Lipopolysaccharide Initiates a Positive Feedback of Epidermal Growth Factor Receptor Signaling by Prostaglandin E2 in Human Biliary Carcinoma Cells

Bacterial products (e.g., LPS) are viewed as critical stimuli in inflammation-associated cancer. Cyclooxygenase 2 (COX-2), a major effector of LPS, and EGFR, are key to carcinogenesis, notably in the hepatobiliary tract. In this study, we tested the hypothesis that LPS can initiate an interaction between the epidermal growth factor receptor (EGFR) and COX-2 pathways. We examined the effect of LPS in biliary carcinoma cells that displayed constitutive COX-2 expression and PGE(2) production and in normal human biliary epithelial cells in which COX-2/PGE(2) expression was virtually absent. LPS induced early phosphorylation of EGFR and ERK1/2 in both types of cells, which reached maximum levels within 30 min (first phase). However, only the carcinoma cells showed a second significant rise in both EGFR and ERK phosphorylation 6 h after exposure to LPS (second phase). Inhibition of COX-2/PGE(2) production prevented the second, but not the first, phase of EGFR and ERK1/2 phosphorylation, implicating COX-2/PGE(2) in the second phase of phosphorylation. LPS induced COX-2-derived PGE2 production at 4 h, which was before the rise in the second phosphorylation that occurred at 6 h. Exogenous PGE(2) also caused EGFR activation via a signaling pathway involving TACE-dependent TGF-alpha release. Inhibition of the second phase of EGFR phosphorylation with EGFR or COX-2 inhibitor prevented LPS-induced cell invasion in vitro, demonstrating the biological importance of this COX-2 feedback signaling in cancer cells. We conclude that LPS triggers a positive feedback loop involving COX-2/PGE(2) in biliary carcinoma cells and that this second phase of EGFR phosphorylation is implicated in cell invasion by LPS.