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 alpha5beta1. 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 alpha5beta1, stimulates the growth of human lung
carcinoma cells, and that this effect is mediated through alpha5beta1-dependent signals, has prompted us to examine the effects of
COX-2 inhibitors on alpha5beta1 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 alpha5 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 alpha5 expression. Transient transfection assays showed that the
COX-2 inhibitors affected
integrin alpha5 gene transcription by acting between -92 to -41 bp of the human
integrin alpha5 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 alpha5 expression and promoter activity. Overall, these findings suggest that
COX-2 inhibitors suppress
alpha5beta1 integrin expression in NSCLC through effects on
integrin alpha5 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 alpha5 gene expression and, consequently, recognition of extracellular matrices (i.e.,
fibronectin) by
tumor cells. (c) 2005 Wiley-Liss, Inc.