Small molecule inhibitors of phospholipase C from a novel high-throughput screen

A novel micellular fluorogenic substrate for quantitating the activity of 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase gamma (PLCγ) enzymes

The activities of the phospholipase C gamma (PLCγ) 1 and 2 enzymes are essential for numerous cellular processes. Unsurprisingly, dysregulation of PLCγ1 or PLCγ2 activity is associated with multiple maladies including immune disorders, cancers, and neurodegenerative diseases. Therefore, the modulation of either of these two enzymes has been suggested as a therapeutic strategy to combat these diseases. To aid in the discovery of PLCγ family enzyme modulators that could be developed into therapeutic agents, we have synthesized a high-throughput screening-amenable micellular fluorogenic substrate called C16CF3-coumarin. Herein, the ability of PLCγ1 and PLCγ2 to enzymatically process C16CF3-coumarin was confirmed, the micellular assay conditions were optimized, and the kinetics of the reaction were determined. A proof-of-principle pilot screen of the Library of Pharmacologically Active Compounds 1280 (LOPAC1280) was performed. This new substrate allows for an additional screening methodology to identify modulators of the PLCγ family of enzymes.

Pacemaking in the lymphatic system

Lymphatic collecting vessels exhibit spontaneous phasic contractions that are critical for lymph propulsion and tissue fluid homeostasis. This rhythmic activity is driven by action potentials conducted across the lymphatic muscle cell (LMC) layer to produce entrained contractions. The contraction frequency of a lymphatic collecting vessel displays exquisite mechanosensitivity, with a dynamic range from <1 to >20 contractions per minute. A myogenic pacemaker mechanism intrinsic to the LMCs was initially postulated to account for pressure-dependent chronotropy. Further interrogation into the cellular constituents of the lymphatic vessel wall identified non-muscle cell populations that shared some characteristics with interstitial cells of Cajal, which have pacemaker functions in the gastrointestinal and lower urinary tracts, thus raising the possibility of a non-muscle cell pacemaker. However, recent genetic knockout studies in mice support LMCs and a myogenic origin of the pacemaker activity. LMCs exhibit stochastic, but pressure-sensitive, sarcoplasmic reticulum calcium release (puffs and waves) from IP3R1 receptors, which couple to the calcium-activated chloride channel Anoctamin 1, causing depolarisation. The resulting electrical activity integrates across the highly coupled lymphatic muscle electrical syncytia through connexin 45 to modulate diastolic depolarisation. However, multiple other cation channels may also contribute to the ionic pacemaking cycle. Upon reaching threshold, a voltage-gated calcium channel-dependent action potential fires, resulting in a nearly synchronous calcium global calcium flash within the LMC layer to drive an entrained contraction. This review summarizes the key ion channels potentially responsible for the pressure-dependent chronotropy of lymphatic collecting vessels and various mechanisms of IP3R1 regulation that could contribute to frequency tuning.

A novel fluorogenic reporter substrate for 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase gamma-2 (PLCγ2): Application to high-throughput screening for activators to treat Alzheimer's disease

A rare coding variant in PLCγ2 (P522R) expressed in microglia induces a mild activation of enzymatic activity when compared to wild-type. This mutation is reported to be protective against the cognitive decline associated with late-onset Alzheimer's disease (LOAD) and therefore, activation of wild-type PLCγ2 has been suggested as a potential therapeutic target for the prevention and treatment of LOAD. Additionally, PLCγ2 has been associated with other diseases such as cancer and some autoimmune disorders where mutations with much greater increases in PLCγ2 activity have been identified. Here, pharmacological inhibition may provide a therapeutic effect. In order to facilitate our investigation of the activity of PLCγ2, we developed an optimized fluorogenic substrate to monitor enzymatic activity in aqueous solution. This was accomplished by first exploring the spectral properties of various "turn-on" fluorophores. The most promising turn-on fluorophore was incorporated into a water-soluble PLCγ2 reporter substrate, which we named C8CF3-coumarin. The ability of PLCγ2 to enzymatically process C8CF3-coumarin was confirmed, and the kinetics of the reaction were determined. Reaction conditions were optimized to identify small molecule activators, and a pilot screen of the Library of Pharmacologically Active Compounds 1280 (LOPAC₁₂₈₀) was performed with the goal of identifying small molecule activators of PLCγ2. The optimized screening conditions allowed identification of potential PLCγ2 activators and inhibitors, thus demonstrating the feasibility of this approach for high-throughput screening.

