PTEN restrains SHH medulloblastoma growth through cell autonomous and nonautonomous mechanisms.

Abstract

A third of patients with the pediatric cerebellar tumor Medulloblastoma (MB) have mutations that activate Sonic hedgehog (SHH) signaling (SHH-MB subgroup). The contribution of secondary mutations to tumor severity, however, is not clear. <i>PTEN</i> mutations are enriched in the SHH-1 subtype that has the lowest survival rate. Widespread heterozygous loss of <i>Pten</i> in two SHH-MB mouse models increases penetrance and accelerates onset of differentiated tumors. We delineated cellular and transcriptional changes that accelerate tumor growth and cause differentiation using a sporadic SHH-MB mouse model expressing oncogenic SmoM2 in rare cerebellar granule cell precursors (GCPs) and scRNA-seq analysis. Homozygous but not heterozygous sporadic loss of <i>Pten</i> resulted in rapid acceleration of tumor growth and end-stage disease by 40 days, compared to ~25% survival in control SmoM2 mice at 100 days. Heterozygous <i>PTEN</i> mutations, therefore, should negatively impact disease outcome primarily with germline mutations. Loss of <i>Pten</i> in normal or SmoM2-expressing GCPs increased proliferation and enhanced progenitor state initially, but by 12 days <i>Pten</i> mutant SmoM2 tumors were highly differentiated due to increased survival of non-proliferating GCPs. Furthermore, macrophage infiltration and cytotoxicity appeared reduced in differentiated regions of tumors lacking <i>Pten</i>, indicating cell nonautonomous changes could also contribute to accelerated tumor growth.