On/off-regulation of phospholipase C-gamma 1-mediated signal transduction

Suppressing phosphoinositide-specific phospholipases Cγ1 promotes mineralization of osteoarthritic subchondral bone osteoblasts via increasing autophagy, thereby ameliorating articular cartilage degeneration

INTRODUCTION

Phosphoinositide-specific phospholipases C-γ1 (PLC-γ1) signaling has been shown to modulate osteoarthritis (OA) chondrocyte metabolism. However, the role of PLC-γ1 in OA osteoblasts remains unclear. Herein, whether and how PLC-γ1 was involved in mineralization in OA subchondral bone osteoblasts were investigated.

METHODS

Primary non-OA and OA osteoblasts of human and rat isolated from the subchondral bone or the calvaria were cultured in vitro, as well as mouse pre-osteoblastic cell line MC3T3-E1 cells. Rat knee OA model was induced by anterior cruciate ligament transection (ACLT), in which bone canal was carried out from the surface of lateral epicondyle of femur using micro-electric drill. Morphological characteristics of subchondral bone structure and articular cartilage were assessed using CT, micro-CT, and Safranin O/Fast green staining, respectively. Mineralization was measured by alizarin red staining. The expression and production of genes involved in osteoblastic phenotype and mineralization were evaluated by qPCR, western blotting, and immunohistochemistry assays, respectively. The inhibitions were performed using inhibitors and ShRNAs.

RESULTS

The decreased relative bone density and thickness in the early stage of OA and the increased one in the late stage of OA were observed in subchondral bone of ACLT-rat model. Decreased ALP and OCN levels and absorbance values of ARS content were observed in in vitro osteoblasts isolated from 2 w post-ACLT rat model, as well as IL-1β-treated (for maintaining and mimicking inflammatory status) human OA and rat osteoblasts. Decreased Atg7 level and LC3BII/I ratio in combination with an increase in the P62 level, was concomitant with decreased ALP and OCN mRNA levels and absorbance values of ARS content in OA or IL-1β-treated osteoblasts. Specific inhibition of PLC-γ1 by ShRNAs or inhibitor (U73122) elevated ALP and OCN mRNA levels and absorbance values of ARS content accompanied with increased Atg7 level and LC3BII/I ratio in combination with a decrease in the P62 level in OA osteoblasts. Furthermore, the promoting effect of PLC-γ1 inhibition on ALP and OCN mRNA levels and absorbance values of ARS content was reversed by endoplasmic reticulum (ER) stress activator HA15, as well as autophagic inhibitors CQ and 3MA. Injection with PLC-γ1 inhibitor U73122 from the surface of lateral epicondyle of femur reduced aberrant subchondral bone formation and attenuated articular cartilage degeneration in ACLT-rat.

CONCLUSION

Aberrant changes of OA subchondral bone structure were concomitant with altered osteoblastic phenotype and mineralization. Impaired autophagy contributed to decreased osteoblastic mineralization in the early stage of OA. PLC-γ1 inhibition promoted osteoblastic mineralization through increasing autophagy in OA osteoblasts, which was partially attributed to suppression of ER stress. Targeting PLC-γ1 in subchondral bone osteoblasts could be more efficacious for OA therapy through treating the bone and cartilage at the same time. In summary, we hypothesize that suppressing PLCγ1 promotes mineralization of osteoarthritic subchondral bone osteoblasts via increasing autophagy, thereby ameliorating articular cartilage degeneration.

PLCγ1 inhibition-driven autophagy of IL-1β-treated chondrocyte confers cartilage protection against osteoarthritis, involving AMPK, Erk and Akt

