Common distal elements orchestrate CIITA isoform-specific expression in multiple cell types.

Area of Science:

• Immunology
• Molecular Biology
• Epigenetics

Background:

• Major histocompatibility class II (MHC-II) expression is crucial for adaptive immunity.
• The MHC-II transactivator CIITA controls MHC-II expression, primarily via transcriptional regulation.
• CIITA expression utilizes distinct promoters (pI, pIII, pIV) depending on cell type and stimulation.

Purpose of the Study:

• To identify novel distal regulatory elements controlling CIITA transcription in B cells.
• To understand the mechanisms governing CIITA promoter choice in hematopoietic cells.

Main Methods:

• DNase I hypersensitivity screening to identify potential regulatory elements.
• Computational and biochemical analyses of identified regions.
• Reporter gene assays to assess regulatory element activity.
• Analysis of promoter interactions and DNA methylation patterns.

Main Results:

• Several novel distal regulatory elements interacting with CIITA promoters were identified in B cells and splenic dendritic cells (spDC).
• Four distal elements interacted with the pIII promoter in B cells and the pI promoter in spDC.
• In pI-knockout spDC, regulatory elements switched to interact with the pIII promoter.
• Significant DNA methylation was observed at the pI promoter in B cells, suggesting inaccessibility.

Conclusions:

• CIITA expression in hematopoietic cells is regulated by common distal elements.
• Promoter accessibility, influenced by epigenetic modifications like DNA methylation, plays a key role in determining CIITA promoter usage.
• These findings provide new insights into the regulation of immune response genes.