10050-TB-1 ADDITIONAL RAS/MAPK PATHWAY ACTIVATION ALLOWS CELLS TO DIFFERENTIATE DURING TUMORIGENESIS.

Abstract Activation of the RAS/MAPK pathway has been introduced in most of the glioblastoma models reported to date. To examine the roles of this pathway in tumorigenesis from different cells of origin, we differentiated human induced pluripotent stem cells (hiPSCs) with CDKN2A/2B null, PTEN null, and TERT promoter mutation (TPM), which we have previously generated, into neural stem cells (NPCs) and astrocytes, and also prepared cell lines with lentiviral EGFRvIII overexpression in both. 4 cell lines were transplanted into the brains of immunodeficient mice, and differences in tumorigenesis were compared between NPCs and astrocyte states with and without MAPK/RAS pathway activity. In NPCs, overexpression of EGFRvIII significantly shortened the time required for tumorigenesis. In Astrocytes, however, tumor formation was observed only in cells with EGFRvIII overexpression. RNA sequencing revealed the primary spheres formed from the tumors with EGFRvIII overexpression clustered similarly regardless of whether they were derived from NPCs or astrocytes, suggesting that similar tumors were formed from both sources. To further clarify the effect on the RAS/MAPK pathway, we prepared CDKN2A/2B null, PTEN null, TPM, and NF1 null iPSCs. Tumor formation was also confirmed when the cell line was differentiated into astrocytes and transplanted into immunodeficient mice. Although the cell of origin of glioblastoma is still controversial, recent reports indicate that tumorigenesis itself starts from undifferentiated cells. Our results suggest that the RAS/MAPK pathway activation in glioblastoma enhances tumorigenesis, allows cells to differentiate during the process, and also enables cells to transform even after differentiation by acquiring the activation.