Activation-induced cytidine deaminase prevents pro-B cell acute lymphoblastic leukemia by functioning as a negative regulator in Rag1 deficient pro-B cells

Franziska Auer,Michael Gombert,Marina Cavazzana,Sven Kracker,Deborah Ingenhag,Julia Hauer,Min-Hui Lin,Isidro Sánchez-García,Carolina Vicente-Dueñas,Stefan Pinkert,Alberto Martin-Lorenzo,Salima Hacein-Bey-Abina,Arndt Borkhardt

doi:10.18632/oncotarget.20563

Abstract

Activation-induced cytidine deaminase (AID) is essential for somatic hypermutation and class switch recombination in mature B-cells, while AID was also shown to play a role in developing pre-BCR/BCR-positive B-cells of the bone marrow. To further elucidate a potential function of Aid in the bone marrow prior to V(D)J-recombination, we utilized an in vivo model which exerts a B-cell developmental arrest at the pro-B cell stage with low frequencies of pro-B cell acute lymphoblastic leukemia (pro-B ALL) development. Therefore, p19Arf-/-Rag1-/- (AR) mice were crossed with Aid-deficient mice (ARA). Surprisingly, loss of Aid expression in pro-B cells accelerated pro-B ALL incidence from 30% (AR) to 98% (ARA). This effect was Aid dose dependent, since Aid+/- animals of the same background displayed a significantly lower incidence (83%). Furthermore, B-cell-specific Aid up-regulation was observed in Aid-competent pro-B ALLs. Additional whole exome/sanger sequencing of murine pro-B ALLs revealed an accumulation of recurrent somatic Jak3 (p.R653H, p.V670A) and Dnm2 (p.G397R) mutations, which highlights the importance of active IL7R signaling in the pro-B ALL blast cells. These findings were further supported by an enhanced proliferative potential of ARA pro-B cells compared to Aid-competent cells from the same genetic background. In summary, we show that both Aid and Rag1 act as a negative regulators in pro-B cells, preventing pro-B ALL.

Highlights

Over the last decade, various studies gave novel insights that improved our understanding about the molecular basis of childhood acute lymphoblastic leukemia (ALL) [1,2,3,4,5]
In order to explore the physiological relevance of Aid at the pro-B cell stage, and independent of Rag1 off-target activity, we designed a mouse model which allows the investigation of an arrested tumor-prone pro-B cell population in combination with Aid deficiency
V(D)J-recombination assays verifying only the presence of the cμ chain were performed to ensure that the model was not leaky, and that pro-B ALL was not derived from mature activation-induced cytidine deaminase (AID)-expressing B-cells which had undergone V(D)J-recombination (Figure 1G and Supplementary Figure 4B)

Summary

Introduction

Various studies gave novel insights that improved our understanding about the molecular basis of childhood acute lymphoblastic leukemia (ALL) [1,2,3,4,5]. While it was shown that the concurrent expression of AID and RAG1 in small preBII cells contributes to the clonal evolution of childhood ALL in the presence of strong inflammatory stimuli [8], absence of AID expression in pre-BI and immature B-cells has been reported to confer implications in the control of self-tolerance, as shown in both mice and humans [2025]. In order to elucidate whether Aid is functional prior to pre-BCR expression, we developed an Aid-deficient mouse model with a tumor prone Rag1-/- background (p19Arf-/-Rag1-/-Aid-/- ARA). Utilizing this model, we were able to assess the influence of Aid at the pro-B cell stage [29], in the context of pro-B ALL development [30] and in the absence of Rag induced alterations. We present in vivo evidence, that the combined absence of Aid and Rag in tumor prone murine pro-B cells accelerates pro-B ALL incidence, which suggests a functional role of Aid in Rag deficient

Methods

Results

Conclusion