15 - DISRUPTION OF FOXP3-EZH2 INTERACTION BY GENETIC MUTATION OR SIGNALING-INDUCED INACTIVATION REPRESENTS A NOVEL PATHOBIOLOGICAL MECHANISM IN INFLAMMATORY BOWEL DISEASE
(Room Pinyon 1/2)
20 Jan 18
8:00 AM
-
8:07 AM
Tracks:
Clinical and Research Challenges, Session III
Background: While FOXP3+ regulatory T cell (Treg) dysfunction has been linked to human inflammatory bowel disease (IBD), molecular mechanisms for disease pathophysiology are unclear. The transcription factor FOXP3 via histone methyltransferase EZH2 suppresses inflammation in mice. Here, we tested the hypothesis that a physical FOXP3-EZH2 protein interaction is essential for gene co-repressive function critical for human Treg physiological functions.
Methods: Disease-relevant human FOXP3 mutations by site-directed mutagenesis, T cell isolation from human blood donors and lamina propria of Crohn’s disease (CD) patients, Proximity Ligation Assay (PLA), confocal microscopy, co-immunoprecipitation (co-IP), Dual Luciferase Reporter (DLR) Assay, Chromatin-immunoprecipitation (ChIP), RT-PCR, Immunofluorescence and Fluorescence-activated Cell Sorting. Results: PLA, confocal imaging and co-IP studies revealed that constitutive FOXP3-EZH2 interaction was uniquely abrogated by early-onset IBD-associated FOXP3 cysteine 232 mutation in contrast to IPEX-FOXP3 variants. Furthermore, FOXP3-C232 mutant displayed impaired repression of IL17 and IFNG genes via DLR and ChIP-PCR respectively, indicative of compromised Treg-physiologic function. Exploring a generalizable mechanism, IL-6 impaired FOXP3-EZH2 interaction in a manner that correlated with increased tyrosine phosphorylation of FOXP3. Notably, IL-6-induced effects were reversed by a clinically available JAK1/2 inhibitor ruxolitinib. Remarkably, in lamina propria-derived CD4+ T cells, reduced FOXP3-EZH2 complex was a feature of CD patients in contrast to non-CD control subjects.
Conclusions: Destabilized FOXP3-EZH2 protein interaction and consequent impairment of EZH2-mediated co-repressor function may drive the pathological characteristics of intestinal inflammation. Our study indicates potential therapeutic approaches and mechanisms for improving Treg function during IBD pathogenesis via stabilizing FOXP3-EZH2 interaction.