Up-regulation of Rac1 by epidermal growth factor mediates COX-2 expression in recurrent respiratory papillomas.

Recurrent respiratory papillomas are epithelial tumors of the airway caused by human papillomaviruses. We previously reported that the epidermal growth factor receptor (EGFR) is overexpressed in papilloma cells, that cyclooxygenase-2 (COX-2) is induced, and that COX-2 expression in primary papilloma cells requires activation of the EGFR but not Erk. Rac1, a member of the Rho family of GTPases, is a key signaling element that is known to control multiple pathways downstream of the EGFR. Here we report that Rac1 is overexpressed in papilloma cells compared with normal laryngeal epithelial cells and that the increased levels of Rac1 are mediated by EGFR activation. Transfecting cells with Rac1-specific siRNA suppressed COX-2 expression. Surprisingly, Rac1 mediated phosphorylation of p38 mitogen-activated kinase in papilloma cells but not normal cells, and inhibition of p38 with the specific inhibitor SB202190 suppressed COX-2 expression in papilloma cells but had no effect on low-level COX-2 expression in normal cells. Thus, the signaling cascades that regulate COX-2 expression are different in HPV-infected papilloma cells, with a significant contribution by the EGFR-- Rac1-->p38 pathway.

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 E2 (PGE2) induced COX-2, whereas celecoxib, a selective COX-2 inhibitor, suppressed levels of COX-2, suggesting a positive feedback loop. Moreover, treatment with PGE2 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 PGE2 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.

2',5'-Oligoadenylate synthetase activity analysis and human papilloma virus typing as prognostic factors in patients with recurrent respiratory papillomatosis.

OBJECTIVE: Determination of early prognostic factors in patients with recurrent respiratory papillomatosis is extremely important, so the major goal of our prospective, multicentre study was to evaluate (1) the feasibility of various factors to determine prognosis of the clinical course, as well as (2) the response to interferon-alpha therapy in recurrent respiratory papillomatosis. METHODS: Forty-two patients with recurrent respiratory papillomatosis were treated with interferon-alpha (3 MU/m(2) three times per week; mean therapy duration was 2.7 +/- 1.8 years) in 1983-1994 and followed-up until 2003. Human papilloma virus (HPV) type, recurrent respiratory papillomatosis severity and 2',5'-oligoadenylate synthetase activity were determined by standard methods and analysed for correlation with the results of long-term clinical outcome. RESULTS AND CONCLUSION: Patients with HPV type 11, a severity score >4, a high number of surgical procedures prior to interferon-alpha therapy and a high basal 2',5'-oligoadenylate synthetase activity should be considered at high risk of an aggressive clinical course, often with spread to lower airway passages, malignant transformation and death. Human papilloma virus type, score for recurrent respiratory papillomatosis severity, number of surgical procedures and 2',5'-oligoadenylate synthetase activity showed significant association with response to interferon-alpha therapy and the long-term clinical course, so these factors have value in predicting prognosis in recurrent respiratory papillomatosis.

Inhibition of cyclooxygenase-2: an approach to preventing cancer of the upper aerodigestive tract.

Multiple lines of evidence suggest that cyclooxygenase-2 (COX-2), an inducible form of COX, represents a potential pharmacologic target to prevent cancer. Key data suggesting a causal relationship between increased COX-2 activity and carcinogenesis and possible mechanisms of action of COX-2 in this context will be discussed. The possibility that COX-2 represents a pharmacological target for preventing upper aerodigestive cancers (head and neck, lung) will be emphasized. Importantly, clinical trials have been initiated to assess the chemopreventive properties of selective COX-2 inhibitors.

Increase in immunogenicity with concomitant loss of tumorigenicity of respiratory tract carcinomas during in vitro culture.

Cell lines were established in vitro from respiratory tract carcinomas induced in rats by carcinogenic, polycyclic hydrocarbons. Propagation of the carcinoma lines in vitro lead to a progressive decrease in tumorigenicity. Tumor transplantation studies in X-irradiated, immunosuppressed recipients and in immunologically reconstituted recipients suggested that the cells are rejected because of their immunogenicity, since a high incidence of tumors was observed in X-irradiated recipients but not in normal or X-irradiated, reconstituted recipients. When immunologically competent rats were immunized with cells from an in vitro tumor line, strong tumor transplantation resistance resulted. Similar immunization with the corresponding in vivo tumor line caused very little if any protection, and immunization with a non-cross-reacting sarcoma line grown in vitro did not produce immunological protection against carcinoma cell lines. A single in vivo passage of the in vitro-adapted tumor line in immunosuppressed recipients fully restored tumorigenicity. The increase in immunogenicity of carcinomas cultured in vitro appears to involve preexisting angigens indigenous to the carcinomas rather than new antigens acquired during tissue culture, such as antigens related to retroviruses, mycoplasmas, or heterologous serum.