The PtdIns-PLC superfamily and signal transduction

PKCα and PKCδ: Friends and Rivals

PKC comprises a large family of serine/threonine kinases that share a requirement for allosteric activation by lipids. While PKC isoforms have significant homology, functional divergence is evident among subfamilies and between individual PKC isoforms within a subfamily. Here, we highlight these differences by comparing the regulation and function of representative PKC isoforms from the conventional (PKCα) and novel (PKCδ) subfamilies. We discuss how unique structural features of PKCα and PKCδ underlie differences in activation and highlight the similar, divergent, and even opposing biological functions of these kinases. We also consider how PKCα and PKCδ can contribute to pathophysiological conditions and discuss challenges to targeting these kinases therapeutically.

Involvement of Phospholipase C in Photosynthesis and Growth of Maize Seedlings

Phospholipase C is an enzyme that catalyzes the hydrolysis of glycerophospholipids and can be classified as phosphoinositide-specific PLC (PI-PLC) and non-specific PLC (NPC), depending on its hydrolytic substrate. In maize, the function of phospholipase C has not been well characterized. In this study, the phospholipase C inhibitor neomycin sulfate (NS, 100 mM) was applied to maize seedlings to investigate the function of maize PLC. Under the treatment of neomycin sulfate, the growth and development of maize seedlings were impaired, and the leaves were gradually etiolated and wilted. The analysis of physiological and biochemical parameters revealed that inhibition of phospholipase C affected photosynthesis, photosynthetic pigment accumulation, carbon metabolism and the stability of the cell membrane. High-throughput RNA-seq was conducted, and differentially expressed genes (DEGS) were found significantly enriched in photosynthesis and carbon metabolism pathways. When phospholipase C activity was inhibited, the expression of genes related to photosynthetic pigment accumulation was decreased, which led to lowered chlorophyll. Most of the genes related to PSI, PSII and TCA cycles were down-regulated and the net photosynthesis was decreased. Meanwhile, genes related to starch and sucrose metabolism, the pentose phosphate pathway and the glycolysis/gluconeogenesis pathway were up-regulated, which explained the reduction of starch and total soluble sugar content in the leaves of maize seedlings. These findings suggest that phospholipase C plays a key role in photosynthesis and the growth and development of maize seedlings.

De Novo Transcriptome of the Flagellate Isochrysis galbana Identifies Genes Involved in the Metabolism of Antiproliferative Metabolites

Haptophytes are important primary producers in the oceans, and among the phylum Haptophyta, the flagellate Isochrysis galbana has been found to be rich in high-value compounds, such as lipids, carotenoids and highly branched polysaccharides. In the present work, I. galbana was cultured and collected at both stationary and exponential growth phases. A transcriptomic approach was used to analyze the possible activation of metabolic pathways responsible for bioactive compound synthesis at the gene level. Differential expression analysis of samples collected at the exponential versus stationary growth phase allowed the identification of genes involved in the glycerophospholipid metabolic process, the sterol biosynthetic process, ADP-ribose diphosphatase activity and others. I. galbana raw extracts and fractions were tested on specific human cancer cells for possible antiproliferative activity. The most active fractions, without affecting normal cells, were fractions enriched in nucleosides (fraction B) and triglycerides (fraction E) for algae collected in the exponential growth phase and fraction E for stationary phase samples. Overall, transcriptomic and bioactivity data confirmed the activation of metabolic pathways involved in the synthesis of bioactive compounds giving new insights on possible Isochrysis applications in the anticancer sector.

Comparative Genomics of Clostridium baratii Reveals Strain-Level Diversity in Toxin Abundance

Clostridium baratii strains are rare opportunistic pathogens associated with botulism intoxication. They have been isolated from foods, soil and be carried asymptomatically or cause botulism outbreaks. Is not taxonomically related to Clostridium botulinum, but some strains are equipped with BoNT/F7 cluster. Despite their relationship with diseases, our knowledge regarding the genomic features and phylogenetic characteristics is limited. We analyzed the pangenome of C. baratii to understand the diversity and genomic features of this species. We compared existing genomes in public databases, metagenomes, and one newly sequenced strain isolated from an asymptomatic subject. The pangenome was open, indicating it comprises genetically diverse organisms. The core genome contained 28.49% of the total genes of the pangenome. Profiling virulence factors confirmed the presence of phospholipase C in some strains, a toxin capable of disrupting eukaryotic cell membranes. Furthermore, the genomic analysis indicated significant horizontal gene transfer (HGT) events as defined by the presence of prophage genomes. Seven strains were equipped with BoNT/F7 cluster. The active site was conserved in all strains, identifying a missing 7-aa region upstream of the active site in C. baratii genomes. This analysis could be important to advance our knowledge regarding opportunistic clostridia and better understand their contribution to disease.

Sphingomyelin synthase-related protein generates diacylglycerol via the hydrolysis of glycerophospholipids in the absence of ceramide

Diacylglycerol (DG) is a well-established lipid second messenger. Sphingomyelin synthase (SMS)-related protein (SMSr) produces DG and ceramide phosphoethanolamine (CPE) by the transfer of phosphoethanolamine from phosphatidylethanolamine (PE) to ceramide. We previously reported that human SMSr overexpressed in COS-7 cells significantly increased DG levels, particularly saturated and/or monounsaturated fatty acid-containing DG molecular species, and provided DG to DG kinase (DGK) δ, which regulates various pathophysiological events, including epidermal growth factor-dependent cell proliferation, type 2 diabetes, and obsessive-compulsive disorder. However, mammalian SMSr puzzlingly produces only trace amounts of CPE/DG. To clarify this discrepancy, we highly purified SMSr and examined its activities other than CPE synthase. Intriguingly, purified SMSr showed a DG-generating activity via hydrolysis of PE, phosphatidic acid (PA), phosphatidylinositol (PI), and phosphatidylcholine (PC) in the absence of ceramide. DG generation through the PA phosphatase (PAP) activity of SMSr was approximately 300-fold higher than that with PE and ceramide. SMSr hydrolyzed PI ten times stronger than PI(4,5)bisphosphate (PI(4,5)P₂). The PAP and PC-phospholipase C (PLC) activities of SMSr were inhibited by propranolol, a PAP inhibitor, and by D609, an SMS/PC-PLC inhibitor. Moreover, SMSr showed substrate selectivity for saturated and/or monounsaturated fatty acid-containing PA molecular species, but not arachidonic-acid-containing PA, which is exclusively generated in the PI(4,5)P₂ cycle. We confirmed that SMSr expressed in COS-7 cells showed PAP and PI-PLC activities. Taken together, our study indicated that SMSr possesses previously unrecognized enzyme activities, PAP and PI/PE/PC-PLC, and constitutes a novel DG/PA signaling pathway together with DGKδ, which is independent of the PI(4,5)P₂ cycle.

Genome-Wide Investigation of the Phospholipase C Gene Family in Zea mays

Phospholipase C (PLC) is one of the main hydrolytic enzymes in the metabolism of phosphoinositide and plays an important role in a variety of signal transduction processes responding to plant growth, development, and stress. Although the characteristics of many plant PLCs have been studied, PLC genes of maize have not been comprehensively identified. According to the study, five phosphatidylinositol-specific PLC (PI-PLC) and six non-specific PLC (NPC) genes were identified in maize. The PI-PLC and NPC genes of maize are conserved compared with homologous genes in other plants, especially in evolutionary relationship, protein sequences, conserved motifs, and gene structures. Transient expression of ZmPLC-GFP fusion protein in Arabidopsis protoplast cells showed that ZmPLCs are multi-localization. Analyses of transcription levels showed that ZmPLCs were significantly different under various different tissues and abiotic stresses. Association analysis shown that some ZmPLCs significantly associated with agronomic traits in 508 maize inbred lines. These results contribute to study the function of ZmPLCs and to provide good candidate targets for the yield and quality of superior maize cultivars.

