Presence and regulation of tyrosinase activity in human neuroblastoma cell variants in vitro

The human neuroblastoma cell line SK-N-SH comprises cells that undergo morphological and biochemical interconversion between a primitive sympathoblast and a variant, epithelial-like cell type which does not express the neuronal characteristics of the SK-N-SH cell line. Since neural crest cells, from which neuroblastomas are presumed to arise, can undergo transdifferentiation in culture from a neuronal phenotype into other cellular phenotypes, particularly into neurilemmal cells and melanocytes, the present study was undertaken to determine whether this capacity is preserved in malignant cells of the peripheral nervous system. Activities for tyrosinase, a melanocyte marker enzyme, and 2':3'-cyclic nucleotide phosphohydrolase, a Schwann-cell marker enzyme, were measured in clones of the two cell types. While no significant differences in 2':3'-cyclic nucleotide phosphohydrolase activity were measurable, tyrosinase activity was detectable only in the flattened neuroblastoma variant cell lines and was comparable to that in some human melanoma cell lines. The tyrosinase activity in neuroblastoma cell variants increased with cell density and was significantly elevated by melanocyte-stimulating hormone and 8-bromo-cyclic adenosine monophosphate, similar to that seen in melanoma cells in culture. Thus, our findings show that human neuroblastoma cells can undergo bidirectional transdifferentiation in vitro between a neuronal and a melanocyte phenotype, possibly reflecting a process which occurs in the patient.