JunB, a major component of the AP-1 transcription factor, is known to act antagonistically to
c-Jun in transcriptional regulation and is proposed to be a negative regulator of cell
proliferation. Employing fibroblasts derived from E9. 5junB−/− mouse embryos we provide
evidence for a novel cell cycle promoting role of JunB. Despite a normal proliferation rate,
primary and immortalizedjunB−/− fibroblasts exhibited an altered cell cycle profile, which
was characterized by an increase in the population of S-phase cells, while that of cells in G …