title: KAI1 suppresses HIF-1α and VEGF expression by blocking CDCP1-enhanced Src activation in prostate cancer.
abstract: BACKGROUND
  KAI1 was initially identified as a metastasis-suppressor gene in prostate cancer. It is a member of the tetraspan transmembrane superfamily (TM4SF) of membrane glycoproteins. As part of a tetraspanin-enriched microdomain (TEM), KAI1 inhibits tumor metastasis by negative regulation of Src. However, the underlying regulatory mechanism has not yet been fully elucidated. CUB-domain-containing protein 1 (CDCP1), which was previously known as tetraspanin-interacting protein in TEM, promoted metastasis via enhancement of Src activity. To better understand how KAI1 is involved in the negative regulation of Src, we here examined the function of KAI1 in CDCP1-mediated Src kinase activation and the consequences of this process, focusing on HIF-1 α and VEGF expression.
  
  
  METHODS
  We used the human prostate cancer cell line PC3 which was devoid of KAI1 expression. Vector-transfected cells (PC3-GFP clone #8) and KAI1-expressing PC3 clones (PC3-KAI1 clone #5 and #6) were picked after stable transfection with KAI1 cDNA and selection in 800 μg/ml G418. Protein levels were assessed by immunoblotting and VEGF reporter gene activity was measured by assaying luciferase activitiy. We followed tumor growth in vivo and immunohistochemistry was performed for detection of HIF-1, CDCP1, and VHL protein level.
  
  
  RESULTS
  We demonstrated that Hypoxia-inducible factor 1α (HIF-1α) and VEGF expression were significantly inhibited by restoration of KAI1 in PC3 cells. In response to KAI1 expression, CDCP1-enhanced Src activation was down-regulated and the level of von Hippel-Lindau (VHL) protein was significantly increased. In an in vivo xenograft model, KAI1 inhibited the expression of CDCP1 and HIF-1α.
  
  
  CONCLUSIONS
  These novel observations may indicate that KAI1 exerts profound metastasis-suppressor activity in the tumor malignancy process via inhibition of CDCP1-mediated Src activation, followed by VHL-induced HIF-1α degradation and, ultimately, decreased VEGF expression.
authors.affiliation: Division of Radiation Effect, Korea Institute of Radiological and Medical Sciences, Nowon-Ku, Seoul 139-706, Korea.
authors.forename: Jung-Jin
authors.initials: JJ
authors.lastname: Park
authors.forename: Yeung Bae
authors.initials: YB
authors.lastname: Jin
authors.forename: Yoon-Jin
authors.initials: YJ
authors.lastname: Lee
authors.forename: Jae-Seon
authors.initials: JS
authors.lastname: Lee
authors.forename: Yun-Sil
authors.initials: YS
authors.lastname: Lee
authors.forename: Young-Gyu
authors.initials: YG
authors.lastname: Ko
authors.forename: Minyoung
authors.initials: M
authors.lastname: Lee
mesh_terms: D015703:Antigens, CD / Q000502:physiology*; D000951:Antigens, Neoplasm; D015815:Cell Adhesion Molecules / Q000502:physiology*; D045744:Cell Line, Tumor; D002465:Cell Movement; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D015151:Immunoblotting; D007150:Immunohistochemistry; D051861:Kangai-1 Protein / Q000378:metabolism / Q000502:physiology*; D008156:Luciferases / Q000378:metabolism; D008297:Male; D009361:Neoplasm Invasiveness; D009363:Neoplasm Proteins / Q000502:physiology*; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D000951:Antigens, Neoplasm; C497688:CD82 protein, human; C432044:CDCP1 protein, human; D015815:Cell Adhesion Molecules; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051861:Kangai-1 Protein; D009363:Neoplasm Proteins; D042461:Vascular Endothelial Growth Factor A; D008156:Luciferases; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D019061:src-Family Kinases; C497446:VHL protein, human