Cooperative Transcriptional Activation by Klf4, Meis2, and Pbx1

Department of Biochemistry and Molecular Genetics and Center for Cell Signaling, University of Virginia, Charlottesville, Virginia 22908, USA.
Molecular and Cellular Biology (Impact Factor: 4.78). 07/2011; 31(18):3723-33. DOI: 10.1128/MCB.01456-10
Source: PubMed


The Kruppel-like factor Klf4 is implicated in tumorigenesis and maintaining stem cell pluripotency, and Klf4 can both activate
and repress gene expression. We show that the Pbx1 and Meis2 homeodomain proteins interact with Klf4 and can be recruited
to DNA elements comprising a Klf4 site or GC box, with adjacent Meis and Pbx sites. Meis2d and Pbx1a activate expression of
p15Ink4a and E-cadherin, dependent on the Meis2d transcriptional activation domain. In HepG2 cells, reducing expression of endogenous
Meis2 or Pbx1 decreases p15 gene expression and increases the number of cells entering S phase. Although DNA binding by all
three proteins contributes to full cooperative activation, the sequence requirements for binding by Meis2 and Pbx1 are variable.
In the E-cadherin promoter, a Pbx-like site is required for full activation, whereas in the p15 promoter, the Klf4 site appears
to play the major role. Through a bioinformatics search we identified additional genes with conserved binding sites for Klf4,
Meis2, and Pbx1 and show that at least some of these genes can be activated cooperatively by Klf4 and Meis2/Pbx1. We suggest
a model in which genes with Klf4 sites can be cooperatively activated by Meis2/Pbx1 and Klf4, dependent primarily on recruitment
by Klf4. This provides a mechanism to modulate transcriptional regulation by the multifunctional Klf4 transcription factor.

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