Expression of phosphoinositide-specific phospholipase C enzymes in human skin fibroblasts.

Fibroblasts are involved in a number of functions regulated by different signal transduction pathways, including the phosphoinositide (PI) signaling system and related converting enzymes, such as phosphoinositide-specific phospholipase C (PI-PLC). The PI-PLC family comprises crucial effector enzymes in the PI signal transduction pathway. Once activated, PI-PLC cleaves an important membrane PI, the phosphatidylinositol (4,5) bisphosphate into inositol trisphosphate and diacylglycerol-both are crucial molecules in the transduction of signals. The activity of selected PI-PLC enzymes was reported in fibroblasts, although the complete panel of expression was not available. Each cell type expresses a group of selected PI-PLC isoforms, and knowledge of the panel of expression is a necessary and preliminary tool to address further studies. In the present study, we delineated the expression panel of PI-PLC enzymes in human skin fibroblasts. PI-PLC ß1, PI-PLC ß3, PI-PLC ß4, PI-PLC γ1, PI-PLC γ2, PI-PLC δ1, PI-PLC δ3, PI-PLC δ4, and PI-PLC ϵ were expressed. PI-PLC ß1 was weakly expressed, PI-PLC δ4 was inconstantly expressed, and PI-PLC γ2 was weakly expressed.

Plant phosphoinositide-specific phospholipase C: an insight.

Phosphoinositide-specific phospholipase C (PI-PLC) belongs to an important class of enzymes involved in signaling related to lipids. They hydrolyze a membrane-associated phospholipid, phosphatidylinositol-4,5-bisphosphate, to produce inositol-1,4,5-trisphosphate and diacylglycerol. The role of PI-PLC and the mechanism behind its functioning is well studied in animal system; however, mechanism of plant PI-PLC functioning remains largely obscure. Here, we attempted to summarize the understanding regarding plant PI-PLC mechanism of regulation, localization, and domain association. Using sedimentation based phospholipid binding assay and surface plasmon resonance spectroscopy, it was demonstrated that C2 domain of plant PI-PLC alone is capable of targeting membranes. Moreover, change in surface hydrophobicity upon calcium stimulus is the key element in targeting plant PI-PLC from soluble fractions to membranes. This property of altering surface hydrophobicity plays a pivot role in regulation of PI-PLC activity.

Cloning, tissue distribution and sub-cellular localisation of phospholipase C X-domain containing protein (PLCXD) isoforms.

Phosphatidylinositol-specific phospholipase C (PI-PLC) enzymes comprise a small family of receptor-regulated phosphodiesterases that control many cellular processes by the regulation of cytosolic calcium and/or the activity of several protein kinases. To date, six distinct classes of PI-PLC are known to exist in mammals. Here we characterise a seventh class of PI-PLC, which contains only the catalytic X domain in its structure, termed phospholipase C X-domain containing protein (PLCXD). At least three tissue-specific PLCXD isoforms exist in humans, comprising hPLCXD-1, hPLCXD-2 and hPLCXD-3, with hPLCXD-2 exhibiting three C-terminal spliceforms (2.1, 2.2 and 2.3). Specific amino acids known to be essential for the catalytic function of PI-PLCs were found to be conserved in all three human PLCXDs and over-expression of hPLCXD-1, 2.1 and 3 in the HeLa cell line increased endogenous PI-PLC activity. Human PLCXD isoforms exhibited tissue-specific expression profiles in mice and humans and immunocytochemistry revealed distinct sub-cellular localisations when over-expressed in human cultured cell lines. These novel proteins may therefore possess fundamental, and as yet uncharacterised roles in cell physiology.

Signal-activated phospholipase regulation of leukocyte chemotaxis.

Signal-activated phospholipases are a recent focus of the rapidly growing field of lipid signaling. The extent of their impact on the pathways regulating diverse cell functions is beginning to be appreciated. A critical step in inflammation is the attraction of leukocytes to injured or diseased tissue. Chemotaxis of leukocytes, a requisite process for monocyte and neutrophil extravasation from the blood into tissues, is a critical step for initiating and maintaining inflammation in both acute and chronic settings. Recent studies have identified new important and required roles for two signal-activated phospholipases A2 (PLA2) in regulating chemotaxis. The two intracellular phospholipases, cPLA2alpha (Group IVA) and iPLA2beta (Group VIA), act in parallel to provide distinct lipid mediators at different intracellular sites that are both required for leukocytes to migrate toward the chemokine monocyte chemoattractant protein-1. This review will summarize the separate roles of these phospholipases as well as what is currently known about the influence of two other classes of intracellular signal-activated phospholipases, phospholipase C and phospholipase D, in regulating chemotaxis in eukaryotic cells, but particularly in human monocytes. The contributions of these phospholipases to chemotaxis both in vitro and in vivo will be highlighted.

Expression and evolution of the phosphoinositide-specific phospholipase C gene family in Arabidopsis thaliana.

Phosphoinositide-specific phospholipase C cleaves the substrate phosphatidylinositol 4,5-bisphosphate and generates inositol 1,4,5-trisphosphate and 1,2-diacylglycerol, both of which are second messengers in the phosphoinositide signal transduction pathways operative in animal cells. Five PI-PLC isoforms, beta, gamma, delta, epsilon and zeta, have been identified in mammals. Plant PI-PLCs are structurally close to the mammalian PI-PLC-zeta isoform. The Arabidopsis genome contains nine AtPLC genes. Expression patterns of all nine genes in different organs and in response to various environmental stimuli were studied by applying a quantitative RT-PCR approach. Multiple members of the gene family were differentially expressed in Arabidopsis organs, suggesting putative roles for this enzyme in plant development, including tissue and organ differentiation. This study also shows that a majority of the AtPLC genes are induced in response to various environmental stimuli, including cold, salt, nutrients Murashige-Skoog salts, dehydration, and the plant hormone abscisic acid. Results of this and previous studies strongly suggest that transcriptional activation of the PI-PLC gene family is important for adapting plants to stress environments. Expression patterns and phylogenetic relationships indicates that AtPLC gene members probably evolved through multiple rounds of gene duplication events, with AtPLC4 and AtPLC5 and AtPLC8 and AtPLC9 being duplicated in tandem in recent times.