Monocyte-Fibronectin Interactions, Via α5β1 Integrin, Induce Expression of CXC Chemokine-Dependent Angiogenic Activity

Abstract

Monocyte-derived macrophages are important sources of angiogenic factors in cancer and other disease states. Upon extravasation from vasculature, monocytes encounter the extracellular matrix. We hypothesized that interaction with extracellular matrix proteins leads monocytes to adopt an angiogenic phenotype. We performed endothelial cell chemotaxis assays on conditioned medium (CM) from monocytes that had been cultured in vitro on various matrix substrates (collagen I, laminin, Matrigel, fibronectin), in the presence of autologous serum, or on tissue culture plastic alone. Monocytes cultured on Matrigel and on fibronectin were the most potent inducers of angiogenic activity compared with tissue culture plastic or autologous serum-differentiated monocytes. This increased angiogenic activity was associated with increased expression of angiogenic CXC chemokines (IL-8, epithelial neutrophil-activating peptide-78, growth-related oncogene α, and growth-related oncogene γ) but not of vascular endothelial growth factor. Additionally, CM from monocytes cultured on fibronectin-depleted Matrigel (MGFN−) induced significantly less angiogenic activity than CM from monocytes cultured on control-depleted Matrigel. ELISA analysis of CM from monocytes cultured on MGFN− revealed a significant decrease in GRO-α and GRO-γ compared with CM from monocytes cultured on MG. Incubation of monocytes before adherence on fibronectin with PHSCN (a competitive peptide inhibitor of the PHSRN sequence of fibronectin binding via α5β1 integrin) results in diminished expression of angiogenic activity and CXC chemokines compared with control peptide. These data suggest that fibronectin, via α5β1 integrin, promotes CXC chemokine-dependent angiogenic activity from monocytes.