Regulation and function of JunB in cell proliferation

JunB is a member of the All (activator protein-1) family of dimeric transcription factors. It exerts a dual action on the cell cycle. it is best known as a cell proliferation inhibitor, a senescence inducer and a tumour suppressor. As for the molecular mechanisms involved, they largely involve both positive actions on genes such as the p16(INK4 alpha) cyclin-dependent kinase inhibitor and negative effects on genes such as cyclin D1 during the G(1)-phase of the cell cycle. However, JunB is also endowed with a cell-division-promoting activity, in particular via stimulation of cyclin A2 gene expression during S-phase. Strikingly, its role in G(2) and M has received little attention so far despite its possible role in the preparation of mitosis. This review addresses the known and possible mechanisms whereby JunB is implicated in the control of the different phases of the cell cycle.