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Rac Activation Is Associated with Hepatocellular Carcinoma Metastasis by Up-regulation of Vascular Endothelial Growth Factor Expression

Authors' Affiliations: Departments of ¹ Surgery and ² Clinical Oncology, The University of Hong Kong, Pokfulam, Hong Kong, China

Requests for reprints: Ronnie T.P. Poon, Department of Surgery, The University of Hong Kong, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong, China. Phone: 852-2855-3641; Fax: 852-2817-5475; E-mail: poontp{at}hkucc.hku.hk.

Purpose: Hepatocellular carcinoma (HCC) is associated with a propensity for vascular invasion and metastasis, which contribute to poor prognosis. Angiogenesis is a crucial process contributing to tumor growth and metastasis. Recently, Rac has been suggested to play a role in angiogenesis. However, the actual role of Rac in HCC angiogenesis remains unclear. Given that vascular endothelial growth factor (VEGF) is an important angiogenic factor in HCC, the purpose of this study was to evaluate the possible correlation between Rac activation and VEGF expression in HCC tumor samples, as well as the mechanism involved in Rac-induced HCC angiogenesis.

Experimental Design: We evaluated Rac and VEGF expression in the HCC tissue microarray of paired primary and metastatic HCC samples using immunohistochemical staining. The role of Rac-induced HCC angiogenesis was also evaluated in vitro in HCC cell lines.

Results: We first showed that activation of Rac was correlated with HCC metastasis (P < 0.001), and its expression was significantly correlated with VEGF expression by tissue microarray. Ectopic Rac-dominant active transfection in Hep3B cells increased VEGF secretion, which induced the morphologic change and proliferation of human umbilical vein endothelial cells, resulting in the promotion of angiogenesis. Rac induced the transcriptional activation of VEGF by direct interaction with hypoxia-inducible factor-1 (HIF-1) expression. In hypoxic conditions, Rac promoted angiogenesis through an increase in HIF-1 stabilization.

Conclusion: This study shows that Rac is a novel angiogenic factor for HCC through the enhancement of HIF-1 protein stability, which provides a possible therapeutic target in the development of inhibitors of angiogenesis.

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