Previous studies identified the involvement of phosphoinositide‐specific phospholipase C (PLC) γ1 in some events of chondrocytes. This study aims to investigate whether and how PLCγ1 modulates autophagy to execute its role in osteoarthritis (OA) progression. Rat normal or human OA chondrocytes were pretreated with IL‐1β for mimicking or sustaining OA pathological condition. Using Western blotting, immunoprecipitation, qPCR, immunofluorescence and Dimethylmethylene blue assays, and ELISA and transmission electron microscope techniques, we found that PLCγ1 inhibitor U73122 enhanced Collagen II, Aggrecan and GAG levels, accompanied with increased LC3B‐II/I ratio and decreased P62 expression level, whereas autophagy inhibitor Chloroquine partially diminished its effect. Meanwhile, U73122 dissociated Beclin1 from Beclin1‐IP3R‐Bcl‐2 complex and blocked mTOR/ULK1 axis, in which the crosstalk between PLCγ1, AMPK, Erk and Akt were involved. Additionally, by haematoxylin and eosin, Safranin O/Fast green, and immunohistochemistry staining, we observed that intra‐articular injection of Ad‐shPLCγ1‐1/2 significantly enhanced Collagen and Aggrecan levels, accompanied with increased LC3B and decreased P62 levels in a rat OA model induced by anterior cruciate ligament transection and medial meniscus resection. Consequently, PLCγ1 inhibition‐driven autophagy conferred cartilage protection against OA through promoting ECM synthesis in OA chondrocytes in vivo and in vitro, involving the crosstalk between PLCγ1, AMPK, Erk and Akt.

Pyruvate Kinase M2 and Cancer: The Role of PKM2 in Promoting Tumorigenesis

Pyruvate kinase plays a pivotal role in regulating cell metabolism. The final and rate-limiting step of glycolysis is the conversion of Phosphoenolpyruvate (PEP) to Pyruvate, which is catalyzed by Pyruvate Kinase. There are four isomeric, tissue-specific forms of Pyruvate Kinase found in mammals: PKL, PKR, PKM1, and PKM2. PKM1 and PKM2 are formed bya single mRNA transcript of the PKM gene by alternative splicing. The oligomers of PKM2 exist in high activity tetramer and low activity dimer forms. The dimer PKM2 regulates the rate-limiting step of glycolysis that shifts the glucose metabolism from the normal respiratory chain to lactate production in tumor cells. Besides its role as a metabolic regulator, it also acts as protein kinase, which contributes to tumorigenesis. This review is focused on the metabolic role of pyruvate kinase M2 in normal cells vs. cancerous cells and its regulation at the transcriptional level. The review also highlights the role of PKM2 as a potential diagnostic marker and as a therapeutic target in cancer treatment.

Phospholipase Cγ in Toll-like receptor-mediated inflammation and innate immunity

Among the phospholipase C (PLC) isoforms, PLCγ not only has unique structural characteristics in terms of harboring SH2 and SH3 domains but also mediates growth factor-induced signaling pathways. PLCγ isoforms are expressed in several innate immune cell types, including macrophages, natural killer cells, mast cells, and neutrophils. Stimulation of Fc receptor or integrin in innate immune cells induces PLCγ activation, which leads to phosphoinositide hydrolysis and calcium increase. The products of PLCγ activity mediate the innate immune response by regulating respiratory burst, phagocytosis, cell adhesion, and cell migration. PLCγ also regulates the inflammatory response by affecting Toll-like receptor-mediated signaling. Here, we briefly review the current understanding of the functional role of PLCγ in inflammation and innate immunity in some innate immune cell types.

SHP-2 phosphatase controls aryl hydrocarbon receptor-mediated ER stress response in mast cells

Previously we reported that exposure of mouse and human mast cells to aryl hydrocarbon receptor (AhR) ligands resulted in reactive oxygen species (ROS)- and calcium (Ca²⁺)-dependent activation of mast cells in vitro and in vivo. However, the mechanisms through which the AhR-ligand axis mediates stress response, Ca²⁺ signaling and subsequent mast cell activation remain to be fully elucidated. Evidence is provided herein that SHP-2 is critical in regulating AhR-mediated ER stress response and intracellular Ca²⁺ dynamics. We found that an AhR ligand, FICZ, induced significant reduction of intracellular GSH and an increased level of intracellular ROS. Significantly, we showed that in FICZ-treated mast cells, SHP-2 promoted, in a ROS-dependent manner, ER stress response involving primarily the PERK signaling pathway, ATF4 activation and eIF2α phosphorylation, which could be reversed by the addition of an antioxidant, NAC, and was inhibited in cells with SHP-2 knockdown. Our findings suggested that SHP-2 is critical in controlling ER stress signals in response to AhR activation, which provides a new mechanistic insight into how the AhR-ligand axis regulates cellular adaptation to the environmental insult in mast cells.

