SC-14 * ASYMMETRY-DEFECTIVE OLIGODENDROCYTE PROGENITORS AS POTENTIAL CELL-OF-ORIGIN OF HYPERACTIVATED RAF-INDUCED MALIGNANT ASTROCYTOMAS

Abstract

BACKGROUND: Studies show that the expression of an activating mutation of BRAF (BRAFV600E) in conjunction with Ink4a/Arf deletion, but not each alteration by itself, lead to formation of malignant astrocytoma (MA)-like tumors. Importantly, BRAFV600E occurs in 39% of pediatric MA and in 7.7% of adult glioblastomas with a preference for young adult patients, and the majority coincides with homozygous deletion of cyclin-dependent kinase inhibitor 2A (CDKN2A) encoding Ink4a/Arf. Responses to pharmacologic inhibition of BRAFV600E in melanoma patients were stunning but led to rapid resistance. A better understanding of the molecular mechanism by which activated Raf signaling transforms adult neural progenitors into high-grade MA cells is needed to overcome resistance. APPROACH AND RESULTS: We hypothesize that BRAFV600E transforms Ink4a/Arf-depleted neural progenitor cells, by disrupting their asymmetric cell division, thereby initiating a cascade of events that fails to restrict cell fate determinants during division, alters cell fate, enhances proliferation and allows for other changes associated with neoplastic transformation. We use a Cre inducible mouse model of BRAFV600E, the BRafCA allele, and of Ink4a/ARf (Ink4a/Arf-loxP) in combination with fluorescence-activated cell sorting to isolate neural progenitor cells from the adult mouse brain subventricular zone. Enriched neural progenitor populations are subjected in vitro modified to express BRAFV600E and deleted Ink4a/Arf by adenovirus-Cre infection. Cell-culture-based assays determine their rate of asymmetric cell division, self-renewal, proliferation and their differentiation capacity. CONCLUSION: BRAFV600E expression causes a cell-type specific decrease in asymmetric cell division in oligodendrocyte progenitor cells (OPC). Asymmetry-defective in vitro modified OPC and OPC-like cells isolated from a tumor cell line are capable of forming tumors when injected into mice. We will present data from our ongoing search for critical molecular regulators and pathway(s) associated with BRAFVE-mediated disruption of asymmetric cell division and malignant transformation.