title: The Dictyostelium prestalk cell inducer DIF regulates nuclear accumulation of a STAT protein by controlling its rate of export from the nucleus.
abstract: Dd-STATc becomes tyrosine phosphorylated, dimerises and accumulates in the nuclei of Dictyostelium cells exposed to DIF, the chlorinated hexaphenone that directs prestalk cell differentiation. By performing cytoplasmic photobleaching of living cells, we show that DIF inhibits the nuclear export of Dd-STATc. Within Dd-STATc there is a 50 amino acid region containing several consensus CRM1 (exportin 1)-dependent nuclear export signals (NESs). Deletion of this region causes Dd-STATc to accumulate in the nucleus constitutively and, when coupled to GFP, the same region directs nuclear export. We show that the N-terminal-proximal 46 amino acids are necessary for nuclear accumulation of Dd-STATc and sufficient to direct constitutive nuclear accumulation when fused to GFP. Combining the photobleaching and molecular analyses, we suggest that DIF-induced dimerisation of Dd-STATc functionally masks the NES-containing region and that this leads to nett nuclear accumulation, directed by the N-terminal-proximal import signals. These results show that the regulated nuclear accumulation of a STAT protein can be controlled at the level of nuclear export and they also provide a better understanding of the mechanism whereby DIF directs cell type divergence.
authors.affiliation: School of Life Sciences, University of Dundee, MSI/WTB Complex, Dow Street, Dundee DD1 5EH, UK.
authors.forename: Masashi
authors.initials: M
authors.lastname: Fukuzawa
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Abe
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Williams
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism*; D004023:Dictyostelium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D006588:Hexanones / Q000378:metabolism* / Q000494:pharmacology; D028884:Karyopherins / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D038761:Photobleaching; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D050791:STAT Transcription Factors; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D000097606:Exportin 1 Protein
chemical_list: D049452:Green Fluorescent Proteins; D006588:Hexanones; D028884:Karyopherins; D008164:Luminescent Proteins; D019913:Nuclear Localization Signals; D015800:Protozoan Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; D050791:STAT Transcription Factors; D015534:Trans-Activators; D000097606:Exportin 1 Protein; C426825:STATc protein, Dictyostelium; C053433:1-((3,5-dichloro)-2,6-dihydroxy-4-methoxyphenyl)-1-hexanone