery for small GTPases.

PLCE1 as a diagnostic and prognostic biomarker by promoting the growth and progression of oral squamous cell carcinoma

OBJECTIVE

This study aimed to explore the role of phospholipase C epsilon1 (PLCE1) in the growth and progression of oral squamous cell carcinoma (OSCC) and determine its potential as a biomarker with respect to diagnosis, prognosis and treatment of OSCC.

METHODS

The expression level of PLCE1 in tissue specimens was detected by immunohistochemistry (182 OSCC cases and 76 controls) and its relationship to clinicopathological parameters was analyzed. Then, the diagnostic value of PLCE1 in OSCC was verified by constructing the receiver operating characteristic (ROC) curve. Kaplan-Meier and Cox analysis were performed to investigate the role of PLCE1 in predicting the prognosis of OSCC patients. Furthermore, the effects of PLCE1 on the occurrence and development of OSCC were revealed by knocking down the level of PLCE1.

RESULTS

PLCE1 was mainly located in the cytoplasm of OSCC cells, and its level in OSCC tissues was obviously higher than in adjacent normal tissues. While the expression of PLCE1 did not correlate with clinicopathological parameters of OSCC. The area under the ROC curve (AUC) of PLCE1 was 0.865 with a sensitivity of 75.8% and a specificity of 78.8%. Besides, high expression of PLCE1 suggested a worse prognosis in OSCC patients than those with low expression. The knockdown of PLCE1 obviously inhibited proliferation, migration, and invasion of OSCC cells, and induce G0 cell cycle phase arrest and apoptosis, thus preventing the progression of OSCC.

CONCLUSION

PLCE1 may cause carcinogenesis and development of OSCC, which provide a novel possibility in diagnosis, prognosis and treatment of OSCC. This article is protected by copyright. All rights reserved.

Thrombin induces morphological and inflammatory astrocytic responses via activation of PAR1 receptor

Spinal cord injury (SCI) will result in the significant elevation of thrombin production at lesion site via either breakage of blood-spinal cord barrier or upregulated expression within nerve cells. Thrombin-induced activation of the protease activated receptors (PARs) evokes various pathological effects that deteriorate the functional outcomes of the injured cord. The cellular consequences of thrombin action on the astrocytes, as well as the underlying mechanism are not fully elucidated by far. In the present study, SCI model of rats was established by contusion, and primary astrocytes were isolated for culture from newborn rats. The expression levels of thrombin and PAR1 receptor at lesion sites of the spinal cord were determined. The primary astrocytes cultured in vitro were stimulated with different concentration of thrombin, and the resultant morphological changes, inflammatory astrocytic responses, as well as PAR1-activated signal pathway of astrocytes were accordingly examined using various agonists or antagonists of the receptor. Thrombin was found to reverse astrocytic stellation, promote proliferation but inhibit migration of astrocytes. Furthermore, the serine protease was shown to facilitate inflammatory response of astrocytes through regulation of MAPKs/NFκB pathway. Our results have provided the morphological evidence of astrocytic reactivity in response to thrombin stimulation and its neuroinflammatory effects following SCI, which will be indicative for the fundamental insights of thrombin-induced neuropathology.

A novel NF-κB regulator encoded by circPLCE1 inhibits colorectal carcinoma progression by promoting RPS3 ubiquitin-dependent degradation

BACKGROUND

Constitutive activation of nuclear factor-κB (NF-κB) signaling plays a key role in the development and progression of colorectal carcinoma (CRC). However, the underlying mechanisms of excessive activation of NF-κB signaling remain largely unknown.

METHODS

We used high throughput RNA sequencing to identify differentially expressed circular RNAs (circRNAs) between normal human intestinal epithelial cell lines and CRC cell lines. The identification of protein encoded by circPLCE1 was performed using LC-MS. The function of novel protein was validated in vitro and in vivo by gain or loss of function assays. Mechanistic results were concluded by immunoprecipitation analyses.

RESULTS

A novel protein circPLCE1-411 encoded by circular RNA circPLCE1 was identified as a crucial player in the NF-κB activation of CRC. Mechanistically, circPLCE1-411 promoted the ubiquitin-dependent degradation of the critical NF-κB regulator RPS3 via directly binding the HSP90α/RPS3 complex to facilitate the dissociation of RPS3 from the complex, thereby reducing NF-κB nuclear translocation in CRC cells. Functionally, circPLCE1 inhibited tumor proliferation and metastasis in CRC cells, as well as patient-derived xenograft and orthotopic xenograft tumor models. Clinically, circPLCE1 was downregulated in CRC tissues and correlated with advanced clinical stages and poor survival.

CONCLUSIONS

circPLCE1 presents an epigenetic mechanism which disrupts NF-κB nuclear translocation and serves as a novel and promising therapeutic target and prognostic marker.

RAS GTPase signalling to alternative effector pathways

RAS GTPases are fundamental regulators of development and drivers of an extraordinary number of human cancers. RAS oncoproteins constitutively signal through downstream effector proteins, triggering cancer initiation, progression and metastasis. In the absence of targeted therapeutics to mutant RAS itself, inhibitors of downstream pathways controlled by the effector kinases RAF and PI3K have become tools in the treatment of RAS-driven tumours. Unfortunately, the efficacy of this approach has been greatly minimized by the prevalence of acquired drug resistance. Decades of research have established that RAS signalling is highly complex, and in addition to RAF and PI3K these small GTPase proteins can interact with an array of alternative effectors that feature RAS binding domains. The consequence of RAS binding to these effectors remains relatively unexplored, but these pathways may provide targets for combinatorial therapeutics. We discuss here three candidate alternative effectors: RALGEFs, RASSF5 and AFDN, detailing their interaction with RAS GTPases and their biological significance. The metastatic nature of RAS-driven cancers suggests more attention should be granted to these alternate pathways, as they are highly implicated in the regulation of cell adhesion, polarity, cell size and cytoskeletal architecture.

