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Action and Function of coagulation FXa on cellular signaling

(2009) Borensztajn, Keren Sarah

In the late 1970s, during a program set to identify potential mitogenic components of serum, thrombin was shown to be a powerful mitogen for fibroblasts and to induce fibroblast migration in wound scratch assays via a direct mechanism requiring thrombin’s catalytic activity and involving receptor activation. The quandary as to how coagulation factors influenced cellular responses, which was suspected since the observation of Trousseau and the eponym syndrome, was elucidated by the identification of the thrombin receptor PAR-1 in 1991. PAR-1 represented the first member of a fundamentally unique subclass within the seven transmembrane domain protein superfamily, as receptors in this subclass are activated by proteolytic cleavage.

At the approximately the same time the structural homology of tissue factor (TF) with the class 2 cytokine receptor superfamily led to the hypothesis that binding of FVIIa to TF would induce intracellular signaling as well. Indeed, FVIIa binding to TF triggers signaling pathways. The interaction of FVIIa with TF is essential for signaling as the binding induces a major structural change in the serine protease domain allowing its full activity. Interestingly, TF/FVIIa signaling appears to be mediated via PAR-2 activation, reuniting the different components of the coagulation signaling-associated plasma membrane-localized components. Over the last decade, a plethora of studies established the pleiotropic role of FVIIa and thrombin in health and disease (e.g. inflammation, cancer, angiogenesis, but also wound healing and bone development for thrombin. However, as an intermediate in the coagulation cascade, FXa has long been considered a passive bystander only, and consequently its role in cell biology remained relatively unexplored. It is now clear that FXa plays a crucial non-haemostatic role.

Thus, it has become clear that vitamin K-dependent coagulation factors in general and factor X in particular are principal players in pathophysiology. Hence understanding its biology better as well as its role in pathophysiology my provide exiting insights in both the understanding of human and animal physiology in general and provide clues to improved therapy in particular. In thesis I explore the biology of factor X and its associated signaling components, in particular factor VII. To this end, following a literature study on the molecular genetics and pathophysiology of coagulation FVII and FX inherited deficiencies (chapter 2), I start in the nucleus with a study on the regulation of splice site selection in the FVII gene as its intron 7 provides an excellent for such a study, with repetition of the intron 7 splice donor site (chapter 3). Next, I investigate the effects of coagulation FVIIa and FXa on signaling and their functional consequences on cell biology. Subsequently it turned out that factor VII is a relatively minor player in pathophysiology (chapter 4) and its downstream target, factor X (which acts as the point of convergence of the intrinsic and extrinsic pathways of coagulation; chapter 5) should actually be the focus point of relevant research. Hence, I decided to mainly explore factor X biology, firstly addressing of this signalling to cell survival (of obvious relevance for cancer cell biology; chapter 6) and migration (chapter 7) and this notion was confirmed in detailed comparisons of the biochemical changes induced by the three major vitamin K-dependent coagulation factors (chapter 8). It appeared, however, that the effects in the clinically highly relevant –but underexplored- phenomenon of fibrosis were a more rewarding of research and the research of these efforts are described in the remaining chapters. Finally I conclude that factor X is essential mediator of tissue repair, whose inappropriate activation may lead to fibrotic responses. In this sense, factor X as a passive mediator of coagulation has been hijacked by the body to mediate repair.

	Title and contents
	Chapter 1
	Chapter 2
	Chapter 3
	Chapter 4
	Chapter 5
	Chapter 6
	Chapter 7
	Chapter 8
	Chapter 9
	Chapter 10
	Summarizing discussion
	Samenvatting
	List of publications
	Complete thesis