Receptor activity-modifying proteins of adrenomedullin (RAMP2/3): Roles in the pathogenesis of ARDS

Acute respiratory distress syndrome (ARDS) is a life-threatening lung condition characterized by widespread inflammation and pulmonary edema. Adrenomedullin (AM), a bioactive peptide with various functions, is expected to be applied in treating ARDS. Its functions are regulated primarily by two receptor activity-modifying proteins, RAMP2 and RAMP3, which bind to the AM receptor calcitonin receptor-like receptor (CLR). However, the roles of RAMP2 and RAMP3 in ARDS remain unclear. We generated a mouse model of ARDS via intratracheal administration of lipopolysaccharide (LPS), and analyzed the pathophysiological significance of RAMP2 and RAMP3. RAMP2 expression declined with LPS administration, whereas RAMP3 expression increased at low doses and decreased at high doses of LPS. After LPS administration, drug-inducible vascular endothelial cell-specific RAMP2 knockout mice (DI-E-RAMP2-/-) showed reduced survival, increased lung weight, and had more apoptotic cells in the lungs. DI-E-RAMP2-/- mice exhibited reduced expression of Epac1 (which regulates vascular endothelial cell barrier function), while RAMP3 was upregulated in compensation. In contrast, after LPS administration, RAMP3-/- mice showed no significant changes in survival, lung weight, or lung pathology, although they exhibited significant downregulation of iNOS, TNF-α, and NLRP3 during the later stages of inflammation. Based on transcriptomic analysis, RAMP2 contributed more to the circulation-regulating effects of AM, whereas RAMP3 contributed more to its inflammation-regulating effects. These findings indicate that, while both RAMP2 and RAMP3 participate in ARDS pathogenesis, their functions differ distinctly. Further elucidation of the pathophysiological significance and functional differences between RAMP2 and RAMP3 is critical for the future therapeutic application of AM in ARDS.

Interferon regulatory factor-2 is required for the establishment of the gut intraepithelial T cell compartment

CD8αα + intestinal intraepithelial lymphocytes (iIELs) are known for their unique role in keeping the integrity of the intestinal epithelial barrier, but factors affecting the development of these cells have not been thoroughly understood. Here we found that the transcriptional regulator interferon regulatory factor-2 (IRF-2) plays a cell-intrinsic, indispensable role in establishing iIEL populations. CD8αα +, but not CD8αβ +, iIELs bearing TCRαβ or TCRγδ were severely reduced in numbers in mice lacking this factor (Irf2–/– mice). Moreover, the majority of residual CD8αα +TCRαβ + iIELs in these mice were immature as judged from their Thy1.2 high phenotype and inefficient T-bet expression. Thymic IEL precursors isolated from Irf2–/– mice failed to efficiently generate CD8αα +TCRαβ + and TCRγδ + IELs upon transfer in vivo and CD8αα +TCRαβ + cells in response to IL-15 in vitro. Double mutant mice lacking both IL-15 and IRF-2 showed an even more severe iIEL defect than in mice lacking IL-15 alone. Upon increasing agonistic TCR signal strength through OT-II TCR transgenesis, CD8αα +TCRαβ + iIELs became more abundant but remained immature on the Irf2–/– background. Our current observations thus revealed the unique bimodal role that IRF-2 plays in promoting not only generation of IEL progenitors in the thymus but also maturation of iIELs in the periphery in IL-15-dependent and -independent manners.

TAK1 Limits Death Receptor Fas-Induced Proinflammatory Cell Death in Macrophages

Fas, a member of the death receptor family, plays a central role in initiating cell death, a biological process crucial for immune homeostasis. However, the immunological and pathophysiological impacts to which enhanced Fas signaling gives rise remain to be fully understood. Here we demonstrate that TGF-β–activated kinase 1 (TAK1) works as a negative regulator of Fas signaling in macrophages. Upon Fas engagement with high concentrations of FasL, mouse primary macrophages underwent cell death, and, surprisingly, Fas stimulation led to proteolytic cleavage of gasdermin (GSDM) family members GSDMD and GSDME, a hallmark of pyroptosis, in a manner dependent on caspase enzymatic activity. Remarkably, TAK1-deficient macrophages were highly sensitive to even low concentrations of FasL. Mechanistically, TAK1 negatively modulated RIPK1 kinase activity to protect macrophages from excessive cell death. Intriguingly, mice deficient for TAK1 in macrophages (TAK1mKO mice) spontaneously developed tissue inflammation, and, more important, the emergence of inflammatory disease symptoms was markedly diminished in TAK1mKO mice harboring a catalytically inactive RIPK1. Taken together, these findings not only revealed an unappreciated role of TAK1 in Fas-induced macrophage death but provided insight into the possibility of perturbation of immune homeostasis driven by aberrant cell death.