Quantitative Trait Loci Mapping of Mineral Element Contents in Brown Rice Using Backcross Inbred Lines Derived From Oryza longistaminata

Mineral elements play an extremely important role in human health, and are worthy of study in rice grain. Wild rice is an important gene pool for rice improvement including grain yield, disease, and pest resistance as well as mineral elements. In this study, we identified 33 quantitative trait loci (QTL) for Fe, Zn, Se, Cd, Hg, and As contents in wild rice Oryza longistaminata. Of which, 29 QTLs were the first report, and 12 QTLs were overlapped to form five clusters as qSe1/qCd1 on chromosome 1, qCd4.2/qHg4 on chromosome 4, qFe5.2/qZn5.2 on chromosome 5, qFe9/qHg9.2/qAs9.2 on chromosome 9, and qCd10/qHg10 on chromosome 10. Importantly, qSe1/qCd1, can significantly improve the Se content while reduce the Cd content, and qFe5.2/qZn5.2 can significantly improve both the Fe and Zn contents, they were delimited to an interval about 53.8 Kb and 26.2 Kb, respectively. These QTLs detected from Oryza longistaminata not only establish the basis for subsequent gene cloning to decipher the genetic mechanism of mineral element accumulation, but also provide new genetic resource for rice quality improvement.

TRPC channels: Structure, function, regulation and recent advances in small molecular probes

Transient receptor potential canonical (TRPC) channels constitute a group of receptor-operated calcium-permeable nonselective cation channels of the TRP superfamily. The seven mammalian TRPC members, which can be further divided into four subgroups (TRPC1, TRPC2, TRPC4/5, and TRPC3/6/7) based on their amino acid sequences and functional similarities, contribute to a broad spectrum of cellular functions and physiological roles. Studies have revealed complexity of their regulation involving several components of the phospholipase C pathway, G_i and G_o proteins, and internal Ca²⁺ stores. Recent advances in cryogenic electron microscopy have provided several high-resolution structures of TRPC channels. Growing evidence demonstrates the involvement of TRPC channels in diseases, particularly the link between genetic mutations of TRPC6 and familial focal segmental glomerulosclerosis. Because TRPCs were discovered by the molecular identity first, their pharmacology had lagged behind. This is rapidly changing in recent years owning to great efforts from both academia and industry. A number of potent tool compounds from both synthetic and natural products that selective target different subtypes of TRPC channels have been discovered, including some preclinical drug candidates. This review will cover recent advancements in the understanding of TRPC channel regulation, structure, and discovery of novel TRPC small molecular probes over the past few years, with the goal of facilitating drug discovery for the study of TRPCs and therapeutic development.

De novo transcriptome profile of coccolithophorid alga Emiliania huxleyi CCMP371 at different calcium concentrations with proteome analysis

The haptophyte alga Emiliania huxleyi is the most abundant coccolithophore in the modern ocean and produces elaborate calcite crystals, called coccolith, in a separate intracellular compartment known as the coccolith vesicle. Despite the importance of biomineralization in coccolithophores, the molecular mechanism underlying it remains unclear. Understanding this precise machinery at the molecular level will provide the knowledge needed to enable further manipulation of biomineralization. In our previous study, altering the calcium concentration modified the calcifying ability of E. huxleyi CCMP371. Therefore in this study, we tested E. huxleyi cells acclimated to three different calcium concentrations (0, 0.1, and 10 mM). To understand the whole transcript profile at different calcium concentrations, RNA-sequencing was performed and used for de novo assembly and annotation. The differentially expressed genes (DEGs) among the three different calcium concentrations were analyzed. The functional classification by gene ontology (GO) revealed that 'intrinsic component of membrane' was the most enriched of the GO terms at the ambient calcium concentration (10 mM) compared with the limited calcium concentrations (0 and 0.1 mM). Moreover, the DEGs in those comparisons were enriched mainly in 'secondary metabolites biosynthesis, transport and catabolism' and 'signal transduction mechanisms' in the KOG clusters and 'processing in endoplasmic reticulum', and 'ABC transporters' in the KEGG pathways. Furthermore, metabolic pathways involved in protein synthesis were enriched among the differentially expressed proteins. The results of this study provide a molecular profile for understanding the expression of transcripts and proteins in E. huxleyi at different calcium concentrations, which will help to identify the detailed mechanism of its calcification.

Phosphoinositides: multipurpose cellular lipids with emerging roles in cell death

Phosphorylated phosphatidylinositol lipids, or phosphoinositides, critically regulate diverse cellular processes, including signalling transduction, cytoskeletal reorganisation, membrane dynamics and cellular trafficking. However, phosphoinositides have been inadequately investigated in the context of cell death, where they are mainly regarded as signalling secondary messengers. However, recent studies have begun to highlight the importance of phosphoinositides in facilitating cell death execution. Here, we cover the latest phosphoinositide research with a particular focus on phosphoinositides in the mechanisms of cell death. This progress article also raises key questions regarding the poorly defined role of phosphoinositides, particularly during membrane-associated events in cell death such as apoptosis and secondary necrosis. The review then further discusses important future directions for the phosphoinositide field, including therapeutically targeting phosphoinositides to modulate cell death.

Autoantibody Signaling in Pemphigus Vulgaris: Development of an Integrated Model

Pemphigus vulgaris (PV) is an autoimmune skin blistering disease effecting both cutaneous and mucosal epithelia. Blister formation in PV is known to result from the binding of autoantibodies (autoAbs) to keratinocyte antigens. The primary antigenic targets of pathogenic autoAbs are known to be desmoglein 3, and to a lesser extent, desmoglein 1, cadherin family proteins that partially comprise the desmosome, a protein structure responsible for maintaining cell adhesion, although additional autoAbs, whose role in blister formation is still unclear, are also known to be present in PV patients. Nevertheless, there remain large gaps in knowledge concerning the precise mechanisms through which autoAb binding induces blister formation. Consequently, the primary therapeutic interventions for PV focus on systemic immunosuppression, whose side effects represent a significant health risk to patients. In an effort to identify novel, disease-specific therapeutic targets, a multitude of studies attempting to elucidate the pathogenic mechanisms downstream of autoAb binding, have led to significant advancements in the understanding of autoAb-mediated blister formation. Despite this enhanced characterization of disease processes, a satisfactory explanation of autoAb-induced acantholysis still does not exist. Here, we carefully review the literature investigating the pathogenic disease mechanisms in PV and, taking into account the full scope of results from these studies, provide a novel, comprehensive theory of blister formation in PV.

Transcriptome assembly and expression profiling of the molecular responses to cadmium toxicity in cerebral ganglia of wolf spider Pardosa pseudoannulata (Araneae: Lycosidae)

Cadmium (Cd) is a heavy metal that can cause irreversible toxicity to animals, and is an environmental pollutant in farmlands. Spiders are considered to be an excellent model for investigating the impacts of heavy metals on the environment. To date, the changes at the molecular level in the cerebral ganglia of spiders are poorly understood. Cd exposure leads to strong damage in the nervous system, such as apoptosis and necrosis of nerve cells, therefore we conducted a transcriptomic analysis of Pardosa pseudoannulata cerebral ganglia under Cd stress to profile differential gene expression (DGE). We obtained a total of 123,328 assembled unigenes, and 1441 Cd stress-associated DEGs between the Cd-treated and control groups. Expression profile analysis demonstrated that many genes involved in calcium signaling, cGMP-PKG signaling, tyrosine metabolism, phototransduction-fly, melanogenesis and isoquinoline alkaloid biosynthesis were up-regulated under Cd stress, whereas oxidative phosphorylation-related, nervous disease-associated, non-alcoholic fatty liver disease-associated, and ribosomal-associated genes were down-regulated. Here, we provide a comprehensive set of DEGs influenced by Cd stress, and heavy metal stress, and provide new information for elucidating the neurotoxic mechanisms of Cd stress in spiders.

