Background: Tumor neovascularization (TNV) is a common pathologic basis for malignant growth and metastasis. However, the mechanism of TNV pathogenesis is not fully understood. Ras homolog gene family, member A (RhoA), a Rho guanosine triphosphatase (GTPase) family member, may be involved in a hypoxia-induced vascular endothelial growth factor (VEGF) pathway that regulates TNV angiogenesis through an unclear mechanism.
Methods: The regulation of RhoA on p53, the p53 binding protein homolog murine double minute 2 (MDM2), and VEGF was analyzed in hypoxic MCF-7 cells using Western blot analysis, real-time polymerase chain reaction (PCR) analysis, coimmunoprecipitation, and immunofluorescence staining assays. Changes in proliferation, invasion, migration, stress fiber formation, and tube formation were detected in an MCF-7 human umbilical vein endothelial cell (HUVEC) coculture system. Correlations of RhoA expression with MDM2, wild-type p53 (wt-p53), and VEGF expression in breast cancer tissues and relations between RhoA and breast cancer clinical features were analyzed by immunohistochemistry.
Results: Activated RhoA down-regulated p53 protein, which increased VEGF expression in hypoxic MCF-7 cells; whereas p53 messenger RNA levels were not altered. In addition, the ubiquitin-mediated degradation of p53 was enhanced by active RhoA. RhoA and MDM2 colocalized in the cytoplasm of hypoxic MCF-7 cells and interacted with each other physically. Furthermore, nutlin-3, a specific MDM2 inhibitor, was capable of reducing activated RhoA-induced p53 protein stability and attenuating VEGF accumulation. In an MCF-7-HUVEC coculture system, nutlin-3 effectively inhibited HUVEC proliferation, invasion, migration, stress fiber formation, and tube formation mediated by activated RhoA under hypoxic conditions. Data from 129 clinical breast cancer specimens with wt-p53 revealed that high RhoA expression was correlated with high MDM2 expression, low wt-p53 expression, and high VEGF expression.
Conclusions: The current data suggested that activated RhoA promotes VEGF expression and hypoxia-induced angiogenesis through the up-regulation of MDM2 to decrease p53 stability.
Copyright © 2012 American Cancer Society.