Klhl6 Deficiency Impairs Transitional B Cell Survival and Differentiation

Abstract

Klhl6 belongs to the KLHL gene family, which is composed of an N-terminal BTB-POZ domain and four to six Kelch motifs in tandem. Several of these proteins function as adaptors of the Cullin3 E3 ubiquitin ligase complex. In this article, we report that Klhl6 deficiency induces, as previously described, a 2-fold reduction in mature B cells. However, we find that this deficit is centered on the inability of transitional type 1 B cells to survive and to progress toward the transitional type 2 B cell stage, whereas cells that have passed this step generate normal germinal centers (GCs) upon a T-dependent immune challenge. Klhl6-deficient type 1 B cells showed a 2-fold overexpression of genes linked with cell proliferation, including most targets of the anaphase-promoting complex/cyclosome complex, a set of genes whose expression is precisely downmodulated upon culture of splenic transitional B cells in the presence of BAFF. These results thus suggest a delay in the differentiation process of Klhl6-deficient B cells between the immature and transitional stage. We further show, in the BL2 Burkitt's lymphoma cell line, that KLHL6 interacts with Cullin3, but also that it binds to HBXIP/Lamtor5, a protein involved in cell-cycle regulation and cytokinesis. Finally, we report that KLHL6, which is recurrently mutated in B cell lymphomas, is an off-target of the normal somatic hypermutation process taking place in GC B cells in both mice and humans, thus leaving open whether, despite the lack of impact of Klhl6 deficiency on GC B cell expansion, mutants could contribute to the oncogenic process.

KLHL6 is a tumor suppressor gene in diffuse large B-cell lymphoma

“…Recently, a second mouse with a constitutive ablation of Klhl6 was generated [14]. This knockout confirms that the loss of Klhl6 does not affect the development of B cells at the early differentiation stages in the bone marrow, but increases the frequency of immature B cells, resulting in the consequential reduction of mature, recirculating B cells.…”

“…This phenotype is cell intrinsic as competitive reconstitution experiments in Rag2 knockout mice with bone marrow from the wild type and Klhl6 deficient mice reveal a deficiency in mature B cells (specifically, T1 and T2-like B cells) in the Klhl6 knockout cells. In line, the transcriptional profiling of Klhl6 deficient T1 B-cells shows a downregulation of genes associated with cell proliferation upon B-cell activating factor (BAFF) stimulation, consistent with a deficiency in the differentiation process of B cells at the immature transition [14].…”

Association of gene mutations with time‐to‐first treatment in 384 treatment‐naive chronic lymphocytic leukaemia patients

“…Very little is understood regarding mutations within KLHL6 in CLL with a previously reported frequency of 1·8% (Puente et al , ) and a frequency of 4·2% in our TN cohort. We and others have associated mutated KLHL6 with mutated IGHV (Puente et al , ; Hu et al , ) with a postulated mechanism through the non‐canonical activation of the nuclear factor‐κB pathway (Bertocci et al , ). In this study, mutated KLHL6 was associated with a 66·3‐month increase in mTTFT as compared to KLHL6 wildtype patients.…”

MoonFit, a minimal interface for fitting ODE dynamical models, bridging simulation by experimentalists and customization by C++ programmers

“…Throughout the next sections, a small biological problem requiring parameter optimization will be developed. Based on the work of Bertocci et al, deficient mice for a specific gene, KLHL6, were phenotyped for the development of B cells in the spleen [19]. Three populations were considered: two transitional stages, T1 and T2 and a mature phenotype, Follicular B cell.…”

“…Here, two cost functions are provided: the rooted sum of squared differences (RMS) or the sum of log B. Experimental cell numbers for the three populations at 14-20 days (young) or adult mice, as an approximation to steady-state [19] C. Associated ODE model, with or without feedback.…”