The human leukocyte antigen A2 interferon-stimulated response element consensus sequence binds a nuclear factor...

Area of Science:

• Immunogenetics
• Molecular Biology
• Gene Regulation

Background:

• Human leukocyte antigen (HLA) class I genes possess promoter elements, including interferon-stimulated response elements (ISREs).
• Previous studies indicated that the HLA-A2 ISRE consensus sequence does not mediate interferon response.

Purpose of the Study:

• To investigate the function of the ISRE consensus sequence in the human HLA-A2 gene.
• To identify proteins binding to the HLA-A2 ISRE and characterize their role in gene expression.

Main Methods:

• Deletion analysis of the HLA-A2 ISRE sequence in K562 and Jurkat cells.
• Electrophoretic mobility shift assays (EMSAs) to detect protein binding to the HLA-A2 ISRE.
• Competition assays using ISRE sequences from HLA-B7 and ISG54 genes.
• Mass determination of the identified binding protein.

Main Results:

• Deletion of the HLA-A2 ISRE consensus sequence significantly reduced constitutive HLA-A2 gene expression.
• A constitutive binding protein, termed ISRE/CBP (105 kDa), specifically binds to the HLA-A2 ISRE.
• ISRE/CBP binding was not effectively competed by HLA-B7 or ISG54 ISRE sequences.
• Substitution with HLA-B7 or ISG54 ISRE sequences also reduced constitutive HLA-A2 expression.

Conclusions:

• The HLA-A2 ISRE consensus sequence is essential for constitutive expression of the HLA-A2 gene, independent of interferon response.
• ISRE/CBP is a novel, constitutively expressed binding protein for the HLA-A2 ISRE.
• ISRE/CBP may function as a positive transcriptional regulator for HLA-A2 and contribute to differential expression between HLA-A and HLA-B genes.