Structure and regulation of phospholipase Cβ and ε at the membrane

Phospholipase C (PLC) β and ε enzymes hydrolyze phosphatidylinositol (PI) lipids in response to direct interactions with heterotrimeric G protein subunits and small GTPases, which are activated downstream of G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs). PI hydrolysis generates second messengers that increase the intracellular Ca²⁺ concentration and activate protein kinase C (PKC), thereby regulating numerous physiological processes. PLCβ and PLCε share a highly conserved core required for lipase activity, but use different strategies and structural elements to autoinhibit basal activity, bind membranes, and engage G protein activators. In this review, we discuss recent structural insights into these enzymes and the implications for how they engage membranes alone or in complex with their G protein regulators.

Inositol polyphosphate multikinase IPMK-1 regulates development through IP3/calcium signaling in Caenorhabditis elegans

Inositol polyphosphate multikinase (IPMK) is a conserved protein that initiates the production of inositol phosphate intracellular messengers and is critical for regulating a variety of cellular processes. Here, we report that the C. elegans IPMK-1, which is homologous to the mammalian inositol polyphosphate multikinase, plays a crucial role in regulating rhythmic behavior and development. The deletion mutant ipmk-1(tm2687) displays a long defecation cycle period and retarded postembryonic growth. The expression of functional ipmk-1::GFP was detected in the pharyngeal muscles, amphid sheath cells, the intestine, excretory (canal) cells, proximal gonad, and spermatheca. The expression of IPMK-1 in the intestine was sufficient for the wild-type phenotype. The IP3-kinase activity of IPMK-1 is required for defecation rhythms and postembryonic development. The defective phenotypes of ipmk-1(tm2687) could be rescued by a loss-of-function mutation in type I inositol 5-phosphatase homolog (IPP-5) and improved by a supplemental Ca²⁺ in the medium. Our work demonstrates that IPMK-1 and the signaling molecule inositol triphosphate (IP3) pathway modulate rhythmic behaviors and development by dynamically regulating the concentration of intracellular Ca²⁺ in C. elegans. Advances in understanding the molecular regulation of Ca²⁺ homeostasis and regulation of organism development may lead to therapeutic strategies that modulate Ca²⁺ signaling to enhance function and counteract disease processes. Unraveling the physiological role of IPMK and the underlying functional mechanism in C. elegans would contribute to understanding the role of IPMK in other species, especially in mammals, and benefit further research on the involvement of IPMK in disease.

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.

Phosphoinositide-Dependent Signaling in Cancer: A Focus on Phospholipase C Isozymes

Phosphoinositides (PI) form just a minor portion of the total phospholipid content in cells but are significantly involved in cancer development and progression. In several cancer types, phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P₃] and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂] play significant roles in regulating survival, proliferation, invasion, and growth of cancer cells. Phosphoinositide-specific phospholipase C (PLC) catalyze the generation of the essential second messengers diacylglycerol (DAG) and inositol 1,4,5 trisphosphate (InsP₃) by hydrolyzing PtdIns(4,5)P₂. DAG and InsP₃ regulate Protein Kinase C (PKC) activation and the release of calcium ions (Ca²⁺) into the cytosol, respectively. This event leads to the control of several important biological processes implicated in cancer. PLCs have been extensively studied in cancer but their regulatory roles in the oncogenic process are not fully understood. This review aims to provide up-to-date knowledge on the involvement of PLCs in cancer. We focus specifically on PLCβ, PLCγ, PLCδ, and PLCε isoforms due to the numerous evidence of their involvement in various cancer types.

A Systemic Review on the Regulatory Roles of miR-34a in Gastrointestinal Cancer

MicroRNAs (miRNAs) are a class of endogenous non-coding single-stranded small-molecule RNAs that regulate gene expression by repressing target messenger RNA (mRNA) translation or degrading mRNA. miR-34a is one of the most important miRNAs participating in various physiological and pathological processes. miR-34a is abnormally expressed in a variety of tumors. The roles of miR-34a in gastrointestinal cancer (GIC) draw lots of attention. Numerous studies have demonstrated that dysregulated miR-34a is closely related to the proliferation, differentiation, migration, and invasion of tumor cells, as well as the diagnosis, prognosis, treatment, and chemo-resistance of tumors. Thus, we systematically reviewed the abnormal expression and regulatory roles of miR-34a in GICs including esophageal cancer (EC), gastric cancer (GC), colorectal cancer (CRC), hepatocellular carcinoma (HCC), pancreatic cancer (PC), and gallbladder cancer (GBC). It may provide a profile of versatile roles of miR-34a in GICs.

The PLCE1 rs2274223 variant is associated with the risk of laryngeal squamous cell carcinoma

Background: Laryngeal squamous cell carcinoma (LSCC) ranks second in the mortality rate in respiratory malignant tumors and has potential similarity in genomic alterations with the esophageal squamous cell carcinoma (ESCC). The PLCE1 rs2274223 variant is the most significant susceptibility loci identified in ESCC. Whether it is also associated with LSCC susceptibility is still unclear. Materials and Methods: A total of 331 LSCC patients and 349 healthy controls were recruited in this study. The PLCE1 rs2274223 variant was genotyped by using the Taqman SNP Genotyping Assay. Association between PLCE1 rs2274223 variant and LSCC risk was estimated by logistic regression analysis, which was performed using SAS software. Results: The PLCE1 rs2274223 variant was identified to be significantly associated with the susceptibility of LSCC in the additive model (OR = 1.40, 95% CI: 1.06-1.86, P=0.019). Compared with the wild-type (AA) carriers, the risk genotype (GG) carriers had a 2.8-fold risk of LSCC (95% CI: 1.13-7.06, P=0.026). Stratified analysis showed that the association between rs2274223 and LSCC risk was with higher significance in individuals above 60 (P = 0.027) males (P = 0.030) or non-smokers (P = 0.026). Conclusion: The PLCE1 rs2274223 variant was significantly associated with risk of LSCC, which may be a potential biomarker and therapeutic target for the LSCC.

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 various 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 on PLC. In addition, references have been provided for more in-depth information regarding areas that are not discussed including tyrosine kinase activation of PLC. Understanding the roles of the individual PLC enzymes, and their distinct cellular functions, will lead to a better understanding of the physiological roles of these enzymes in the development of diseases and the maintenance of homeostasis.

