Invertebrate phosphatidylinositol-specific phospholipases C and their role in cell signaling

PLCG2 promotes hepatocyte proliferation in vitro via NF-κB and ERK pathway by targeting bcl2, myc and ccnd1

Phospholipase Cγ2 (PLCG2) has been implicated in the regulation of cell proliferation, transformation, and tumor growth. In this study, we investigate the mechanism of PLCG2 action using a short interference RNA (siRNA) method. The effects of PLCG2 on rat liver BRL-3A cells treated siRNA were studied by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT assay), bromodeoxyuridine (BrdU) labelling assay, flow cytometry method (FCM), quantitative real-time polymerase chain reaction (qRT-PCR) and western blot. The results showed when PLCG2 was reduced, cell vitality and proliferation rate were significantly decreased (p < .05 vs. control). FCM analysis showed that the number of cell division phase (G2 + M) was declined (p < .05 vs. control). RT-PCR and western blot revealed that the expression of signalling related genes NF-κB, FOS, JUN and ELK, target genes BCL2, CCNB1 and CCND1 were remarkably down-regulated in cells treated with PLCG2 siRNAs. Based on these results, we conclude PLCG2 plays an important role in rat liver cell proliferation via ERK and NF-κB pathway by regulating the expression of BCl2, MYC and CCND1.

Gαq and the Phospholipase Cβ3 X-Y Linker Regulate Adsorption and Activity on Compressed Lipid Monolayers

Phospholipase Cβ (PLCβ) enzymes are peripheral membrane proteins required for normal cardiovascular function. PLCβ hydrolyzes phosphatidylinositol 4,5-bisphosphate, producing second messengers that increase intracellular Ca²⁺ level and activate protein kinase C. Under basal conditions, PLCβ is autoinhibited by its C-terminal domains and by the X-Y linker, which contains a stretch of conserved acidic residues required for interfacial activation. Following stimulation of G protein-coupled receptors, the heterotrimeric G protein subunit Gα_q allosterically activates PLCβ and helps orient the activated complex at the membrane for efficient lipid hydrolysis. However, the molecular basis for how the PLCβ X-Y linker, its C-terminal domains, Gα_q, and the membrane coordinately regulate activity is not well understood. Using compressed lipid monolayers and atomic force microscopy, we found that a highly conserved acidic region of the X-Y linker is sufficient to regulate adsorption. Regulation of adsorption and activity by the X-Y linker also occurs independently of the C-terminal domains. We next investigated whether Gα_q-dependent activation of PLCβ altered interactions with the model membrane. Gα_q increased PLCβ adsorption in a manner that was independent of the PLCβ regulatory elements and targeted adsorption to specific regions of the monolayer in the absence of the C-terminal domains. Thus, the mechanism of Gα_q-dependent activation likely includes a spatial component.

Vesicle-Mediated Steroid Hormone Secretion in Drosophila melanogaster

Steroid hormones are a large family of cholesterol derivatives regulating development and physiology in both the animal and plant kingdoms, but little is known concerning mechanisms of their secretion from steroidogenic tissues. Here, we present evidence that in Drosophila, endocrine release of the steroid hormone ecdysone is mediated through a regulated vesicular trafficking mechanism. Inhibition of calcium signaling in the steroidogenic prothoracic gland results in the accumulation of unreleased ecdysone, and the knockdown of calcium-mediated vesicle exocytosis components in the gland caused developmental defects due to deficiency of ecdysone. Accumulation of synaptotagmin-labeled vesicles in the gland is observed when calcium signaling is disrupted, and these vesicles contain an ABC transporter that functions as an ecdysone pump to fill vesicles. We propose that trafficking of steroid hormones out of endocrine cells is not always through a simple diffusion mechanism as presently thought, but instead can involve a regulated vesicle-mediated release process.

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.

Substitution of a non-retinal phospholipase C in Drosophila phototransduction

The Drosophila norpA gene encodes at least two subtypes of phospholipase C (PLC), one of which is essential for phototransduction and the other is utilized in signalling pathways other than phototransduction. The two subtypes of norpA-PLC differ by 14 amino acids that have been proposed as important for the function of PLC in different signalling pathways. The present study aimed to determine whether norpA subtype II enzyme can functionally substitute for the subtype I enzyme in the phototransduction pathway. We found that the non-retinal norpA-PLC enzyme can substitute for its retinal counterpart, but that there is a reduced rate of repolarization of photoreceptors following intense light stimuli. This reduced repolarization might be due to the inability of a regulatory component being able to interact with the non-retinal norpA-PLC enzyme.

Mosaic analyses reveal the function ofDrosophila Rasin embryonic dorsoventral patterning and dorsal follicle cell morphogenesis

In Drosophila melanogaster, the Ras signal transduction pathway is the primary effector of receptor tyrosine kinases, which govern diverse developmental programs. During oogenesis, epidermal growth factor receptor signaling through the Ras pathway patterns the somatic follicular epithelium, establishing the dorsoventral asymmetry of eggshell and embryo. Analysis of follicle cell clones homozygous for a null allele of Ras demonstrates that Ras is required cell-autonomously to repress pipe transcription, the critical first step in embryonic dorsoventral patterning. The effects of aberrant pipe expression in Ras mosaic egg chambers can be ameliorated, however, by post-pipe patterning events, which salvage normal dorsoventral polarity in most embryos derived from egg chambers with dorsal Ras clones. The patterned follicular epithelium also determines the final shape of the eggshell, including the dorsal respiratory appendages, which are formed by the migration of two dorsolateral follicle cell populations. Confocal analyses of mosaic egg chambers demonstrate that Ras is required both cell- and non cell-autonomously for morphogenetic behaviors characteristic of dorsal follicle cell migration, and reveal a novel, Ras-dependent pattern of basal E-cadherin localization in dorsal midline follicle cells.

Families of phosphoinositide-specific phospholipase C: structure and function

A large number of extracellular signals stimulate hydrolysis of phosphatidylinositol 4,5-bisphosphate by phosphoinositide-specific phospholipase C (PI-PLC). PI-PLC isozymes have been found in a broad spectrum of organisms and although they have common catalytic properties, their regulation involves different signalling pathways. A number of recent studies provided an insight into domain organisation of PI-PLC isozymes and contributed towards better understanding of the structural basis for catalysis, cellular localisation and molecular changes that could underlie the process of their activation.

Evolution and overview of classical transmitter molecules and their receptors

All the classical transmitter ligand molecules evolved at least 1000 million years ago. With the possible exception of the Porifera and coelenterates (Cnidaria), they occur in all the remaining phyla. All transmitters have evolved the ability to activate a range of ion channels, resulting in excitation, inhibition and biphasic or multiphasic responses. All transmitters can be synthesised in all three basic types of neurones, i.e. sensory, interneurone and motoneurone. However their relative importance as sensory, interneurone or motor transmitters varies widely between the phyla. It is likely that all neurones contain more than one type of releasable molecule, often a combination of a classical transmitter and a neuroactive peptide. Second messengers, i.e. G proteins and phospholipase C systems, appeared early in evolution and occur in all phyla that have been investigated. Although the evidence is incomplete, it is likely that all the classical transmitter receptor subtypes identified in mammals, also occur throughout the phyla. The invertebrate receptors so far cloned show some interesting homologies both between those from different invertebrate phyla and with mammalian receptors. This indicates that many of the basic receptor subtypes, including benzodiazepine subunits, evolved at an early period, probably at least 800 million years ago. Overall, the evidence stresses the similarity between the major phyla rather than their differences, supporting a common origin from primitive helminth stock.