Biomedical subjects

Michael J O Wakelam

Publications and source records attributed to Michael J O Wakelam.

At least 19 recordsLinked to original sources

PubMed2006

A comprehensive proteomics and genomics analysis reveals novel transmembrane proteins in human platelets and mouse megakaryocytes including G6b-B, a novel immunoreceptor tyrosine-based inhibitory motif protein.

The platelet surface is poorly characterized due to the low abundance of many membrane proteins and the lack of specialist tools for their investigation. In this study we identified novel human platelet and mouse megakaryocyte membrane proteins using specialist proteomics and genomics approaches. Three separate methods were used to enrich platelet surface proteins prior to identification by liquid chromatography and tandem mass spectrometry: lectin affinity chromatography, biotin/NeutrAvidin affinity chromatography, and free flow electrophoresis. Many known, abundant platelet surface transmembrane proteins and several novel proteins were identified using each receptor enrichment strategy. In total, two or more unique peptides were identified for 46, 68, and 22 surface membrane, intracellular membrane, and membrane proteins of unknown subcellular localization, respectively. The majority of these were single transmembrane proteins. To complement the proteomics studies, we analyzed the transcriptome of a highly purified preparation of mature primary mouse megakaryocytes using serial analysis of gene expression in view of the increasing importance of mutant mouse models in establishing protein function in platelets. This approach identified all of the major classes of platelet transmembrane receptors, including multitransmembrane proteins. Strikingly 17 of the 25 most megakaryocyte-specific genes (relative to 30 other serial analysis of gene expression libraries) were transmembrane proteins, illustrating the unique nature of the megakaryocyte/platelet surface. The list of novel plasma membrane proteins identified using proteomics includes the immunoglobulin superfamily member G6b, which undergoes extensive alternate splicing. Specific antibodies were used to demonstrate expression of the G6b-B isoform, which contains an immunoreceptor tyrosine-based inhibition motif. G6b-B undergoes tyrosine phosphorylation and association with the SH2 domain-containing phosphatase, SHP-1, in stimulated platelets suggesting that it may play a novel role in limiting platelet activation.

Animals↗

PubMed2006

Evaluation of the accuracy of serum MMP-9 as a test for colorectal cancer in a primary care population.

BACKGROUND: Bowel cancer is common and is a major cause of death. Meta-analysis of randomised controlled trials estimates that screening for colorectal cancer using faecal occult blood (FOB) test reduces mortality from colorectal cancer by 16%. However, FOB testing has a low positive predictive value, with associated unnecessary cost, risk and anxiety from subsequent investigation, and is unacceptable to a proportion of the target population. Increased levels of an enzyme called matrix metalloproteinase 9 (MMP-9) have been found to be associated with colorectal cancer, and this can be measured from a blood sample. Serum MMP-9 is potentially an accurate, low risk and cost-effective population screening tool. This study aims to evaluate the accuracy of serum MMP-9 as a test for colorectal cancer in a primary care population. METHODS/DESIGN: People aged 50 to 69 years, who registered in participating general practices in the West Midlands Region, will be asked to complete a questionnaire that asks about symptoms. Respondents who describe any colorectal symptoms (except only abdominal bloating and/or anal symptoms) and are prepared to provide a blood sample for MMP9 estimation and undergo a colonoscopy (current gold standard investigation) will be recruited at GP based clinics by a research nurse. Those unfit for colonoscopy will be excluded. Colonoscopies will be undertaken in dedicated research clinics. The accuracy of MMP-9 will be assessed by comparing the MMP-9 level with the colonoscopy findings, and the combination of factors (e.g. symptoms and MMP-9 level) that best predict a diagnosis of malignancy (invasive disease or polyps) will be determined. DISCUSSION: Colorectal cancer is a major cause of morbidity and mortality. Most colorectal cancers arise from adenomas and there is a period for early detection by screening, but available tests have risks, are unacceptable to many, have high false positive rates or are expensive. This study will establish the potential of serum MMP-9 as a screening test for colorectal cancer. If it is confirmed as accurate and acceptable, this serum marker has the potential to assist with reducing the morbidity and mortality from colorectal cancer.