MicroRNA-34a functions as a tumor suppressor by directly targeting oncogenic PLCE1 in Kazakh esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the frequent malignant tumors with poor prognosis worldwide. Identifying the prognostic biomarkers and potential mechanisms of such tumors has attracted increasing interest in esophageal cancer biology. Our previous study showed that phospholipase C elipson 1 (PLCE1) expression is up-regulated and associated with disease progression in esophageal carcinoma. MicroRNAs (miRNAs) play vital roles in regulating its target gene expression. However, studies on miRNA-regulated PLCE1 expression and its cellular function are still very few. We found that miR-34a is significantly expressed lower in ESCC tissues. We further showed that PLCE1 is a direct functional target gene of miR-34a, and the functional roles of miR-34a in ESCC cell lines in vitro were also determined through gain- and loss-of-function analyses. Results revealed that miR-34a functions as a tumor suppressor by inhibiting the proliferation, migration, and EMT phenotype, as well as promoting apoptosis of ESCC cell lines. Moreover, PLCE1 is overexpressed in ESCC tumors and promotes tumorigenicity in vivo and vitro. PLCE1 expression is negatively correlated with miR-34a profiles in ESCC tissues. Our data suggest that miR-34a exerts its anti-cancer function by suppressing PLCE1. The newly identified miR-34a/PLCE1 axis partially illustrates the molecular mechanism of ESCC metastasis and represents a new candidate therapeutic target for ESCC treatment.

The controversial role of phospholipase C epsilon (PLCε) in cancer development and progression

The phospholipase C (PLC) enzymes are important regulators of membrane phospholipid metabolism. PLC proteins can be activated by the receptor tyrosine kinases (RTK) or G-protein coupled receptors (GPCR) in response to the different extracellular stimuli including hormones and growth factors. Activated PLC enzymes hydrolyze phosphoinositides to increase the intracellular level of Ca²⁺ and produce diacylglycerol, which are important mediators of the intracellular signaling transduction. PLC family includes 13 isozymes belonging to 6 subfamilies according to their domain structures and functions. Although importance of PLC enzymes for key cellular functions is well established, the PLC proteins belonging to the ε, ζ and η subfamilies were identified and characterized only during the last decade. As a largest known PLC protein, PLCε is involved in a variety of signaling pathways and controls different cellular properties. Nevertheless, its role in carcinogenesis remains elusive.

The aim of this review is to provide a comprehensive and up-to-date overview of the experimental and clinical data about the role of PLCε in the development and progression of the different types of human and experimental tumors.

Low PLCE1 levels are correlated with poor prognosis in hepatocellular carcinoma

Background

Previous reports show that phospholipase C epsilon-1 (PLCE1) expression is positively correlated with esophageal squamous cell carcinoma and gastric cardia adenocarcinomas; however, the expression of PLCE1 in hepatocellular carcinoma (HCC) and its correlation with clinical outcome still remain unclear. The aim of this study was to explore the expression of PLCE1 in HCC tissue and to determine whether PLCE1 was a prognostic factor for HCC patients.

Materials and methods

PLCE1 levels in 20 paired HCC tissues and corresponding paracarcinomatous tissues was investigated by quantitative real-time polymerase chain reaction and Western blot assays. In addition, protein levels of PLCE1 in one normal liver epithelial cell and four HCC cell lines were examined using Western blot assay. Moreover, immunohistochemistry was applied to determine the expression of PLCE1 in HCC and corresponding surrounding tissues from 90 patients. Statistical analyses were used to examine the association between PLCE1 levels and clinicopathological features.

Results

We found that the expression of PLCE1 in tumor tissues was significantly lower than those in paracarcinomatous tissues at both mRNA and protein levels (P<0.05). We also determined that PLCE1 protein expression levels were lower in HCC cell lines than normal liver epithelial cells (P<0.05). Notably, immunohistochemical assay showed that PLCE1 expression was significantly low in HCC tissues compared with the adjacent normal liver tissues (40% vs 18.9%; P<0.05). Besides, PLCE1 levels were negatively correlated with tumor capsulae, vascular invasion, Edmondson grade, alpha-fetoprotein, and tumor-node-metastasis stage (P<0.05). Univariate analysis revealed that lower level expression of PLCE1 was significantly associated with poorer overall survival (OS) rate (P<0.001) and disease-free survival rate (P<0.001). Multivariate analysis revealed that low PLCE1 level was an independent poor prognostic factor of OS and recurrence-free survival (P<0.001 and P=0.003, respectively).

Conclusion

In brief, our results revealed that decreased PLCE1 expression was associated with tumor progression in HCC and may function as a promising biomarker for HCC prognosis.

Targeting oncogenic PLCE1 by miR-145 impairs tumor proliferation and metastasis of esophageal squamous cell carcinoma

Phospholipase C epsilon 1 (PLCE1) is a susceptibility gene in esophageal squamous cell carcinoma (ESCC). Nevertheless, the role of PLCE1 in ESCC tumorigenesis has not been elucidated. In this study, we determined the function of PLCE1 and its regulatory microRNA (miRNA) in ESCC. PLCE1 protein was excessively expressed in ESCC and precancerous lesions compared with that in normal tissues. High PLCE1 expression levels in ESCC were significantly linked with poor overall survival. Knockdown of PLCE1 promoted the apoptosis, cytokine-induced apoptosis, and sensitivity of cancer cells to chemotherapeutic drugs but abrogated the proliferation and EMT phenotype of ESCC in vitro. Notably, miR-145 was newly identified as a potent repressor of PLCE1 expression by directly targeting the 3′UTR of PLCE1. MiR-145 also inhibited cell proliferation, migration, and metastasis, as well as controlled the cytoskeleton dynamics of esophageal cancer. Moreover, miR-145 was expressed at low levels in a large cohort of patients with ESCC and was inversely correlated with PLCE1 protein expression in cancer cells and tissues. These findings demonstrate that PLCE1 functions as tumor promoter in ESCC and can be suppressed by miR-145 through inhibition of PLCE1 translation. Hence, delivery of PLCE1-targeting miR-145 is a potential therapeutic approach for esophageal cancer.

