APO‐1 (Fas/CD95), a member of the tumor necrosis factor receptor superfamily, induces apoptosis upon receptor oligomerization. In a search to identify intracellular signaling molecules coupling to oligomerized APO‐1, several cytotoxicity‐dependent APO‐1‐associated proteins (CAP) were immunoprecipitated from the apoptosis‐sensitive human leukemic T cell line HUT78 and the lymphoblastoid B cell line SKW6.4. CAP1–3 (27–29 kDa) and CAP4 (55 kDa), instantly detectable after the crosslinking of APO‐1, were associated only with aggregated (the signaling form of APO‐1) and not with monomeric APO‐1. CAP1 and CAP2 were identified as serine phosphorylated MORT1/FADD. The association of CAP1–4 with APO‐1 was not observed with C‐terminally truncated non‐signaling APO‐1. In addition, CAP1 and CAP2 did not associate with an APO‐1 cytoplasmic tail carrying the lprcg amino acid replacement. Moreover, no APO‐1‐CAP association was found in the APO‐1+, anti‐APO‐1‐resistant pre‐B cell line Boe. Our data suggest that in vivo CAP1–4 are the APO‐1 apoptosis‐transducing molecules.

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Thrombin is the pivotal enzyme in the biochemistry of secondary hemostasis crucial to maintaining homeostasis of hemostasis. In contrast to routine coagulation tests (PT or aPTT) or procoagulant or anticoagulant factor assays (e.g. fibrinogen, factor VIII, antithrombin or protein C), the thrombin generation assay (TGA), also named thrombin generation test (TGT) is a so‐called “global assay” that provides a picture of the hemostasis balance though a continuous and simultaneous measurement of thrombin formation and inhibition. First described in the early 1950s, as a manual assay, efforts have been made in order to standardize and automate the assay to offer researchers, clinical laboratories and the pharmaceutical industry a versatile tool covering a wide range of clinical and non‐clinical applications. This review describes technical options offered to properly run TGA, including a review of preanalytical and analytical items, performance, interpretation, and applications in physiology research and pharmacy.

Determining patient's coagulation profile, i.e. detecting a bleeding tendency or the opposite, a thrombotic risk, is crucial for clinicians in many situations. Routine coagulation assays and even more specialized tests may not allow a relevant characterization of the hemostatic balance. In contrast, thrombin generation assay (TGA) is a global assay allowing the dynamic continuous and simultaneous recording of the combined effects of both thrombin generation and thrombin inactivation. TGA thus reflects the result of procoagulant and anticoagulant activities in blood and plasma. Because of this unique feature, TGA has been widely used in a wide array of settings from both research, clinical and pharmaceutical perspectives. This includes diagnosis, prognosis, prophylaxis, and treatment of inherited and acquired bleeding and thrombotic disorders. In addition, TGA has been shown to provide relevant information for the diagnosis of coagulopathies induced by infectious diseases, comprising also disturbance of the coagulation system in COVID‐19, or for the assessment of early recurrence in breast cancer. This review article aims to document most clinical applications of TGA.

Distinct binding interactions between cell-surface receptors and extracellular matrix components are characteristic of multifunctional adhesion proteins such as vitronectin. The close proximity of binding sites for A v -integrins and plasminogen activator inhibitor-1 (PAI-1) on vitronectin may have consequences for cell adhesion and migration, or for the localized inhibition of plasminogen activators. In this study, the kinetics and reversibility of vitronectin-dependent cell adhesion via A v -integrins was investigated using RGD peptides and PAI-1 as competitors. Active, but not latent or cleaved PAI-1, and RGD peptides were effective in preventing cell adhesion to vitronectin provided the inhibitor was present at the time of cell seeding. In a concentration-dependent manner urokinase or thrombin abrogated the inhibitory effect of PAI-1. Following cell seeding onto a vitronectin substratum, delayed addition of RGD peptides or active PAI-1 (10Ϫ20 min post-seeding) resulted in the loss of their inhibitory potential. These data were supported by experiments in a purified system where delayed addition of active PAI-1 could no longer prevent vitronectin binding to immobilized A v β 3 , while a cyclic RGD peptide gave some moderate inhibition. The apparent stabilization of vitronectinϪintegrin contacts was observed with immobilized native or multimeric vitronectin but not with the more rigid form of denatured, aggregated multimers. These results demonstrate that the cell adhesive properties of vitronectin depend on its conformational flexibility and can be tightly regulated in a spatio-temporal manner through direct competition of cellular integrins by soluble or matrix-bound factors such as PAI-1.

Summary. In the present study the ability of plasminogen activator inhibitor type-1 (PAI-1) to interfere with platelet and megakaryoblastic cell adhesion was investigated. Both cell types exhibited integrin-dependent adhesion in a static system, mediated by aIIbb3 on platelets and av-integrins on different megakaryoblastic cell lines, even though they also expressed aIIbb3. In a concentration-dependent manner, active, but not latent or complexed, PAI-1 abrogated cell adhesion onto vitronectin but not onto fibrinogen or other matrix substrata. Urokinase as well as thrombin neutralized the anti-adhesive effect of active PAI-1. The direct binding of vitronectin, but not of other matrix proteins, to integrin aIIbb3 was blocked by active PAI-1 in a purified system. Since activated platelets release active and latent PAI-1 as well as structurally and functionally distinct forms of vitronectin, the described interactions appear to be physiologically significant. Co-distribution of vitronectin and PAI-1 at sites of fibrin polymers within platelet thrombi was demonstrated by transmission electron microscopy, suggesting an extracellular functional relationship of both release products with regard to cell adhesion. Our data emphasize the regulatory role of active PAI-1 in platelet adhesion to provisional matrix proteins as found during wound healing independent of its anti-proteolytic activity. Furthermore, megakaryocyte maturation may depend on the intact vitronectin-integrin adhesion system that is influenced by PAI-1, thereby proposing a regulatory role for the inhibitor in cellular differentiation.

Max-Planck-lnstitut, Bad Nauheim, Germany !ntroduction contacts between the basolateral face of endothelial cells and the underlying basal lamina as well as to w,urent tight anchorage of smooth muscle cells and fibroblasts with their ECM. While integrins initiate cell attachment and spreading to extracellular matrix molecules, heparinoid-type proteoglycans are critical for the reorganization of actin microfilaments into stress-fibers and for the formation of focal adhesions. In particular, vascular cell syndecan-4 was fonnd associated as coreceptor with 0l-and B3-integrins in these stable adhesion points (4). Although integrin ligation appears to be necessary for triggering phosphorylation of specific intracellular focal adhesion components, cell surface proteoglycans are required to transduce signals for adhesion receptor clustering through activation of protein kinase C (5). Modulation of cell-cell and cell-ECM contacts by changes in the expression, affinity or specificity of adhesion molecules or by pericellular proteolysis results in variable and dynamic short-term adhesion or detachment events and is pivotal for the control of cell migration and invasion (6-8). The strength and duration of adhesive interactions not only depend on the expression pattern or the extent of adhesion receptor clustering (9) but also on the availability

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