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Biomedical subjects

D Cantrell

Publications and source records attributed to D Cantrell.

At least 19 recordsLinked to original sources

Safety and tolerance of rapidly infused Depacon. A randomized trial in subjects with epilepsy.

BACKGROUND: Valproate sodium injection (Depacon(R)) is an intravenous form of valproate for use in absence and complex partial seizures when circumstances preclude oral administration. Certain situations may warrant larger and more rapid infusions than permitted by the original labeling. This study evaluated the safety of more rapid infusions. METHODS: Subjects with epilepsy were randomized in a 2:1 ratio to receive up to 15 mg/kg of valproate sodium infused at 3.0 or 1.5 mg/kg/min. Up to four infusions were allowed within 24 h to achieve target plasma valproate concentrations of 50-100 mcg/ml. Primary safety endpoints were the changes in the 5-min and minimum post-first infusion blood pressures (BPs). RESULTS: One hundred twelve subjects were treated, (3.0 mg/kg/min group: n=72, 1.5 mg/kg/min group: n=40). No significant treatment differences were detected for changes in the primary BP endpoints. Two subjects in the 3.0 mg/kg/min group had potentially clinically significant low systolic BP values during the study. Similar proportions of subjects in the two groups reported adverse events during or within 6 h following the first infusion. CONCLUSIONS: Valproate sodium injection dosages up to 15 mg/kg and rates of 1.5 and 3.0 mg/kg/min were well tolerated in this population.

Adolescent↗

Activation loop Ser744 and Ser748 in protein kinase D are transphosphorylated in vivo.

The importance of activation loop phosphorylation in the regulation of protein kinase D (PKD/protein kinase C (PKC) mu) activity has become controversial. In order to clarify the mechanism(s) of PKD activation, we developed a novel phosphospecific antibody recognizing phosphorylated Ser(748) in PKD (pS748). Western blot analysis with the pS748 antibody, carried out with a variety of PKD forms and in a variety of cell types including full-length PKD transfected in COS-7 and HEK 293 cells, a green fluorescent protein-PKD fusion protein transfected in either Swiss 3T3 fibroblasts or Madin-Darby canine kidney epithelial cells, and endogenous PKD expressed in A20 lymphocytes and Rat-1 fibroblasts, indicated that Ser(748) phosphorylation was absent from unstimulated cells. In contrast, dramatic increases in Ser(748) phosphorylation were induced by phorbol esters, bombesin, or cross-linking of B lymphocyte antigen receptors or by cotransfection with active PKCepsilon or PKCeta. Western analysis using a second phosphospecific antibody, which primarily recognizes PKD phosphorylated at Ser(744), revealed that Ser(744) phosphorylation accompanies Ser(748) phosphorylation during PKD activation in vivo. Ser(744)/Ser(748) phosphorylation requires PKC but not PKD activity, indicative of transphosphorylation. Our results provide new experimental evidence indicating that activation loop phosphorylation at Ser(744) and Ser(748) occurs during PKD activation in vivo and support the notion of a PKC-PKD phosphorylation cascade.

3T3 Cells↗

Rapid protein kinase D translocation in response to G protein-coupled receptor activation. Dependence on protein kinase C.

Protein kinase D (PKD)/protein kinase C (PKC) mu is a serine/threonine protein kinase that can be activated by physiological stimuli like growth factors, antigen-receptor engagement and G protein-coupled receptor (GPCR) agonists via a phosphorylation-dependent mechanism that requires PKC activity. In order to investigate the dynamic mechanisms associated with GPCR signaling, the intracellular translocation of a green fluorescent protein-tagged PKD was analyzed by real-time visualization in fibroblasts and epithelial cells stimulated with bombesin, a GPCR agonist. We found that bombesin induced a rapidly reversible plasma membrane translocation of green fluorescent protein-tagged PKD, an event that can be divided into two distinct mechanistic steps. The first step, which is exclusively mediated by the cysteine-rich domain in the N terminus of PKD, involved its translocation from the cytosol to the plasma membrane. The second step, i.e. the rapid reverse translocation of PKD from the plasma membrane to the cytosol, required its catalytic domain and surprisingly PKC activity. These findings provide evidence for a novel mechanism by which PKC coordinates the translocation and activation of PKD in response to bombesin-induced GPCR activation.