Aged↗

PubMed2006

A prospective study to assess the value of MMP-9 in improving the appropriateness of urgent referrals for colorectal cancer.

BACKGROUND: Bowel cancer is common and is a major cause of death. Most people with bowel symptoms who meet the criteria for urgent referral to secondary care will not be found to have bowel cancer, and some people who are found to have cancer will have been referred routinely rather than urgently. If general practitioners could better identify people who were likely to have bowel cancer or conditions that may lead to bowel cancer, the pressure on hospital clinics may be reduced, enabling these patients to be seen more quickly. Increased levels of an enzyme called matrix metalloproteinase 9 (MMP-9) have been found to be associated with such conditions, and this can be measured from a blood sample. This study aims to find out whether measuring MMP-9 levels could improve the appropriateness of urgent referrals for patients with bowel symptoms. METHODS: People aged 18 years or older referred to a colorectal clinic will be asked to complete a questionnaire about symptoms, recent injuries or chronic illnesses (these can increase the level of matrix metalloproteinases) and family history of bowel cancer. A blood sample will be taken from people who consent to take part to assess MMP-9 levels, and the results of examination at the clinic and/or investigations arising from the clinic visit will be collected from hospital records. The accuracy of MMP-9 will be assessed by comparing the MMP-9 level with the resulting diagnosis. The combination of factors (e.g. symptoms and MMP-9 level) that best predict a diagnosis of malignancy (invasive disease or polyps) will be determined. DISCUSSION: Although guidelines are in place to facilitate referrals to colorectal clinics, symptoms alone do not adequately distinguish people with malignancy from people with benign conditions. This study will establish whether MMP-9 could assist this process. If this were the case, measurement of MMP-9 levels could be used by general practitioners to assist in the identification of people who were most likely to have bowel cancer or conditions that may lead to bowel cancer, and who should, therefore, be referred most urgently to secondary care.

Adolescent↗

PubMed2006

Analysis of intact phosphoinositides in biological samples.

It is now apparent that each of the known, naturally occurring polyphosphoinositides, the phosphatidylinositol monophosphates (PtdIns3P, PtdIns4P, PtdIns5P), phosphatidylinositol bisphosphates [PtdIns(3,4)P(2), PtdIns(3,5)P(2), PtdIns(4,5)P(2)], and phosphatidylinositol trisphosphate [PtdIns(3,4,5)P(3)], have distinct roles in regulating many cellular events, including intracellular signaling, migration, and vesicular trafficking. Traditional identification techniques require [(32)P]inorganic phosphate or [(3)H]inositol radiolabeling, acidified lipid extraction, deacylation, and ion-exchange head group separation, which are time-consuming and not suitable for samples in which radiolabeling is impractical, thus greatly restricting the study of these lipids in many physiologically relevant systems. Thus, we have developed a novel, high-efficiency, buffered citrate extraction methodology to minimize acid-induced phosphoinositide degradation, together with a high-sensitivity liquid chromatography-mass spectrometry (LC-MS) protocol using an acetonitrile-chloroform-methanol-water-ethylamine gradient with a microbore silica column that enables the identification and quantification of all phosphoinositides in a sample. The liquid chromatograph is sufficient to resolve PtdInsP(3) and PtdInsP(2) regioisomers; however, the PtdInsP regioisomers require a combination of LC and diagnostic fragmentation to MS(3). Data are presented using this approach for the analysis of phosphoinositides in human platelet and yeast samples.

Blood Platelets↗

PubMed2006

Autotaxin, a secreted lysophospholipase D, is essential for blood vessel formation during development.

