PS 1-1 : ROS-Induced Activation of YAP-1 through a c-Myc Pathway is a Therapeutic Target in Hepatocellular Carcinoma

Aims: The Hippo signaling pathway regulates organ size by controlling both cell proliferation and apoptosis via effectors such as yes-associated protein (YAP). Dysregulation of the Hippo pathway has been suggested as one of the therapeutic target in hepatocarcinogenesis. Reactive oxygen species (ROS) levels increase during the progression from early to advanced hepatocellular carcinoma (HCC). Activated YAP-1 by ROS-induced damage has been hypothesized to aggravate progression of HCC, but it remains unclear which signaling pathway is involved. Methods: The expression of YAP-1 was quantified using real-time PCR and immunoblotting. Human HCC cells (Huh-7, HepG2, SNU-761) were grown under H2O2 treatment which is a major component of ROS in living organisms, either with YAP-1 siRNA or with control siRNA. MTT assays were performed to evaluate the role of YAP-1 in HCC under H2O2 treatment. To investigate the signaling pathway responsible for the activation of YAP-1, immunoblotting was performed. 88 surgically resected frozen HCC and 88 non-tumor liver tissue samples were used for gene expression analyses. Results: H2O2 treatment increased the mRNA and protein expressions of YAP-1 in HCC cells (Huh-7, HepG2, and SNU-761). Suppression of YAP-1 using siRNA transfection resulted in significant decrease in tumor proliferation under H2O2 treatment, both in vitro and in vivo. The oncogenic action of YAP-1 occurred via activation of the c-myc pathway, leading to up-regulation of unfolded protein response (UPR), including the 78-kDa glucose-regulated protein (GRP78/BiP) and activating transcription factor 6 (ATF-6). YAP mRNA levels in human HCC tissues were upregulated 2.6-fold compared with non-tumor tissues and positively correlated with ATF-6 levels. Conclusions: ROS-induced activation of YAP-1 via the c-myc pathway, which leads to activation of the UPR pathway, might be a therapeutic target in HCC. Funding: This study was supported by the Research Supporting Program of the Korean Association for the Study of the Liver and The Korean Liver Foundation in 2017.