Hongshan Wang

BAFF-induced NEMO-independent processing of NF-|[kappa]|B2 in maturing B cells

NF-κB is usually activated by signal-induced, ubiquitin-mediated degradation of its inhibitor, IκB. This process is initiated by phosphorylation of IκB by the IκB kinase (IKK) complex, predominantly by the IKKβ catalytic subunit, and requires the regulatory subunit IKKγ (NEMO). Another activation pathway, with no known physiological inducers, involves ubiquitin-mediated processing of the NF-κB2 inhibitory protein p100 and is dependent on phosphorylation of p100 by IKKα. We show here that B cell–activating factor (BAFF) activates this second pathway and that this requires the BAFF receptor (BAFF-R), the NF-κB–inducing kinase (NIK) and protein synthesis, but not NEMO. This NEMO-independent cascade is physiologically relevant for the survival and, hence, progression of maturing splenic B cells.

The Adaptor Protein CIKS/Act1 Is Essential for IL-25-Mediated Allergic Airway Inflammation

IL-17 is the signature cytokine of recently discovered Th type 17 (Th17) cells, which are prominent in defense against extracellular bacteria and fungi as well as in autoimmune diseases, such as rheumatoid arthritis and experimental autoimmune encephalomyelitis in animal models. IL-25 is a member of the IL-17 family of cytokines, but has been associated with Th2 responses instead and may negatively cross-regulate Th17/IL-17 responses. IL-25 can initiate an allergic asthma-like inflammation in the airways, which includes recruitment of eosinophils, mucus hypersecretion, Th2 cytokine production, and airways hyperreactivity. We demonstrate that these effects of IL-25 are entirely dependent on the adaptor protein CIKS (also known as Act1). Surprisingly, this adaptor is necessary to transmit IL-17 signals as well, despite the very distinct biologic responses that these two cytokines elicit. We identify CD11c+ macrophage-like lung cells as physiologic relevant targets of IL-25 in vivo.

Interleukin-17 Cytokines Are Critical in Development of Fatal Lupus Glomerulonephritis

Systemic lupus erythematosus is a potentially fatal autoimmune disease. Although interleukin-17 (IL-17) has been linked to human lupus and mouse models of this disease, it has not been addressed whether this cytokine plays a critical role in fatal lupus pathology. Here we have demonstrated that increased production of IL-17 cytokines and their signaling via the adaptor protein CIKS (a.k.a. Traf3ip2, Act1) critically contributed to lethal pathology in an FcgammaR2b-deficient mouse model of lupus. Mice lacking IL-17 and especially those lacking CIKS showed greatly improved survival and were largely protected from development of glomerulonephritis. Importantly in this model, potential effects of IL-17 cytokines on antibody production could be distinguished from critical local contributions in kidneys, including recruitment of neutrophils and monocytes. These findings provide the proof of principle that signaling by IL-17 family cytokines mediated via CIKS presents promising therapeutic targets for the treatment of systemic lupus erythematosus, especially in cases with kidney involvement.

IL-17 drives psoriatic inflammation via distinct, target cell-specific mechanisms

Significance Psoriasis is an inflammatory disease affecting the skin, a barrier site. The disease is characterized by abnormal growth of keratinocytes and infiltration of inflammatory cells. Clinical trials targeting the IL-17 cytokine have shown remarkable efficacy, and IL-17 also has been strongly implicated in the imiquimod-induced mouse model of psoriasis. However why IL-17 cytokines should be so central is not known, because target cells and their functions have not been clearly delineated. Here we demonstrate that IL-17 signaling into nonkeratinocytes, specifically dermal fibroblasts, induces mediators that further increase IL-17 production by innate γδT cells and promote cellular infiltration, whereas IL-17 signaling into keratinocytes aids proliferation and blocks their differentiation. These findings reveal the circuitry underpinning critical disease-driving effects of IL-17. Psoriasis is a chronic inflammatory skin disease characterized by abnormal keratinocyte proliferation and differentiation and by an influx of inflammatory cells. The mechanisms underlying psoriasis in humans and in mouse models are poorly understood, although evidence strongly points to crucial contributions of IL-17 cytokines, which signal via the obligatory adaptor CIKS/Act1. Here we identify critical roles of CIKS/Act1-mediated signaling in imiquimod-induced psoriatic inflammation, a mouse model that shares features with the human disease. We found that IL-17 cytokines/CIKS-mediated signaling into keratinocytes is essential for neutrophilic microabscess formation and contributes to hyperproliferation and markedly attenuated differentiation of keratinocytes, at least in part via direct effects. In contrast, IL-17 cytokines/CIKS-mediated signaling into nonkeratinocytes, particularly into dermal fibroblasts, promotes cellular infiltration and, importantly, leads to enhanced the accumulation of IL-17–producing γδT cells in skin, comprising a positive feed-forward mechanism. Thus, CIKS-mediated signaling is central in the development of both dermal and epidermal hallmarks of psoriasis, inducing distinct pathologies via target cell-specific effects. CIKS-mediated signaling represents a potential therapeutic target in psoriasis.

