Patients with Parkinson's disease (PD) generally have reduced risk of developing many types of cancers, except melanoma-a malignant tumor of melanin-producing cells in the skin. For decades, a large number of epidemiological studies have reported that the occurrence of melanoma is higher than expected among subjects with PD, and the occurrence of PD is reciprocally higher than expected among patients with melanoma. More recent epidemiological studies further indicated a bidirectional association, not only in the patients themselves but also in their relatives. This association between PD and melanoma offers a unique opportunity to understand PD. Here, we summarize epidemiological, clinical, and biological evidence in regard to shared risk factors and possible underlying mechanisms for these two seemingly distinct conditions.

Background Activating V600E in BRAF is a common driver mutation in cancers of multiple tissue origins, including melanoma and glioma. BRAFV600E has also been implicated in neurodegeneration. The present study aims to characterize BRAFV600E 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. BRAFV600E as well as BRAFWT 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, BRAFV600E induces cell proliferation, and the proliferative effect in microglia is mediated by activated ERK but not JNK. Conditioned medium from BRAFV600E-expressing microglia induced neuronal cell death. In neuronal cells, BRAFV600E 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.

No abstract