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

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.

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Klein RH, Stephens DN, Ho H, Chen JK, Salmans ML, Wang W, Yu Z, Andersen B