YAP1 Enhances Mesenchymal-Type Gene Expression in Human Adrenergic-Type Neuroblastoma Cells

<b>Background/Objectives</b>: Neuroblastoma cells are phenotypically plastic, transitioning between mesenchymal and adrenergic states. Core functional genes (e.g., <i>YAP1</i>) mark the mesenchymal state, which is linked to unfavorable prognosis. We and others previously demonstrated relapse-specific Hippo-YAP pathway activation in matched primary/relapsed neuroblastomas. Here we explored the role of <i>YAP1</i> in neuroblastoma aggressiveness and response to therapy. <b>Methods</b>: RT-qPCR and immunoblotting assessed <i>YAP1</i> expression in neuroblastoma cell lines. RNA-sequencing detected <i>YAP1</i>-dependent gene signatures in Tet-ON SK-N-AS and SH-EP neuroblastoma cell models expressing wildtype YAP1 or constitutively activated YAP1^S127A. Data from cell models were compared with our published <i>YAP1</i> expression data from neuroblastomas. Efficacy of commonly used chemotherapeutics was comparatively analyzed in the cell models. <b>Results</b>: YAP1 expression showed marked variability across a panel of neuroblastoma cell lines, assessed by mRNA analysis in 10 cell lines and protein analysis in a subset of 9 cell lines. RNA sequencing in constitutively activated YAP1^S127A mutant and wildtype YAP1 models detected 2162 and 1837 significantly differentially expressed genes in the SK-N-AS and SH-EP backgrounds, respectively. Continuously activating YAP1 in SK-N-AS cells upregulated mesenchymal signature genes and mesenchymal-associated transcription factors. Gene expression influenced by YAP1 activity in the cell models significantly overlapped with YAP1-associated genes (e.g., <i>CYR61</i> and <i>SPRY4</i>) in published tumor data. Functionally, <i>YAP1^S127A</i> expression rendered neuroblastoma cells resistant to chemotherapy. <b>Conclusions</b>: Findings corroborate the idea of a mechanistic role for <i>YAP1</i> in neuroblastoma adrenergic to mesenchymal reprogramming and therapy resistance. The <i>YAP1</i>-mediated plastic switch towards a mesenchymal expression state in neuroblastoma cells may provide the molecular basis for novel therapeutic avenues.