RESUMO
Immunoglobulin variable region exons are assembled in developing B cells by V(D)J recombination. Once mature, these cells undergo class-switch recombination (CSR) when activated by antigen. CSR changes the heavy chain constant region exons (Ch) expressed with a given variable region exon from Cmu to a downstream Ch (for example, Cgamma, Cepsilon or Calpha), thereby switching expression from IgM to IgG, IgE or IgA. Both V(D)J recombination and CSR involve the introduction of DNA double-strand breaks and their repair by means of end joining. For CSR, double-strand breaks are introduced into switch regions that flank Cmu and a downstream Ch, followed by fusion of the broken switch regions. In mammalian cells, the 'classical' non-homologous end joining (C-NHEJ) pathway repairs both general DNA double-strand breaks and programmed double-strand breaks generated by V(D)J recombination. C-NHEJ, as observed during V(D)J recombination, joins ends that lack homology to form 'direct' joins, and also joins ends with several base-pair homologies to form microhomology joins. CSR joins also display direct and microhomology joins, and CSR has been suggested to use C-NHEJ. Xrcc4 and DNA ligase IV (Lig4), which cooperatively catalyse the ligation step of C-NHEJ, are the most specific C-NHEJ factors; they are absolutely required for V(D)J recombination and have no known functions other than C-NHEJ. Here we assess whether C-NHEJ is also critical for CSR by assaying CSR in Xrcc4- or Lig4-deficient mouse B cells. C-NHEJ indeed catalyses CSR joins, because C-NHEJ-deficient B cells had decreased CSR and substantial levels of IgH locus (immunoglobulin heavy chain, encoded by Igh) chromosomal breaks. However, an alternative end-joining pathway, which is markedly biased towards microhomology joins, supports CSR at unexpectedly robust levels in C-NHEJ-deficient B cells. In the absence of C-NHEJ, this alternative end-joining pathway also frequently joins Igh locus breaks to other chromosomes to generate translocations.
Assuntos
Genes de Cadeia Pesada de Imunoglobulina/genética , Switching de Imunoglobulina/genética , Recombinação Genética/genética , Translocação Genética/genética , Animais , Linfócitos B/citologia , Linfócitos B/metabolismo , Linfócitos B/efeitos da radiação , Sequência de Bases , Proliferação de Células , Células Cultivadas , Quebra Cromossômica , Proteínas de Ligação a DNA/deficiência , Proteínas de Ligação a DNA/genética , Imunoglobulina G/genética , Imunoglobulina G/metabolismo , Hibridização in Situ Fluorescente , Camundongos , Radiação Ionizante , Telômero/genéticaRESUMO
Helicobacter pylori is an important human pathogen that causes chronic gastritis and is associated with development of peptic ulcer disease and gastric malignancies. The vacuolating cytotoxin (vacA), cagA gene, and babA2 gene are important virulence factor involving gastric diseases. Eighty-nine Helicobacter pylori-positive gastric biopsies were analyzed by polymerase chain reaction and Southern blotting for H. pylori detection and genotyping with primer pairs from each virulence gene. Fifty-three strains (59%) were common vacA genotype s1/m1, and only 14 (16%) were s2/m2, 12% of strains was found to have multiple infection. The cagA presence was detected in 48% (43 strains) and babA2 gene was detected in 44% of our H. pylori strains. We observed high percentage of s1/m1 strains with chronic gastritis and peptic ulcer and a significant correlation between cagA presence with the s1 allele and babA2 gene with chronic gastritis.