3T3 Cells↗

The T cell antigen receptor activates phosphatidylinositol 3-kinase-regulated serine kinases protein kinase B and ribosomal S6 kinase 1.

The present study has explored T cell antigen receptor-regulated serine kinases in human T cells. The results identify two phosphatidylinositol 3-kinase (PI3K)-controlled serine kinases operating downstream of the T cell receptor (TCR) in primary T cells: (i) protein kinase B whose activation regulates the phosphorylation of glycogen synthase kinase 3 and (ii) ribosomal S6 kinase 1, a kinase with a critical role in the regulation of protein synthesis and cell growth. T cells express two isoforms of S6k1: a 70 kDa cytoplasmic kinase and an 85 kDa isoform that has a classic nuclear localisation. TCR ligation triggers a parallel engagement of both the 70 and 85 kDa isoforms of S6k1 in a response that requires PI3K function.

Antibodies↗

Phosphoinositide 3-kinase-dependent phosphorylation of the dual adaptor for phosphotyrosine and 3-phosphoinositides by the Src family of tyrosine kinase.

We recently identified a novel adaptor protein, termed dual adaptor for phosphotyrosine and 3-phosphoinositides (DAPP1), that possesses a Src homology (SH2) domain and a pleckstrin homology (PH) domain. DAPP1 exhibits a high-affinity interaction with PtdIns(3,4,5)P(3) and PtdIns(3,4)P(2), which bind to the PH domain. In the present study we show that when DAPP1 is expressed in HEK-293 cells, the agonists insulin, insulin-like growth factor-1 and epidermal growth factor induce the phosphorylation of DAPP1 at Tyr(139). Treatment of cells with phosphoinositide 3-kinase (PI 3-kinase) inhibitors or expression of a dominant-negative PI 3-kinase prevent phosphorylation of DAPP1 at Tyr(139), and a PH-domain mutant of DAPP1, which does not interact with PtdIns(3,4,5)P(3) or PtdIns(3,4)P(2), is not phosphorylated at Tyr(139) following agonist stimulation of cells. Overexpression of a constitutively active form of PI 3-kinase induced the phosphorylation of DAPP1 in unstimulated cells. We demonstrated that Tyr(139) of DAPP1 is likely to be phosphorylated in vivo by a Src-family tyrosine kinase, since the specific Src-family inhibitor, PP2, but not an inactive variant of this drug, PP3, prevented the agonist-induced tyrosine phosphorylation of DAPP1. Src, Lyn and Lck tyrosine kinases phosphorylate DAPP1 at Tyr(139) in vitro at similar rates in the presence or absence of PtdIns(3,4,5)P(3), and overexpression of these kinases in HEK-293 cells induces the phosphorylation of Tyr(139). These findings indicate that, following activation of PI 3-kinases, PtdIns(3,4,5)P(3) or PtdIns(3,4)P(2) bind to DAPP1, recruiting it to the plasma membrane where it becomes phosphorylated at Tyr(139) by a Src-family tyrosine kinase.

Adaptor Proteins, Signal Transducing↗

Protein kinase D. A selective target for antigen receptors and a downstream target for protein kinase C in lymphocytes.

Protein kinase Cs (PKCs) are activated by antigen receptors in lymphocytes, but little is known about proximal targets for PKCs in antigen receptor-mediated responses. In this report, we define a role for diacylglycerol-regulated PKC isoforms in controlling the activity of the serine/threonine kinase protein kinase D (PKD; also known as PKC mu) in T cells, B cells, and mast cells. Antigen receptor activation of PKD is a rapid and sustained response that can be seen in T cells activated via the T cell antigen receptor, B cells activated via the B cell antigen receptor, and in mast cells triggered via the high-affinity receptor for IgE (FcepsilonR1). Herein, we show that antigen receptor activation of PKD requires the activity of classical/novel PKCs. Moreover, PKC activity is sufficient to bypass the requirement for antigen receptor signals in the induction of PKD activity. These biochemical and genetic studies establish a role for antigen receptor-regulated PKC enzymes in the control of PKD activity. Regulation of PKD activity through upstream PKCs reveals a signaling network that exists between different members of the PKC superfamily of kinases that can operate to amplify and disseminate antigen receptor signals generated at the plasma membrane.

