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Cofactors of LIM domain (CLIM) proteins modulate Wnt signaling and regulate corneal epithelial stem cell maintenance

ABSTRACT: Cofactors of LIM domain proteins (CLIM1 and CLIM2) are widely expressed transcriptional cofactors that are recruited to gene regulatory regions by DNA-binding proteins, including LIM domain transcription factors. In the cornea, epithelial specific expression of a dominant negative (DN) CLIM under the Keratin 14 (K14) promoter causes blistering, inflammation, epithelial hyperplasia and neovascularization, followed by epithelial thinning and subsequent epidermal-like differentiation of the cornea epithelium. This phenotype resembles aspects of limbal stem cell deficiency, suggesting that CLIM proteins may be involved in regulating cornea stem cell maintenance. Consistent with this notion, the K14-DN-Clim cornea epithelium has fewer progenitor cells, and altered proliferation dynamics during epithelial development. Differentially regulated genes in DN-CLIM corneas include those in pathways crucial for stem cell maintenance and regulation of proliferation. In vivo ChIP-Seq experiments in the cornea epithelium show that CLIM associates with DNA regulatory elements containing binding sites for HLH and other non-LIM homeodomain factors, and that many genes that are highly expressed in the limbal epithelium, as well as genes with known roles in stem cell maintenance, are directly regulated by CLIM cofactors. DN-CLIM decreases the expression of Wnt inhibitors, including the direct target Wnt5a, causing increased Wnt signaling in the limbal region of DN-CLIM corneas. Together our results indicate that CLIMs regulate cornea stem cell maintenance by controlling Wnt activity and suggest the possibility that this pathway may be altered in limbal stem cell deficiency.

ORGANISM(S): Mus musculus

PROVIDER: GSE59205 | GEO | 2016/04/28

SECONDARY ACCESSION(S): PRJNA254727

REPOSITORIES: GEO

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Project description:The nuclear LIM-only protein LMO4 is upregulated in breast cancer, especially estrogen receptor negative tumors, and its overexpression in mice leads to hyperplasia and tumor formation. Here, we show that deletion of LMO4 in the mammary glands of mice leads to impaired lobuloalveolar development due to decreased epithelial cell proliferation. With the goal of discovering potential LMO4-target genes, we also developed a conditional expression system in MCF-7 cells for both LMO4 and a dominant negative (DN) form of its co-regulator, Co-factor of LIM domains (Clim/Ldb/Nli). We then used DNA microarrays to identify genes responsive to LMO4 and DN-Clim upregulation. One of the genes common to both datasets was BMP7, whose expression is also significantly correlated with LMO4 transcript levels in a large dataset of human breast cancers, suggesting that BMP7 is a bona fide target gene of LMO4 in breast cancer. Inhibition of BMP7 partially blocks the effects of LMO4 on apoptosis, indicating that BMP7 mediates at least some functions of LMO4. Gene transfer studies show that LMO4 regulates the BMP7 promoter, and chromatin immunoprecipitation studies show that LMO4 and its co-factor Clim2 are recruited to the BMP7 promoter. Furthermore, we demonstrate that HDAC2 recruitment to the BMP7 promoter is inhibited by upregulation of LMO4 and that HDAC2 knockdown upregulates the promoter. These studies suggest a novel mechanism of action for LMO4: LMO4, Clim2 and HDAC2 are part of a transcriptional complex, and increased LMO4 levels can disrupt the complex, leading to decreased HDAC2 recruitment and increased promoter activity. Experiment Overall Design: We used the Tet-off system to establish several distinct MCF-7 cell clones, referred to as MCF7-LMO4-TetOff and MCF7-DN-Clim-TetOff cells, in which the expression of Myc-tagged LMO4 or DN-Clim was repressed by the presence of doxycycline in the medium. Total RNA was isolated from three distinct MCF7-LMO4-TetOff cell lines and three distinct MCF7-DN-Clim-TetOff cell lines in presence and absence of doxycycline after 6 days. Treatment with doxycycline To decrease variability, we pooled RNAs from three experiments for each of the three cell lines.

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Cofactors of LIM domain (CLIM) proteins modulate Wnt signaling and regulate corneal epithelial stem cell maintenance

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