Abstract

Hepatocellular carcinoma (HCC) typicallyrelies on angiogenesis for its malignant behavior, including growth andmetastasis. Vasohibin 2 (VASH2) was previously identified as an angiogenicfactor, but its role in tumorigenesis is unknown. Using quantitative PCR andwestern blot analyses, we found that VASH2 is overexpressed in HCC cells andtissues. Using chromatin immunoprecipitation, we detected histone modificationsat the putative VASH2 promoter, with increased H3K4 trimethylation and H3acetylation and decreased H3K27 trimethylation, suggesting that epigeneticmechanisms are responsible for the deregulated VASH2 transcription in HCC.Knockdown of VASH2 via siRNA inhibited the proliferation of the hepatoma celllines by delaying cell cycle progression and increasing apoptosis. Importantly,we found VASH2 secreted in the culture supernatant, and co-expression of itssecretory chaperone small vasohibin-binding protein (SVBP) further enhancedVASH2 secretion. The supernatant from HepG2 cells expressing VASH2 enhanced theproliferation, migration and tube formation of human umbilical vein endothelialcells, and knockdown of VASH2 significantly inhibited these effects. In an invivo study using a nude mouse model, we found that exogenous VASH2significantly contributed to tumor growth, microvessel density and hemoglobinconcentration in the tumors. Further analyses showed that the VASH2-mediatedincrease in the transcription of fibroblast growth factor-2, vascularendothelial growth factor and vasohibin 1 may be the mechanism underlying theseeffects. Taken together, these data indicate that VASH2 is abnormally expressedin HCC cells as a result of histone modifications and that VASH2 contributes tothe angiogenesis in HCC via an SVBP-mediated paracrine mechanism. These resultsindicate a novel and important role for VASH2 in HCC angiogenesis and malignanttransformation.