title: The Dictyostelium prestalk inducer DIF-1 directs phosphorylation of a bZIP transcription factor.
abstract: DIF-1, a chlorinated hexaphenone produced by developing Dictyostelium cells, induces prestalk differentiation. DimB is a bZIP transcription factor that accumulates in the nucleus upon exposure to DIF-1, where it directly activates transcription of DIF-responsive genes. The signaling steps upstream of DimB and downstream of DIF-1 are entirely unknown. Analysis by mass spectrometry shows that incubation with DIF-1 rapidly stimulates phosphorylation at several sites in DimB. We characterize the most highly responsive site, S590, which is located very close to the C terminus. A point mutation in this site, S590A, does not inhibit DimB nuclear accumulation in response to DIF. However, this seems likely to reflect functional redundancy with other sites; because a panel of chemical variants on the structure of DIF-1 show a correlation between their potencies as inducers of DimB nuclear accumulation and their potencies as inducers of phosphorylation at S590. Furthermore, the S590A mutant is fully active in mutant rescue of a dimB null strain, arguing against an alternative role in transcriptional activation of target genes. We conclude that i) DIF-1 directs phosphorylation at S590, ii) although it is not essential for nuclear accumulation in response to DIF-1 correlative evidence, based upon a panel of DIF-1 related molecules, suggests that this modification may play a redundant role in the process. iii) We also present evidence that the kinase activity, which phosphorylates S590, is non-nuclear and that this signalling pathway is, in part at least, independent of the DIF-regulated STATc activation pathway.
authors.affiliation: College of Life Sciences, Welcome Trust Biocentre, University of Dundee, UK.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yamada
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Kubohara
authors.forename: Haruhisa
authors.initials: H
authors.lastname: Kikuchi
authors.forename: Yoshiteru
authors.initials: Y
authors.lastname: Oshima
authors.forename: Hong-Yu
authors.initials: HY
authors.lastname: Wang
authors.forename: Susan
authors.initials: S
authors.lastname: Ross
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Williams
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000595:Amino Acid Sequence; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism; D004023:Dictyostelium / Q000737:chemistry / Q000166:cytology*; D006588:Hexanones / Q000494:pharmacology*; D008969:Molecular Sequence Data; D010766:Phosphorylation / Q000187:drug effects; D017354:Point Mutation; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D050791:STAT Transcription Factors / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000235:genetics / Q000378:metabolism
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D006588:Hexanones; D015800:Protozoan Proteins; D050791:STAT Transcription Factors; C053433:1-((3,5-dichloro)-2,6-dihydroxy-4-methoxyphenyl)-1-hexanone; D012694:Serine