Mammalian phospholipase C

Arachidonic acid hyperpolarizes mesenchymal stromal cells from the human adipose tissue by stimulating TREK1 K+ channels

The current knowledge of electrogenesis in mesenchymal stromal cells (MSCs) remains scarce. Earlier, we demonstrated that in MSCs from the human adipose tissue, transduction of certain agonists involved the phosphoinositide cascade. Its pivotal effector PLC generates DAG that can regulate ion channels directly or via its derivatives, including arachidonic acid (AA). Here we showed that AA strongly hyperpolarized MSCs by stimulating instantly activating, outwardly rectifying TEA-insensitive K⁺ channels. Among AA-regulated K⁺ channels, K2P channels from the TREK subfamily appeared to be an appropriate target. The expression of K2P channels in MSCs was verified by RT-PCR, which revealed TWIK-1, TREK-1, and TASK-5 transcripts. The TREK-1 inhibitor spadin antagonized the electrogenic action of AA, which was simulated by the channel activator BL 1249. This functional evidence suggested that TREK-1 channels mediated AA-dependent hyperpolarization of MSCs. Being mostly silent at rest, TREK-1 negligibly contributed to the “background” K⁺ current. The dramatic stimulation of TREK-1 channels by AA indicates their involvement in AA-dependent signaling in MSCs.

The regulation of insulin secretion via phosphoinositide-specific phospholipase Cβ signaling

Phospholipase Cβ (PLCβ) is a membrane-associated enzyme activated by membrane receptors, especially G-protein coupled receptors (GPCRs). It propagates intracellular signaling by mediating phospholipid metabolism and generating key second messengers, such as inositol triphosphate and diacylglycerol, leading to intracellular Ca²⁺ mobilization and activation of kinases, such as protein kinases C. In pancreatic β-cells, PLCβ-mediated signaling activated by various factors, such as free fatty acids and neuronal and hormonal ligands, has been confirmed as being involved in the regulation of insulin secretion, and PLCβs have been regarded as essential mediators for augmenting insulin secretion. In this review, we describe the physiological function of PLCβs in the regulation of glucose-stimulated insulin secretion and discuss emerging data on GPCR/PLCβ signaling that is being developed as a target for the treatment of diabetes mellitus.

Targeting Cellular Trafficking of Fibroblast Growth Factor Receptors as a Strategy for Selective Cancer Treatment

Fibroblast growth factor receptors (FGFRs) in response to fibroblast growth factors (FGFs) transmit signals across the cell membrane, regulating important cellular processes, like differentiation, division, motility, and death. The aberrant activity of FGFRs is often observed in various diseases, especially in cancer. The uncontrolled FGFRs' function may result from their overproduction, activating mutations, or generation of FGFRs' fusion proteins. Besides their typical subcellular localization on the cell surface, FGFRs are often found inside the cells, in the nucleus and mitochondria. The intracellular pool of FGFRs utilizes different mechanisms to facilitate cancer cell survival and expansion. In this review, we summarize the current stage of knowledge about the role of FGFRs in oncogenic processes. We focused on the mechanisms of FGFRs' cellular trafficking-internalization, nuclear translocation, and mitochondrial targeting, as well as their role in carcinogenesis. The subcellular sorting of FGFRs constitutes an attractive target for anti-cancer therapies. The blocking of FGFRs' nuclear and mitochondrial translocation can lead to the inhibition of cancer invasion. Moreover, the endocytosis of FGFRs can serve as a tool for the efficient and highly selective delivery of drugs into cancer cells overproducing these receptors. Here, we provide up to date examples how the cellular sorting of FGFRs can be hijacked for selective cancer treatment.

Role of a Small Molecule in the Modulation of Cell Death Signal Transduction Pathways

Inflammasomes activate caspase-1 in response to molecular signals from pathogens and other dangerous stimuli as a part of the innate immune response. A previous study discovered a small-molecule, 4-fluoro- N'-[1-(2-pyridinyl)ethylidene]benzohydrazide, which we named DN1, that reduces the cytotoxicity of anthrax lethal toxin (LT). We determined that DN1 protected cells irrespectively of LT concentration and reduced the pathogenicity of an additional bacterial exotoxin and several viruses. Using the LT cytotoxicity pathway, we show that DN1 does not prevent LT internalization and catalytic activity or caspase-1 activation. Moreover, DN1 does not affect the proteolytic activity of host cathepsin B, which facilitates the cytoplasmic entry of toxins. PubChem Bioactivities lists two G protein-coupled receptors (GPCR), type-1 angiotensin II receptor and apelin receptor, as targets of DN1. The inhibition of phosphatidylinositol 3-kinase, phospholipase C, and protein kinase B, which are downstream of GPCR signaling, synergized with DN1 in protecting cells from LT. We hypothesize that DN1-mediated antagonism of GPCRs modulates signal transduction pathways to induce a cellular state that reduces LT-induced pyroptosis downstream of caspase-1 activation. DN1 also reduced the susceptibility of Drosophila melanogaster to toxin-associated bacterial infections. Future experiments will aim to further characterize how DN1 modulates signal transduction pathways to inhibit pyroptotic cell death in LT-sensitive macrophages. DN1 represents a novel chemical probe to investigate host cellular mechanisms that mediate cell death in response to pathogenic agents.

Direct observation of conformational dynamics of the PH domain in phospholipases Cϵ and β may contribute to subfamily-specific roles in regulation

Phospholipase C (PLC) enzymes produce second messengers that increase the intracellular Ca2+ concentration and activate protein kinase C (PKC). These enzymes also share a highly conserved arrangement of core domains. However, the contributions of the individual domains to regulation are poorly understood, particularly in isoforms lacking high-resolution information, such as PLCϵ. Here, we used small-angle X-ray scattering (SAXS), EM, and functional assays to gain insights into the molecular architecture of PLCϵ, revealing that its PH domain is conformationally dynamic and essential for activity. We further demonstrate that the PH domain of PLCβ exhibits similar dynamics in solution that are substantially different from its conformation observed in multiple previously reported crystal structures. We propose that this conformational heterogeneity contributes to subfamily-specific differences in activity and regulation by extracellular signals.

Atypical activation of the G protein Gαq by the oncogenic mutation Q209P

The causative role of G protein-coupled receptor (GPCR) pathway mutations in uveal melanoma (UM) has been well-established. Nearly all UMs bear an activating mutation in a GPCR pathway mediated by G proteins of the G_q/11 family, driving tumor initiation and possibly metastatic progression. Thus, targeting this pathway holds therapeutic promise for managing UM. However, direct targeting of oncogenic Gα_q/11 mutants, present in ∼90% of UMs, is complicated by the belief that these mutants structurally resemble active Gα_q/11 WT. This notion is solidly founded on previous studies characterizing Gα mutants in which a conserved catalytic glutamine (Gln-209 in Gα_q) is replaced by leucine, which leads to GTPase function deficiency and constitutive activation. Whereas Q209L accounts for approximately half of GNAQ mutations in UM, Q209P is as frequent as Q209L and also promotes oncogenesis, but has not been characterized at the molecular level. Here, we characterized the biochemical and signaling properties of Gα_q Q209P and found that it is also GTPase-deficient and activates downstream signaling as efficiently as Gα_q Q209L. However, Gα_q Q209P had distinct molecular and functional features, including in the switch II region of Gα_q Q209P, which adopted a conformation different from that of Gα_q Q209L or active WT Gα_q, resulting in altered binding to effectors, Gβγ, and regulators of G-protein signaling (RGS) proteins. Our findings reveal that the molecular properties of Gα_q Q209P are fundamentally different from those in other active Gα_q proteins and could be leveraged as a specific vulnerability for the ∼20% of UMs bearing this mutation.

