Involvement of mitogen-activated protein kinase in the cytokine-regulated phosphorylation of transcription factor GATA-1.

Gene-targeting experiments in transgenic mice have revealed an essential role for GATA-1 in the normal differentiation and development of erythroid cells. GATA-1 is phosphorylated in vivo on seven of its serine residues; the regulation and function of GATA-1 phosphorylation, however, is not understood. Here we demonstrate a role for MAP kinase (MAPK) signalling in the control of GATA-1 phosphorylation. We show that EGF-induced MAPK signalling results in the phosphorylation of ectopically expressed GATA-1 in COS cells. This phosphorylation can be positively or negatively regulated by genetic manipulation of the MAPK pathway through expression of constitutively activated, or dominant-negative, mutants of MAPK kinase (MAPKK), an upstream regulator of MAPK activity. In vitro phosphorylation experiments using purified MAPK and either recombinant GATA-1 or synthetic GATA-1 peptides suggest that GATA-1 is a MAPK substrate with MAPK phosphorylation occurring primarily on Ser26 and Ser178. We also show that GATA-1 is phosphorylated in factor-dependent haemopoietic progenitor cells in response to cytokine-induced signalling. Through the further use of a dominant-negative MAPKK mutant as well as chemical inhibitors of specific MAPKs, we identify ERK as an in vivo GATA-1 kinase. Finally, we demonstrate that mutation of serines 26 and 178 compromises the ability of GATA-1 to interact with the LIM-only protein LMO2 when both proteins are expressed in COS cells. These data implicate receptor-mediated signalling through the MAPK pathway as a control point in the regulation of transcription factor GATA-1.