DNA binding and transcriptional activation by a PDX1.PBX1b.MEIS2b trimer and cooperation with a pancreas-specific basic helix-loop-helix complex.
In pancreatic acinar cells, the HOX-like factor PDX1 acts as part of a trimeric complex with two TALE class homeodomain factors, PBX1b and MEIS2b. The complex binds to overlapping half-sites for PDX1 and PBX. The trimeric complex activates transcription in cells to a level about an order of magnitude greater than PDX1 alone. The N-terminal PDX1 activation domain is required for detectable transcriptional activity of the complex, even though PDX1 truncations bearing only the PDX1 C-terminal homeodomain and pentapeptide motifs can still participate in forming the trimeric complex. The conserved N-terminal PBC-B domain of PBX, as well as its homeodomain, is required for both complex formation and transcriptional activity. Only the N-terminal region of MEIS2, including the conserved MEIS domains, is required for formation of a trimer on DNA and transcriptional activity: the MEIS homeodomain is dispensable. The activity of the pancreas-specific ELA1 enhancer requires the cooperation of the trimer-binding element and a nearby element that binds the pancreatic transcription factor PTF1. We show that the PDX1. PBX1b.MEIS2b complex cooperates with the PTF1 basic helix-loop-helix complex to activate an ELA1 minienhancer in HeLa cells and that this cooperation requires all three homeoprotein subunits, including the PDX1 activation domain.
Liu
Y
Y
Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9148, USA.
MacDonald
R J
RJ
Swift
G H
GH
D002460:Cell Line; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D018257:Helix-Loop-Helix Motifs; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D010179:Pancreas; D011485:Protein Binding; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; C491172:MEIS2 protein, human; D015534:Trans-Activators; D014157:Transcription Factors; C084010:pancreatic and duodenal homeobox 1 protein; D004247:DNA