Distinct Roles of Small GTPases Rac1 and Rac2 in Histamine H4 Receptor-Mediated Chemotaxis of Mast Cells

Histamine induces chemotaxis of mast cells through the H4 receptor. However, little is known about the precise intracellular signaling pathway that mediates this process. In this study, we identified small GTPases Rac1 and Rac2 as intracellular binding partners of the H4 receptor and characterized their roles in H4 receptor signaling. We showed that histamine induced Rac GTPase activation via the H4 receptor. A Rac inhibitor NSC23766 attenuated chemotaxis of mast cells toward histamine, as well as histamine-induced calcium mobilization and extracellular signal-regulated kinase (ERK) activation. Histamine-induced migration of mast cells was also sensitive to PD98059, an inhibitor of the mitogen-activated protein kinase kinase, indicating that the Rac-ERK pathway was involved in chemotaxis through the H4 receptor. Inhibition of phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) by LY294002 suppressed the histamine-induced chemotaxis and activation of Rac GTPases, suggesting that PI3K regulates chemotaxis upstream of Rac activation. Specific knockdown of Rac1 and Rac2 by short-hairpin RNA revealed that both Rac GTPases are necessary for histamine-induced migration. Downregulation of Rac1 and Rac2 led to attenuated response in calcium mobilization and ERK activation, respectively. These observations suggested that Rac1 and Rac2 have distinct and essential roles in intracellular signaling downstream of H4 receptor-PI3K in histamine-induced chemotaxis of mast cells.

Targeting G protein-coupled receptor signalling by blocking G proteins

G protein-coupled receptors (GPCRs) are the largest class of drug targets, largely owing to their druggability, diversity and physiological efficacy. Many drugs selectively target specific subtypes of GPCRs, but high specificity for individual GPCRs may not be desirable in complex multifactorial disease states in which multiple receptors may be involved. One approach is to target G protein subunits rather than the GPCRs directly. This approach has the potential to achieve broad efficacy by blocking pathways shared by multiple GPCRs. Additionally, because many GPCRs couple to multiple G protein signalling pathways, blocking specific G protein subunits can 'bias' GPCR signals by inhibiting only a subset of these signals. Molecules that target G protein α or βγ-subunits have been developed and show strong efficacy in multiple preclinical disease models and biased inhibition of G protein signalling. In this Review, we discuss the development and characterization of G protein α and βγ-subunit ligands and the preclinical evidence that this exciting new approach has potential for therapeutic efficacy in a number of indications, such as pain, thrombosis, asthma and heart failure.

Of local translation control and lipid signaling in neurons

Fine-tuned regulation of new proteins synthesis is key to the fast adaptation of cells to their changing environment and their response to external cues. Protein synthesis regulation is particularly refined and important in the case of highly polarized cells like neurons where translation occurs in the subcellular dendritic compartment to produce long-lasting changes that enable the formation, strengthening and weakening of inter-neuronal connection, constituting synaptic plasticity. The changes in local synaptic proteome of neurons underlie several aspects of synaptic plasticity and new protein synthesis is necessary for long-term memory formation. Details of how neuronal translation is locally controlled only start to be unraveled. A generally accepted view is that mRNAs are transported in a repressed state and are translated locally upon externally cued triggering signaling cascades that derepress or activate translation machinery at specific sites. Some important yet poorly considered intermediates in these cascades of events are signaling lipids such as diacylglycerol and its balancing partner phosphatidic acid. A link between these signaling lipids and the most common inherited cause of intellectual disability, Fragile X syndrome, is emphasizing the important role of these secondary messages in synaptically controlled translation.

Phosphatidylinositol 4-phosphate is a major source of GPCR-stimulated phosphoinositide production

Phospholipase C (PLC) enzymes hydrolyze the plasma membrane (PM) lipid phosphatidylinositol 4,5-bisphosphate (PI4,5P₂) to generate the second messengers inositol trisphosphate (IP₃) and diacylglycerol (DAG) in response to receptor activation in almost all mammalian cells. We previously found that stimulation of G protein-coupled receptors (GPCRs) in cardiac cells leads to the PLC-dependent hydrolysis of phosphatidylinositol 4-phosphate (PI4P) at the Golgi, a process required for the activation of nuclear protein kinase D (PKD) during cardiac hypertrophy. We hypothesized that GPCR-stimulated PLC activation leading to direct PI4P hydrolysis may be a general mechanism for DAG production. We measured GPCR activation-dependent changes in PM and Golgi PI4P pools in various cells using GFP-based detection of PI4P. Stimulation with various agonists caused a time-dependent reduction in PI4P-associated, but not PI4,5P₂-associated, fluorescence at the Golgi and PM. Targeted depletion of PI4,5P₂ from the PM before GPCR stimulation had no effect on the depletion of PM or Golgi PI4P, total inositol phosphate (IP) production, or PKD activation. In contrast, acute depletion of PI4P specifically at the PM completely blocked the GPCR-dependent production of IPs and activation of PKD but did not change the abundance of PI4,5P₂ Acute depletion of Golgi PI4P had no effect on these processes. These data suggest that most of the PM PI4,5P₂ pool is not involved in GPCR-stimulated phosphoinositide hydrolysis and that PI4P at the PM is responsible for the bulk of receptor-stimulated phosphoinositide hydrolysis and DAG production.

Kv12.1 channels are not sensitive to GqPCR-triggered activation of phospholipase Cβ

K_v12.1 K⁺ channels are expressed in several brain areas, but no physiological function could be attributed to these subunits so far. As genetically-modified animal models are not available, identification of native K_v12.1 currents must rely on characterization of distinct channel properties. Recently, it was shown in Xenopus laevis oocytes that K_v12.1 channels were modulated by membrane PI(4,5)P₂. However, it is not known whether these channels are also sensitive to physiologically-relevant PI(4,5)P₂ dynamics. We thus studied whether K_v12.1 channels were modulated by activation of phospholipase C β (PLCβ) and found that they were insensitive to receptor-triggered depletion of PI(4,5)P₂. Thus, K_v12.1 channels add to the growing list of K⁺ channels that are insensitive to PLCβ signaling, although modulated by PI(4,5)P₂ in Xenopus laevis oocytes.

