Retinoic acid- and staurosporine-induced bidirectional differentiation of human neuroblastoma cell lines

The differentiation pattern of two related human neuroblastoma cell lines, SK-N-SHF and SK-N-SHN, induced by retinoic acid and staurosporine was studied. Immunohistochemical and electron microscopic examination of the cells indicated that the SHF variant could undergo differentiation along a melanocytic route when treated with retinoic acid and to neuronal cells when treated with retionic acid and staurosporine together. Treatment of SHN cells with either or both these agents caused neuronal differentiation. The melanocytic pathway was characterized in part by the flattening of the cells, the appearance of melanocytic antigens and various forms of melanosomes, an increase in tyrosinase activity, and the absence of neuronal marker proteins. The neuronal route was typified by the development of long neuritic processes containing microtubules and numerous neurosecretory granules as well as by immunohistochemical reactions for neural cell adhesion molecule, synaptophysin, and neurofilament proteins. The significance of these results is discussed in terms of the differentiation responses of neuroblastoma cells to chemical agents as well as some of the factors involved in the regulation of phenotype expressions of these cells.