The transcription factor E2A can bind to and cleave single-stranded immunoglobulin heavy chain locus DNA

Class switch recombination (CSR) changes the constant region of the immunoglobulin heavy chain (IgH), and somatic hypermutation (SH) introduces point mutations in the variable regions of the antibody genes. Both these processes that optimize antibody responses of B lymphocytes are initiated by the enzyme Activation Induced cytidine Deaminase (AID). Here we have searched for CSR or SH coupled activities of the transcription factor E2A, since E2A is in a complex with AID and the transcription factors PAX5, ETS1 and IRF4 on key sequences of the Igh locus in B lymphocytes activated to CSR and SH. We report that E2A in contrast to other described transcription factors binds sequence specifically also to single-stranded DNA. The binding of E2A to single-stranded DNA has a strong sequence preference for one strand of a site in the intronic enhancer of the Igh locus. Furthermore, E2A was also found to cleave single-stranded DNA. The sequence profile of substrates cleaved by E2A is coupled to the sequences of substrates and products of AID, suggesting that E2A has a role not only in targeting of AID to switch regions and SH parts of antibody genes but also in cleavage of DNA at these sites.

Helix-Loop-Helix Proteins in Adaptive Immune Development

The E/ID protein axis is instrumental for defining the developmental progression and functions of hematopoietic cells. The E proteins are dimeric transcription factors that activate gene expression programs and coordinate changes in chromatin organization. Id proteins are antagonists of E protein activity. Relative levels of E/Id proteins are modulated throughout hematopoietic development to enable the progression of hematopoietic stem cells into multiple adaptive and innate immune lineages including natural killer cells, B cells and T cells. In early progenitors, the E proteins promote commitment to the T and B cell lineages by orchestrating lineage specific programs of gene expression and regulating VDJ recombination of antigen receptor loci. In mature B cells, the E/Id protein axis functions to promote class switch recombination and somatic hypermutation. E protein activity further regulates differentiation into distinct CD4+ and CD8+ T cells subsets and instructs mature T cell immune responses. In this review, we discuss how the E/Id proteins define the adaptive immune system lineages, focusing on their role in directing developmental gene programs.

Allelic exclusion of IgH through inhibition of E2A in a VDJ recombination complex

A key feature of the immune system is the paradigm that one lymphocyte has only one Ag specificity that can be selected for or against. This requires that only one of the alleles of genes for AgR chains is made functional. However, the molecular mechanism of this allelic exclusion has been an enigma. In this study, we show that B lymphocytes with E2A that cannot be inhibited by calmodulin are dramatically defective in allelic exclusion of the IgH locus. Furthermore, we provide data supporting that E2A, PAX5, and the RAGs are in a VDJ recombination complex bound to key sequences on the Igh gene. We show that pre-BCR activation releases the VDJ recombination complex through calmodulin binding to E2A. We also show that pre-BCR signaling downregulates several components of the recombination machinery, including RAG1, RAG2, and PAX5, through calmodulin inhibition of E2A.

A genome-wide association study identifies multiple susceptibility loci for chronic lymphocytic leukemia

Genome-wide association studies (GWAS) of chronic lymphocytic leukemia (CLL) have shown that common genetic variation contributes to the heritable risk of CLL. To identify additional CLL susceptibility loci, we conducted a GWAS and performed a meta-analysis with a published GWAS totaling 1,739 individuals with CLL (cases) and 5,199 controls with validation in an additional 1,144 cases and 3,151 controls. A combined analysis identified new susceptibility loci mapping to 3q26.2 (rs10936599, P = 1.74 × 10(-9)), 4q26 (rs6858698, P = 3.07 × 10(-9)), 6q25.2 (IPCEF1, rs2236256, P = 1.50 × 10(-10)) and 7q31.33 (POT1, rs17246404, P = 3.40 × 10(-8)). Additionally, we identified a promising association at 5p15.33 (CLPTM1L, rs31490, P = 1.72 × 10(-7)) and validated recently reported putative associations at 5p15.33 (TERT, rs10069690, P = 1.12 × 10(-10)) and 8q22.3 (rs2511714, P = 2.90 × 10(-9)). These findings provide further insights into the genetic and biological basis of inherited genetic susceptibility to CLL.