The crucial role of cyclooxygenase-2 in osteopontin-induced protein kinase C α/c-Src/IκB kinase α/β-dependent prostate tumor progression and angiogenesis

The regulation of tumor progression towards its malignancy needs the interplay among several cytokines, growth factors, and enzymes, which are controlled in the tumor microenvironment. Here, we report that osteopontin, a small integrin-binding ligand N-linked glycoprotein family of calcified extracellular matrix-associated protein, regulates prostate tumor growth by regulating the expression of cyclooxygenase-2 (COX-2). We have shown that osteopontin stimulates the activation of protein kinase C α/nuclear factor-inducing kinase/nuclear factor-κB-dependent signaling cascades that induces COX-2 expression, which in turn regulates the prostaglandin E ₂ production, matrix metalloproteinase-2 activation, and tumor progression and angiogenesis. We have revealed that suppression of osteopontin-induced COX-2 expression by the nonsteroidal anti-inflammatory drug celecoxib or blocking the EP2 receptor by its blocking antibody resulted in significant inhibition of cell motility and tumor growth and angiogenesis. The data also showed that osteopontin-induced mice PC-3 xenograft exhibits higher tumor load, increased tumor cell infiltration, nuclear polymorphism, and neovascularization. Interestingly, use of celecoxib or anti-EP2 blocking antibody drastically suppressed osteopontin-induced tumor growth that further indicated that suppression of COX-2 or its metabolites could significantly inhibit osteopontin-induced tumor growth. Human clinical prostate cancer specimen analysis also supports our in vitro and animal model studies. Our findings suggest that blockage of osteopontin and/or COX-2 is a promising therapeutic approach for the inhibition of prostate tumor progression and angiogenesis.