Characterization of a novel OTX2-driven self-renewal program in Group 3 and Group 4 medulloblastoma [expression]

Medulloblastoma (MB) is the most common malignant primary pediatric brain cancer. Among the most aggressive subtypes, Group 3 and Group 4 originate from stem/progenitor cells, frequently metastasize, and often display the worst prognosis, yet, as the names imply, we know the least about the molecular mechanisms driving their progression. Here, we show that the transcription factor orthodenticle homeobox 2 (OTX2) promotes self-renewal while inhibiting differentiation in vitro and increases tumor-initiating capacity from MB stem cell populations in vivo. Characterization of the OTX2 regulatory network revealed a novel relationship between OTX2 and genes associated with multiple axon guidance signaling pathways in Group 3 and Group 4 MB stem/progenitor cells. In particular, OTX2 levels were negatively correlated with semaphorin (SEMA) signaling, as expression of 9 SEMA pathway genes is upregulated following OTX2 knockdown with some being potential direct OTX2 targets. Importantly, this negative correlation between OTX2 and SEMA pathway genes was also observed in patient samples, with lower expression of SEMA4D associated with poor outcome in Group 3 and 4 tumors. Functional studies using established and newly derived MB cell lines demonstrated that increased levels of SEMA pathway genes are associated with decreased self-renewal and growth, and that RHO signaling, known to mediate the effects of SEMA genes, is contributing to the OTX2 KD phenotype. Our study provides critical mechanistic insight into the networks controlled by OTX2 in self-renewing MB cells and reveals novel roles for axon guidance genes and their downstream effectors as putative tumor suppressors and therapeutic targets in Group 3 and Group 4 MB.

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Stromecki M, Tatari N, Morrison LC, Kaur R, Zagozewski J, Palidwor G, Ramaswamy V, Skowron P, Wölfl M, Milde T, Del Bigio MR, Taylor MD, Werbowetski-Ogilvie TE