Effects of Fe and Mn deficiencies on the protein profiles of tomato (Solanum lycopersicum) xylem sap as revealed by shotgun analyses

The aim of this work was to study the effects of Fe and Mn deficiencies on the xylem sap proteome of tomato using a shotgun proteomic approach, with the final goal of elucidating plant response mechanisms to these stresses. This approach yielded 643 proteins reliably identified and quantified with 70% of them predicted as secretory. Iron and Mn deficiencies caused statistically significant and biologically relevant abundance changes in 119 and 118 xylem sap proteins, respectively. In both deficiencies, metabolic pathways most affected were protein metabolism, stress/oxidoreductases and cell wall modifications. First, results suggest that Fe deficiency elicited more stress responses than Mn deficiency, based on the changes in oxidative and proteolytic enzymes. Second, both nutrient deficiencies affect the secondary cell wall metabolism, with changes in Fe deficiency occurring via peroxidase activity, and in Mn deficiency involving peroxidase, Cu-oxidase and fasciclin-like arabinogalactan proteins. Third, the primary cell wall metabolism was affected by both nutrient deficiencies, with changes following opposite directions as judged from the abundances of several glycoside-hydrolases with endo-glycolytic activities and pectin esterases. Fourth, signaling pathways via xylem involving CLE and/or lipids as well as changes in phosphorylation and N-glycosylation also play a role in the responses to these stresses. Biological significance In spite of being essential for the delivery of nutrients to the shoots, our knowledge of xylem responses to nutrient deficiencies is very limited. The present work applies a shotgun proteomic approach to unravel the effects of Fe and Mn deficiencies on the xylem sap proteome. Overall, Fe deficiency seems to elicit more stress in the xylem sap proteome than Mn deficiency, based on the changes measured in proteolytic and oxido-reductase proteins, whereas both nutrients exert modifications in the composition of the primary and secondary cell wall. Cell wall modifications could affect the mechanical and permeability properties of the xylem sap vessels, and therefore ultimately affect solute transport and distribution to the leaves. Results also suggest that signaling cascades involving lipid and peptides might play a role in nutrient stress signaling and pinpoint interesting candidates for future studies. Finally, both nutrient deficiencies seem to affect phosphorylation and glycosylation processes, again following an opposite pattern.

Fibronectin binding protein and Ca2+ play an access key role to mediate pathogenesis in Mycobacterium tuberculosis: An overview

The anomalous distribution of adhesive proteins throughout on the cell surface of the Mycobacterium tuberculosis H₃₇ Rv and their contribution in cell surface adhesion and host-pathogen interaction remain elusive. The completion of M. tuberculosis H₃₇ Rv genome sequence analysis gives some interesting information about polymorphic GC-rich repetitive sequence (PGRS) subfamily of M. tuberculosis that encodes fibronectin binding proteins (FnBP), which have been extensively studied, but the function in the pathogenesis of most of these proteins remains unknown and unclear. This review addresses the M. tuberculosis entry mechanism in the host cell. In particular, an effort has been made to focus on several aspects, (a) association of FnBP encodes by PE_PGRS protein family of M. tuberculosis during host-pathogen interactions. (b) Effect of calcium ions in and outside of the host cell is overriding to maintenance of calcium trafficking in phagocytosis. Furthermore, FnBP may be a potential source of antigenic variation that participating in evoking immune response. M. tuberculosis entry mechanism does not have a major influence alone, involvement of calcium ions, perhaps shed light on host-pathogen interaction relationship, and could open up new avenues for development of novel drug by targeting M. tuberculosis FnBP and blockade of selective adhesions could be useful for therapeutics.

Expression and Characterization of a Novel Glycerophosphodiester Phosphodiesterase from Pyrococcus furiosus DSM 3638 That Possesses Lysophospholipase D Activity

Glycerophosphodiester phosphodiesterases (GDPD) are enzymes which degrade various glycerophosphodiesters to produce glycerol-3-phosphate and the corresponding alcohol moiety. Apart from this, a very interesting finding is that this enzyme could be used in the degradation of toxic organophosphorus esters, which has resulted in much attention on the biochemical and application research of GDPDs. In the present study, a novel GDPD from Pyrococcus furiosus DSM 3638 (pfGDPD) was successfully expressed in Escherichia coli and biochemically characterized. This enzyme hydrolyzed bis(p-nitrophenyl) phosphate, one substrate analogue of organophosphorus diester, with an optimal reaction temperature 55 °C and pH 8.5. The activity of pfGDPD was strongly dependent on existing of bivalent cations. It was strongly stimulated by Mn(2+) ions, next was Co(2+) and Ni(2+) ions. Further investigations were conducted on its substrate selectivity towards different phospholipids. The results indicated that except of glycerophosphorylcholine (GPC), this enzyme also possessed lysophospholipase D activity toward both sn1-lysophosphatidylcholine (1-LPC) and sn2-lysophosphatidylcholine (2-LPC). Higher activity was found for 1-LPC than 2-LPC; however, no hydrolytic activity was found for phosphatidylcholine (PC). Molecular docking based on the 3D-modeled structure of pfGDPD was conducted in order to provide a structural foundation for the substrate selectivity.

Genome-wide identification and expression analysis of SWI1 genes in Boechera species

As a mode of reproduction in plants, apomixis leads to the generation of clones via seeds. Apomictic plants form viable diploid female gametes without meiosis (apomeiosis) and produce embryos without fertilization (parthenogenesis). Apomeiosis, as a major component of apomixis, has recently been reported in some Arabidopsis thaliana mutants; dyad mutants of SWI1 showed developmental processes common to apomeiosis, such as producing functional diploid gametes. However, the orthologs of SWI1 genes in natural apomicts has not been previously reported. To identify the relationship between the SWI1 gene and the apomeiosis process, we isolated and sequenced SWI1 orthologs from Boechera species, including apomictic and sexual species. Boechera species are close relatives of A. thaliana and thus are advantageous model species for apomixis research. The SWI1 cDNAs were obtained by RT-PCR from apomictic and sexual Boechera young flower buds. We sequenced partial SWI1 transcripts that were 650bp for B. holboellii and 684bp for B. stricta. These SWI1-like sequences showed 86% similarity for B. holboellii and 92% for B. stricta to the A. thaliana SWI1 transcript. We also used available genome data and amplified genomic sequences for SWI1 orthologs in B. holboellii and B. stricta. The predicted proteins contain a phospholipase C domain and a nuclear localization signal. Sequence analysis did not show significant mutations related to apomixis, and phylogenetic analysis showed that SWI1-like sequences were common across plant families, regardless of the presence of a sexual or apomictic reproduction system. We also investigated the expression levels of SWI1 mRNA in the B. holboellii and B. stricta young unopened flower buds and found that relatively high levels of expression occurred in apomicts.