Presence of periodontitis may synergistically contribute to cancer progression via Treg and IL-6

A close causal relationship has been suggested to exist between cancer and periodontitis. We hypothesized that the immune surveillance system is impaired in patients with periodontitis, which contributes to cancer development and growth. Therefore, the present study investigated the relationship between immune surveillance mechanisms and periodontitis in cancer patients. The presence or absence of periodontitis was assessed and the peripheral blood (PB) concentrations of IL-6, immunosuppressive cytokines (VEGF, TGF-β1, and CCL22) and proportion of T regulatory cells (Treg, CD3 + CD4 + CD25 + Foxp3 +) were measured. Subjects were classified into the following four groups: non-cancer patients without periodontitis (C − P −), non-cancer patients with periodontitis (C − P +), cancer patients without periodontitis (C + P −), and cancer patients with periodontitis (C + P +). The results of a multivariate analysis showed that the PB concentration of IL-6 was significantly higher in C + than in C- and higher in C + P + than in C + P −. The PB proportion of Treg was significantly higher in C + P + than in C + P −, C − P + , and C − P −. The results of this study suggested that the presence of periodontitis and cancer synergistically increased Treg in PB, which may be one of the underlying causes of immunosuppression and immune evasion in cancer. It was also suggested that the presence of periodontal disease and/or cancer also increases IL-6 in PB, which would be associated with cancer progression. These results suggest the possibility that the presence of periodontitis might synergistically contribute to cancer progression.

Circulating T cells and resident non-T cells restrict type 2 innate lymphoid cell expansion in the small intestine

Interaction among various adaptive, circulating cells and tissue-resident cells including innate lymphocytes during the establishment and maintenance of the barrier-tissue immune system has only recently started to be explored. Here, we show that the cellular crosstalk with circulating T cells and other resident cells regulated the population size of type 2 innate lymphoid cells (ILC2s) in the small intestine lamina propria. Rag1^-/- mice had excessive numbers of both ILC2s and ILC3s, and such an over-expansion was corrected by establishing parabiosis with wild type mice or by adoptively transferring wild type CD4⁺ T cells. In contrast, anti-CD3 antibody-mediated T cell depletion in wild type mice increased ILC2 but not ILC3 numbers. Unconventional CD4^-CD8^- αβ T and γδ T cells could also restrict ILC2 expansion as the numbers of ILC2s were not altered even in mice treated with anti-CD4/anti-CD8 antibodies. ILC3 restriction seemed to be through the control of proliferation, but that for ILC2s did not. In addition, elevation in ILC2 numbers seen in mice lacking the transcription factors RORγt and STAT6 was found to be T cell-independent. Our current findings altogether uncovered the homeostatic 'quota' restriction imposed on intestinal ILC2s in the steady state by resident non-T cells via RORγt- and STAT6-dependent mechanisms as well as by conventional and nonconventional T cells.

Adrenomedullin Ameliorates Pulmonary Fibrosis by Regulating TGF-ß-Smads Signaling and Myofibroblast Differentiation

Pulmonary fibrosis is an irreversible, potentially fatal disease. Adrenomedullin (AM) is a multifunctional peptide whose activity is regulated by receptor activity-modifying protein 2 (RAMP2). In the present study, we used the bleomycin (BLM)-induced mouse pulmonary fibrosis model to investigate the pathophysiological significance of the AM-RAMP2 system in the lung. In heterozygous AM knockout mice (AM+/-), hydroxyproline content and Ashcroft scores reflecting the fibrosis severity were significantly higher than in wild-type mice (WT). During the acute phase after BLM administration, FACS analysis showed significant increases in eosinophil, monocyte, and neutrophil infiltration into the lungs of AM+/-. During the chronic phase, fibrosis-related molecules were upregulated in AM+/-. Notably, nearly identical changes were observed in RAMP2+/-. AM administration reduced fibrosis severity. In the lungs of BLM-administered AM+/-, the activation level of Smad3, a receptor-activated Smad, was higher than in WT. In addition, Smad7, an antagonistic Smad, was downregulated and microRNA-21, which targets Smad7, was upregulated compared to WT. Isolated AM+/- lung fibroblasts showed less proliferation and migration capacity than WT fibroblasts. Stimulation with TGF-β increased the numbers of α-SMA-positive myofibroblasts, which were more prominent among AM+/- cells. TGF-β-stimulated AM+/- myofibroblasts were larger and exhibited greater contractility and extracellular matrix production than WT cells. These cells were α-SMA (+), F-actin (+), and Ki-67(-) and appeared to be nonproliferating myofibroblasts (non-p-MyoFbs), which contribute to the severity of fibrosis. Our findings suggest that in addition to suppressing inflammation, the AM-RAMP2 system ameliorates pulmonary fibrosis by suppressing TGF-β-Smad3 signaling, microRNA-21 activity and differentiation into non-p-MyoFbs.

