Enhanced PKCδ and ERK Signaling Mediate Cell Migration of Retinal Pigment Epithelial Cells Synergistically Induced by HGF and EGF

Proliferative vitreoretinopathy (PVR) and proliferative diabetic retinopathy (PDR) are characterized by the development of epi-retinal membranes which may exert a tractional force on retina. A lot of inflammatory growth factors may disturb the local ocular cells such as retinal pigment epithelial (RPE) cells, causing them to migrate and proliferate in the vitreous cavity and ultimately forming the PVR membrane. In this study, the signal pathways mediating cell migration of RPE induced by growth factors were investigated. Hepatocyte growth factor (HGF), epidermal growth factor (EGF) or heparin-binding epidermal growth factor (HB-EGF) induced a greater extent of migration of RPE50 and ARPE19 cells, compared with other growth factors. According to inhibitor studies, migration of RPE cells induced by each growth factor was mediated by protein kinase C (PKC) and ERK (MAPK). Moreover, HGF coupled with EGF or HB-EGF had synergistic effects on cell migration and enhanced activation of PKC and ERK, which were attributed to cross activation of growth factor receptors by heterogeneous ligands. Furthermore, using the shRNA technique, PKCδ was found to be the most important PKC isozyme involved. Finally, vitreous fluids from PVR and PDR patients with high concentration of HGF may induce RPE cell migration in PKCδ- and ERK- dependent manner. In conclusion, migration of RPE cells can be synergistically induced by HGF coupled with HB-EGF or EGF, which were mediated by enhanced PKCδ activation and ERK phosphorylation.

增生性玻璃体视网膜病变（proliferative vitreoretinopathy, PVR）与增生性糖尿病视网膜病变（proliferative diabetic retinopathy, PDR）以视网膜前膜形成为特征，此类膜性结构可对视网膜产生牵拉作用力。多种炎性生长因子可干扰眼部局部细胞，例如视网膜色素上皮（retinal pigment epithelial, RPE）细胞，促使其向玻璃体腔迁移并增殖，最终形成PVR膜。本研究针对生长因子诱导RPE细胞迁移的信号通路展开了系统探究。相较于其他生长因子，肝细胞生长因子（hepatocyte growth factor, HGF）、表皮生长因子（epidermal growth factor, EGF）以及肝素结合表皮生长因子（heparin-binding epidermal growth factor, HB-EGF）可更显著地促进RPE50与ARPE19细胞的迁移。经抑制剂实验证实，各生长因子诱导的RPE细胞迁移均由蛋白激酶C（protein kinase C, PKC）与ERK（MAPK）介导。此外，HGF联合EGF或HB-EGF可对细胞迁移产生协同效应，并增强PKC与ERK的激活，该现象归因于异源性配体对生长因子受体的交叉激活。进一步通过短发夹RNA（short hairpin RNA, shRNA）技术发现，PKCδ是参与该过程的最重要的PKC同工酶。最后，携高浓度HGF的PVR与PDR患者玻璃体液可通过PKCδ及ERK依赖的方式诱导RPE细胞迁移。综上，HGF联合HB-EGF或EGF可协同诱导RPE细胞迁移，该效应通过增强PKCδ激活与ERK磷酸化实现。