Hippo-YAP pathway activation favors neuroblastoma progression

Background:

Neuroblastoma is a solid tumor of childhood originating from neural crest progenitors. We had previously identified a relapse-specific pattern of Hippo-YAP pathway activation in RNA-sequencing data from paired primary and relapse neuroblastoma samples, which is consistent with reports that the mesenchymal phenotype is more prevalent in relapse tumors. We here aimed to analyze the contribution of YAP1 to oncogenic processes using neuroblastoma cell lines and models.

Methods:

YAP1 mRNA and protein levels were determined by real-time PCR and immunoblotting. Knockdown experiments were performed using RNAinterference. For overexpression of YAP1, we stably transfected SH-EP, SK-N-AS and IMR-5 with a Tet-ON system harboring a constitutively active YAP1(S127A). Cell proliferation rates and and cell death were analyzed by cell counting, BrdU-ELISA and FACS-based cell cycle analyses.

Results:

YAP1 expression varied greatly among the 19 neuroblastoma cell lines that we profiled, emphasizing the idea of distinct neuroblastoma cell types, inter alia characterized by different YAP1 levels. A YAP1 knockdown significantly reduced viability in 5 of 9 cell lines as well as proliferation without altering the cell death rate or proportion of apoptotic cells in 2 of 4 cell lines, suggesting that a threshold level of YAP1 is needed to maintain cell growth and viability. Enforced expression of YAP1(S127A) increased resistance of neuroblastoma cells to chemotherapy and serum starvation compared to control cells. Intriguingly, supernatant analyses of YAP1(S127A)-expressing SH-EP and IMR-5 revealed increased glucose consumption rates and lactate production.

Conlusion:

Our findings delineate a metabolic switch triggered by YAP1-activation, which might enable mesenchymal-type neuroblastoma cells to evade first line treatment and gain resistance against chemotherapeutics and drugs leading to relapse development.