PLCβ2 Promotes VEGF-Induced Vascular Permeability

BACKGROUND

Regulation of vascular permeability is critical to maintaining tissue metabolic homeostasis. VEGF (vascular endothelial growth factor) is a key stimulus of vascular permeability in acute and chronic diseases including ischemia reperfusion injury, sepsis, and cancer. Identification of novel regulators of vascular permeability would allow for the development of effective targeted therapeutics for patients with unmet medical need.

METHODS

In vitro and in vivo models of VEGFA-induced vascular permeability, pathological permeability, quantitation of intracellular calcium release and cell entry, and phosphatidylinositol 4,5-bisphosphate levels were evaluated with and without modulation of PLC (phospholipase C) β2.

RESULTS

Global knock-out of PLCβ2 in mice resulted in blockade of VEGFA-induced vascular permeability in vivo and transendothelial permeability in primary lung endothelial cells. Further work in an immortalized human microvascular cell line modulated with stable knockdown of PLCβ2 recapitulated the observations in the mouse model and primary cell assays. Additionally, loss of PLCβ2 limited both intracellular release and extracellular entry of calcium following VEGF stimulation as well as reduced basal and VEGFA-stimulated levels of phosphatidylinositol 4,5-bisphosphate compared to control cells. Finally, loss of PLCβ2 in both a hyperoxia-induced lung permeability model and a cardiac ischemia:reperfusion model resulted in improved animal outcomes when compared with wild-type controls.

CONCLUSIONS

The results implicate PLCβ2 as a key positive regulator of VEGF-induced vascular permeability through regulation of both calcium flux and phosphatidylinositol 4,5-bisphosphate levels at the cellular level. Targeting of PLCβ2 in a therapeutic setting may provide a novel approach to regulating vascular permeability in patients.

Identification of Prazosin as a Potential Flagellum Attachment Zone 1(FAZ1) Inhibitor for the Treatment of Human African Trypanosomiasis

Human African trypanosomiasis (HAT) remains a health threat to sub-Saharan Africa. The current treatments suffer from drug resistance and life-threatening side effects, making drug discovery for HAT still important. A high-throughput screening of the library of pharmaceutically active compounds identified prazosin, an α-adrenoceptor antagonist, that showed selective activity toward Trypanosoma brucei brucei. Furthermore, a series of prazosin analogues were examined, and overall, the new analogues had improved activity and selectivity. To elucidate the binding partner, a biotin-conjugated probe was synthesized, and a protein pulldown assay combined with a proteomic analysis identified the flagellum attachment zone 1 (FAZ1) filament as an interacting partner. Additionally, prazosin treatment resulted in dysfunction of the flagellum of trypanosome cells, which is indicative of a FAZ1 irregularity. We also examined the drug distribution by utilizing immunofluorescence with a designed fluorescent analogue that showed partial colocalization with FAZ1. With the activity of the prazosin analogues, a structure-activity relationship (SAR) was summarized for future lead optimization. Our findings provide a new group of FAZ1 inhibitors as novel antitrypanosomal agents.

