Prostaglandins and activation of AC/cAMP prevents anoikis in IEC-18

Recent data indicates that chronic inflammation of the intestine such as Crohn's or ulcerative colitis puts those individuals at heightened risk for colorectal adenocarcinoma. In this study, we examine the effect of the inflammatory mediator PGE(2) and associated signalling on detachment-induced cell death (anoikis) in intestinal epithelial cells. Treatment of detached IEC-18 with 0.01-0.05 mu M PGE(2) increased cell viability as well as induced aggregation. As EP4 prostaglandin receptors on IEC are coupled to adenylate cyclase, we next treated cells with agents that promote cAMP signalling (Forskolin, dbcAMP, and etazolate), all of which promoted IIEC aggregation as well as survival. We next treated detached IECs with specific inhibitors of adenylate cyclase or PKA, which accelerated anoikis. To explore the mechanism of cell-cell adhesion, we next treated detached IECs with an anti-E-cadherin blocking antibody which dispersed aggregates induced by dbcAMP, and an adenovirus expressing a dominant negative E-cadherin (Ecad Delta EC) prevented aggregate formation. Interestingly Ecad Delta EC prevented aggregation of IEC induced by dbcAMP but did not significantly reduce viability. This suggests that cAMP signalling is important in both aggregate formation and promoting viability but these are distinct events. Taken together, these data support a mechanism whereby elevated PGE(2) levels characteristic of colitis prevent anoikis by activating an AC-, cAMP-, and PKA-dependent signalling pathway. The delay of apoptosis by PGE(2) may be one mechanism by which inflammation may contribute to carcinogenesis.