Hypertonic Stress Induces VEGF Production in Human Colon Cancer Cell Line Caco-2: Inhibitory Role of Autocrine PGE(2)

Vascular Endothelial Growth Factor (VEGF) is a major regulator of angiogenesis. VEGF expression is up regulated in response to micro-environmental cues related to poor blood supply such as hypoxia. However, regulation of VEGF expression in cancer cells is not limited to the stress response due to increased volume of the tumor mass. Lipid mediators in particular arachidonic acid-derived prostaglandin (PG)E(2) are regulators of VEGF expression and angiogenesis in colon cancer. In addition, increased osmolarity that is generated during colonic water absorption and feces consolidation seems to activate colon cancer cells and promote PGE(2) generation. Such physiological stimulation may provide signaling for cancer promotion. Here we investigated the effect of exposure to a hypertonic medium, to emulate colonic environment, on VEGF production by colon cancer cells. The role of concomitant PGE(2) generation and MAPK activation was addressed by specific pharmacological inhibition. Human colon cancer cell line Caco-2 exposed to a hypertonic environment responded with marked VEGF and PGE(2) production. VEGF production was inhibited by selective inhibitors of ERK 1/2 and p38 MAPK pathways. To address the regulatory role of PGE(2) on VEGF production, Caco-2 cells were treated with cPLA(2) (ATK) and COX-2 (NS-398) inhibitors, that completely block PGE(2) generation. The Caco-2 cells were also treated with a non selective PGE(2) receptor antagonist. Each treatment significantly increased the hypertonic stress-induced VEGF production. Moreover, addition of PGE(2) or selective EP(2) receptor agonist to activated Caco-2 cells inhibited VEGF production. The autocrine inhibitory role for PGE(2) appears to be selective to hypertonic environment since VEGF production induced by exposure to CoCl(2) was decreased by inhibition of concomitant PGE(2) generation. Our results indicated that hypertonicity stimulates VEGF production in colon cancer cell lines. Also PGE(2) plays an inhibitory role on VEGF production by Caco-2 cells exposed to hyperosmotic stress through EP(2) activation.