Recent advances in understanding the molecular role of phosphoinositide-specific phospholipase C gamma 1 as an emerging onco-driver and novel therapeutic target in human carcinogenesis

Phosphoinositide metabolism is crucial intracellular signaling system that regulates a plethora of biological functions including mitogenesis, cell proliferation and division. Phospholipase C gamma 1 (PLCγ1) which belongs to phosphoinositide-specific phospholipase C (PLC) family, is activated by many extracellular stimuli including hormones, neurotransmitters, growth factors and modulates several cellular and physiological functions necessary for tumorigenesis such as cell survival, migration, invasion and angiogenesis by generating inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DAG) via hydrolysis of phosphatidylinositol 4,5-biphosphate (PIP2). Cancer remains as a leading cause of global mortality and aberrant expression and regulation of PLCγ1 is linked to a plethora of deadly human cancers including carcinomas of the breast, lung, pancreas, stomach, prostate and ovary. Although PLCγ1 cross-talks with many onco-drivers and signaling circuits including PI3K, AKT, HIF1-α and RAF/MEK/ERK cascade, its precise role in carcinogenesis is not completely understood. This review comprehensively discussed the status quo of this ubiquitously expressed phospholipase as a tumor driver and highlighted its significance as a novel therapeutic target in cancer. Furthermore, we have highlighted the significance of somatic driver mutations in PLCG1 gene and molecular roles of PLCγ1 in several major human cancers, a knowledgebase that can be utilized to develop novel, isoform-specific small molecule inhibitors of PLCγ1.

Update on Calcium Signaling in Cystic Fibrosis Lung Disease

Cystic fibrosis (CF) is an autosomal recessive disorder characterized by mutations in the cystic fibrosis transmembrane conductance regulator gene, which causes multifunctional defects that preferentially affect the airways. Abnormal viscosity of mucus secretions, persistent pathogen infections, hyperinflammation, and lung tissue damage compose the classical pathological manifestation referred to as CF lung disease. Among the multifunctional defects associated with defective CFTR, increasing evidence supports the relevant role of perturbed calcium (Ca²⁺) signaling in the pathophysiology of CF lung disease. The Ca²⁺ ion is a critical player in cell functioning and survival. Its intracellular homeostasis is maintained by a fine balance between channels, transporters, and exchangers, mediating the influx and efflux of the ion across the plasma membrane and the intracellular organelles. An abnormal Ca²⁺ profile has been observed in CF cells, including airway epithelial and immune cells, with heavy repercussions on cell function, viability, and susceptibility to pathogens, contributing to proinflammatory overstimulation, organelle dysfunction, oxidative stress, and excessive cytokines release in CF lung. This review discusses the role of Ca²⁺ signaling in CF and how its dysregulation in airway epithelial and immune cells contributes to hyperinflammation in the CF lung. Finally, we provide an outlook on the therapeutic options that target the Ca²⁺ signaling to treat the CF lung disease.

Potential therapeutic targets shared between leishmaniasis and cancer

The association of leishmaniasis and malignancies in human and animal models has been highlighted in recent years. The misdiagnosis of coexistence of leishmaniasis and cancer and the use of common drugs in the treatment of such diseases prompt us to further survey the molecular biology of Leishmania parasites and cancer cells. The information regarding common expressed proteins, as possible therapeutic targets, in Leishmania parasites and cancer cells is scarce. Therefore, the current study reviews proteins, and investigates the regulation and functions of several key proteins in Leishmania parasites and cancer cells. The up- and down-regulations of such proteins were mostly related to survival, development, pathogenicity, metabolic pathways and vital signalling in Leishmania parasites and cancer cells. The presence of common expressed proteins in Leishmania parasites and cancer cells reveals valuable information regarding the possible shared mechanisms of pathogenicity and opportunities for therapeutic targeting in leishmaniasis and cancers in the future.

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.