Animals↗

Spatial and temporal regulation of protein kinase D (PKD).

Protein kinase D (PKD; also known as PKCmicro) is a serine/threonine kinase activated by diacylglycerol signalling pathways in a variety of cells. PKD has been described previously as Golgi-localized, but herein we show that it is present within the cytosol of quiescent B cells and mast cells and moves rapidly to the plasma membrane after antigen receptor triggering. The membrane redistribution of PKD requires the diacylglycerol-binding domain of the enzyme, but is independent of its catalytic activity and does not require the integrity of the pleckstrin homology domain. Antigen receptor signalling initiates in glycosphingolipid-enriched microdomains, but membrane-associated PKD does not co-localize with these specialized structures. Membrane targeting of PKD is transient, the enzyme returns to the cytosol within 10 min of antigen receptor engagement. Strikingly, the membrane-recycled PKD remains active in the cytosol for several hours. The present work thus characterizes a sustained antigen receptor-induced signal transduction pathway and establishes PKD as a serine kinase that temporally and spatially disseminates antigen receptor signals away from the plasma membrane into the cytosol.

B-Lymphocytes↗

Antigen receptor signal transduction: activating and inhibitory antigen receptors regulate STAT1 serine phosphorylation.

Antigen receptors are crucial regulators of the mammalian immune response. Immediate antigen receptor proximal signal transduction pathways mediated by tyrosine (Tyr) kinases are well defined. In contrast, much less is known about the network of serine (Ser) kinases and Ser kinase substrates that are linked to antigen receptor function. Here we describe a new signaling module for antigen receptors in lymphocytes; a Ser kinase pathway that phosphorylates Ser 727 in STAT1alpha, a member of the signal transducer and activator of transcription gene family. In the present study we have explored the regulation of STAT1 Ser 727 phosphorylation in human T and B lymphocytes and show that it is controlled by both positive and negative antigen receptor signaling cascades. Ligation of antigen receptors in both B and T cells induce a delayed but then sustained phosphorylation of STAT1 on Ser 727. STAT1 Ser phosphorylation is induced by the TCR in the absence of STAT1 Tyr phosphorylation, indicating that in T cells STAT1 Ser and Tyr phosphorylation are independent events. Antigen receptor regulation of STAT Ser phosphorylation is dependent on phosphatidylinositol 3-kinase-mediated signals. Furthermore, the negative regulatory receptor FcgammaRIIb, which mediates vital feedback control of B cell responses, prevents antigen receptor-induced phosphorylation of STAT1 Ser 727. The ability of antigen receptors to both positively and negatively regulate STAT1 Ser 727 phosphorylation reveals a Ser kinase network that operated during sustained responses to antigen receptor engagement.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

T cell activation and the cytoskeleton.

Ligation of the T cell antigen receptor (TCR) stimulates protein tyrosine kinases (PTKs), which regulate intracellular calcium and control the activity of protein kinase C (PKC) isozymes. PTKs activated by antigen receptors and costimulatory molecules also couple to phosphatidylinositol-3 kinase (PI3K) and control the activity of Ras- and Rho-family GTPases. T cell signal transduction is triggered physiologically by antigen in the context of antigen presenting cells (APC). The formation of stable and prolonged contacts between T cells and APCs is not necessary to initiate T cell signaling but is required for effective T cell proliferation and differentiation. The stabilization of the T cell/ APC conjugate is regulated by intracellular signals induced by antigen receptors and costimulators. These coordinate the regulation of the actin and microtubule cytoskeleton and organize a specialized signaling zone that allows sustained TCR signaling.