Tau-Driven Neuronal and Neurotrophic Dysfunction in a Mouse Model of Early Tauopathy

Tauopathies are neurodegenerative diseases characterized by intraneuronal inclusions of hyperphosphorylated tau protein and abnormal expression of brain-derived neurotrophic factor (BDNF), a key modulator of neuronal survival and function. The severity of both these pathological hallmarks correlate with the degree of cognitive impairment in patients. However, how tau pathology specifically modifies BDNF signaling and affects neuronal function during early prodromal stages of tauopathy remains unclear. Here, we report that the mild tauopathy developing in retinal ganglion cells (RGCs) of the P301S tau transgenic (P301S) mouse induces functional retinal changes by disrupting BDNF signaling via the TrkB receptor. In adult P301S mice, the physiological visual response of RGCs to pattern light stimuli and retinal acuity decline significantly. As a consequence, the activity-dependent secretion of BDNF in the vitreous is impaired in P301S mice. Further, in P301S retinas, TrkB receptors are selectively upregulated, but uncoupled from downstream extracellular signal-regulated kinase (ERK) 1/2 signaling. We also show that the impairment of TrkB signaling is triggered by tau pathology and mediates the tau-induced dysfunction of visual response. Overall our results identify a neurotrophin-mediated mechanism by which tau induces neuronal dysfunction during prodromal stages of tauopathy and define tau-driven pathophysiological changes of potential value to support early diagnosis and informed therapeutic decisions.

SIGNIFICANCE STATEMENT

This work highlights the potential molecular mechanisms by which initial tauopathy induces neuronal dysfunction. Combining clinically used electrophysiological techniques (i.e., electroretinography) and molecular analyses, this work shows that in a relevant model of early tauopathy, the retina of the P301S mutant human tau transgenic mouse, mild tau pathology results in functional changes of neuronal activity, likely due to selective impairment of brain-derived neurotrophic factor signaling via its receptor, TrkB. These findings may have important translational implications for early diagnosis in a subset of Alzheimer's disease patients with early visual symptoms and emphasize the need to clarify the pathophysiological changes associated with distinct tauopathy stages to support informed therapeutic decisions and guide drug discovery.

PKM2 and cancer: The function of PKM2 beyond glycolysis

Metabolic reprogramming is a hallmark of cancer cells and is used by cancer cells for growth and survival. Pyruvate kinase muscle isozyme M2 (PKM2) is a limiting glycolytic enzyme that catalyzes the final step in glycolysis, which is key in tumor metabolism and growth. The present review discusses the expression and regulation of PKM2, and reports the dominant role that PKM2 plays in glycolysis to achieve the nutrient demands of cancer cell proliferation. In addition, the present study discusses the non-metabolic function of PKM2, and its role as a coactivator and protein kinase, which contributes to tumorigenesis. Furthermore, conflicting studies concerning the role of PKM2 as a therapeutic target are reviewed. The improved understanding of PKM2 may provide a noval approach for cancer treatment.

Vanadium Compounds as Pro-Inflammatory Agents: Effects on Cyclooxygenases

This paper discusses how the activity and expression of cyclooxygenases are influenced by vanadium compounds at anticancer concentrations and recorded in inorganic vanadium poisonings. We refer mainly to the effects of vanadate (orthovanadate), vanadyl and pervanadate ions; the main focus is placed on their impact on intracellular signaling. We describe the exact mechanism of the effect of vanadium compounds on protein tyrosine phosphatases (PTP), epidermal growth factor receptor (EGFR), PLCγ, Src, mitogen-activated protein kinase (MAPK) cascades, transcription factor NF-κB, the effect on the proteolysis of COX-2 and the activity of cPLA₂. For a better understanding of these processes, a lot of space is devoted to the transformation of vanadium compounds within the cell and the molecular influence on the direct targets of the discussed vanadium compounds.