A High-Throughput Assay to Identify Allosteric Inhibitors of the PLC-γ Isozymes Operating at Membranes

The two phospholipase C-γ (PLC-γ) isozymes are major signaling hubs and emerging therapeutic targets for various diseases, yet there are no selective inhibitors for these enzymes. We have developed a high-throughput, liposome-based assay that features XY-69, a fluorogenic, membrane-associated reporter for mammalian PLC isozymes. The assay was validated using a pilot screen of the Library of Pharmacologically Active Compounds 1280 (LOPAC₁₂₈₀) in 384-well format; it is highly reproducible and has the potential to capture both orthosteric and allosteric inhibitors. Selected hit compounds were confirmed with secondary assays, and further profiling led to the interesting discovery that adenosine triphosphate potently inhibits the PLC-γ isozymes through noncompetitive inhibition, raising the intriguing possibility of endogenous, nucleotide-dependent regulation of these phospholipases. These results highlight the merit of the assay platform for large scale screening of chemical libraries to identify allosteric modulators of the PLC-γ isozymes as chemical probes and for drug discovery.

Fgd5 is a Rac1-specific Rho GEF that is selectively inhibited by aurintricarboxylic acid

Rho proteins are signalling molecules that control cellular dynamics, movement and morphological changes. They are activated by Rho guanine-nucleotide exchange factors (Rho GEFs) that transduce upstream signals into Rho-mediated activation of downstream processes. Fgd5 is a Rho GEF involved in angiogenesis and its target Rho protein for this process has been linked to Cdc42 activation. Here, we examined the function of purified Fgd5, specifically, which Rho proteins it activates and pinpoint the structural domains required for enzymatic activity. Using a GEF enzyme assay, we found that purified Fgd5 showed preferential activation of Rac1 and direct binding of Rac1 in pull-down and co-immunoprecipitation assays. Structural comparisons showed that the Fgd5 DH domain is highly similar to the Rac1 GEF, TrioN, supporting a role for Fgd5 as a Rac1 GEF. Compounds that bind to purified Fgd5 DH-PH protein were identified by screening a small molecule library via surface plasmon resonance. The effects of eleven ligands were further examined for their ability to inhibit the Fgd5 GEF enzymatic activity and Rac1 interaction. From these studies, we found that the compound aurintricarboxylic acid, and to a lesser extent mitoxantrone dihydrochloride, inhibited both Fgd5 GEF activation of Rac1 and their interaction. Aurintricarboxylic acid had no effect on the activity or binding of the Rac1 GEF, TrioN, thus demonstrating the feasibility of selectively disrupting Rho GEF activators. Abbreviations: a.a.: amino acid; ATA: aurintricarboxylic acid; DH: Dbl homology; DOCK: dictator of cytokinesis; Fgd: faciogenital dysplasia; GEF: guanine-nucleotide exchange factor; GST: glutathione S-transferase; LOPAC: library of pharmacologically active compounds; PH: pleckstrin homology; PDB: protein data bank; s.e.m.: standard error of the mean; SPR: surface plasmon resonance.

PLCB3 Loss of Function Reduces Pseudomonas aeruginosa-Dependent IL-8 Release in Cystic Fibrosis

The lungs of patients with cystic fibrosis (CF) are characterized by an exaggerated inflammation driven by secretion of IL-8 from bronchial epithelial cells and worsened by Pseudomonas aeruginosa infection. To identify novel antiinflammatory molecular targets, we previously performed a genetic study of 135 genes of the immune response, which identified the c.2534C>T (p.S845L) variant of phospholipase C-β3 (PLCB3) as being significantly associated with mild progression of pulmonary disease. Silencing PLCB3 revealed that it potentiates the Toll-like receptor's inflammatory signaling cascade originating from CF bronchial epithelial cells. In the present study, we investigated the role of the PLCB3-S845L variant together with two synthetic mutants paradigmatic of impaired catalytic activity or lacking functional activation in CF bronchial epithelial cells. In experiments in which cells were exposed to P. aeruginosa, the supernatant of mucopurulent material from the airways of patients with CF or different agonists revealed that PLCB3-S845L has defects of 1) agonist-induced Ca²⁺ release from endoplasmic reticulum and rise of Ca²⁺ concentration, 2) activation of conventional protein kinase C isoform β, and 3) induction of IL-8 release. These results, besides identifying S845L as a loss-of-function variant, strengthen the importance of targeting PLCB3 to mitigate the CF inflammatory response in bronchial epithelial cells without blunting the immune response.

