Transgenic Overexpression of G5PR That Is Normally Augmented in Centrocytes Impairs the Enrichment of High-Affinity Antigen-Specific B Cells, Increases Peritoneal B-1a Cells, and Induces Autoimmunity in Aged Female Mice

Abstract

To investigate signals that control B cell selection, we examined expression of G5PR, a regulatory subunit of the serine/threonine protein phosphatase 2A, which suppresses JNK phosphorylation. G5PR is upregulated in activated B cells, in Ki67-negative centrocytes at germinal centers (GCs), and in purified B220+Fas+GL7+ mature GC B cells following Ag immunization. G5PR rescues transformed B cells from BCR-mediated activation-induced cell death by suppression of late-phase JNK activation. In G5PR-transgenic (G5PRTg) mice, G5PR overexpression leads to an augmented generation of GC B cells via an increase in non-Ag–specific B cells and a consequent reduction in the proportion of Ag-specific B cells and high-affinity Ab production after immunization with nitrophenyl-conjugated chicken γ-globulin. G5PR overexpression impaired the affinity–maturation of Ag-specific B cells, presumably by diluting the numbers of high-affinity B cells. However, aged nonimmunized female G5PRTg mice showed an increase in the numbers of peritoneal B-1a cells and the generation of autoantibodies. G5PR overexpression did not affect the proliferation of B-1a and B-2 cells but rescued B-1a cells from activation-induced cell death in vitro. G5PR might play a pivotal role in B cell selection not only for B-2 cells but also for B-1 cells in peripheral lymphoid organs.

JNK Regulatory Molecule G5PR Induces IgG Autoantibody–Producing Plasmablasts from Peritoneal B1a Cells

“…Peritoneal B1a cells similarly showed augmented expression of aicda and g5pr as the early-stage transcripts of GC B cells after iGB culture. g5pr ex- pression is selectively upregulated in GC B cells of the light zone area (14). B1a cells showed increased expression of g5pr.…”

“…Anti-dsDNA Abs in culture supernatants were detected by ELISA as described previously (14). In brief, culture supernatants were incubated for 1 h at room temperature in 96-well plates coated with 500 ng dsDNA (SigmaAldrich).…”

“…B cell-conditional targeting of g5pr in cd19-cre transgenic mice results in the impairment of GC B cell survival (35). Interestingly, transgenic G5PR overexpression (G5PR Tg ) under the control of the Lck proximal promoter and Em enhancer regions leads to abnormal survival of B1a cells in the peritoneal cavity and development of autoimmunity after aging in female mice (14). These findings suggest that G5PR is involved in both the survival of GC B cells and the differentiation of peritoneal B1a cells into autoantibody-producing plasma cells.…”

“…Thus, the molecules involved in differentiation of GC B cells may be also associated with differentiation of B1a cells that appear in the peritoneal cavity. G5PR is a kind of regulatory subunit for protein phosphatases (34), which is characterized as a molecule expressed in GC B cells (14). G5PR is associated with the catalytic subunit of protein phosphatase 2A and is involved in suppression of JNK activation, leading to Bim dephosphorylation (35,36).…”

“…Peritoneal B cells are thought to be the source of autoantibody-producing long-lived plasma cells in various autoimmune-prone mice such as New Zealand Black (NZB) and BXSB mice (5,6), and mice genetically engineered for various molecules involved in signal transduction pathways of B cell survival and apoptosis (7)(8)(9)(10)(11)(12)(13)(14) …”