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Biomedical subjects

P J Parker

Publications and source records attributed to P J Parker.

At least 19 recordsLinked to original sources
PubMed2006

Compartmental signal modulation: Endosomal phosphatidylinositol 3-phosphate controls endosome morphology and selective cargo sorting.

It is increasingly recognized that the compartmental organization of signaling processes has a profound influence on cellular behavior. However, our inability to influence these compartmental events in a spatially restricted and acute manner limits our understanding of causation. To determine whether local compartmental loss of a phosphoinositide disrupts the normal traffic of specific cargoes through endosomes, we developed the use of a regulated dimerization device, here designed to compartmentally modify the phosphoinositide content of Rab5-positive endosomes. This modification is effected through the specific regulated recruitment of the 3-phosphatase myotubularin to endosomal membranes in intact cells. The selective manipulation of endosomal phosphatidylinositols (PIs) demonstrates that it is the phosphatidylinositol 3-phosphate (PtdIns3P) or its metabolite PtdIns(3,5)P2 within this compartment that determines the normal maturation of the endosomal compartment and the flux of receptors through it. On local loss of PtdIns3P/PtdIns(3,5)P2, the endosomal compartment itself fails to continue its normal maturation process, leading to the microtubule-dependent tubularization of the endosomal network. Furthermore, it is shown that endosomal PtdIns3P/PtdIns(3,5)P2 is necessary for transferrin receptor traffic through this compartment while having an effect on EGF receptor (EGFR) entry into and sorting from this endosome compartment. The ability to acutely and selectively influence compartmental behavior as exemplified here for endomsomes clearly illustrates the power of the approach used to dissect the role of localized signals and events.

Animals↗
PubMed2005

c-Met signalling: spatio-temporal decisions.

The spatial control of signalling events is critical in determining the outcome of a cellular response. Recent studies on the signal output from the growth factor/receptor HGF/c-Met, demonstrates that the PKC-regulated location of downstream transducers, specifically the MAPkinase ERK1/2, has a profound positive influence on cell migration, despite apparently reducing the steady state level of ERK1/2 activation. The mechanisms involved and the implications for signalling studies are discussed.

Animals↗
PubMed2005

First military use of activated Factor VII in an APC-III pelvic fracture.

A male soldier in shock with an APC-III pelvic fracture was flown to an Air Assault Surgical Group (AASG) of 16 Close Support Medical Regiment at Al Amarah in Iraq. A pelvic external fixator was applied and his condition stabilized. Ultrasound scanning (FAST) showed an absent bladder, and a spreading retroperitoneal haematoma combined with intra-abdominal, free blood. Unfortunately he continued to bleed and required transfusion with the unit's entire stock of type-specific blood. At emergency laparotomy, uncontrollable pelvic bleeding was encountered and the abdominal aorta required clamping above the iliac bifurcation. Branches of the right internal iliac artery were the source and this was ligated. Some bleeding continued post-operatively: administration of activated Factor VII was associated with a marked reduction in the oozing from his fixator pin-sites and an improvement in his pH from 7.1 to 7.3. In total, 25 units of blood were transfused, 8 of which were fresh whole blood donated by individual members of the AASG. The patient survived, returned to the UK, had his injuries reconstructed, and is currently undergoing rehabilitation. This case illustrates the benefits of forward resuscitation surgery in wartime and the need for a multidisciplinary approach to trauma care.

Factor VIIa↗
PubMed2005

Forward surgery on Operation Telic--Iraq 2003.

Two Air Assault Surgical Groups (AASGs) from 16 Close Support Medical Regiment deployed to Kuwait on Operation Telic in February 2003. Each AASG was comprised of a four-table resuscitation facility, a two table FST and a twin-bedded ITU facility. An A+E Consultant and nurse, an experienced radiographer and laboratory technician with two further RGNs and CMTs provided resuscitation support. Each FST had an orthopaedic and a general surgeon, two anaesthetists and eight operating department practitioners. Further equipment consisted of a Polymobil 111 X-ray unit, a Sonosite 180 ultrasound scanner and an ISTAT gas, haematocrit and electrolyte analyser. 100 units of mixed blood were carried by each AASG. Fifty-one surgical procedures were performed on thirty one patients. Twenty one of these patients were Iraqi prisoners of war or civilians. Seventeen wound debridements, five amputations, five laparotomies, four insertions of Denham pins with Thomas splintage for femoral fracture, three external fixations and one axillary artery repair formed the basis of the major cases undertaken. The first field use of activated factor VII by the British Army was successful in the resuscitation of a patient with exsanguinating haemorrhage after an open-book (APC-III) pelvic fracture and a ruptured intrapelvic haematoma. The other cases included eleven manipulations under anaesthetic/application of plaster and four finger terminalisations. Forward military surgery has a continued role to play on the modern fast moving battlefield. 16 Close Support Medical Regiment normally supports 16 Air Assault Brigade with its remit for expeditionary operations and SF support. Its experience on Op Telic should influence planning for future deployment.