Knockout of phospholipase Cε attenuates N-butyl-N-(4-hydroxybutyl) nitrosamine-induced bladder tumorigenesis

Bladder cancer frequently shows mutational activation of the oncogene Ras, which is associated with bladder carcinogenesis. However, the signaling pathway downstream of Ras remains to be fully elucidated. N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) is able to induce bladder cancer by driving the clonal expansion of initiated cells carrying the activated form of Ras. Phospholipase Cε (PLCε) is the main target of BBN, while the tumor promoting role of PLCε remains controversial. The present study examined the role of PLCε in BBN-induced bladder carcinogenesis of mice with genetically inactivated PLCε. Using light and electron microscopy, the present study demonstrated that PLCε^−/− mice were resistant to BBN-induced bladder carcinogenesis. Furthermore, it was demonstrated that cyclooxygenase 2 and vascular endothelial growth factor-A were affected by the PLCε background of the mice, suggesting that the role of PLCε in tumor promotion may be ascribed to augmentation of inflammatory responses and angiogenesis. These results indicated that PLCε is crucial for BBN-induced bladder carcinogenesis as well as signaling downstream of Ras, and that PLCε is a candidate molecular target for the development of anti-cancer drugs.

Thrombin promotes sustained signaling and inflammatory gene expression through the CDC25 and Ras-associating domains of phospholipase Cϵ

Phospholipase C-epsilon (PLCϵ) plays a critical role in G-protein-coupled receptor-mediated inflammation. In addition to its ability to generate the second messengers inositol 1,4,5-trisphosphate and diacylglycerol, PLCϵ, unlike the other phospholipase C family members, is activated in a sustained manner. We hypothesized that the ability of PLCϵ to function as a guanine nucleotide exchange factor (GEF) for Rap1 supports sustained downstream signaling via feedback of Rap1 to the enzyme Ras-associating (RA2) domain. Using gene deletion and adenoviral rescue, we demonstrate that both the GEF (CDC25 homology domain) and RA2 domains of PLCϵ are required for long term protein kinase D (PKD) activation and subsequent induction of inflammatory genes. PLCϵ localization is largely intracellular and its compartmentalization could contribute to its sustained activation. Here we show that localization of PLCϵ to the Golgi is required for activation of PKD in this compartment as well as for subsequent induction of inflammatory genes. These data provide a molecular mechanism by which PLCϵ mediates sustained signaling and by which astrocytes mediate pathophysiological inflammatory responses.

Ras effector switching as a developmental strategy

Organisms pattern and specify cell fates with remarkably high fidelity and robustness, and cancer may be considered in part to be a disease of fate specification gone awry. During C. elegans vulval development an initial EGF signal prompts Ras to activate its canonical effector pathway, Raf-MEK-ERK, to induce a primary cell, which subsequently signals its 2 neighbors via Notch to develop as secondary cells. We have shown that Ras signaling through an alternate effector pathway, RalGEF-Ral, antagonizes Ras-Raf pro-primary signaling. Ras-RalGEF-Ral instead promotes secondary fate in support of Notch. We validated a previous model that EGF can also contribute to secondary fate, and argue that Ras-RalGEF-Ral mediates this EGF pro-secondary activity. Ras-Raf-MEK-ERK signaling was previously shown to be extinguished from secondary cells by secondary-specific expression of MAP kinase phosphatase, and we found that Ral expression is transcriptionally restricted to secondary cells. Thus during vulval development Ras switches effectors from Raf to RalGEF to promote divergent and mutually antagonistic cell fates, perhaps mirroring divergent effector usage in Ras-dependent tumors with differential pharmacological responsiveness.

Ras history: The saga continues

Although the roots of Ras sprouted from the rich history of retrovirus research, it was the discovery of mutationally activated RAS genes in human cancer in 1982 that stimulated an intensive research effort to understand Ras protein structure, biochemistry and biology. While the ultimate goal has been developing anti-Ras drugs for cancer treatment, discoveries from Ras have laid the foundation for three broad areas of science. First, they focused studies on the origins of cancer to the molecular level, with the subsequent discovery of genes mutated in cancer that now number in the thousands. Second, elucidation of the biochemical mechanisms by which Ras facilitates signal transduction established many of our fundamental concepts of how a normal cell orchestrates responses to extracellular cues. Third, Ras proteins are also founding members of a large superfamily of small GTPases that regulate all key cellular processes and established the versatile role of small GTP-binding proteins in biology. We highlight some of the key findings of the last 28 years.

PLCε mediated sustained signaling pathways

Phospholipase C-ε (PLCε) integrates signaling from G-protein coupled receptors (GPCRs) to downstream kinases to regulate a broad range of biological and pathophysiological responses. Relative to other PLCs, PLCε is unique in that it not only serves a catalytic function in phosphoinositide hydrolysis but also functions as an exchange factor small the low molecular weight G-protein Rap1. PLCε is selectively stimulated by agonists for GPCRs that couple to RhoA, which bind directly to the enzyme to regulate its activity. Rap1 also regulates PLCε activity by binding to its RA2 domain and this generates a feedback mechanism allowing sustained signaling. As a result of its regulation by inflammatory ligands for GPCRs and its ability to promote chronic signals, PLCε has been implicated in diseases ranging from cancer to ischemia/reperfusion injury. This review will discuss the regulation of PLCε, molecular mechanisms that contribute to sustained signaling, and the role of the enzyme in various disease contexts.

Mechanotransduction in C. elegans morphogenesis and tissue function

Mechanobiology is an emerging field that investigates how living cells sense and respond to their physical surroundings. Recent interest in the field has been sparked by the finding that stem cells differentiate along different lineages based on the stiffness of the cell surroundings (Engler et al., 2006), and that metastatic behavior of cancer cells is strongly influenced by the mechanical properties of the surrounding tissue (Kumar and Weaver, 2009). Many questions remain about how cells convert mechanical information, such as viscosity, stiffness of the substrate, or stretch state of the cells, into the biochemical signals that control tissue function. Caenorhabditis elegans researchers are making significant contributions to the understanding of mechanotransduction in vivo. This review summarizes recent insights into the role of mechanical forces in morphogenesis and tissue function. Examples of mechanical regulation across length scales, from the single-celled zygote, to the intercellular coordination that enables cohesive tissue function, to the mechanical influences between tissues, are considered. The power of the C. elegans system as a gene discovery and in vivo quantitative bioimaging platform is enabling an important discoveries in this exciting field.

