Matilda Johnell

Mutation of a Src phosphorylation site in the PDGF beta-receptor leads to increased PDGF-stimulated chemotaxis but decreased mitogenesis

Ligand induced activation of the beta‐receptor for platelet‐derived growth factor (PDGF) leads to activation of Src family tyrosine kinases. We have explored the possibility that the receptor itself is a substrate for Src. We show that Tyr934 in the kinase domain of the PDGF receptor is phosphorylated by Src. Cell lines expressing a beta‐receptor mutant, in which Tyr934 was replaced with a phenyalanine residue, showed reduced mitogenic signaling in response to PDGF‐BB. In contrast, the mutant receptor mediated increased signals for chemotaxis and actin reorganization. Whereas the motility responses of cells expressing wild‐type beta‐receptors were attenuated by inhibition of phosphatidylinositol 3′‐kinase, those of cells expressing the mutant receptor were only slightly influenced. In contrast, PDGF‐BB‐induced chemotaxis of the cells with the mutant receptor was attenuated by inhibition of protein kinase C, whereas the chemotaxis of cells expressing the wild‐type beta‐receptor was less affected. Moreover, the PDGF‐BB‐stimulated tyrosine phosphorylation of phospholipase C‐gamma was increased in the mutant receptor cells compared with wild‐type receptor cells. In conclusion, the characteristics of the Y934F mutant suggest that the phosphorylation of Tyr934 by Src negatively modulates a signal transduction pathway leading to motility responses which involves phospholipase C‐gamma, and shifts the response to increased mitogenicity.

Greater reduction of platelet activation markers and platelet-monocyte aggregates by prasugrel compared to clopidogrel in stable coronary artery disease

Prasugrel, a novel P2Y(12) ADP-receptor antagonist, has been reported to achieve greater inhibition of platelet aggregation compared to clopidogrel as assessed by light transmission aggregometry. It was the objective of this study to investigate the effect of prasugrel on alternative markers of platelet activation in comparison to a high loading dose and the approved maintenance dose of clopidogrel. One hundred ten aspirin-treated patients with stable coronary artery disease were randomized to a loading dose (LD, day 1)/ maintenance dose (MD, days 2-29) of prasugrel 60 mg/10 mg or clopidogrel 600 mg/75 mg. Platelet activation markers were analyzed by whole blood flow cytometry pre-dose and at 2 and 24 hours after LD and pre-dose at 14 and 29 days. After stimulation with 20 muM ADP, 2 hours after LD, significantly lower expression of activated GPIIb/IIIa (4.3 vs. 21.8 [mean fluorescent intensity (MFI)], p < 0.001) and P-selectin (2.0 vs. 11.7 MFI, p < 0.001) along with decreased formation of platelet-monocyte aggregates (16.4% vs. 29.6% positive cells, p < 0.001) was observed with prasugrel versus clopidogrel. All these effects were maintained through 24 hours and during the MD period. In conclusion, prasugrel 60 mg LD and 10 mg MD inhibit several markers of platelet activation and the formation of platelet-monocyte aggregates more effectively than a 600 mg LD and 75 mg MD of clopidogrel. Attenuated platelet aggregation and reduced expression of platelet pro-coagulant and pro-inflammatory markers with prasugrel suggest the potential to reduce cardiovascular events both in the acute setting and in long-term treatment.

Evaluation of microparticles in whole blood by multicolour flow cytometry assay

Abstract Objective. To develop and evaluate a multicolour flow cytometry method for analysis of microparticles (MPs) in fresh whole blood without any centrifugation steps or freezing/thawing procedure. Materials and methods. Flow cytometry was performed using a FC500 MPL cytometer. The compensation in the protocol was performed based on the platelet population. Polystyrene microspheres 0.50–1.27 μm were used for size position, and the MP gate was set as particles 0.5–1.0 μm. Whole blood was incubated with annexin V and antibodies to tissue factor (TF), platelets (CD41 and CD62P), monocyte (CD14) and endothelial cells (CD144). For comparison, MPs from platelet free supernatant was used. The TF activity was evaluated by Calibrated Automated Thrombogram. Results. Annexin V was used to distinguish true events from background noise. For standardization, each analysis included 10,000 events in the gate of platelets. There were 622(462–1001) MPannV+/10,000 platelets and of these, 66 (49–82)/10,000 platelets expressed TF. After correction for the individual platelet counts, the amount of circulating MPannV+ was 17.1 (12.1–24.9) × 109/L in whole blood, and of these, 10% (6–12%) expressed TF. The majority of the MPs expressed CD41, and 5.6% (2.2–6.9%) of these co-expressed TF. The amount of CD41 + MPannV+ tended to correlate to the TF activity in whole blood. There was no correlation between the MPannV+ in whole blood and MPs derived from platelet free supernatant. Patients with pulmonary arterial hypertension and stable coronary artery disease had increased concentrations of CD41 + MPannV+ in whole blood. Conclusion. This multicolour flow cytometry assay in whole blood mimics the in vivo situation by avoiding several procedure steps interfering with the MP count. By standardized quantification of MPs a reference interval of MPs can be created.

