Polycomb recruitment at the Class II transactivator gene

Area of Science:

• Epigenetics and Gene Regulation
• Molecular Immunology
• Chromatin Biology

Background:

• The Class II Transactivator (CIITA) is essential for Major Histocompatibility Class II (MHC II) gene expression.
• CIITA transcription is regulated by epigenetic mechanisms, including histone modifications like H3K27me3, catalyzed by EZH2 within PRC2.
• The recruitment mechanism of PRC2 to inducible promoters like CIITA pIV remains poorly understood.

Purpose of the Study:

• To identify DNA-binding proteins involved in PRC2 recruitment to the CIITA promoter IV (CIITA pIV).
• To elucidate the roles of Yin Yang 1 (YY1) and Jumonji domain containing protein 2 (JARID2) in regulating CIITA pIV expression.
• To investigate the formation of a novel regulatory complex involving YY1, JARID2, and PRC2.

Main Methods:

• Chromatin immunoprecipitation (ChIP) assays to assess protein binding and H3K27me3 levels at CIITA pIV.
• Co-immunoprecipitation (Co-IP) to confirm protein-protein interactions between EZH2, YY1, and JARID2.
• RNA interference (RNAi) to knockdown YY1 and JARID2 expression and analyze CIITA mRNA levels.

Main Results:

• YY1 and JARID2 were identified as binding partners of EZH2 at the CIITA pIV.
• IFN-γ stimulation led to YY1 dissociation and JARID2 binding increase at CIITA pIV, correlating with altered EZH2 and H3K27me3 levels.
• Knockdown of YY1 or JARID2 reduced EZH2 binding and H3K27me3 at CIITA pIV, while JARID2 knockdown increased CIITA mRNA.

Conclusions:

• YY1 and JARID2 play critical roles in recruiting PRC2 to the CIITA pIV, thereby regulating CIITA expression epigenetically.
• JARID2 is important for CIITA pIV silencing, and YY1 contributes to the recruitment of the PRC2 complex.
• A novel YY1-JARID2-PRC2 regulatory complex is proposed to explain differential PRC2 recruitment in inducible gene expression.