title: Smad4-mediated signaling inhibits intestinal neoplasia by inhibiting expression of β-catenin.
abstract: OBJECTIVE
  Mutational inactivation of adenomatous polyposis coli (APC) is an early event in colorectal cancer (CRC) progression that affects the stability and increases the activity of β-catenin, a mediator of Wnt signaling. Progression of CRC also involves inactivation of signaling via transforming growth factor β and bone morphogenetic protein (BMP), which are tumor suppressors. However, the interactions between these pathways are not clear. We investigated the effects of loss of the transcription factor Smad4 on levels of β-catenin messenger RNA (mRNA) and Wnt signaling.
  
  
  METHODS
  We used microarray analysis to associate levels of Smad4 and β-catenin mRNA in colorectal tumor samples from 250 patients. We performed oligonucleotide-mediated knockdown of Smad4 in human embryonic kidney (HEK293T) and in HCT116 colon cancer cells and transgenically expressed Smad4 in SW480 colon cancer cells. We analyzed adenomas from (APC(Δ1638/+)) and (APC(Δ1638/+)) × (K19Cre(ERT2)Smad4(lox/lox)) mice by using laser capture microdissection.
  
  
  RESULTS
  In human CRC samples, reduced levels of Smad4 correlated with increased levels of β-catenin mRNA. In Smad4-depleted cell lines, levels of β-catenin mRNA and Wnt signaling increased. Inhibition of BMP or depletion of Smad4 in HEK293T cells increased binding of RNA polymerase II to the β-catenin gene. Expression of Smad4 in SW480 cells reduced Wnt signaling and levels of β-catenin mRNA. In mice with heterozygous disruption of Apc(APC(Δ1638/+)), Smad4-deficient intestinal adenomas had increased levels of β-catenin mRNA and expression of Wnt target genes compared with adenomas from APC(Δ1638/+) mice that expressed Smad4.
  
  
  CONCLUSIONS
  Transcription of β-catenin is inhibited by BMP signaling to Smad4. These findings provide important information about the interaction among transforming growth factor β, BMP, and Wnt signaling pathways in progression of CRC.
authors: Department of Surgery, Vanderbilt University Medical Center, Nashville, Tennessee 37232-2730, USA.
authors: Tanner J
authors: TJ
authors: Freeman
authors: J Joshua
authors: JJ
authors: Smith
authors: Xi
authors: X
authors: Chen
authors: M Kay
authors: MK
authors: Washington
authors: Joseph T
authors: JT
authors: Roland
authors: Anna L
authors: AL
authors: Means
authors: Steven A
authors: SA
authors: Eschrich
authors: Timothy J
authors: TJ
authors: Yeatman
authors: Natasha G
authors: NG
authors: Deane
authors: R Daniel
authors: RD
authors: Beauchamp
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control; D011125:Adenomatous Polyposis Coli / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control; D000368:Aged; D000818:Animals; D001665:Binding Sites; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control; D015536:Down-Regulation; D005260:Female; D017491:Genes, APC; D045325:HCT116 Cells; D057809:HEK293 Cells; D006801:Humans; D061346:Laser Capture Microdissection; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D012319:RNA Polymerase II / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051901:Smad4 Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D060449:Wnt Signaling Pathway / Q000235:genetics; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
chemical_list: D019485:Bone Morphogenetic Proteins; C495270:CTNNB1 protein, human; C495267:CTNNB1 protein, mouse; D012333:RNA, Messenger; C497796:SMAD4 protein, human; D051901:Smad4 Protein; C490810:Smad4 protein, mouse; D051176:beta Catenin; D012319:RNA Polymerase II