Extracellular mRNA transported to the nucleus exerts translation-independent function

RNA in extracellular vesicles (EVs) are uptaken by cells, where they regulate fundamental cellular functions. EV-derived mRNA in recipient cells can be translated. However, it is still elusive whether “naked nonvesicular extracellular mRNA” (nex-mRNA) that are not packed in EVs can be uptaken by cells and, if so, whether they have any functions in recipient cells. Here, we show the entrance of nex-mRNA in the nucleus, where they exert a translation-independent function. Human nex-interleukin-1β (IL1β)-mRNA outside cells proved to be captured by RNA-binding zinc finger CCCH domain containing protein 12D (ZC3H12D)-expressing human natural killer (NK) cells. ZC3H12D recruited to the cell membrane binds to the 3′-untranslated region of nex-IL1β-mRNA and transports it to the nucleus. The nex-IL1β-mRNA in the NK cell nucleus upregulates antiapoptotic gene expression, migration activity, and interferon-γ production, leading to the killing of cancer cells and antimetastasis in mice. These results implicate the diverse actions of mRNA.

Nonvesicular extracellular RNA (nex-RNA) that are not packed in extracellular vesicles is detected outside the cell, but it is poorly understood. Here the authors report that nex-RNA is captured by a zinc finger protein and transported to the nucleus to enhance antimetastatic characters of the cell.

Staphylococcal superantigen-like 12 activates murine bone marrow derived mast cells

Staphylococcal superantigen-like (SSL) protein is a family of exotoxins that consists of 14 SSLs, and the roles of several SSLs in immune evasion of the cocci have been revealed. However little is known whether they act as immune activators and are involved in inflammatory disorders such as atopic dermatitis. In this study we examined whether SSLs activate mast cells, the key player of local inflammation. SSL12 evoked the release of a granule enzyme β-hexosaminidase from bone marrow derived mast cells (BMMCs) in the absence of IgE. The release of the granule enzyme caused by SSL12 was not accompanied with the leakage of a cytosolic enzyme lactate dehydrogenase (LDH), unlike staphylococcal δ-toxin that was reported to induce both the release of β-hexosaminidase and the leakage of LDH from the cells, suggesting that SSL12 evokes the degranulation of mast cells without cell membrane damage. Furthermore SSL12 induced IL-6 and IL-13 in both mRNA and protein levels indicating that SSL12 induces de novo synthesis of the cytokines. Evans blue extravasation was elevated by the intradermal injection of SSL12, suggesting that SSL12 is also able to evoke local inflammation in vivo. These findings indicate the novel mast cell activating activity of SSLs, and SSL12 is likely an important factor in both initiation phase and effector phase of allergic and immune responses.

Generation of a common innate lymphoid cell progenitor requires interferon regulatory factor 2

Innate lymphoid cells (ILCs), composed of heterogeneous populations of lymphoid cells, contribute critically to immune surveillance at mucosal surfaces. ILC subsets develop from common lymphoid progenitors through stepwise lineage specification. However, the composition and temporal regulation of the transcription factor network governing such a process remain incompletely understood. Here, we report that deletion of the transcription factor interferon regulatory factor 2 (IRF-2), known also for its importance in the maturation of conventional NK cells, resulted in an impaired generation of ILC1, ILC2 and ILC3 subsets with lymphoid tissue inducer (LTi)-like cells hardly affected. In IRF-2-deficient mice, PD-1hi ILC precursors (ILCPs) that generate these three ILCs but not LTi-like cells were present at normal frequency, while their sub-population expressing high amounts of PLZF, another marker for ILCPs, was severely reduced. Notably, these IRF-2-deficient ILCPs contained normal quantities of PLZF-encoding Zbtb16 messages, and PLZF expression in developing invariant NKT cells within the thymus was unaffected in these mutant mice. These results point to a unique, cell-type selective role for IRF-2 in ILC development, acting at a discrete step critical for the generation of functionally competent ILCPs.

