Atypical MAPK regulates translocation of GATA transcription factor in response to chemoattractant stimulation

Abstract

The Dictyostelium atypical MAPK Erk2 (a.k.a. ErkB) is required for chemotactic responses to external cAMP as individual amoeba aggregate and undergo a multicellular developmental program. External cAMP also stimulates the translocation of the GATA transcription factor, GtaC, a key regulator of developmental gene expression and a developmental timer of repeated cAMP stimulation of developing cells. In this study, atypical MAPK Erk2 was found to be essential for the translocation of GtaC in response to external cAMP as indicated by the cellular distribution of GFP-GtaC reporters. Erk2 was also demonstrated to mediate the translocation of GtaC in response to external folate, a signal that directs the foraging of amoeba for bacterial food sources. Erk1, the only other Dictyostelium MAPK, was not required for the GtaC translocation to either chemoattractant, indicating that GFP-GtaC is a kinase translocation reporter specific for atypical MAPKs. The translocation of GFP-GtaC in response to folate was absent in mutants lacking the folate receptor, Far1 (a.k.a. GrlL) or the coupled G protein, G4 subunit. Loss of GtaC function resulted in enhanced chemotactic movement to folate. Inspection of the GtaC primary sequence revealed four sites recognized as Erk2 preferred phosphorylation sites. The creation and analysis of GFP-GtaC mutants with alterations at these sites determined that these sites are required for translocation in response to folate. Consistent with the role of translocation for GtaC function certain combinations of these phosphorylation site alterations interfered with the ability of GFP-GtaC reporter to rescue aggregation of gtaC- cells. These findings provide the first evidence that atypical MAPKs can regulate transcription factors through specific phosphorylation sites in response to chemoattractants. The ability of different stimuli to regulate GtaC translocation through Erk2 indicates atypical MAPKs can regulate different cell fates in part through the translocation of transcription factors.