Filamin and Phospholipase C-ε are required for calcium signaling in the Caenorhabditis elegans Spermatheca

Mechanical properties of the microenvironment are fundamental in orchestrating normal tissue function, disease progression, and organismal development. Studies of mechanotransduction in cultured cells on artificial substrates have revealed underlying principles, but the in vivo roles of mechanotransduction remain unclear. We recently reported that the Caenorhabditis elegans spermatheca—a myoepithelial tube composed of a cell monolayer—may be mechanosensitive. Live imaging with the genetically encoded calcium indicator GCaMP revealed that oocyte-induced stretching of the spermatheca resulted in calcium oscillations and constriction of the tube. FLN-1/filamin, a mechanosensitive cytoskeletal scaffolding protein, is required to correctly trigger the calcium transients. PLC-1/phospholipase C-epsilon and ITR-1/IP₃ receptor are required to produce the calcium transients, and may function downstream of filamin. In addition to providing important insights into the biology of C. elegans, our studies offer a novel and genetically tractable model for studying mechanotransduction in a myoepithelial tissue.

Canonical RTK-Ras-ERK signaling and related alternative pathways

Receptor Tyrosine Kinase (RTK)-Ras-Extracellular signal-regulated kinase (ERK) signaling pathways control many aspects of C. elegans development and behavior. Studies in C. elegans helped elucidate the basic framework of the RTK-Ras-ERK pathway and continue to provide insights into its complex regulation, its biological roles, how it elicits cell-type appropriate responses, and how it interacts with other signaling pathways to do so. C. elegans studies have also revealed biological contexts in which alternative RTK- or Ras-dependent pathways are used instead of the canonical pathway.

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.

Overexpression of PLCE1 in Kazakh esophageal squamous cell carcinoma: implications in cancer metastasis and aggressiveness

Three recent large-scale genome-wide association studies (GWAS) in Chinese Han populations have identified an esophageal squamous cell carcinoma (ESCC) susceptibility locus within phospholipase C epsilon 1 (PLCE1) gene, which encodes a phospholipase involved in intracellular signaling. The expressed PLCE1 in ESCC, however, are inconsistent. This study examined PLCE1 expression by immunohistochemistry (IHC) from 110 ethnic Kazakh ESCC patients and 50 from adjacent normal esophageal tissues (NETs). The expressed PLCE1 was localized in cytoplasm, especially in the peripheral layers of cancer cell nests, which was significantly higher in tumors than in NETs (p < 0.001). Increased expression of PLCE1 was correlated with advanced tumor-node-metastasis (TNM) stages (p = 0.015) and lymph node metastasis (p = 0.003) in patients with ESCC. Of the 110 patients, we examined 50 paired ESCC tissues and corresponding NETs by quantitative RT-PCR (polymerase chain reaction) and the mean mRNA level of PLCE1 in ESCC was 1.85-fold higher compared with those in corresponding NETs (p = 0.0012). Meanwhile, 4 of 5 ESCC cell lines also showed elevated expression of PLCE1 mRNA. Furthermore, elevated expression of PLCE1 mRNA in Kazakh ESCC was associated with its immunoreactivity (ρ = 0.297, p = 0.040), lymph node metastasis (p < 0.001), and advanced TNM stages of ESCC (p = 0.013). To our knowledge, this study demonstrates for the first time that PLCE1 overexpression correlates with lymph node metastasis and advanced TNM stages of Kazakh ESCC, implicating a role of PLCE1 in cancer metastasis and aggressiveness in ethnic Kazakh patients with ESCC. Furthermore, the current findings may warrant investigations into whether inhibiting PLCE1 could be a strategy for targeted anticancer therapy particularly for Kazakh ESCC.

Filamin and phospholipase C-ε are required for calcium signaling in the Caenorhabditis elegans spermatheca

The Caenorhabditis elegans spermatheca is a myoepithelial tube that stores sperm and undergoes cycles of stretching and constriction as oocytes enter, are fertilized, and exit into the uterus. FLN-1/filamin, a stretch-sensitive structural and signaling scaffold, and PLC-1/phospholipase C-ε, an enzyme that generates the second messenger IP₃, are required for embryos to exit normally after fertilization. Using GCaMP, a genetically encoded calcium indicator, we show that entry of an oocyte into the spermatheca initiates a distinctive series of IP₃-dependent calcium oscillations that propagate across the tissue via gap junctions and lead to constriction of the spermatheca. PLC-1 is required for the calcium release mechanism triggered by oocyte entry, and FLN-1 is required for timely initiation of the calcium oscillations. INX-12, a gap junction subunit, coordinates propagation of the calcium transients across the spermatheca. Gain-of-function mutations in ITR-1/IP₃R, an IP₃-dependent calcium channel, and loss-of-function mutations in LFE-2, a negative regulator of IP₃ signaling, increase calcium release and suppress the exit defect in filamin-deficient animals. We further demonstrate that a regulatory cassette consisting of MEL-11/myosin phosphatase and NMY-1/non-muscle myosin is required for coordinated contraction of the spermatheca. In summary, this study answers long-standing questions concerning calcium signaling dynamics in the C. elegans spermatheca and suggests FLN-1 is needed in response to oocyte entry to trigger calcium release and coordinated contraction of the spermathecal tissue.

During organism development and normal physiological function cells sense, integrate, and respond to a variety of cues or signals including biochemical and mechanical stimuli. In this study we used Caenorhabditis elegans, a small transparent worm, to study filamin (FLN-1), a structural protein that may act as a molecular strain gauge. The C. elegans spermatheca is a contractile tube that is stretched during normal function, making it an ideal candidate for study of how cells respond to stretch. Oocytes are ovulated into the spermatheca, fertilized, and then pushed into the uterus by constriction of the spermatheca. The ability of the spermatheca to constrict depends on inositol 1,4,5-triphosphate (IP₃), a signaling molecule produced by the enzyme phospholipase C (PLC-1) that triggers calcium release within cells. In animals with mutated FLN-1 or PLC-1 the spermathecal cells fail to constrict. Using genetic analysis and a calcium-sensitive fluorescent protein, we show that FLN-1 functions with PLC-1 to regulate IP₃ production, calcium release, and contraction of the spermatheca. Filamin may function to sense stretch caused by entering oocytes and to trigger constriction. These findings establish a link between filamin and calcium signaling that may apply to similar signaling pathways in other systems.

