The apoptosis-inducing effect of gastrin on colorectal cancer cells relates to an increased IEX-1 expression mediating NF-kappa B inhibition.
Addressing the puzzling role of amidated gastrin(17) (G17) and the gastrin/CCKB/CCK2 receptor in colorectal carcinogenesis, we analysed potential candidate genes involved in G17-dependent NF-kappaB inhibition and apoptosis. The colorectal carcinoma cell line Colo320 overexpressing the wild-type CCK2 receptor (Colo320wt) underwent G17-induced apoptosis along with suppressed NF-kappaB activation and decreased expression of the antiapoptotic NF-kappaB 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 (TNFalpha)- 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-kappaB activity remained unaffected by G17, in particular in Colo320wt cells co-treated with TNFalpha 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 TNFalpha- 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-kappaB-dependent antiapoptotic protection and thereby exerts tumor-suppressive potential.
Sebens Müerköster
S
S
Laboratory of Molecular Gastroenterology and Hepatology, 1st Department of Medicine, University Hospital of Schleswig-Holstein, Kiel, Germany.
Rausch
A V
AV
Isberner
A
A
Minkenberg
J
J
Blaszczuk
E
E
Witt
M
M
Fölsch
U R
UR
Schmitz
F
F
Schäfer
H
H
Arlt
A
A
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000378:metabolism* / Q000473:pathology; D005260:Female; D005755:Gastrins / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D016147:Genes, Tumor Suppressor / Q000502:physiology; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D051379:Mice; D016513:Mice, SCID; D009154:Mutation; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D043887:Receptor, Cholecystokinin B / Q000172:deficiency / Q000235:genetics; D051996:Transcription Factor RelA
D051017:Apoptosis Regulatory Proteins; D005755:Gastrins; C099815:IER3 protein, human; D008565:Membrane Proteins; D016328:NF-kappa B; D043887:Receptor, Cholecystokinin B; D051996:Transcription Factor RelA