Regulation of COX-2-mediated signaling by α3 type IV noncollagenous domain in tumor angiogenesis

Human alpha 3 chain, a noncollagenous domain of type IV collagen [alpha 3(IV)NC1], inhibits angiogenesis and tumor growth. These biologic functions are partly attributed to the binding of alpha 3(IV)NC1 to alpha V beta 3 and alpha 3 beta 1 integrins. alpha 3(IV)NC1 binds alpha V beta 3 integrin, leading to translation inhibition by inhibiting focal adhesion kinase/phosphatidylinositol 3-kinase/Akt/ mTOR/4E-BP1 pathways. In the present study, we evaluated the role of alpha 3 beta 1 and alpha V beta 3 integrins in tube formation and regulation of cyclooxygenase-2 (COX-2) on alpha 3(IV)NC1 stimulation. We found that al- though both integrins were required for the inhibition of tube formation by alpha 3(IV)NC1 in endothelial cells, only alpha 3 beta 1 integrin was sufficient to regulate COX-2 in hypoxic endothelial cells. We show that binding of alpha 3(IV)NC1 to alpha 3 beta 1 integrin leads to inhibition of COX-2-mediated pro-angiogenic factors, vascular endothelial growth factor, and basic fibroblast growth factor by regulating IKB alpha/NF kappa B axis, and is independent of alpha V beta 3 integrin. Furthermore, beta 3 integrin-null endothelial cells, when treated with alpha 3(IV)NC1, inhibited hypoxia-mediated COX-2 expression, whereas COX-2 inhibition was not observed in alpha 3 integrin-null endothelial cells, indicating that regulation of COX-2 by alpha 3(IV)NCI is mediated by integrin alpha 1. Our in vitro and in vivo findings demonstrate that alpha 3 beta 1 integrin is critical for alpha 3(IV)NC1 -mediated inhibition of COX-2-dependent angiogenic signaling and inhibition of tumor progression.