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Decreased ID2 Promotes Metastatic Potentials of Hepatocellular Carcinoma by Altering Secretion of Vascular Endothelial Growth Factor

Authors' Affiliations: ¹ Department of Digestive Surgery and Surgical Oncology, Yamaguchi University Graduate School of Medicine; ² Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists; ³ Department of Complementary Medicine, Yamaguchi University Graduate School of Medicine; and ⁴ Department of Biological Chemistry, Faculty of Agriculture, Yamaguchi University, Yamaguchi, Japan

Requests for reprints: Masaaki Oka, Department of Digestive Surgery and Surgical Oncology, Yamaguchi University Graduate School of Medicine, 1-1-1 Minami-Kogushi, Ube, Yamaguchi 755-8505, Japan. Phone/Fax: 81-836-22-2262; E-mail: 2geka-1{at}po.cc.yamaguchi-u.ac.jp.

Purpose: We aimed to explore the molecular and biological functions of Inhibitor of DNA binding/differentiation 2 (ID2), which was found to be responsible for portal vein invasion of hepatocellular carcinoma (HCC).

Experimental Design: We measured ID2 mRNA levels in 92 HCC patients by real-time reverse transcription-PCR and examined the relation to clinicopathologic features. To clarify the precise roles of ID2, we did in vitro analysis with expression vectors and small interfering RNAs. Effects of ID2 on cell invasive potential and expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1 were analyzed by Matrigel-coated invasion chamber, ELISA, and Western blot analysis, respectively.

Results: ID2 mRNA level correlated inversely with portal vein invasion (P < 0.001), tumor-node-metastasis stage (P < 0.001), tumor size (P < 0.001), and early intrahepatic recurrence (P < 0.05). When limited to a cohort of hepatitis C virus–related HCCs, patients with low levels of ID2 had significantly shorter disease-free survival time than those with high levels of ID2. Invasive potential of cells transfected with ID2 expression vector was lower than that of empty vector–transfected cells. Cells overexpressing ID2 also showed decreased VEGF secretion and hypoxia-inducible factor-1 protein levels. The results of ID2-knockdown experiments were opposite to those of ID2 overexpression experiments.

Conclusions: On the basis of our clinical and in vitro data, we suggest that ID2 plays a significant role in the metastatic process during progression of HCC. This action might be explained, at least in part, by altered cell mobility due to decreased secretion of VEGF.