The N-terminal homology (ENTH) domain of Epsin 1 is a sensitive reporter of physiological PI(4,5)P2 dynamics

Phospholipase Cβ (PLCβ)-induced depletion of phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P₂) transduces a plethora of signals into cellular responses. Importance and diversity of PI(4,5)P₂-dependent processes led to strong need for biosensors of physiological PI(4,5)P₂ dynamics applicable in live-cell experiments. Membrane PI(4,5)P₂ can be monitored with fluorescently-labelled phosphoinositide (PI) binding domains that associate to the membrane depending on PI(4,5)P₂ levels. The pleckstrin homology domain of PLCδ1 (PLCδ1-PH) and the C-terminus of tubby protein (tubby_CT) are two such sensors widely used to study PI(4,5)P₂ signaling. However, certain limitations apply to both: PLCδ1-PH binds cytoplasmic inositol-1,4,5-trisphosphate (IP₃) produced from PI(4,5)P₂ through PLCβ, and tubby_CT responses do not faithfully report on PLCβ-dependent PI(4,5)P₂ dynamics. In searching for an improved biosensor, we fused N-terminal homology domain of Epsin1 (ENTH) to GFP and examined use of this construct as genetically-encoded biosensor for PI(4,5)P₂ dynamics in living cells. We utilized recombinant tools to manipulate PI or G_q protein-coupled receptors (G_qPCR) to stimulate PLCβ signaling and characterized PI binding properties of ENTH-GFP with total internal reflection (TIRF) and confocal microscopy. ENTH-GFP specifically recognized membrane PI(4,5)P₂ without interacting with IP₃, as demonstrated by dialysis of cells with the messenger through a patch pipette. Utilizing Ci-VSP to titrate PI(4,5)P₂ levels, we found that ENTH-GFP had low PI(4,5)P₂ affinity. Accordingly, ENTH-GFP was highly sensitive to PLCβ-dependent PI(4,5)P₂ depletion, and in contrast to PLCδ1-PH, overexpression of ENTH-GFP did not attenuate G_qPCR signaling. Taken together, ENTH-GFP detects minute changes of PI(4,5)P₂ levels and provides an important complementation of experimentally useful reporters of PI(4,5)P₂ dynamics in physiological pathways.

Revisiting Netrin-1: One Who Guides (Axons)

Proper patterning of the nervous system requires that developing axons find appropriate postsynaptic partners; this entails microns to meters of extension through an extracellular milieu exhibiting a wide range of mechanical and chemical properties. Thus, the elaborate networks of fiber tracts and non-fasciculated axons evident in mature organisms are formed via complex pathfinding. The macroscopic structures of axon projections are highly stereotyped across members of the same species, indicating precise mechanisms guide their formation. The developing axon exhibits directionally biased growth toward or away from external guidance cues. One of the most studied guidance cues is netrin-1, however, its presentation in vivo remains debated. Guidance cues can be secreted to form soluble or chemotactic gradients or presented bound to cells or the extracellular matrix to form haptotactic gradients. The growth cone, a highly specialized dynamic structure at the end of the extending axon, detects these guidance cues via transmembrane receptors, such as the netrin-1 receptors deleted in colorectal cancer (DCC) and UNC5. These receptors orchestrate remodeling of the cytoskeleton and cell membrane through both chemical and mechanotransductive pathways, which result in traction forces generated by the cytoskeleton against the extracellular environment and translocation of the growth cone. Through intracellular signaling responses, netrin-1 can trigger either attraction or repulsion of the axon. Here we review the mechanisms by which the classical guidance cue netrin-1 regulates intracellular effectors to respond to the extracellular environment in the context of axon guidance during development of the central nervous system and discuss recent findings that demonstrate the critical importance of mechanical forces in this process.

Whole exome sequencing identifies a novel dominant missense mutation underlying leukonychia in a Pakistani family

Hereditary leukonychia (also known as porcelain nails or white nails) is a genetic disorder. It may exist as an isolated feature or associated with other cutaneous or systemic disorders. Although a number of genes have been described to cause leukonychia, still the underlying genetic etiologies of many cases remain unknown. Here, we report a Pakistani family presenting leukonychia and koilonychia nails in mother and five of her kids. All the affected individuals had white to pale nails in appearance exhibiting complete and partial leukonychia, respectively. Similarly, nails of finger and toe appeared brittle and concave, showing the characteristics features of koilonychia. Whole exome sequencing and subsequent Sanger sequencing identified a pathogenic novel missense mutation (c.1390G>A, p.Glu464Lys) in PLCD1, co-segregating with the disorder in an autosomal dominant pattern. In silico prediction tools supported the pathogenicity of the identified mutation. Literature review determined that mutations in PLCD1 only cause leukonychia. Therefore, our findings add another pathogenic variant to the PLCD1 mutation pool causing leukonychia that would help to understand the underlying molecular mechanism.

Protein kinase C alpha-mediated phosphorylation of PIM-1L promotes the survival and proliferation of acute myeloid leukemia cells

FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD) is a constitutively active mutant of FLT3 and causes 20%-30% of acute myeloid leukemia (AML) cases. FLT3-ITD upregulates the proviral integration site for Moloney murine leukemia virus 1 (PIM-1) expression and promotes the proliferation of AML cells. In this study, we investigated the role of protein kinase C (PKC)-mediated phosphorylation on the expression and function of PIM-1L. Drug screening in leukemia cell lines revealed that sotrastaurin (a PKC inhibitor) suppressed the proliferation of the FLT3-ITD-positive AML cell line MV4-11 but not of K562, HL60, or KG-1a cells, similar to SGI-1776 (a PIM-1/FLT3 inhibitor) and quizartinib (an FLT3 inhibitor). Sotrastaurin decreased the expression of pro-survival protein myeloid cell leukemia (MCL-1) and the phosphorylation of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), both of which are downstream effectors of PIM-1. PKCα directly phosphorylated Ser65 of PIM-1L, which is a long isoform of PIM-1. The PKCα-mediated phosphorylation stabilized PIM-1L. The phosphorylation-mimicked mutant, PIM-1L-S65D, was more stable and showed higher kinase activity than PIM-1L-S65A. Expression of PIM-1L-wildtype or -S65D reduced sotrastaurin-mediated apoptosis and growth inhibition in MV4-11 transfectants. These results suggest that PKCα directly upregulates PIM-1L, resulting in promotion of the survival and proliferation of AML cells.

Identification of a novel PLCD1 mutation in Chinese Han pedigree with hereditary leukonychia and koilonychia

BACKGROUND

Hereditary leukonychia is a rare nail dystrophy characterized by distinctive whitening of the nail plate. Mutations in the PLCD1 gene have been identified as a major causative factor in hereditary leukonychia (HL). However, few reports have analyzed the relationship between genotype and phenotype, especially in Chinese HL patients. Our study aims to explore the typical clinical features of hereditary leukonychia cases in Chinese Han pedigree and the correlations with PLCD1 gene mutation.

PATIENTS AND METHODS

In this study, two Chinese patients presented with leukonychia and koilonychia. Whole-exome sequencing (WES) was performed to screen for the mutations in PLCD1 gene and other candidate genes for hereditary leukonychia. Parents with PLCD1 mutation were selected for Sanger sequencing.

RESULTS

A novel heterozygote missense mutation in exon 9 of PLCD1 gene was identified in the proband and his mother. Whole-exome sequencing revealed both, the proband (III.5) and his mother (II.4) carrying c.1451A>G mutation, while other family members had a normal sequence of the PLCD1 gene.

CONCLUSION

For the first time, a hereditary leukonychia case with PLCD1 mutation has been described in Chinese Han pedigree. This finding suggests the PLCD1 mutation maybe involved in hereditary leukonychia.