Cytoskeleton↗

Characterization of serine 916 as an in vivo autophosphorylation site for protein kinase D/Protein kinase Cmu.

Activation of the serine kinase protein kinase D (PKD)/PKCmicro is controlled by the phosphorylation of two serine residues within its activation loop via a PKC-dependent signaling cascade. In this study we have identified the C-terminal serine 916 residue as an in vivo phosphorylation site within active PKD/PKCmu. An antibody that recognized PKD/PKCmu proteins specifically phosphorylated on the serine 916 residue was generated and used to show that phosphorylation of Ser-916 is induced by phorbol ester treatment of cells. Thus, the pS916 antibody is a useful tool to study the regulation of PKD/PKCmu activity in vivo. Antigen receptor ligation of T and B lymphocytes also induced phosphorylation of the serine 916 residue of PKD/PKCmu. Furthermore the regulatory FcgammaRIIB receptor, which mediates vital negative feedback signals to the B cell antigen receptor complex, inhibited the antigen receptor-induced activation and serine 916 phosphorylation of PKD/PKCmu. The degree of serine 916 phosphorylation during lymphocyte activation and inhibition exactly correlated with the activation status of PKD/PKCmu. Moreover, using different mutants of PKD/PKCmu, we show that serine 916 is not trans-phosphorylated by an upstream kinase but is rather an autophosphorylation event that occurs following activation of PKD/PKCmu.

Amino Acid Sequence↗

Dynamic re-distribution of protein kinase D (PKD) as revealed by a GFP-PKD fusion protein: dissociation from PKD activation.

Protein kinase D (PKD)/protein kinase Cmicro (PKCmicro, a serine/threonine protein kinase with distinct structural and enzymological properties, is rapidly activated in intact cells via PKC. The amino-terminal region of PKD contains a cysteine-rich domain (CRD) that directly binds phorbol esters with a high affinity. Here, we show that treatment of transfected RBL 2H3 cells with phorbol 12,13-dibutyrate (PDB) induces a striking CRD-dependent translocation of PKD from the cytosol to the plasma membrane, as shown by real time visualization of a functional green fluorescent protein (GFP)-PKD fusion protein. A single amino acid substitution in the second cysteine-rich motif of PKD (P287G) prevented PDB-induced membrane translocation but did not affect PKD activation. Our results indicate that PKD translocation and activation are distinct processes that operate in parallel to regulate the activity and localization of this enzyme in intact cells.

Amino Acid Substitution↗

The dynamics of protein kinase B regulation during B cell antigen receptor engagement.

This study has used biochemistry and real time confocal imaging of green fluorescent protein (GFP)-tagged molecules in live cells to explore the dynamics of protein kinase B (PKB) regulation during B lymphocyte activation. The data show that triggering of the B cell antigen receptor (BCR) induces a transient membrane localization of PKB but a sustained activation of the enzyme; active PKB is found in the cytosol and nuclei of activated B cells. Hence, PKB has three potential sites of action in B lymphocytes; transiently after BCR triggering PKB can phosphorylate plasma membrane localized targets, whereas during the sustained B cell response to antigen, PKB acts in the nucleus and the cytosol. Membrane translocation of PKB and subsequent PKB activation are dependent on BCR activation of phosphatidylinositol 3-kinase (PI3K). Moreover, PI3K signals are both necessary and sufficient for sustained activation of PKB in B lymphocytes. However, under conditions of continuous PI3K activation or BCR triggering there is only transient recruitment of PKB to the plasma membrane, indicating that there must be a molecular mechanism to dissociate PKB from sites of PI3K activity in B cells. The inhibitory Fc receptor, the FcgammaRIIB, mediates vital homeostatic control of B cell function by recruiting an inositol 5 phosphatase SHIP into the BCR complex. Herein we show that coligation of the BCR with the inhibitory FcgammaRIIB prevents membrane targeting of PKB. The FcgammaRIIB can thus antagonize BCR signals for PKB localization and prevent BCR stimulation of PKB activity which demonstrates the mechanism for the inhibitory action of the FcgammaRIIB on the BCR/PKB response.

