An upstream CRE-E-box element is essential for gastrin-dependent activation of the cyclooxygenase-2 gene in human colon cancer cells

The -1195G allele increases the transcriptional activity of cyclooxygenase-2 gene (COX-2) in colon cancer cell lines

Up-regulation of cyclooxygenase-2 (COX-2) is an early and key event in human colorectal carcinogenesis (CRC). Nevertheless, the molecular mechanisms leading to this over-expression are largely unknown. We previously reported an association between the -1195G allele and higher predisposition for CRC in a Caucasian population. The biological explanation for the involvement of this polymorphism in CRC remains elusive. We aimed to functionally characterize the influence of the -1195A>G promoter region polymorphism on COX-2 transcription activity in colon cancer cell lines. Luciferase reporter assays were performed to assess whether the -1195A/G alleles influenced COX-2 transcription. The COX-2 promoter's region containing either the -1195A or -1195G alleles was cloned into pGL3-basic reporter vector. The reporter vectors were transiently co-transfected with the pGL4.73 control plasmid to HCT-116 and HCA-7 colon cancer cell lines. The levels of reporter gene expression driven by the -1195G allele-containing COX-2 promoter were significantly higher in both colon cancer cell lines. A 2.2-fold increase in promoter activity was observed in the HCT-116 cell line (P < 0.001), and this over-expression was even more noticeable in the HCA-7 COX-2 expressing cell line with a threefold higher transcriptional activity (P = 0.001). The -1195G allele appeared to enhance COX-2 transcription, providing a molecular basis underlying the increased susceptibility for CRC and potentially a new mechanism for COX-2 overexpression.

Gastrin activates paracrine networks leading to induction of PAI-2 via MAZ and ASC-1

The gastric hormone gastrin regulates the expression of a variety of genes involved in control of acid secretion and also in the growth and organization of the gastric mucosa. One putative target is plasminogen activator inhibitor-2 (PAI-2), which is a component of the urokinase activator system that acts extracellularly to inhibit urokinase plasminogen activator (uPA) and intracellularly to suppress apoptosis. Previous studies have demonstrated that gastrin induces PAI-2 both in gastric epithelial cells expressing the gastrin (CCK-2) receptor and, via activation of paracrine networks, in adjacent cells that do not express the receptor. We have now sought to identify the response element(s) in the PAI-2 promoter targeted by paracrine mediators initiated by gastrin. Mutational analysis identified two putative response elements in the PAI-2 promoter that were downstream of gastrin-activated paracrine signals. One was identified as a putative MAZ site, mutation of which dramatically reduced both basal and gastrin-stimulated responses of the PAI-2 promoter by a mechanism involving PGE(2) and the small GTPase RhoA. Yeast one-hybrid screening identified the other as binding the activating signal cointegrator-1 (ASC-1) complex, which was shown to be the target of IL-8 released by gastrin. RNA interference (RNAi) knockdown of two subunits of the ASC-1 complex (p50 and p65) inhibited induction of PAI-2 expression by gastrin. The data reveal previously unsuspected transcriptional mechanisms activated as a consequence of gastrin-triggered paracrine networks and emphasize the elaborate and complex cellular control mechanisms required for a key component of tissue responses to damage and infection.