Lipid Peroxidation Drives Gasdermin D-Mediated Pyroptosis in Lethal Polymicrobial Sepsis

Sepsis is a life-threatening condition caused by pathogen infection and associated with pyroptosis. Pyroptosis occurs upon activation of proinflammatory caspases and their subsequent cleavage of gasdermin D (GSDMD), resulting in GSDMD N-terminal fragments that form membrane pores to induce cell lysis. Here, we show that antioxidant defense enzyme glutathione peroxidase 4 (GPX4) and its ability to decrease lipid peroxidation, negatively regulate macrophage pyroptosis, and septic lethality in mice. Conditional Gpx4 knockout in myeloid lineage cells increases lipid peroxidation-dependent caspase-11 activation and GSDMD cleavage. The resultant N-terminal GSDMD fragments then trigger macrophage pyroptotic cell death in a phospholipase C gamma 1 (PLCG1)-dependent fashion. Administration of the antioxidant vitamin E that reduces lipid peroxidation, chemical inhibition of PLCG1, or genetic Caspase-11 deletion or Gsdmd inactivation prevents polymicrobial sepsis in Gpx4-/- mice. Collectively, this study suggests that lipid peroxidation drives GSDMD-mediated pyroptosis and hence constitutes a potential therapeutic target for lethal infection.

A PIP2-derived amplification loop fuels the sustained initiation of B cell activation

Lymphocytes have evolved sophisticated signaling amplification mechanisms to efficiently activate downstream signaling after detection of rare ligands in their microenvironment. B cell receptor microscopic clusters (BCR microclusters) are assembled on the plasma membrane and recruit signaling molecules for the initiation of lymphocyte signaling after antigen binding. We identified a signaling amplification loop derived from phosphatidylinositol 4,5-biphosphate (PIP₂) for the sustained B cell activation. Upon antigen recognition, PIP₂ was depleted by phospholipase C-γ2 (PLC-γ2) within the BCR microclusters and was regenerated by phosphatidic acid-dependent type I phosphatidylinositol 4-phosphate 5-kinase outside the BCR microclusters. The hydrolysis of PIP₂ inside the BCR microclusters induced a positive feedback mechanism for its synthesis outside the BCR microclusters. The falling gradient of PIP₂ across the boundary of BCR microclusters was important for the efficient formation of BCR microclusters. Our results identified a PIP₂-derived amplification loop that fuels the sustained initiation of B cell activation.

An InDel in Phospholipase-C-B-1 Is Linked with Euthyroid Multinodular Goiter

BACKGROUND

Euthyroid multinodular goiter (MNG) is common, but little is known about the genetic variations conferring predisposition. Previously, a family with MNG of adolescent onset was reported in which some family members developed papillary thyroid carcinomas (PTC).

METHODS

Genome-wide linkage analysis and next-generation sequencing were conducted to identify genetic variants that may confer disease predisposition. A multipoint nonparametric LOD score of 3.01 was obtained, covering 19 cM on chromosome 20p. Haplotype analysis reduced the region of interest to 10 cM.

RESULTS

Analysis of copy number variation identified an intronic InDel (∼1000 bp) in the PLCB1 gene in all eight affected family members and carriers (an unaffected person who has inherited the genetic trait). This InDel is present in approximately 1% of "healthy" Caucasians. Next-generation sequencing of the region identified no additional disease-associated variant, suggesting a possible role of the InDel. Since PLCB1 contributes to thyrocyte growth regulation, the InDel was investigated in relevant Caucasian cohorts. It was detected in 0/70 PTC but 4/81 unrelated subjects with MNG (three females; age at thyroidectomy 27-59 years; no family history of MNG/PTC). The InDel frequency is significantly higher in MNG subjects compared to controls (χ² = 5.076; p = 0.024. PLCB1 transcript levels were significantly higher in thyroids with the InDel than without (p < 0.02).

CONCLUSIONS

The intronic PLCB1 InDel is the first variant found in familial multiple papilloid adenomata-type MNG and in a subset of patients with sporadic MNG. It may function through overexpression, and increased PLC activity has been reported in thyroid neoplasms. The potential role of the deletion as a biomarker to identify MNG patients more likely to progress to PTC merits exploration.

MARCKS and MARCKS-like proteins in development and regeneration

BACKGROUND

The Myristoylated Alanine-Rich C-kinase Substrate (MARCKS) and MARCKS-like protein 1 (MARCKSL1) have a wide range of functions, ranging from roles in embryonic development to adult brain plasticity and the inflammatory response. Recently, both proteins have also been identified as important players in regeneration. Upon phosphorylation by protein kinase C (PKC) or calcium-dependent calmodulin-binding, MARCKS and MARCKSL1 translocate from the membrane into the cytosol, modulating cytoskeletal actin dynamics and vesicular trafficking and activating various signal transduction pathways. As a consequence, the two proteins are involved in the regulation of cell migration, secretion, proliferation and differentiation in many different tissues.

MAIN BODY

Throughout vertebrate development, MARCKS and MARCKSL1 are widely expressed in tissues derived from all germ layers, with particularly strong expression in the nervous system. They have been implicated in the regulation of gastrulation, myogenesis, brain development, and other developmental processes. Mice carrying loss of function mutations in either Marcks or Marcksl1 genes die shortly after birth due to multiple deficiencies including detrimental neural tube closure defects. In adult vertebrates, MARCKS and MARCKL1 continue to be important for multiple regenerative processes including peripheral nerve, appendage, and tail regeneration, making them promising targets for regenerative medicine.

CONCLUSION

This review briefly summarizes the molecular interactions and cellular functions of MARCKS and MARCKSL1 proteins and outlines their vital roles in development and regeneration.

A PKC-MARCKS-PI3K regulatory module links Ca2+ and PIP3 signals at the leading edge of polarized macrophages

The leukocyte chemosensory pathway detects attractant gradients and directs cell migration to sites of inflammation, infection, tissue damage, and carcinogenesis. Previous studies have revealed that local Ca²⁺ and PIP₃ signals at the leading edge of polarized leukocytes play central roles in positive feedback loop essential to cell polarization and chemotaxis. These prior studies showed that stimulation of the leading edge Ca²⁺ signal can strongly activate PI3K, thereby triggering a larger PIP₃ signal, but did not elucidate the mechanistic link between Ca²⁺ and PIP₃ signaling. A hypothesis explaining this link emerged, postulating that Ca²⁺-activated PKC displaces the MARCKS protein from plasma membrane PIP₂, thereby releasing sequestered PIP₂ to serve as the target and substrate lipid of PI3K in PIP₃ production. In vitro single molecule studies of the reconstituted pathway on lipid bilayers demonstrated the feasibility of this PKC-MARCKS-PI3K regulatory module linking Ca²⁺ and PIP₃ signals in the reconstituted system. The present study tests the model predictions in live macrophages by quantifying the effects of: (a) two pathway activators—PDGF and ATP that stimulate chemoreceptors and Ca²⁺ influx, respectively; and (b) three pathway inhibitors—wortmannin, EGTA, and Go6976 that inhibit PI3K, Ca²⁺ influx, and PKC, respectively; on (c) four leading edge activity sensors—AKT-PH-mRFP, CKAR, MARCKSp-mRFP, and leading edge area that report on PIP₃ density, PKC activity, MARCKS membrane binding, and leading edge expansion/contraction, respectively. The results provide additional evidence that PKC and PI3K are both essential elements of the leading edge positive feedback loop, and strongly support the existence of a PKC-MARCKS-PI3K regulatory module linking the leading edge Ca²⁺ and PIP₃ signals. As predicted, activators stimulate leading edge PKC activity, displacement of MARCKS from the leading edge membrane and increased leading edge PIP₃ levels, while inhibitors trigger the opposite effects. Comparison of the findings for the ameboid chemotaxis of leukocytes with recently published findings for the mesenchymal chemotaxis of fibroblasts suggests that some features of the emerging leukocyte leading edge core pathway (PLC-DAG-Ca²⁺-PKC-MARCKS-PIP₂-PI3K-PIP₃) may well be shared by all chemotaxing eukaryotic cells, while other elements of the leukocyte pathway may be specialized features of these highly optimized, professional gradient-seeking cells. More broadly, the findings suggest a molecular mechanism for the strong links between phospho-MARCKS and many human cancers.