The adaptor protein CIKS/ACT1 is necessary for collagen‐induced arthritis, and it contributes to the production of collagen‐specific antibody

OBJECTIVE CIKS/ACT1 is an adaptor molecule that is necessary for signaling by members of the interleukin-17 cytokine family. The aim of this study was to determine whether this adaptor is required for the initiation of collagen-induced arthritis (CIA). If it is required, then CIKS-mediated signaling could be a potential target for therapeutic intervention in patients with rheumatoid arthritis (RA). METHODS CIA model studies were performed with CIKS-deficient and CIKS-sufficient mice on an otherwise wild-type (WT) C57BL/6 background or on a C57BL/6 background lacking Fcγ receptor IIb (FcγRIIb). In addition, collagen antibody-induced arthritis (CAIA) studies were performed in WT and CIKS-deficient mice. Pathologic changes of arthritis were evaluated by visual inspection of the paws, by histochemical analysis of tissue sections, and by measurements of collagen-specific antibodies. RESULTS Pathologic changes of CIA were readily induced in WT mice, with exacerbation of the changes in FcγRIIb-deficient mice. In contrast, CIKS-deficient mice were protected from all aspects of CIA pathology, even on an FcγRIIb-deficient background. The absence of CIKS completely prevented neutrophil infiltration into joints, bone erosion, and cartilage damage; furthermore, the production of type II collagen (CII)-specific antibodies was reduced. In contrast to the CIA model, CIKS-deficient mice in the CAIA model remained susceptible to arthritis. CONCLUSION CIKS-mediated signaling is necessary for the pathogenesis of CIA, but not CAIA. These findings suggest critical functions of CIKS during the development of arthritis in the CIA model, including in the formation of CII antibodies, and they mark the CIKS adaptor as a potential therapeutic target in RA.

Improved Antibacterial Host Defense and Altered Peripheral Granulocyte Homeostasis in Mice Lacking the Adhesion Class G Protein Receptor CD97

ABSTRACT CD97 is a member of the adhesion family of G protein-coupled receptors. Alternatively spliced forms of CD97 bind integrins α5β1 and αvβ3, decay accelerating factor, or dermatan sulfate. CD97 is expressed on myeloid cells at high levels and a variety of other cell types at lower levels. Little is known about the physiological function of CD97. To begin dissecting the function of CD97, we evaluated the immune response of CD97 null mice to systemic infection by Listeria monocytogenes. CD97 null mice were significantly more resistant to listeriosis than matched wild-type mice. A major determinant of the difference in survival appeared to be the comparatively more robust accumulation of granulocytes in the blood and in infected livers of CD97 null mice within 18 h of inoculation, correlating with a decrease in the number of bacteria. CD97 null mice also displayed a mild granulocytosis in the nonchallenged state. Because there is a strong suggestion that CD97 functions in an adhesive capacity, we examined the migratory properties of granulocytes in CD97 null mice. In chimeric animals, CD97 null and wild-type granulocytes migrated similarly, as determined by inflammation-induced emigration from the bone marrow and accumulation in the peritoneum. Granulocyte development in the bone marrow of CD97 null mice was comparable to that of wild-type mice, and CD97 deficiency did not appear to stimulate granulocytosis secondary to peripheral inflammation and resultant granulocyte colony-stimulating factor induction, unlike various other models of adhesion deficiencies. Our results suggest that CD97 plays a role in peripheral granulocyte homeostasis.

Cell-Autonomous Role for NF-κB in Immature Bone Marrow B Cells

The NF-κB transcription factors have many essential functions in B cells, such as during differentiation and proliferation of Ag-challenged mature B cells, but also during final maturation of developing B cells in the spleen. Among the various specific functions NF-κB factors carry out in these biologic contexts, their ability to assure the survival of mature and maturing B cells in the periphery stands out. Less clear is what if any roles NF-κB factors play during earlier stages of B cell development in the bone marrow. Using mice deficient in both NF-κB1 and NF-κB2, which are thus partially compromised in both the classical and alternative activation pathways, we demonstrate a B cell-autonomous contribution of NF-κB to the survival of immature B cells in the bone marrow. NF-κB1 and NF-κB2 also play a role during the earlier transition from proB to late preB cells; however, in this context these factors do not act in a B cell-autonomous fashion. Although NF-κB1 and NF-κB2 are not absolutely required for survival and progression of immature B cells in the bone marrow, they nevertheless make a significant contribution that marks the beginning of the profound cell-autonomous control these factors exert during all subsequent stages of B cell development. Therefore, the lifelong dependency of B cells on NF-κB-mediated survival functions is set in motion at the time of first expression of a full BCR.

