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Neurol Genet. 2018 Oct 26;4(6):e280. doi: 10.1212/NXG.0000000000000280. eCollection 2018 Dec.

Molecular pathogenesis of human CD59 deficiency.

Author information

1
Rheumatology Research Center (N.K., A.T., H.H., D.M.), Center of Rare Diseases, and Department of Medicine, Hadassah-Hebrew University Medical Center, Jerusalem; The Weizmann Institute (Y.E.-E., E.P.), Rehovot, Israel; Systems Immunity Research Institute (B.P.M.), Cardiff University, Cardiff, Wales, UK; and Hebrew University (O.S.-F., D.M.), Jerusalem, Israel.

Abstract

Objective:

To characterize all 4 mutations described for CD59 congenital deficiency.

Methods:

The 4 mutations, p.Cys64Tyr, p.Asp24Val, p.Asp24Valfs*, and p.Ala16Alafs*, were described in 13 individuals with CD59 malfunction. All 13 presented with recurrent Guillain-Barré syndrome or chronic inflammatory demyelinating polyneuropathy, recurrent strokes, and chronic hemolysis. Here, we track the molecular consequences of the 4 mutations and their effects on CD59 expression, localization, glycosylation, degradation, secretion, and function. Mutants were cloned and inserted into plasmids to analyze their expression, localization, and functionality.

Results:

Immunolabeling of myc-tagged wild-type (WT) and mutant CD59 proteins revealed cell surface expression of p.Cys64Tyr and p.Asp24Val detected with the myc antibody, but no labeling by anti-CD59 antibodies. In contrast, frameshift mutants p.Asp24Valfs* and p.Ala16Alafs* were detected only intracellularly and did not reach the cell surface. Western blot analysis showed normal glycosylation but mutant-specific secretion patterns. All mutants significantly increased MAC-dependent cell lysis compared with WT. In contrast to CD59 knockout mice previously used to characterize phenotypic effects of CD59 perturbation, all 4 hCD59 mutations generate CD59 proteins that are expressed and may function intracellularly (4) or on the cell membrane (2). None of the 4 CD59 mutants are detected by known anti-CD59 antibodies, including the 2 variants present on the cell membrane. None of the 4 inhibits membrane attack complex (MAC) formation.

Conclusions:

All 4 mutants generate nonfunctional CD59, 2 are expressed as cell surface proteins that may function in non-MAC-related interactions and 2 are expressed only intracellularly. Distinct secretion of soluble CD59 may have also a role in disease pathogenesis.

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