7-Ketocholesterol impairs phagocytosis and efferocytosis via dysregulation of phosphatidylinositol 4,5-bisphosphate

The plasma membrane is inhomogeneously organized containing both highly ordered and disordered nanodomains. 7-Ketocholesterol (7KC), an oxysterol formed from the nonenzymatic oxidation of cholesterol, is a potent disruptor of membrane order. Importantly, 7KC is a component of oxidized low-density lipoprotein and accumulates in macrophage and foam cells found in arterial plaques. Using a murine macrophage cell line, J774, we report that both IgG-mediated and phosphatidylserine-mediated phagocytic pathways are inhibited by the accumulation of 7KC. Examination of the well-studied Fcγ receptor pathway revealed that the cell surface receptor abundance and ligand binding are unaltered while downstream signaling and activation of spleen tyrosine kinase is not affected. However, while the recruitment of phospholipase Cγ1 was unaffected its apparent enzymatic activity was compromised resulting in sustained phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂ ] levels and polymerized actin at the base of the phagocytic cup. Additionally, we found that 7KC prevented the activation of PLCβ downstream of the P2Y₆ G-protein coupled receptor and that 7KC impaired PLCγ activity in response to a direct elevation of cytosolic calcium induced by ionomycin. Finally, we demonstrate that 7KC partly attenuates the activity of rapamycin recruitable constitutively active PLCβ3. Together, our results demonstrate that the accumulation of 7KC impairs macrophage function by altering PtdIns(4,5)P₂ catabolism and, thus, impairing actin depolymerization required for the completion of phagocytosis.

The inositol pyrophosphate pathway in health and diseases

Inositol pyrophosphates (IPPs) are present in organisms ranging from plants, slime moulds and fungi to mammals. Distinct classes of kinases generate different forms of energetic diphosphate-containing IPPs from inositol phosphates (IPs). Conversely, polyphosphate phosphohydrolase enzymes dephosphorylate IPPs to regenerate the respective IPs. IPPs and/or their metabolizing enzymes regulate various cell biological processes by modulating many proteins via diverse mechanisms. In the last decade, extensive research has been conducted in mammalian systems, particularly in knockout mouse models of relevant enzymes. Results obtained from these studies suggest impacts of the IPP pathway on organ development, especially of brain and testis. Conversely, deletion of specific enzymes in the pathway protects mice from various diseases such as diet-induced obesity (DIO), type-2 diabetes (T2D), fatty liver, bacterial infection, thromboembolism, cancer metastasis and aging. Furthermore, pharmacological inhibition of the same class of enzymes in mice validates the therapeutic importance of this pathway in cardio-metabolic diseases. This review critically analyses these findings and summarizes the significance of the IPP pathway in mammalian health and diseases. It also evaluates benefits and risks of targeting this pathway in disease therapies. Finally, future directions of mammalian IPP research are discussed.

Peptide microarray profiling identifies phospholipase C gamma 1 (PLC-γ1) as a potential target for t(8;21) AML

The t(8;21) (q22;q22) chromosomal translocation is one of the most frequent genetic alterations in acute myeloid leukemia (AML) which has a need for improved therapeutic strategies. We found PLC-γ1 as one of the highest phosphorylated peptides in t(8;21) AML samples compared to NBM or CN-AML in our previous peptide microarray. PLC-γ1 is known to play a role in cancer progression, however, the impact of PLC-γ1 in AML is currently unknown. Therefore, we aimed to study the functional role of PLC-γ1 by investigating the cellular growth, survival and its underlying mechanism in t(8;21) AML.

