論文

In the multistep process of metastasis, "anchorage-independent growth," where cancer cells need to survive without cell-substratum interaction, is supposed to be important. In this study, we found that anchorage-independent growth analyzed using the soft agar colony formation assay correlated with hematogeneous intrahepatic metastasis of liver cancer cell lines and also Akt activation status. Two highly metastatic liver cancer cell lines showed high Akt activity and formed many colonies in soft agar, whereas three nonmetastatic cell lines showed less Akt activity and formed fewer colonies. Inhibition of Akt activation in the highly metastatic cell line Li7 by transfection with kinase-dead Akt or the phosphatidylinositol 3-kinase inhibitor, LY294002, resulted in formation of fewer colonies in soft agar than was the case with control cells. Moreover, in orthotopic implantation model, this inhibition resulted in a reduced rate of hematogeneous intrahepatic metastasis. These findings indicated that anchorage-independent growth regulated by phosphatidylinositol 3-kinase/Akt pathway plays a critical role in metastasis, and that this could be a potential therapeutic target to combat metastasis.

Human hepatocellular carcinoma (HCC) is one of the most common and aggressive malignancies. In order to identify genes involved in HCC progression, we conducted a differential display analysis and found osteopontin (OPN) to be overexpressed in HCC. OPN is known to be a secreted adhesive glycoprotein, associated with tumorigenesis and metastasis in several cancers. Quantitative polymerase chain reaction analysis of 30 HCC cases revealed the average ratio of OPN to glyceraldehyde-3-phosphate dehydrogenase in tumors to be significantly higher than that in the surrounding non-cancerous liver (4.7 +/- 1.6 vs 0.18 +/- 0.04, P = 0.0072). Immunohistochemistry confirmed the OPN protein was expressed mainly on cancer cells, and was positive in 12 of 30 HCC, most of which showed transcript overexpression. Both OPN transcript and OPN protein were significantly overexpressed in HCC with capsular infiltration, compared with HCC without capsular infiltration. Moreover, OPN-positive cancer cells were often dispersed in the periphery of cancer nodules and were adjacent to stromal cells. Although OPN overexpression was not related to vascular invasion or intrahepatic metastasis, OPN was suggested to play a role in HCC, especially in cancer-stromal interactions.