Virulent Diuraphis noxia Aphids Over-Express Calcium Signaling Proteins to Overcome Defenses of Aphid-Resistant Wheat Plants

The Russian wheat aphid, Diuraphis noxia, an invasive phytotoxic pest of wheat, Triticum aestivum, and barley, Hordeum vulgare, causes huge economic losses in Africa, South America, and North America. Most acceptable and ecologically beneficial aphid management strategies include selection and breeding of D. noxia-resistant varieties, and numerous D. noxia resistance genes have been identified in T. aestivum and H. vulgare. North American D. noxia biotype 1 is avirulent to T. aestivum varieties possessing Dn4 or Dn7 genes, while biotype 2 is virulent to Dn4 and avirulent to Dn7. The current investigation utilized next-generation RNAseq technology to reveal that biotype 2 over expresses proteins involved in calcium signaling, which activates phosphoinositide (PI) metabolism. Calcium signaling proteins comprised 36% of all transcripts identified in the two D. noxia biotypes. Depending on plant resistance gene-aphid biotype interaction, additional transcript groups included those involved in tissue growth; defense and stress response; zinc ion and related cofactor binding; and apoptosis. Activation of enzymes involved in PI metabolism by D. noxia biotype 2 aphids allows depletion of plant calcium that normally blocks aphid feeding sites in phloem sieve elements and enables successful, continuous feeding on plants resistant to avirulent biotype 1. Inhibition of the key enzyme phospholipase C significantly reduced biotype 2 salivation into phloem and phloem sap ingestion.

Translational profiling identifies a cascade of damage initiated in motor neurons and spreading to glia in mutant SOD1-mediated ALS

Ubiquitous expression of amyotrophic lateral sclerosis (ALS)-causing mutations in superoxide dismutase 1 (SOD1) provokes noncell autonomous paralytic disease. By combining ribosome affinity purification and high-throughput sequencing, a cascade of mutant SOD1-dependent, cell type-specific changes are now identified. Initial mutant-dependent damage is restricted to motor neurons and includes synapse and metabolic abnormalities, endoplasmic reticulum (ER) stress, and selective activation of the PRKR-like ER kinase (PERK) arm of the unfolded protein response. PERK activation correlates with what we identify as a naturally low level of ER chaperones in motor neurons. Early changes in astrocytes occur in genes that are involved in inflammation and metabolism and are targets of the peroxisome proliferator-activated receptor and liver X receptor transcription factors. Dysregulation of myelination and lipid signaling pathways and activation of ETS transcription factors occur in oligodendrocytes only after disease initiation. Thus, pathogenesis involves a temporal cascade of cell type-selective damage initiating in motor neurons, with subsequent damage within glia driving disease propagation.

Genome-Wide Analysis and Expression Profiling of the Phospholipase C Gene Family in Soybean (Glycine max)

Phosphatidylinositol-specific phospholipase C (PI-PLC) hydrolyses phosphatidylinositol-4,5-bisphosphate to produce diacylglycerol and inositol 1,4,5-trisphosphate. It plays an important role in plant development and abiotic stress responses. However, systematic analysis and expression profiling of the phospholipase C (PLC) gene family in soybean have not been reported. In this study, 12 putative PLC genes were identified in the soybean genome. Soybean PLCs were found on chromosomes 2, 11, 14 and 18 and encoded 58.8-70.06 kD proteins. Expression pattern analysis by RT-PCR demonstrated that expression of the GmPLCs was induced by PEG, NaCl and saline-alkali treatments in roots and leaves. GmPLC transcripts accumulated specifically in roots after ABA treatment. Furthermore, GmPLC transcripts were analyzed in various tissues. The results showed that GmPLC7 was highly expressed in most tissues, whereas GmPLC12 was expressed in early pods specifically. In addition, subcellular localization analysis was carried out and confirmed that GmPLC10 was localized in the plasma membrane in Nicotiana benthamiana. Our genomic analysis of the soybean PLC family provides an insight into the regulation of abiotic stress responses and development. It also provides a solid foundation for the functional characterization of the soybean PLC gene family.

Androgens in pregnancy: roles in parturition

BACKGROUND

Understanding the physiology of pregnancy enables effective management of pregnancy complications that could otherwise be life threatening for both mother and fetus. A functional uterus (i) retains the fetus in utero during pregnancy without initiating stretch-induced contractions and (ii) is able to dilate the cervix and contract the myometrium at term to deliver the fetus. The onset of labour is associated with successful cervical remodelling and contraction of myometrium, arising from concomitant activation of uterine immune and endocrine systems. A large body of evidence suggests that actions of local steroid hormones may drive changes occurring in the uterine microenvironment at term. Although there have been a number of studies considering the potential role(s) played by progesterone and estrogen at the time of parturition, the bio-availability and effects of androgens during pregnancy have received less scrutiny. The aim of this review is to highlight potential roles of androgens in the biology of pregnancy and parturition.

METHODS

A review of published literature was performed to address (i) androgen concentrations, including biosynthesis and clearance, in maternal and fetal compartments throughout gestation, (ii) associations of androgen concentrations with adverse pregnancy outcomes, (iii) the role of androgens in the physiology of cervical remodelling and finally (iv) the role of androgens in the physiology of myometrial function including any impact on contractility.

RESULTS

Some, but not all, androgens increase throughout gestation in maternal circulation. The effects of this increase are not fully understood; however, evidence suggests that increased androgens might regulate key processes during pregnancy and parturition. For example, androgens are believed to be critical for cervical remodelling at term, in particular cervical ripening, via regulation of cervical collagen fibril organization. Additionally, a number of studies highlight potential roles for androgens in myometrial relaxation via non-genomic, AR-independent pathways critical for the pregnancy reaching term. Understanding of the molecular events leading to myometrial relaxation is an important step towards development of novel targeted tocolytic drugs.

CONCLUSIONS

The increase in androgen levels throughout gestation is likely to be important for establishment and maintenance of pregnancy and initiation of parturition. Further investigation of the underlying mechanisms of androgen action on cervical remodelling and myometrial contractility is needed. The insights gained may facilitate the development of new therapeutic approaches to manage pregnancy complications such as preterm birth.

Quercetin acutely relaxes airway smooth muscle and potentiates β-agonist-induced relaxation via dual phosphodiesterase inhibition of PLCβ and PDE4

Asthma is a disease of the airways with symptoms including exaggerated airway narrowing and airway inflammation. Early asthma therapies used methylxanthines to relieve symptoms, in part, by inhibiting cyclic nucleotide phosphodiesterases (PDEs), the enzyme responsible for degrading cAMP. The classification of tissue-specific PDE subtypes and the clinical introduction of PDE-selective inhibitors for chronic obstructive pulmonary disease (i.e., roflumilast) have reopened the possibility of using PDE inhibition in the treatment of asthma. Quercetin is a naturally derived PDE4-selective inhibitor found in fruits, vegetables, and tea. We hypothesized that quercetin relaxes airway smooth muscle via cAMP-mediated pathways and augments β-agonist relaxation. Tracheal rings from male A/J mice were mounted in myographs and contracted with acetylcholine (ACh). Addition of quercetin (100 nM-1 mM) acutely and concentration-dependently relaxed airway rings precontracted with ACh. In separate studies, pretreatment with quercetin (100 μM) prevented force generation upon exposure to ACh. In additional studies, quercetin (50 μM) significantly potentiated isoproterenol-induced relaxations. In in vitro assays, quercetin directly attenuated phospholipase C activity, decreased inositol phosphate synthesis, and decreased intracellular calcium responses to Gq-coupled agonists (histamine or bradykinin). Finally, nebulization of quercetin (100 μM) in an in vivo model of airway responsiveness significantly attenuated methacholine-induced increases in airway resistance. These novel data show that the natural PDE4-selective inhibitor quercetin may provide therapeutic relief of asthma symptoms and decrease reliance on short-acting β-agonists.

