Tissue Factor regulation, signaling and functions beyond coagulation with a focus on diabetes

Abstract: Background: Tissue factor (TF) is a 47 kDa transmembrane glycoprotein best known for initiating the coagulation cascade upon binding of its ligand FVIIa. Apart from its physiological role in coagulation, TF and TF/FVIIa signaling has proved to be involved in diseases such as diabetes, cancer and cardiovascular diseases. Biological functions coupled to TF/FVIIa signaling include diet-induced obesity, apoptosis, angiogenesis and migration.Aim: The aim of this thesis was to investigate the role of TF/FVIIa in cells of importance in diabetes, to further investigate the mechanism behind TF/FVIIa anti-apoptotic signaling in cancer cells and lastly to examine the regulation of TF expression in monocytes by micro RNAs (miRNA).Results: In paper I we found that TF/FVIIa signaling augments cytokine-induced beta cell death and impairs glucose stimulated insulin secretion from human pancreatic islets. In paper II the relevance of TF/FVIIa in isolated human primary adipocytes was investigated. Adipocytes are a target cell for insulin and diabetics typically have increased lipolysis and impaired glucose uptake. No evidence was found for a role of TF/FVIIa in lipolysis or glucose uptake in adipocytes. However, adipocytes were found to express TF and FVII. The FVII produced was sufficient to initiate coagulation in the adipocytes. In paper III an anti-apoptotic TF/FVIIa induced signaling pathway in prostate and breast cancer cells was investigated in depth. Previous research has shown that TF/FVIIa signaling results in transactivation of insulin-like growth factor 1 receptor (IGF-1R) leading to subsequent protection from apoptosis induced by TNF-related apoptosis inducing ligand (TRAIL). The current results propose a mechanism where IGF-1R transactivation by TF/FVIIa is dependent on integrin β1 (ITGβ1) signaling. TF/FVIIa/ ITGβ1 signaling was found to result in phosphorylation of src and subsequent phosphorylation of caveolin 1 (Cav1). Once phosphorylated, the inhibitory effect of Cav1 on IGF-1R is cancelled, resulting in IGF-1R activation. In paper IV the role of miRNA regulation of TF expression in monocytic cells was investigated. The miRNA miR-223-3p was identified to be differentially expressed in U937 cells undergoing differentiation to a more monocyte-like phenotype and an anti-parallel correlation between TF and miR-223-3p expression in monocytes was proved. Hence, miR-223-3p regulates the inducible expression of TF in monocytes.Conclusions: The work in this thesis furthers the knowledge of molecular mechanisms behind TF regulation and TF/FVIIa signaling and some functional consequences as well as their biological relevance in diabetes.