Reduced level of smoothened suppresses intestinal tumorigenesis by down-regulation of Wnt signaling.
OBJECTIVE
Although the Hedgehog (Hh) pathway regulates development and progression of several types of cancer, its involvement in colon cancer remains unclear. We aimed to clarify the roles of Hh signaling in intestinal tumorigenesis.


METHODS
We studied expression of the Hh signaling components in the intestinal tumors of Apc(+/Delta716) mouse, a model for familial adenomatous polyposis. We used small interfering RNAs against Smoothened (SMO), which encodes the major signal transducer of the Hh pathway, to knockdown SMO expression and explore its function in human colon cancer cell lines. We also compared the intestinal tumor phenotypes of Apc(+/Delta716)Smo(+/-) mice with those of Apc(+/Delta716) mice.


RESULTS
Expression of Smo was markedly increased in the intestinal adenoma epithelium of Apc(+/Delta716) mice. Importantly, SMO knockdown in human colon cancer cell lines suppressed proliferation in culture; cells arrested at the G1/S phase. Furthermore, Apc(+/Delta716)Smo(+/-) mice had decreased numbers of polyps in the large size class (Phi >or= 1-2 mm) and recessed polyp morphology, accompanied by reduced proliferation of the tumor epithelial cells. Unexpectedly, reduced expression of Smo suppressed beta-catenin-dependent transcription, rather than Hh-responsive Gli-dependent transcription. Interestingly, SMO knockdown reduced protein levels of active beta-catenin and induced its nuclear exclusion.


CONCLUSIONS
Smo contributes to intestinal tumorigenesis by increasing Wnt signaling. SMO might be a good therapeutic target for patients with colorectal polyps and carcinomas, even in the absence of Hh signal activation.
Arimura
Sumimasa
S
Department of Pharmacology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Matsunaga
Akihiro
A
Kitamura
Takanori
T
Aoki
Koji
K
Aoki
Masahiro
M
Taketo
Makoto M
MM
D011125:Adenomatous Polyposis Coli / Q000235:genetics* / Q000473:pathology; D000818:Animals; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology; D004195:Disease Models, Animal; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D020022:Genetic Predisposition to Disease; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D051379:Mice; D011897:Random Allocation; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics*; D000072086:Smoothened Receptor; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*; D000071676:Zinc Finger Protein GLI1; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism
C400551:GLI1 protein, human; D043562:Receptors, G-Protein-Coupled; C491023:SMO protein, human; D000072086:Smoothened Receptor; D014157:Transcription Factors; D051153:Wnt Proteins; D000071676:Zinc Finger Protein GLI1; D051176:beta Catenin