Restoration of responsiveness of phospholipase Cγ2-deficient platelets by enforced expression of phospholipase Cγ1

Receptor-mediated platelet activation requires phospholipase C (PLC) activity to elevate intracellular calcium and induce actin cytoskeleton reorganization. PLCs are classified into structurally distinct β, γ, δ, ε, ζ, and η isoforms. There are two PLCγ isoforms (PLCγ1, PLCγ2), which are critical for activation by tyrosine kinase-dependent receptors. Platelets express both PLCγ1 and PLCγ2. Although PLCγ2 has been shown to play a dominant role in platelet activation, the extent to which PLCγ1 contributes has not been evaluated. To ascertain the relative contributions of PLCγ1 and PLCγ2 to platelet activation, we generated conditionally PLCγ1-deficient, wild-type (WT), PLCγ2-deficient, and PLCγ1/PLCγ2 double-deficient mice and measured the ability of platelets to respond to different agonists. We found that PLCγ2 deficiency abrogated αIIbβ3-dependent platelet spreading, GPVI-dependent platelet aggregation, and thrombus formation on collagen-coated surfaces under shear conditions, which is dependent on both GPVI and αIIbβ3. Addition of exogenous ADP overcame defective spreading of PLCγ2-deficient platelets on immobilized fibrinogen, suggesting that PLCγ2 is required for granule secretion in response to αIIbβ3 ligation. Consistently, αIIbβ3-mediated release of granule contents was impaired in the absence of PLCγ2. In contrast, PLCγ1-deficient platelets spread and released granule contents normally on fibrinogen, exhibited normal levels of GPVI-dependent aggregation, and formed thrombi normally on collagen-coated surfaces. Interestingly, enforced expression of PLCγ1 fully restored GPVI-dependent aggregation and αIIbβ3-dependent spreading of PLCγ2-deficient platelets. We conclude that platelet activation through GPVI and αIIbβ3 utilizes PLCγ2 because PLCγ1 levels are insufficient to support responsiveness, but that PLCγ1 can restore responsiveness if expressed at levels normally achieved by PLCγ2.

Direct imaging of ER calcium with targeted-esterase induced dye loading (TED)

Visualization of calcium dynamics is important to understand the role of calcium in cell physiology. To examine calcium dynamics, synthetic fluorescent Ca(2+) indictors have become popular. Here we demonstrate TED (= targeted-esterase induced dye loading), a method to improve the release of Ca(2+) indicator dyes in the ER lumen of different cell types. To date, TED was used in cell lines, glial cells, and neurons in vitro. TED bases on efficient, recombinant targeting of a high carboxylesterase activity to the ER lumen using vector-constructs that express Carboxylesterases (CES). The latest TED vectors contain a core element of CES2 fused to a red fluorescent protein, thus enabling simultaneous two-color imaging. The dynamics of free calcium in the ER are imaged in one color, while the corresponding ER structure appears in red. At the beginning of the procedure, cells are transduced with a lentivirus. Subsequently, the infected cells are seeded on coverslips to finally enable live cell imaging. Then, living cells are incubated with the acetoxymethyl ester (AM-ester) form of low-affinity Ca(2+) indicators, for instance Fluo5N-AM, Mag-Fluo4-AM, or Mag-Fura2-AM. The esterase activity in the ER cleaves off hydrophobic side chains from the AM form of the Ca(2+) indicator and a hydrophilic fluorescent dye/Ca(2+) complex is formed and trapped in the ER lumen. After dye loading, the cells are analyzed at an inverted confocal laser scanning microscope. Cells are continuously perfused with Ringer-like solutions and the ER calcium dynamics are directly visualized by time-lapse imaging. Calcium release from the ER is identified by a decrease in fluorescence intensity in regions of interest, whereas the refilling of the ER calcium store produces an increase in fluorescence intensity. Finally, the change in fluorescent intensity over time is determined by calculation of ΔF/F0.

Phospholipases of mineralization competent cells and matrix vesicles: roles in physiological and pathological mineralizations

