Scaffold functions of 14-3-3 adaptors in B cell immunoglobulin class switch DNA recombination

PLoS One. 2013 Nov 25;8(11):e80414. doi: 10.1371/journal.pone.0080414. eCollection 2013.

Abstract

Class switch DNA recombination (CSR) of the immunoglobulin heavy chain (IgH) locus crucially diversifies antibody biological effector functions. CSR involves the induction of activation-induced cytidine deaminase (AID) expression and AID targeting to switch (S) regions by 14-3-3 adaptors. 14-3-3 adaptors specifically bind to 5'-AGCT-3' repeats, which make up for the core of all IgH locus S regions. They selectively target the upstream and downstream S regions that are set to undergo S-S DNA recombination. We hypothesized that 14-3-3 adaptors function as scaffolds to stabilize CSR enzymatic elements on S regions. Here we demonstrate that all seven 14-3-3β, 14-3-3ε, 14-3-3γ, 14-3-3η, 14-3-3σ, 14-3-3τ and 14-3-3ζ adaptors directly interacted with AID, PKA-Cα (catalytic subunit) and PKA-RIα (regulatory inhibitory subunit) and uracil DNA glycosylase (Ung). 14-3-3 adaptors, however, did not interact with AID C-terminal truncation mutant AIDΔ(180-198) or AIDF193A and AIDL196A point-mutants (which have been shown not to bind to S region DNA and fail to mediate CSR). 14-3-3 adaptors colocalized with AID and replication protein A (RPA) in B cells undergoing CSR. 14-3-3 and AID binding to S region DNA was disrupted by viral protein R (Vpr), an accessory protein of human immunodeficiency virus type-1 (HIV-1), which inhibited CSR without altering AID expression or germline IH-CH transcription. Accordingly, we demonstrated that 14-3-3 directly interact with Vpr, which in turn, also interact with AID, PKA-Cα and Ung. Altogether, our findings suggest that 14-3-3 adaptors play important scaffold functions and nucleate the assembly of multiple CSR factors on S regions. They also show that such assembly can be disrupted by a viral protein, thereby allowing us to hypothesize that small molecule compounds that specifically block 14-3-3 interactions with AID, PKA and/or Ung can be used to inhibit unwanted CSR.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 14-3-3 Proteins / metabolism
  • 14-3-3 Proteins / physiology*
  • B-Lymphocytes / immunology*
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Cytidine Deaminase / metabolism
  • Gene Products, vpr / metabolism
  • Humans
  • Immunoglobulin Class Switching / genetics*
  • Immunoglobulin Switch Region
  • Models, Genetic
  • Models, Molecular
  • Optical Imaging
  • Protein Isoforms / metabolism
  • Protein Isoforms / physiology
  • Recombination, Genetic*
  • Uracil-DNA Glycosidase / metabolism

Substances

  • 14-3-3 Proteins
  • Gene Products, vpr
  • Protein Isoforms
  • Cyclic AMP-Dependent Protein Kinases
  • Uracil-DNA Glycosidase
  • AICDA (activation-induced cytidine deaminase)
  • Cytidine Deaminase