Differentiation of B16-BL6 Melanoma Cells into Microtubule-Associated Protein 2-Positive Cells after Treatment with the Histone Deacetylase Inhibitors Butyrate and Trichostatin A

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Inhibition of histone deacetylase (HDAC) modulates the expression of many genes and induces cell cycle arrest, apoptosis, and differentiation in several cancer cell lines. Melanoma is a malignant phase of cutaneous melanocytes originally derived from the neural crest and is highly metastatic. A therapeutic agent capable of inducing differentiation of metastatic melanoma cells into a nonmalignant stage would be useful to prevent metastasis. We examined whether HDAC inhibitors can induce differentiation of the murine melanoma cell line B16-BL6 into neural-type cells in vitro. A morphologic change accompanied by extended dendrites was induced in melanoma cells after treatment with the HDAC inhibitors butyrate and trichostatin A (TSA). The altered morphology was similar to that of neural cells. Many of the extended dendrites fused with other dendrites of neighboring cells and had synapse-like knobs on their dendrites. These dendrites showed positive labeling with anti-α/β-tubulin and anti-L1 cell adhesion molecule (L1CAM) antibodies but were seldom stained with phalloidin, suggesting that the neural cell-related proteins were major components of the extended dendrites but that actin stress fibers were not. Furthermore, the mature neuron-specific cytoskeletal protein, microtubule-associated protein 2 (MAP2), was detected with the specific antibody in the extended dendrites of cells treated with butyrate and TSA. Butyrate treatment increased the levels of MAP2 and neural cell adhesion molecule (NCAM) mRNA expression in the cells. However, the treatment did not alter the expression of neurofilament light chain (NF-L) mRNA. The observations suggest that the differentiated cells were neural-type cells but not complete neural cells.