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Assessing Somatic Hypermutation in Ramos B Cells after Overexpression or Knockdown of Specific Genes
Published on: November 1, 2011
Regulation of hypermutation by activation-induced cytidine deaminase phosphorylation
Kevin M McBride1, Anna Gazumyan, Eileen M Woo
1Laboratory of Molecular Immunology and Laboratory of Mass Spectrometry, The Rockefeller University and Howard Hughes Medical Institute, New York, NY 10021, USA.
Abstract:
Activation-induced cytidine deaminase (AID) initiates Ig class switch recombination and somatic hypermutation by producing U:G mismatches in DNA. These mismatches also have the potential to induce DNA damage including double-stranded breaks and chromosome translocations; therefore, strict regulation of AID is important for maintaining genomic stability. In addition to transcriptional regulation, it has been proposed that phosphorylation can also modulate AID activity. Using a combination of MS and immunochemical approaches we found that 5-15% of the AID expressed in activated B cells was phosphorylated at serine-38 (p38AID). This form of AID was enriched in the chromatin fraction in activated B cells, suggesting a role for phosphorylation in targeting AID to DNA. Consistent with this idea, serine-38 to alanine mutant AID (AID(S38A)) showed diminished somatic hypermutation activity on artificial and physiological DNA targets. We conclude that a small fraction of AID is phosphorylated in activated B cells and that the modified form contributes disproportionately to hypermutation.
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