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High NaCl (200 mM) increases the transcription of phospholipase Dδ (PLDδ) in roots and leaves of the salt-resistant woody species Populus euphratica. We isolated a 1138 bp promoter fragment upstream of the translation initiation codon of PePLDδ. A promoter-reporter construct, PePLDδ-pro::GUS, was introduced into Arabidopsis plants (Arabidopsis thaliana) to demonstrate the NaCl-induced PePLDδ promoter activity in root and leaf tissues. Mass spectrometry analysis of DNA pull-down-enriched proteins in P. euphratica revealed that PeGLABRA3, a basic helix-loop-helix transcription factor, was the target transcription factor for binding the promoter region of PePLDδ. The PeGLABRA3 binding to PePLDδ-pro was further verified by virus-induced gene silencing, luciferase reporter assay (LRA), yeast one-hybrid assay, and electrophoretic mobility shift assay (EMSA). In addition, the PeGLABRA3 gene was cloned and overexpressed in Arabidopsis to determine the function of PeGLABRA3 in salt tolerance. PeGLABRA3-overexpressed Arabidopsis lines (OE1 and OE2) had a greater capacity to scavenge reactive oxygen species (ROS) and to extrude Na[sup.+] under salinity stress. Furthermore, the EMSA and LRA results confirmed that PeGLABRA3 interacted with the promoter of AtPLDδ in transgenic plants. The upregulated AtPLDδ in PeGLABRA3-transgenic lines resulted in an increase in phosphatidic acid species under no-salt and saline conditions. We conclude that PeGLABRA3 activated AtPLDδ transcription under salt stress by binding to the AtPLDδ promoter region, conferring Na[sup.+] and ROS homeostasis control via signaling pathways mediated by PLDδ and phosphatidic acid.

The hypothalamus plays a central role in monitoring and regulating systemic glucose metabolism. The brain is enriched with phospholipids containing poly-unsaturated fatty acids, which are biologically active in physiological regulation. Here, we show that intraperitoneal glucose injection induces changes in hypothalamic distribution and amounts of phospholipids, especially arachidonic-acid-containing phospholipids, that are then metabolized to produce prostaglandins. Knockdown of cytosolic phospholipase A2 (cPLA2), a key enzyme for generating arachidonic acid from phospholipids, in the hypothalamic ventromedial nucleus (VMH), lowers insulin sensitivity in muscles during regular chow diet (RCD) feeding. Conversely, the down-regulation of glucose metabolism by high fat diet (HFD) feeding is improved by knockdown of cPLA2 in the VMH through changing hepatic insulin sensitivity and hypothalamic inflammation. Our data suggest that cPLA2-mediated hypothalamic phospholipid metabolism is critical for controlling systemic glucose metabolism during RCD, while continuous activation of the same pathway to produce prostaglandins during HFD deteriorates glucose metabolism. The ventromedial hypothalamus regulates systemic glucose metabolism. Here the authors show that cytosolic phospholipase A2 mediated phospholipid metabolism contributes to this regulation in healthy animals but exert deteriorating effects on glucose homeostasis under high-fat-diet feeding.

Darapladib, an oral inhibitor of lipoprotein-associated phospholipase A2, was compared with placebo in 15,828 patients with stable coronary heart disease. Darapladib did not significantly reduce the risk of cardiovascular death, myocardial infarction, or stroke. Atherosclerotic lesions in humans — in particular, vulnerable 1 and ruptured plaques — are characterized by inflammatory activity and a high expression of lipoprotein-associated phospholipase A 2 . 2 , 3 In atherosclerotic plaques, lipoprotein-associated phospholipase A 2 increases the production of proinflammatory and proapoptotic mediators. 4 – 8 In a meta-analysis of individual records from 79,036 participants in 32 prospective studies, there was a continuous association between lipoprotein-associated phospholipase A 2 activity and the risk of coronary heart disease, with a relative increase in risk of 1.10 (95% confidence interval [CI], 1.05 to 1.16) for each 1-SD increase in lipoprotein-associated phospholipase A 2 activity, . . .