Glycolipid membrane anchored recombinant protein production from CHO cells cultGred on porous microcarriers

Recombinant proteins were harvested from Chinese hamster ovary (CHO) cells by a controlled release process, which increased the purity and concentration of the harvested protein. Recombinant human melano-transferrin (p97) was expressed linked to the outer surface of CHO cells by a glycosyl-phosphatidylinositol (GPI) membrane anchor. Cells were grown to confluence in T-flask culture, and the p97 harvested by replacing the growth medium for 30 min with phosphate-buffered saline (PBS) containing 10 mU/mL phosphatidylinositol-phospholipase C (PI-PLC). The GPI anchor was selectively cleaved by PI-PLC. In fresh medium, the CHO cells regained over 95% of their p97 expression within 40 h. The process was repeated for eight harvests. Harvested protein concentrations varied from 1.5 to 3.8 microg/mL due to difficulties in maintaining stable confluent T-flask cultures. Harvesting from cells growing on porous microcarriers was investigated to increase p97 product concentrations and to overcome culture stability problems. Semicontinuous cultures were maintained in spinners for up to 76 days with average bioreactor cell densities of over 10(7) cell/mL. The p97 was harvested at up to 100 microg/mL and 30% purity with protein production remaining stable for 4 harvest cycles. Production of high levels of p97 from CHO cells was maintained at 0.5% serum.

Defense activation triggers differential expression of phospholipase-C (PLC) genes and elevated temperature induces phosphatidic acid (PA) accumulation in tomato

Recently, we provided the first genetic evidence for the requirement of tomato PLC4 and PLC6 genes in defense activation and disease resistance. The encoded enzymes were catalytically active as they were able to degrade phosphatidylinositol (PI), thereby producing diacylglycerol (DG). Here we report differential PLC gene expression following the initiation of defense signaling by the interaction between Cladosporium fulvum resistance (R) protein Cf-4 and its matching effector Avr4 in tomato hybrid seedlings that express both Cf-4 and Avr4. Furthermore, we observed that PLC3 and PLC6 gene expression is upregulated by elevated temperature in the control seedlings. This upregulation coincides with an increase in the levels of phosphatidic acid (PA) and a decrease in the levels of PI and phosphatidylinositol phosphate (PIP). The decrease in PI and PIP levels matches with the activation of PLC. In addition, the levels of the structural phospholipids phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) declined transiently during recovery after the exposure to elevated temperature., Further studies will be required to explain the mechanism causing the sustained accumulation of PA during recovery, combined with a reduction in the levels of structural phospholipids.

In silico prediction and analysis of Caenorhabditis EF-hand containing proteins

Calcium (Ca⁺²) is a ubiquitous messenger in eukaryotes including Caenorhabditis. Ca⁺²-mediated signalling processes are usually carried out through well characterized proteins like calmodulin (CaM) and other Ca⁺² binding proteins (CaBP). These proteins interact with different targets and activate it by bringing conformational changes. Majority of the EF-hand proteins in Caenorhabditis contain Ca⁺² binding motifs. Here, we have performed homology modelling of CaM-like proteins using the crystal structure of Drosophila melanogaster CaM as a template. Molecular docking was applied to explore the binding mechanism of CaM-like proteins and IQ1 motif which is a ∼25 residues and conform to the consensus sequence (I, L, V)QXXXRXXXX(R,K) to serve as a binding site for different EF hand proteins. We made an attempt to identify all the EF-hand (a helix-loop-helix structure characterized by a 12 residues loop sequence involved in metal coordination) containing proteins and their Ca⁺² binding affinity in Caenorhabditis by analysing the complete genome sequence. Docking studies revealed that F165, F169, L29, E33, F44, L57, M61, M96, M97, M108, G65, V115, F93, N104, E144 of CaM-like protein is involved in the interaction with IQ1 motif. A maximum of 170 EF-hand proteins and 39 non-EF-hand proteins with Ca⁺²/metal binding motif were identified. Diverse proteins including enzyme, transcription, translation and large number of unknown proteins have one or more putative EF-hands. Phylogenetic analysis revealed seven major classes/groups that contain some families of proteins. Various domains that we identified in the EF-hand proteins (uncharacterized) would help in elucidating their functions. It is the first report of its kind where calcium binding loop sequences of EF-hand proteins were analyzed to decipher their calcium affinities. Variation in Ca⁺²-binding affinity of EF-hand CaBP could be further used to study the behaviour of these proteins. Our analyses postulated that Ca⁺² is likely to be key player in Caenorhabditis cell signalling.

Characterization and expression analysis of a gene encoding a secreted lipase-like protein expressed in the salivary glands of the larval Hessian fly, Mayetiola destructor (Say)

In a salivary gland transcriptomics study we identified a cDNA with a full-length open reading frame for a gene (MdesL1) encoding a lipase-like protein expressed in the salivary glands of the larval Hessian fly, Mayetiola destructor (Say). Fluorescent in situ hybridization on salivary polytenes positioned MdesL1 on the long arm of Autosome 1. BLASTp and conserved domain searches revealed the deduced amino acid sequence contained a lipase superfamily domain with similarity to lipases and phospholipases from other insects. A secretion signal peptide was identified at the amino terminus of the deduced amino acid sequence. Analysis of the transcript of MdesL1 in larval Hessian fly tissues by quantitative real-time PCR (qPCR) revealed the greatest abundance was in salivary glands. Analysis of transcript levels during development showed the greatest level was detected in feeding 1st-instar and early 2nd-instar larvae. Transcript levels increased dramatically over time in larvae feeding on susceptible wheat but were detected at low levels in larvae feeding on resistant wheat. These data suggest the protein encoded by MdesL1 is likely secreted into host-plant cells during larval feeding and could be involved in extra-oral digestion and changes in host-cell permeability or in generating a second messenger in a host-cell-signaling cascade.

Glucocorticoid-regulated crosstalk between arachidonic acid and endocannabinoid biochemical pathways coordinates cognitive-, neuroimmune-, and energy homeostasis-related adaptations to stress

Arachidonic acid and its derivatives constitute the major group of signaling molecules involved in the innate immune response and its communication with all cellular and systemic aspects involved on homeostasis maintenance. Glucocorticoids spread throughout the organism their influences over key enzymatic steps of the arachidonic acid biochemical pathways, leading, in the central nervous system, to a shift favoring the synthesis of anti-inflammatory endocannabinoids over proinflammatory metabolites, such as prostaglandins. This shift modifies local immune-inflammatory response and neuronal activity to ultimately coordinate cognitive, behavioral, neuroendocrine, neuroimmune, physiological, and metabolic adjustments to basal and stress conditions. In the hypothalamus, a reciprocal feedback between glucocorticoids and arachidonate-containing molecules provides a mechanism for homeostatic control. This neurochemical switch is susceptible to fine-tuning by neuropeptides, cytokines, and hormones, such as leptin and interleukin-1beta, assuring functional integration between energy homeostasis control and the immune/stress response.

