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Mesotheliomas are frequently characterized by disruption of Hippo pathway due to deletion and/or mutation in genes, such as neurofibromin 2 (NF2). Hippo disruption attenuates yes-associated protein (YAP) phosphorylation allowing YAP to translocate to the nucleus and regulate gene expression. The role of disrupted Hippo pathway in maintenance of established mesotheliomas has been extensively investigated using cell lines; however, its involvement in development of human mesothelioma has not been explored much. Here, we employed immortalized human mesothelial cells to disrupt Hippo pathway. YAP phosphorylation was reduced on NF2 knockdown and the cells exhibited altered growth in vitro, developing tumors when transplanted into nude mice. Similar results were obtained from enforced expression of wildtype or constitutively active (S127A) YAP, indicating the crucial role of activated YAP in the transformation of mesothelial cells. Gene expression analysis comparing control- and YAP-transduced immortalized human mesothelial cells revealed phospholipase-C beta 4 (PLCB4) to be among the genes highly upregulated by YAP. PLCB4 was upregulated by YAP in immortalized human mesothelial cells and downregulated on YAP knockdown in Hippo-disrupted mesothelioma cell lines. PLCB4 knockdown attenuated the growth of YAP-transduced immortalized mesothelial cells and YAP-active, but not YAPnonactive, 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 mesothelioma. [ABSTRACT FROM AUTHOR]