B-MYB TRANSCRIPTIONAL REGULATION AND MESSENGER-RNA STABILITY DURING DIFFERENTIATION OF NEUROBLASTOMA-CELLS

B-myb and c-myb expression is high in neuroblastoma cells and declines during retinoic acid-induced differentiation. We show here that B-myb downregulation during retinoic acid-induced differentiation of LAN-5 neuroblastoma cells occurs at the transcriptional level. In addition, we measured B-myb and c-myb messenger RNA half-lives, and found that, unlike c-myb, B-myb messenger RNA was remarkably stable (>10 h). Inhib ition of protein synthesis by treatment with cycloheximide increased B -myb messenger RNA levels, suggesting that one or more labile proteins act as repressors of B-myb transcription, In the same cell line, bloc king protein synthesis decreased the level of c-myb mRNA under both no rmal and differentiative conditions. Thus, B-myb and c-myb undergo sim ilar transcriptional regulation, but there are specific differences in the stability of their messenger RNAs and in the mechanisms through w hich their transcription is controlled. These differences could reflec t different functional roles played by c-myb and B-myb in neuroblastom a cells. (C) 1995 Academic Press, Inc.