Water intake increases mesenteric lymph flow and the total flux of albumin, long-chain fatty acids, and IL-22 in rats: new concept of absorption in jejunum

The traditional Japanese health care custom recommends that a suitable volume of water is consumed. However, physiological and immunological mechanisms in support of this practice are unknown. Therefore, we conducted rat and rabbit in vivo experiments to investigate the effects of intragastric administration of distilled water on the jejunal-originated lymph flow and the concentrations and total flux of cells, albumin, long-chain fatty acids, and innate lymphoid cell 3 (ILC-3)-secreted interleukin-22 (IL-22) through mesenteric lymph vessels. The distribution and activity of ILC-3 in rat small intestine by water intake were evaluated using flow cytometry and RT-PCR. The intragastric administration of distilled water caused significant increases in rat mesenteric lymph flow and in the total flux of cells, albumin, long-chain fatty acids, and IL-22 through the lymph vessels. Intravenously injected Evans blue dye was rapidly transported into rabbit mesenteric lymph vessel and cisterna chyli. The distribution of ILC-3 and the expression of IL-22 mRNA were maximal in the lamina propria cells of the rat jejunum. No significant presence of ILC-3 in the lymph was observed in the control and under water intake conditions. In conclusion, the absorbed water in the jejunum is transported through mesenteric lymph vessels. The higher permeability of albumin in the jejunal microcirculation may play key roles in the transport of consumed water and the reservoir and transporter of long-chain fatty acids. Water intake also accelerates the transfer of IL-22 to the mesenteric lymph, which may contribute, in part, to maintaining and promoting the innate immunity in the body. NEW & NOTEWORTHY The higher permeability of albumin-mediated transport of water-soluble substances in mesenteric lymph vessels of the jejunum may have a large impact on the classic concept suggesting that water-soluble small molecules travel to the liver via the portal vein. ILC-3 is mainly housed in the lamina propria of the jejunum, especially its upper part. IL-22 released from the ILC-3 is also transported through mesenteric lymph in collaboration with the albumin-mediated movement of consumed water.

Topologically protected surface states in a centrosymmetric superconductor β-PdBi2

The topological aspects of electrons in solids can emerge in real materials, as represented by topological insulators. In theory, they show a variety of new magneto-electric phenomena, and especially the ones hosting superconductivity are strongly desired as candidates for topological superconductors. While efforts have been made to develop possible topological superconductors by introducing carriers into topological insulators, those exhibiting indisputable superconductivity free from inhomogeneity are very few. Here we report on the observation of topologically protected surface states in a centrosymmetric layered superconductor, β-PdBi₂, by utilizing spin- and angle-resolved photoemission spectroscopy. Besides the bulk bands, several surface bands are clearly observed with symmetrically allowed in-plane spin polarizations, some of which crossing the Fermi level. These surface states are precisely evaluated to be topological, based on the Z₂ invariant analysis in analogy to three-dimensional strong topological insulators. β-PdBi₂ may offer a solid stage to investigate the topological aspect in the superconducting condensate.

Materials possessing topologically non-trivial electronic surface states are predicted to host exotic Majorana fermion excitations in the superconducting state. Here, the authors demonstrate the existence of topologically-protected surface states in the centrosymmetric layered superconductor β-PdBi2.

Conditional Deletion of TAK1 in T Cells Reveals a Pivotal Role of TCRαβ+ Intraepithelial Lymphocytes in Preventing Lymphopenia-Associated Colitis

The kinase TAK is required for the development of conventional and regulatory T cells. We previously reported that mice with conditional deletion of TAK1 in T cells (Lck-cre:TAK1fl/fl mice) exhibited severe T lymphopenia, and were nevertheless predisposed to spontaneous colitis with unknown etiology. Here we focused on the immunopathological mechanism in colitic Lck-cre:TAK1fl/fl mice. We found that 'leaky' CD4+ T cells retaining TAK1 acquired inflammatory phenotypes that contribute to disease onset in Lck-cre:TAK1fl/fl mice. Furthermore, the gut microbiota-triggered signaling was also a key event leading to the pathogenesis. We discovered that Lck-cre:TAK1fl/fl mice were almost completely devoid of TCRαβ+CD8α+ intestinal intraepithelial lymphocytes (IELs) and this was largely due to the developmental defect of the thymic precursors by TAK1 deficiency. Remarkably, transfer of TCRαβ+CD8α+ IELs from wild-type mice ameliorated colitis in Lck-cre:TAK1fl/fl mice. Taken together, our current study highlighted the emerging role of TAK1 in configuring the gut-specialized T cell subset, which regulates mucosal homeostasis under lymphopenic conditions.

