Ajuba Functions as a Histone Deacetylase-dependent Co-repressor for Autoregulation of the Growth Factor-independent-1 Transcription Factor

Abstract

Growth factor independent-1 (Gfi1) is a zinc finger protein with a SNAG-transcriptional repressor domain. Ajuba is a LIM domain protein that shuttles between the cytoplasm and the nucleus. Ajuba functions as a co-repressor for synthetic Gfi1 SNAG-repressor domain-containing constructs, but a role for Ajuba co-repression of the cognate DNA bound Gfi1 protein has not been defined. Co-immunoprecipitation of synthetic and endogenous proteins and co-elution with gel filtration suggest that an endogenous Ajuba⅐Gfi1⅐HDAC multiprotein complex is possible. Active histone deacetylase activity co-immunoprecipitates with Ajuba or Gfi1, and both proteins depend upon histone deacetylases for full transcriptional repression activity. Ajuba LIM domains directly bind to Gfi1, but the association is not SNAG domain-dependent. ChIP analysis and reciprocal knockdown experiments suggest that Ajuba selectively functions as a co-repressor for Gfi1 autoregulation. The data suggest that Ajuba is utilized as a corepressor selectively on Gfi1 target genes.

The LIM protein Ajuba promotes adipogenesis by enhancing PPARγ and p300/CBP interaction

“…Ajuba further recruits Prmt5 and HDACs through its preLIM region to repress E-cadherin expression, a known Snail target gene. 17,18,20,21 Moreover, we demonstrated that Ajuba contains functional NR boxes and directly interacts with RARα, 22 where Ajuba functions as a co-repressor and negatively regulates RAR signaling. Here, we describe the novel findings that Ajuba interacts with PPARγ via its non-NR box module within the preLIM region and functions as a co-activator for PPARγ by recruiting p300/CBP via its LIM domain.…”

“…In the nucleus, Ajuba functions as a co-repressor for various transcription factors such as Gfi-1, Snail and ISI1 by recruiting HDACs and PRMT5. 17,18,20,21,41 We recently discovered that Ajuba contains three conserved functional nuclear receptor (NR) boxes mediating a direct interaction with RARα and functions as a typical co-repressor for RARα in a ligand-dependent manner. 22 Here, we demonstrate that Ajuba interacts with PPARγ by different mechanism: the conserved NR boxes of Ajuba do not contribute to the interaction between Ajuba and PPARγ, instead, a region in the preLIM is required for the interaction with PPARγ; Ajuba binds the DNA-binding domain of PPARγ in a ligand-independent manner.…”

“…16,19 In addition, the preLIM region also mediates the protein-protein interaction, such as HDACs and Prmt5. 20,21 Depending on cell types, Ajuba can be located near the membrane, in the cytoplasm and/or in the nucleus and the stimulation of signals or interaction with proteins will also change its localization in cells. [16][17][18]22 Ajuba functions as a scaffold involving assembly of multiple protein complexes to regulate cell adhesion, migration, mitosis, microRNA maturation, cell differentiation and tissue development.…”

“…[16][17][18]22 Ajuba functions as a scaffold involving assembly of multiple protein complexes to regulate cell adhesion, migration, mitosis, microRNA maturation, cell differentiation and tissue development. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Ajuba can directly participate in transcriptional regulation where it serves as a transcriptional co-repressor and downregulate gene expression. We lately identified Ajuba as a co-repressor for Snail and as an essential regulator of mesenchymal-epithelial transition and metastasis.…”

The transcription factor Gfi1 regulates G-CSF signaling and neutrophil development through the Ras activator RasGRP1

“…Gfi1 can bind consensus DNA target sequences by a C-terminal zinc-finger domain and repress transcription by its N-terminal SNAG domain, 15 in part by recruiting corepressors. [16][17][18][19] Besides acting as a transcriptional repressor, Gfi1 interacts with protein inhibitor of activated signal transducer and activator of transcription (STAT), which can bind to and inhibit STAT3 signaling. 20 As a result, Gfi1 can relieve STAT3 from protein inhibitor of activated STAT3-induced inhibition, resulting in enhanced STAT3 signaling.…”