In this study, PLC-γ1 expression was significantly higher in t(8;21) AML compared to other karyotypes. The PLC-γ1 protein expression was suppressed in AML1-ETO knock down cells indicating that it might induce kasumi-1 cell death. ShRNA-mediated PLC-γ1 knockdown in kasumi-1 cells significantly blocked cell growth, induced apoptosis and cell cycle arrest which was explained by the increased activation of apoptotic related and cell cycle regulatory protein expressions. Gene expression array analysis showed the up-regulation of apoptotic and DNA damage response genes together with the downregulation of cell growth, proliferation and differentiation genes in the PLC-γ1 suppressed kasumi-1 cells, consistent with the observed phenotypic effects. Importantly, PLC-γ1 suppressed kasumi-1 cells showed higher chemosensitivity to the chemotherapeutic drug treatments and lower cell proliferation upon hypoxic stress.

Taken together, these in vitro finding strongly support an important role for PLC-γ1 in the survival of t(8;21) AML mimicking kasumi-1 cells and identify PLC-γ1 as a potential therapeutic target for t(8;21) AML treatment.

Phosphoinositide-3-Kinase Is the Primary Mediator of Phosphoinositide-Dependent Inhibition in Mammalian Olfactory Receptor Neurons

Odorants inhibit as well as excite primary olfactory receptor neurons (ORNs) in many animal species. Growing evidence suggests that inhibition of mammalian ORNs is mediated by phosphoinositide (PI) signaling through activation of phosphoinositide 3-kinase (PI3K), and that canonical adenylyl cyclase III signaling and PI3K signaling interact to provide the basis for ligand-induced selective signaling. As PI3K is known to act in concert with phospholipase C (PLC) in some cellular systems, the question arises as to whether they work together to mediate inhibitory transduction in mammalian ORNs. The present study is designed to test this hypothesis. While we establish that multiple PLC isoforms are expressed in the transduction zone of rat ORNs, that odorants can activate PLC in ORNs in situ, and that pharmacological blockade of PLC enhances the excitatory response to an odorant mixture in some ORNs in conjunction with PI3K blockade, we find that by itself PLC does not account for an inhibitory response. We conclude that PLC does not make a measurable independent contribution to odor-evoked inhibition, and that PI3K is the primary mediator of PI-dependent inhibition in mammalian ORNs.

Charge Shielding of PIP2 by Cations Regulates Enzyme Activity of Phospholipase C

Hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) of the plasma membrane by phospholipase C (PLC) generates two critical second messengers, inositol-1,4,5-trisphosphate and diacylglycerol. For the enzymatic reaction, PIP2 binds to positively charged amino acids in the pleckstrin homology domain of PLC. Here we tested the hypothesis that positively charged divalent and multivalent cations accumulate around the negatively charged PIP2, a process called electrostatic charge shielding, and therefore inhibit electrostatic PIP2-PLC interaction. This charge shielding of PIP2 was measured quantitatively with an in vitro enzyme assay using WH-15, a PIP2 analog, and various recombinant PLC proteins (β1, γ1, and δ1). Reduction of PLC activity by divalent cations, polyamines, and neomycin was well described by a theoretical model considering accumulation of cations around PIP2 via their electrostatic interaction and chemical binding. Finally, the charge shielding of PIP2 was also observed in live cells. Perfusion of the cations into cells via patch clamp pipette reduced PIP2 hydrolysis by PLC as triggered by M1 muscarinic receptors with a potency order of Mg2+ < spermine4+ < neomycin6+. Accumulation of divalent cations into cells through divalent-permeable TRPM7 channel had the same effect. Altogether our results suggest that Mg2+ and polyamines modulate the activity of PLCs by controlling the amount of free PIP2 available for the enzymes and that highly charged biomolecules can be inactivated by counterions electrostatically.