The present review aims to systematically and critically analyze the current knowledge on phospholipases and their role in physiological and pathological mineralization undertaken by mineralization competent cells. Cellular lipid metabolism plays an important role in biological mineralization. The physiological mechanisms of mineralization are likely to take place in tissues other than in bones and teeth under specific pathological conditions. For instance, vascular calcification in arteries of patients with renal failure, diabetes mellitus or atherosclerosis recapitulates the mechanisms of bone formation. Osteoporosis—a bone resorbing disease—and rheumatoid arthritis originating from the inflammation in the synovium are also affected by cellular lipid metabolism. The focus is on the lipid metabolism due to the effects of dietary lipids on bone health. These and other phenomena indicate that phospholipases may participate in bone remodelling as evidenced by their expression in smooth muscle cells, in bone forming osteoblasts, chondrocytes and in bone resorbing osteoclasts. Among various enzymes involved, phospholipases A₁ or A₂, phospholipase C, phospholipase D, autotaxin and sphingomyelinase are engaged in membrane lipid remodelling during early stages of mineralization and cell maturation in mineralization-competent cells. Numerous experimental evidences suggested that phospholipases exert their action at various stages of mineralization by affecting intracellular signaling and cell differentiation. The lipid metabolites—such as arachidonic acid, lysophospholipids, and sphingosine-1-phosphate are involved in cell signaling and inflammation reactions. Phospholipases are also important members of the cellular machinery engaged in matrix vesicle (MV) biogenesis and exocytosis. They may favour mineral formation inside MVs, may catalyse MV membrane breakdown necessary for the release of mineral deposits into extracellular matrix (ECM), or participate in hydrolysis of ECM. The biological functions of phospholipases are discussed from the perspective of animal and cellular knockout models, as well as disease implications, development of potent inhibitors and therapeutic interventions.

EGFR-induced and PKCε monoubiquitylation-dependent NF-κB activation upregulates PKM2 expression and promotes tumorigenesis

Many types of human tumor cells have overexpressed pyruvate kinase M2 (PKM2). However, the mechanism underlying this increased PKM2 expression remains to be defined. We demonstrate here that EGFR activation induces PLCγ1-dependent PKCε monoubiquitylation at Lys321 mediated by RINCK1 ubiquitin ligase. Monoubiquitylated PKCε interacts with a ubiquitin-binding domain in NEMO zinc finger and recruits the cytosolic IKK complex to the plasma membrane, where PKCε phosphorylates IKKβ at Ser177 and activates IKKβ. Activated RelA interacts with HIF1α, which is required for RelA to bind the PKM promoter. PKCε- and NF-κB-dependent PKM2 upregulation is required for EGFR-promoted glycolysis and tumorigenesis. In addition, PKM2 expression correlates with EGFR and IKKβ activity in human glioblastoma specimens and with grade of glioma malignancy. These findings highlight the distinct regulation of NF-κB by EGF, in contrast to TNF-α, and the importance of the metabolic cooperation between the EGFR and NF-κB pathways in PKM2 upregulation and tumorigenesis.

Mammalian phospholipase C

Phospholipase C (PLC) converts phosphatidylinositol 4,5-bisphosphate (PIP(2)) to inositol 1,4,5-trisphosphate (IP(3)) and diacylglycerol (DAG). DAG and IP(3) each control diverse cellular processes and are also substrates for synthesis of other important signaling molecules. PLC is thus central to many important interlocking regulatory networks. Mammals express six families of PLCs, each with both unique and overlapping controls over expression and subcellular distribution. Each PLC also responds acutely to its own spectrum of activators that includes heterotrimeric G protein subunits, protein tyrosine kinases, small G proteins, Ca(2+), and phospholipids. Mammalian PLCs are autoinhibited by a region in the catalytic TIM barrel domain that is the target of much of their acute regulation. In combination, the PLCs act as a signaling nexus that integrates numerous signaling inputs, critically governs PIP(2) levels, and regulates production of important second messengers to determine cell behavior over the millisecond to hour timescale.

Unraveling the influence of endothelial cell density on VEGF-A signaling

Vascular endothelial growth factor-A (VEGF) is the master determinant for the activation of the angiogenic program leading to the formation of new blood vessels to sustain solid tumor growth and metastasis. VEGF specific binding to VEGF receptor-2 (VEGFR-2) triggers different signaling pathways, including phospholipase C-γ (PLC-γ) and Akt cascades, crucial for endothelial proliferation, permeability, and survival. By combining biologic experiments, theoretical insights, and mathematical modeling, we found that: (1) cell density influences VEGFR-2 protein level, as receptor number is 2-fold higher in long-confluent than in sparse cells; (2) cell density affects VEGFR-2 activation by reducing its affinity for VEGF in long-confluent cells; (3) despite reduced ligand-receptor affinity, high VEGF concentrations provide long-confluent cells with a larger amount of active receptors; (4) PLC-γ and Akt are not directly sensitive to cell density but simply transduce downstream the upstream difference in VEGFR-2 protein level and activation; and (5) the mathematical model correctly predicts the existence of at least one protein tyrosine phosphatase directly targeting PLC-γ and counteracting the receptor-mediated signal. Our data-based mathematical model quantitatively describes VEGF signaling in quiescent and angiogenic endothelium and is suitable to identify new molecular determinants and therapeutic targets.

