FUNCTIONAL-EFFECTS OF A NATURAL POLYMORPHISM IN THE TRANSCRIPTIONAL REGULATORY SEQUENCE OF HLA-DQB1

DNA sequence polymorphism in the genes encoding HLA class II proteins accounts for allelic diversity in antigen recognition and presentation and, thus, in the role of these cell surface glycoproteins as determi nants of the scope of the T-cell repertoire. In addition, sequence pol ymorphism in the promoter-proximal transcriptional regulatory regions of these genes has been described, particularly for the HLA-DQB1 locus , where these differences may contribute to variation in locus- and al lele-specific expression. In this study, we measured the effect of suc h regulatory sequence polymorphism on the expression of endogenous all eles of DQB1 in heterozygous cells. Quantitative reverse transcriptase -mediated PCR analysis showed that expression of the DQB10301 allele responded more rapidly to gamma interferon induction than that of DQB1 0302. We have analyzed functional effects of a prominent allelic poly morphism that consists of a TG dinucleotide present between the W and X(1) consensus elements in the DQB10302 allele but missing in the DQB 10301 allele. The dominant effect of this polymorphism was to introdu ce a variation in the spacing between the W and X(1) elements of these two alleles, A secondary compensatory effect was specific for the TG dinucleotide itself, which was essential for the binding of a nuclear protein complex to the 0302 regulatory region immediately 5' of the X (1) element. Derivatives of the DQB1 5' regulatory region were used to drive expression of the chloramphenicol acetyltransferase gene in tra nsient transfections of human B-lymphoblastoid and gamma interferon-tr eated melanoma cell lines, demonstrating that the additional spacing b etween the W and X(1) elements caused by the presence of the TG dinucl eotide in the 0302 allele resulted in reduced expression compared wit h that driven by the 0301 fragment; this difference overshadowed an u p-regulating effect on expression which corresponded to the binding of the TG-dependent nuclear protein complex. The presence of this polymo rphism in multiple HLA-DQB1 alleles and in several species suggests se lection for two alternative transcriptional regulatory mechanisms infl uencing expression of alleles of the same HLA locus.