Differential Expression of Mitochondrial Biogenesis Markers in Mouse and Human SHH-Subtype Medulloblastoma

Medulloblastoma is a brain tumor that arises predominantly in infants and children. It is the most common pediatric brain malignancy. Around 25% of medulloblastomas are driven by constitutive activation of the Hedgehog signaling pathway. Hedgehog-driven medulloblastoma is often studied in the laboratory using genetic mouse models with overactive Hedgehog signaling, which recapitulate many of the pathological features of human Hedgehog-dependent tumors. However, we show here that on a molecular level the human and mouse HH-dependent MB are quite distinct, with human, but not mouse, tumors characterized by the presence of markers of increased oxidative phosphorylation and mitochondrial biogenesis. The latter suggests that, unlike for many other types of tumors, a switch to glycolytic metabolism might not be co-opted by human SHH-MB to perpetuate their survival and growth. This needs to be taken into consideration and could potentially be exploited in the design of therapies

BCOR expression in paediatric pineoblastoma

BCOR is expressed in a new brain tumour entity, i.e. ‘CNS tumour with BCOR internal tandem duplication’ (HGNET BCOR) but not in several other high grade paediatric brain tumours investigated. Immunohistochemical detection of BCOR expression may therefore serve as a potential diagnostic marker. Nevertheless, in rare paediatric glioma cases recurrent EP300-BCOR fusions were detected, which resulted in strong BCOR immunopositivity. We have therefore examined other, not analysed so far, types of central nervous system (CNS) tumours, pineoblastoma and germinoma, to assess a potential involvement of BCOR in these tumours. Levels of BCOR RNA expression were investigated by NanoString nCounter system analysis in a series of altogether 66 high grade paediatric tumours, including four pineoblastoma cases. Immunohistological detection of BCOR was performed in eight pineoblastoma, five germinoma and four atypical teratoid rhabdoid tumours (ATRTs), all located in the pineal region. We detected BCOR expression in all pineoblastomas, at the RNA and protein levels, but not in germinomas and ATRTs. Further analysis of pineoblastoma samples did not reveal the presence of either BCOR internal tandem duplication or BCOR fusion involvement. Positive immunohistological BCOR nuclear reaction in pineoblastoma may therefore differentiate this type of tumour from other high grade tumours located in the pineal region

Identification of a novel inherited ALK variant M1199L in the WNT type of medulloblastoma

Rearrangements involving the ALK gene were identified in a variety of cancers, including paediatric tumour neuroblastoma where presence of ALK expression is also associated with adverse prognosis. Microarrays data indicate that ALK is expressed in another paediatric tumour – medulloblastoma. Therefore, we investigated if the ALK gene is mutated in medulloblastoma and performed simultaneously the molecular profiling of tumours. Tumours from sixty-four medulloblastoma patients were studied for detection of ALK alterations in exons 23 and 25 using Sanger method. The molecular subtypes of tumours were identified by detection of mutations in the CTNNB1 gene, monosomy 6 and by immunohistochemistry using a panel of representative antibodies. Among three ALK variants detected two resulted in intron variants (rs3738867, rs113866835) and the third one was a novel heterozygous variant c.3595A>T in exon 23 identified in the WNT type of tumour. It resulted in methionine to leucine substitution at codon position 1199 (M1199L) of the kinase domain of ALK protein. Results of analysis using three in silico algorithms confirmed the pathogenicity of this single nucleotide variation. The same gene alteration was detected in both patient and maternal peripheral blood leukocytes indicating an inherited type of the detected variant. Presence of ALK expression in tumour tissue was confirmed by immunohistochemistry. The tumour was diagnosed as classic medulloblastoma, however with visible areas of focal anaplastic features. The patient has been disease free for 6 years since diagnosis. This is the first evidence of an inherited ALK variant in the WNT type of medulloblastoma, what altogether with presence of ALK expression may point towards involvement of the ALK gene in this type of tumours