Positive feedback within a kinase signaling complex functions as a switch mechanism for NF-κB activation

A switchlike response in nuclear factor-κB (NF-κB) activity implies the existence of a threshold in the NF-κB signaling module. We show that the CARD-containing MAGUK protein 1 (CARMA1, also called CARD11)-TAK1 (MAP3K7)-inhibitor of NF-κB (IκB) kinase-β (IKKβ) module is a switch mechanism for NF-κB activation in B cell receptor (BCR) signaling. Experimental and mathematical modeling analyses showed that IKK activity is regulated by positive feedback from IKKβ to TAK1, generating a steep dose response to BCR stimulation. Mutation of the scaffolding protein CARMA1 at serine-578, an IKKβ target, abrogated not only late TAK1 activity, but also the switchlike activation of NF-κB in single cells, suggesting that phosphorylation of this residue accounts for the feedback.

Essential roles of K63-linked polyubiquitin-binding proteins TAB2 and TAB3 in B cell activation via MAPKs

Polyubiquitination of proteins plays a critical role in the activation of immune cells. K63-linked polyubiquitin-binding proteins TGF-β-activated kinase 1 (TAK1)-binding protein (TAB)2 and TAB3 are implicated in NF-κB signaling via TAK1 activation. However, TAB2 alone is dispensable for NF-κB activation in embryonic fibroblasts, and the functional roles of TAB2 and TAB3 in immune cells has yet to be clarified. In this study, we demonstrate that TAB2 and TAB3 are essential for B cell activation leading to Ag-specific Ab responses, as well as B-1 and marginal zone B cell development. TAB2 and TAB3 are critical for the activation of MAPKs, especially ERK, but not NF-κB, in response to TLR and CD40 stimulation in B cells. Surprisingly, TAB2 and TAB3 are dispensable for TAK1 activation in B cells, indicating that TAB2 and TAB3 activate MAPKs via a pathway independent of TAK1. In contrast to B cells, macrophages lacking TAB2 and TAB3 did not show any defects in the cytokine production and the signaling pathway in response to TLR stimulation. Furthermore, TAB2 and TAB3 were dispensable for TNF-induced cytokine production in embryonic fibroblasts. Thus, TAB2- and TAB3-mediated K63-linked polyubiquitin recognition controls B cell activation via MAPKs, but not the TAK1/NF-κB axis.

Differential requirements for IRF-2 in generation of CD1d-independent T cells bearing NK cell receptors

NK cell receptors (NKRs) such as NK1.1, NKG2D, and Ly49s are expressed on subsets of CD1d-independent memory phenotype CD8(+) and CD4(-)CD8(-) T cells. However, the mechanism for the generation and functions of these NKR(+) T cells remained elusive. In this study, we found that CD1d-independent Ly49(+) T cells were reduced severely in the spleen, bone marrow, and liver, but not thymus, in mice doubly deficient for IFN regulatory factor-2 (IRF-2) and CD1d, in which the overall memory phenotype T cell population was contrastingly enlarged. Because a large fraction of Ly49(+) T cells coexpressed NK1.1 or NKG2D, the reduction of Ly49(+) T cells resulted indirectly in underrepresentation of NK1.1(+) or NKG2D(+) cells. Ly49(+) T cell deficiency was observed in IRF-2(-/-) mice additionally lacking IFN-α/βR α-chain (IFNAR1) as severely as in IRF-2(-/-) mice, arguing against the involvement of the accelerated IFN-α/β signals due to IRF-2 deficiency. Rather, mice lacking IFN-α/βR alone also exhibited relatively milder Ly49(+) T cell reduction, and IL-2 could expand Ly49(+) T cells from IFNAR1(-/-), but not from IRF-2(-/-), spleen cells in vitro. These results together indicated that IRF-2 acted in Ly49(+) T cell development in a manner distinct from that of IFN-α/β signals. The influence of IRF-2 deficiency on Ly49(+) memory phenotype T cells observed in this study suggested a unique transcriptional program for this T cell population among other NKR(+) T and memory phenotype T cells.

Polymorphic variants of LIGHT (TNF superfamily-14) alter receptor avidity and bioavailability

