THE HEMOCHROMATOSIS FOUNDER MUTATION IN HLA-H DISRUPTS BETA(2)-MICROGLOBULIN INTERACTION AND CELL-SURFACE EXPRESSION

We recently reported the positional cloning of a candidate gene for he reditary hemochromatosis (HH), called HLA-H, which is a novel member o f the major histocompatibility complex class I family, A mutation in t his gene, cysteine 282 --> tyrosine (C282Y), was found to be present i n 83% of HH patient DNAs, while a second variant, histidine 63 --> asp artate (H63D), was enriched in patients heterozygous for C282Y, The fu nctional relevance of either mutation has not been described. Co-immun oprecipitation studies of cell lysates from human embryonic kidney cel ls transfected with wild-type or mutant HLA-H cDNA demonstrate that wi ld-type HLA-H binds beta(2)-microglobulin and that the C282Y mutation, but not the H63D mutation, completely abrogates this interaction, Imm unofluorescence labelling and subcellular fractionations demonstrate t hat while the wild-type and H63D HLA-H proteins are expressed on the c ell surface, the C282Y mutant protein is localized exclusively intrace llularly. This report describes the first functional significance of t he C282Y mutation by suggesting that an abnormality in protein traffic king and/or cell-surface expression of HLA-H leads to HH disease.