Search

B cells are selected for an intermediate level of B-cell antigen receptor (BCR) signalling strength: attenuation below minimum (for example, non-functional BCR) or hyperactivation above maximum (for example, self-reactive BCR) thresholds of signalling strength causes negative selection. In ∼25% of cases, acute lymphoblastic leukaemia (ALL) cells carry the oncogenic BCR-ABL1 tyrosine kinase (Philadelphia chromosome positive), which mimics constitutively active pre-BCR signalling. Current therapeutic approaches are largely focused on the development of more potent tyrosine kinase inhibitors to suppress oncogenic signalling below a minimum threshold for survival. We tested the hypothesis that targeted hyperactivation--above a maximum threshold--will engage a deletional checkpoint for removal of self-reactive B cells and selectively kill ALL cells. Here we find, by testing various components of proximal pre-BCR signalling in mouse BCR-ABL1 cells, that an incremental increase of Syk tyrosine kinase activity was required and sufficient to induce cell death. Hyperactive Syk was functionally equivalent to acute activation of a self-reactive BCR on ALL cells. Despite oncogenic transformation, this basic mechanism of negative selection was still functional in ALL cells. Unlike normal pre-B cells, patient-derived ALL cells express the inhibitory receptors PECAM1, CD300A and LAIR1 at high levels. Genetic studies revealed that Pecam1, Cd300a and Lair1 are critical to calibrate oncogenic signalling strength through recruitment of the inhibitory phosphatases Ptpn6 (ref. 7) and Inpp5d (ref. 8). Using a novel small-molecule inhibitor of INPP5D (also known as SHIP1), we demonstrated that pharmacological hyperactivation of SYK and engagement of negative B-cell selection represents a promising new strategy to overcome drug resistance in human ALL.

Severe malaria, including cerebral malaria (CM) and placental malaria (PM), have been recognized to have many of the features of uncontrolled inflammation. We recently showed that in mice genetic susceptibility to the lethal inflammatory autoimmune disease, systemic lupus erythematosus (SLE), conferred resistance to CM. Protection appeared to be mediated by immune mechanisms that allowed SLE-prone mice, prior to the onset of overt SLE symptoms, to better control their inflammatory response to Plasmodium infection. Here we extend these findings to ask does SLE susceptibility have 1) a cost to reproductive fitness and/or 2) an effect on PM in mice? The rates of conception for WT and SLE susceptible (SLE(s)) mice were similar as were the number and viability of fetuses in pregnant WT and SLE(s) mice indicating that SLE susceptibility does not have a reproductive cost. We found that Plasmodium chabaudi AS (Pc) infection disrupted early stages of pregnancy before the placenta was completely formed resulting in massive decidual necrosis 8 days after conception. Pc-infected pregnant SLE(s) mice had significantly more fetuses (∼1.8 fold) but SLE did not significantly affect fetal viability in infected animals. This was despite the fact that Pc-infected pregnant SLE(s) mice had more severe symptoms of malaria as compared to Pc-infected pregnant WT mice. Thus, although SLE susceptibility was not protective in PM in mice it also did not have a negative impact on reproductive fitness.

The inositol phosphatases phosphatase and tensin homologue (PTEN) and Src homology 2 domain-containing inositol phosphatase (SHIP) negatively regulate phosphatidylinositol-3-kinase (PI3K)-mediated growth, survival, and proliferation of hematopoietic cells. Although deletion of PTEN in mouse T cells results in lethal T cell lymphomas, we find that animals lacking PTEN or SHIP in B cells show no evidence of malignancy. However, concomitant deletion of PTEN and SHIP (bPTEN/SHIP(-/-)) results in spontaneous and lethal mature B cell neoplasms consistent with marginal zone lymphoma or, less frequently, follicular or centroblastic lymphoma. bPTEN/SHIP(-/-) B cells exhibit enhanced survival and express more MCL1 and less Bim. These cells also express low amounts of p27(kip1) and high amounts of cyclin D3 and thus appear poised to undergo proliferative expansion. Unlike normal B cells, bPTEN/SHIP(-/-) B cells proliferate to the prosurvival factor B cell activating factor (BAFF). Interestingly, although BAFF availability may promote lymphoma progression, we demonstrate that BAFF is not required for the expansion of transferred bPTEN/SHIP(-/-) B cells. This study reveals that PTEN and SHIP act cooperatively to suppress B cell lymphoma and provides the first direct evidence that SHIP is a tumor suppressor. As such, assessment of both PTEN and SHIP function are relevant to understanding the etiology of human B cell malignancies that exhibit augmented activation of the PI3K pathway.

Introduction Lupus nephritis is one of the most severe organ manifestations of systemic lupus erythematosus (SLE) and a main cause of morbidity in patients who progress to end-stage kidney disease [...], Lupus nephritis is a severe organ manifestation in systemic lupus erythematosus leading to kidney failure in a subset of patients. In lupus-prone mice, controlled infection with Plasmodium parasites protects against the progression of autoimmune pathology including lethal glomerulonephritis. Here, we demonstrate that parasite-induced protection was not due to a systemic effect of infection on autoimmunity as previously assumed, but rather to specific alterations in immune cell infiltrates into kidneys and renal draining lymph nodes. Infection of lupus-prone mice with a Plasmodium parasite did not reduce the levels or specificities of autoreactive antibodies, vasculitis, immune complex-induced innate activation, or hypoxia. Instead, infection uniquely reduced kidney-infiltrating CCL17-producing bone marrow-derived type 2 inflammatory dendritic cells (iDC2s). Bone marrow reconstitution experiments revealed that infection with Plasmodium caused alterations in bone marrow cells that hindered the ability of DC2s to infiltrate the kidneys. The essential role for CCL17 in lupus nephritis was confirmed by in vivo depletion with a blocking antibody, which reduced kidney pathology and immune infiltrates, while bypassing the need for parasitic infection. Therefore, infiltration into the kidneys of iDC2s, with the potential to prime local adaptive responses, is an essential regulated event in the transition from manageable glomerulonephritis to lethal tubular injury.

