Retinoic acid receptor-nuclear factor-interleukin 6 antagonism - A novel mechanism of retinoid-dependent inhibition of a keratinocyte hyperproliferative differentiation marker

Retinoids inhibit the expression of migration inhibitory factor-related protein-8 (MRP-8), a marker of hyperproliferative or abnormal keratinocyte differentiation, in a retinoic acid receptor (RAR)-dependent manner in various cell culture systems. MRP-8 expression is also down-regulated in vivo in psoriatic lesions after topical application of an anti-psoriatic RAR beta/gamma-selective synthetic retinoid, tazarotene. We demonstrate that an MRP-8 promoter linked to a chloramphenicol acetyltransferase reporter (MRP8CAT) faithfully replicates the differentiation-specific regulation of the endogenous keratinocyte MRP-8 gene. Further, interferon gamma and serum-induced expression of MRP8CAT is inhibited by retinoid receptors in a ligand-dependent manner, We also show that NF-IL6 acts as a transcriptional enhancer of MRP-8, and that RARs inhibit MRP8CAT by inhibiting the enhancer action of nuclear factor-interleukin-6 (NF-IL6), The NF-IL6 antagonism function of RAR is a complex of the core of the DNA binding domain and the hydrophobic zipper region. This manuscript identifies NF-IL6 as another transcription factor, in addition to API, whose activity is inhibited by RAR in a ligand-dependent manner, The interdiction of NF-IL6-dependent signal transduction pathway by RARs may explain some of the therapeutic effects of retinoids in inflammatory and proliferative diseases.