Yoshiji H, Kuriyama S, Ways D K, Yoshii J, Miyamoto Y, Kawata M, Ikenaka Y, Tsujinoue H, Nakatani T, Shibuya M, Fukui H
Third Department of Internal Medicine, Nara Medical University, Japan.
Cancer Res. 1999 Sep 1;59(17):4413-8.
The growth of any solid tumor depends on angiogenesis. Among the known angiogenic factors, vascular endothelial growth factor (VEGF) has been shown to play a pivotal role in tumor angiogenesis. However, to date, the signal transduction pathway initiated by VEGF is still not fully understood. It has been suggested that protein kinase C (PKC) plays an important role in the VEGF-induced signal transduction pathway in vitro, although the role of PKC in tumor angiogenesis in vivo still remains to be elucidated. By delivering the VEGF gene within the self-contained tetracycline-regulated retroviral vector (Retro-Tet) into hepatocellular carcinoma (HCC) cells, we manipulated VEGF expression by providing tetracycline in the drinking water to assess the tumor kinetics mediated exclusively by VEGF. In this study, we combined this Retro-tet system and LY333531, an inhibitor of the PKC-beta isoform, to elucidate the role of PKC-beta in tumor development and angiogenesis. Using a syngenic xenograft model, tumor augmentation induced by VEGF overexpression in HCC was markedly suppressed by oral administration of the PKC-beta inhibitor, with an accompanying reduction of neovascularization and p44/42 mitogen-activated protein kinase activation. This inhibitory effect was achieved even after the tumor was fully established. Immunohistochemical analysis revealed that apoptosis increased markedly in the tumor upon PKC-beta inhibitor treatment, whereas tumor cell proliferation itself did not change. Furthermore, with orthotopical transplantation, PKC-beta inhibition suppressed HCC tumor development in the liver. These results suggest that PKC-beta lies on the signal transduction pathway by which VEGF augments development and angiogenesis not only at the initial stage but also after the tumor is fully established.
任何实体瘤的生长都依赖于血管生成。在已知的血管生成因子中，血管内皮生长因子（VEGF）已被证明在肿瘤血管生成中起关键作用。然而，迄今为止，由VEGF启动的信号转导途径仍未完全明确。有研究表明，蛋白激酶C（PKC）在体外VEGF诱导的信号转导途径中起重要作用，尽管PKC在体内肿瘤血管生成中的作用仍有待阐明。通过将VEGF基因装载于自含四环素调控的逆转录病毒载体（Retro-Tet）中导入肝癌（HCC）细胞，我们通过在饮用水中添加四环素来调控VEGF的表达，以评估仅由VEGF介导的肿瘤动力学。在本研究中，我们将这种Retro-tet系统与PKC-β亚型抑制剂LY333531相结合，以阐明PKC-β在肿瘤发展和血管生成中的作用。使用同基因异种移植模型，口服PKC-β抑制剂可显著抑制HCC中VEGF过表达诱导的肿瘤增大，同时伴有新血管形成减少和p44/42丝裂原活化蛋白激酶激活降低。即使在肿瘤完全形成后，这种抑制作用仍然存在。免疫组织化学分析显示，PKC-β抑制剂处理后肿瘤细胞凋亡明显增加，而肿瘤细胞增殖本身并未改变。此外，在原位移植中，PKC-β抑制可抑制肝脏中HCC肿瘤的发展。这些结果表明，PKC-β不仅在肿瘤发展的初始阶段，而且在肿瘤完全形成后，都处于VEGF促进肿瘤发展和血管生成的信号转导途径上。
