mTORC1 promotes malignant large cell/anaplastic histology and is a targetable vulnerability in SHH-TP53 mutant medulloblastoma
Valentina Conti, … , Pietro L. Poliani, Rossella Galli
Valentina Conti, … , Pietro L. Poliani, Rossella Galli
Published October 21, 2021
Citation Information: JCI Insight. 2021;6(23):e153462. https://doi.org/10.1172/jci.insight.153462.
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Research Article Neuroscience Oncology

mTORC1 promotes malignant large cell/anaplastic histology and is a targetable vulnerability in SHH-TP53 mutant medulloblastoma

Abstract

Medulloblastoma (MB), one of the most malignant brain tumors of childhood, comprises distinct molecular subgroups, with p53 mutant sonic hedgehog–activated (SHH-activated) MB patients having a very severe outcome that is associated with unfavorable histological large cell/anaplastic (LC/A) features. To identify the molecular underpinnings of this phenotype, we analyzed a large cohort of MB developing in p53-deficient Ptch+/– SHH mice that, unexpectedly, showed LC/A traits that correlated with mTORC1 hyperactivation. Mechanistically, mTORC1 hyperactivation was mediated by a decrease in the p53-dependent expression of mTORC1 negative regulator Tsc2. Ectopic mTORC1 activation in mouse MB cancer stem cells (CSCs) promoted the in vivo acquisition of LC/A features and increased malignancy; accordingly, mTORC1 inhibition in p53-mutant Ptch+/– SHH MB and CSC-derived MB resulted in reduced tumor burden and aggressiveness. Most remarkably, mTORC1 hyperactivation was detected only in p53-mutant SHH MB patient samples, and treatment with rapamycin of a human preclinical model phenocopying this subgroup decreased tumor growth and malignancy. Thus, mTORC1 may act as a specific druggable target for this subset of SHH MB, resulting in the implementation of a stringent risk stratification and in the potentially rapid translation of this precision medicine approach into the clinical setting.

Authors

Valentina Conti, Manuela Cominelli, Valentina Pieri, Alberto L. Gallotti, Ilaria Pagano, Matteo Zanella, Stefania Mazzoleni, Flavia Pivetta, Monica Patanè, Giulia M. Scotti, Ignazio S. Piras, Bianca Pollo, Andrea Falini, Alessio Zippo, Antonella Castellano, Roberta Maestro, Pietro L. Poliani, Rossella Galli

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Figure 5

Enforced hyperactivation of mTORC1 in HH/HN CSCs increases tumor malignancy, induces an LC/A phenotype, and regulates MB subgroup specification by modulating the expression of subgroup-restricted markers.

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Enforced hyperactivation of mTORC1 in HH/HN CSCs increases tumor maligna...
(A) Western blot showing that mTORC1 hyperactivation in HH/HN RhebQ64L CSC lines also promotes the activation of mTORC2 (HH CSC line LB and HN CSC line L83). (B) Hyperactivation of RhebQ64L in classic HH CSCs (LB) give rise to tumors that grow faster and larger than controls (volume measured at 54 days after transplant for LB). The same hyperactivation in LC/A HN CSCs (L83) does not significantly affect the rate of tumorigenesis (volume measured at 83 days after transplant for L83). (C) H&E staining showing pS6 and p4EBP1 hyperactivation in tumor cells in MB derived from classic HH CSCs (LB) after transduction with RhebQ64L. HH RhebQ64L MB are endowed with typical LC/A features— e.g., nuclear molding, large cells (white arrow) and several mitotic figures (white arrowheads). The mTORC2 marker pNdrg1 is also strongly hyperactivated in HH RhebQ64L MB. The mTORC1 regulated gene Gpnmb is highly expressed in RhebQ64L MB. All scale bars: 50 μm. Quantification of the level of marker expression (shown as arbitrary units) is shown in the graphs (right panels). (D) The WNT-associated classifier β-catenin is significantly downregulated in RhebQ64L HH CSC-derived MB (CSC line LB), whereas markers typical of p53 mutant SHH MB, such as Yap1, N-Myc, Gli2, and Sox2, are upregulated. The Group 3 classifier c-Myc is also overexpressed in RhebQ64L HH CSC–derived MB. All scale bars: 50 μm. Quantification of the level of marker expression (shown as arbitrary units) is shown in the graphs (right panels). Quantitative data are presented as floating bars from minimum to maximum values, line at mean. Student’s t test, unpaired. See Supplemental Table 5 for detailed statistical analysis. *P < 0.05; **P < 0.01; ***P < 0.005.