COX-2 inhibitors suppress integrin α5 expression in human lung carcinoma cells through activation of Erk: Involvement of Sp1 and AP-1 sites

Abstract

Tumor cell expression of COX‐2 has been implicated in the progression of murine and human lung cancer. Inhibition of COX‐2 by nonsteroidal antiinflammatory drugs reduces the risk of cancer development in humans and suppresses tumor growth in animal models. However, the underlying mechanisms for this beneficial effect are not fully understood. Here we explore the potential link between the anticancer effects of COX‐2 inhibitors and the expression of the integrin α5β1. Expression of this integrin in carcinoma cells is associated with invasiveness and malignant progression. This, together with our studies showing that fibronectin, the ligand of α5β1, stimulates the growth of human lung carcinoma cells, and that this effect is mediated through α5β1‐dependent signals, has prompted us to examine the effects of COX‐2 inhibitors on α5β1 expression in human non small cell lung carcinoma (NSCLC) cells. We found that the selective COX‐2 inhibitors NS398 and Nimesulide decreased mRNA expression and protein production of the integrin α5 subunit. This effect was associated with inhibition of NSCLC cell adhesion to fibronectin. The COX‐2 inhibitors triggered the phosphorylation of extracellular signal‐regulated kinase (Erk) in a time‐dependent manner, and the inhibitor of Mek‐1/Erk PD98095 prevented their inhibitory effects on integrin α5 expression. Transient transfection assays showed that the COX‐2 inhibitors affected integrin α5 gene transcription by acting between −92 to −41 bp of the human integrin α5 gene promoter. Gel mobility shift assays showed that the COX‐2 inhibitors increased Sp1 DNA binding, but decreased that of AP‐1. These effects were accompanied by an increase in Sp1 protein and a decrease in c‐Jun protein expression, as well as inhibition of SAPK/JNK phosphorylation. The Sp1 inhibitor, Mithramycin A, also blocked the inhibitory effect of the COX‐2 inhibitors on α5 expression and promoter activity. Overall, these findings suggest that COX‐2 inhibitors suppress α5β1 integrin expression in NSCLC through effects on integrin α5 gene transcription mediated by Erk activation, increased Sp1, decreased AP‐1 DNA binding and inactivation of SAPK/JNK signals. Our observations unveil a new mechanism of action against NSCLC for COX‐2 inhibitors that relates to regulation of integrin α5 gene expression and, consequently, recognition of extracellular matrices (i.e., fibronectin) by tumor cells.