Prostate-Derived ETS Factor (PDEF) Regulates Yes Associated Protein 1 (YAP1) in Prostate Cancer Cells: A Potential Cross-Talk between PDEF and Hippo Signaling

PDEF is expressed in luminal epithelial cells of the prostate gland and associates with luminal phenotype. Hippo pathway regulates cell growth/proliferation, cellular homeostasis, and organ development by modulating phosphorylation of its downstream effectors. In previous studies, we observed decreased levels of PDEF during prostate cancer progression. In the present studies, we evaluated the effects of PDEF on total and phospho (Ser-127)YAP1 protein(a downstream effector of the Hippo pathway) levels in PC3 cells, a line of castrate resistant prostate cancer. We observed that the expression of PDEF in PC3 cells resulted in increased increased phospho(Ser127) -YAP1 protein levels. Our immunofluorescence analysis for YAP1 revealed an increased cytoplasmic/nuclear ratio of YAP1 in PDEF-PC3 cells as compared to VC-PC3 cells, suggesting PDEF may play a critical role in modulating YAP1 phosphorylation, and by extension in the regulation of the Hippo pathway. We also observed a decrease in YAP1 protein levels in prostate cancer tissues as compared to normal prostate tissues. Our analysis of multiple publicly available clinical cohorts revealed a gradual decrease in YAP1 mRNA expression during prostate cancer progression and metastasis. This decrease was similar to the decrease in PDEF levels which we reported earlier. In addition we observed further decreased in PDEF and YAP1 expression in Neuro-Endocrine Prostate Cancer (NEPC), and a direct correlation between PDEF and YAP1 expression. To the best of our knowledge, these results provide the first demonstration of modulation of YAP1 by PDEF in any system and suggest a cross-talk between PDEF and the Hippo pathway.