Loss-of-phosphorylation of IKZF1 results in gain-of-function associated with immune dysregulation

Akihiro Hoshino; Benoît Heid Picard; Sophia Polychronopoulou; Charikleia Kelaidi; Saba Azarnoush; Sven Kracker; Frédéric Rieux-Laucat; David Boutboul; Sylvain Latour

doi:10.1016/j.jaci.2024.01.029

Loss-of-phosphorylation of IKZF1 results in gain-of-function associated with immune dysregulation

J Allergy Clin Immunol. 2024 Mar 2:S0091-6749(24)00230-6. doi: 10.1016/j.jaci.2024.01.029. Online ahead of print.

Authors

Akihiro Hoshino¹, Benoît Heid Picard², Sophia Polychronopoulou³, Charikleia Kelaidi³, Saba Azarnoush⁴, Sven Kracker⁵, Frédéric Rieux-Laucat⁶, David Boutboul¹, Sylvain Latour⁷

Affiliations

¹ Laboratory of Lymphocyte Activation and Susceptibility to EBV Infection, INSERM UMR 1163, Imagine Institute, Paris, France.
² Laboratory of Lymphocyte Activation and Susceptibility to EBV Infection, INSERM UMR 1163, Imagine Institute, Paris, France; Université de Paris-Cité, Paris, France.
³ Department of Pediatric Hematology-Oncology, Aghia Sophia Children's Hospital, Goudi-Athens, Athens, Greece.
⁴ Department of Pediatric Immuno-Hematology, Hôpital Robert-Debré, Assistance Publique-Hôpitaux de Paris, Paris, France.
⁵ Université de Paris-Cité, Paris, France; Laboratory of Human Lymphohematopoiesis, INSERM UMR 1163, Imagine Institute, Paris, France.
⁶ Université de Paris-Cité, Paris, France; Laboratory of Immunogenetics of Pediatric Autoimmunity, INSERM UMR 1163, Imagine Institute, Paris, France.
⁷ Laboratory of Lymphocyte Activation and Susceptibility to EBV Infection, INSERM UMR 1163, Imagine Institute, Paris, France; Université de Paris-Cité, Paris, France. Electronic address: sylvain.latour@inserm.fr.

PMID: 38438084
DOI: 10.1016/j.jaci.2024.01.029

Abstract

Background: Immune dysregulation often presents as autoimmunity, inflammation, and/or lymphoproliferation. Several germline genetic defects have been associated with immune dysregulation; they include heterozygous gain-of-function (GOF) mutations in IKZF1, an essential transcription factor for hematopoiesis containing zinc finger domains (ZFs). However, in a large percentage of patients, the genetic origin of their immunedysregulation remains undetermined.

Objective: A family with 2 members presenting immune dysregulation signs was studied to identify the genetic cause of their disease.

Methods: Whole exome sequencing, analysis of immunologic parameters, and functional assays (including Western blotting, electrophoretic mobility shift assay during the cell cycle, and T_H cell differentiation) were performed.

Results: The 2 patients carried a novel heterozygous mutation in IKZF1 (IKZF1^T398M). IKZF1 heterozygous mutations have previously been shown to be responsible for several distinct human immunologic diseases by directly affecting the ability of ZFs to bind to DNA or to dimerize. Herein, we showed that the IKZF1^T398M, which is outside the ZFs, caused impaired phosphorylation of IKZF1, resulting in enhanced DNA-binding ability at the S phase of the cell cycle, reduction of the G1-S phase transition, and decreased proliferation. Confirming these data, similar functional alterations were observed with IKZF1^T398A, but not with IKZF1^T398D, mimicking dephosphorylation and phosphorylation, respectively. In T lymphocytes, expression of IKZF1^T398M led to T_H cell differentiation skewed toward T_H2 cells. Thus, our data indicate that IKZF1^T398M behaves as a GOF variant underlying immune dysregulation.

Conclusion: Disturbed IKZF1 phosphorylation represents a novel GOF mechanism (GOF by loss of phosphorylation (termed as GOF-LOP) associated with immune dysregulation, highlighting the regulatory role of IKZF1 during cell cycle progression through phosphorylation.

Keywords: IKAROS; IKZF1; Immune dysregulation; T(H)2 cell differentiation; gain-of-function; genetic; inborn errors of immunity; mutation; phosphorylation.