Disease-associated CTNNBL1 mutation impairs somatic hypermutation by decreasing nuclear AID
Marcel Kuhny, … , Jordan S. Orange, Eric Meffre
Marcel Kuhny, … , Jordan S. Orange, Eric Meffre
Published June 2, 2020
Citation Information: J Clin Invest. 2020;130(8):4411-4422. https://doi.org/10.1172/JCI131297.
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Research Article Autoimmunity Immunology

Disease-associated CTNNBL1 mutation impairs somatic hypermutation by decreasing nuclear AID

Abstract

Patients with common variable immunodeficiency associated with autoimmune cytopenia (CVID+AIC) generate few isotype-switched B cells with severely decreased frequencies of somatic hypermutations (SHMs), but their underlying molecular defects remain poorly characterized. We identified a CVID+AIC patient who displays a rare homozygous missense M466V mutation in β-catenin–like protein 1 (CTNNBL1). Because CTNNBL1 binds activation-induced cytidine deaminase (AID) that catalyzes SHM, we tested AID interactions with the CTNNBL1 M466V variant. We found that the M466V mutation interfered with the association of CTNNBL1 with AID, resulting in decreased AID in the nuclei of patient EBV-transformed B cell lines and of CTNNBL1 466V/V Ramos B cells engineered to express only CTNNBL1 M466V using CRISPR/Cas9 technology. As a consequence, the scarce IgG+ memory B cells from the CTNNBL1 466V/V patient showed a low SHM frequency that averaged 6.7 mutations compared with about 18 mutations per clone in healthy-donor counterparts. In addition, CTNNBL1 466V/V Ramos B cells displayed a decreased incidence of SHM that was reduced by half compared with parental WT Ramos B cells, demonstrating that the CTNNBL1 M466V mutation is responsible for defective SHM induction. We conclude that CTNNBL1 plays an important role in regulating AID-dependent antibody diversification in humans.

Authors

Marcel Kuhny, Lisa R. Forbes, Elif Çakan, Andrea Vega-Loza, Valentyna Kostiuk, Ravi K. Dinesh, Salomé Glauzy, Asbjorg Stray-Pedersen, Ashley E. Pezzi, I. Celine Hanson, Alexander Vargas-Hernandez, Mina LuQuing Xu, Zeynep H. Coban-Akdemir, Shalini N. Jhangiani, Donna M. Muzny, Richard A. Gibbs, James R. Lupski, Ivan K. Chinn, David G. Schatz, Jordan S. Orange, Eric Meffre

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Figure 2

CTNNBL1 M446V mutation decreases AID association with CTNNBL1.

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CTNNBL1 M446V mutation decreases AID association with CTNNBL1. (A) Lysat...
(A) Lysates of EBV BLCLs from a healthy donor (HD), CTNNBL1 466V/V patient, or AID-deficient patient were immunoprecipitated with an anti-CTNNBL1 antibody; precipitates and total cell lysates were analyzed by Western blotting with the indicated antibodies (shown are representative blots). (B) Summary of densitometric quantification of at least 6 independent experiments. Represented are values relative to HDs, indicated by dashed lines; bars represent the mean. (C) Lysates of parental WT, CTNNBL1 466V/V, and AID–/– Ramos B cells were analyzed as in A (shown are representative blots). (D) Summary of densitometric quantification of 5 independent experiments. Represented are values relative to parental WT cells, indicated by dashed lines; bars represent the mean.