The apoptosis-inducing effect of gastrin on colorectal cancer cells relates to an increased IEX-1 expression mediating NF-κB inhibition.

Addressing the puzzling role of amidated gastrin17 (G17) and the gastrin/CCKB/CCK2 receptor in colorectal carcinogenesis, we analysed potential candidate genes involved in G17-dependent NF-κB inhibition and apoptosis. The colorectal carcinoma cell line Colo320 overexpressing the wild-type CCK2 receptor (Colo320wt) underwent G17-induced apoptosis along with suppressed NF-κB activation and decreased expression of the antiapoptotic NF-κB target genes cIAP1 and cIAP2, whereas G17 was without effect on Colo320 cells expressing a CCK2 receptor bearing a loss of function mutation (Colo320mut). Gene microarray analysis revealed an elevated expression of the stress response gene IEX-1 in G17-treated Colo320wt but not Colo320mut cells. Quantitative real-time PCR and conventional RT–PCR confirmed this G17-dependent increase of IEX-1 expression in Colo320wt cells. If these cells were subjected to IEX-1 knockdown by small interfering RNA transfection, the apoptosis-inducing effect of G17 was abolished. Moreover, tumor necrosis factor alpha (TNFα)- or 5-FU-induced apoptosis that is greatly enhanced by G17 treatment in Colo320wt cells was prevented if IEX-1 expression was repressed. Under these conditions of blocked IEX-1 expression, the NF-κB activity remained unaffected by G17, in particular in Colo320wt cells co-treated with TNFα and also the suppressive effect of G17 on cIAP1 and cIAP2 expression was not observed anymore if IEX-1 expression was blocked. Conversely, IEX-1 overexpression in Colo320mut cells caused an increase of basal and TNFα- or 5-FU-induced apoptosis, an effect not further triggered by G17 treatment. Using a xenograft tumor model in severe combined immune deficiency mice, we could show that experimental systemic hypergastrinemia induced by the administration of omeprazole led to enhanced apoptosis as well as to a marked increase of IEX-1 expression in Colo320wt tumors, but not in Colo320mut tumors. These observations indicate that the proapoptotic effect of G17 on human colon cancer cells expressing the wild-type CCK2 receptor is mediated by IEX-1, which modulates NF-κB-dependent antiapoptotic protection and thereby exerts tumor-suppressive potential.Oncogene (2008) 27, 1122–1134; doi:10.1038/sj.onc.1210728; published online 20 August 2007 [ABSTRACT FROM AUTHOR]