title: Scaffold functions of 14-3-3 adaptors in B cell immunoglobulin class switch DNA recombination.
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.
authors.affiliation: Institute for Immunology, School of Medicine and School of Biological Sciences, University of California Irvine, Irvine, California, United States of America ; Department of Microbiology and Immunology, School of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.
authors.forename: Tonika
authors.initials: T
authors.lastname: Lam
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Thomas
authors.forename: Clayton A
authors.initials: CA
authors.lastname: White
authors.forename: Guideng
authors.initials: G
authors.lastname: Li
authors.forename: Egest J
authors.initials: EJ
authors.lastname: Pone
authors.forename: Zhenming
authors.initials: Z
authors.lastname: Xu
authors.forename: Paolo
authors.initials: P
authors.lastname: Casali
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism / Q000502:physiology*; D001402:B-Lymphocytes / Q000276:immunology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003564:Cytidine Deaminase / Q000378:metabolism; D016336:Gene Products, vpr / Q000378:metabolism; D006801:Humans; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D007134:Immunoglobulin Switch Region; D008957:Models, Genetic; D008958:Models, Molecular; D061848:Optical Imaging; D020033:Protein Isoforms / Q000378:metabolism / Q000502:physiology; D011995:Recombination, Genetic; D051981:Uracil-DNA Glycosidase / Q000378:metabolism; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D048948:14-3-3 Proteins; D016336:Gene Products, vpr; D020033:Protein Isoforms; D017868:Cyclic AMP-Dependent Protein Kinases; D051981:Uracil-DNA Glycosidase; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase