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

Abstract

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.

Up-regulation of Rac1 by Epidermal Growth Factor Mediates COX-2 Expression in Recurrent Respiratory Papillomas

“…We previously reported that overexpression of COX-2 in papillomas is a consequence of both EGFR and PI3K signaling. However, COX-2 expression in papilloma cells, unlike most tumor lines, does not require Erk signaling (10). Thus, we reasoned that at least one other signaling pathway mediated the EGFR/PI3K induction of COX-2 in these cells.…”

“…We had previously reported that treating papilloma cells with celecoxib, a selective COX-2 inhibitor, reduced proliferation and increased apoptosis (10). Because p38 activation increased COX-2 levels in papilloma cells, but also contributed to activation of both Erk and Akt, we investigated whether inhibiting p38-α/β with SB202190 would enhance or decrease papilloma cell survival.…”

“…The alterations include constitutive phosphorylation of Erks (5), elevated phosphatidylinositol 3-kinase (PI3K) activity but reduced activation of Akt and Stat-3 due to overexpression of the phosphatase PTEN (7,8), and increased activation of NF-κB (9). Cyclooxygenase-2 (COX-2) expression is elevated in respiratory papilloma tissues and cultured cells, and COX-2 expression requires EGFR and PI3K activity (10). In tumor cell lines, COX-2 expression is regulated by multiple pathways, including activation of Erk, PI3K, and G-protein coupled receptors (11).…”

“…In tumor cell lines, COX-2 expression is regulated by multiple pathways, including activation of Erk, PI3K, and G-protein coupled receptors (11). However, the EGFR-MekErk pathway plays no role in induction of COX-2 in papilloma cells (10), suggesting that one or more other pathways is involved in these cells. We postulated that a Rac1-dependent pathway might play this role.…”

Detection of Anti-HPV11-L1 Antibodies in Immune Sera from Patients Suffering from Recurrent Respiratory Papillomatosis Using ELISA

“…R ecurrent respiratory papillomatosis (RRP) is a chronic disease, and its etiological agents are mainly HPV6 and HPV11, viruses that stimulate proliferation of mucosal epithelium, leading to the growth of papillomas (3,5,25), which are sustained by alterations in cell signal transduction, thus promoting HPV's spread and persistence in infected tissues (40). The major problem in treating RRP is the regular regrowth of papillomas (14) in the upper respiratory tract, in some cases in its distal parts, especially in lungs (18,13).…”