The TNF superfamily member homologous to lymphotoxins, exhibits inducible expression, and competes with HSV glycoprotein D for herpesvirus entry mediator (HVEM), a receptor expressed by T lymphocytes (LIGHT) [TNF superfamily (SF)-14], is a key cytokine that activates T cells and dendritic cells and is implicated as a mediator of inflammatory, metabolic, and malignant diseases. LIGHT engages the lymphotoxin-beta receptor (LTbetaR) and HVEM (TNFRSF14), but is competitively limited in activating these receptors by soluble decoy receptor-3 (DcR3; TNFRSF6B). Two variants in the human LIGHT alter the protein at E214K (rs344560) in the receptor-binding domain and S32L (rs2291667) in the cytosolic domain; however, the functional impact of these polymorphisms is unknown. A neutralizing Ab failed to bind the LIGHT-214K variant, indicating this position as a part of the receptor-binding region. Relative to the predominant reference variant S32/E214, the other variants showed altered avidity with LTbetaR and less with HVEM. Heterotrimers of the LIGHT variants decreased binding avidity to DcR3 and minimized the inhibitory effect of DcR3 toward LTbetaR-induced activation of NF-kappaB. In patients with immune-mediated inflammatory diseases, such as rheumatoid arthritis, DcR3 protein levels were significantly elevated. Immunohistochemistry revealed synoviocytes as a significant source of DcR3 production, and DcR3 hyperexpression is controlled by posttranscriptional mechanisms. The increased potential for LTbetaR signaling, coupled with increased bioavailability due to lower DcR3 avidity, provides a mechanism of how polymorphic variants in LIGHT could contribute to the pathogenesis of inflammatory diseases.

Allosteric regulation of the ubiquitin:NIK and ubiquitin:TRAF3 E3 ligases by the lymphotoxin-beta receptor

The lymphotoxin-beta receptor (LTbetaR) activates the NF-kappaB2 transcription factors, p100 and RelB, by regulating the NF-kappaB-inducing kinase (NIK). Constitutive proteosomal degradation of NIK limits NF-kappaB activation in unstimulated cells by the ubiquitin:NIK E3 ligase comprised of subunits TNFR-associated factors (TRAF)3, TRAF2, and cellular inhibitor of apoptosis (cIAP). However, the mechanism releasing NIK from constitutive degradation remains unclear. We found that insertion of a charge-repulsion mutation in the receptor-binding crevice of TRAF3 ablated binding of both LTbetaR and NIK suggesting a common recognition site. A homologous mutation in TRAF2 inhibited cIAP interaction and blocked NIK degradation. Furthermore, the recruitment of TRAF3 and TRAF2 to the ligated LTbetaR competitively displaced NIK from TRAF3. Ligated LTbetaR complexed with TRAF3 and TRAF2 redirected the specificity of the ubiquitin ligase reaction to polyubiquitinate TRAF3 and TRAF2, leading to their proteosomal degradation. Stimulus-dependent degradation of TRAF3 required the RING domain of TRAF2, but not of TRAF3, implicating TRAF2 as a key E3 ligase in TRAF turnover. The combined action of competitive displacement of NIK and TRAF degradation halted NIK turnover, and promoted its association with IKKalpha and signal transmission. These results indicate the LTbetaR modifies the ubiquitin:NIK E3 ligase, and also acts as an allosteric regulator of the ubiquitin:TRAF E3 ligase.

T cell intrinsic heterodimeric complexes between HVEM and BTLA determine receptivity to the surrounding microenvironment

The inhibitory cosignaling pathway formed between the TNF receptor herpesvirus entry mediator (HVEM, TNFRSF14) and the Ig superfamily members, B and T lymphocyte attenuator (BTLA) and CD160, limits the activation of T cells. However, BTLA and CD160 can also serve as activating ligands for HVEM when presented in trans by adjacent cells, thus forming a bidirectional signaling pathway. BTLA and CD160 can directly activate the HVEM-dependent NF-kappaB RelA transcriptional complex raising the question of how NF-kappaB activation is repressed in naive T cells. In this study, we show BTLA interacts with HVEM in cis, forming a heterodimeric complex in naive T cells that inhibits HVEM-dependent NF-kappaB activation. The cis-interaction between HVEM and BTLA is the predominant form expressed on the surface of naive human and mouse T cells. The BTLA ectodomain acts as a competitive inhibitor blocking BTLA and CD160 from binding in trans to HVEM and initiating NF-kappaB activation. The TNF-related ligand, LIGHT (homologous to lymphotoxins, exhibits inducible expression, and competes with HSV glycoprotein D for HVEM, a receptor expressed by T lymphocytes, or TNFSF14) binds HVEM in the cis-complex, but NF-kappaB activation was attenuated, suggesting BTLA prevents oligomerization of HVEM in the cis-complex. Genetic deletion of BTLA or pharmacologic disruption of the HVEM-BTLA cis-complex in T cells promoted HVEM activation in trans. Interestingly, herpes simplex virus envelope glycoprotein D formed a cis-complex with HVEM, yet surprisingly, promoted the activation NF-kappaB RelA. We suggest that the HVEM-BTLA cis-complex competitively inhibits HVEM activation by ligands expressed in the surrounding microenvironment, thus helping maintain T cells in the naive state.

