Activation of thromboxane receptor α induces expression of cyclooxygenase-2 through multiple signaling pathways in A549 human lung adenocarcinoma cells

Abstract

Human lung adenocarcinoma A549 cells stably transfected with TPα (A549-TPα) were used to study agonist I-BOP-induced expression of cyclooxygenase-2 (COX-2) and the related mechanisms of induced expression. I-BOP, a TP agonist, induced a time and dose dependent expression of COX-2 in A549-TPα cells as revealed by Western blot and by the synthesis of PGE 2 and TXB 2 which was totally inhibited by COX-2 inhibitors. The signaling pathways of I-BOP-induced COX-2 expression were elucidated by using various inhibitors of the signaling molecules. The effects of these inhibitors were assessed at three different levels of COX-2 expression: protein, enzyme activity and promoter activity. Within MAPK family, both ERK and p38 MAPK but not JNK/SAPK pathways were involved in the induction. Other pathways such as JAK/Stat3 pathway and β-catenin/TCF/LEF pathway also participated in the induction. The activation of key signaling molecules, ERK, p38 MAPK, CREB and NF-κB, involved in the COX-2 transcription was further studied at the phosphorylation step. Activation of ERK and p38 MAPK appeared to be mediated primarily by transactivation of EGFR, whereas activation of CREB and NF-κB was mediated by PKA, PKC and ERK. The role of CREB and NF-κB in I-BOP-induced COX-2 expression was further explored at the COX-2 promoter level. Studies on promoter fragments of different length and mutation of responsive motifs indicated that CRE and NF-κB sites are critical for the COX-2 induction. Distal NF-κB site is essential for the basal induction of the COX-2 transcription, whereas CRE and proximal NF-κB sites are important for the induced transcription. These results indicate that I-BOP induced COX-2 expression through multiple signaling pathways leading to the activation of CREB and NF-κB transcriptional factors and subsequent COX-2 transcription.

4-Methylnitrosamino-1-3-pyridyl-1-butanone (NNK) promotes lung cancer cell survival by stimulating thromboxane A2 and its receptor

“…There are an increasing number of publications describing the potential role of TxA 2 and its related molecules in promoting progression of lung cancer (Ermert et al, 2003;Wei et al, 2007;Leung et al, 2009;Li and Tai, 2009). Unfortunately, the possible role of TxA 2 in smoking-associated lung cancer has received limited attention.…”

“…CREB is one such transcription factor (Sakamoto and Frank, 2009), and it is constitutively activated in both NSCLC and SCLC cells (Ma et al, 2007;Aggarwal et al, 2008). Additionally, CREB has been shown to be activated by NNK, TxA 2 or TxA 2 mimetic in lung cancer cells (Laag et al, 2006;Wei et al, 2007;Li and Tai, 2009). Therefore, CREB activation and its related proteins, PCNA and Bcl-2, were evaluated in this study.…”

“…It is noted that the PI3K/Akt and ERK pathways are two principal signalings associated with NNK (West et al, 2003;Hung and Hung, 2009). These two pathways can also be activated by TxA 2 mimetic in cancer cells Wei et al, 2007). Although there are common signaling targets, no study has been previously done to correlate NNK with TxA 2 .…”

“…It is well known that mitogen-activated protein kinase (MAPK) signaling pathways, which mainly include ERK, p38 and c-Jun NH(2)-terminal kinase (JNK) three members, are crucial for cell proliferation/survival in cancer Wei et al, 2007). Therefore, we also examined whether TxA 2 affected their activation in the cells treated with NNK.…”

“…Overexpression of TxAS has been documented to have a potential role in promoting the progression of many types of cancers (Nie et al, 2004;Sakai et al, 2006;Moussa et al, 2008a;Leung et al, 2009;Cathcart et al, 2010). In addition to TxAS, the important role of TxA 2 receptor in tumorigenesis and cancer progression has emerged (Sakai et al, 2006;Wei et al, 2007;Li and Tai, 2009;Cathcart et al, 2010). Particularly, we have previously demonstrated that inhibition of TxAS results in the p27-related induction of cell death or apoptosis in both human non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) cells (Leung et al, 2009), and other authors have recently reported that the activation of TxA 2 receptor induces cell proliferation in NSCLC cells (Li and Tai, 2009).…”