Insights into the inhibitory mechanism of triazole-based small molecules on phosphatidylinositol-4,5-bisphosphate binding pleckstrin homology domain

Background

Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] is an important regulator of several cellular processes and a precursor for other second messengers which are involved in cell signaling pathways. Signaling proteins preferably interact with PI(4,5)P₂ through its pleckstrin homology (PH) domain. Efforts are underway to design small molecule-based antagonist, which can specifically inhibit the PI(4,5)P₂/PH-domain interaction to establish an alternate strategy for the development of drug(s) for phosphoinositide signaling pathways.

Methods

Surface plasmon resonance, molecular docking, circular dichroism, competitive Förster resonance energy transfer, isothermal titration calorimetric analyses and liposome pull down assay were used.

Results

In this study, we employed 1,2,3-triazol-4-yl methanol containing small molecule (CIPs) as antagonists for PI(4,5)P₂/PH-domain interaction and determined their inhibitory effect by using competitive-surface plasmon resonance analysis (IC₅₀ ranges from 53 to 159 nM for PI(4,5)P₂/PLCδ1-PH domain binding assay). We also used phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P₃], phosphatidylinositol 3,4-bisphosphate [PI(3,4)P₂], PI(4,5)P₂ specific PH-domains to determine binding selectivity of the compounds. Various physicochemical analyses showed that the compounds have weak affect on fluidity of the model membrane but, strongly interact with the phospholipase C δ1 (PLCδ1)-PH domains. The 1,2,3-triazol-4-yl methanol moiety and nitro group of the compounds are essential for their exothermic interaction with the PH-domains. Potent compound can efficiently displace PLCδ1-PH domain from plasma membrane to cytosol in A549 cells.

Conclusions

Overall, our studies demonstrate that these compounds interact with the PIP-binding PH-domains and inhibit their membrane recruitment.

General significance

These results suggest specific but differential binding of these compounds to the PLCδ1-PH domain and emphasize the role of their structural differences in binding parameters. These triazole-based compounds could be directly used/further developed as potential inhibitor for PH domain-dependent enzyme activity.

Dysfunction of phospholipase Cγ in immune disorders and cancer

The surge in genetic and genomic investigations over the past 5 years has resulted in many discoveries of causative variants relevant to disease pathophysiology. Although phospholipase C (PLC) enzymes have long been recognized as important components in intracellular signal transmission, it is only recently that this approach highlighted their role in disease development through gain-of-function mutations. In this review we describe the new findings that link the PLCγ family to immune disorders and cancer, and illustrate further efforts to elucidate the molecular mechanisms that underpin their dysfunction.

Phospholipase cε, an effector of ras and rap small GTPases, is required for airway inflammatory response in a mouse model of bronchial asthma

Background

Phospholipase Cε (PLCε) is an effector of Ras and Rap small GTPases and expressed in non-immune cells. It is well established that PLCε plays an important role in skin inflammation, such as that elicited by phorbol ester painting or ultraviolet irradiation and contact dermatitis that is mediated by T helper (Th) 1 cells, through upregulating inflammatory cytokine production by keratinocytes and dermal fibroblasts. However, little is known about whether PLCε is involved in regulation of inflammation in the respiratory system, such as Th2-cells-mediated allergic asthma.

Methods

We prepared a mouse model of allergic asthma using PLCε^+/+ mice and PLCε^ΔX/ΔX mutant mice in which PLCε was catalytically-inactive. Mice with different PLCε genotypes were immunized with ovalbumin (OVA) followed by the challenge with an OVA-containing aerosol to induce asthmatic response, which was assessed by analyzing airway hyper-responsiveness, bronchoalveolar lavage fluids, inflammatory cytokine levels, and OVA-specific immunoglobulin (Ig) levels. Effects of PLCε genotype on cytokine production were also examined with primary-cultured bronchial epithelial cells.

