Abstract 4013: The positive role of TPγ in the induction of COX-2, TxA2 and cell growth by NNK in human lung cancer cells
Authors: Huang Runyue , Chen George Gong , Lai Paul B.s. 
Published: August 2012

Abstract
Many studies have shown that 4-Methylnitrosamino-1-3-pyridyl-1-butanone (NNK), the most potent carcinogen present in tobacco smoke, can induce lung tumor growth. We previously demonstrated that the activation of extracellular regulated protein kinases (ERK) and cAMP response element-binding protein (CREB) is responsible for the pro-survival and proliferative effects of thromboxane A2 (TxA2) and its receptor (TP) in the human lung cancer cells stimulated with NNK (reported in oncogene journal). In current study, we further determined the role of cyclooxygenase(COX)-2/TxA2/TP pathway in lung cancer cell growth mediated by NNK. TP exists as two isoforms, ≤ and β, in human beings. Western blotting showed that TPα, but not TPα, was widely expressed in a series of human lung cells. NCI-H23 and CRL-2066, which express both TPγ and TPα, were selected as models in this study. COX-2 inhibitor NS398 could significantly reduce NNK-stimulated TxA2 synthesis. Moreover, NS398 and BM567, an agent combining TxA2 synthase inhibition and TP antagonism, had the similar effects to reverse NNK-induced activation of ERK and CREB and the increase in cell growth. Furthermore, the administration of TxA2 mimetic U46619 could almost reconstituted NNK-induced ERK and CREB activation in the presence of COX-2-siRNA. Collectively, these findings suggest that in lung cancer cells stimulated with NNK, TxA2 is mainly derived from COX-2 and acts as a key mediator for tumor-promoting effects of COX-2. Interestingly, TP antagonist SQ29548 could inhibit NNK-induced COX-2 protein expression and TxA2 production, indicating that TP is able to modulate NNK-induced COX-2 expression and activity, thereby constituting an auto-amplification mechanism of TxA2 synthesis in lung cancer cells stimulated with NNK. We further examined which TP isoform contributes to the NNK effects. We observed that the protein expression of TPα, but not TPα, was time-dependently increased by NNK. Moreover, the activation of ERK and CREB and the production of COX-2 and TxA2 by NNK were potentiated in cells transfected with pcDNA3-TPγ as compared with cells transfected with control vector or pcDNA3-TPα, and such effects could be reversed by SQ29548. However, in cells transfected with pcDNA3-TPα, the COX-2, TxA2, phospho-ERK and phospho-CREB levels were similar to that seen in the cells transfected with control vector, and neither NNK nor SQ29548 had any additional effects when compared to the control cells. Taken together, these data strongly suggest that TPγ rather than TPγ is, at least in part, responsible for the induction of COX-2, TxA2 and cell growth by NNK in lung cancer cells. Our study implies that targeting TxA2 and its receptor TPγ may represent a promising strategy for prevention of smoking-associated lung cancer.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4013. doi:1538-7445.AM2012-4013