PLC-β3 signals upstream of PKCε in acute and chronic inflammatory hyperalgesia

While protein kinase C epsilon has been shown to contribute to acute and chronic mechanical hyperalgesia, its upstream signaling pathway has received little attention. Since phospholipase C can signal to PKC epsilon and has been implicated in nociceptor sensitization, we tested if it is upstream of PKC epsilon in mechanisms underlying primary mechanical hyperalgesia. In the rat, the PKC epsilon-dependent mechanical hyperalgesia and hyperalgesic priming (i.e., a form of chronic latent enhanced hyperalgesia) induced by carrageenan were attenuated by a non-selective PLC inhibitor U-73122. A lipid mediator of PLC signaling, l-alpha-lysophosphatidylcholine produced dose-dependent mechanical hyperalgesia and hyperalgesic priming, which was attenuated by EAVSLKPT, a selective PKC epsilon inhibitor. However, U-73122 did not attenuate hyperalgesia induced by psi epsilon RACK, a selective PKC epsilon activator. Antisense to PLC-beta 3 isoform, which was found in small-diameter dorsal root ganglion neurons, also attenuated carrageenan-induced acute and chronic-latent hyperalgesia. These studies support the suggestion that PLC-beta 3 is an important upstream signaling molecule for PKC epsilon-mediated acute and chronic inflammatory pain.

Mutation and divergence of the phospholipase C gene in Neurospora crassa

In the fungus Neurospora crassa we have used RIP to obtain a presumptive null mutation of the phospholipase C-1 gene, thought to be important in intracellular calcium signaling, notably maintenance of the tip-high calcium gradient. The mutant is viable but has slow, aberrant growth and branching. Hence plc-1 is not required for polar growth at the tip, but is necessary to modulate growth to give normal form. The mutant has residual PLC activity suggesting that this enzyme function can be provided from other parts of the genome. Sequencing natural isolates has shown that the plc-1 gene is highly variable in nature. A large proportion of the variable sites are in a region that is unique to Neurospora. A phylogeny for this gene shows that New and Old World strains have diverged the most. Within the Americas, morphs are found throughout the continent suggesting extensive strain dispersal.

Lipid–protein interactions in GPCR-associated signaling

Signal transduction via G-protein-coupled receptors (GPCRs) is a fundamental pathway through which the functions of an individual cell can be integrated within the demands of a multicellular organism. Since this family of receptors first discovered, the proteins that constitute this signaling cascade and their interactions with one another have been studied intensely. In parallel, the pivotal role of lipids in the correct and efficient propagation of extracellular signals has attracted ever increasing attention. This is not surprising given that most of the signal transduction machinery is membrane-associated and therefore lipid-related. Hence, lipid-protein interactions exert a considerable influence on the activity of these proteins. This review focuses on the post-translational lipid modifications of GPCRs and G proteins (palmitoylation, myristoylation, and isoprenylation) and their significance for membrane binding, trafficking and signaling. Moreover, we address how the particular biophysical properties of different membrane structures may regulate the localization of these proteins and the potential functional consequences of this phenomenon in signal transduction. Finally, the interactions that occur between membrane lipids and GPCR effector enzymes such as PLC and PKC are also considered.

The structure and function of a novel glycerophosphodiesterase from Enterobacter aerogenes

The structure of the glycerophosphodiesterase (GDPD) from Enterobacter aerogenes, GpdQ, has been solved by SAD phasing from the active site metal ions. Structural analysis indicates that GpdQ belongs to the alpha/beta sandwich metallo-phosphoesterase family, rather than the (alpha/beta)(8) barrel GDPD family, suggesting that GpdQ is a structurally novel GDPD. Hexameric GpdQ is generated by interactions between three dimers. The dimers are formed through domain swapping, stabilised by an inter-chain disulfide bond, and beta-sheet extension. The active site contains a binuclear metal centre, with a fully occupied alpha-metal ion site, and partially occupied beta-metal ion site, as revealed by anomalous scattering analysis. Using a combination of TLS refinement and normal mode analysis, the dynamic movement of GpdQ was investigated. This analysis suggests that the hexameric quaternary structure stabilises the base of the dimer, which promotes "breathing" of the active site cleft. Comparison with other metallo-phosphodiesterases shows that although the central, catalytic, domain is highly conserved, many of these enzymes possess structurally unrelated secondary domains located at the entrance of the active site. We suggest that this could be a common structural feature of metallo-phosphodiesterases that constrains substrate specificity, preventing non-specific phosphodiester hydrolysis.

Nitroproteins from a human pituitary adenoma tissue discovered with a nitrotyrosine affinity column and tandem mass spectrometry

The aim of this study was to characterize endogenous nitroproteins, and those proteins that interact with nitroproteins, in a human pituitary nonfunctional adenoma so as to clarify the role of protein nitration in adenomas. A nitrotyrosine affinity column (NTAC) was used to preferentially enrich and isolate endogenous nitroproteins and nitroprotein-protein complexes from a tissue homogenate that was prepared from a human pituitary nonfunctional pituitary adenoma. The preferentially enriched endogenous nitroproteins and nitroprotein-protein complexes were subjected to trypsin digestion, desalination, and tandem mass spectrometry analysis. Nine nitroproteins (Rho-GTPase-activing protein 5, leukocyte immunoglobulin-like receptor subfamily A member 4 precursor, zinc finger protein 432, cAMP-dependent protein kinase type I-beta regulatory subunit, sphingosine-1-phosphate lyase 1, centaurin beta 1, proteasome subunit alpha type 2, interleukin 1 family member 6, and rhophilin 2) and three proteins (interleukin 1 receptor-associated kinase-like 2, glutamate receptor-interacting protein 2, and ubiquitin) that interacted with nitroproteins were discovered. The nitration site of each nitroprotein was located onto the functional domain where nitration occurred, and each nitroprotein was related to a corresponding functional system. Those data indicate that protein nitration might be an important molecular event in the formation of a human pituitary nonfunctional adenoma.

Changes in the lipid turnover, composition, and organization, as sphingolipid-enriched membrane domains, in rat cerebellar granule cells developing in vitro

In the present paper, we report on the properties of sphingolipid-enriched domains of rat cerebellar granule cells in culture at different stages of neuronal development. The major lipid components of these domains were glycerophospholipids and cholesterol. Glycerophospholipids were 45-75% and cholesterol 15-45% of total lipids of the domains. This corresponded to 5-17% of total cell glycerophospholipids and 15-45% of total cell cholesterol. Phosphatidylcholine, mainly dipalmitoylphosphatidylcholine, was 66-85% of all the glycerophospholipids associated with these domains. Consequently, the palmitoyl residue was significantly enriched in the domains. The surface occupied by these structures increased during development. 40-70% of cell sphingolipids segregated in sphingolipid-enriched membrane domains, with the maximum ganglioside density in fully differentiated neurons. A high content of ceramide was found in the domains of aging neurons. Then, the sphingolipid/glycerophospholipid molar ratio was more than doubled during the initial stage of development, whereas the cholesterol/glycerophospholipid molar ratio gradually decreased during in vitro differentiation. Phosphorylated phosphoinositides, which were scant in the domains of undifferentiated cells, dramatically increased during differentiation and aging in culture. Proteins were minor components of the domains (0.1-2.8% of all domain components). Phosphotyrosine-containing proteins were selectively recovered in the sphingolipid-enriched domain. Among these, Src family protein-tyrosine kinases, known to participate to the process of neuronal differentiation, were associated with the sphingolipid-enriched domains in a way specific for the type of kinase and for the developmental stage of the cell. Proteins belonging to other signaling pathways, such as phosphoinositide 3-kinase and its downstream target, Akt, were not associated with the domains.