Insulin receptor-mediated signaling via phospholipase C-γ regulates growth and differentiation in Drosophila

Coordination between growth and patterning/differentiation is critical if appropriate final organ structure and size is to be achieved. Understanding how these two processes are regulated is therefore a fundamental and as yet incompletely answered question. Here we show through genetic analysis that the phospholipase C-γ (PLC-γ) encoded by small wing (sl) acts as such a link between growth and patterning/differentiation by modulating some MAPK outputs once activated by the insulin pathway; particularly, sl promotes growth and suppresses ectopic differentiation in the developing eye and wing, allowing cells to attain a normal size and differentiate properly. sl mutants have previously been shown to have a combination of both growth and patterning/differentiation phenotypes: small wings, ectopic wing veins, and extra R7 photoreceptor cells. We show here that PLC-γ activated by the insulin pathway participates broadly and positively during cell growth modulating EGF pathway activity, whereas in cell differentiation PLC-γ activated by the insulin receptor negatively regulates the EGF pathway. These roles require different SH2 domains of PLC-γ, and act via classic PLC-γ signaling and EGF ligand processing. By means of PLC-γ, the insulin receptor therefore modulates differentiation as well as growth. Overall, our results provide evidence that PLC-γ acts during development at a time when growth ends and differentiation begins, and is important for proper coordination of these two processes.

Identification of phospholipase C gamma1 as a protein tyrosine phosphatase mu substrate that regulates cell migration

The receptor protein tyrosine phosphatase PTPµ has a cell-adhesion molecule-like extracellular segment and a catalytically active intracellular segment. This structure gives PTPµ the ability to transduce signals in response to cell-cell adhesion. Full-length PTPµ is down-regulated in glioma cells by proteolysis which is linked to increased migration of these cells in the brain. To gain insight into the substrates PTPµ may be dephosphorylating to suppress glioma cell migration, we used a substrate trapping method to identify PTPµ substrates in tumor cell lines. We identified both PKCδ and PLCγ1 as PTPµ substrates. As PLCγ1 activation is linked to increased invasion of cancer cells, we set out to determine whether PTPµ may be upstream of PLCγ1 in regulating glioma cell migration. We conducted brain slice assays using U87-MG human glioma cells in which PTPµ expression was reduced by shRNA to induce migration. Treatment of the same cells with PTPµ shRNA and a PLCγ1 inhibitor prevented migration of the cells within the brain slice. These data suggest that PLCγ1 is downstream of PTPµ and that dephosphorylation of PLCγ1 is likely to be a major pathway through which PTPµ suppresses glioma cell migration.

Phospholipase C-η1 is activated by intracellular Ca(2+) mobilization and enhances GPCRs/PLC/Ca(2+) signaling

Phospholipase C-η1 (PLC-η1) is the most recently identified PLC isotype and is primarily expressed in nerve tissue. However, its functional role is unclear. In the present study, we report for the first time that PLC-η1 acts as a signal amplifier in G protein-coupled receptor (GPCR)-mediated PLC and Ca(2+) signaling. Short-hairpin RNA (shRNA)-mediated knockdown of endogenous PLC-η1 reduced lysophosphatidic acid (LPA)-, bradykinin (BK)-, and PACAP-induced PLC activity in mouse neuroblastoma Neuro2A (N2A) cells, indicating that PLC-η1 participates in GPCR-mediated PLC activation. Interestingly, ionomycin-induced PLC activity was significantly decreased by PLC-η1, but not PLC-η2, knockdown. In addition, we found that intracellular Ca(2+) source is enough for PLC-η1 activation. Furthermore, the IP(3) receptor inhibitor, 2-APB, inhibited LPA-induced PLC activity in control N2A cells, whereas this effect was not observed in PLC-η1 knockdown N2A cells, suggesting a pivotal role of intracellular Ca(2+) mobilization in PLC-η1 activation. Finally, we found that LPA-induced ERK1/2 phosphorylation and expression of the downstream target gene, krox-24, were significantly decreased by PLC-η1 knockdown, and these knockdown effects were abolished by 2-APB. Taken together, our results strongly suggest that PLC-η1 is activated via intracellular Ca(2+) mobilization from the ER, and therefore amplifies GPCR-mediated signaling.