Autotaxin (ATX), or nucleotide pyrophosphatase-phosphodiesterase 2, is a secreted lysophospholipase D that promotes cell migration, metastasis, and angiogenesis. ATX generates lysophosphatidic acid (LPA), a lipid mitogen and motility factor that acts on several G protein-coupled receptors. Here we report that ATX-deficient mice die at embryonic day 9.5 (E9.5) with profound vascular defects in yolk sac and embryo resembling the Galpha13 knockout phenotype. Furthermore, at E8.5, ATX-deficient embryos showed allantois malformation, neural tube defects, and asymmetric headfolds. The onset of these abnormalities coincided with increased expression of ATX and LPA receptors in normal embryos. ATX heterozygous mice appear healthy but show half-normal ATX activity and plasma LPA levels. Our results reveal a critical role for ATX in vascular development, indicate that ATX is the major LPA-producing enzyme in vivo, and suggest that the vascular defects in ATX-deficient embryos may be explained by loss of LPA signaling through Galpha13.

Animals↗

PubMed2005

Diacylglycerol induces fusion of nuclear envelope membrane precursor vesicles.

Purified membrane vesicles isolated from sea urchin eggs form nuclear envelopes around sperm nuclei following GTP hydrolysis in the presence of cytosol. A low density subfraction of these vesicles (MV1), highly enriched in phosphatidylinositol (PtdIns), is required for nuclear envelope formation. Membrane fusion of MV1 with a second fraction that contributes most of the nuclear envelope can be initiated without GTP by an exogenous bacterial PtdIns-specific phospholipase C (PI-PLC) which hydrolyzes PtdIns to form diacylglycerides and inositol 1-phosphate. This PI-PLC hydrolyzes a subset of sea urchin membrane vesicle PtdIns into diglycerides enriched in long chain, polyunsaturated species as revealed by a novel liquid chromatography-mass spectrometry analysis. Large unilammelar vesicles (LUVs) enriched in PtdIns can substitute for MV1 in PI-PLC induced nuclear envelope formation. Moreover, MV1 prehydrolyzed with PI-PLC and washed to remove inositols leads to spontaneous nuclear envelope formation with MV2 without further PI-PLC treatment. LUVs enriched in diacylglycerol mimic prehydrolyzed MV1. These results indicate that production of membrane-destabilizing diglycerides in membranes enriched in PtdIns may facilitate membrane fusion in a natural membrane system and suggest that MV1, which binds only to two places on the sperm nucleus, may initiate fusion locally.

Animals↗

PubMed2005

Phospholipase D activity is essential for actin localization and actin-based motility in Dictyostelium.

PLD (phospholipase D) activity catalyses the generation of the lipid messenger phosphatidic acid, which has been implicated in a number of cellular processes, particularly the regulation of membrane traffic. In the present study, we report that disruption of PLD signalling causes unexpectedly profound effects on the actin-based motility of Dictyostelium. Cells in which PLD activity is inhibited by butan-1-ol show a complete loss of actin-based structures, accompanied by relocalization of F-actin into small clusters, and eventually the nucleus, without a visible fall in levels of F-actin. Addition of exogenous phosphatidic acid reverses the effects of butan-1-ol, confirming that these effects are caused by inhibition of PLD. Loss of motility correlates with complete inhibition of endocytosis and a reduction in phagocytosis. Inhibition of PLD caused a major decrease in the synthesis of PtdIns(4,5)P2, which could again be reversed by exogenously applied phosphatidic acid. Thus the essential role of PLD signalling in both motility and endocytosis appears to be mediated directly via regulation of PtdIns(4)P kinase activity. This implies that localized PLD-regulated synthesis of PtdIns(4,5)P2 is essential for Dictyostelium actin function.

Actins↗

PubMed2005

Phospholipase D2 stimulates integrin-mediated adhesion via phosphatidylinositol 4-phosphate 5-kinase Igamma b.

