Abstract 5174: Modeling mesothelioma initiation through disruption of the Hippo pathway revealed involvement of PLCB4 in YAP-driven mesothelioma cell proliferation

Abstract

Abstract Disruption of the Hippo pathway as a result of deletion and/or mutation of the involved genes (e.g., neurofibromin 2 [NF2]) is frequently observed in mesothelioma. The disruption results in reduced phosphorylation of yes-associated protein (YAP), and the non-phosphorylated YAP translocates to the nucleus and regulates gene expression. While the roles of the disrupted Hippo pathway in the maintenance of established tumors have been investigated using mesothelioma cell lines, its involvement in the initiation of mesothelioma remains unclear. We used immortalized human mesothelial cells to study the transformation process, and found that NF2 knockdown led to transformation of the cells concurrently with reduction in YAP phosphorylation. The cells exhibited enhanced growth in vitro, and formed tumors following transplantation into nude mice. Similar results to those obtained by NF2 knockdown were also obtained using enforced expression of wild-type (wt) or constitutively active (S127A) YAP. Although enforced expression of YAPwt or YAPS127A was insufficient to transform primary (unimmortalized) human mesothelial cells, our findings provide evidence for the crucial roles of activated YAP in the transformation of mesothelial cells. To identify YAP-regulated genes critical for mesothelial tumorigenesis, we conducted gene expression analysis comparing control- and YAP-transduced immortalized human mesothelial cells. Gene Set Enrichment Analysis (GSEA) using a gene set down-regulated by YAP knock-down in mesothelioma cell lines revealed phospholipase C beta 4 (PLCB4) to be among the top-ranking genes up-regulated by YAP in our experiments. PLCB4 was up-regulated by YAP in immortalized human mesothelial cells, and down-regulated by YAP knock-down in YAP-driven mesothelioma cells. shRNA-mediated silencing of PLCB4 attenuated the growth of YAP-transduced mesothelial cells and Hippo-disrupted, but not -proficient, mesothelioma cell lines. Our model system thus provides a versatile tool to investigate the mechanisms underlying mesothelioma development. We suggest that PLCB4 may be an attractive drug target for the treatment of malignant mesothelioma. Citation Format: tatsuo kakiuchi. Modeling mesothelioma initiation through disruption of the Hippo pathway revealed involvement of PLCB4 in YAP-driven mesothelioma cell proliferation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5174.