[No authors listed]
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 (Pâ=â0.030), high HIF-1α expression (Pâ=â0.028), high VEGF expression (Pâ=â0.048), increased tumor angiogenesis (Pâ=â0.033) and poor prognosis (Pâ=â0.037); high MVD was associated with high HIF-1α expression (Pâ=â0.034), high VEGF expression (Pâ=â0.001) and poor prognosis (Pâ=â0.040). Multivariate analysis indicated that RBP2 had an independent influence on the survival of patients with stage I NSCLC (Pâ=â0.044). 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.
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