Evidence For Hmgn2 Involvement in Mouse Embryo Implantation and Decidualization.

BACKGROUND/AIMS: Hmgn2 is involved in regulating embryonic development, but its physiological function during embryo implantation and decidualization remains unknown. METHODS: In situ hybridization, real-time PCR, RNA interference, gene overexpression and MTS assay were used to examine the expression of Hmgn2 in mouse uterus during the pre-implantation period and explore its function and regulatory mechanisms in epithelial adhesion junction and stromal cell proliferation and differentiation. RESULTS: Hmgn2 was primarily accumulated in uterine luminal epithelia on day 4 of pregnancy and subluminal stromal cells around the implanting blastocyst at implantation sites on day 5. Similar results were observed during delayed implantation and activation. Meanwhile, Hmgn2 expression was visualized in the decidua. In uterine epithelial cells, silencing of Hmgn2 by specific siRNA reduced the expression of adhesion molecules Cdh1, Cdh2 and Ctnnb1 and enhanced the expression of Muc1, whereas constitutive activation of Hmgn2 exhibited the opposite effects, suggesting a role for Hmgn2 in attachment reaction during embryo implantation. Estrogen stimulated the expression of Hmgn2 in uterine epithelia, but the stimulation was abrogated by ER antagonist ICI 182,780. Further analysis evidenced that attenuation of Hmgn2 might eliminate the regulation of estrogen on the expression of Cdh1, Cdh2 and Ctnnb1. In uterine stromal cells, progesterone induced the accumulation of Hmgn2 which advanced the expression of Prl8a2 and Prl3c1, two well-known differentiation markers for decidualization, but did not affect the proliferation of stromal cells. Knockdown of Hmgn2 blocked the progesterone-induced differentiation of uterine stromal cells. Moreover, Hmgn2 might serve as an intermediate to mediate the regulation of progesterone on Hand2. CONCLUSION: Hmgn2 may play an important role during embryo implantation and decidualization.

Chromatin-associated HMG-17 is a major regulator of homeodomain transcription factor activity modulated by Wnt/beta-catenin signaling.

Homeodomain (HD) transcriptional activities are tightly regulated during embryogenesis and require protein interactions for their spatial and temporal activation. The chromatin-associated high mobility group protein (HMG-17) is associated with transcriptionally active chromatin, however its role in regulating gene expression is unclear. This report reveals a unique strategy in which, HMG-17 acts as a molecular switch regulating HD transcriptional activity. The switch utilizes the Wnt/beta-catenin signaling pathway and adds to the diverse functions of beta-catenin. A high-affinity HMG-17 interaction with the PITX2 HD protein inhibits PITX2 DNA-binding activity. The HMG-17/PITX2 inactive complex is concentrated to specific nuclear regions primed for active transcription. beta-Catenin forms a ternary complex with PITX2/HMG-17 to switch it from a repressor to an activator complex. Without beta-catenin, HMG-17 can physically remove PITX2 from DNA to inhibit its transcriptional activity. The PITX2/HMG-17 regulatory complex acts independently of promoter targets and is a general mechanism for the control of HD transcriptional activity. HMG-17 is developmentally regulated and its unique role during embryogenesis is revealed by the early embryonic lethality of HMG-17 homozygous mice. This mechanism provides a new role for canonical Wnt/beta-catenin signaling in regulating HD transcriptional activity during development using HMG-17 as a molecular switch.

The chromosomal protein HMGN2 mediates lipopolysaccharide-induced expression of ß-defensins in A549 cells.

Human ß-defensin-2 (HBD-2) is an antimicrobial peptide produced by the epithelial cells that plays an important role in innate and adaptive immunity. Here we report that high mobility group protein N2 (HMGN2), a member of the high mobility group superfamily that affects chromatin function, modulates the expression of HBD-2 in A549 cells treated by lipopolysaccharide. Mechanistically, HMGN2 prolongs the retention time and enhances the accumulation of nuclear factor κB p65 in the nucleus, and promotes the acetylation of p65 through increasing histone acetyltransferase activity and enhancing p65-Ser536 phosphorylation. Additionally, chromatin immunoprecipitation reveals that HMGN2 and p65 synergistically promote their specific binding to HBD-2 promoter, thereby affecting the downstream transcription. Taken together, these results suggest that HMGN2 acts as a positive modulator of nuclear factor κB signalling to promote lipopolysaccharide-induced ß-defensin expression.