Abstract
Simple SummaryMedulloblastoma (MB) is the most common malignant brain tumor in childhood. Currently, MB is assigned in four molecular subgroups (SHH, WNT, Group 3, and Group 4) and subtyped in 12 variants. The alpha subtype of the SHH subgroup bears TP53 mutation and is considered very high risk by the World Health Organization (WHO). In the current study, we have investigated the role of YAP1 expression in SHH MBs. Herein, we show: (1) SHH MB patients genotypically profiled as resistant to SMOi and the aggressive alpha subtype overexpress YAP1; (2) SHH-like cell lines bearing TP53 mutation show improved responsiveness to SMOi upon YAP1 depletion; (3) Sonidegib (smoothened inhibitor) and Verteporfin (YAP1 inhibitor) synergize at specific doses; (4) distinct cell populations in the single-cell RNA-seq patient setting express YAP1 and SMO.Advances in genomics have led to the identification of twelve relevant molecular subtypes within medulloblastoma (MB). The alpha subtype of Sonic hedgehog-driven MB is resistant to therapy (including smoothened inhibitors) due to activation of genes from the non-canonical SHH pathway, such as MYCN, YAP1, or TP53. Using retrospective cohort microarray data, we found that YAP1 is overexpressed in SHH alpha MB and patients profiled as resistant to SMO inhibitors compared to good responders. Here, we performed YAP1 depletion via CRISPR/Cas9 in two in vitro models of SHH-like MB cells and found that this protein is involved in responsiveness to the SMO inhibitor regarding proliferation, apoptosis, and colony formation. Further, considering the synergic combination of YAP1 depletion with SMO inhibition, we assessed single-cell RNA-seq data from five patients and found that SMO and YAP1 are enriched within cells of SHH MB. Importantly, our data suggest that YAP1 is not only a reliable biomarker for cellular response to SMOi but may indicate prospective testing of combination therapy using YAP1 and SMO inhibitors in preclinical models of SHH MB.
Highlights
The Context of YAP1 in Sonic hedgehog pathway (SHH) MedulloblastomaMedulloblastoma (MB) is a heterogeneous malignant brain tumor that commonly affects infants and children
We have withdrawn single-cell data from public data sets explored in recent studies and found that SMO and YAP1 are enriched in SHH medulloblastoma (SHH MB) cells
YAP1 is overexpressed in predicted non-responsive SHH MB patients and SHH alpha subtype patients
Summary
The Context of YAP1 in SHH MedulloblastomaMedulloblastoma (MB) is a heterogeneous malignant brain tumor that commonly affects infants and children. In the context of SHH MB, resistance to targeted therapy using agents such as SMO inhibitors (e.g., Sonidegib and Vismodegib) is frequently associated with alterations in genome and transcriptome, such as TP53 mutation and transcriptional activation of oncogenes such as MYCN and YAP1 [1,4,5]. Other authors showed that YAP1 is induced by smoothened, a G-protein coupled receptor and transmembrane protein of the Sonic hedgehog pathway (SHH) It is still unclear whether it is a single-axis canonical activation or if YAP1 is induced by non-canonical effectors downstream of SMO [7]. We have assessed transcriptomic public records of two microarray datasets and found that YAP1 is explicitly overexpressed in patients profiled as poor responders to SMO inhibitors (e.g., Sonidegib, Vismodegib) and in SHH medulloblastoma subtype alpha. These findings open new avenues for synergic combination therapy utilizing a YAP1 inhibitor in association with an SMO inhibitor
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