SEQUENCE COMPARISON OF PUTATIVE REGULATORY DNA OF THE 5' FLANKING REGION OF THE MYELOPEROXIDASE GENE IN NORMAL AND LEUKEMIC BONE-MARROW CELLS

Myeloperoxidase (MPO) is an enzyme which is exclusively expressed in i mmature myeloid cells with downregulation of gene expression occurring during granulocytic maturation. Levels of MPO RNA, protein, and enzym e activity differ, usually in a concordant fashion, among the various classes of acute leukemia and among different cases within a particula r class. One portion of the gene thought to be involved in regulation of MPO expression is the proximal 5' flanking region. To determine if mutations in this putatively regulatory region of the MPO gene might b e responsible for some of the differences in level of MPO expression a mong different cases or classes of acute leukemia, we compared the nuc leotide sequence of this part of the gene from 16 patients with acute leukemia, with DNA from normal human bone marrow cells and selected ot her neoplasms and cell lines. The sequence of this regulatory region w as found to be identical in cases of acute myeloid leukemia (AML) with that of normal DNA except for a dA to dG transition in the Alu region , 463 bases upstream from the transcription start site. This bass subs titution was seen in almost all cases of AML studied, regardless of th e level of MPO which they expressed. It was absent from normal human D NA obtained from various tissues, and cases of acute and chronic lymph ocytic leukemia, carcinoma of lung, and most cell lines examined. The bass substitution was also absent in a remission blood sample from one of the cases which showed the dA to dG transition in leukemic marrow, suggesting that the base substitution is a mutation rather than a pol ymorphism. Our results suggest thal mutations in promoter or enhancer DNA are not an important cause of the differences in level of MPO gene expression seen among different cases or different classes of AML. Ho wever, the base substitution we have detected could potentially serve as a useful marker for detection of residual disease in patients with AML following treatment.