The tumor suppressor CREBBP and the oncogene MYCN cooperate to induce malignant brain tumors in mice

The tumor suppressor CREBBP (CREB binding protein) and the MYCN proto-oncogene are critically involved in brain development. Both genes are frequently mutated in the same tumor entities, including high-grade glioma and medulloblastoma. Therefore, we hypothesized that alterations in both genes cooperate to induce brain tumor formation. For further investigation, hGFAP-cre::CrebbpFl/Fl::lsl-MYCN mice were generated, which combine a Crebbp deletion with an overexpression of MYCN in neural stem cells (NSCs). Within eight months, these animals developed aggressive forebrain tumors that resulted in tumor-related death with a penetrance of 75 percent. The earliest tumors were detectable in the olfactory bulbs of seven-day-old mice. In order to examine the cellular biology of these tumors, single-cell RNA sequencing (scRNA-seq) was performed, which revealed high intratumoral heterogeneity. Data comparison with reference CNS cell types indicated the highest similarity of tumor cells with transit-amplifying or activated NSCs of the ventricular-subventricular zone (V-SVZ). Consequently, we analyzed V-SVZ NSCs of our mouse model with the aim of confirming that the tumors originate from this stem cell niche. Mutant V-SVZ NSCs showed significantly increased cell viability and proliferation as well as reduced glial and neural differentiation in vitro compared to control cells. In summary, we demonstrate the oncogenic potential of a combined loss of function of CREBBP and overexpression of MYCN in this cell population. This mouse model thus provides a valuable tool to study tumor-driving mechanisms in a key neural stem/progenitor cell niche. We investigated the transcriptomes of two tumors from a conditional knockout mouse model (hGFAP-cre::CrebbpFl/Fl::lsl-MYCNFl/Fl, tumors extracted from a 90 day old male and 100 days old female). This model combines a homozygous deletion of murine Crebbp and biallelic expression of exogenous human MYCN. Single-cell suspensions were generated from both tumors and further processed for single-cell RNA sequencing (scRNA-seq) using 10x Genomics technology.