title: Tumor suppressor, AT motif binding factor 1 (ATBF1), translocates to the nucleus with runt domain transcription factor 3 (RUNX3) in response to TGF-beta signal transduction.
abstract: OBJECTIVE
  AT motif binding factor 1 (ATBF1), a homeotic transcription factor, was identified as a tumor suppressor, and loss of heterozygosity at ATBF1 locus occurs frequently in gastric cancers. We previously showed that ATBF1 expression inversely correlated with the malignant character of gastric cancer and that ATBF1 enhanced the promoter activity of p21Waf1/Cip1. We also found that ATBF1 moves between cytoplasm and nucleus, but the precise mechanism of translocation is unknown. In this study, we investigated the mechanism of ATBF1 translocation to the nucleus with the runt domain transcription factor 3 (RUNX3) in cooperation with TGF-beta signal transduction.
  
  
  METHODS
  To analyze the expression of ATBF1 and RUNX3 in gastric cancer cells, we performed immunohistochemistry on 98 resected gastric cancer tissue samples and scored the nuclear staining intensity as grade 0 to grade 5. Co-immunoprecipitation (co-IP) of ATBF1 and RUNX3 was performed. Dual luciferase assays were performed by transfecting ATBF1 and RUNX3 with a p21Waf1/Cip1 reporter vector. To investigate the nuclear translocation of endogenous ATBF1 and RUNX3 in response to TGF-beta signal, we examined the subcellular localization of ATBF1 and RUNX3 in gastric cancer cells treated with recombinant TGF-beta1 using confocal laser scanning microscopy.
  
  
  RESULTS
  Strong immunohistochemical nuclear staining of ATBF1 was observed in 37 (37.8%) of the gastric cancer tissue samples, and RUNX3 nuclear staining was observed in 15 (15.3%). There was a statistically significant correlation between ATBF1 and RUNX3 nuclear localization (rs=0.433, p<0.001). Co-IP revealed a physical association between ATBF1 and RUNX3. ATBF1 and RUNX3 up-regulated p21Waf1/Cip1 promoter activity synergistically. In SNU16 gastric cancer cells, ATBF1 and RUNX3 were cytoplasmic before TGF-beta1 stimulation, but after 24h of TGF-beta1 stimulation, endogenous ATBF1 and RUNX3 translocated to the nucleus.
  
  
  CONCLUSIONS
  ATBF1 associates with RUNX3 and translocates to the nucleus in response to TGF-beta signal transduction and might function in the nucleus as tumor suppressor and transcriptional regulator.
authors.affiliation: Department of Gastroenterology and Metabolism, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan.
authors.forename: Motoshi
authors.initials: M
authors.lastname: Mabuchi
authors.forename: Hiromi
authors.initials: H
authors.lastname: Kataoka
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Miura
authors.forename: Tae-Sun
authors.initials: TS
authors.lastname: Kim
authors.forename: Makoto
authors.initials: M
authors.lastname: Kawaguchi
authors.forename: Masahide
authors.initials: M
authors.lastname: Ebi
authors.forename: Mamoru
authors.initials: M
authors.lastname: Tanaka
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Mori
authors.forename: Eiji
authors.initials: E
authors.lastname: Kubota
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizushima
authors.forename: Takaya
authors.initials: T
authors.lastname: Shimura
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Mizoshita
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tanida
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kamiya
authors.forename: Kiyofumi
authors.initials: K
authors.lastname: Asai
authors.forename: Takashi
authors.initials: T
authors.lastname: Joh
mesh_terms: D021581:Active Transport, Cell Nucleus; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D050677:Core Binding Factor Alpha 3 Subunit / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics; D003593:Cytoplasm / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D013274:Stomach Neoplasms / Q000378:metabolism* / Q000473:pathology; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: C493956:CDKN1A protein, human; D050677:Core Binding Factor Alpha 3 Subunit; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018398:Homeodomain Proteins; C493729:Runx3 protein, human; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; C071660:ZFHX3 protein, human