Oncogenic Ras expression increases cytoplasmic distribution and phosphorylation of CSE1L in B16F10 melanoma cells

Ras activation confers the transformation activities of melanocytic lesions and malignant progression of melanoma. The CSE1L/CAS (chromosome segregation 1-like/cellular apoptosis susceptibility) gene is located in 20q13, a chromosomal region that correlates with melanoma development. CSE1L is highly expressed in melanoma and correlated with cancer stage and the poor prognosis of the disease. We studied the relation of Ras activation and the cytoplasmic distribution and phosphorylation of CAS in melanoma cells. Immunoblotting showed B16F10 melanoma cells overexpressing Ras increased CSE1L phosphorylation. Immunofluorescence showed that phosphorylated CSE1L mainly distributed in the cytoplasm of B16F10 melanoma cells, and Ras overexpression resulted in increased cytoplasmic distribution of phosphorylated CSE1L. CSE1L knockdown decreased the phosphorylation of the extracellular signal-regulated kinase1/2 (ERK1/2) induced by Ras in B16F10 melanoma cells. In immunohistochemistry, the tumor cells of melanoma showed strong cytoplasmic phosphor-CSE1L staining, while nevus cells showed weak cytoplasmic phosphor-CSE1L staining. Our results indicated that phosphorylated CSE1L plays a role in modulating the signaling pathway and progression of melanoma harboring Ras mutation.