The eye lens of vertebrates is composed of fibre cells in which all membrane-bound organelles undergo degradation during terminal differentiation to form an organelle-free zone 1 . The mechanism that underlies this large-scale organelle degradation remains largely unknown, although it has previously been shown to be independent of macroautophagy 2 , 3 . Here we report that phospholipases in the PLAAT (phospholipase A/acyltransferase, also known as HRASLS) family—Plaat1 (also known as Hrasls) in zebrafish and PLAAT3 (also known as HRASLS3, PLA2G16, H-rev107 or AdPLA) in mice 4 – 6 —are essential for the degradation of lens organelles such as mitochondria, the endoplasmic reticulum and lysosomes. Plaat1 and PLAAT3 translocate from the cytosol to various organelles immediately before organelle degradation, in a process that requires their C-terminal transmembrane domain. The translocation of Plaat1 to organelles depends on the differentiation of fibre cells and damage to organelle membranes, both of which are mediated by Hsf4. After the translocation of Plaat1 or PLAAT3 to membranes, the phospholipase induces extensive organelle rupture that is followed by complete degradation. Organelle degradation by PLAAT-family phospholipases is essential for achieving an optimal transparency and refractive function of the lens. These findings expand our understanding of intracellular organelle degradation and provide insights into the mechanism by which vertebrates acquired transparent lenses. In the eye lens of zebrafish and mice, the phospholipases Plaat1 and PLAAT3, respectively, are essential for macroautophagy-independent organelle degradation that produces an organelle-free zone and achieves optimal transparency.

A constitutively active mutant of the receptor protein tyrosine kinase KIT is a major cause of gastrointestinal stromal tumours (GISTs). Recently, we discovered that, during biosynthetic transport, the KIT mutant (KIT mut ) is retained in the Golgi/ trans- Golgi network (TGN), where it activates downstream molecules. This retention is dependent on the phospholipase Cγ2–protein kinase D2–PI4 kinase IIIβ (PLCγ2–PKD2–PI4KIIIβ) pathway, which KIT mut activates at the Golgi/TGN. The activated cascade aberrantly recruits GGA1 and the γ-adaptin subunit of AP1, resulting in KIT mut retention in the Golgi/TGN. However, the precise mechanisms, including the mediators and effectors of the pathway, remain unclear. In humans, the phosphatidic acid-generating enzymes, phospholipase D1 (PLD1) and PLD2 are known downstream proteins of PKD. In the presence of the PLD inhibitor CAY10594, KIT mut is released from the Golgi/TGN and subsequently degraded in lysosomes, leading to signal inactivation. Knockdown experiments indicated that PLD2 plays a role in KIT mut retention. KIT mut activates PLD2 through PKD2, but not PI4KIIIβ, for Golgi/TGN retention. PLD activity is required for the association of γ-adaptin with GGA1. Therefore, the KIT–PLCγ2–PKD2 pathway separately activates PLD2 and PI4KIIIβ to recruit γ-adaptin and GGA1. Collectively, these results suggest that KIT mut retention is dependent on the activation of the PLCγ2–PKD2–PLD2 cascade in GIST cells.

Pathogen infection of higher plants often induces rapid production of phosphatidic acid (PA) and changes in lipid profiles, but the enzymatic basis and the function of the lipid change in pathogen–plant interactions are not well understood. Infection of phospholipase D β1 (PLDβ1)-deficient plants by Pseudomonas syringae tomato pv DC3000 (Pst DC30000) resulted in less bacterial growth than in wild-type plants, and the effect was more profound in virulent Pst DC3000 than avirulent Pst DC3000 (carrying the avirulence gene avrRpt2) infection. The expression levels of salicylic acid (SA)-inducible genes were higher, but those inducible by jasmonic acid (JA) showed lower expression in PLDβ1 mutants than in wild-type plants. However, PLDβ1-deficient plants were more susceptible than wild-type plants to the fungus Botrytis cinerea. The PLDβ1-deficient plants had lower levels of PA, JA and JA-related defense gene expression after B. cinerea inoculation. PLDβ1 plays a positive role in pathogen-induced JA production and plant resistance to the necrotrophic fungal pathogen B. cinerea, but a negative role in the SA-dependent signaling pathway and plant tolerance to infection with biotrophic Pst DC3000. PLDβ1 is responsible for most of the increase in PA production in response to necrotrophic B. cinerea and virulent Pst DC3000 infection, but contributes less to avirulent Pst DC3000 (avrRpt2)-induced PA production.

