Beta-catenin/Tcf-4 inhibition after progastrin targeting reduces growth and drives differentiation of intestinal tumors.
OBJECTIVE
Aberrant activation of the beta-catenin/Tcf-4 transcriptional complex represents an initiating event for colorectal carcinogenesis, shifting the balance from differentiation toward proliferation in colonic crypts. Here, we assessed whether endogenous progastrin, encoded by a target gene of this complex, was in turn able to regulate beta-catenin/Tcf-4 activity in adenomatous polyposis coli (APC)-mutated cells, and we analyzed the impact of topical progastrin depletion on intestinal tumor growth in vivo.


METHODS
Stable or transient RNA silencing of the GAST gene was induced in human tumor cells and in mice carrying a heterozygous Apc mutation (APCDelta14), which overexpress progastrin but not amidated or glycine-extended gastrin.


RESULTS
Depletion of endogenous progastrin production strongly decreased intestinal tumor growth in vivo through a marked inhibition of constitutive beta-catenin/Tcf-4 activity in tumor cells. This effect was mediated by the de novo expression of the inhibitor of beta-catenin and Tcf-4 (ICAT), resulting from a down-regulation of integrin-linked kinase in progastrin-depleted cells. Accordingly, ICAT down-regulation was correlated with progastrin overexpression and Tcf-4 target gene activation in human colorectal tumors, and ICAT repression was detected in the colon epithelium of tumor-prone, progastrin-overexpressing mice. In APCDelta14 mice, small interfering RNA-mediated progastrin depletion not only reduced intestinal tumor size and numbers, but also increased goblet cell lineage differentiation and cell apoptosis in the remaining adenomas.


CONCLUSIONS
Thus, depletion of endogenous progastrin inhibits the tumorigenicity of APC-mutated colorectal cancer cells in vivo by promoting ICAT expression, thereby counteracting Tcf-4 activity. Progastrin targeting strategies should provide an exciting prospect for the differentiation therapy of colorectal cancer.
Pannequin
Julie
J
CNRS UMR5203, Montpellier, France.
Delaunay
Nathalie
N
Buchert
Michael
M
Surrel
Fanny
F
Bourgaux
Jean-François
JF
Ryan
Joanne
J
Boireau
Stéphanie
S
Coelho
Jessica
J
Pélegrin
André
A
Singh
Pomila
P
Shulkes
Arthur
A
Yim
Mildred
M
Baldwin
Graham S
GS
Pignodel
Christine
C
Lambeau
Gérard
G
Jay
Philippe
P
Joubert
Dominique
D
Hollande
Frédéric
F
D048868:Adaptor Proteins, Signal Transducing; D000236:Adenoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D011125:Adenomatous Polyposis Coli / Q000235:genetics; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D005755:Gastrins / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D017491:Genes, APC; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D011498:Protein Precursors / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D011897:Random Allocation; D012097:Repressor Proteins; D015398:Signal Transduction / Q000502:physiology; D051820:TCF Transcription Factors / Q000378:metabolism*; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014183:Transplantation, Heterologous; D051176:beta Catenin / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D005755:Gastrins; D019869:Phosphatidylinositol 3-Kinases; D011498:Protein Precursors; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D051820:TCF Transcription Factors; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors; D051176:beta Catenin; C498785:Ctnnbip1 protein, mouse; C544894:TCF7L2 protein, human; C544895:Tcf7l2 protein, mouse; C013706:big gastrin