(786.3) HMGN2 regulates transcription factor activity through chromatin modifications and protein interactions, developmentally modulated by microRNA-23

Poster Board Number: A19

Brad Amendt (University of Iowa), Steven Eliason (University of Iowa), Dan Su (University of Iowa)

The chromatin-associated high mobility group protein N2 (HMGN2) regulates transcription factor activity through both chromatin and protein interactions. Several homeodomain and HMG-box domain transcription factors regulate development and differentiation and are modulated by protein interactions and epigenetic factors. We demonstrate that HMGN2 inhibits the activity of multiple transcription factors as a general mechanism to regulate early development. Bimolecular fluorescence complementation, pull-down and co-immunoprecipitation assays show HMGN2 directly interacts with Lef-1 through its HMG-box domain. Furthermore, electrophoretic mobility shift assays demonstrate that HMGN2 inhibits Lef-1 DNA binding activity. Thus, HMGN2 inhibits the transcriptional activities of Lef-1, Dlx2, FoxJ1 as well as Pitx2. Pitx2 and Lef-1 activate the Hmgn2 promoter and HMGN2 expression inhibits their transcriptional activation. Pitx2 and Hmgn2 associate with H4K5ac and H3K4me2 chromatin marks in the proximal Dlx2 promoter demonstrating Hmgn2 association with open chromatin. Hmgn2 expression is developmentally regulated however, the post-transcriptional mechanisms that regulate Hmgn2 expression remain unclear. We demonstrate that miR-23a and miR-23b directly target Hmgn2, promoting transcriptional activation of several gene promoters including the amelogenin promoter, regulated by Pitx2. Hmgn2 expression decreases correlating with increased miR-23 expression in craniofacial tissues as the murine embryo develops. Analyses of Hmgn2 LacZ expression demonstrate that Hmgn2 expression is gradually decreased during embryonic development. Ablation of Hmgn2 in mice results in increased amelogenin expression due to increased Pitx2, Dlx2, Lef-1 and FoxJ1 transcriptional activity. We demonstrate both post-transcriptional regulation of Hmgn2 by miR-23a/b and post-translational gene expression by Hmgn2 protein interactions. HMGN2 appears to regulate tooth development through its interaction with multiple transcription factors.

This work was supported by funds from the University of Iowa Carver College of Medicine and the National Institutes of Health grants DE13941, DE028527 and NIDCR T90/R90 training grant DE023520.



HMGN2 recruits transcription factors to open chromatin poised to bind to promoter sequences upon co-factor activation.