The classic medulloblastoma (CMB) and the desmoplastic medulloblastoma (DMB) subtypes represent the major medulloblastoma variants. In contrast to CMB, DMB display high levels of the low-affinity nerve growth factor receptor p75(NTR) . Given the reports of a better clinical course of DMB, we hypothesized that p75(NTR) might act as a tumor suppressor in medulloblastomas. In a large set of medulloblastomas, p75(NTR) was screened for mutations, and its mRNA expression and the DNA methylation status of its 5'-region were assessed. p75(NTR) immunostainings were performed in wild-type murine cerebella and medulloblastomas arising in patched heterozygous mice, and murine cerebellar granule cell precursors (GCP) were analyzed in vitro. Medulloblastoma cells engineered to express p75(NTR) were characterized flow cytometrically and morphologically. One CMB displayed a mutation of the p75(NTR) coding sequence. p75(NTR) mRNA levels clearly delineated DMB and CMB; however, CpG island hypermethylation was excluded as the cause of low p75(NTR) expression in CMB. Sonic Hedgehog-treated GCP showed elevated p75(NTR) expression, and strong expression of p75(NTR) was detected in the external granule cell layer of wild-type mice and in murine ptc(±) medulloblastomas. CMB cells overexpressing p75(NTR) displayed a significant increase in apoptosis. In summary, our data link activated Hedgehog signaling in DMB with p75(NTR) expression and characterize p75(NTR) as a biologically relevant inductor of apoptosis in MB.
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