Adolescent↗
PubMed2004

The ubiquitous phosphoinositides.

There are now known to exist seven phosphoinositides all derived through various metabolic routes from the parent lipid phosphatidylinositol. With one additional metabolite, diacylglycerol, these represent a rich resource of bioactive lipids responsible for recruiting protein effectors and marking membrane compartments. The metabolic map of this pathway and the nature of the binding partner interactions are reviewed.

Animals↗
PubMed2003

Integrin-protein kinase C relationships.

The integrins have an ability to interact with extracellular matrix proteins to confer adhesive and motile properties on cells. The means by which these activities operate and the manner in which they are integrated with cell functions is of particular relevance to many biological processes. In the present paper, the developing understanding of the bi-directional relationship between the protein kinase C family of signal transducers and integrins is discussed.

Amino Acid Sequence↗
PubMed2001

Protein kinase Cepsilon is required for macrophage activation and defense against bacterial infection.

To assess directly the role of protein kinase C (PKC)epsilon in the immune system, we generated mice that carried a homozygous disruption of the PKCepsilon locus. PKCepsilon(-/-) animals appeared normal and were generally healthy, although female mice frequently developed a bacterial infection of the uterus. Macrophages from PKCepsilon(-/-) animals demonstrated a severely attenuated response to lipopolysaccharide (LPS) and interferon (IFN)gamma, characterized by a dramatic reduction in the generation of NO, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-1beta. Further analysis revealed that LPS-stimulated macrophages from PKCepsilon(-/-) mice were deficient in the induction of nitric oxide synthase (NOS)-2, demonstrating a decrease in the activation of IkappaB kinase, a reduction in IkappaB degradation, and a decrease in nuclear factor (NF)kappaB nuclear translocation. After intravenous administration of Gram-negative or Gram-positive bacteria, PKCepsilon(-/-) mice demonstrated a significantly decreased period of survival. This study provides direct evidence that PKCepsilon is critically involved at an early stage of LPS-mediated signaling in activated macrophages. Furthermore, we demonstrate that in the absence of PKCepsilon, host defense against bacterial infection is severely compromised, resulting in an increased incidence of mortality.

Animals↗
PubMed2001

Endosomal localization of phospholipase D 1a and 1b is defined by the C-termini of the proteins, and is independent of activity.

The factors regulating the activity of cellular phospholipase D (PLD) have been well characterized; however, the cellular distribution of specific PLD isoforms and the factors defining localization are less clear. Two specific PLD1 isoforms, PLD1a and PLD1b, are shown in the present study to be localized in endosomal compartments with early endosomal autoantigen 1, internalizing epidermal growth factor receptor (ErbB1) and lysobisphosphatidic acid. Novel C-terminal splice variants of PLD1, PLD1a2 and PLD1b2, do not exhibit this endosomal localization. Studies using catalytically inactive and C-terminal deletion mutants of the four PLD1 isoforms led to the conclusion that the C-terminus plays an important part in the catalytic activity of PLD1, but that the endosomal localization of PLD1a and PLD1b is defined by the C-terminus and not catalytic activity.

Base Sequence↗
PubMed2001

Ezrin is a downstream effector of trafficking PKC-integrin complexes involved in the control of cell motility.

Protein kinase C (PKC) alpha has been implicated in beta1 integrin-mediated cell migration. Stable expression of PKCalpha is shown here to enhance wound closure. This PKC-driven migratory response directly correlates with increased C-terminal threonine phosphorylation of ezrin/moesin/radixin (ERM) at the wound edge. Both the wound migratory response and ERM phosphorylation are dependent upon the catalytic function of PKC and are susceptible to inhibition by phosphatidylinositol 3-kinase blockade. Upon phorbol 12,13-dibutyrate stimulation, green fluorescent protein-PKCalpha and beta1 integrins co-sediment with ERM proteins in low-density sucrose gradient fractions that are enriched in transferrin receptors. Using fluorescence lifetime imaging microscopy, PKCalpha is shown to form a molecular complex with ezrin, and the PKC-co-precipitated endogenous ERM is hyperphosphorylated at the C-terminal threonine residue, i.e. activated. Electron microscopy showed an enrichment of both proteins in plasma membrane protrusions. Finally, overexpression of the C-terminal threonine phosphorylation site mutant of ezrin has a dominant inhibitory effect on PKCalpha-induced cell migration. We provide the first evidence that PKCalpha or a PKCalpha-associated serine/threonine kinase can phosphorylate the ERM C-terminal threonine residue within a kinase-ezrin molecular complex in vivo.

