THE CONTROL OF GENE-EXPRESSION IN MELANOCYTES AND MELANOMAS

Powerful evidence exists that deregulation of cell type-specific gene expression is a major feature of the genesis of several cancers, with many oncogenic proteins known to possess transcription regulation prop erties. As a consequence of this deregulation, melanomas may ectopical ly express HLA-DR and also fail to express enzymes required for melani n synthesis, resulting in amelanotic melanoma. Recent work has demonst rated that these phenomena may be accounted for by the expression of a transcription factor called Brn-2, now known to be involved with the development of neural crest-derived tissues. Brn-2 is normally express ed at high levels in melanoblasts and melanomas but only at low levels in normal melanocytes. Brn-2 may act by competing with another transc ription factor, mi, necessary for normal melanocyte development.