REGULATION OF THE ERYTHROID TRANSCRIPTION FACTOR NF-E2 BY CYCLIC ADENOSINE MONOPHOSPHATE-DEPENDENT PROTEIN-KINASE

Activation of cyclic adenosine monophosphate (cAMP)-dependent protein kinase (A-kinase) promotes hemoglobin synthesis in several erythropoie tin-dependent cell lines, whereas A-kinase-deficient murine erythroleu kemia (MEL) cells show impaired hemoglobin production; A-kinase may re gulate the erythroid transcription factor NF-E2 by directly phosphoryl ating its p45 subunit or by changing p45 interactions with other prote ins. We have mapped the major A-kinase phosphorylation site of p45 to Ser(169); Ala substitution for Ser(169) resulted in a protein that was no longer phosphorylated by A-kinase in vitro or in vivo. The mutant protein formed NF-E2 complexes that bound to DNA with the same affinit y as wild-type p45 and functioned normally to restore beta-globin gene expression in a p45-deficient MEL cell line. Transactivation properti es of the (Ser(169) --> Ala) mutant p45 were also indistinguishable fr om wild-type p45 when Gal4-p45 fusion constructs were tested with a Ga l4-dependent reporter gene. Transactivation of the reporter by both mu tant and wild-type p45 was significantly enhanced when A-kinase was ac tivated by membrane-permeable cAMP analogs or when cells were cotransf ected with the catalytic subunit of A-kinase, Stimulation of p45 trans activation by A-kinase required only the N-terminal transactivation do main of p45, suggesting that A-kinase regulates the interaction of p45 with downstream effecters, (C) 1998 by The American Society of Hemato logy.