Regulation of mast cell responses in health and disease

Mast cells are multifunctional cells that initiate not only IgE-dependent allergic diseases but also play a fundamental role in innate and adaptive immune responses to microbial infection. They are also thought to play a role in angiogenesis, tissue remodeling, wound healing, and tumor repression or growth. The broad scope of these physiologic and pathologic roles illustrates the flexible nature of mast cells, which is enabled in part by their phenotypic adaptability to different tissue microenvironments and their ability to generate and release a diverse array of bioactive mediators in response to multiple types of cell-surface and cytosolic receptors. There is increasing evidence from studies in cell cultures that release of these mediators can be selectively modulated depending on the types or groups of receptors activated. The intent of this review is to foster interest in the interplay among mast cell receptors to help understand the underlying mechanisms for each of the immunological and non-immunological functions attributed to mast cells. The second intent of this review is to assess the pathophysiologic roles of mast cells and their products in health and disease. Although mast cells have a sufficient repertoire of bioactive mediators to mount effective innate and adaptive defense mechanisms against invading microorganisms, these same mediators can adversely affect surrounding tissues in the host, resulting in autoimmune disease as well as allergic disorders.

Subtype-specific roles of phospholipase C-β via differential interactions with PDZ domain proteins

Since we first identified the PLC-β isozyme, enormous studies have been conducted to investigate the functional roles of this protein (Min et al., 1993; Suh et al.,1988). It is now well-known that the four PLC-β subtypes are major effector molecules in GPCR-mediated signaling, especially for intracellular Ca2+ signaling. Nonetheless, it is still poorly understood why multiple PLC-β subtype exist. Most cells express multiple subtypes of PLC-β in different combinations, and each subtype is involved in somewhat different signaling pathways. Therefore, studying the differential roles of each PLC-β subtype is a very interesting issue. In this regard, we focus here on PDZ domain proteins which are novel PLC-β interacting proteins. As scaffolders, PDZ domain proteins recruit various target proteins ranging from membrane receptors to cytoskeletal proteins to assemble highly organized signaling complexes; this can give rise to efficiency and diversity in cellular signaling. Because PLC-β subtypes have different PDZ-binding motifs, it is possible that they are engaged with different PDZ domain proteins, and in turn participate in distinct physiological responses. To date, several PDZ domain proteins, such as the NHERF family, Shank2, and Par-3, have been reported to selectively interact with certain PLC-β subtypes and GPCRs. Systematic predictions of potential binding partners also suggests differential binding properties between PLC-β subtypes. Furthermore, we elucidated parallel signaling processes for multiple PLC-β subtypes, which still perform distinct functions resulting from differential interactions with PDZ domain proteins within a single cell. Therefore, these results highlight the novel function of PDZ domain proteins as intermediaries in subtype-specific role of PLC-β in GPCR-mediated signaling. Future studies will focus on the physiological meanings of this signaling complex formation by different PDZ domain proteins and PLC-β subtypes. It has been observed for a long time that the expression of certain PLC-β subtype fluctuates during diverse physiological conditions. For example, the expression of PLC-β1 is selectively increased during myoblast and adipocyte differentiation (Faenza et al., 2004; O'Carroll et al., 2009). Likewise, PLC-β2 is highly up-regulated during breast cancer progression and plays a critical role in cell migration and mitosis (Bertagnolo et al., 2007). Although PLC-β3 is selectively down-regulated in neuroendocrine tumors, the expression of PLC-β1 is increased in small cell lung carcinoma (Stalberg et al., 2003; Strassheim et al., 2000). In our hypothetical model, it is most likely that up- and down regulation of certain PLC-β subtypes are due to their selective coupling with specific GPCR-mediated signaling, implicated in these pathophysiologic conditions. Therefore, better understanding of selective coupling between PLC-β subtypes, PDZ domain proteins, and GPCRs will shed light on new prognosis and therapy of diverse diseases, and provide potential targets for drug development.

Emerging anticancer therapeutic targets and the cardiovascular system: is there cause for concern?

