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Evidence for a pretranslational defect in hereditary and acquired myeloperoxidase deficiency
A Tobler1, M E Selsted, C W Miller
1Department of Medicine, UCLA Medical Center, Los Angeles, CA 90024.
Abstract:
Myeloperoxidase (MPO) is a heme containing enzyme involved in the oxygen-dependent microbicidal activity of human polymorphonuclear leukocytes (PMN). Complete hereditary and acquired MPO deficiencies are defined as lack of peroxidase activity in PMN. Using this criterion, we studied a patient with complete hereditary MPO deficiency, and a MPO deficient variant cell line of HL-60 (HL-60-A7), which we used as a model for acquired MPO deficiency. Western blot analysis showed complete absence of mature and precursor protein of MPO both in PMN from the patient and in HL-60-A7 cells. PMN from both parents had one half of normal levels of these proteins. To study further the molecular basis of this defect, we isolated an intron specific probe for MPO and used it and a cDNA probe. Both normal human bone marrow cells and the promyelocytic HL-60 leukemia cells contained MPO mRNA species of 2.8, 3.3, approximately 4, and greater than 8 kilobase (kb). The transcripts of greater than 8 and approximately 4 kb contained sequences hybridizing to a probe specific for intron 7 of the MPO gene. Bone marrow cells of the MPO deficient patient contained two species of heterogeneous nuclear (hn) RNA of greater than 8 and approximately 4 kb, but only trace amounts of the normal sized 3.3 kb MPO mRNA and undetectable 2.8 kb MPO mRNA. HL-60-A7 cells contained both greater than 8 and approximately 4 kb hnRNA, but only small amounts of normal sized 2.8 kb MPO mRNA and undetectable levels of the 3.3 kb mRNA. Southern blot analyses revealed no gross alteration of the MPO gene in both cases. Our results suggest that a pretranslational defect is one mechanism leading to MPO deficiency.
Insights
Myeloperoxidase (MPO) deficiency, affecting microbicidal activity in human polymorphonuclear leukocytes (PMN), results from a pretranslational defect. This study investigated hereditary and acquired MPO deficiencies using patient samples and cell lines.
Area of Science:
- Biochemistry
- Immunology
- Genetics
Background:
- Myeloperoxidase (MPO) is a key enzyme in the oxygen-dependent microbicidal activity of human polymorphonuclear leukocytes (PMN).
- MPO deficiency, both hereditary and acquired, is characterized by a lack of peroxidase activity in PMN.
- This study investigates the molecular basis of MPO deficiency using a patient with hereditary deficiency and an HL-60 cell line model for acquired deficiency.
Observation:
- Western blot analysis revealed a complete absence of MPO protein in PMN from the patient and HL-60-A7 cells.
- Parental PMN samples showed half the normal levels of MPO protein.
- Analysis of MPO gene transcripts in patient bone marrow and HL-60-A7 cells showed altered mRNA species and heterogeneous nuclear RNA patterns.
Findings:
- MPO-deficient patient bone marrow cells exhibited abnormal hnRNA and reduced levels of mature MPO mRNA (2.8 and 3.3 kb).
- HL-60-A7 cells displayed similar hnRNA patterns with diminished mature MPO mRNA.
- Southern blot analysis indicated no gross alterations in the MPO gene structure.
Implications:
- The findings suggest a pretranslational defect, likely affecting mRNA processing or stability, as a mechanism underlying MPO deficiency.
- Understanding these molecular defects is crucial for diagnosing and potentially treating MPO-related immunodeficiencies.
- This research provides insights into the regulation of MPO gene expression and its role in innate immunity.