title: Multifunctional role of the Pitx2 homeodomain protein C-terminal tail.
abstract: Pitx2 is a newly described bicoid-like homeodomain transcription factor that is defective in Rieger syndrome and shows a striking leftward developmental asymmetry. We have previously shown that Pitx2 (also called Ptx2 and RIEG) transactivates a reporter gene containing a bicoid enhancer and synergistically transactivates the prolactin promoter in the presence of the POU homeodomain protein Pit-1. In this report, we focused on the C-terminal region which is mutated in some Rieger patients and contains a highly conserved 14-amino-acid element. Deletion analysis of Pitx2 revealed that the C-terminal 39-amino-acid tail represses DNA binding activity and is required for Pitx2-Pit-1 interaction and Pit-1 synergism. Pit-1 interaction with the Pitx2 C terminus masks the inhibitory effect and promotes increased DNA binding activity. Interestingly, cotransfection of an expression vector encoding the C-terminal 39 amino acids of Pitx2 specifically inhibits Pitx2 transactivation activity. In contrast, the C-terminal 39-amino-acid peptide interacts with Pitx2 to increase its DNA binding activity. These data suggest that the C-terminal tail intrinsically inhibits the Pitx2 protein and that this inhibition can be overcome by interaction with other transcription factors to allow activation during development.
authors.affiliation: Department of Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242, USA. brad-amendt@utulsa.edu
authors.forename: B A
authors.initials: BA
authors.lastname: Amendt
authors.forename: L B
authors.initials: LB
authors.lastname: Sutherland
authors.forename: A F
authors.initials: AF
authors.lastname: Russo
mesh_terms: D000015:Abnormalities, Multiple / Q000235:genetics*; D000595:Amino Acid Sequence; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D029721:Drosophila Proteins; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008957:Models, Genetic; D009687:Nuclear Proteins; D051761:Paired Box Transcription Factors; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D011388:Prolactin / Q000235:genetics; D011485:Protein Binding; D013577:Syndrome; D015534:Trans-Activators / Q000235:genetics; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation; D000097577:Homeobox Protein PITX2
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D051761:Paired Box Transcription Factors; D010446:Peptide Fragments; D011388:Prolactin; D015534:Trans-Activators; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2; C494187:POU1F1 protein, human; C056478:bcd protein, Drosophila; C101485:homeobox protein PITX1; C433629:homeobox protein PITX3