Frequent interferon regulatory factor 1 (IRF1) binding at remote elements without histone modification.

Area of Science:

• * Molecular Biology
• * Epigenetics
• * Immunology

Background:

• * Transcriptional activators bind DNA and recruit cofactors to alter chromatin structure.
• * The interplay between DNA binding and cofactor recruitment in chromatin modification is not fully understood.
• * Interferon-gamma (IFNγ) signaling involves key transcription factors like STAT1 and IRF1.

Purpose of the Study:

• * To investigate whether DNA binding and cofactor recruitment by transcriptional activators are separable events.
• * To determine the role of STAT1 and IRF1 in IFNγ-induced chromatin modifications.
• * To characterize IFNγ-induced
• orphan sites
• and their associated regulatory mechanisms.

Main Methods:

• * Custom ChIP tiling array to map chromatin modifications.
• * Analysis of histone acetylation (H3ac, H4ac) and other modifications (H3K4me1, H3K4me2, H3K27me3).
• * Investigation of cofactor recruitment, including SMARCA4 (BRG1), CBP, and p300.

Main Results:

• * STAT1 recruitment to IRF1 sites induced histone acetylation.
• * IRF1 binding alone at
• orphan sites
• did not lead to inducible histone acetylation.
• * These orphan sites were often devoid of activating marks and associated with repressive marks.
• * IRF1 binding at orphan sites required SMARCA4 but lacked CBP/p300 corecruitment.

Conclusions:

• * Transcriptional activators can bind DNA independently of cofactor-mediated chromatin modification.
• * IRF1 can initiate enhanceosome formation without STAT1, but its ability to modify chromatin depends on local epigenetic cues.
• * The existence of
• orphan sites
• highlights context-dependent regulation of gene activation.