Targeting mitosis‐regulating genes in cisplatin‐sensitive and ‐resistant melanoma cells: A live‐cell RNAi screen displays differential nucleus‐derived phenotypes

Chemoresistance in malignant melanoma remains an unresolved clinical issue. In the search for novel molecular targets, a live‐cell high‐content RNAi screen based on gene expression data was performed in cisplatin‐sensitive and cisplatin‐resistant MeWo melanoma cells, Mel‐28 cells and a melanocyte cell line. Cells were exposed to 91 siRNAs and distinct nucleus‐derived phenotypes such as cell division, cell death and migration phenotypes were detected by time‐lapse microscopy over 60 h. Using this approach, cisplatin‐sensitive and cisplatin‐resistant melanoma cells were compared by automated image analysis and visual inspection. In cisplatin‐sensitive MeWo melanoma cells, 14 genes were identified that showed distinct phenotype abnormalities after exposure to gene‐specific siRNAs. In cisplatin‐resistant MeWo cells, five genes were detected. Nine genes were detected whose knock‐down led to differential nuclear phenotypes in cisplatin‐sensitive and ‐resistant cells. In Mel‐28 cells, nine genes were identified which induced nuclear phenotypes including all eight genes which were identified in cisplatin‐resistant MeWo cells. An analogous RNAi screen on melanocytes revealed no detectable phenotype abnormalities after RNAi. Pathway analysis showed in cisplatin‐sensitive MeWo cells and Mel‐28 cells an enrichment of at least three genes in major mitotic pathways. We hereby show that siRNA screening may help to identify tumor‐specific genes leading to phenotype abnormalities. These genes may serve as potential therapeutic targets in the treatment of melanoma.