Js. Beaty et al., FUNCTIONAL-EFFECTS OF A NATURAL POLYMORPHISM IN THE TRANSCRIPTIONAL REGULATORY SEQUENCE OF HLA-DQB1, Molecular and cellular biology, 15(9), 1995, pp. 4771-4782
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.