title: Retinoblastoma binding protein 2 (RBP2) promotes HIF-1α-VEGF-induced angiogenesis of non-small cell lung cancer via the Akt pathway.
abstract: BACKGROUND
  Pathological angiogenesis plays an essential role in tumor aggressiveness and leads to unfavorable prognosis. The aim of this study is to detect the potential role of Retinoblastoma binding protein 2 (RBP2) in the tumor angiogenesis of non-small cell lung cancer (NSCLC).
  
  
  METHODS
  Immunohistochemical staining was used to detect the expression of RBP2, hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and CD34. Two pairs of siRNA sequences and pcDNA3-HA-RBP2 were used to down-regulate and up-regulate RBP2 expression in H1975 and SK-MES-1 cells. An endothelial cell tube formation assay, VEGF enzyme-linked immunosorbent assay, real-time PCR and western blotting were performed to detect the potential mechanisms mediated by RBP2 in tumor angiogenesis.
  
  
  RESULTS
  Of the 102 stage I NSCLC specimens analyzed, high RBP2 protein expression is closely associated with tumor size (P = 0.030), high HIF-1α expression (P = 0.028), high VEGF expression (P = 0.048), increased tumor angiogenesis (P = 0.033) and poor prognosis (P = 0.037); high MVD was associated with high HIF-1α expression (P = 0.034), high VEGF expression (P = 0.001) and poor prognosis (P = 0.040). Multivariate analysis indicated that RBP2 had an independent influence on the survival of patients with stage I NSCLC (P = 0.044). By modulating the expression of RBP2, our findings suggested that RBP2 protein depletion decreased HUVECs tube formation by down-regulating VEGF in a conditioned medium. RBP2 stimulated the up-regulation of VEGF, which was dependent on HIF-1α, and activated the HIF-1α via phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Moreover, VEGF increased the activation of Akt regulated by RBP2.
  
  
  CONCLUSIONS
  The RBP2 protein may stimulate HIF-1α expression via the activation of the PI3K/Akt signaling pathway under normoxia and then stimulate VEGF expression. These findings indicate that RBP2 may play a critical role in tumor angiogenesis and serve as an attractive therapeutic target against tumor aggressiveness for early-stage NSCLC patients.
authors.affiliation: Department of Thoracic Surgery, Qi Lu Hospital, Shandong University, Jinan, Shandong Province, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Qi
authors.affiliation: Department of Thoracic Surgery, Shan dong Provincial Chest Hospital, Jinan, Shandong Province, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhu
authors.affiliation: Department of Thoracic Surgery, Qi Lu Hospital, Shandong University, Jinan, Shandong Province, China.
authors.forename: Shu-Hai
authors.initials: SH
authors.lastname: Li
authors.affiliation: Department of Thoracic Surgery, Qi Lu Hospital, Shandong University, Jinan, Shandong Province, China.
authors.forename: Li-Bo
authors.initials: LB
authors.lastname: Si
authors.affiliation: Department of Thoracic Surgery, Qi Lu Hospital, Shandong University, Jinan, Shandong Province, China.
authors.forename: Li-Kuan
authors.initials: LK
authors.lastname: Hu
authors.affiliation: Department of Thoracic Surgery, Qi Lu Hospital, Shandong University, Jinan, Shandong Province, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Tian
mesh_terms: D018952:Antigens, CD34 / Q000235:genetics / Q000378:metabolism; D002289:Carcinoma, Non-Small-Cell Lung / Q000098:blood supply / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D045744:Cell Line, Tumor; D042783:Endothelial Cells / Q000378:metabolism / Q000473:pathology; D005260:Female; D005500:Follow-Up Studies; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics* / Q000378:metabolism; D008175:Lung Neoplasms / Q000098:blood supply / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D009389:Neovascularization, Pathologic; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D054840:Retinol-Binding Proteins, Cellular / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D016019:Survival Analysis; D047368:Tumor Burden; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics* / Q000378:metabolism
chemical_list: D018952:Antigens, CD34; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C518459:RBP2 protein, human; D034741:RNA, Small Interfering; D054840:Retinol-Binding Proteins, Cellular; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D051057:Proto-Oncogene Proteins c-akt