Vascular smooth muscle cell proliferation as a therapeutic target. Part 1: molecular targets and pathways

Cardiovascular diseases are a major cause of human death worldwide. Excessive proliferation of vascular smooth muscle cells contributes to the etiology of such diseases, including atherosclerosis, restenosis, and pulmonary hypertension. The control of vascular cell proliferation is complex and encompasses interactions of many regulatory molecules and signaling pathways. Herein, we recapitulated the importance of signaling cascades relevant for the regulation of vascular cell proliferation. Detailed understanding of the mechanism underlying this process is essential for the identification of new lead compounds (e.g., natural products) for vascular therapies.

HMMER Cut-off Threshold Tool (HMMERCTTER): Supervised classification of superfamily protein sequences with a reliable cut-off threshold

Background

Protein superfamilies can be divided into subfamilies of proteins with different functional characteristics. Their sequences can be classified hierarchically, which is part of sequence function assignation. Typically, there are no clear subfamily hallmarks that would allow pattern-based function assignation by which this task is mostly achieved based on the similarity principle. This is hampered by the lack of a score cut-off that is both sensitive and specific.

Results

HMMER Cut-off Threshold Tool (HMMERCTTER) adds a reliable cut-off threshold to the popular HMMER. Using a high quality superfamily phylogeny, it clusters a set of training sequences such that the cluster-specific HMMER profiles show cluster or subfamily member detection with 100% precision and recall (P&R), thereby generating a specific threshold as inclusion cut-off. Profiles and thresholds are then used as classifiers to screen a target dataset. Iterative inclusion of novel sequences to groups and the corresponding HMMER profiles results in high sensitivity while specificity is maintained by imposing 100% P&R self detection. In three presented case studies of protein superfamilies, classification of large datasets with 100% precision was achieved with over 95% recall. Limits and caveats are presented and explained.

Conclusions

HMMERCTTER is a promising protein superfamily sequence classifier provided high quality training datasets are used. It provides a decision support system that aids in the difficult task of sequence function assignation in the twilight zone of sequence similarity. All relevant data and source codes are available from the Github repository at the following URL: https://github.com/BBCMdP/HMMERCTTER.

Lowered dietary phosphorus affects intestinal and renal gene expression to maintain mineral homeostasis with immunomodulatory implications in weaned piglets

BACKGROUND

In monogastric animals, phosphorus (P) homeostasis is maintained by regulating intestinal absorption, bone mobilization, and renal excretion. Since P is a non-renewable resource, a shortage is imminent due to widespread over-usage in the farming and animal husbandry industries. As a consequence, P efficiency should be improved in pig production. We sought to characterize the transcriptional response in re-/absorbing and excreting tissues in pigs to diets varying in calcium: phosphorus ratios. Weaned piglets were assigned to one of three groups fed diets varying in digestible P content for a period of five weeks. Gene expression profiles were analyzed in jejunum, colon, and kidney.

RESULTS

Transcriptome analysis revealed that reduced dietary P intake affects gene expression in jejunum and kidney, but not in colon. The regulation of mineral homeostasis was reflected via altered mRNA abundances of CYP24A1, CYP27A1, TRPM6, SPP1, and VDR in jejunum and kidney. Moreover, lowered abundances of transcripts associated with the classical complement system pathway were observed in the jejunum. In kidney, shifted transcripts were involved in phospholipase C, calcium signaling, and NFAT signaling, which may have immunomodulatory implications.

CONCLUSIONS

Our results revealed local transcriptional consequences of variable P intake in intestinal and renal tissues. The adaptive responses are the result of organismal efforts to maintain systemic mineral homeostasis while modulating immune features at local tissue sites. Therefore, the deviation from the currently recommended dietary P supply must be carefully considered, as the endogenous mechanisms that respond to low P diets may impact important adaptive immune responses.

G protein βγ subunits directly interact with and activate phospholipase Cϵ

Phospholipase C (PLC) enzymes hydrolyze membrane phosphatidylinositol 4,5 bisphosphate (PIP₂) and regulate Ca²⁺ and protein kinase signaling in virtually all mammalian cell types. Chronic activation of the PLCϵ isoform downstream of G protein-coupled receptors (GPCRs) contributes to the development of cardiac hypertrophy. We have previously shown that PLCϵ-catalyzed hydrolysis of Golgi-associated phosphatidylinositol 4-phosphate (PI4P) in cardiac myocytes depends on G protein βγ subunits released upon stimulation with endothelin-1. PLCϵ binds and is directly activated by Ras family small GTPases, but whether they directly interact with Gβγ has not been demonstrated. To identify PLCϵ domains that interact with Gβγ, here we designed various single substitutions and truncations of WT PLCϵ and tested them for activation by Gβγ in transfected COS-7 cells. Deletion of only a single domain in PLCϵ was not sufficient to completely block its activation by Gβγ, but blocked activation by Ras. Simultaneous deletion of the C-terminal RA2 domain and the N-terminal CDC25 and cysteine-rich domains completely abrogated PLCϵ activation by Gβγ, but activation by the GTPase Rho was retained. In vitro reconstitution experiments further revealed that purified Gβγ directly interacts with a purified fragment of PLCϵ (PLCϵ-PH-RA2) and increases PIP₂ hydrolysis. Deletion of the RA2 domain decreased Gβγ binding and eliminated Gβγ stimulation of PIP₂ hydrolysis. These results provide first evidence that Gβγ directly interacts with PLCϵ and yield insights into the mechanism by which βγ subunits activate PLCϵ.

Epidermal growth factor receptor and EGFRvIII in glioblastoma: signaling pathways and targeted therapies

Amplification of epidermal growth factor receptor (EGFR) and its active mutant EGFRvIII occurs frequently in glioblastoma (GBM). While EGFR and EGFRvIII play critical roles in pathogenesis, targeted therapy with EGFR-tyrosine kinase inhibitors (TKIs) or antibodies has only shown limited efficacy in patients. Here we discuss signaling pathways mediated by EGFR/EGFRvIII, current therapeutics, and novel strategies to target EGFR/EGFRvIII-amplified GBM.

High capacity in G protein-coupled receptor signaling

G protein-coupled receptors (GPCRs) constitute a large family of receptors that activate intracellular signaling pathways upon detecting specific extracellular ligands. While many aspects of GPCR signaling have been uncovered through decades of studies, some fundamental properties, like its channel capacity—a measure of how much information a given transmission system can reliably transduce—are still debated. Previous studies concluded that GPCRs in individual cells could transmit around one bit of information about the concentration of the ligands, allowing only for a reliable on or off response. Using muscarinic receptor-induced calcium response measured in individual cells upon repeated stimulation, we show that GPCR signaling systems possess a significantly higher capacity. We estimate the channel capacity of this system to be above two, implying that at least four concentration levels of the agonist can be distinguished reliably. These findings shed light on the basic principles of GPCR signaling.

G protein-coupled receptors (GPCRs) activate intracellular signalling pathways upon extracellular stimulation. Here authors record single cell responses of GPCR signalling which allows the direct estimation of its channel capacity for each cell along with the reproducibility of its response.

