Serum amyloid A protects murine macrophages from lethal toxin-mediated death.

Lethal toxin, a key virulence factor produced by Bacillus anthracis, induces cell death, in part by disrupting numerous signaling pathways, in mouse macrophages. However, exposure to sublethal doses of lethal toxin allows some cells to survive. Because these pro-survival signaling events occur within a few hours after exposure to sublethal doses, we hypothesized that acute phase proteins might influence macrophage survival. Our data show that serum amyloid A (SAA) is produced in response to lethal toxin treatment. Moreover, pre-treatment of macrophages with exogenous SAA protected macrophages from lethal toxin-mediated death. Exogenous SAA activated the p38 mitogen activated protein kinase (MAP) kinase pathway, while lethal toxin mutants incapable of p38 activation were incapable of causing cell death. Chemical inhibition of the p38 activation pathway abrogated the protective effects of SAA. These data show that SAA affords protection against lethal toxin in mouse macrophages and link this response to the p38 pathway.

Deficiencies in the DNA Binding Protein ARID3a Alter Chromatin Structures Important for Early Human Erythropoiesis.

ARID3a is a DNA-binding protein important for normal hematopoiesis in mice and for in vitro lymphocyte development in human cultures. ARID3a knockout mice die in utero with defects in both early hematopoietic stem cell populations and erythropoiesis. Recent transcriptome analyses in human erythropoietic systems revealed increases in ARID3a transcripts implicating potential roles for ARID3a in human erythrocyte development. However, ARID3a transcript levels do not faithfully reflect protein levels in many cells, and the functions and requirements for ARID3a protein in those systems have not been explored. We used the erythroleukemic cell line K562 as a model to elucidate functions of ARID3a protein in early human erythropoiesis. ARID3a knockdown of hemin-stimulated K562 cells resulted in lack of fetal globin production and modifications in gene expression. Temporal RNA sequencing data link ARID3a expression with the important erythroid regulators Gata1, Gata2, and Klf1 Ablation of ARID3a using CRISPR-Cas9 further demonstrated it is required to maintain chromatin structures associated with erythropoietic differentiation potential. These data demonstrate that the ARID3a protein is required for early erythropoietic events and provide evidence for the requirement of ARID3a functions for proper maintenance of appropriate chromatin structures.

Disease activity in systemic lupus erythematosus correlates with expression of the transcription factor AT-rich-interactive domain 3A.

OBJECTIVE: Systemic lupus erythematosus (SLE) is a complex and multifactorial autoimmune disease with striking clinical, immunologic, and genetic heterogeneity, despite nearly ubiquitous antinuclear antibody (ANA) production. Multiple gene polymorphisms have been associated with the disease, but these individually account for only a very small percentage of overall SLE risk. In earlier studies, constitutive expression of the DNA-binding protein AT-rich-interactive domain 3A (ARID3a) in transgenic mouse B lymphocyte lineage cells led to spontaneous ANA production and preferential development of B cells associated with production of polyreactive antibodies. Therefore, we undertook this study to determine whether ARID3a was overexpressed in B lymphocytes of SLE patients and whether ARID3a expression was associated with disease severity. METHODS: A cross-section of SLE patients, rheumatoid arthritis patients, and age- and sex-matched controls was analyzed longitudinally for lupus disease activity, numbers of ARID3a+ peripheral blood mononuclear B cells from multiple B cell subsets, and immunoglobulin and cytokine levels. RESULTS: Fifty of 115 SLE patients (43%) had dramatically increased numbers of ARID3a+ B cells compared to healthy controls. ARID3a was not expressed in naive B cells of healthy controls, but was abundant in these precursors of antibody-secreting cells in SLE patients. Total numbers of ARID3a+ B cells correlated with increased disease activity as defined by SLE Disease Activity Index scores in individuals assessed at 3 time points. CONCLUSION: These findings identify B cell anomalies in SLE that allow stratification of patient samples based on ARID3a expression and implicate ARID3a as a potential marker of CD19+ B lymphocytes correlated with disease activity.

The ARID family transcription factor bright is required for both hematopoietic stem cell and B lineage development.

Bright/Arid3a has been characterized both as an activator of immunoglobulin heavy-chain transcription and as a proto-oncogene. Although Bright expression is highly B lineage stage restricted in adult mice, its expression in the earliest identifiable hematopoietic stem cell (HSC) population suggests that Bright might have additional functions. We showed that >99% of Bright(-/-) embryos die at midgestation from failed hematopoiesis. Bright(-/-) embryonic day 12.5 (E12.5) fetal livers showed an increase in the expression of immature markers. Colony-forming assays indicated that the hematopoietic potential of Bright(-/-) mice is markedly reduced. Rare survivors of lethality, which were not compensated by the closely related paralogue Bright-derived protein (Bdp)/Arid3b, suffered HSC deficits in their bone marrow as well as B lineage-intrinsic developmental and functional deficiencies in their peripheries. These include a reduction in a natural antibody, B-1 responses to phosphocholine, and selective T-dependent impairment of IgG1 class switching. Our results place Bright/Arid3a on a select list of transcriptional regulators required to program both HSC and lineage-specific differentiation.