Cellular adhesion can be regulated by, as yet, poorly defined intracellular signalling events. Phospholipase D enzymes generate the messenger lipid phosphatidate and here we demonstrate that suppression of this reaction inhibits cellular adhesion. This effect was reversed by the addition of cell-permeable analogues of either phosphatidate or phosphatidylinositol 4,5-bisphosphate. By contrast, neither diacylglycerol nor lysophosphatidic acid were able to reverse this effect suggesting that phosphatidate itself acts directly on a target protein(s) to regulate adhesion rather than as the result of its conversion to either of these metabolite lipids. Antibodies that block beta1 and beta2 integrin-substrate interactions inhibited adhesion stimulated by both phosphatidate and phosphatidylinositol 4,5-bisphosphate indicating that these lipids regulate beta1 and beta2 integrin-mediated adhesion. In vivo, these lipids can be generated by phospholipase D2 and phosphatidylinositol 4-phosphate 5-kinase Igamma b, respectively, and over-expression of catalytically-functional forms of these enzymes dose-dependently stimulated adhesion while siRNA depletion of PLD2 levels inhibited adhesion. Furthermore the ability of over-expressed phospholipase D2 to stimulate adhesion was inhibited by a dominant-negative version of phosphatidylinositol 4-phosphate 5-kinase Igamma b. Consistent with this, phosphatidylinositol 4-phosphate 5-kinase Igamma b-mediated adhesion was dependent upon phospholipase D2's product, phosphatidate indicating that phosphatidylinositol 4-phosphate 5-kinase Igamma b is downstream of, and necessary for, phospholipase D2's regulation of adhesion. It is likely that this phospholipase D2-generated phosphatidate directly stimulates phosphatidylinositol 4-phosphate 5-kinase Igamma b to generate phosphatidylinositol 4,5-bisphosphate as this mechanism has previously been demonstrated in vitro. Thus, our data indicates that during the initial stages of adhesion, phospholipase D2-derived phosphatidate stimulates phosphatidylinositol 4-phosphate 5-kinase Igamma b to generate phosphatidylinositol 4,5-bisphosphate and that consequently this inositol phospholipid promotes adhesion through its regulation of cell-surface integrins.

Animals↗

PubMed2005

Induction of autotaxin by the Epstein-Barr virus promotes the growth and survival of Hodgkin lymphoma cells.

A proportion of patients with Hodgkin lymphoma carry Epstein-Barr virus (EBV), an oncogenic herpesvirus, in their tumor cells. Although it is generally assumed that EBV contributes to the malignant phenotype of Hodgkin lymphoma cells, direct evidence in support of this is lacking. Here we show that EBV infection of Hodgkin lymphoma cells results in the induction of autotaxin, a secreted tumor-associated factor with lysophospholipase-D activity. Up-regulation of autotaxin increased the generation of lysophosphatidic acid (LPA) and led to the enhanced growth and survival of Hodgkin lymphoma cells, whereas specific down-regulation of autotaxin decreased LPA levels and reduced cell growth and viability. In lymphoma tissues, autotaxin expression was mainly restricted to CD30+ anaplastic large-cell lymphomas and Hodgkin lymphoma; in the latter, high levels of autotaxin were strongly associated with EBV positivity (P = .006). Our results identify the induction of autotaxin and the subsequent generation of LPA as key molecular events that mediate the EBV-induced growth and survival of Hodgkin lymphoma cells and suggest that this pathway may provide opportunities for novel therapeutic intervention.

Cell Line, Tumor↗

PubMed2005

Exocytosis of CTLA-4 is dependent on phospholipase D and ADP ribosylation factor-1 and stimulated during activation of regulatory T cells.

CTLA-4 is an essential protein in the regulation of T cell responses that interacts with two ligands found on the surface of APCs (CD80 and CD86). CTLA-4 is itself poorly expressed on the T cell surface and is predominantly localized to intracellular compartments. We have studied the mechanisms involved in the delivery of CTLA-4 to the cell surface using a model Chinese hamster ovary cell system and compared this with activated and regulatory human T cells. We have shown that expression of CTLA-4 at the plasma membrane (PM) is controlled by exocytosis of CTLA-4-containing vesicles and followed by rapid endocytosis. Using selective inhibitors and dominant negative mutants, we have shown that exocytosis of CTLA-4 is dependent on the activity of the GTPase ADP ribosylation factor-1 and on phospholipase D activity. CTLA-4 was identified in a perinuclear compartment overlapping with the cis-Golgi marker GM-130 but did not colocalize strongly with lysosomal markers such as CD63 and lysosome-associated membrane protein. In regulatory T cells, activation of phospholipase D was sufficient to trigger release of CTLA-4 to the PM but did not inhibit endocytosis. Taken together, these data suggest that CTLA-4 may be stored in a specialized compartment in regulatory T cells that can be triggered rapidly for deployment to the PM in a phospholipase D- and ADP ribosylation factor-1-dependent manner.