The race for a cure to cancer continues, fueled by unprecedented discoveries of fundamental biology underlying carcinogenesis and tumorigenesis. The expansion of the target list and tools to approach them is moving the oncology community extraordinarily rapidly to clinical trials, bringing new hope for cancer patients. This effort is also propelling biological discoveries in cardiovascular research, because many of the targets being explored in cancer play fundamental roles in the heart and vasculature. The combined efforts of cardiovascular and cancer biologists, along with clinical investigators in these fields, will be needed to understand how to safely exploit these efforts. Here, we discuss a few of the many research foci in oncology where we believe such collaboration will be particularly important.

Phosphoinositide-Phospholipase C β1 Mono-Allelic Deletion Is Associated With Myelodysplastic Syndromes Evolution Into Acute Myeloid Leukemia

Purpose

To evaluate the association between the presence of phosphoinositide-phospholipase C β1 (PI-PLCβ1) mono-allelic deletion with the clinical outcome of myelodysplastic syndromes (MDS) patients.

Methods

PI-PLCβ1, PI-PLCβ4, and PI-PLCγ1 cytogenetic investigations were performed on 80 newly diagnosed MDS patients (18 low risk, 26 intermediate 1, 18 intermediate 2, 18 high risk) comparing the results with the clinical outcome of the patients. Moreover, fluorescent in situ hybridization results were validated by real-time polymerase chain reaction (PCR). Finally, PI-PLCβ1 gene and protein expression were assessed by both real-time PCR and immunocytochemical experiments.

Results

Collectively, 35 (43.75%) of 80 of the MDS patients showed a specific mono-allelic deletion of PI-PLCβ1. Kaplan-Meier analysis revealed a significant association (P < .0001) between the PI-PLCβ1 mono-allelic deletion and a higher risk of evolution into acute myeloid leukemia (AML), since 23 of 35 MDS patients (65.7%) bearing the PI-PLCβ1 mono-allelic deletion evolved into AML. Even in multivariate analysis, the PI-PLCβ1 mono-allelic deletion retained a higher significance, with a P < .001, as a prognostic factor of evolution into AML (odds ratio [OR] 1.83; 95% CI, 2.26 to 17.24; P = .00045). Finally, PI-PLCβ1 deletion was related to an altered gene and protein expression.

Conclusion

PI-PLCβ1 mono-allelic deletion is associated with a worse clinical outcome in MDS patients, hinting at the identification of a new group at higher risk of AML evolution and representing a reliable prognostic tool. Moreover, targeting PI-PLCβ1 pathways might emerge as a new therapeutic strategy for MDS.

Inhibitory effect of Qigesan and its separated formula on angiogenesis of esophageal carcinoma Eca109 cell-transplanted nude mouse tumor

AIM: To explore the effects and mechanism of Qigesan and its separated formula on tumor angiogenesis.

METHODS: Exponentially growing Eca109 human esophageal carcinoma cells (1 × 10⁶ cells/mouse) were injected subcutaneously into the flank of 6- week-old female BALB/c nude mice. On the next day after inoculation, the decoctions (40 folds of adult dosage) of Qigesan (W) and its separated formula (blood-activating group P and resolving phlegm group R) were administered by oral gavage once a day for 60 days. Microvessel density (MVD) and VEGF expression in the transplanted tumor was detected using immunohistochemtry, and the protein expressions of EGFR, PDGFR, VEGF and phospholipase C-γ1 (PLC-γ1) were determined using Western blot.

RESULTS: Microvessel density (MVD) in the transplanted tumor of all treatment groups were markedly decreased compared with that in control group (36.43 ± 4.16, 40.29 ± 2.87 42.43 ± 3.04 vessels/mm²vs 48.57 ± 7.45 vessels/mm², P < 0.05 or 0.01) MVD and VEGF had statistically positive correlation by SPASS13.0 (r = 0.712, P = 0.0005). The protein expressions of EGFR, PDGFR, VEGF and phospholipase C-γ1 (PLC-γ1) were obviously decreased compared with that in control group. Inhibitory effects of Qigesan and its separated formula on MVD and those protein expressions were the best in group W and second in group P.

CONCLUSION: Qigesan and its separated formula can inhibit tumor angiogenesis, which is related to the inhibition of protein expressions of EGFR, PDGFR, VEGF and PLC-γ1.