Protein kinase C isozyme-specific phosphorylation of profilin

Profilin, a cytoskeletal protein, is emerging as an important link between signal transduction pathways and cytoskeletal dynamics. Profilin is phosphorylated on its C-terminal serine by protein kinase C (PKC). The protein kinase used for the in vitro phosphorylation studies reported earlier was a mixture of isozymes, and therefore, attempts were made to address the isozyme specificity on profilin phosphorylation under in vitro conditions. Profilin was subjected to phosphorylation by PKCalpha, PKCepsilon, and PKCzeta isozymes individually, and it was observed that profilin phosphorylation is cofactor-independent. PKCzeta phosphorylates profilin to a higher extent, but exhibits cofactor dependency with respect to phosphoinositides. The stoichiometry of phosphorylation was measured in the presence of these different isozymes, and a maximum stoichiometry of 0.8 (mole phosphate incorporated/mole profilin) was obtained in the presence of PKCzeta. Phosphorylation of profilin by PKCzeta was maximal in the presence of phosphatidylinositol4,5-bisphosphate (PI4,5-P2) when compared to the other phosphoinositides studied.

TAS-301 blocks receptor-operated calcium influx and inhibits rat vascular smooth muscle cell proliferation induced by basic fibroblast growth factor and platelet-derived growth factor

The purpose of this study was to determine the effect of a recently synthesized drug, TAS-301 [3-bis(4-methoxyphenyl)methylene-2-indolinone], on vascular smooth muscle cell (VSMC) proliferation and the intracellular signal transduction pathways involved in VSMC proliferation. In an in vitro assay, TAS-301 inhibited the proliferation of rat VSMCs stimulated by platelet-derived growth factor (PDGF)-BB, basic fibroblast growth factor, or 2% fetal bovine serum in a concentration-dependent manner. TAS-301 dose-dependently inhibited the PDGF-induced Ca2+ influx; the concentration for the inhibition of Ca2+ influx was nearly identical to that for inhibition of VSMC proliferation. The Ca2+ influx induced by PDGF was also attenuated by NiCl2 but not by nifedipine, suggesting that PDGF-induced Ca2+ influx would be mediated by some non-voltage-dependent mechanisms. Furthermore, TAS-301 inhibited PDGF-induced activation of protein kinase C (PKC) and the phorbol 12-myristate 13-acetate-mediated induction of activator protein 1 (AP-1) in a concentration-dependent manner. These findings indicate that TAS-301 inhibited the proliferation of VSMCs by blocking voltage-independent Ca2+ influx and downstream signals such as the Ca2+/PKC signaling pathway, leading to AP-1 induction.

Metabotropic glutamate receptor-mediated hippocampal phosphoinositide turnover is blunted in spatial learning-impaired aged rats

Maximal phosphoinositide (PI) turnover was examined in the hippocampus of young and aged Long-Evans rats that were behaviorally characterized for spatial learning in the Morris water maze. The type 1 metabotropic glutamate receptor (mGluR) agonist 1S,3R ACPD was used to stimulate PI turnover and to determine the E(MAX) for each rat. Protein levels in hippocampus for type 1 mGluRs, Galphaq11, and phospholipase Cbeta-1 (PLCbeta-1) were also measured by quantitative Western blotting. The results show that PI turnover mediated by the mGluRs was blunted in the aged rats. The magnitude of the decrement in PI turnover was also significantly correlated with age-related spatial memory decline. The decrease in mGluR-mediated PI turnover occurred without changes in the protein level of either the mGluRs or the G-protein coupled to those receptors, Galphaq11. A significant decrease in the immunoreactivity of PLCbeta-1, however, was observed in the hippocampus of aged rats; PLCbeta-1 immunoreactivity was significantly correlated with spatial learning only when the young and aged rats were considered together. The decrement in mGluR-mediated signal transduction in the hippocampus that is related to cognitive impairment in aging may be attributable, at least in part, to a deficiency in the enzyme PLCbeta-1. That deficiency may also contribute to a blunted response in muscarinic stimulation of hippocampal PI turnover that we previously found in this same study population. An age-related alteration in this signal transduction system may provide a functional basis for cognitive decline independent of any loss of neurons in the hippocampus.

Functional expression and characterisation of a new human phosphatidylinositol 4-kinase PI4K230

By constructing DNA probes we have identified and cloned a human PtdIns 4-kinase, PI4K230, corresponding to a mRNA of 7.0 kb. The cDNA encodes a protein of 2044 amino acids. The C-terminal part of ca. 260 amino acids represents the catalytic domain which is highly conserved in all recently cloned PtdIns 4-kinases. N-terminal motifs indicate multiple heterologous protein interactions. Human PtdIns 4-kinase PI4K230 expressed in vitro exhibits a specific activity of 58 micromol mg-1min-1. The enzyme expressed in Sf9 cells is essentially not inhibited by adenosine, it shows a high Km for ATP of about 300 microM and it is half-maximally inactivated by approximately 200 nM wortmannin. These data classify this enzyme as type 3 PtdIns 4-kinase. Antibodies raised against the N-terminal part moderately activate and those raised against the C-terminal catalytic domain inhibit the enzymatic activity. The coexistence of two different type 3 PtdIns 4-kinases, PI4K92 and PI4K230, in several human tissues, including brain, suggests that these enzymes are involved in distinct basic cellular functions.

Altered Gq/G11 guanine nucleotide regulatory protein expression in a rat model of hepatocellular carcinoma: role in mitogenesis

Guanine nucleotide regulatory proteins (G-proteins) represent an important transmembrane pathway whereby extra-cellular signals are transduced to intracellular signaling pathways. The mitogen-activated protein kinase (MAPK) cascade has been identified as a key factor in transducing numerous mitogenic stimuli. MAPK activity is regulated via numerous receptor types, including those linked to Gq/G11-proteins, which regulate phospholipase-C activity. We hypothesized that alterations in a Gq/G11-PLC pathway may contribute to the enhanced cellular mitogenesis characteristic of hepatocellular carcinoma (HCC), possibly via a MAPK-dependent pathway. By using an in vivo model of HCC we investigated changes in Gq/G11-protein expression in tumorigenic tissue versus adjacent, non-neoplastic liver. In addition we addressed the role of Gq/G11-proteins in the regulation of MAPK-linked mitogenesis by using rat hepatic tumorigenic cells (H4IIE) and isolated hepatocytes in culture. Western blot analysis showed significant increases in Gqalpha and G11alpha expression in tumorigenic liver versus normal liver specimens, an effect that was augmented in cultured H4IIE cells versus isolated cultured hepatocytes. Furthermore, phosphoinositol specific phospholipase-C (PLC) activity was significantly increased in HCC versus normal liver. A specific PLC inhibitor (Et-18-OCH3) caused a dose-dependent decrease in serum stimulated DNA synthesis in both cultured H4IIE cells and isolated rat hepatocytes, the H4IIE cell line showing greater sensitivity to Et-18-OCH3. In addition, serum-stimulated MAPK activity was significantly enhanced in H4IIE versus cultured hepatocytes. Moreover, treatment with Et-18-OCH3 significantly attenuated serum stimulated MAPK activity in both cultured hepatocytes and H4IIE cells. Furthermore, U73122 (Gqalpha-PLC specific uncoupler) and GP2A (Gqalpha specific inhibitor) mirrored the effects of those observed for Et-18-OCH3 whereas PD98059 (specific MEK inhibitor) completely abolished serum-stimulated DNA synthesis in tumorigenic H4IIE cells. We conclude that HCC is associated with enhanced Gq/G11-PLC expression/activity as compared with normal liver. Furthermore, a PLC-linked MAPK cascade plays a significant role in the progression of the enhanced mitogenesis characteristic of HCC.