Knockdown of phospholipase C-epsilon by short-hairpin RNA-mediated gene silencing induces apoptosis in human bladder cancer cell lines

Transitional cell carcinoma of bladder (TCCB) is a common malignancy worldwide, and outcomes for patients with advanced bladder cancer remain poor. To study the pathogenesis of TCCB, we investigated roles of Phospholipase C (PLC)ɛ, an effector of Ras and Rap small GTPases. RNA interference was used to knockdown PLCɛ expression in human bladder cancer cell lines (BIU-87 and T24). The expression levels of PLCɛ mRNA and protein were detected by reverse transcriptase-polymerase chain reaction and Western blot, respectively. Flow cytometry (FCM) was used to detect distribution of cell cycle. Cellular apoptosis was reflected by transmission electron microscopy and the expression of bcl-2 and bax. We found that PLCɛ could be efficiently knocked down by shRNA. FCM assay showed that the pGenesil-PLCɛ-transfected cells were arrested at the G0/G1 phase. Silence of PLCɛ might induce apoptosis via modulation of bcl-2 and bax. In conclusion, our results suggest that PLCɛ plays an important role in the pathogenesis of human bladder cancer cells. PLCɛ may be used as a potential target of gene therapy for bladder cancer in future.

Mammalian phospholipase C

Phospholipase C (PLC) converts phosphatidylinositol 4,5-bisphosphate (PIP(2)) to inositol 1,4,5-trisphosphate (IP(3)) and diacylglycerol (DAG). DAG and IP(3) each control diverse cellular processes and are also substrates for synthesis of other important signaling molecules. PLC is thus central to many important interlocking regulatory networks. Mammals express six families of PLCs, each with both unique and overlapping controls over expression and subcellular distribution. Each PLC also responds acutely to its own spectrum of activators that includes heterotrimeric G protein subunits, protein tyrosine kinases, small G proteins, Ca(2+), and phospholipids. Mammalian PLCs are autoinhibited by a region in the catalytic TIM barrel domain that is the target of much of their acute regulation. In combination, the PLCs act as a signaling nexus that integrates numerous signaling inputs, critically governs PIP(2) levels, and regulates production of important second messengers to determine cell behavior over the millisecond to hour timescale.

Role of phospholipase Cε in physiological phosphoinositide signaling networks

Receptor-initiated phospholipase C activation and generation of IP(3) and DAG are important common triggers for a diversity of signal transduction processes in many cell types. Contributing to this diversity is the existence and differential cellular and subcellular distribution of distinct phospholipase C isoforms with distinct regulatory properties. The recently identified PLCε enzyme is an isoform that is uniquely regulated by multiple upstream signals including ras-family GTP binding proteins as well as heterotrimeric G-proteins. In this review we will consider the well documented biochemical regulation of this isoform in the context of cell and whole animal physiology and in the context of other G protein-regulated PLC isoforms. These studies together reveal a surprisingly wide range of unexpected functions for PLCε in cellular signaling, physiology and disease.

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.

Genetic analysis of IP3 and calcium signalling pathways in C. elegans

BACKGROUND

The nematode, Caenorhabditis elegans is an established model system that is particularly well suited to genetic analysis. C. elegans is easily manipulated and we have an in depth knowledge of many aspects of its biology. Thus, it is an attractive system in which to pursue integrated studies of signalling pathways. C. elegans has a complement of calcium signalling molecules similar to that of other animals.

SCOPE OF REVIEW

We focus on IP3 signalling. We describe how forward and reverse genetic approaches, including RNAi, have resulted in a tool kit which enables the analysis of IP3/Ca2+ signalling pathways. The importance of cell and tissue specific manipulation of signalling pathways and the use of epistasis analysis are highlighted. We discuss how these tools have increased our understanding of IP3 signalling in specific developmental, physiological and behavioural roles. Approaches to imaging calcium signals in C. elegans are considered.

MAJOR CONCLUSIONS

A wide selection of tools is available for the analysis of IP3/Ca2+ signalling in C. elegans. This has resulted in detailed descriptions of the function of IP3/Ca2+ signalling in the animal's biology. Nevertheless many questions about how IP3 signalling regulates specific processes remain.

GENERAL SIGNIFICANCE

Many of the approaches described may be applied to other calcium signalling systems. C. elegans offers the opportunity to dissect pathways, perform integrated studies and to test the importance of the properties of calcium signalling molecules to whole animal function, thus illuminating the function of calcium signalling in animals. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signalling.

Therapeutic strategies for targeting ras proteins

Ras genes are frequently activated in cancer. Attempts to develop drugs that target mutant Ras proteins have, so far, been unsuccessful. Tumors bearing these mutations, therefore, remain among the most difficult to treat. Most efforts to block activated Ras have focused on pathways downstream. Drugs that inhibit Raf kinase have shown clinical benefit in the treatment of malignant melanoma. However, these drugs have failed to show clinical benefit in Ras mutant tumors. It remains unclear to what extent Ras depends on Raf kinase for transforming activity, even though Raf proteins bind directly to Ras and are certainly major effectors of Ras action in normal cells and in development. Furthermore, Raf kinase inhibitors can lead to paradoxical activation of the MAPK pathway. MEK inhibitors block the Ras-MAPK pathway, but often activate the PI3'-kinase, and have shown little clinical benefit as single agents. This activation is mediated by EGF-R and other receptor tyrosine kinases through relief of a negative feedback loop from ERK. Drug combinations that target multiple points within the Ras signaling network are likely to be necessary to achieve substantial clinical benefit. Other effectors may also contribute to Ras signaling and provide a source of targets. In addition, unbiased screens for genes necessary for Ras transformation have revealed new potential targets and have added to our understanding of Ras cancer biology.

