Epidermal Growth Factor–Induced Cyclooxygenase-2 Expression Is Mediated through Phosphatidylinositol-3 Kinase, Not Mitogen-Activated Protein/Extracellular Signal-Regulated Kinase Kinase, in Recurrent Respiratory Papillomas

Purpose: Recurrent respiratory papillomas, caused by human papillomaviruses, are premalignant tumors that overexpress the epidermal growth factor receptor (EGFR). The goals of this study were as follows: ( a ) to evaluate the expression of cyclooxygenase-2 (COX-2) in papillomas, ( b ) to investigate the role of EGFR signaling in COX-2 expression, and ( c ) to determine whether COX-2 activity is important for the growth of papilloma cells. Experimental Design: Immunohistochemistry, Western blotting, and real-time PCR were used to determine levels of COX-2 in papilloma and normal laryngeal tissue. Explant cultures of both normal laryngeal and papilloma cells were used to define the signaling pathways that regulate COX-2 expression and investigate the potential of targeting COX-2 as a strategy to suppress papilloma growth. Results: COX-2 levels were markedly increased in papillomas. In vitro studies suggested that overexpression in papillomas reflected activation of EGFR→phosphatidylinositol 3-kinase signaling. Treatment with prostaglandin E 2 (PGE 2 ) induced COX-2, whereas celecoxib, a selective COX-2 inhibitor, suppressed levels of COX-2, suggesting a positive feedback loop. Moreover, treatment with PGE 2 stimulated papilloma cell growth, whereas celecoxib suppressed proliferation and induced apoptosis. Conclusions: Overexpression of COX-2 in papillomas seems to be a consequence of enhanced EGFR→phosphatidylinositol 3-kinase signaling. We propose a positive feedback loop for COX-2 expression, with induction of COX-2 resulting in enhanced PGE 2 synthesis and further expression of COX-2 that contributes to the growth of papillomas in vivo . These data strengthen the rationale for evaluating whether nonsteroidal anti-inflammatory drugs, prototypic COX inhibitors, will be useful in the management of respiratory papillomas.