Functional Landscape of PCGF Proteins Reveals Both RING1A/B-Dependent-and RING1A/B-Independent-Specific Activities

Area of Science:

• Epigenetics and chromatin biology
• Molecular and cellular biology
• Gene regulation

Background:

• Polycomb repressive complexes 1 and 2 (PRC1 and PRC2) are crucial for cell identity.
• PRC1 mediates H2Aub1 deposition via RING1A/B E3 ligases.
• PRC1 comprises six distinct subcomplexes based on PCGF protein composition, but their specific functions are largely unknown.

Purpose of the Study:

• To investigate the specific activities of different PRC1 subcomplexes.
• To determine the roles of various PCGF proteins in gene regulation.
• To elucidate the mechanisms of PRC1 subcomplex recruitment to target genes.

Main Methods:

• Biochemical characterization of PRC1 subcomplexes.
• Analysis of PCGF protein interactions and functions.
• Chromatin immunoprecipitation (ChIP) assays to assess gene targeting.
• Investigation of recruitment mechanisms for PCGF3 and PCGF6 complexes.

Main Results:

• PCGF1 and PCGF2 exhibit functional compensation, while other PCGF proteins display high target gene specificity.
• PCGF2 is associated with transcriptional repression.
• PCGF3 and PCGF6 associate with actively transcribed genes and can be recruited independently of RING1A/B activity.
• PCGF6 recruitment depends on MGA-MAX and E2F6-DP1 subunits.
• PCGF3 recruitment requires interaction with the USF1 transcription factor.

Conclusions:

• PRC1 subcomplexes exhibit specialized roles in gene regulation beyond general repression.
• Specific PCGF proteins confer distinct targeting and functional properties to PRC1.
• Certain PRC1 subcomplexes (PCGF3, PCGF6) can engage with active gene regulatory processes, sometimes independent of canonical PRC1 activity.