Regulation of chemotaxis by the cytoplasmic domain of tissue factor

We previously demonstrated that FVIIa bound to tissue factor (TF) induces a hyperchemotactic response towards PDGF-BB. The aim of the present study was to investigate the role of the cytoplasmic domain of TF in cell migration. Porcine aortic endothelial (PAE) cells expressing human PDGF beta-receptors (PAE/PDGFRbeta) were transfected for expression of human wildtype TF (PAE/PDGFRbeta,TF), a construct lacking the cytoplasmic domain (PAE/PDGFRbeta,TFDeltacyto), a construct with alanine replacement of serine 258 (PAE/PDGFRbeta,TFS258A), or a construct with alanine replacement of serine 253, 258 and 263 in the cytoplasmic domain (PAE/PDGFRbeta,TF3SA). All stably transfected cell lines expressed functional TF. Chemotaxis was analyzed in a modified Boyden chamber assay. PAE/PDGFRbeta,TF cells stimulated with FVIIa migrated towards a 100-fold lower concentration of PDGF-BB than in the absence of FVIIa, however, hyperchemotaxis was not seen in PAE/PDGFRbeta,TFDeltacyto cells. PAE/PDGFRbeta/TFS258A and PAE/PDGFRbeta,TF3SA cells responded to low levels of PDGF-BB, but migrated a significantly shorter distance than PAE/PDGFRbeta,TF cells. Thus, hyperchemotaxis towards PDGF-BB is likely to depend in part on phosphorylation of the cytoplasmic domain of TF. We conclude that the cytoplasmic domain of TF plays a pivotal role in modulating cellular migration response. Our results suggest that the FVIIa/TF complex mediates intracellular signaling by alternative signal transduction pathway(s).

TF/FVIIa Transactivate PDGFRβ to Regulate PDGF-BB–Induced Chemotaxis in Different Cell Types: Involvement of Src And PLC

Background—We have previously reported the potentiation of PDGF-BB–induced chemotaxis of fibroblasts, vascular smooth muscle cells, and endothelial cells by FVIIa. Here we studied the role of TF/FVIIa and the induced signaling pathways in regulation of chemotaxis of human monocytes, fibroblasts, and porcine aorta endothelial cells. Methods and Results—Human monocytes were obtained by using Ficoll-Paque gradient and the MACS system (for highly purified population), fibroblasts and PAE cells have been characterized previously. Inhibitors of selected signaling intermediates were used, and the effect of TF/FVIIa on the migratory response of all cells to chemotactic agents was analyzed. The induced signaling was studied by immunoprecipitation and Western blotting. TF/FVIIa complex selectively enhanced PDGF-BB–induced chemotaxis in a Src-family, PLC, and PAR-2–dependent manner. Using PAE cells we identified c-Src and c-Yes as the Src-family members activated by TF/FVIIa. We report for the first time the PAR-2 and Src family-dependent transactivation of PDGFR&bgr; by TF/FVIIa involving phosphorylation of a subset of PDGFR&bgr; tyrosines. Conclusions—The described transactivation is a likely mechanism of TF/FVIIa-mediated regulation of PDGF-BB–induced chemotaxis. Similar behavior of 3 principally different cell types in our experimental setup may reflect a general function of TF in regulation of cell migration.

Cell adhesion and tissue factor upregulation in oxygenators used during coronary artery bypass grafting are modified by the Corline Heparin Surface

Objective : Cardiopulmonary bypass (CPB) is associated with inflammatory response and activation of coagulation. We investigated the influence of a new heparin surface on the activation of cells retrieved from oxygenators used during coronary artery bypass grafting (CABG). Design : Sixty patients undergoing CABG with CPB were randomly assigned to either uncoated or completely Corline Heparin Surface (CHS)-coated circuits with one of three different levels of systemic heparin: standard, high or low. At end of surgery adhered cells were retrieved from the oxygenators and cell count, tissue factor (TF)- and CD11b-expression on monocytes and monocytic TFmRNA were analysed. Results : The heparin coating of the oxygenator prevented adhesion of granulocytes, monocytes and platelets. TF-expression on monocytes from the oxygenators was significantly higher than on circulating cells in all groups. Monocytes from the uncoated oxygenators showed low levels of TF-expression with high levels of TFmRNA. The coated group with high level of heparin showed higher surface-expression of TF with low levels of TFmRNA. Conclusion : The CHS was most biocompatible with the standard level of heparin used during CABG whereas elevation of systemic heparin rather increased the activation and TF upregulation in monocytes from oxygenators.