Phospholipase C epsilon plays a suppressive role in incidence of colorectal cancer

In our previous study, we have found that PLCE1 was down-regulated in sporadic colorectal cancer. But the role of PLCE1 in the incidence of colorectal cancer is still not definite. Therefore, in order to validate whether PLCE1 displays a suppressive role, in this study, we examined the expression of PLCE1 in sporadic colorectal cancer with a larger sample size and the effect of PLCE1 overexpression on cancer cell malignant degree. The expression level of PLCE1 in 50 colorectal cancers with their pair-matched normal tissues was measured by RT-PCR, Western blot, and immunohistochemistry. The effect of PLCE1 overexpression on cancer cell malignant degree was measured by MTT assay, plate colony formation assay, soft agar colony formation assay, cell cycle and apoptosis analysis, and xenograft assay. We found that PLCE1 was down-regulated in 42% (21/50) of colorectal cancer tissues compared with pair-matched normal tissues, more frequent in the poor differentiation tumor in patients under 60. Overexpression of PLCE1 significantly inhibited the proliferation of colon cancer cells and degraded its malignant degree. These results suggest that PLCE1 may be involved in the development of sporadic colorectal cancer through its inhibitory effect on cell proliferation. PLCE1 exhibits a suppressive role in incidence of colorectal cancer.

Phospholipase Cɛ has a crucial role in ultraviolet B-induced neutrophil-associated skin inflammation by regulating the expression of CXCL1/KC

Phospholipase C (PLC) ɛ is a phosphoinositide-specific PLC regulated by small GTPases including Ras and Rap. We previously demonstrated that PLCɛ has an important role in the development of phorbol ester-induced skin inflammation. In this study, we investigated the role of PLCɛ in ultraviolet (UV) B-induced acute inflammatory reactions in the skin. Wild-type (PLCɛ+/+) and PLCɛ gene knockout (PLCɛ⁻/⁻) mice were irradiated with a single dose of UVB at 1, 2.5, and 10 kJ/m² on the dorsal area of the skin, and inflammatory reactions in the skin were histologically evaluated up to 168 h after irradiation. In PLCɛ+/+ mice, irradiation with 1 and 2.5 kJ/m² UVB resulted in dose-dependent neutrophil infiltration in the epidermis at 24 and 48 h after irradiation. When mice were irradiated with 10 kJ/m² of UVB, most mice developed skin ulcers by 48 h and these ulcers became more severe at 168 h. In PLCɛ⁻/⁻ mice, UVB (1 or 2.5 kJ/m²)-induced neutrophil infiltration was markedly suppressed compared with PLCɛ+/+ mice. The suppression of neutrophil infiltration in PLCɛ⁻/⁻ mice was accompanied by attenuation of UVB-induced production of CXCL1/keratinocyte-derived chemokine (KC), a potent chemokine for neutrophils, in the whole skin. Cultured epidermal keratinocytes and dermal fibroblasts produced CXCL1/KC in a PLCɛ-dependent manner after UVB irradiation, and the UVB-induced upregulation of CXCL1/KC in these cells was significantly abolished by a PLC inhibitor. Furthermore, UVB-induced epidermal thickening was noticeably reduced in the skin of PLCɛ⁻/⁻ mice. These results indicate that PLCɛ has a crucial role in UVB-induced acute inflammatory reactions such as neutrophil infiltration and epidermal thickening by at least in part regulating the expression of CXCL1/KC in skin cells such as keratinocytes and fibroblasts.

Ras effector switching promotes divergent cell fates in C. elegans vulval patterning

The C. elegans vulva is patterned by epidermal growth factor (EGF) activation of Ras to control 1° fate, and 1° fate induces antagonistic Notch-dependent 2° fate. Furthermore, a spatial EGF gradient, in addition to inducing 1° fate, directly contributes to 2° fate via an unknown pathway. We find that in addition to its canonical effector, Raf, vulval Ras utilizes an exchange factor for the Ral small GTPase (RalGEF), such that Ras-RalGEF-Ral antagonizes Ras-Raf pro-1° fate activity. Consistent with its restricted expression pattern, Ral participates in EGF pro-2° activity. Thus, we have delineated a Ras effector-switching mechanism whereby position within the morphogen gradient dictates that Ras effector usage is switched to RalGEF from Raf to promote 2° instead of 1° fate. Our observations define the utility of Ras effector switching during normal development and may provide a possible mechanistic basis for cell and cancer-type differences in effector dependency and activation.

Enhancement of ultraviolet B-induced skin tumor development in phospholipase Cε-knockout mice is associated with decreased cell death

Phospholipase C (PLC) ε is a phosphoinositide-specific PLC regulated by small guanosine triphosphatases including Ras and Rap. Our previous studies revealed that PLCε gene-knockout (PLCε(-/-)) mice exhibit marked resistance to tumor formation in two-stage skin chemical carcinogenesis using 7,12-dimethylbenz(a)anthracene as an initiator and 12-O-tetradecanoylphorbol-13-acetate as a promoter. In this model, PLCε functions in tumor promotion through augmentation of 12-O-tetradecanoylphorbol-13-acetate-induced inflammation. In this study, we have further assessed the role of PLCε in tumorigenesis using a mouse model of ultraviolet (UV) B-induced skin tumor development. We irradiated PLCε(+/+), PLCε(+/-) or PLCε(-/-) mice with doses of UVB increasing from 1 to 10 kJ/m(2) three times a week for a total of 25 weeks and observed tumor formation for up to 50 weeks. In sharp contrast to the results from the two-stage chemical carcinogenesis study, PLCε(-/-) mice developed a large number of neoplasms including malignant tumors, whereas PLCε(+/+) and PLCε(+/-) mice developed a relatively small number of benign tumors. However, UVB-induced skin inflammation was greatly suppressed in PLCε(-/-) mice, as observed with 12-O-tetradecanoylphorbol-13-acetate-induced inflammation, implying that PLCε's role in the suppression of UVB-induced tumorigenesis is not mediated by inflammation. Studies of the tumor initiation stage revealed that UVB-induced cell death in the skin was markedly suppressed in PLCε(-/-)mice. Our findings identify a novel function for PLCε as a critical molecule regulating UVB-induced cell death and suggest that resistance to UVB-induced cell death conferred by the absence of PLCε is closely related to the higher incidence of skin tumor formation.