Extracellular signal-regulated protein kinase 2 is required for efficient generation of B cells bearing antigen-specific immunoglobulin G

Activation of extracellular signal-regulated protein kinase (ERK) has been implicated in proliferation as well as differentiation in a wide variety of cell types. Using B-cell-specific gene-targeted mice, we report here that in T-cell-dependent immune responses, ERK2 is required to generate efficient immunoglobulin G (IgG) production. In its absence, the proportion of antigen-specific surface IgG1-bearing cells and the subsequent number of IgG1 antibody-secreting cells were decreased, despite apparently unimpaired class switch recombination. Notably, this defect was countered by overexpression of the antiapoptotic factor Bcl-2. Together, our results suggest that ERK2 plays a key role in efficient generation of antigen-specific IgG-bearing B cells by promoting their survival.

TAK1 is indispensable for development of T cells and prevention of colitis by the generation of regulatory T cells

Transforming growth factor (TGF)-beta-activating kinase 1 (TAK1) is critical for Toll-like receptor- and tumor necrosis factor-mediated cellular responses. In B cells, TAK1 is essential for the activation of mitogen-activated protein kinases (MAPKs), but not nuclear factor-kappaB (NF-kappaB), in antigen receptor signaling. In this study, we generate T cell-specific TAK1-deficient (Lck(Cre/(+))Tak1(flox/flox)) mice and show that TAK1 is indispensable for the maintenance of peripheral CD4 and CD8 T cells. In thymocytes, TAK1 is essential for TCR-mediated activation of both NF-kappaB and MAPKs. Additionally, Lck(Cre/(+))Tak1(flox/flox) mice developed colitis as they aged. In these mice, accumulations of activated/memory T cells as well as B cells were observed. Development of regulatory T (Treg) cells in thymus was abrogated in Lck(Cre/(+))Tak1(flox/flox) mice, suggesting that the loss of Treg cells is the cause of the disease. Together, the results show that TAK1, by controlling the generation of central Treg cells, is important for preventing spontaneously developing colitis.

Key function for the Ubc13 E2 ubiquitin-conjugating enzyme in immune receptor signaling

The Ubc13 E2 ubiquitin-conjugating enzyme is key in the process of 'tagging' target proteins with lysine 63-linked polyubiquitin chains, which are essential for the transmission of immune receptor signals culminating in activation of the transcription factor NF-kappaB. Here we demonstrate that conditional ablation of Ubc13 resulted in defective B cell development and in impaired B cell and macrophage activation. In response to all tested stimuli except tumor necrosis factor, Ubc13-deficient cells showed almost normal NF-kappaB activation but considerably impaired activation of mitogen-activated protein kinase. Ubc13-induced activation of mitogen-activated protein kinase required, at least in part, ubiquitination of the adaptor protein IKKgamma. These results show that Ubc13 is key in the mammalian immune response.

TAK1 is a master regulator of epidermal homeostasis involving skin inflammation and apoptosis

Transforming growth factor beta-activated kinase 1 (TAK1) functions downstream of inflammatory cytokines to activate c-Jun N-terminal kinase (JNK) as well as NF-kappaB in several cell types. However, the functional role of TAK1 in an in vivo setting has not been determined. Here we have demonstrated that TAK1 is the major regulator of skin inflammation as well as keratinocyte death in vivo. Epidermal-specific deletion of TAK1 causes a severe inflammatory skin condition by postnatal day 6-8. The mutant skin also exhibits massive keratinocyte death. Analysis of keratinocytes isolated from the mutant skin revealed that TAK1 deficiency results in a striking increase in apoptosis in response to tumor necrosis factor (TNF). TAK1-deficient keratinocytes cannot activate NF-kappaB or JNK upon TNF treatment. These results suggest that TNF induces TAK1-deficient keratinocyte death because of the lack of NF-kappaB (and possibly JNK)-mediated cell survival signaling. Finally, we have shown that deletion of the TNF receptor can largely rescue keratinocyte death as well as inflammatory skin condition in epidermal-specific TAK1-deficient mice. Our results demonstrate that TAK1 is a master regulator of TNF signaling in skin and regulates skin inflammation and keratinocyte death.

Macrophage/cancer cell interactions mediate hormone resistance by a nuclear receptor derepression pathway

Defining the precise molecular strategies that coordinate patterns of transcriptional responses to specific signals is central for understanding normal development and homeostasis as well as the pathogenesis of hormone-dependent cancers. Here we report specific prostate cancer cell/macrophage interactions that mediate a switch in function of selective androgen receptor antagonists/modulators (SARMs) from repression to activation in vivo. This is based on an evolutionarily conserved receptor N-terminal L/HX7LL motif, selectively present in sex steroid receptors, that causes recruitment of TAB2 as a component of an N-CoR corepressor complex. TAB2 acts as a sensor for inflammatory signals by serving as a molecular beacon for recruitment of MEKK1, which in turn mediates dismissal of the N-CoR/HDAC complex and permits derepression of androgen and estrogen receptor target genes. Surprisingly, this conserved sensor strategy may have arisen to mediate reversal of sex steroid-dependent repression of a limited cohort of target genes in response to inflammatory signals, linking inflammatory and nuclear receptor ligand responses to essential reproductive functions.

