DNA Binding and Transcriptional Activation by a PDX1·PBX1b· MEIS2b Trimer and Cooperation with a Pancreas-specific Basic Helix-Loop-Helix Complex

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52 Scopus citations

Abstract

In pancreatic acinar cells, the HOX-like factor PDX1 acts as part of a trimeric complex with two TALE class homeodomain factors, PBXlb 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.

Original languageEnglish (US)
Pages (from-to)17985-17993
Number of pages9
JournalJournal of Biological Chemistry
Volume276
Issue number21
DOIs
StatePublished - Jan 25 2001

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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