Inositol 1,4,5-trisphosphate signalling regulates the avoidance response to nose touch in Caenorhabditis elegans

When Caenorhabditis elegans encounters an unfavourable stimulus at its anterior, it responds by initiating an avoidance response, namely reversal of locomotion. The amphid neurons, ASHL and ASHR, are polymodal in function, with roles in the avoidance responses to high osmolarity, nose touch, and both volatile and non-volatile repellents. The mechanisms that underlie the ability of the ASH neurons to respond to such a wide range of stimuli are still unclear. We demonstrate that the inositol 1,4,5-trisphosphate receptor (IP₃R), encoded by itr-1, functions in the reversal responses to nose touch and benzaldehyde, but not in other known ASH-mediated responses. We show that phospholipase Cβ (EGL-8) and phospholipase Cγ (PLC-3), which catalyse the production of IP₃, both function upstream of ITR-1 in the response to nose touch. We use neuron-specific gene rescue and neuron-specific disruption of protein function to show that the site of ITR-1 function is the ASH neurons. By rescuing plc-3 and egl-8 in a neuron-specific manner, we show that both are acting in ASH. Imaging of nose touch–induced Ca²⁺ transients in ASH confirms these conclusions. In contrast, the response to benzaldehyde is independent of PLC function. Thus, we have identified distinct roles for the IP₃R in two specific responses mediated by ASH.

In order to avoid potential hazards, animals detect and discriminate between a wide range of aversive stimuli. To detect some of these stimuli, animals use polymodal sensory neurons, that is neurons of a single type that can detect a range of different stimuli and transmit an appropriate signal to the downstream nervous system. Pain-sensing nociceptors in humans and the ASH neurons in C. elegans are both polymodal. The ASH neurons mediate responses to high osmotic strength, nose touch, high ambient oxygen, and volatile and non-volatile compounds. It remains unclear how these cells detect and discriminate between these different stimuli. We show that signalling through the second messenger inositol 1,4,5-trisphosphate (IP₃) and its receptor (IP₃R) is required in ASH for animals to respond to nose touch. We also show that IP₃Rs are required for the response to the volatile compound benzaldehyde. However, these signalling components are not required for a range of other ASH-mediated responses. Thus, we have identified a signalling mechanism that is specific to a small subset of ASH-mediated responses. These results add to our understanding of how ASH discriminates between a variety of stimuli and thus to our understanding of polymodal neurons in general.

Caenorhabditis elegans FOS-1 and JUN-1 regulate plc-1 expression in the spermatheca to control ovulation

Fos and Jun are components of activator protein-1 (AP-1) and play crucial roles in the regulation of many cellular, developmental, and physiological processes. Caenorhabditis elegans fos-1 has been shown to act in uterine and vulval development. Here, we provide evidence that C. elegans fos-1 and jun-1 control ovulation, a tightly regulated rhythmic program in animals. Knockdown of fos-1 or jun-1 blocks dilation of the distal spermathecal valve, a critical step for the entry of mature oocytes into the spermatheca for fertilization. Furthermore, fos-1 and jun-1 regulate the spermathecal-specific expression of plc-1, a gene that encodes a phospholipase C (PLC) isozyme that is rate-limiting for inositol triphosphate production and ovulation, and overexpression of PLC-1 rescues the ovulation defect in fos-1(RNAi) worms. Unlike fos-1, regulation of ovulation by jun-1 requires genetic interactions with eri-1 and lin-15B, which are involved in the RNA interference pathway and chromatin remodeling, respectively. At least two isoforms of jun-1 are coexpressed with fos-1b in the spermatheca, and different AP-1 dimers formed between these isoforms have distinct effects on the activation of a reporter gene. These findings uncover a novel role for FOS-1 and JUN-1 in the reproductive system and establish C. elegans as a model for studying AP-1 dimerization.

Reduction in ovulation or male sex phenotype increases long-term anoxia survival in a daf-16-independent manner in Caenorhabditis elegans

Identifying genotypes and phenotypes that enhance an organism's ability to survive stress is of interest. We used Caenorhabditis elegans mutants, RNA interference (RNAi), and the chemical 5-fluorodeoxyuridine (FUDR) to test the hypothesis that a reduction in progeny would increase oxygen deprivation (anoxia) survival. In the hermaphrodite gonad, germ line processes such as spermatogenesis and oogenesis can be simultaneously as well as independently disrupted by genetic mutations. We analyzed genetic mutants [glp-1(q158), glp-4(bn2ts), plc-1(rx1), ksr-1(ku68), fog-2(q71), fem-3(q20), spe-9(hc52ts), fer-15(hc15ts)] with reduced progeny production due to various reproductive defects. Furthermore, we used RNAi to inhibit the function of gene products in the RTK/Ras/MAPK signaling pathway, which is known to be involved in a variety of developmental processes including gonad function. We determined that reduced progeny production or complete sterility enhanced anoxia survival except in the case of sterile hermaphrodites [spe-9(hc52ts), fer-15(hc15ts)] undergoing oocyte maturation and ovulation as exhibited by the presence of laid unfertilized oocytes. Furthermore, the fog-2(q71) long-term anoxia survival phenotype was suppressed when oocyte maturation and ovulation were induced by mating with males that have functional or nonfunctional sperm. The mutants with a reduced progeny production survive long-term anoxia in a daf-16- and hif-1-independent manner. Finally, we determined that wild-type males were able to survive long-term anoxia in a daf-16-independent manner. Together, these results suggest that the insulin signaling pathway is not the only mechanism to survive oxygen deprivation and that altering gonad function, in particular oocyte maturation and ovulation, leads to a physiological state conducive for oxygen deprivation survival.

Phospholipase C isozymes as effectors of Ras superfamily GTPases

The physiological effects of many extracellular stimuli are initiated through receptor-promoted activation of phospholipase C and inositol lipid signaling pathways. The historical view that phospholipase C-promoted signaling primarily occurs through activation of heterotrimeric G proteins or tyrosine kinases has expanded in recent years with the realization that at least three different mammalian phospholipase C isozymes are directly activated by members of the Ras superfamily of GTPases. Thus, Ras, Rap, Rac, and Rho GTPases all specifically regulate certain phospholipase C isozymes, and insight into the physiological significance of these signaling responses is beginning to accrue. High resolution three-dimensional structures of phospholipase C isozymes also are beginning to shed light on their mechanism of activation.