Mutations in receptor tyrosine kinase (RTK) growth factor receptors (epidermal growth factor receptor, platelet-derived growth factor receptor, MET and ERBB2), which result in downstream activation of the RAS/RAF/MEK/ERK mitogen-activated protein kinase (MAPK) pathway and PI(3)K/Akt pathway, are found in almost all high-grade gliomas and MAPK signaling is necessary for continued glioma maintenance. In addition, BRAF is mutated in the majority of low-grade gliomas and its expression and activity is significantly increased in the majority of high-grade gliomas. Although the importance of RTKs and RAS signaling in glioma development has been shown, the role of BRAF has yet to be characterized. We evaluated the effect of activated BRAF in glioma formation using the retroviral replication-competent avian leukosis virus long terminal repeat, splice acceptor (RCAS)/TVA system to transfer genes encoding activated forms of BRAF, KRas, Akt and Cre to nestin-expressing neural progenitor cells in Ink4a/Arf lox/lox mice in vivo. Although expression of activated BRAF alone is not sufficient for tumorigenesis, the combination of activated BRAF and Akt or BRAF with Ink4a/Arf loss is transforming. Interestingly, activated BRAF generates gliomas with characteristics similar to activated KRas in the context of Akt but not Ink4a/Arf loss. Our studies show a role for BRAF activation and signaling in glioma development and as potential target for glioma therapy.
Bibliographical noteFunding Information:
This work was supported by the Nevada Cancer Institute, the National Brain Tumor Foundation, and RSG-06–198–01-TBE from the American Cancer Society. We thank Nick Henderson and Robert Kirsh for animal husbandry. We also thank Eric Holland, Martin McMahon, and Ronald DePinho for the reagents. SLH designed the research; JPR, MWV and SLH performed the research; SB performed the pathological analysis; DLS and ARG provided technical support; JPR and SLH prepared the images and wrote the paper.
- BRAF; KRas