Isolation and functional analysis of keratinocyte-derived corepressors of liganded nuclear receptors

Date of Completion

January 2006


Biology, Molecular|Health Sciences, Toxicology|Health Sciences, Pharmacology




Keratinocyte gene expression is regulated by members of the nuclear receptor superfamily including retinoic acid receptors (RARs), retinoid X receptors (RXR), and peroxisome proliferator activated receptors (PPARs). In addition to ligand, nuclear receptor transcriptional activity is controlled by interaction with proteins, collectively known as coregulators, which function as corepressors or coactivators. To improve our understanding of coregulators expressed in epidermis, we screened a keratinocyte cDNA library for PPARα-interacting proteins. The screen yielded previously unknown proteins including two we designated 7a and 43a. We also report on NRBF-2, a longer variant of 7a. 7a and NRBF-2 target the AF-2 domains of nuclear receptors but exhibit quantitative differences in their functional interactions with RARs, RXRα, and PPARs. An NR box (nuclear receptor box) and CoRNR box (corepressor nuclear receptor box) contribute to, but are not solely responsible for, functional and physical association with agonist bound RXRα. They decrease the activity of liganded RXRα, but because of an autonomous activation domain do not completely repress it.^ 43a is a partial length clone of a Naf1α, also known as VAN. Both the partial length and full length clones are PPAR and RAR interacting proteins. The interaction is ligand dependent, receptor helix 12 dependent, and partially NR box dependent. These properties are typically associated with coactivators. However, Naf functions as a repressor of agonist bound PPARs.^ This adds 7a, NRBF-2, and Naf to the small but growing group of repressors of liganded nuclear receptors, such as LCoR and REA. Naf may also provide a connection between HIV, Nef, and PPARs. 7a, NRBF-2, and Naf all contain CoRNR boxes, suggesting that coregulators containing both motifs do not fit fully in either category. Our work here expands on the currently small group of NR box containing repressors of liganded nuclear receptors. This type of corepressor may serve to limit excessive or prolonged receptor activation. ^