A Cyclooxygenase-2/Prostaglandin E2 Pathway Augments Activation-Induced Cytosine Deaminase Expression within Replicating Human B Cells

Abstract

Within inflammatory environments, B cells encountering foreign or self-Ag can develop tertiary lymphoid tissue expressing activation-induced cytosine deaminase (AID). Recently, this DNA-modifying enzyme was detected in nonlymphoid cells within several inflamed tissues and strongly implicated in malignant transformation. This study examines whether a cyclooxygenase 2 (COX-2) pathway, often linked to inflammation, influences AID expression in activated B lymphocytes. In this paper, we report that dividing human B cells responding to surrogate C3d-coated Ag, IL-4, and BAFF express AID, as well as COX-2. A progressive increase in AID with each division was paralleled by a division-related increase in a COX-2–linked enzyme, microsomal PGE2 synthase-1, and the PGE2R, EP2. Cells with the greatest expression of AID expressed the highest levels of EP2. Although COX-2 inhibitors diminished both AID expression and IgG class switching, exogenous PGE2 and butaprost, a selective EP2 agonist, augmented AID mRNA/protein and increased the numbers of IgG+ progeny. Despite the latter, the proportion of IgG+ cells within viable progeny generally declined with PGE2 supplementation. This was not due to PGE2-promoted differentiation to plasma cells or to greater downstream switching. Rather, because phosphorylated ataxia telangiectasia mutated levels were increased in progeny of PGE2-supplemented cultures, it appears more likely that PGE2 facilitates AID-dependent DNA double-strand breaks that block B cell cycle progression or promote activation-induced cell death, or both. Taken together, the results suggest that a PGE2 feed-forward mechanism for augmenting COX-2 pathway proteins promotes progressively increased levels of AID mRNA, protein, and function.

IGHV-unmutated and IGHV-mutated chronic lymphocytic leukemia cells produce activation-induced deaminase protein with a full range of biologic functions

“…Although the induction rate and protein amount varied ( Figure 3A,F), cell division and the presence of AID protein appeared to be linked: undivided clones did not up-regulate protein, whereas clones that had divided exhibited at least some protein up-regulation even if this was only after several cell cycles ( Figure 3F-G). Most cases showed a progressive increase in AID protein levels with each division ( Figure 3F), which is reminiscent of normal B cells, 37,38 and consistent with the idea that, within lymphoid sections, AID ϩ cells were principally Ki-67 ϩ (Figure 2 and Leuenberger et al 39 ). However, because most Ki-67 ϩ cells were AID Ϫ (Figure 2B), either only a small subset of cells are competent to express AID, which seems unlikely based on our in vitro stimulation data (Figure 3), or many of the Ki-67 ϩ CLL cells had not divided a sufficient number of times at the time of analysis to produce AID protein.…”

A p53 Axis Regulates B Cell Receptor-Triggered, Innate Immune System-Driven B Cell Clonal Expansion

“…We have reported that progeny from this response are characterized by elevated levels of CD23, CD86, CD38 and CD27 and sustained expression of CD20 (6). Interestingly, they show minimal evidence of plasmablast differentiation (6, 7) and bear some resemblance to the “marginal zone-like” cells observed within salivary glands of BAFF-overexpressing mice (8) and humans with Sjogren’s Syndrome (9). Importantly, during this TI response, dividing progeny contemporaneously upregulate activation-induced cytosine deaminase (AID) and several proteins of the cyclooxygenase 2 (COX-2) pathway (7).…”

The properties of human CD40-activated B cells as antigen-presenting cells are not affected by PGE2

“…These data were further substantiated by gene expression analyses showing no differential EP2 and EP4 gene expression of CD40-activated B cells compared to unstimulated B cells (data not shown). These findings are of special interest as it has been shown both for mouse and human B cells that under defined activation B cells express EP2 and EP4 receptors (43,44). Thus, it has to be addressed by further investigations whether the utilized method to generate CD40-activated B cells precludes the expression of EP2 and EP4.…”