title: RACK1 suppresses gastric tumorigenesis by stabilizing the β-catenin destruction complex.
abstract: OBJECTIVE
  Dysregulation of Wnt signaling has been involved in gastric tumorigenesis by mechanisms that are not fully understood. The receptor for activated protein kinase C (RACK1, GNB2L1) is involved in development of different tumor types, but its expression and function have not been investigated in gastric tumors.
  
  
  METHODS
  We analyzed expression of RACK1 in gastric tumor samples and their matched normal tissues from 116 patients using immunohistochemistry. Effects of knockdown with small interfering RNAs or overexpression of RACK1 in gastric cancer cell lines were evaluated in cell growth and tumor xenograft. RACK1 signaling pathways were investigated in cells and zebrafish embryos using immunoblot, immunoprecipitation, microinjection, and in situ hybridization assays.
  
  
  RESULTS
  Expression of RACK1 was reduced in gastric tumor samples and correlated with depth of tumor infiltration and poor differentiation. Knockdown of RACK1 in gastric cancer cells accelerated their anchorage-independent proliferation in soft agar, whereas overexpression of RACK1 reduced their tumorigenicity in nude mice. RACK1 formed a complex with glycogen synthase kinase Gsk3β and Axin to promote the interaction between Gsk3β and β-catenin and thereby stabilized the β-catenin destruction complex. On stimulation of Wnt3a, RACK1 repressed Wnt signaling by inhibiting recruitment of Axin by Dishevelled 2 (Dvl2). Moreover, there was an inverse correlation between expression of RACK1 and localization of β-catenin to the cytoplasm/nucleus in human gastric tumor samples.
  
  
  CONCLUSIONS
  RACK1 negatively regulates Wnt signaling pathway by stabilizing the β-catenin destruction complex and act as a tumor suppressor in gastric cancer cells.
authors.affiliation: Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Yue-Zhen
authors.initials: YZ
authors.lastname: Deng
authors.forename: Fan
authors.initials: F
authors.lastname: Yao
authors.forename: Jing-Jing
authors.initials: JJ
authors.lastname: Li
authors.forename: Zheng-Fa
authors.initials: ZF
authors.lastname: Mao
authors.forename: Ping-Ting
authors.initials: PT
authors.lastname: Hu
authors.forename: Ling-Yun
authors.initials: LY
authors.lastname: Long
authors.forename: Guo
authors.initials: G
authors.lastname: Li
authors.forename: Xiao-Dan
authors.initials: XD
authors.lastname: Ji
authors.forename: Shuo
authors.initials: S
authors.lastname: Shi
authors.forename: Dong-Xian
authors.initials: DX
authors.lastname: Guan
authors.forename: Yuan-Yuan
authors.initials: YY
authors.lastname: Feng
authors.forename: Lei
authors.initials: L
authors.lastname: Cui
authors.forename: Dang-Sheng
authors.initials: DS
authors.lastname: Li
authors.forename: Yong
authors.initials: Y
authors.lastname: Liu
authors.forename: Xiang
authors.initials: X
authors.lastname: Du
authors.forename: Ming-Zhou
authors.initials: MZ
authors.lastname: Guo
authors.forename: Li-Yan
authors.initials: LY
authors.lastname: Xu
authors.forename: En-Min
authors.initials: EM
authors.lastname: Li
authors.forename: Hong-Yang
authors.initials: HY
authors.lastname: Wang
authors.forename: Dong
authors.initials: D
authors.lastname: Xie
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D060465:Axin Signaling Complex / Q000235:genetics / Q000378:metabolism*; D016022:Case-Control Studies; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D000072261:Dishevelled Proteins; D005260:Female; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D057809:HEK293 Cells; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009368:Neoplasm Transplantation; D010750:Phosphoproteins / Q000378:metabolism; D034622:RNA Interference; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D013274:Stomach Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control; D013997:Time Factors; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D060449:Wnt Signaling Pathway / Q000235:genetics; D060509:Wnt3A Protein / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology / Q000235:genetics; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D060465:Axin Signaling Complex; C495270:CTNNB1 protein, human; C000606581:DVL2 protein, human; D000072261:Dishevelled Proteins; C000606582:Dvl2 protein, mouse; D009363:Neoplasm Proteins; D010750:Phosphoproteins; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D025521:Tumor Suppressor Proteins; C555510:WNT3A protein, human; D060509:Wnt3A Protein; D029961:Zebrafish Proteins; D051176:beta Catenin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D019204:GTP-Binding Proteins