Münster (Westfalen), Universiẗat, Diss., 2008 (Nur beschränkt für den Austausch).

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xix, 135 p.; also includes graphics (some col.) Includes bibliographical references (p. 128-135). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 378-405). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Platelets permeabilized by high voltage electric discharges have provided a valuable model system in which to analyse the roles of Ca²⁺ ions and guanine nucleotides in the regulation of secretion by exocytosis. In the present study, the effects of fluoride or fluoroaluminate and of vanadate or pervanadate on secretion of platelet dense granule constituents, and the roles of activation of phospholipase D (PLD), phospholipase C (PLC) and protein kinase C (PKC) in secretion, have been investigated. Electropermeabilized human platelets containing [¹⁴C]5-HT in their dense granules were suspended in a glutamate medium containing ATP and incubated for 10 min at 25°C with, variously, Ca²⁺ buffers, KF/AlCl₃, vanadate/H₂O₂, guanine nucleotides and phorbol 12-myristate 13-acetate (PMA). KF/AlCl₃, which activates heterotrimeric G proteins but not low-M, GTP-binding proteins, caused a Ca²⁺ -dependent [¹⁴C]5-HT secretion; maximal effects were obtained with 10 mM KF plus 10 μM AlCl₃ at a pCa of 6, when 53% of [¹⁴C]5-HT was released. Secretion induced by KF/AlCl₃ in the presence of Ca²⁺ correlated with the stimulation of [3H]diacylglycerol accumulation in permeabilized platelets containing [³H]arachidonate-labelled phospholipids. KF/AlCl₃ also stimulated the phosphorylation of pleckstrin (P47) in permeabilized platelets incubated with [γ-³²P]ATP, indicating the activation of PKC. In the absence of Ca²⁺ (pCa > 9), KF/AlCl₃ caused none of the above effects. These actions of KF/AlCl₃ were attnbutable to the activation of PLC, since KF/AlCl₃ also stimulated the formation of [³H]inositol phosphates in [³H]inositol-labelled permeabilized platelets in the presence of Ca²⁺. PLD activity, measured as the formation of[³H]phosphatidylethanol (PEt) from [³H]arachidonate-labelled phospholipids in the presence of ethanol, could not be detected after stimulation of platelets by KF/AlCl₃ in the absence or presence of Ca²⁺. However, KF/AlCl₃ inhibited the [³H]PEt formation (PLD activity) induced by GTPγS. In the absence of Ca²⁺ (pCa >9), the inhibitory effects of KF/AlCl₃ on [¹⁴C]5-HT secretion induced by GTPγS alone or GTPγS plus PMA correlated well with their inhibitory effects on [³H]PEt formation. At pCa 6, KF/AlCl₃ had only a small inhibitory effect on GTPγS-induced secretion and inhibited GTPγS-induced PLD activity more strongly than GTPγS-induced PLC activity. These results suggest that PLD is important for Ca²⁺ -independent secretion, and that, although both PLD and PLC may play roles in Ca²⁺ -dependent secretion, PLC is likely to be the more important. In the presence of Ca²⁺, either vanadate or H₂O₂ caused concentration-dependent stimulations of [¹⁴C]5-HT secretion, [³H]DAG formation and [³H]PEt formation. At pCa 6, low concentrations of vanadate and H₂O₂, which would be expected to form pervanadate, acted synergistically to stimulate [¹⁴C]5-HT secretion, which correlated with [³H]DAG formation. However, vanadate with H₂O₂ had a biphasic effect on PLD activity that did not correlate with secretion. In addition, at pCa 6, GTPγS-induced PLD activity was abolished by vanadate with H₂O₂, whereas GTPγS-induced secretion and PLC activity were only partially inhibited. These results support the idea that both PLC and PLD are involved in the regulation of secretion but have different contributions to Ca²⁺ dependent and Ca²⁺ -independent secretion. The results are consistent with activation of platelet PLC by a heterotrimeric G protein, but suggest that different mechanisms, possibly involving a low-M, GTP-binding protein, may be involved in the regulation of PLD activity. / Thesis / Master of Science (MSc)

Phospholipase Cε (PLCε) is a member of the PLC family of enzymes, which hydrolyze phosphatidylinositol lipids following the activation of G protein coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs). PLCε is unique among the PLC superfamily as it contains an N-terminal CDC25 domain, which has a guanine nucleotide exchange factor (GEF) activity for the small G protein Rap1A, and two C-terminal Ras association (RA) domains that bind scaffolding proteins and activated G proteins. PLCε activity plays an important role in cardiomyocyte contractility and survival. The best-characterized pathway of PLCε activation is mediated by β-adrenergic (β-AR) receptors. Stimulation of these receptors culminates in the activation of the small GTPase Rap1A, which binds to PLCε at the sarcoplasmic reticulum. There, PLCε hydrolyzes phosphatidylinol-4-phosphate (PI₄P) to produce diacylglycerol (DAG). Prolonged activation of this pathway results in increased Ca²⁺-induced Ca²⁺ release (CICR) and increased expression of hypertrophy-related genes. However, the structural basis of PLCε basal activity, and the mechanism of Rap1A activation are largely unknown. We have now obtained the first high-resolution structure of PLCε. These studies, together with biochemical validation of our structure-based hypotheses, provide the first molecular insights into this enzyme.

Removal of apoptotic cells by macrophages is required in order to prevent autoimmune responses. Previous studies have reported that group IIA secretory phospholipase A2 (sPLA2) preferentially binds to apoptotic cells and induces a chemotactic factor which promotes the migration of macrophages to apoptotic cells. Based on these observations, we hypothesized that the pool of sPLA2 trapped on apoptotic cells produces chemoattractant lipids that recruit macrophages to phagocytose the apoptotic cells. To test this hypothesis, Jurkat cells were cultured under normal conditions and induced to undergo early apoptosis through treatment with D,L-threo-dihydrosphingosine. Live and early apoptotic cells were incubated with catalytically active sPLA2 and then cell-associated catalytic activity was assessed. In contrast to previous reports, we observed no difference in the ability of live or early apoptotic cells to trap group IIA sPLA2 on their surfaces. However, transmigration assays involving THP-1 monocytes confirmed that the cell-bound pool of sPLA2 generates chemoattractants when bound to the surfaces of live cells. Surprisingly, sPLA2 does not have to be catalytically active to attract THP-1 monocytes. The treatment of live Jurkat cells with heparinase showed a marked reduction in the ability of sPLA2 to bind to live cells and exert catalytic activity, suggesting heparan sulfate proteoglycans are possibly receptors for sPLA2. Future experiments are being planned to identify sPLA2 receptor(s) on THP-1 monocytes.

Thesis (M.S.)--Brigham Young University. Dept. of Physiology and Developmental Biology, 2004. / Includes bibliographical references (p. 17-21).

Ph.d.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Non-Latin script record Includes bibliographical references (leaves 125-151). Also available on the World Wide Web.