OTX2 drives medulloblastoma proliferation via direct regulation of cell cycle genes and inhibits differentiation

The transcription factor OTX2 has been implicated as an oncogene in medulloblastoma, which is the most common malignant brain tumor in children. It is highly expressed in most medulloblastomas and amplified in a subset of them. The role of OTX2 in medulloblastoma and its downstream targets are unclear. Therefore, we generated D425 medulloblastoma cells in which we can silence endogenous OTX2 by inducible shRNA. Silencing of OTX2 strongly inhibited cell proliferation and resulted in a neuronal-like differentiation. Expression profiling of time courses after silencing showed a progressive change in gene expression for many cellular processes. Down regulated genes were highly enriched for cell cycle and visual perception genes, while up regulated genes were enriched for genes involved in development and differentiation. This shift in expression profiles is reminiscent to changes described to occur during normal cerebellum development. OTX2 is expressed in proliferating granular progenitor cells, but the expression diminishes when these cells exit the cell cycle and start differentiating. ChIP-on-chip analyses of OTX2 in D425 cells showed that cell cycle and perception genes were direct OTX2 targets, while regulation of most differentiation genes appears to be indirect. These analyses provide the first insight in the molecular network of OTX2, demonstrating that OTX2 is essential in medulloblastoma and directly drives proliferation by regulating the expression of cell cycle genes. Since many of these genes also correlate in expression with OTX2 in primary tumors, they might be potential targets for therapy in medulloblastoma patients.

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Bunt J, Hasselt NE, Zwijnenburg DA, Hamdi M, Koster J, Versteeg R, Kool M