A functional and protein-protein interaction analysis of neuroepithelial cell transforming gene 1 in hepatocellular carcinoma

In our previous study, we reported that the expression of neuroepithelial transforming gene 1 (NET1) was increased in hepatocellular carcinoma (HCC) tissues and suggested that NET1 may serve as a novel prognostic predictor and a useful target for HCC therapy. The aim of this study was to determine the role of NET1 in HCC by monitoring the proliferation, migration, invasion, and metastasis of HCC cells in which NET1 has been stably knocked down. Additionally, to provide targets for therapeutic intervention, we aimed to identify the protein which interacts with NET1. NET1 knockdown significantly reduced the migration, invasion, and metastasis of MHCC-97H cells by 44, 65, and 77 %, respectively, while cell proliferation was not significantly altered following NET1 knockdown. During our efforts to find potential NET1 modulators through protein-protein interactions, we identified merlin as a NET1-binding protein in a yeast two-hybrid screen. The interaction between NET1 and merlin was confirmed by co-immunoprecipitation. We found that the levels of NET1 protein decreased along with the increase of merlin levels. Furthermore, we demonstrated that merlin facilitates NET1 ubiquitination via the ubiquitin-proteasome pathway. Taken together, this study suggests that NET1 plays an important role in HCC cell migration, invasion, and metastasis, which are key aspects of HCC progression. Furthermore, merlin may serve as a tumor suppressor for HCC by facilitating ubiquitination of NET1.