Results

After OVA challenge, the OVA-immunized PLCε^ΔX/ΔX mice exhibited substantially attenuated airway hyper-responsiveness and broncial inflammation, which were accompanied by reduced Th2 cytokine content in the bronchoalveolar lavage fluids. In contrast, the serum levels of OVA-specific IgGs and IgE were not affected by the PLCε genotype, suggesting that sensitization was PLCε-independent. In the challenged mice, PLCε deficiency reduced proinflammatory cytokine production in the bronchial epithelial cells. Primary-cultured bronchial epithelial cells prepared from PLCε^ΔX/ΔX mice showed attenuated pro-inflammatory cytokine production when stimulated with tumor necrosis factor-α, suggesting that reduced cytokine production in PLCε^ΔX/ΔX mice was due to cell-autonomous effect of PLCε deficiency.

Conclusions

PLCε plays an important role in the pathogenesis of bronchial asthma through upregulating inflammatory cytokine production by the bronchial epithelial cells.

Chemical modulation of glycerolipid signaling and metabolic pathways

Thirty years ago, glycerolipids captured the attention of biochemical researchers as novel cellular signaling entities. We now recognize that these biomolecules occupy signaling nodes critical to a number of physiological and pathological processes. Thus, glycerolipid-metabolizing enzymes present attractive targets for new therapies. A number of fields-ranging from neuroscience and cancer to diabetes and obesity-have elucidated the signaling properties of glycerolipids. The biochemical literature teems with newly emerging small molecule inhibitors capable of manipulating glycerolipid metabolism and signaling. This ever-expanding pool of chemical modulators appears daunting to those interested in exploiting glycerolipid-signaling pathways in their model system of choice. This review distills the current body of literature surrounding glycerolipid metabolism into a more approachable format, facilitating the application of small molecule inhibitors to novel systems. This article is part of a Special Issue entitled Tools to study lipid functions.

Role of phospholipase C in cell invasion and metastasis

Phospholipases are enzymes that use phospholipids as substrate and are classified in three major classes A, C and D based on the reaction they catalyse. Phosphatidylinositol-specific Phospholipase C enzymes utilize phosphatidylinositol 4,5-bisphosphate as substrate and cleave the bond between the glycerol and the phosphate to produce important second messenger such as inositol trisphosphate and diacylglycerol. The Phospholipase C members are the most well-known phospholipases for their role in lipid signalling and cell proliferation and comprise 13 isoforms classified in 6 distinct sub-families. In particular, signalling activated by Phospholipase C γ, mostly activated by receptor and non-receptor tyrosine kinases, is well characterized in different cell systems. Increasing evidence suggest that Phospholipase C γ plays a key role in cell migration and invasion. Because of its role in cell growth and invasion, aberrant Phospholipase C γ signalling can contribute to carcinogenesis. A major challenge facing investigators who seek to target Phospholipase C γ directly is the fact that it is considered an "undruggable" protein. Indeed, isoform specificity and toxicity represents a big hurdle in the development of Phospholipase C γ small molecule inhibitors. Therefore, a future development in the field could be the identification of interacting partners as therapeutic targets that could be more druggable than Phospholipase C γ.

Structural insights into phospholipase C-β function

Phospholipase C (PLC) enzymes convert phosphatidylinositol-4,5-bisphosphate into the second messengers diacylglycerol and inositol-1,4,5-triphosphate. The production of these molecules promotes the release of intracellular calcium and activation of protein kinase C, which results in profound cellular changes. The PLCβ subfamily is of particular interest given its prominent role in cardiovascular and neuronal signaling and its regulation by G protein-coupled receptors, as PLCβ is the canonical downstream target of the heterotrimeric G protein Gαq. However, this is not the only mechanism regulating PLCβ activity. Extensive structural and biochemical evidence has revealed regulatory roles for autoinhibitory elements within PLCβ, Gβγ, small molecular weight G proteins, and the lipid membrane itself. Such complex regulation highlights the central role that this enzyme plays in cell signaling. A better understanding of the molecular mechanisms underlying the control of its activity will greatly facilitate the search for selective small molecule modulators of PLCβ.

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.