Growth regulated expression of B‐MYB in fibroblasts and hematopoietic cells

Abstract

The B‐myb cDNA has extensive sequence similarities to the c‐myb protooncogene, but, at variance with c‐myb, it is expressed in cells other than hematopoietic cells. In this paper, we show that (1) B‐myb is expressed in mouse, human, and hamster fibroblasts; (2) B‐myb mRNA levels are growth‐regulated in both fibroblasts and peripheral blood mononuclear cells; (3) by its mode of growth regulation (peak of expression, behavior in G₁‐specific temperature sensitive (ts) mutants and in the presence of cycloheximide), B‐myb can be classified, like c‐myb, thymidine kinase, PCNA, and others, as a late growth‐regulated gene; (4) B‐myb mRNA levels decrease when HL‐60 cells are induced to differentiate; and (5) the increase in mRNA levels in serum‐stimulated cells is only partially explained by an increase in rate of transcription. The possibility that the B‐myb gene may be the equivalent in fibroblasts and epithelial cells of the c‐myb proto‐oncogene of hematopoietic cells is discussed.