title: Down-regulation of DNA polymerase beta accompanies somatic hypermutation in human BL2 cell lines.
abstract: Somatic hypermutation (SHM) is a fundamental process in immunoglobulin gene maturation that results in increased affinity of antibodies toward antigens. In one hypothesis explaining SHM in human B cells, the process is initiated by enzymatic deamination of cytosine to uracil in the immunoglobulin gene V-region and this in turn triggers mutation-prone forms of uracil-DNA base excision repair (BER). Yet, an uncertainty with this model is that BER of uracil-DNA in mammalian cells is generally error-free, wherein DNA polymerase beta (pol beta) conducts gap-filling synthesis by insertion of bases according to Watson-Crick rules. To evaluate this inconsistency, we examined pol beta expression in various SHM proficient human BL2 cell line subclones. We report that expression of pol beta in SHM proficient cell lines was strongly down-regulated. In contrast, in other BL2 subclones, we found that SHM was deficient and that pol beta expression was much higher than in the SHM proficient subclones. We also found that overexpression of recombinant human pol beta in a SHM proficient subclone abrogated its capacity for SHM. These results suggest that down-regulation of the normal BER gap-filling DNA polymerase, pol beta, accompanies induced SHM in BL2 cells. This is consistent with the hypothesis that normal error-free BER must be silenced to make way for an error-prone BER process that may be required during somatic hypermutation.
authors.affiliation: Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T.W. Alexander Drive, PO Box 12233, MD B2-06, Research Triangle Park, NC 27709, USA.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Poltoratsky
authors.forename: Rajendra
authors.initials: R
authors.lastname: Prasad
authors.forename: Julie K
authors.initials: JK
authors.lastname: Horton
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Wilson
mesh_terms: D000328:Adult; D001483:Base Sequence; D002460:Cell Line; D019951:DNA Polymerase beta / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D015536:Down-Regulation; D006801:Humans; D007135:Immunoglobulin Variable Region / Q000235:genetics; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D016296:Mutagenesis; D009838:Oligodeoxyribonucleotides / Q000235:genetics / Q000378:metabolism; D014066:Palatine Tonsil / Q000201:enzymology; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D027041:Somatic Hypermutation, Immunoglobulin; D013379:Substrate Specificity
chemical_list: D007135:Immunoglobulin Variable Region; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D019951:DNA Polymerase beta