Orchestration of NLRP3 Inflammasome Activation by Ion Fluxes

The assembly of the NLRP3 inflammasome can promote the release of IL-1β/IL-18 and initiate pyroptosis. Accordingly, the dysregulation of NLRP3 inflammasome activation is involved in a variety of human diseases, including gout, diabetes, and Alzheimer's disease. NLRP3 can sense a variety of structurally unrelated pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs) to trigger inflammation, but the unifying mechanism of NLRP3 activation is still poorly understood. Increasing evidence suggests that intracellular ions, such as K⁺, Ca²⁺, and Cl^-, have a significant role in NLRP3 inflammasome activation. Here, we review the current knowledge about the role of ionic fluxes in NLRP3 inflammasome activation and discuss how disturbances in intracellular ionic levels orchestrate different signaling events upstream of NLRP3.

Synaptic neuron-astrocyte communication is supported by an order of magnitude analysis of inositol tris-phosphate diffusion at the nanoscale in a model of peri-synaptic astrocyte projection

Background

Astrocytes were conceived for decades only as supporting cells of the brain. However, the observation of Ca2+ waves in astrocyte synctitia, their neurotransmitter receptor expression and gliotransmitter secretion suggested a role in information handling, conception that has some controversies. Synaptic Neuron-Astrocyte metabotropic communication mediated by Inositol tris-phosphate (SN-AmcIP3) is supported by different reports. However, some models contradict this idea and Ca2+ stores are 1000 ± 325 nm apart from the Postsynaptic Density in the Perisynaptic Astrocyte Projections (PAP’s), suggesting that SN-AmcIP3 is extrasynaptic. However, this assumption does not consider IP3 Diffusion Coefficient (Dab), that activates IP3 Receptor (IP3R) releasing Ca2+ from intracellular stores.

Results

In this work we idealized a model of a PAP (PAPm) to perform an order of magnitude analysis of IP3 diffusion using a transient mass diffusion model. This model shows that IP3 forms a concentration gradient along the PAPm that reaches the steady state in milliseconds, three orders of magnitude before IP3 degradation. The model predicts that IP3 concentration near the Ca2+ stores may activate IP3R, depending upon Phospholipase C (PLC) number and activity. Moreover, the PAPm supports that IP3 and extracellular Ca2+ entry synergize to promote global Ca2+ transients.

Conclusion

The model presented here indicates that Ca2+ stores position in PAP’s does not limit SN-AmcIP3.

Electronic supplementary material

The online version of this article (10.1186/s13628-018-0043-3) contains supplementary material, which is available to authorized users.

Melanopsin and rhodopsin mediate UVA-induced immediate pigment darkening: Unravelling the photosensitive system of the skin

The mammalian skin has a photosensitive system comprised by several opsins, including rhodopsin (OPN2) and melanopsin (OPN4). Recently, our group showed that UVA (4.4 kJ/m²) leads to immediate pigment darkening (IPD) in murine normal and malignant melanocytes. We show the role of OPN2 and OPN4 as UVA sensors: UVA-induced IPD was fully abolished when OPN4 was pharmacologically inhibited by AA9253 or when OPN2 and OPN4 were knocked down by siRNA in both cell lines. Our data, however, demonstrate that phospholipase C/protein kinase C pathway, a classical OPN4 pathway, is not involved in UVA-induced IPD in either cell line. Nonetheless, in both cell types we have shown that: a) intracellular calcium signal is necessary for UVA-induced IPD; b) the involvement of CaMK II, whose inhibition, abolished the UVA-induced IPD; c) the role of CAMK II/NOS/sGC/cGMP pathway in the process since inhibition of either NOS or sGC abolished the UVA-induced IPD. Taken altogether, we show that OPN2 and OPN4 participate in IPD induced by UVA in murine normal and malignant melanocytes through a conserved common pathway. Interestingly, upon knockdown of OPN2 or OPN4, the UVA-driven IPD is completely lost, which suggests that both opsins are required and cooperatively signal in murine both cell lines. The participation of OPN2 and OPN4 system in UVA radiation-induced response, if proven to take place in human skin, may represent an interesting pharmacological target for the treatment of depigmentary disorders and skin-related cancer.

Osmotic activation of a Ca2+-dependent phospholipase C pathway that regulates ∆N TRPV1-mediated currents in rat supraoptic neurons

The magnocellular neurosecretory cells (MNCs) of the hypothalamus regulate body fluid balance by releasing the hormones vasopressin (VP) and oxytocin (OT) in an osmolality‐dependent manner. Elevations of external osmolality increase MNC firing and hormone release. MNC osmosensitivity is largely due to activation of a mechanosensitive non‐selective cation current that responds to osmotically‐evoked changes in MNC volume and is mediated by an N‐terminal variant of the TRPV1 channel (∆N TRPV1). We report a novel mechanism by which increases in osmolality may modulate ∆N TRPV1‐mediated currents and thus influence MNC electrical behaviour. We showed previously that acute elevations of external osmolality activate the enzyme phospholipase C (PLC) in isolated MNCs. We now show that the osmotic activation of PLC has a time course and dose‐dependence that is consistent with a role in MNC osmosensitivity and that it contributes to the osmotically‐evoked increase in non‐selective cation current in MNCs through a protein kinase C‐dependent pathway. We furthermore show that the mechanism of osmotic activation of PLC requires an increase in internal Ca²⁺ that depends on influx through L‐type Ca²⁺ channels. Our data therefore suggest that MNCs possess an osmotically‐activated Ca²⁺‐dependent PLC that contributes to the osmotic activation of ∆N TRPV1 and may therefore be important in MNC osmosensitivity and in central osmoregulation.

The PPI network analysis of mRNA expression profile of uterus from primary dysmenorrheal rats

To elucidate the mechanisms of molecular regulations underlying primary dysmenorrhea (PD), we used our previously published mRNA expression profile of uterus from PD syndrome rats to construct protein-protein interactions (PPI) network via STRING Interactome. Consequently, 34 subnetworks, including a "continent" (Subnetwork 1) and 33 "islands" (Subnetwork 2-34) were generated. The nodes, with relative expression ratios, were visualized in the PPI networks and their connections were identified. Through path and module exploring in the network, the bridges were found from pathways of cellular response to calcium ion, SMAD protein signal transduction, regulation of transcription from RNA polymerase II promoter in response to stress and muscle stretch that were significantly enriched by the up-regulated mRNAs, to the cascades of cAMP metabolic processes and positive regulation of cyclase activities by the down-regulated ones. This link is mainly dependent on Fos/Jun - Vip connection. Our data, for the first time, report the PPI network analysis of differentially expressed mRNAs in the uterus of PD syndrome rats, to give insight into screening drugs and find new therapeutic strategies to relieve PD.

Phospholipases: An Overview

Phospholipases are lipolytic enzymes that hydrolyze phospholipid substrates at specific ester bonds. Phospholipases are widespread in nature and play very diverse roles from aggression in snake venom to signal transduction, lipid mediator production, and metabolite digestion in humans. Phospholipases vary considerably in structure, function, regulation, and mode of action. Tremendous advances in understanding the structure and function of phospholipases have occurred in the last decades. This introductory chapter is aimed at providing a general framework of the current understanding of phospholipases and a discussion of their mechanisms of action and emerging biological functions.

Synthesis of enzyme-responsive phosphoramidate dendrimers for cancer drug delivery

Enzyme-responsive phosphoramidate dendrimers were successfully synthesized and their surfaces were modified with zwitterionic groups for cancer drug delivery.