Conditional deletion of Ccm2 causes hemorrhage in the adult brain: a mouse model of human cerebral cavernous malformations

Cerebral cavernous malformations (CCM) are irregularly shaped and enlarged capillaries in the brain that are prone to hemorrhage, resulting in headaches, seizures, strokes and even death in patients. The disease affects up to 0.5% of the population and the inherited form has been linked to mutations in one of three genetic loci, CCM1, CCM2 and CCM3. To understand the pathophysiology underlying the vascular lesions in CCM, it is critical to develop a reproducible mouse genetic model of this disease. Here, we report that limited conditional ablation of Ccm2 in young adult mice induces observable neurological dysfunction and reproducibly results in brain hemorrhages whose appearance is highly reminiscent of the lesions observed in human CCM patients. We first demonstrate that conventional or endothelial-specific deletion of Ccm2 leads to fatal cardiovascular defects during embryogenesis, including insufficient vascular lumen formation as well as defective arteriogenesis and heart malformation. These findings confirm and extend prior studies. We then demonstrate that the inducible deletion of Ccm2 in adult mice recapitulates the CCM-like brain lesions in humans; the lesions display disrupted vascular lumens, enlarged capillary cavities, loss of proper neuro-vascular associations and an inflammatory reaction. The CCM lesions also exhibit damaged neuronal architecture, the likely cause of neurologic defects, such as ataxia and seizure. These mice represent the first CCM2 animal model for CCM and should provide the means to elucidate disease mechanisms and evaluate therapeutic strategies for human CCM.

The IκB Family Member Bcl-3 Coordinates the Pulmonary Defense against Klebsiella pneumoniae Infection

Bcl-3 is an atypical member of the IκB family that has the potential to positively or negatively modulate nuclear NF-κB activity in a context-dependent manner. Bcl-3’s biologic impact is complex and includes roles in tumorigenesis and diverse immune responses, including innate immunity. Bcl-3 may mediate LPS tolerance, suppressing cytokine production, but it also seems to contribute to defense against select systemic bacterial challenges. However, the potential role of Bcl-3 in organ-specific host defense against bacteria has not been addressed. In this study, we investigated the relevance of Bcl-3 in a lung challenge with the Gram-negative pathogen Klebsiella pneumoniae. In contrast to wild-type mice, Bcl-3–deficient mice exhibited significantly increased susceptibility toward K. pneumoniae pneumonia. The mutant mice showed increased lung damage marked by neutrophilic alveolar consolidation, and they failed to clear bacteria in lungs, which correlated with increased bacteremic dissemination. Loss of Bcl-3 incurred a dramatic cytokine imbalance in the lungs, which was characterized by higher levels of IL-10 and a near total absence of IFN-γ. Moreover, Bcl-3–deficient mice displayed increased lung production of the neutrophil-attracting chemokines CXCL-1 and CXCL-2. Alveolar macrophages and neutrophils are important to antibacterial lung defense. In vitro stimulation of Bcl-3–deficient alveolar macrophages with LPS or heat-killed K. pneumoniae recapitulated the increase in IL-10 production, and Bcl-3–deficient neutrophils were impaired in intracellular bacterial killing. These findings suggest that Bcl-3 is critically involved in lung defense against Gram-negative bacteria, modulating functions of several cells to facilitate efficient clearance of bacteria.

The Oncoprotein and Transcriptional Regulator Bcl-3 Governs Plasticity and Pathogenicity of Autoimmune T Cells

Bcl-3 is an atypical member of the IκB family that modulates transcription in the nucleus via association with p50 (NF-κB1) or p52 (NF-κB2) homodimers. Despite evidence attesting to the overall physiologic importance of Bcl-3, little is known about its cell-specific functions or mechanisms. Here we demonstrate a T-cell-intrinsic function of Bcl-3 in autoimmunity. Bcl-3-deficient T cells failed to induce disease in T cell transfer-induced colitis and experimental autoimmune encephalomyelitis. The protection against disease correlated with a decrease in Th1 cells that produced the cytokines IFN-γ and GM-CSF and an increase in Th17 cells. Although differentiation into Th1 cells was not impaired in the absence of Bcl-3, differentiated Th1 cells converted to less-pathogenic Th17-like cells, in part via mechanisms involving expression of the RORγt transcription factor. Thus, Bcl-3 constrained Th1 cell plasticity and promoted pathogenicity by blocking conversion to Th17-like cells, revealing a unique type of regulation that shapes adaptive immunity.