Characterization and retinal neuron differentiation of WERI-Rb1 cancer stem cells

PURPOSE The evidence is increasing that cancer stem cells (CSCs) expressing embryonic and neuronal stem cell markers are present in human retinoblastoma (Rb). This study was conducted to determine whether stem-like cancer cells (SLCCs) in Rb express retinal stem cell-related genes and whether SLCCs can directly differentiate into retinal neurons. METHODS The cancer stem cell characteristics in WERI-Rb1 cells were determined with Hoechst 33,342 staining, clone formation assay, and CD133 flow cytometry. The expression of embryonic stem cell and retinal stem cell-related genes was analyzed with real-time PCR and immunofluorescence. The SLCCs were induced to differentiate into retinal neurons by the addition of Dickkopf-related protein 1 and Lefty-A. RESULTS A small but persistent population of cells excluding Hoechst dye in a verapamil-sensitive manner exhibited a cancer stem cell-like phenotype. The SLCCs displayed highly clonogenic abilities and increased CD133 expression with isolation and expansion in culture in serum-free medium. By comparing the expression of stem cell markers, we found Oct3/4 was more highly expressed in the SLCCs than in human embryonic stem cells. Together with the properties of intrinsic retinal stem cell-related gene expression, we found SLCCs can be induced into neuron-like cells that express glial fibrillary acidic protein and rhodopsin (a photoreceptor cell marker). CONCLUSIONS These findings provide new insight into cancer stem cells and used a strategy of an artificial change of cancer stem cell fate with transcription factors.