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Department of Immunohematology and Blood Bank, Leiden University Medical Center, Leiden, The Netherlands
The IFN-stimulated response element (ISRE) is an important
conserved cis-acting regulatory element in the promoter
of MHC class I genes, but displays considerable locus-specific
nucleotide variation. In this report, the putative ISREs of classical
and nonclassical HLA class I genes were investigated for their
contribution to MHC class I transactivation. It is shown that IFN-
induced MHC class I transactivation through the ISRE of HLA-A, HLA-B,
HLA-C, and HLA-F. This is congruent with the binding of IFN regulatory
factor-1 to the ISREs of these loci upon IFN-
treatment. Sp1 was
shown to bind to the CG-rich sequences in the ISRE regions of HLA-B,
HLA-C, and HLA-G. The putative E box 5' of the ISRE in most HLA-B
alleles was shown to bind the upstream stimulatory factors (USF) 1 and
2. The Sp1 and USF binding sites did not influence IFN-
-induced
transactivation. However, the USF binding site played a suppressive
role in the constitutive expression of HLA-B. The locus-specific
transcriptional control through the ISRE could be an important
mechanism in the differential regulation of classical and nonclassical
MHC class I expression, which determines adequate Ag presentation upon
pathogenic challenge.
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