Animals↗

Inhibition of Rho at different stages of thymocyte development gives different perspectives on Rho function.

Development of thymocytes can be staged according to the levels of expression of the cell-surface markers CD4, CD8, CD44, CD25 and CD2. Thymocyte development is regulated by a complex signalling network [1], one component of which is the GTPase Rho. The bacterial enzyme C3 transferase from Clostridium botulinum selectively ADP-ribosylates Rho in its effector-binding domain and thereby abolishes its biological function [2,3]. To explore the function of Rho in thymocyte development, we previously used the proximal promoter of the gene encoding the Src-family kinase p56lck to make transgenic mice that selectively express C3 transferase in the thymus [4,6]. In these mice, which lack Rho function from the earliest thymocyte stages, thymocyte numbers are reduced by approximately 50- to 100-fold. Here, we describe transgenic mice that express C3 transferase under the control of the locus control region (LCR) of the CD2 gene; this regulatory element drives expression at a later stage of thymocyte development than the lck proximal promoter [7]. In these mice, thymocyte numbers were also reduced by 50- to 100-fold, but unlike the lck-C3 mice, in which the reduction predominantly results from defects in cell survival of CD25(+) thymocyte progenitors, the CD2-C3 transgenic mice had a pre-T-cell differentiation block at the CD25(+) stage after rearrangement of the T-cell receptor (TCR) beta chains. Analysis of CD2-C3 mice demonstrated that Rho acts as an intracellular switch for TCR beta selection, the critical thymic-differentiation checkpoint. These results show that Rho-mediated survival signals for CD25(+) pre-T cells are generated by the extracellular signals that act on earlier thymocyte precursors and also that temporal cell-type-specific elimination of Rho can reveal different functions of this GTPase in vivo.

ADP Ribose Transferases↗

p70(s6k) integrates phosphatidylinositol 3-kinase and rapamycin-regulated signals for E2F regulation in T lymphocytes.

In T lymphocytes, the hematopoietic cytokine interleukin-2 (IL-2) uses phosphatidylinositol 3-kinase (PI 3-kinase)-induced signaling pathways to regulate E2F transcriptional activity, a critical cell cycle checkpoint. PI 3-kinase also regulates the activity of p70(s6k), the 40S ribosomal protein S6 kinase, a response that is abrogated by the macrolide rapamycin. This immunosuppressive drug is known to prevent T-cell proliferation, but the precise point at which rapamycin regulates T-cell cycle progression has yet to be elucidated. Moreover, the effects of rapamycin on, and the role of p70(s6k) in, IL-2 and PI 3-kinase activation of E2Fs have not been characterized. Our present results show that IL-2- and PI 3-kinase-induced pathways for the regulation of E2F transcriptional activity include both rapamycin-resistant and rapamycin-sensitive components. Expression of a rapamycin-resistant mutant of p70(s6k) in T cells could restore rapamycin-suppressed E2F responses. Thus, the rapamycin-controlled processes involved in E2F regulation appear to be mediated by p70(s6k). However, the rapamycin-resistant p70(s6k) could not rescue rapamycin inhibition of T-cell cycle entry, consistent with the involvement of additional, rapamycin-sensitive pathways in the control of T-cell cycle progression. The present results thus show that p70(s6k) is able to regulate E2F transcriptional activity and provide direct evidence for the first time for a link between IL-2 receptors, PI 3-kinase, and p70(s6k) that regulates a crucial G1 checkpoint in T lymphocytes.

