Rac activation is associated with hepatocellular carcinoma metastasis by up-regulation of vascular endothelial growth factor expression.
OBJECTIVE
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.


METHODS
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-1alpha (HIF-1alpha) expression. In hypoxic conditions, Rac promoted angiogenesis through an increase in HIF-1alpha stabilization.


CONCLUSIONS
This study shows that Rac is a novel angiogenic factor for HCC through the enhancement of HIF-1alpha protein stability, which provides a possible therapeutic target in the development of inhibitors of angiogenesis.
Lee
Terence K
TK
Department of Surgery, The University of Hong Kong, Pokfulam, Hong Kong, China.
Poon
Ronnie T P
RT
Yuen
Anthony P
AP
Man
Kwan
K
Yang
Zhen Fan
ZF
Guan
Xin Yuan
XY
Fan
Sheung Tat
ST
D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology / Q000556:secondary*; D045744:Cell Line, Tumor; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis / Q000378:metabolism; D007150:Immunohistochemistry; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015854:Up-Regulation / Q000235:genetics; D042442:Vascular Endothelial Growth Factors / Q000096:biosynthesis* / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D042442:Vascular Endothelial Growth Factors; D020744:rac GTP-Binding Proteins