title: Rap1 stabilizes beta-catenin and enhances beta-catenin-dependent transcription and invasion in squamous cell carcinoma of the head and neck.
abstract: OBJECTIVE
  In head and neck squamous cell carcinoma (HNSCC) cells, Rap1 shuttles between the nucleus and cytoplasm. Prior findings suggested that Rap1 may modulate the beta-catenin-independent Wnt pathway in some settings, but the role of Rap1 in beta-catenin-dependent Wnt signaling remains undefined.
  
  
  RESULTS
  We observed that beta-catenin bound to active Rap1 in vitro and Rap1 activated beta-catenin/T-cell factor (TCF)-dependent transcription. Immunofluorescence studies showed that ectopic expression of Rap1 increased nuclear translocation of beta-catenin. Overexpression of active Rap1 facilitated an increase in beta-catenin-mediated transcription that was abrogated by dominant-negative TCF4. Conversely, small interfering RNA-mediated inhibition of endogenous Rap1 expression inhibited beta-catenin/TCF-mediated transcription as well as invasion of HNSCC. Furthermore, inhibition of Rap1 expression downregulated the expression of matrix metalloproteinase 7, a transcriptional target of beta-catenin/TCF. In HNSCC cells stably transfected with beta-catenin or treated with lithium chloride or Wnt3A to stabilize endogenous beta-catenin, inhibition of Rap1 expression led to decreases in the free pool of beta-catenin. Immunohistochemical studies of tissue from HNSCC patients revealed that increased beta-catenin intensity correlated with higher tumor stage. Furthermore, the prognostic effect of active Rap1 on tumor N stage was found to depend on cytosolic beta-catenin expression (P < 0.013). When beta-catenin is high, higher Rap1GTP intensity is associated with more advanced N stage.
  
  
  CONCLUSIONS
  The findings suggest that Rap1 enhances beta-catenin stability and nuclear localization. In addition to indicating that Rap1 has a significant role in regulating beta-catenin and beta-catenin-dependent progression to more advanced N-stage lesions, these data highlight Rap1 as a potential therapeutic target in HNSCC.
authors.affiliation: Departments of Periodontics and Oral Medicine and Biologic and Materials Science, University of Michigan School of Dentistry, Ann Arbor, Michigan 48109-1078, USA.
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Goto
authors.forename: Raj S
authors.initials: RS
authors.lastname: Mitra
authors.forename: Min
authors.initials: M
authors.lastname: Liu
authors.forename: Julia
authors.initials: J
authors.lastname: Lee
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Henson
authors.forename: Thomas
authors.initials: T
authors.lastname: Carey
authors.forename: Carol
authors.initials: C
authors.lastname: Bradford
authors.forename: Mark
authors.initials: M
authors.lastname: Prince
authors.forename: Cun-Yu
authors.initials: CY
authors.lastname: Wang
authors.forename: Eric R
authors.initials: ER
authors.lastname: Fearon
authors.forename: Nisha J
authors.initials: NJ
authors.lastname: D'Silva
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000235:genetics; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic; D006258:Head and Neck Neoplasms / Q000235:genetics; D006801:Humans; D000089804:Shelterin Complex; D015398:Signal Transduction; D034501:Telomere-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D015533:Transcriptional Activation; D014162:Transfection; D051153:Wnt Proteins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism*
chemical_list: D000089804:Shelterin Complex; C440809:TERF2IP protein, human; D034501:Telomere-Binding Proteins; D051153:Wnt Proteins; D051176:beta Catenin