A membrane-associated, fluorogenic reporter for mammalian phospholipase C isozymes

A diverse group of cell-surface receptors, including many G protein-coupled receptors and receptor tyrosine kinases, activate phospholipase C (PLC) isozymes to hydrolyze phosphatidylinositol 4,5-bisphosphate into the second messengers diacylglycerol and 1,4,5-inositol trisphosphate. Consequently, PLCs control various cellular processes, and their aberrant regulation contributes to many diseases, including cancer, atherosclerosis, and rheumatoid arthritis. Despite the widespread importance of PLCs in human biology and disease, it has been impossible to directly monitor the real-time activation of these enzymes at membranes. To overcome this limitation, here we describe XY-69, a fluorogenic reporter that preferentially partitions into membranes and provides a selective tool for measuring the real-time activity of PLCs as either purified enzymes or in cellular lysates. Indeed, XY-69 faithfully reported the membrane-dependent activation of PLC-β3 by Gα_q Therefore, XY-69 can replace radioactive phosphatidylinositol 4,5-bisphosphate used in conventional PLC assays and will enable high-throughput screens to identify both orthosteric and allosteric PLC inhibitors. In the future, cell-permeable variants of XY-69 represent promising candidates for reporting the activation of PLCs in live cells with high spatiotemporal resolution.

Phospholipase Cβ3 Membrane Adsorption and Activation Are Regulated by Its C-Terminal Domains and Phosphatidylinositol 4,5-Bisphosphate

Phospholipase Cβ (PLCβ) enzymes hydrolyze phosphatidylinositol 4,5-bisphosphate to produce second messengers that regulate intracellular Ca²⁺, cell proliferation, and survival. Their activity is dependent upon interfacial activation that occurs upon localization to cell membranes. However, the molecular basis for how these enzymes productively interact with the membrane is poorly understood. Herein, atomic force microscopy demonstrates that the ∼300-residue C-terminal domain promotes adsorption to monolayers and is required for spatial organization of the protein on the monolayer surface. PLCβ variants lacking this C-terminal domain display differences in their distribution on the surface. In addition, a previously identified autoinhibitory helix that binds to the PLCβ catalytic core negatively impacts membrane binding, providing an additional level of regulation for membrane adsorption. Lastly, defects in phosphatidylinositol 4,5-bisphosphate hydrolysis also alter monolayer adsorption, reflecting a role for the active site in this process. Together, these findings support a model in which multiple elements of PLCβ modulate adsorption, distribution, and catalysis at the cell membrane.

The role of phospholipase Cγ1 in breast cancer and its clinical significance

Breast cancer, the most common malignancy among women, is usually detected at an early stage and has a low risk of relapse. Nevertheless, a significant number of patients cannot be cured solely by local treatment. Distinguishing between patients who are of low risk of relapse from those who are of high risk may have important implications to improve treatment outcomes. The PLC-γ1 signaling pathway promotes many physiological processes, including cell migration and invasion. Increasing evidence shows aberrant PLC-γ1 signaling implication in carcinogenesis including breast cancer. In this review, the role of PLC-γ1 in breast cancer and its clinical implications will be discussed, as well as its potential as a prognostic factor and a therapeutic target.

A Reaction-Diffusion Model Explains Amplification of the PLC/PKC Pathway in Fibroblast Chemotaxis

During the proliferative phase of cutaneous wound healing, dermal fibroblasts are recruited into the clotted wound by a concentration gradient of platelet-derived growth factor (PDGF), together with other spatial cues. Despite the importance of this chemotactic process, the mechanisms controlling the directed migration of slow-moving mesenchymal cells such as fibroblasts are not well understood. Here, we develop and analyze a reaction-diffusion model of phospholipase C/protein kinase C (PKC) signaling, which was recently identified as a requisite PDGF-gradient-sensing pathway, with the goal of identifying mechanisms that can amplify its sensitivity in the shallow external gradients typical of chemotaxis experiments. We show that phosphorylation of myristoylated alanine-rich C kinase substrate by membrane-localized PKC constitutes a positive feedback that is sufficient for local pathway amplification. The release of phosphorylated myristoylated alanine-rich C kinase substrate and its subsequent diffusion and dephosphorylation in the cytosol also serves to suppress the pathway in down-gradient regions of the cell. By itself, this mechanism only weakly amplifies signaling in a shallow PDGF gradient, but it synergizes with other feedback mechanisms to enhance amplification. This model offers a framework for a mechanistic understanding of phospholipase C/PKC signaling in chemotactic gradient sensing and can guide the design of experiments to assess the roles of putative feedback loops.

The binding of activated Gαq to phospholipase C-β exhibits anomalous affinity

Upon activation by the G_q family of Gα subunits, Gβγ subunits, and some Rho family GTPases, phospholipase C-β (PLC-β) isoforms hydrolyze phosphatidylinositol 4,5-bisphosphate to the second messengers inositol 1,4,5-trisphosphate and diacylglycerol. PLC-β isoforms also function as GTPase-activating proteins, potentiating G_q deactivation. To elucidate the mechanism of this mutual regulation, we measured the thermodynamics and kinetics of PLC-β3 binding to Gα_q FRET and fluorescence correlation spectroscopy, two physically distinct methods, both yielded K_d values of about 200 nm for PLC-β3-Gα_q binding. This K_d is 50-100 times greater than the EC₅₀ for Gα_q-mediated PLC-β3 activation and for the Gα_q GTPase-activating protein activity of PLC-β. The measured K_d was not altered either by the presence of phospholipid vesicles, phosphatidylinositol 4,5-bisphosphate and Ca²⁺, or by the identity of the fluorescent labels. FRET-based kinetic measurements were also consistent with a K_d of 200 nm We determined that PLC-β3 hysteresis, whereby PLC-β3 remains active for some time following either Gα_q-PLC-β3 dissociation or PLC-β3-potentiated Gα_q deactivation, is not sufficient to explain the observed discrepancy between EC₅₀ and K_d These results indicate that the mechanism by which Gα_q and PLC-β3 mutually regulate each other is far more complex than a simple, two-state allosteric model and instead is probably kinetically determined.

Selective regulation of clathrin-mediated epidermal growth factor receptor signaling and endocytosis by phospholipase C and calcium

Clathrin-mediated endocytosis is a major regulator of cell-surface protein internalization. Clathrin and other proteins assemble into small invaginating structures at the plasma membrane termed clathrin-coated pits (CCPs) that mediate vesicle formation. In addition, epidermal growth factor receptor (EGFR) signaling is regulated by its accumulation within CCPs. Given the diversity of proteins regulated by clathrin-mediated endocytosis, how this process may distinctly regulate specific receptors is a key question. We examined the selective regulation of clathrin-dependent EGFR signaling and endocytosis. We find that perturbations of phospholipase Cγ1 (PLCγ1), Ca²⁺, or protein kinase C (PKC) impair clathrin-mediated endocytosis of EGFR, the formation of CCPs harboring EGFR, and EGFR signaling. Each of these manipulations was without effect on the clathrin-mediated endocytosis of transferrin receptor (TfR). EGFR and TfR were recruited to largely distinct clathrin structures. In addition to control of initiation and assembly of CCPs, EGF stimulation also elicited a Ca²⁺- and PKC-dependent reduction in synaptojanin1 recruitment to clathrin structures, indicating broad control of CCP assembly by Ca²⁺ signals. Hence EGFR elicits PLCγ1-calcium signals to facilitate formation of a subset of CCPs, thus modulating its own signaling and endocytosis. This provides evidence for the versatility of CCPs to control diverse cellular processes.

