Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress
Cecilia Domínguez Conde, … , Mirjam van der Burg, Kaan Boztug
Cecilia Domínguez Conde, … , Mirjam van der Burg, Kaan Boztug
Published August 26, 2019
Citation Information: J Clin Invest. 2019;129(10):4194-4206. https://doi.org/10.1172/JCI128903.
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Research Article Genetics Immunology

Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress

Abstract

Polymerase δ is essential for eukaryotic genome duplication and synthesizes DNA at both the leading and lagging strands. The polymerase δ complex is a heterotetramer comprising the catalytic subunit POLD1 and the accessory subunits POLD2, POLD3, and POLD4. Beyond DNA replication, the polymerase δ complex has emerged as a central element in genome maintenance. The essentiality of polymerase δ has constrained the generation of polymerase δ–knockout cell lines or model organisms and, therefore, the understanding of the complexity of its activity and the function of its accessory subunits. To our knowledge, no germline biallelic mutations affecting this complex have been reported in humans. In patients from 2 independent pedigrees, we have identified what we believe to be a novel syndrome with reduced functionality of the polymerase δ complex caused by germline biallelic mutations in POLD1 or POLD2 as the underlying etiology of a previously unknown autosomal-recessive syndrome that combines replicative stress, neurodevelopmental abnormalities, and immunodeficiency. Patients’ cells showed impaired cell-cycle progression and replication-associated DNA lesions that were reversible upon overexpression of polymerase δ. The mutations affected the stability and interactions within the polymerase δ complex or its intrinsic polymerase activity. We believe our discovery of human polymerase δ deficiency identifies the central role of this complex in the prevention of replication-related DNA lesions, with particular relevance to adaptive immunity.

Authors

Cecilia Domínguez Conde, Özlem Yüce Petronczki, Safa Baris, Katharina L. Willmann, Enrico Girardi, Elisabeth Salzer, Stefan Weitzer, Rico Chandra Ardy, Ana Krolo, Hanna Ijspeert, Ayca Kiykim, Elif Karakoc-Aydiner, Elisabeth Förster-Waldl, Leo Kager, Winfried F. Pickl, Giulio Superti-Furga, Javier Martínez, Joanna I. Loizou, Ahmet Ozen, Mirjam van der Burg, Kaan Boztug

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Figure 1

Identification of hypomorphic mutations affecting the polymerase δ complex in patients presenting with syndromic combined immunodeficiency.

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Identification of hypomorphic mutations affecting the polymerase δ compl...
(A) Molluscum contagiosum skin infection in P1. (B) Longitudinal peripheral blood CD4+ T cell, CD8+ T cell, B cell, and NK cell counts in P1 and P2. Dotted lines represent the range of reference values. (C) Viral skin warts in P2. (D) Familial segregation of the identified POLD1 and POLD2 mutations in the families of P1 and P2, indicating an autosomal-recessive pattern of inheritance. (E) Domain structure of POLD1 showing the polymerase domain, the exonuclease domain, the nuclear localization signal (NLS) domain, and the cysteine-rich, metal-binding domains CysA and CysB. Domain structure of POLD2 depicting the PDE and oligonucleotide binding (OB) domains. Mutation sites are indicated in red. (F) Protein levels of POLD1, POLD2, POLD3, and CYCA in PBMCs after anti-CD3 and anti-CD28 stimulation for 48 hours. See complete unedited blots in the supplemental material.(G) Protein levels of POLD1, POLD2, and POLD3 in primary fibroblasts. GAPDH was used as a loading control. Cells were untreated (Unt) or synchronized by double-thymidine (Thy) treatment or aphidicolin (Aph) treatment for 24 hours. α, anti.