Osteopontin (Eta-1) and Fibroblast Growth Factor-2 Cross-Talk in Angiogenesis

Abstract

The cytokine/extracellular matrix protein osteopontin (OPN/Eta-1) is an important component of cellular immunity and inflammation. It also acts as a survival, cell-adhesive, and chemotactic factor for endothelial cells. Here, subtractive suppression hybridization showed that serum-deprived murine aortic endothelial (MAE) cells transfected with the angiogenic fibroblast growth factor-2 (FGF2) overexpress OPN compared with parental cells. This was confirmed by Northern blotting and Western blot analysis of the conditioned media in different clones of endothelial cells overexpressing FGF2 and in endothelial cells treated with the recombinant growth factor. In vivo, FGF2 caused OPN expression in newly formed endothelium of the chick embryo chorioallantoic membrane (CAM) and of murine s.c. Matrigel plug implants. Recombinant OPN (rOPN), the fusion protein GST-OPN, and the deletion mutant GST-ΔRGD-OPN were angiogenic in the CAM assay. Angiogenesis was also triggered by OPN-transfected MAE cells grafted onto the CAM. OPN-driven neovascularization was independent from endothelial αvβ3 integrin engagement and was always paralleled by the appearance of a massive mononuclear cell infiltrate. Accordingly, rOPN, GST-OPN, GST-ΔRGD-OPN, and the conditioned medium of OPN-overexpressing MAE cells were chemotactic for isolated human monocytes. Also, rOPN triggered a proangiogenic phenotype in human monocytes by inducing the expression of the angiogenic cytokines TNF-α and IL-8. OPN-mediated recruitment of proangiogenic monocytes may represent a mechanism of amplification of FGF2-induced neovascularization during inflammation, wound healing, and tumor growth.

Role of osteopontin in tumour progression

“…While there have been sporadic reports of OPN functioning to promote angiogenesis, firm evidence linking the protein to vessel development in the in vivo systems has been scarce. Recent data demonstrating that OPN accelerates blood vessel formation in matrigel and chorioallantoic membrane assays in the presence of FGF-2, however, suggest that OPN may act in concert with other proangiogenic molecules to enhance angiogenesis (Leali et al, 2003). Again, these results underscore the idea that the exact function of OPN in any given situation may be determined by interactions with other factors in the microenvironment.…”

Fibroblast growth factor/fibroblast growth factor receptor system in angiogenesis

“…Transient exposure to FGF1 and FGF2 upregulates the expression of cell adhesion molecules ICAM-1 and VCAM-1 in endothelial cells, increasing polymorphonuclear leukocyte adhesion and transendothelial migration [223]. Also, FGF2-stimulated endothelial cells upregulate the synthesis of various chemoattractants, including VEGF, that may exert a chemotactic activity on monocytes [224], the angiogenic/monocyte chemotactic protein osteopontin [225], monocyte chemoattractant protein-1 [107,226], and the proangiogenic cyclooxygenase-2 [227]. Moreover, FGF2 exerts a direct chemotactic effect on monocytes (Presta, unpublished observations).…”

Cutting Edge: IL-1β Mediates the Proangiogenic Activity of Osteopontin-Activated Human Monocytes

“…In keeping with the tight cross-talk among angiogenic growth factors and cytokines, we have shown that OPN upregulation in endothelial cells may represent a mechanism of amplification of growth factor-induced neovascularization (11). The experimental evidence suggests that OPN may affect angiogenesis indirectly via mononuclear phagocyte recruitment and up-regulation of the expression of monocyte-derived proangiogenic cytokine(s).…”

“…The serum-free medium HYQCCM1 and FBS were obtained from HyClone. Mouse OPN and its RGD deletion mutant (⌬RGD-OPN) were expressed in Escherichia coli as GST fusion proteins, as described previously (11). Endotoxin levels were always Ͻ0.06 EU/ml (6 pg/ml), as determined by the Limulus amebocyte lysate method (Cambrex).…”

“…OPN exists both as an immobilized extracellular matrix component and as a soluble molecule implicated in inflammation, cell-mediated immunity, tissue remodeling, and tumor metastases (8 -10). OPN acts as a proinflammatory cytokine that plays important roles in monocyte/macrophage functions (11)(12)(13). Experiments performed on OPN-null mice implicate OPN in Th1 cell-mediated immunity during infection, autoimmune demyelinating disease, rheumatoid arthritis, wound healing, and bone resorption (14).…”