title: PBX1 nuclear export is regulated independently of PBX-MEINOX interaction by PKA phosphorylation of the PBC-B domain.
abstract: The regulation of PBC protein function through subcellular distribution is a crucial evolutionarily conserved mechanism for appendage patterning. We investigated the processes controlling PBX1 nuclear export. Here we show that in the absence of MEINOX proteins nuclear export is not a default pathway for PBX1 subcellular localization. In different cell backgrounds, PBX1 can be imported or exported from the nucleus independently of its capacity to interact with MEINOX proteins. The cell context-specific balance between nuclear export and import of PBX1 is controlled by the PBC-B domain, which contains several conserved serine residues corresponding to phosphorylation sites for Ser/Thr kinases. PBX1 subcellular localization correlates with the phosphorylation state of these residues whose dephosphorylation induces nuclear export. Protein kinase A (PKA) specifically phosphorylates PBX1 at these serines, and stimulation of endogenous PKA activity in vivo blocks PBX1 nuclear export in distal limb mesenchymal cells. Our results reveal a novel mechanism for the control of PBX1 nuclear export in addition to the absence of MEINOX protein, which involves the inhibition of PKA-mediated phosphorylation at specific sites within the PBC-B domain.
authors.affiliation: Transcriptional Regulation in Development, DIBIT H San Raffaele, Milan, Italy.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Kilstrup-Nielsen
authors.forename: Massimo
authors.initials: M
authors.lastname: Alessio
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Zappavigna
mesh_terms: D016475:3T3 Cells; D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D007525:Isoelectric Focusing; D007700:Kinetics; D007930:Leucine; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011518:Proto-Oncogene Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D004268:DNA-Binding Proteins; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; C083400:PBX1 protein, human; D010769:Phosphothreonine; D010768:Phosphoserine; D017868:Cyclic AMP-Dependent Protein Kinases; D007930:Leucine