Activator Protein-1 Transcription Factor Mediates Bombesin-stimulated Cyclooxygenase-2 Expression in Intestinal Epithelial Cells

Abstract

Colorectal carcinogenesis is a complex, multistep process involving genetic alterations and progressive changes in signaling pathways regulating intestinal epithelial cell proliferation, differentiation, and apoptosis. Although cyclooxygenase-2 (COX-2), gastrin-releasing peptide (GRP), and its receptor, GRP-R, are not normally expressed by the epithelial cells lining the human colon, the levels of all three proteins are aberrantly overexpressed in premalignant adenomatous polyps and colorectal carcinomas of humans. Overexpression of these proteins is associated with altered epithelial cell growth, adhesion, and tumor cell invasiveness, both in vitro and in vivo; however, a mechanistic link between GRP-R-mediated signaling pathways and increased COX-2 overexpression has not been established. We report that bombesin, a homolog of GRP, potently stimulates the expression of COX-2 mRNA and protein as well as the release of prostaglandin E 2 from a rat intestinal epithelial cell line engineered to express GRP-R. Bombesin stimulation of COX-2 expression requires an increase in [Ca 2؉ ] i , activation of extracellular signal-regulated kinase (ERK)-1 and -2 and p38 MAPK , and increased activation and expression of the transcription factors Elk-1, ATF-2, c-Fos, and c-Jun. These data suggest that the expression of GRP-R in intestinal epithelial cells may play a role in carcinogenesis by stimulating COX-2 overexpression through an activator protein-1-dependent pathway.Colorectal cancers are the third leading cause of cancer deaths in the United States (1). One in 20 Americans is at risk of developing this disease during their lifetime. Considerable experimental data have accumulated indicating an important role for cyclooxygenase-2 (COX-2) 1 in colorectal carcinogenesis. COX-2 is a key enzyme in the biosynthesis of prostaglandins from arachidonic acid and is overexpressed in 85-90% of human colon cancers and 40 -50% of premalignant adenomas (2). Several large epidemiological studies have shown that mortality from colorectal cancers decreases (40 -50%) in persons who regularly take aspirin or other nonsteroidal antiinflammatory drugs (3), which inhibit COX activity. Additionally, experiments with adenomatous polyposis coli (APC) gene-deficient mice (Min mice) revealed that inhibition of COX activity with nonsteroidal antiinflammatory drugs resulted in a reduction in the number and multiplicity of spontaneously formed tumors (4 -6), and APC ⌬716 /COX-2 double-knockout mice showed reduction in both the neoplastic growth and number of intestinal tumors (7). Although mounting evidence supports an important role for COX-2 in colorectal carcinogenesis, the molecular mechanisms leading to COX-2 overexpression in intestinal epithelial cells are not completely understood.Like COX-2, the mammalian homologue of bombesin (BBS), gastrin-releasing peptide (GRP) and its cognate G-protein-coupled receptor, GRP receptor (GRP-R), are aberrantly overexpressed in premalignant adenomatous polyps and colorectal cancers. Preston et al. (8) showed...

Bombesin induces cyclooxygenase-2 expression through the activation of the nuclear factor of activated T cells and enhances cell migration in Caco-2 colon carcinoma cells

“…Moreover, peptidases present in the serum may interfere with BBS/GRP and GRP-R binding or function (Jensen et al, 2001), which may explain the discrepancies between data of binding affinities (measured in the absence of serum and after short periods of incubation) and concentrations reported for biological effects (requiring a longer period of incubation in the presence of serum). In this regard, similar concentrations of GRP/BBS as those used in our study have been reported for the induction of Cox-2 in other cell types (Hecht et al, 1997;Guo et al, 2001) as well as for regulating motility of Caco-2 cells upon BBS treatment (Glover et al, 2005). Results from triplicate assays of three independent experiments are shown as mean fold induction 7s.e.…”

“…Aberrant expression of Cox-2, BBS/GRP and GRP-R has been observed in a variety of tumors, including colorectal carcinomas (Preston et al, 1995;Carroll et al, 1999Carroll et al, , 2000Gupta and Dubois, 2001;Jensen et al, 2001) and several lines of evidence suggest a link among these proteins in cancer progression (Hecht et al, 1997;Guo et al, 2001;Iishi et al, 2003). We have analysed the potential association between BBS-mediated signaling and Cox-2 in colon carcinoma cells, demonstrating that BBS stimulation of Caco-2 cells leads to a rapid upregulation of Cox-2 expression at both mRNA and protein levels resulting in increased production of PGE 2 .…”

“…Both transcriptional and post-transcriptional mechanisms regulate Cox-2 expression in colon carcinoma (Shao et al, 2000;Cheng and Harris, 2002;Inoue et al, 2002;Ramsay et al, 2003;Dixon, 2004). Moreover, depending on the stimuli, multiple signaling pathways including mitogen-activated protein kinases extracellular signalregulated kinase 1/2, c-Jun N-terminal kinase and p38 have been shown to mediate Cox-2 induction in human colon cancer cells (Guo et al, 2001;Liu et al, 2003;Shao et al, 2004;Sun and Sinicrope, 2005).…”

“…Recent studies have described that bombesin (BBS), a homologue of the mammalian gastrin-release peptide (GRP), induces Cox-2 expression in fibroblasts and epithelial cells, requiring an increase in [Ca 2 þ ] i (Hecht et al, 1997;Guo et al, 2001). Even more, GRP and its cognate G-protein-coupled receptor (GRP-R), as well as Cox-2, are overexpressed in a substantial fraction of human colorectal carcinomas (38-76% ) (Preston et al, 1995;Carroll et al, 1999Carroll et al, , 2000Gupta and Dubois, 2001;Jensen et al, 2001).…”

Dominant-negative mutant of c-Jun gene transfer: a novel therapeutic strategy for colorectal cancer

“…8 Although relatively little is known about the role of AP-1 activation in colorectal cancer growth, there are some reports indicating that AP-1 activation is related to colorectal cancer growth. [9][10][11] In contrast, other reports suggest that AP-1 is important for differentiation, apoptosis or resistance to therapy. Thus, the role of AP-1 in colorectal cancer has been controversial, and it remains to be determined whether AP-1 is essential for the multiplication of colorectal cancer.…”