α5β1 Integrin Ligand PHSRN Induces Invasion and α5 mRNA in Endothelial Cells to Stimulate Angiogenesis

Abstract

Angiogenesis requires endothelial cell invasion and is crucial for wound healing and for tumor growth and metastasis. Invasion of native collagen is mediated by the α5β1 integrin fibronectin receptor. Thus, α5β1 up-regulation on the surfaces of endothelial cells may induce endothelial cell invasion to stimulate angiogenesis. We report that the interaction of α5β1 with its PHSRN peptide ligand induces human microvascular endothelial cell invasion and that PHSRN-induced endothelial cell invasion is regulated by α4β1 integrin and requires matrix metalloproteinase 1 (MMP-1). Moreover, our results show that exposure to PHSRN causes rapid, specific up-regulation of surface levels of α5β1 integrin and significantly increases α5 integrin mRNA in microvascular endothelial cells. Consistent with these results, α5 small interfering RNA abrogates PHSRN-induced surface α5 and MMP-1 up-regulation, as well as blocking invasion induction. We also observed dose-dependent, PHSRN-induced α5β1 integrin up-regulation on endothelial cells in vivo in Matrigel plugs. We further report that the PHSCN peptide, an α5β1-targeted invasion inhibitor, blocks PHSRN-induced invasion, α5β1 up-regulation, α5 mRNA induction, and MMP-1 secretion in microvascular endothelial cells and that systemic PHSCN administration prevents PHSRN-induced α5β1 up-regulation and angiogenesis in Matrigel plugs. These results demonstrate a critical role for α5β1 integrin and MMP-1 in mediating the endothelial cell invasion and angiogenesis and suggest that PHSRN-induced α5 transcription and α5β1 up-regulation may form an important feed-forward mechanism for stimulating angiogenesis.