OR14-03 The Transcriptional Coactivation Function of EHMT2 Restricts Chronic Glucocorticoid Exposure Induced Insulin Resistance

Abstract

Glucocorticoids are required for metabolic adaptations during times of stress. However, chronic glucocorticoid exposure is associated with metabolic disorders such as insulin resistance. Glucocorticoids mainly convey their signals through an intracellular glucocorticoid receptor (GR). GR is a transcription factor that requires interactions with transcriptional coregulators to modulate the transcription of GR primary target genes, which in turn regulate specific aspects of physiology. Euchromatic Histone Methyltransferase 2 (Ehmt2) is a transcriptional coregulator for GR that can act as a corepressor or a coactivator. We found that glucocorticoid-induced insulin resistance was exacerbated when Ehmt2 levels were reduced in the liver. Intriguingly, this phenotype resulted from the transactivation function of Ehmt2. This is because a mutation at the lysine 182 automethylation site, which is required for the coactivation but not the corepression function of Ehmt2, results in similar exacerbated GC-induced insulin resistance. These results suggest that Ehmt2 coactivation dependent GR primary target genes restrict the extent of glucocorticoid-induced insulin resistance. Gene expression analysis identified Dusp4 (a.k.a. Mkp-2) as an Ehmt2 coactivation dependent GR-activated gene, which when overexpressed in liver, attenuated glucocorticoid-induced insulin resistance. Thus, we have identified a novel GR-Ehmt2-Dusp4 axis that plays a key role in controlling the extent of the development of insulin resistance. Notably, the classical view of how GC induce hepatic insulin resistance is that GR activates genes that inhibit insulin signaling and enhance hepatic gluconeogenesis. Our study, however, provides a revolutionary concept in which the extent of GC-induced insulin resistance is controlled by the balance of GR-activated genes that promote insulin sensitivity or insulin resistance.