A PLC-γ1 Feedback Pathway Regulates Lck Substrate Phosphorylation at the T-Cell Receptor and SLP-76 Complex

Phospholipase C gamma 1 (PLC-γ1) occupies a critically important position in the T-cell signaling pathway. While its functions as a regulator of both Ca²⁺ signaling and PKC-family kinases are well characterized, PLC-γ1's role in the regulation of early T-cell receptor signaling events is incompletely understood. Activation of the T-cell receptor leads to the formation of a signalosome complex between SLP-76, LAT, PLC-γ1, Itk, and Vav1. Recent studies have revealed the existence of both positive and negative feedback pathways from SLP-76 to the apical kinase in the pathway, Lck. To determine if PLC-γ1 contributes to the regulation of these feedback networks, we performed a quantitative phosphoproteomic analysis of PLC-γ1-deficient T cells. These data revealed a previously unappreciated role for PLC-γ1 in the positive regulation of Zap-70 and T-cell receptor tyrosine phosphorylation. Conversely, PLC-γ1 negatively regulated the phosphorylation of SLP-76-associated proteins, including previously established Lck substrate phosphorylation sites within this complex. While the positive and negative regulatory phosphorylation sites on Lck were largely unchanged, Tyr¹⁹² phosphorylation was elevated in Jgamma1. The data supports a model wherein Lck's targeting, but not its kinase activity, is altered by PLC-γ1, possibly through Lck Tyr¹⁹² phosphorylation and increased association of the kinase with protein scaffolds SLP-76 and TSAd.

Regulation of PI3K by PKC and MARCKS: Single-Molecule Analysis of a Reconstituted Signaling Pathway

In chemotaxing ameboid cells, a complex leading-edge signaling circuit forms on the cytoplasmic leaflet of the plasma membrane and directs both actin and membrane remodeling to propel the leading edge up an attractant gradient. This leading-edge circuit includes a putative amplification module in which Ca(2+)-protein kinase C (Ca(2+)-PKC) is hypothesized to phosphorylate myristoylated alanine-rich C kinase substrate (MARCKS) and release phosphatidylinositol-4,5-bisphosphate (PIP2), thereby stimulating production of the signaling lipid phosphatidylinositol-3,4,5-trisphosphate (PIP3) by the lipid kinase phosphoinositide-3-kinase (PI3K). We investigated this hypothesized Ca(2+)-PKC-MARCKS-PIP2-PI3K-PIP3 amplification module and tested its key predictions using single-molecule fluorescence to measure the surface densities and activities of its protein components. Our findings demonstrate that together Ca(2+)-PKC and the PIP2-binding peptide of MARCKS modulate the level of free PIP2, which serves as both a docking target and substrate lipid for PI3K. In the off state of the amplification module, the MARCKS peptide sequesters PIP2 and thereby inhibits PI3K binding to the membrane. In the on state, Ca(2+)-PKC phosphorylation of the MARCKS peptide reverses the PIP2 sequestration, thereby releasing multiple PIP2 molecules that recruit multiple active PI3K molecules to the membrane surface. These findings 1) show that the Ca(2+)-PKC-MARCKS-PIP2-PI3K-PIP3 system functions as an activation module in vitro, 2) reveal the molecular mechanism of activation, 3) are consistent with available in vivo data, and 4) yield additional predictions that are testable in live cells. More broadly, the Ca(2+)-PKC-stimulated release of free PIP2 may well regulate the membrane association of other PIP2-binding proteins, and the findings illustrate the power of single-molecule analysis to elucidate key dynamic and mechanistic features of multiprotein signaling pathways on membrane surfaces.

The signalling receptor MCAM coordinates apical-basal polarity and planar cell polarity during morphogenesis

The apical-basal (AB) polarity and planar cell polarity (PCP) provide an animal cell population with different phenotypes during morphogenesis. However, how cells couple these two patterning systems remains unclear. Here we provide in vivo evidence that melanoma cell adhesion molecule (MCAM) coordinates AB polarity-driven lumenogenesis and c-Jun N-terminal kinase (JNK)/PCP-dependent ciliogenesis. We identify that MCAM is an independent receptor of fibroblast growth factor 4 (FGF4), a membrane anchor of phospholipase C-γ (PLC-γ), an immediate upstream receptor of nuclear factor of activated T-cells (NFAT) and a constitutive activator of JNK. We find that MCAM-mediated vesicular trafficking towards FGF4, while generating a priority-grade transcriptional response of NFAT determines lumenogenesis. We demonstrate that MCAM plays indispensable roles in ciliogenesis through activating JNK independently of FGF signals. Furthermore, mcam-deficient zebrafish and Xenopus exhibit a global defect in left-right (LR) asymmetric establishment as a result of morphogenetic failure of their LR organizers. Therefore, MCAM coordination of AB polarity and PCP provides insight into the general mechanisms of morphogenesis.

Heterotrimeric G-protein regulatory circuits in plants: Conserved and novel mechanisms

ARTICLE ADDENDUM Efficient activation and deactivation of Gα protein is critical for the regulation of heterotrimeric G-protein mediated signaling pathways. While the core G-protein components and their activation/deactivation chemistries are broadly conserved throughout the eukaryotic evolution, their regulatory mechanisms seem to have been rewired in plants to meet specific needs. Plants such as Arabidopsis, which have a limited number of G-protein components and their regulators, offer a unique opportunity to dissect the mechanistic details of distinct signaling pathways. We have recently established an interaction between the regulator of G-protein signaling 1 (RGS1) and phospholipase Dα1 (PLDα1); 2 of the GTPase activity accelerating proteins (GAPs) of the Arabidopsis Gα protein, GPA1. We now show that phosphatidic acid (PA), a key product of PLDα1 activity, can bind with and modulate the GAP activity of RGS1, uncovering a molecular link between lipid and G-protein signaling and its role in providing the specificity of response regulation.

Genome-wide identification and characterization of phospholipase C gene family in cotton (Gossypium spp.)

Phospholipase C (PLC) are important regulatory enzymes involved in several lipid and Ca²⁺-dependent signaling pathways. Previous studies have elucidated the versatile roles of PLC genes in growth, development and stress responses of many plants, however, the systematic analyses of PLC genes in the important fiber-producing plant, cotton, are still deficient. In this study, through genome-wide survey, we identified twelve phosphatidylinositol-specific PLC (PI-PLC) and nine non-specific PLC (NPC) genes in the allotetraploid upland cotton Gossypium hirsutum and nine PI-PLC and six NPC genes in two diploid cotton G. arboretum and G.raimondii, respectively. The PI-PLC and NPC genes of G. hirsutum showed close phylogenetic relationship with their homologous genes in the diploid cottons and Arabidopsis. Segmental and tandem duplication contributed greatly to the formation of the gene family. Expression profiling indicated that few of the PLC genes are constitutely expressed, whereas most of the PLC genes are preferentially expressed in specific tissues and abiotic stress conditions. Promoter analyses further implied that the expression of these PLC genes might be regulated by MYB transcription factors and different phytohormones. These results not only suggest an important role of phospholipase C members in cotton plant development and abiotic stress response but also provide good candidate targets for future molecular breeding of superior cotton cultivars.