Modulation of cyclooxygenase in endothelial cells by fibronectin: relevance to angiogenesis.

Cyclooxygenases (COX), which catalyze the formation of prostaglandins (PGs), have been implicated in angiogenesis. Adhesion of endothelial cells (ECs) to extracellular matrix (ECM) induces the expression of COX-2 and PG production. The present study was carried out to analyze the influence of the adhesive ECM protein, fibronectin (FN), in modulating COX expression and its implications to angiogenesis using in vitro cultures of human umbilical vein ECs. RT-PCR analysis showed that the level of COX-2 mRNA was significantly high while that of COX-1 decreased in ECs maintained on FN. On treatment with p38 MAPK inhibitor and anti-alpha(5)beta(1) integrin antibody, FN dependent effect on COX expression was not observed. Analysis by ELISA and immunoblotting confirmed FN-dependent upregulation of COX-2 protein. The ratio of PG E(2):PG D(2) was significantly high in cells maintained on FN and on treatment with p38 MAPK inhibitor, the relative level of PG D(2) increased and that of PG E(2) decreased. Concomitant with the modulation of COX-2 and changes in PGs, ECs maintained on FN showed angiogenic response in an alpha(5)beta(1) integrin/p38 MAPK dependent manner as evidenced by the expression of angiogenic markers, CD 31 and E-selectin. These results suggest a FN-alpha(5)beta(1)/FAK/p38 MAPK dependent upregulation of COX-2 causing a shift in the relative levels of PGs in HUVECs which contributes to the angiogenic effect of FN.