Mammalian Bre1 complexes (BRE1A/B (RNF20/40) in humans and Bre1a/b (Rnf20/40) in mice) function similarly to their yeast homolog Bre1 as ubiquitin ligases in monoubiquitination of histone H2B. This ubiquitination facilitates methylation of histone H3 at K4 and K79, and accounts for the roles of Bre1 and its homologs in transcriptional regulation. Recent studies by others suggested that Bre1 acts as a tumor suppressor, augmenting expression of select tumor suppressor genes and suppressing select oncogenes. In this study we present an additional mechanism of tumor suppression by Bre1 through maintenance of genomic stability. We track the evolution of genomic instability in Bre1-deficient cells from replication-associated double-strand breaks (DSBs) to specific genomic rearrangements that explain a rapid increase in DNA content and trigger breakage-fusion-bridge cycles. We show that aberrant RNA-DNA structures (R-loops) constitute a significant source of DSBs in Bre1-deficient cells. Combined with a previously reported defect in homologous recombination, generation of R-loops is a likely initiator of replication stress and genomic instability in Bre1-deficient cells. We propose that genomic instability triggered by Bre1 deficiency may be an important early step that precedes acquisition of an invasive phenotype, as we find decreased levels of BRE1A/B and dimethylated H3K79 in testicular seminoma and in the premalignant lesion in situ carcinoma.

A hallmark of SLE is the production of high-titer, high-affinity, isotype-switched IgG autoantibodies directed against nucleic acid-associated antigens. Several studies have established a role for both type I IFN (IFN-I) and the activation of TLRs by nucleic acid-associated autoantigens in the pathogenesis of this disease. Here, we demonstrate that 2 IFN-I signaling molecules, IFN regulatory factor 9 (IRF9) and STAT1, were required for the production of IgG autoantibodies in the pristane-induced mouse model of SLE. In addition, levels of IgM autoantibodies were increased in pristane-treated Irf9 -/-mice, suggesting that IRF9 plays a role in isotype switching in response to self antigens. Upregulation of TLR7 by IFN-α was greatly reduced in Irf9 -/-and Stat1 -/-B cells. Irf9 -/-B cells were incapable of being activated through TLR7, and Stat1 -/-B cells were impaired in activation through both TLR7 and TLR9. These data may reveal a novel role for IFN-I signaling molecules in both TLR-specific B cell responses and production of IgG autoantibodies directed against nucleic acid-associated autoantigens. Our results suggest that IFN-I is upstream of TLR signaling in the activation of autoreactive B cells in SLE.

Lymphoid deficiency after allogeneic hematopoietic cell transplantation (HCT) results in increased susceptibility to infection; however, transplantation of mature lymphocytes frequently results in a serious complication known as graft-versushost disease (GVHD). Here we demonstrate in mice that both congenic as well as allogeneic transplantation of low numbers of highly purified common lymphoid progenitors ( IntroductionMyeloablative doses of chemoradiation therapy used in preparation for hematopoietic cell transplantation (HCT) lead to depletion of hematopoietic stem cells (HSCs), progenitor cells, and mature cells. The resulting immunodeficiency results in a profound susceptibility to bacterial, fungal, and viral infections. The recovery of a functional immune system after HCT is dependent upon the de novo regeneration of all hematopoietic lineages from HSCs and progenitor cells and on the function of mature cells contained in the graft. Infections after HCT typically follow a reproducible temporal pattern correlating with the kinetics of immune reconstitution. Viral infections occur later during the phase of lymphoid deficiency resulting from reactivation of herpesviruses such as cytomegalovirus (CMV), varicella zoster, and Epstein-Barr virus. 1 T-and B-cell deficiency is usually protracted, resolving only after several months to years. The nature of the immunodeficiency following allogeneic HCT is further complicated by the potential to develop graft-versushost disease (GVHD), which has been shown to contribute to thymic stroma perturbations, lymphoid hypoplasia, and B-cell dysfunction. [2][3][4][5][6] Consequently, GVHD and the resultant administration of immunosuppressive agents are both associated with a significantly increased risk of lethal infectious complications.One of the most common and potentially lethal manifestations of lymphoid deficiency is infection with CMV. 7 Therefore, numerous clinical and animal studies were undertaken to characterize the complex immune response to CMV and to develop treatment strategies involving antiviral drugs as well as cellular therapies and vaccination. 8,9 Although advances were made, new strategies to prevent infections after HCT while minimizing GVHD are still warranted. We propose that modifying grafts by inclusion of committed progenitor cells can be used to protect against infections. 10 Hematopoietic cell populations at different levels of commitment have been phenotypically identified in both mice and humans and can be prospectively isolated. These populations include HSCs, common lymphoid progenitors (CLPs), common myeloid progenitors (CMPs), and, downstream of CMPs, granulocyte-monocyte progenitors (GMPs) and megakaryocyte-erythroid progenitors (MEPs). [11][12][13][14][15][16][17] In vivo studies using competitive reconstitution assays in congenic mice showed that transplantation of CLPs, CMPs, GMPs, or MEPs resulted in accelerated reconstitution of the respective mature cell compartments compared with transplantation of HSCs alone. 13,16 Our studies show...