Oncogenic BRAF V600E induces glial proliferation through ERK and neuronal death through JNK

Abstract

Background: Activating V600E in BRAF is a common driver mutation in cancers of multiple tissue origins, including melanoma and glioma. BRAF V600E has also been implicated in neurodegeneration. The present study aims to characterize BRAF V600E on cell death and survival in three major cell types of the CNS: neurons, astrocytes, and microglia. Methods : Multiple primary cultures and cell lines of glial cells and neurons were employed. BRAF V600E as well as BRAF WT expression was mediated by lentivirus or retrovirus. Blockage of downstream effectors were achieved by siRNA. Gene expression data from patients with Parkinson’s disease was analyzed. Results : In astrocytes and microglia, BRAF V600E induces cell proliferation, and the proliferative effect in microglia is mediated by activated ERK but not JNK. Conditioned medium from BRAF V600E -expressing microglia induced neuronal cell death. In neuronal cells, BRAF V600E directly induces cell death, through JNK but not ERK. We further show that BRAF-related genes are enriched in pathways in patients with Parkinson’s disease. Conclusions : Our study identifies distinct consequences mediated by distinct downstream effectors in dividing glial cells and in neurons following the same BRAF mutational activation and a causal link between BRAF-activated microglia and neuronal cell death that does not require physical proximity. It provides insight into a possibly important role of BRAF in neurodegeneration as a result of either dysregulated BRAF in neurons or its impact on glial cells.