Analysis of the sequence polymorphism within class II transactivator gene promoters

Area of Science:

• Immunogenetics
• Molecular Biology
• Gene Regulation

Background:

• The Class II Transactivator (CIITA) is crucial for MHC class II gene expression.
• CIITA transcription is regulated by four cell-type-specific promoters (PI, PII, PIII, PIV).
• CIITA PIII is active in B cells; PIV is induced by interferon-gamma.

Purpose of the Study:

• To investigate sequence variability in CIITA promoters PIII and PIV.
• To determine if CIITA promoter polymorphisms contribute to differences in MHC class II expression levels.
• To assess the functional impact of detected CIITA PIV polymorphisms.

Main Methods:

• Isolation and sequencing of CIITA PIII and PIV fragments from healthy individuals and rheumatoid arthritis patients.
• Screening for sequence polymorphisms in PIII and PIV.
• Cloning of variable PIV fragments upstream of a luciferase reporter gene.
• Transfection into monocytes, melanoma, and HeLa cells, followed by interferon-gamma stimulation and promoter activity analysis.

Main Results:

• Single base pair substitutions were identified in 9% of CIITA PIV fragments, primarily upstream of known cis-acting elements.
• CIITA PIII showed no polymorphisms.
• Functional analysis revealed no significant differences in promoter activity despite PIV sequence variations across different cell types.

Conclusions:

• Sequence variability in CIITA promoters PIII and PIV is limited and does not significantly impact CIITA expression levels.
• Observed inter-individual differences in MHC class II expression are likely attributable to polymorphisms within the MHC class II promoters themselves, not CIITA.
• CIITA expression levels are generally consistent across the population.