Mikael Åberg

Tissue factor non-coagulant signaling – molecular mechanisms and biological consequences with a focus on cell migration and apoptosis

Tissue factor (TF), a transmembrane glycoprotein, is the main initiator of the blood coagulation cascade. TF is also recognized as a true signaling receptor. There is accumulating evidence that the downstream signaling effects of the TF complexes are transduced by several mechanisms, including: activation of protease‐activated receptor (PAR)‐1 and PAR‐2, and the PAR‐dependent pathways, via the TF cytoplasmic domain and by transactivation of receptor tyrosine kinases. Triggering of signaling cascades such as the mitogen‐activated protein kinase and phosphoinositide 3‐kinase/AKT pathways couples TF to a multitude of functions within the cell, such as proliferation, cell migration, and survival. Thus, TF has a Janus face; on the one hand, it has vital life‐maintaining functions, and on the other it has harmful effects, exemplified by inflammation, the acute coronary syndromes, and cancer. TF mediates a broad spectrum of signaling mechanisms. Learning more about these different mechanisms/pathways will lead to new treatment strategies, which can ultimately be personalized.

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.

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.

Tissue Factor Noncoagulant Signaling : Mechanisms and Implications for Cell Migration and Apoptosis

Tissue factor (TF) is a 47-kDa transmembrane glycoprotein and the main initiator of the blood coagulation cascade. Binding to its ligand factor VIIa (FVIIa) also initiates noncoagulant signaling with broad biological implications. In this review, we discuss how TF interacts with other cell-surface proteins, which affect biological functions such as cell migration and cell survival. A vast number of publications have demonstrated the importance of TF-induced activation of protease-activated receptors, but recently published research has indicated a more complicated picture. As it has been discovered that TF interacts with integrins and receptor tyrosine kinases, novel signaling mechanisms for the TF/FVIIa complex have been presented. The knowledge of these new aspects of TF signaling may, for instance, facilitate the development of new treatment strategies for cancer and acute coronary syndromes, two examples of diseases characterized by aberrant TF expression and signaling.

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.

Tissue factor/factor VIIa induces cell survival and gene transcription by transactivation of the insulin-like growth factor 1 receptor

The insulin-like growth factor 1 receptor (IGF-1R) is known to promote survival and has also been implicated in the pathogenesis of several disease states, including cardiovascular disorders and cancer. Recently, we showed that binding of coagulation factor VIIa (FVIIa) to its receptor tissue factor (TF) protects cancer cells from TNF-related apoptosis inducing ligand (TRAIL)-induced apoptosis. Here we present evidence that this biological function of TF/FVIIa is dependent on the IGF-1R. IGF-1R inhibitors AG1024 and PPP as well as siRNA-mediated downregulation of IGF-1R, abolished the TF/FVIIa-mediated protection against TRAIL-induced apoptosis. Moreover, FVIIa rapidly induced a time- and concentration-dependent tyrosine phosphorylation of the IGF-1R in MDA-MB-231 breast cancer cells and in primary human monocytes, an event that was accompanied by IGF-1R chromatin binding and gene transcription. We hereby present novel evidence of a cross-talk between the coagulation and IGF-1R signalling systems, and propose that the IGF-1R is a key player in mediating TF/FVIIa-induced cell survival.