Carrier Proteins↗

p21ras initiates Rac-1 but not phosphatidyl inositol 3 kinase/PKB, mediated signaling pathways in T lymphocytes.

p21ras is activated by the T cell antigen receptor (TCR) and then co-ordinates important signaling pathways for T lymphocyte activation. Effector pathways for this guanine nucleotide binding protein in T cells are mediated by the serine/threonine kinase Raf-1 and the Ras-related GTPase Rac-1. In fibroblasts, an important effector for the Ras oncogene is Phosphatidylinositol 3-kinase (PtdIns 3-kinase). Activation of this lipid kinase is able to induce critical Rac-1 signaling pathways and can couple p21ras to cell survival mechanisms via the serine/threonine kinase Akt/PKB. The role of PtdIns 3-kinase in Ras signaling in T cells has not been explored. In the present study, we examined the ability of PtdIns 3-kinase to initiate the Rac-1 signaling pathways important for T cell activation. We also examined the possibility that Akt/PKB is regulated by Ras signaling pathways in T lymphocytes. The results show that Ras can initiate a Rac-1 mediated pathway that regulates the transcriptional function of AP-1 complexes. PtdIns 3-kinase signals cannot mimic p21ras and induce the Rac mediated responses of AP-1 transcriptional activation. Moreover, neither TCR or Ras activation of AP-1 is dependent on PtdIns 3-kinase. PKB is activated in response to triggering of the T cell antigen receptor; PtdIns 3-kinase activity is both required and sufficient for this TCR response. In contrast, p21ras signals are unable to induce Akt/PKB activity in T cell nor is Ras function required for Akt/PKB activation in response to the TCR. The present data thus highlight that PtdIns 3-kinase and Akt/PKB are not universal Ras effector molecules. Ras can initiate Rac-1 regulated signaling pathways in the context of T cell antigen receptor function independently of PtdIns 3-kinase activity.

Calcium-Calmodulin-Dependent Protein Kinases↗

Lymphocyte signalling: a coordinating role for Vav?

Vav1 is a guanine nucleotide exchange factor that selectively activates the Rac1 GTPase and is expressed specifically in haematopoietic cells. Recent work has revealed how Vav1 integrates signals from lymphocyte antigen receptors and costimulatory receptors to control immune function.

Actins↗

Involvement of phosphoinositide 3-kinase and Rac in membrane ruffling induced by IL-2 in T cells.

IL-2 is known to play a critical role in regulating T lymphocyte proliferation. We show here that IL-2 also provokes an instantaneous and sustained membrane ruffling in cloned human or murine T cells as well as in lectin-activated peripheral blood lymphocytes. In the IL-2-induced lamellipodia, tubulin is depolymerized whereas actin is strongly polymerized, forming caps. IL-2-induced membrane ruffling is protein kinase C (PKC) independent, as judged by the absence of effects of bisindolylmaleimide, an efficient inhibitor of all PKC isoforms. The formation of lamellipodia by IL-2 is blocked by wortmannin and LY294002, two inhibitors of phosphoinositide 3-kinase (PI3-kinase). Moreover, expression in murine T cells of an inactive form of P13-kinase inhibits IL-2-induced membrane ruffling, whereas expression of a constitutively active p110 increases the basal membrane ruffling. Rac is also involved in IL-2-induced membrane ruffling since an inactive form of Rac (N17rac) blocks the IL-2-induced lamellipodia, whereas the constitutive form of Rac (Val12rac) can also lead to membrane ruffling. In the signaling cascade, Rac is downstream of PI3-kinase since constitutive membrane ruffling in Val12rac cells is insensitive to wortmannin. Thus, through a signaling cascade involving PI3-kinase and Rac, IL-2 can induce profound alterations of the T cell cytoskeleton, a phenomenon which might be of importance for T cell physiology.

Animals↗

The real LAT steps forward.

Antigen receptors initiate T-cell activation and determine the specificity of the immune response by activating membrane-localized protein tyrosine kinases. Signalling pathways initiated by these kinases control expression of the genes that mediate T-cell effector function. A major challenge in immunology is to work out the route taken by membrane-generated signals as they transit to the nucleus. Substrates for the ZAP70/Syk tyrosine kinases are important, but 'missing', links in this process. There has finally been some progress in characterizing one of these important linkers: LAT, an integral membrane protein that acts as an adaptor to couple antigen receptors to intracellular signalling cascades.

Adaptor Proteins, Signal Transducing↗