SLE is an autoimmune disease characterized by chronic stimulation of the innate immune system by endogenous nucleic acids (1,6). SLE patients are often treated with strong immunosuppressive regimens' including cytotoxic [...], Glucocorticoids are widely used to treat patients with autoimmune diseases such as systemic lupus erythematosus (SLE) (1,2). However, regimens used to treat many such conditions cannot maintain disease control in the majority of SLE patients and more aggressive approaches such as high-dose methylprednisolone pulse therapy are used to provide transient reductions in disease activity (3,4). The primary anti-inflammatory mechanism of glucocorticoids is thought to be NF-κB inhibition (5). Recognition of self nucleic acids by toll-like receptors TLR7 and TLR9 on B cells and plasmacytoid dendritic cells (PDCs) is an important step in the pathogenesis of SLE (6), promoting anti-nuclear antibodies and the production of type I interferon (IFN), both correlated with the severity of disease (1,7). Following their activation by self-nucleic acid-associated immune complexes, PDCs migrate to the tissues (8,9). We demonstrate, in vitro and in vivo, that stimulation of PDCs through TLR7 and 9 can account for the reduced activity of glucocorticoids to inhibit the IFN pathway in SLE patients and in two lupus-prone mouse strains. The triggering of PDCs through TLR7 and 9 by nucleic acid-containing immune complexes or by synthetic ligands activates the NF-κB pathway essential for PDC survival. Glucocorticoids do not affect NF-κB activation in PDCs, preventing glucocorticoid induction of PDC death and the consequent reduction of systemic IFN-α levels. These findings unveil a new role for self nucleic acid recognition by TLRs and indicate that inhibitors of TLR7 and 9 signalling could prove to be effective corticosteroid-sparing drugs.

This paper reports an analysis of the functional interactions between type IV secretion systems (T4SS) that are part of the conjugative machinery for horizontal DNA transfer (cT4SS), and T4SS involved in bacterial pathogenicity (pT4SS). The authors' previous work showed that a conjugative coupling protein (T4CP) interacts with the VirB10-type component of the T4SS in order to recruit the protein-DNA complex to the transporter for conjugative DNA transfer. This study now shows by two-hybrid analysis that conjugative T4CPs also interact with the VirB10 element of the pT4SS of Agrobacterium tumefaciens (At), Bartonella tribocorum (Bt) and Brucella suis (Bs). Moreover, the VirB10 component of a cT4SS (protein TrwE of plasmid R388) could be partially substituted by that of a pT4SS (protein TrwE of Bt) for conjugation. This result opens the way for the construction of hybrid T4SS that deliver DNA into animal cells. Interestingly, in the presence of part of the Bs T4SS the R388 T4SS protein levels were decreased and R388 conjugation was strongly inhibited. Complementation assays between the Trw systems of R388 and Bt showed that only individual components from the so-called 'core complex' could be exchanged, supporting the concept that this core is the common scaffold for the transport apparatus while the other 'peripheral components' are largely system-specific.

Author(s): Zhengshan Chen; Seyedmehdi Shojaee; Maike Buchner; Huimin Geng; Jae Woong Lee; Lars Klemm; Bjrn Titz; Thomas G. Graeber; Eugene Park; Ying Xim Tan; Anne Satterthwaite; Elisabeth Paietta; Stephen P. [...]

An inositol polyphosphate 5'-phosphatase, SHIP, and a tyrosine phosphatase, SHP-1, play a key role in the modulation of immune receptor activation by inhibitory coreceptors. A study was conducted to examine the necessity, interaction or redundancy of these signaling molecules. The findings indicate that SHP-1-mediated inhibitory signaling prevents apoptosis while SHIP recruitment attenuates a proapoptotic signal initiated by FcgammaRIIB.

Inhibitory signalling by the Fc receptor, FcgammaRIIB, proceeds without the involvement of the SH2-domain containing protein tyrosine phosphatase, SHP-1, in the mast cells. This results in the attachment of the SH2-domain containing inositol polyphosphate 5-phosphatase or SHIP to the tyrosine-phosphorylated 13-amino-acid of Fcgamma RIIB in both B-cells and mast cells. The hydrolysis of 5-phosphate of phosphatidylinositol/inositol gives a mechanism for the FcgammaRIIB inhibition of calcium influx triggered by immune receptors.

A single active site has been theorized to catalyze the three chemical steps involved in the non-replicative transposition of transposon-transposase protein Tn10/IS10 complex. The single active site was determined after studies of four tranposase mutations showed an intact synaptic complex even with the deletion of a chemical step. A single transposase monomer at each end of the DNA catalyzes the cleavage of two strands, with the strand transfer catalyzed by the same monomer that catalyzed the cleavage.

Plasmid R388 oriT is capable of site-specific recombination of its direct repeat in the presence of the region R388, involved in DNA processing during conjugation. Gene trwC in the region is essential for plasmid R388 oriT specific recombination. A nicking-closing enzyme is involved in conjugal DNA transfer and influences oriT specific recombination of two oriT copies in the absence of conjugation.