Phospholipase C (PLC) regulates a number of cellular behaviours including cell motility, cell transformation, differentiation and cell growth. PLC plays a regulatory role in cancer cells partly by acting as signalling intermediates for cytokines such as EGF and interleukins. The current study examined the expression of the PLC isozymes in human breast cancer and corresponding clinical relevance. Transcript levels of human PLC-α, -β1, -δ, -ε, and -γ1 in human breast cancer tissues were quantitatively determined by real-time PCR. Immunochemical staining was performed for PLC-δ. The clinical relevance was analysed with clinic pathological information. Mammary tissues widely expressed PLC-α, -β1, -δ, -ε, and -γ1. Significantly high levels of PLC -β1 and -ε were seen in breast cancer tissues in comparison with normal mammary gland tissues. PLC-γ1 however, showed marginally low levels in tumour tissues. No significant difference was seen in the expression of the PLC isozymes in tumours with lymph node metastases. Moderately and poorly differentiated breast tumours (grade 2 and grade 3) had significantly higher levels of PLC-γ1, compared with well differentiated tumours. High levels of PLC-δ were significantly correlated with a shorter disease-free survival. The altered expression of other isozymes had no correlation with the survival. It is concluded that mammary tissues differentially expressed PLC isozymes. These isozymes have certain implications in the disease development and progression, with PLC-δ showing a significant correlation with shorter disease-free survival.

Mammalian cells are surrounded by neighbouring cells and extracellular matrix (ECM), which provide cells with structural support and mechanical cues that influence diverse biological processes 1 . The Hippo pathway effectors YAP (also known as YAP1) and TAZ (also known as WWTR1) are regulated by mechanical cues and mediate cellular responses to ECM stiffness 2 , 3 . Here we identified the Ras-related GTPase RAP2 as a key intracellular signal transducer that relays ECM rigidity signals to control mechanosensitive cellular activities through YAP and TAZ. RAP2 is activated by low ECM stiffness, and deletion of RAP2 blocks the regulation of YAP and TAZ by stiffness signals and promotes aberrant cell growth. Mechanistically, matrix stiffness acts through phospholipase Cγ1 (PLCγ1) to influence levels of phosphatidylinositol 4,5-bisphosphate and phosphatidic acid, which activates RAP2 through PDZGEF1 and PDZGEF2 (also known as RAPGEF2 and RAPGEF6). At low stiffness, active RAP2 binds to and stimulates MAP4K4, MAP4K6, MAP4K7 and ARHGAP29, resulting in activation of LATS1 and LATS2 and inhibition of YAP and TAZ. RAP2, YAP and TAZ have pivotal roles in mechanoregulated transcription, as deletion of YAP and TAZ abolishes the ECM stiffness-responsive transcriptome. Our findings show that RAP2 is a molecular switch in mechanotransduction, thereby defining a mechanosignalling pathway from ECM stiffness to the nucleus. The Ras-related GTPase RAP2 is a key intracellular signal transducer by which extracellular matrix rigidity controls mechanosensitive cellular activities through YAP and TAZ.

Background Phosphorus is a macronutrient necessary for plant growth and development and its availability and efficient use affect crop yields. Leaves are the largest tissue that uses phosphorus in plants, and membrane phospholipids are the main source of cellular phosphorus usage. Results Here we identify a key process for plant cellular phosphorus recycling mediated by membrane phospholipid hydrolysis during leaf senescence. Our results indicate that over 90% of lipid phosphorus, accounting for more than one-third of total cellular phosphorus, is recycled from senescent leaves before falling off the plants. Nonspecific phospholipase C4 ( NPC4 ) and phospholipase Dζ2 ( PLDζ2 ) are highly induced during leaf senescence, and knockouts of PLDζ2 and NPC4 decrease the loss of membrane phospholipids and delay leaf senescence. Conversely, overexpression of PLDζ2 and NPC4 accelerates the loss of phospholipids and leaf senescence, promoting phosphorus remobilization from senescent leaves to young tissues and plant growth. We also show that this phosphorus recycling process in senescent leaves mediated by membrane phospholipid hydrolysis is conserved in plants. Conclusions These results indicate that PLDζ2- and NPC4-mediated membrane phospholipid hydrolysis promotes phosphorus remobilization from senescent leaves to growing tissues and that the phospholipid hydrolysis-mediated phosphorus recycling improves phosphorus use efficiency in plants.