ADP-Ribosylation Factor 1↗

PubMed2005

Assays to study phospholipase D regulation by inositol phospholipids and ADP-ribosylation factor 6.

Phospholipase D (PLD) is an enzyme implicated in the regulation of both exocytic and endocytic vesicle trafficking as well as many other processes. Consistent with this, the small GTPase Arf6 and regulated changes in inositol phospholipids levels are two factors that regulate both PLD and vesicle trafficking. Here we describe three methodologies through which the activation of PLD by Arf6 and inositol phospholipids may be investigated. The first method described is an in vitro protocol that allows the analysis of purified proteins or cell lysates. Furthermore, this protocol can be used to analyze the effects of different inositol phospholipids by changing the composition of the substrate vesicle. The major advantage of this protocol lies in the ability to analyze the effects of direct interactions on PLD activation by using pure proteins and lipids. The other two methods are in vivo protocols for the analysis of PLD activation in response to extracellular stimuli. Modification of cellular composition using overexpression/deletion or knockout of specific genes can be utilized with these protocols to characterize PLD activation pathways. The first of these methods uses the detection of radiolabeled PLD products and can be used for most cell types whereas the second of these two protocols is used to measure PLD products when radiolabeling of cells is not possible, such as freshly isolated cells that will not survive long enough to attain radiochemical equilibrium.

ADP-Ribosylation Factor 6↗

PubMed2004

Activation of Syk in neutrophils by antineutrophil cytoplasm antibodies occurs via Fcgamma receptors and CD18.

Antineutrophil cytoplasm antibodies (ANCA) activate TNF-alpha-primed neutrophils to undergo a respiratory burst. The intracellular signals that mediate activation have not been studied extensively but could increase the understanding of the pathogenesis small vessel vasculitis. It was demonstrated that ANCA-IgG induced phosphorylation of the tyrosine kinase Syk in TNF-alpha-primed neutrophils from healthy donors. Syk was not phosphorylated in response to ANCA F(ab')(2). Furthermore, Syk phosphorylation was attenuated by blockade of both low-affinity Fcgamma receptors and CD18. Similarly, low-affinity Fcgamma receptor blockade reduced ANCA-induced superoxide production. In patient-derived neutrophils, the high-affinity Fcgamma receptor FcgammaRI was also demonstrated to be involved in ANCA-induced superoxide production. However, Syk phosphorylation was not attenuated by blockade of the FcgammaRI, present on neutrophils from vasculitis patients. The tyrosine kinase inhibitor 4-Amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine inhibited the ANCA-induced respiratory burst and Syk phosphorylation, suggesting that Src kinases lie upstream of Syk activation but downstream of ANCA engagement of Fcgamma receptors. Piceatannol, another tyrosine kinase inhibitor, also inhibited ANCA-induced Syk phosphorylation and the ANCA-stimulated respiratory burst, supporting the proposed functional role for Syk in ANCA signaling. ANCA-induced phosphorylation of Cbl and intracellular calcium transients, potential downstream mediators of Syk activation, were also blocked by tyrosine kinase inhibitors. While it has previously been shown that pertussis toxin diminishes the ANCA-induced respiratory burst, indicating heterotrimeric G protein involvement, Syk phosphorylation and calcium transients were unaffected by pertussis toxin. Collectively, these data show that Syk phosphorylation is induced during ANCA-triggered neutrophil activation.

Antibodies, Antineutrophil Cytoplasmic↗

PubMed2004

Phospholipase D.

