Hypertonic environment elicits cyclooxygenase-2-driven prostaglandin E 2 generation by colon cancer cells: Role of cytosolic phospholipase A 2-α and kinase signaling pathways

Abstract

Cyclooxygenase (COX)-2-derived prostaglandin (PG)E 2 controls many aspects of colon cancer development, modulating from apoptosis resistance and cell proliferation to angiogenesis, invasion, and metastasis. Here, we investigated the role of different phospholipases (PL)A 2 in supplying arachidonic acid (AA) for COX-2-dependent PGE 2 generation and signaling pathways involved in activation of colon cancer cells by a physiologically relevant stimulus. To emulate the hypertonic environment found physiologically in colon, the human colon cancer cell line Caco-2 was maintained in hypertonic complete DMEM medium. Human colon cancer cell line Caco-2 exposed to a hypertonic environment responded with marked AA release, COX-2 induction and PGE 2 generation. Selective secretory (s)PLA 2 and calcium-independent (i)PLA 2 inhibitors did not modify PGE 2 generation, while either COX-2 or cytosolic (c)PLA 2 inhibitors completely inhibited PGE 2 generation. cPLA 2-α was responsible for AA supply for PGE 2 generation, but had no role in COX-2 induction. Mitogen-activated protein (MAP) kinases, ERK 1/2, p38, and JNK, participated in the signaling events that lead to PGE 2 generation by modulating AA release, but only ERK 1/2 was involved in COX-2 upregulation. Our results indicate that hypertonic stress activates PGE 2 generation by Caco-2 cells through a mechanism dependent on MAP kinase-regulated AA mobilization, increased cPLA 2-α activity, and COX-2 induction.