Immunolocalization of phospholipase C isoforms in rat kidney

BACKGROUND

Phospholipase C (PLC) is an important factor in signal transduction because this enzyme is activated by several hormones and growth factors. Eight PLC isoforms have been described raising the possibility that different cells express a single isoform or activate specific isoforms in different cells. Therefore, the goal of this study was to determine which PLC isoforms are expressed in specific regions of rat kidney.

METHODS

Western blot analysis was performed in microdissected nephron segments of rat kidney, while immunohistochemical analysis was performed on whole rat kidney slices using PLC isoform-specific antibodies.

RESULTS

All three families of PLC isoforms (beta, gamma, and delta) were present throughout the cortical and medullary regions of the kidney. Only the PLC-beta1 isoform was observed in the brush border of the proximal tubule, but all isoforms were present in glomeruli and in the cytoplasm of tubular epithelial cells. In addition, only the PLC-gamma1 isoform was expressed in the internal elastic lamina of the renal artery, while vasa recta expressed PLC-beta1 most intensely. Medullary thick ascending limbs showed an intense level of expression of all three isoforms.

CONCLUSION

Multiple PLC isoforms are present in glomeruli, renal tubules, and renal vasculature in vivo, but with some segment-specific differences. These findings suggest that the response of a specific cell is not determined by expression of only one PLC isoform, with the exception of the brush border of the proximal tubule and the renal arteries. Instead, the presence of multiple PLC isoforms in specific regions of the kidney suggests that hormonal regulation in vivo involves mechanisms beyond cell-specific isoforms of PLC.

The Arabidopsis thaliana genome has multiple divergent forms of phosphoinositol-specific phospholipase C1

Highly degenerate primers to conserved regions of the eukaryotic phosphoinositol-specific phospholipase C (PLC) were used to amplify fragments of plant PLCs from Arabidopsis thaliana genomic DNA. Eight completely different fragment sequences that showed high homology to PLCs of both animals and plants were isolated. The variation between these putative PLCs was high and suggests that, like animals, plants have multiple isoforms of PLC. Using one of the PCR clones, we isolated a corresponding full-length Arabidopsis PLC gene (ATHATPLC1G), and sequence analysis indicated that it was most like a delta-type PLC. This gene is 2.5 kb and contains seven introns, all but one of which has intron/exon border sequences that conform to the Arabidopsis consensus. The structural complexity of the gene is relatively simple compared to mammalian beta-type PLCs that can be 15 kb long with up to 30 introns. The plant gene is a single copy and was mapped to four Arabidopsis YACs, one located on chromosome 2. The promoter region contained two TATA-like elements at -43 and -185 and other putative regulatory elements that suggest that this PLC is hormonally regulated. This is the first plant PLC gene and the first delta type-PLC gene from a higher organism to be sequenced.

Angiopeptin, a somatostatin analogue, inhibits rat coronary artery and aorta smooth muscle cell proliferation induced by the thromboxane A2 mimetic U46619

Thromboxane A2 (TXA2) is a potent mitogenic agent. Its synthesis is increased in transplant patients during rejection episodes, which is the suspected etiology of accelerated transplant arteriosclerosis. Angiopeptin, a stable analogue of somatostatin, inhibits arterial myointimal thickening in a number of vascular balloon injury models of angioplasty and in vivo models of transplant arteriosclerosis. In this study, we investigated whether TXA2-induced smooth muscle cell proliferation is inhibited by Angiopeptin in vitro. Primary rat coronary and aorta smooth muscle cells were cultured in the presence of U46619, a TXA2 mimetic. Proliferation induced by U46619, as determined by 3H-thymidine incorporation, was abrogated by two specific thromboxane receptor antagonists, SQ 30741 and SQ 29548, indicating that the effect of U46619 on smooth muscle cells is a specific receptor-mediated response. We found Angiopeptin to inhibit proliferation following exposure of both coronary and aorta smooth muscle cells to varying concentrations of U46619 for 3 and 6 days. This study demonstrates that U46619 exerts a specific receptor-mediated response stimulating the rat coronary and aorta smooth muscle cell proliferation. This mitogenic effect is obtained by increasing the G1 to S transition rate. Angiopeptin inhibits thromboxane-induced cell proliferation to the same extent as a thromboxane antagonist. This inhibition is obtained by maintaining the noncycling fraction in that Angiopeptin prevents a progression from G0-G1 to S phase.

Structural and mechanistic features of phospholipases C: effectors of inositol phospholipid-mediated signal transduction

The production of the intracellular second messengers inositol (1,4,5)-trisphosphate (InsP3) and sn 1,2-diacylglycerol (DG) in response to a wide variety of extracellular primary messengers is achieved by an extended family of inositol phospholipid phosphodiesterases termed phospholipases C (PLC, E.C. 3.1.4.11). This family has been the subject of extensive research and it is clear that the different isoenzymes exhibit some common characteristics (e.g., interactions with substrates) and other distinctive features (e.g., modes of regulation). The recent description of the X-ray crystal structure of a mammalian PLC has served to clarify much about the behaviour of the PLCs, emphasising the "modular" structure of these enzymes. The main focus of this review will concern the specific adaptations of PLC molecules which make them efficient lipid-metabolising enzymes. We also describe what is known about how these enzymes interact with their lipid substrates, which will serve as a basis for considering how PLCs may be activated.

Activation of the G protein Gq/11 through tyrosine phosphorylation of the alpha subunit

Various receptors coupled to the heterotrimeric guanine nucleotide-binding protein Gq/11 stimulate formation of inositol-1,4,5-trisphosphate (IP3). Activation of these receptors also induces protein tyrosine phosphorylation. Formation of IP3 in response to stimulated receptors that couple to Gq/11 was blocked by protein tyrosine kinase inhibitors. These inhibitors appeared to act before activation of Gq/11. Moreover, stimulation of receptors coupled to Gq/11 induced phosphorylation on a tyrosine residue (Tyr356) of the Galphaq/11 subunit, and this tyrosine phosphorylation event was essential for Gq/11 activation. Tyrosine phosphorylation of Galphaq/11 induced changes in its interaction with receptors. Therefore, tyrosine phosphorylation of Galphaq/11 appears to regulate the activation of Gq/11 protein.

Evidence for the involvement of docosahexaenoic acid in cholinergic stimulated signal transduction at the synapse

[4,5-3H]Docosahexaenoic acid ([3H]DHA) or [9,10-3H]palmitic acid ([3H]PAM) was infused intravenously for 5 min to awake, adult male rats before and after treatment with arecoline (15 mg/kg, i.p.), a cholinergic agonist. Animals were killed 15 min post-infusion, the brains were rapidly removed and subcellular fractions were obtained after sucrose density centrifugation. In control animals, [3H]DHA and [3H]PAM were incorporated into the synaptosomal fractions, representing 50%-60% of total membrane label. Most remaining membrane label (30%-40%) was in the microsomal fraction. Both fractions contained the synaptic marker synaptophysin. The remaining 10% of radioactivity was in the myelin and mitochondrial fractions. Arecoline significantly increased [3H]DHA entry into the synaptosomal fractions by 100% and into the microsomal fraction by 50%. In these fractions 60%-65% of the [3H]DHA was in phospholipid, the rest corresponding to free fatty acid and diacylglycerol. In contrast, arecoline did not change [3H]PAM incorporation into any brain fraction. These results demonstrate that plasma [3H]DHA incorporation is selectively increased into synaptic membrane phospholipids of the rat brain in response to cholinergic activation. The increased incorporation of DHA but not of PAM into synaptic membranes in response to cholinergic stimulation indicates a primary role for DHA in phospholipid mediated signal transduction at the synapse involving activation of phospholipase A2 and/or C.