Phospholipase D catalyses the hydrolysis of the phosphodiester bond of glycerophospholipids to generate phosphatidic acid and a free headgroup. Phospholipase D activities have been detected in simple to complex organisms from viruses and bacteria to yeast, plants, and mammals. Although enzymes with broader selectivity are found in some of the lower organisms, the plant, yeast, and mammalian enzymes are selective for phosphatidylcholine. The two mammalian phospholipase D isoforms are regulated by protein kinases and GTP binding proteins of the ADP-ribosylation and Rho families. Mammalian and yeast phospholipases D are also potently stimulated by phosphatidylinositol 4,5-bisphosphate. This review discusses the identification, characterization, structure, and regulation of phospholipase D. Genetic and pharmacological approaches implicate phospholipase D in a diverse range of cellular processes that include receptor signaling, control of intracellular membrane transport, and reorganization of the actin cytoskeleton. Most ideas about phospholipase D function consider that the phosphatidic acid product is an intracellular lipid messenger. Candidate targets for phospholipase-D-generated phosphatidic acid include phosphatidylinositol 4-phosphate 5-kinases and the raf protein kinase. Phosphatidic acid can also be converted to two other lipid mediators, diacylglycerol and lyso phosphatidic acid. Coordinated activation of these phospholipase-D-dependent pathways likely accounts for the pleitropic roles for these enzymes in many aspects of cell regulation.

Animals↗

PubMed2003

Inhibition of phosphatidylinositol 3-kinase- and ERK MAPK-regulated protein synthesis reveals the pro-apoptotic properties of CD40 ligation in carcinoma cells.

CD40, a member of the tumor necrosis factor receptor superfamily, is frequently expressed in carcinomas where its stimulation results in induction of apoptosis when de novo protein synthesis is inhibited. The requirement of protein synthesis inhibition for efficient killing suggests that CD40 transduces potent survival signals capable of suppressing its pro-apoptotic effects. We have found that inhibition of CD40 signaling on the phosphatidylinositol 3-kinase (PI3K) and ERK MAPK but not on the p38 MAPK axis disrupts this balance and sensitizes carcinoma cells to CD40-mediated cell death. The CD40-mediated PI3K and ERK activities were found to converge on the regulation of protein synthesis in carcinoma cells via a pathway involving the activation of p90 ribosomal S6 kinase (p90Rsk) and p70S6 kinases, upstream of the translation elongation factor eEF2. In addition, CD40 ligation was found to mediate a PI3K- and mammalian target of rapamycin (mTOR)-dependent phosphorylation of 4E-BP1 and its subsequent dissociation from the mRNA cap-binding protein eIF4E as well as an ERK-dependent phosphorylation of eIF4E, thus promoting translation initiation. Concomitantly, the antiapoptotic protein cFLIP was found to be induced in CD40 ligand-stimulated carcinoma cells in a PI3K-, ERK-, and mammalian target of rapamycin (mTOR)-dependent manner and down-regulation of cFLIPS expression sensitized to CD40-mediated carcinoma cell death. These data underline the significance of the PI3K and ERK pathways in controlling the balance between CD40-mediated survival and death signals through the regulation of the protein synthesis machinery. Pharmacological agents that target this machinery or its upstream kinases could, therefore, be exploited for CD40-based tumor therapy.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Activation of the G(i) heterotrimeric G protein by ANCA IgG F(ab')2 fragments is necessary but not sufficient to stimulate the recruitment of those downstream mediators used by intact ANCA IgG.

