title: Overexpression of human DNA polymerase mu (Pol mu) in a Burkitt's lymphoma cell line affects the somatic hypermutation rate.
abstract: DNA polymerase mu (Pol mu) is a DNA-dependent DNA polymerase closely related to terminal deoxynucleotidyl transferase (TdT), and prone to induce template/primer misalignments and misincorporation. In addition to a proposed general role in non-homologous end joining of double-strand breaks, its mutagenic potential and preferential expression in secondary lymphoid tissues support a role in somatic hypermutation (SHM) of immunoglobulin genes. Here, we show that human Pol mu protein is expressed in the nucleus of centroblasts obtained from human tonsils, forming a characteristic foci pattern resembling that of other DNA repair proteins in response to DNA damage. Overexpression of human Pol mu in Ramos cells, in which the SHM process is constitutive, augmented the somatic mutations specifically at the variable (V) region of the immunoglobulin genes. The nature of the mutations introduced, mostly base substitutions, supports the contribution of Pol mu to mutation of G and C residues during SHM. In vitro analysis of Pol mu misincorporation on specific templates, that mimic DNA repair intermediates and correspond to mutational hotspots, indicated that many of the mutations observed in vivo can be explained by the capacity of Pol mu to induce transient template/primer misalignments.
authors.affiliation: Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónoma, Madrid, Spain.
authors.forename: José F
authors.initials: JF
authors.lastname: Ruiz
authors.forename: Daniel
authors.initials: D
authors.lastname: Lucas
authors.forename: Esther
authors.initials: E
authors.lastname: García-Palomero
authors.forename: Ana I
authors.initials: AI
authors.lastname: Saez
authors.forename: Manuel A
authors.initials: MA
authors.lastname: González
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Piris
authors.forename: Antonio
authors.initials: A
authors.lastname: Bernad
authors.forename: Luis
authors.initials: L
authors.lastname: Blanco
mesh_terms: D001402:B-Lymphocytes / Q000201:enzymology; D002051:Burkitt Lymphoma / Q000235:genetics*; D045744:Cell Line, Tumor; D004260:DNA Repair; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D018858:Germinal Center / Q000166:cytology / Q000276:immunology; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007135:Immunoglobulin Variable Region / Q000235:genetics; D027041:Somatic Hypermutation, Immunoglobulin; D013698:Templates, Genetic; D014161:Transduction, Genetic
chemical_list: D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; C407743:DNA polymerase mu; D004259:DNA-Directed DNA Polymerase