Monocyte-fibronectin interactions, via alpha(5)beta(1) integrin, induce expression of CXC chemokine-dependent angiogenic activity

Monocyte-derived macrophages are important sources of angiogenic factors in cancer and other disease states. Upon extravasation from vasculature, mono cytes encounter the extracellular matrix. We hypothesized that interaction with extracellular matrix proteins leads monocytes to adopt an angiogenic p henotype. We performed endothelial cell chemotaxis assays on conditioned me dium (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 o n Matrigel and on fibronectin were the most potent inducers of angiogenic a ctivity compared with tissue culture plastic or autologous serum-differenti ated monocytes. This increased angiogenic activity was associated with incr eased expression of angiogenic CXC chemokines (IL-8, epithelial neutrophil- activating peptide-78, growth-related oncogene a, and growth-related oncoge ne gamma) but not of vascular endothelial growth factor. Additionally, CM f rom monocytes cultured on fibronectin-depleted Matrigel (MG(FN-)) induced s ignificantly less angiogenic activity than CM from monocytes cultured on co ntrol-depleted Matrigel. ELISA analysis of CM from monocytes cultured on MG (FN-) revealed a significant decrease in GRO-alpha and GRO-gamma compared w ith CM from monocytes cultured on MG. Incubation of monocytes before adhere nce on fibronectin with PHSCN (a competitive peptide inhibitor of the PHSRN sequence of fibronectin binding via a,p, integrin) results in diminished e xpression of angiogenic activity and CXC chemokines compared with control p eptide. These data suggest that fibronectin, via a,P, integrin, promotes CX C chemokine-dependent angiogenic activity from monocytes.