REGULATION OF NF-E2 ACTIVITY IN ERYTHROLEUKEMIA CELL-DIFFERENTIATION

The erythroid transcription factor NF-ES is an obligate heterodimer co mposed of two different subunits (p45 and p18), each containing a basi c region-leucine zipper DNA binding domain, and it plays a critical ro le in erythroid differentiation as an enhancer-binding protein for exp ression of the beta-globin gene. We show here that dimethyl sulfoxide treatment of wild-type murine erythroleukemia cells, but not a mutant clone of dimethyl sulfoxide-resistant cells, increases NF-E2 activity significantly, which involves both up-regulation of DNA binding and tr ansactivation activities, Both activities were reduced markedly by tre atment of cells with a-aminopurine but not by genistein, Activation of the Ras-Raf-MAP kinase signaling cascade increased NF-E2 activity sig nificantly, but this was suppressed when MafK was overexpressed, Domai n analysis revealed an activation domain in the NH2-terminal region of p45 and a suppression domain in the basic region-leucine zipper of Ma fK. These findings indicate that induction of NF-ES activity is essent ial for erythroid differentiation of murine erythroleukemia cells, and serine/threonine phosphorylation may be involved in this process. In addition, they also suggest that a MafK homodimer can suppress transcr iption, not only by competition for the DNA binding site, but also by direct inhibition of transcription, Hence, MafK may function as an act ive transcription repressor.