RESUMEN
Background: Fibrinogen is a large polyfunctional plasma protein consisting of a number of structural and functional domains. Among them, two αC-domains, each formed by the amino acid residues Ðα392-610, are involved in fibrin polymerization, activation of fibrinolysis, platelet aggregation, and interaction with different cell types. Previous study revealed that each fibrinogen αC-domain consists of the N-terminal and C-terminal sub-domains. The major objections of the present study were to test functional role of these sub-domains in the above mentioned processes. Methods: To achieve these objections, we used specific proteases to prepare two truncated forms of fibrinogen, fibrinogen desAα505-610 and fibrinogen desAα414-610, missing their N-terminal and both N- and C-terminal sub-domains, respectively. Results: Our study with these truncated forms using turbidity measurements and electron microscopy revealed that the N- and C-terminal subdomains both contribute to protofibril formation and their lateral aggregation into fibers during fibrin polymerization process. These two sub-domains also contributed to platelet aggregation with the N-terminal sub-domains playing a more significant role in this process. At the same time, the C-terminal sub-domains make the major contribution to the plasminogen activation process. Further, our experiments revealed that the C-terminal sub-domains are involved in endothelial cell viability and migration of cancer cells. Conclusions: Thus, the results obtained establish the functional role of individual sub-domains of the αC-domains in fibrin polymerization, activation of fibrinolytic system, platelet aggregation, and cellular interactions. General significance: The present study expands our understanding of the functional role of individual fibrinogen domains and their specific portions in various fibrin(ogen)-dependent processes.
RESUMEN
The effects of several forms of plasminogen on the state of actin cytoskeleton of human platelets were studied. A ratio between various actin pools, which were detected by immunoblotting, was taken as indicator of platelet cytoskeleton reorganization. It was revealed that intact platelets contain globular (G) actin and membrane cortex (MC) actin in amounts that are 56 and 40% of filamentous (F) actin level, respectively. In both thrombin- and collagen-activated platelets, actin is almost entirely presented in F-form. Incubation of resting platelets with Lys-plasminogen causes elevation of MC-actin level up to 79% in respect to F-form content. In addition, Lys-plasminogen inhibits reorganization of actin cytoskeleton typical for activated platelets. In contrast to Lys-form, Glu-plasminogen affects neither platelet aggregation nor redistribution of actin pools. Thus, these data indicate that cytoskeletal structures of platelets are involved in realization of anti-aggregating effects of Lys-plasminogen.
