Abstract B170: Downregulation of Yes-associated protein 1 (YAP1) expression reduces cell proliferation and clonogenicity of pancreatic cancer cells

Abstract

Abstract Recent genetic studies in Drosophila have shown the Hippo pathway to be a potential tumor suppressor pathway that could play vital role(s) in mammalian cancer development. The Hippo pathway regulates organ size by inhibiting cell proliferation and promotes cell apoptosis upon its activation. The Yes Associated Protein 1 (YAP1) is a nuclear effector that promotes cell growth as a transcription co-activator. In human cancer, YAP1 has been shown to be a candidate oncogene as the chromosomal region containing YAP1 (11q22) has been reported as amplified and over-expressed in several tumor types, such as colon, liver, and lung (Overholtzer et al. 2006 PNAS, 103: 12405–12410). To determine the role of YAP1 in the tumorigenesis and progression of pancreatic cancer, here we examine YAP1 protein expression in pancreatic tumors and investigate the phenotypic effects of YAP1 down-regulation in cultured pancreatic cancer cells. Initially, we evaluated YAP1 expression in pancreatic tumors through immunohistochemistry (IHC) using tissue microarrays (TMA) to determine relative protein abundance and localization at the tissue and cellular level. YAP1 staining intensities were moderate to strong in the nucleus and cytoplasm of the cells, whereas the companion normal pancreas tissue showed negative to weak staining. In cultured cells, YAP1 expression and localization was modulated by cell densities. YAP1 total protein expression and Ser127 phosphorylation increased concurrently with cell density in whole cell lysates and cytosolic fractions, but does not in nuclear fractions. Additionally, transfection of YAP1-targeting siRNA oligonucleotides within pancreatic cancer cell lines, BxPC-3 and PANC-1, significantly decreased cell viability and reduced cell proliferation in vitro. An additional observation was the diminished anchorage-independent growth on soft agar of BxPC-3 and PANC-1 cells upon transfection with YAP1 siRNA oligonucleotides. The number of colonies formed were approximately 5% in BxPC-3 (p<0.007) and 20% (p<0.04) in PANC-1 compared to the negative siRNA control. Furthermore, the reduction of YAP1 protein expression by siRNA oligonucleotides correlates with the reduced growth on soft agar. The silencing of YAP1 abated clonogenicity of pancreatic cancer cells, suggesting a role of YAP1 in tumorigenesis. In summary, we demonstrate that YAP1 is overexpressed in pancreatic cancer and potentially plays an important role in the tumorigenesis and growth of pancreatic cancer. (This work was supported by a grant from the National Foundation for Cancer Research.) Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B170.