Amino Acid Substitution↗
PubMed2001

Gab1 phosphorylation: a novel mechanism for negative regulation of HGF receptor signaling.

Signal transduction by HGF receptor, the tyrosine kinase encoded by the MET oncogene, switches on a genetic program called 'invasive growth' inducing epithelial cell dissociation, migration, growth, and ultimately leading to differentiation into branched tubular structures. Sustained tyrosine phosphorylation of the downstream adaptor protein Gab1 is required for the HGF response. Here we show that serine/threonine phosphorylation of Gab1 provides a control mechanism for negative regulation. Treatment with okadaic acid, a potent inhibitor of the serine/threonine protein phosphatases PP1 and PP2A, was followed by activation of a number of serine/threonine kinases, hyper-phosphorylation in serine and threonine of Gab1 and severe inhibition of the HGF-induced biological responses. Under these conditions, Gab1 was found to be concomitantly hypo-phosphorylated in tyrosine, and thus endowed with reduced ability to recruit SH2 containing signal transducers such as PI3 kinase. Among the serine-threonine kinases activated by PP1 and PP2A inhibition, we found that PKC-alpha and PKC-beta1 are required for negative regulation of Gab1. These data provide a novel negative mechanism for the HGF receptor signaling pathways and highlight a potentially useful target for inhibitors of invasive growth.

Adaptor Proteins, Signal Transducing↗
PubMed2001

AGC protein kinase phosphorylation and protein kinase C.

Protein kinase cascades feature in many signal transduction pathways. For those discussed here, a single upstream protein kinase appears to be responsible for the control of multiple downstream targets. So how is specificity introduced into these events? For the downstream kinases (substrates) described here, it would appear that specificity is determined by substrate-directed events that are permissive for phosphorylation. There are also distinctions relating to the turnover of these phosphorylations providing a further element of specificity.

Allosteric Site↗
PubMed2001

The treatment role of the plastic nail guard for ingrowing toenails.

An illustrative case of bilateral ingrowing toe-nails highlights the practical advantages of the use of the plastic nail guard (PNG). Insertion of the PNG is inexpensive and is easy to learn and perform. The technique is described and discussed. Its recurrence rate compares favourably with simple avulsion and wedge resection.

Acute Disease↗
PubMed2001

Synthesis and function of 3-phosphorylated inositol lipids.

The 3-phosphorylated inositol lipids fulfill roles as second messengers by interacting with the lipid binding domains of a variety of cellular proteins. Such interactions can affect the subcellular localization and aggregation of target proteins, and through allosteric effects, their activity. Generation of 3-phosphoinositides has been documented to influence diverse cellular pathways and hence alter a spectrum of fundamental cellular activities. This review is focused on the 3-phosphoinositide lipids, the synthesis of which is acutely triggered by extracellular stimuli, the enzymes responsible for their synthesis and metabolism, and their cell biological roles. Much knowledge has recently been gained through structural insights into the lipid kinases, their interaction with inhibitors, and the way their 3-phosphoinositide products interact with protein targets. This field is now moving toward a genetic dissection of 3-phosphoinositide action in a variety of model organisms. Such approaches will reveal the true role of the 3-phosphoinositides at the organismal level in health and disease.

1-Phosphatidylinositol 4-Kinase↗
PubMed2000

Beta1-integrin and PTEN control the phosphorylation of protein kinase C.