Anti-neutrophil cytoplasm autoantibodies (ANCA) are implicated in the pathogenesis of systemic vasculitis. Intact ANCA IgG activate superoxide generation in cytokine-primed neutrophils after binding their antigens and co-engaging Fcgamma receptors (FcgammaR). The contribution of antigen binding via ANCA F(ab')(2) fragments to signaling has been unclear. This study shows that both ANCA IgG and F(ab')(2) fragments of ANCA IgG induce significant GTPase activity, which could be blocked with pertussis toxin and anti-G(i) protein antibodies. Pertussis toxin inhibited ANCA IgG-induced superoxide generation but was without effect on superoxide production after conventional FcgammaR ligation. ANCA F(ab')(2) fragments did not induce superoxide generation. ANCA IgG activated PI 3-kinase-generating PIP(3), activated protein kinase B (PKB), and p21(ras); activation of each mediator was inhibited with pertussis toxin, but PI3K and PKB were not activated by ANCA IgG F(ab')(2) fragments. Intact ANCA IgG induced tyrosine phosphorylation, whereas F(ab')(2) fragments did not, and ANCA IgG-mediated superoxide generation was inhibited with genistein. Both genistein and pertussis toxin together completely abrogated the ANCA-induced oxidative burst. Genistein also inhibited ANCA IgG-induced PIP(3) generation and p21(ras) activation. These data implicate a novel ANCA IgG stimulated signaling pathway that involves both F(ab')(2)-mediated antigen binding and Fc-mediated FcgammaR ligation in cooperative interactions between G(i) proteins and tyrosine kinases that facilitates activation of downstream mediators.

Antibodies, Antineutrophil Cytoplasmic↗

PubMed2002

The regulation of phospholipase D by inositol phospholipids and small GTPases.

Phospholipase D1 and D2 (PLD1, PLD2) both have PX and PH domains in their N-terminal regions with these inositol lipid binding domains playing key roles in regulating PLD activity and localisation. The activity of PLD1 is also regulated by protein kinase C and members of the Rho and Arf families of GTPases. Each of these proteins binds to unique sites; however, there appears to be little in vitro discrimination between individual family members. In agonist-stimulated cells, however, there is specificity, with, for example in RBL-2H3 cells, antigen stimulating the activation of PLD1 by association with Arf6, Rac1 and protein kinase Calpha. PLD2 appears to be less directly regulated by GTPases and rather is primarily controlled through interaction with phosphatidylinositol 4-phosphate 5-kinase that generates the activating phosphatidylinositol 4,5-bisphosphate.

ADP-Ribosylation Factors↗

PubMed2002

Breast cancer cell-derived EMMPRIN stimulates fibroblast MMP2 release through a phospholipase A(2) and 5-lipoxygenase catalyzed pathway.

Metalloproteinases (MMP) produced by both cancer and normal stromal fibroblast cells play a critical role in the metastatic spread of tumours, however little is known of the regulation of their release. In this report we demonstrate that breast cancer cells in culture release apparently full length soluble EMMPRIN that promotes the release of pro-MMP2 from fibroblasts. The generation of MMP2 is mediated by activation of phospholipase A(2) and 5-lipoxygenase. These results suggest that the production of soluble EMMPRIN, phospholipase A(2) and 5-lipoxygenase activities are sites for potential therapeutic intervention.

Antigens, CD↗

PubMed2002

TAPAS-1, a novel microdomain within the unique N-terminal region of the PDE4A1 cAMP-specific phosphodiesterase that allows rapid, Ca2+-triggered membrane association with selectivity for interaction with phosphatidic acid.

Here we identify an 11-residue helical module in the unique N-terminal region of the cyclic AMP-specific phosphodiesterase PDE4A1 that determines association with phospholipid bilayers and shows a profound selectivity for interaction with phosphatidic acid (PA). This module contains a core bilayer insertion unit that is formed by two tryptophan residues, Trp(19) and Trp(20), whose orientation is optimized for bilayer insertion by the Leu(16):Val(17) pairing. Ca(2+), at submicromolar levels, interacts with Asp(21) in this module and serves to gate bilayer insertion, which is completed within 10 ms. Selectivity for interaction with PA is suggested to be achieved primarily through the formation of a charge network of the form (Asp(21-):Ca(2+):PA(2-):Lys(24+)) with overall neutrality at the bilayer surface. This novel phospholipid-binding domain, which we call TAPAS-1 (tryptophan anchoring phosphatidic acid selective-binding domain 1), is here identified as being responsible for membrane association of the PDE4A1 cAMP-specific phosphodiesterase. TAPAS-1 may not only serve as a paradigm for other PA-binding domains but also aid in detecting related phospholipid-binding domains and in generating simple chimeras for conferring membrane association and intracellular targeting on defined proteins.

3',5'-Cyclic-AMP Phosphodiesterases↗