Tissue Factor/ FVIIa prevents the extrinsic pathway of apoptosis by regulation of the tumor suppressor Death-Associated Protein Kinase 1 (DAPK1)

INTRODUCTION This study determines the impact of tissue factor (TF)-signaling on the extrinsic pathway of apoptosis in cancer cells and propose death associated protein kinase-1 (DAPK1) as a novel key regulator. MATERIALS AND METHODS In MDA-MB-231 breast and PC3 prostate cancer cells, mRNA levels were analyzed by real-time PCR and protein expressions were assessed by flow cytometry or western blot. Caspase-8 and -3 levels, cell size, and changes in nuclear morphology were recorded using the ArrayScan microscope and 84 apoptosis-related genes were screened with the RT2 Profiler™ PCR Array. RESULTS In serum starved MDA-MB-231 cells, a TF/FVIIa-sensitive upregulation of apoptosis markers was recorded. Similarly, TRAIL-induced apoptosis was negatively regulated by TF/FVIIa (10 and 100 nM) and TF/FVIIa/FXa but not by active-site inhibited FVIIa. FVIIa, moreover, decreased the transcription of DAPK1 and thereby diminished the association between DAPK1 and FADD in the caspase-8 activating death-inducing signaling complex (DISC). TF/FVIIa regulation of caspase-8 and DAPK1 was dependent on PI3-kinase/AKT and independent of the protease activated receptors (PAR) 1 and 2. Despite of receptor expression and functional signaling, both PAR-agonist treatment and PAR-blocking antibodies in combination with FVIIa failed to influence the anti-apoptotic signal. CONCLUSIONS We hereby report that TF/FVIIa-induced signaling governs the extrinsic pathway of apoptosis by reducing the levels of DAPK1 in the DISC independently of PAR1 and PAR2. This implies the conceivable involvement of cell surface components other than the PARs and entails the search for TF-dependent regulators of DAPK1 transcription.

The Influence of Direct Thrombin Inhibitors on the Formation of Platelet-leukocyte Aggregates and Tissue Factor Expression

INTRODUCTION High concentrations of platelet-monocyte aggregates (PMAs) have been found in patients with myocardial infarction (MI). Oral direct thrombin inhibitors (DTIs) are under evaluation as long-term antithrombotic treatment. The aim was to evaluate whether DTIs affect the formation of platelet-leukocyte aggregates, TF expression and procoagulant microparticles (MPs). MATERIAL AND METHODS DTIs were added to an experimental whole blood model before platelet activation with thrombin or ADP. The concentrations of PMAs, platelet-granulocyte aggregates (PGAs), the amount of platelets bound per leukocyte and MPs were investigated by flow cytometry. TF mRNA and activity were recorded in all settings. TF activity was evaluated in a MI population treated with or without an oral DTI. RESULTS In vitro, thrombin and ADP increased the formation of PMAs and PGAs as well as TF mRNA expression. DTIs reduced the amount platelets bound to monocytes (p=0.02) and to granulocytes (p=0.001) upon thrombin stimulation together with a reduction of TF mRNA. In contrast, the ADP-induced formation of PMAs, PGAs and TF mRNA was not affected by the DTIs. Both thrombin and ADP stimulation increased the amount of TF-expressing MPs, which was effectively inhibited by the DTIs (p=0.02-0.002). In the MI population, the DTI reduced the TF activity (p<0.001). CONCLUSION DTIs modulate the formation of PMAs, PGAs and the TF production therein. Together with a reduction of procoagulant MPs, these results may contribute to the clinical benefit found of oral DTIs. Targeting different mechanisms in platelet and coagulation activation may be of importance due to the lack of effect of DTIs on ADP-induced platelet-leukocyte aggregates and TF production.

Simvastatin reduces the production of prothrombotic prostasomes in human prostate cancer cells

Cancer confers a prothrombotic state and statins are associated with a lowered risk for prostate cancer in vivo by unknown mechanisms. Prostate cancer cells release tissue factor (TF)-bearing, cholesterol-rich prostasomes which are pro-coagulant in vitro and a possible source for the blood-borne TF found in prostate cancer patients. We investigated the effect of cholesterol depletion on the production of prostasomes and on the TF activity in the conditioned medium of simvastatin-treated PC3 cells. Human PC3 prostate cancer cells were treated with high and low concentrations of simvastatin for different time periods. Caspase-3 was detected with the Array Scan microscope, whereas TF mRNA and protein were analyzed by TaqMan and flow cytometry. TF activity was assessed by measuring the cleavage of a chromogenic thrombin substrate. Prostasomes were isolated by repeated centrifugations and detected and quantified by flow cytometry. A micromolar dose of simvastatin caused reduction of TF expression and induction of apoptosis in the PC3 cells. The levels of TF on the prostasomes were also decreased but the TF activity in the conditioned medium of the simvastatin-treated PC3 cells was increased due to apoptosis-dependent release of prostasomes. Treatment with a nanomolar dose of simvastatin did not induce apoptosis or alter the expression of TF but instead decreased the production and release of the prostasomes. The TF activity was reduced in parity with the decline in prostasome release. In conclusion, in prostate cancer, a nanomolar dose of simvastatin may have an anti-thrombotic effect due to decreased levels of circulating TF-bearing prostasomes.