Phosphorylation of protein kinase C (PKC) provides an amplitude control that operates in conjunction with allosteric effectors. Under many conditions, PKC isotypes appear to be highly phosphorylated; however, the cellular inputs that maintain these phosphorylations are not characterized. In the present work, it is shown that there is a differential phosphorylation of PKCdelta in adherent versus suspension cultures of transfected HEK-293 cells. It is established that integrin activation is sufficient to trigger PKCdelta phosphorylation and that this signals through phosphoinositide 3-kinase (PI3-kinase) to stimulate the phosphorylation of two sites, T505 and S662. The loss of signal input to PKCdelta in suspension culture is dependent on the tumour suppressor gene PTEN, which encodes a bi-functional phosphotyrosine/phosphoinositide 3-phosphate phosphatase. In the PTEN(-/-) UM-UC-3 bladder carcinoma cell line grown in suspension, transfected PKCdelta no longer accumulates in a dephospho-form on serum removal. By contrast, in a UM-UC-3-derivative cell line stably expressing PTEN, PKCdelta does become dephosphorylated under these conditions. Employing the PTEN Gly(129)-->Glu mutant, which is selectively defective in lipid phosphatase activity, it was established that it is the lipid phosphatase activity that controls PKCdelta phosphorylation. The evidence indicates that PKCdelta phosphorylation and its latent activity are maintained in serum-deprived adherent cultures through integrin-matrix interactions. This control acts through a pathway involving a lipid product of PI3-kinase in a manner that can be suppressed by PTEN.

Cell Line↗
PubMed2000

Lipopolysaccharide induces jun N-terminal kinase activation in macrophages by a novel Cdc42/Rac-independent pathway involving sequential activation of protein kinase C zeta and phosphatidylcholine-dependent phospholipase C.

The activation of kinases of the mitogen-activated protein kinase superfamily initiated by lipopolysaccharide (LPS) plays an important role in transducing inflammatory signals. The pathway leading to the induction of stress-activated protein kinases in macrophages stimulated with LPS was investigated. The activation of Jun N-terminal kinases (JNK) by LPS is herbimycin sensitive. Using specific inhibitors, it was shown that the pathway involves the activation of phosphoinositide 3-kinase (PI 3-K). However, in contrast to previous reports, the small GTPases Cdc42 and Rac are not required downstream of PI 3-K for JNK activation. Instead, the phosphoinositides produced by PI 3-K stimulate protein kinase C (PKC) zeta activation through PDK1. In turn, activation of this atypical PKC leads to the stimulation of phosphatidylcholine phospholipase C (PC-PLC) and acidic sphingomyelinase (ASMase). It is therefore proposed that PKCzeta regulates the PC-PLC/ASMase pathway, and it is hypothesized that the resultant ceramide accumulation mediates the activation of the SEK/JNK module by LPS.

Androstadienes↗
PubMed2000

Sac phosphatase domain proteins.

Advances in our understanding of the roles of phosphatidylinositol phosphates in controlling cellular functions such as endocytosis, exocytosis and the actin cytoskeleton have included new insights into the phosphatases that are responsible for the interconversion of these lipids. One of these is an entirely novel class of phosphatase domain found in a number of well characterized proteins. Proteins containing this Sac phosphatase domain include the yeast Saccharomyces cerevisiae proteins Sac1p and Fig4p. The Sac phosphatase domain is also found within the mammalian phosphoinositide 5-phosphatase synaptojanin and the yeast synaptojanin homologues Inp51p, Inp52p and Inp53p. These proteins therefore contain both Sac phosphatase and 5-phosphatase domains. This review describes the Sac phosphatase domain-containing proteins and their actions, with particular reference to the genetic and biochemical insights provided by study of the yeast Saccharomyces cerevisiae.

Amino Acid Sequence↗
PubMed2000

Rho GTPase control of protein kinase C-related protein kinase activation by 3-phosphoinositide-dependent protein kinase.

The protein kinase C-related protein kinases (PRKs) have been shown to be under the control of the Rho GTPases and influenced by autophosphorylation. In analyzing the relationship between these inputs, it is shown that activation in vitro and in vivo involves the activation loop phosphorylation of PRK1/2 by 3-phosphoinositide-dependent protein kinase-1 (PDK1). Rho overexpression in cultured cells is shown to increase the activation loop phosphorylation of endogenous PRKs and is demonstrated to influence this process by controlling the ability of PRKs to bind to PDK1. The interaction of PRK1/2 with PDK1 is shown to be dependent upon Rho. Direct demonstration of ternary (Rho.PRK.PDK1) complex formation in situ is provided by the observation that PDK1 is recruited to RhoB-containing endosomes only if PRK is coexpressed. Furthermore, this in vivo complex is maintained after phosphoinositide 3-kinase inhibition. The control of PRKs by PDK1 thus evidences a novel strategy of substrate-directed control involving GTPases.

3-Phosphoinositide-Dependent Protein Kinases↗