Nonproteolytic Properties of Murine Alternatively Spliced Tissue Factor: Implications for Integrin-Mediated Signaling in Murine Models

Abstract

This study was performed to determine whether murine alternatively spliced tissue factor (masTF) acts analogously to human alternatively spliced tissue factor (hasTF) in promoting neovascularization via integrin ligation. Immunohistochemical evaluation of a spontaneous murine pancreatic ductal adenocarcinoma model revealed increased levels of masTF and murine full-length tissue factor (mflTF) in tumor lesions compared with benign pancreas; furthermore, masTF colocalized with mflTF in spontaneous aortic plaques of Ldlr -/-mice, indicating that masTF is likely involved in atherogenesis and tumorigenesis. Recombinant masTF was used to perform in vitro and ex vivo studies examining its integrin-mediated biologic activity. Murine endothelial cells (ECs) rapidly adhered to masTF in a β3-dependent fashion. Using adult and embryonic murine ECs, masTF potentiated cell migration in transwell assays. Scratch assays were performed using murine and primary human ECs; the effects of masTF and hasTF were comparable in murine ECs, but in human ECs, the effects of hasTF were more pronounced. In aortic sprouting assays, the potency of masTF-triggered vessel growth was undistinguishable from that observed with hasTF. The proangiogenic effects of masTF were found to be Ccl2-mediated, yet independent of vascular endothelial growth factor. In murine ECs, masTF and hasTF upregulated genes involved in inflammatory responses; murine and human ECs stimulated with masTF and hasTF exhibited increased interaction with murine monocytic cells under orbital shear. We propose that masTF is a functional homolog of hasTF, exerting some of its key effects via β3 integrins. Our findings have implications for the development of murine models to examine the interplay between blood coagulation, atherosclerosis and cancer.

“Soluble Tissue Factor” in the 21st Century: Definitions, Biochemistry, and Pathophysiological Role in Thrombus Formation

“…61 Unfortunately, no flTF transduction was performed by Giannarelli et al to compare the effects of flTF versus asTF in this setting. One possible explanation may be that human asTF protein was expressed in a murine vessel: our groups recently reported that murine asTF, while very similar to the human asTF in terms of its integrin-mediated proangiogenic/monocyte recruitment potential, utilizes a slightly distinct repertoire of integrins to exert its biological functions 65 and no studies were performed to date that compared human versus murine asTF's effects on human and/or murine SMC. We note that we initially identified murine asTF in cultured murine SMC, and showed that it elicits minimal procoagulant activity in the presence of PS-containing phospholipids.…”

Role of the protein C receptor in cancer progression

“…While TF procoagulant function is crucial for tumor cell metastasis, asTF does not contribute to this process (58). Instead, purified asTF was shown to induce endothelial cell sprouting by ligating endothelial cell-expressed integrins α6β1 and αvβ3 (59) and upregulates leukocyte adhesion molecules to enhance monocyte transmigration (60;61). In addition, inhibitory antibodies specific for asTF have shown a role for asTF in regulating tumor cell proliferation in vivo (62).…”

Tissue factor and cancer

“…asTF ligates integrins α6β1 and αvβ3 to regulate endothelial cell migration, tube formation, and sprouting and has tumor promoting activities in vivo (7; 10). In addition, asTF regulates endothelial cell function and induces leukocyte recruitment through the upregulation of adhesion receptors (33; 34). It will be of interest to further define the relative contributions of full-length and asTF in regulating angiogenesis, immune cell function, and tumor progression in appropriate animal models in vivo.…”