BANK Negatively Regulates Akt Activation and Subsequent B Cell Responses

BANK is an adaptor protein that is highly expressed in B cells. To investigate its physiological role, we generated BANK-deficient mice. BANK-deficient mice displayed enhanced germinal center formation and IgM production in response to T-dependent antigens, whereas this phenotype was blocked in CD40-BANK double knockout mice. Involvement of BANK in CD40 signaling was further demonstrated by in vitro analysis. CD40-mediated proliferation and survival were significantly increased in BANK-deficient B cells, with enhanced Akt activation, whereas introduction of dominant-negative Akt into BANK-deficient B cells suppressed the augmented CD40-mediated responses. Together, our findings suggest that BANK attenuates CD40-mediated Akt activation, thereby preventing hyperactive B cell responses.

TAK1 is a component of the Epstein-Barr virus LMP1 complex and is essential for activation of JNK but not of NF-kappaB

Epstein-Barr virus latent membrane protein 1 (LMP1) activates NF-kappaB and c-Jun N-terminal kinase (JNK), which is essential for LMP1 oncogenic activity. Genetic analysis has revealed that tumor necrosis factor receptor-associated factor 6 (TRAF6) is an indispensable intermediate of LMP1 signaling leading to activation of both NF-kappaB and JNK. However, the mechanism by which LMP1 engages TRAF6 for activation of NF-kappaB and JNK is not well understood. Here we demonstrate that TAK1 mitogen-activated protein kinase kinase kinase and TAK1-binding protein 2 (TAB2), together with TRAF6, are recruited to LMP1 through its N-terminal transmembrane region. The C-terminal cytoplasmic region of LMP1 facilitates the assembly of this complex and enhances activation of JNK. In contrast, IkappaB kinase gamma is recruited through the C-terminal cytoplasmic region and this is essential for activation of NF-kappaB. Furthermore, we found that ablation of TAK1 resulted in the loss of LMP1-induced activation of JNK but not of NF-kappaB. These results suggest that an LMP1-associated complex containing TRAF6, TAB2, and TAK1 plays an essential role in the activation of JNK. However, TAK1 is not an exclusive intermediate for NF-kappaB activation in LMP1 signaling.

PKC beta regulates BCR-mediated IKK activation by facilitating the interaction between TAK1 and CARMA1

The B cell antigen receptor (BCR)–mediated activation of IκB kinase (IKK) and nuclear factor–κB require protein kinase C (PKC)β; however, the mechanism by which PKCβ regulates IKK is unclear. Here, we demonstrate that another protein kinase, TGFβ-activated kinase (TAK)1, is essential for IKK activation in response to BCR stimulation. TAK1 interacts with the phosphorylated CARMA1 (also known as caspase recruitment domain [CARD]11, Bimp3) and this interaction is mediated by PKCβ. IKK is also recruited to the CARMA1–Bcl10–mucosal-associated lymphoid tissue 1 adaptor complex in a PKCβ-dependent manner. Hence, our data suggest that phosphorylation of CARMA1, mediated by PKCβ, brings two key protein kinases, TAK1 and IKK, into close proximity, thereby allowing TAK1 to phosphorylate IKK.

Essential function for the kinase TAK1 in innate and adaptive immune responses

Transforming growth factor-beta-activated kinase 1 (TAK1) has been linked to interleukin 1 receptor and tumor necrosis factor receptor signaling. Here we generated mouse strains with conditional expression of a Map3k7 allele encoding part of TAK1. TAK1-deficient embryonic fibroblasts demonstrated loss of responses to interleukin 1beta and tumor necrosis factor. Studies of mice with B cell-specific TAK1 deficiency showed that TAK1 was indispensable for cellular responses to Toll-like receptor ligands, CD40 and B cell receptor crosslinking. In addition, antigen-induced immune responses were considerably impaired in mice with B cell-specific TAK1 deficiency. TAK1-deficient cells failed to activate transcription factor NF-kappaB and mitogen-activated protein kinases in response to interleukin 1beta, tumor necrosis factor and Toll-like receptor ligands. However, TAK1-deficient B cells were able to activate NF-kappaB but not the kinase Jnk in response to B cell receptor stimulation. These results collectively indicate that TAK1 is key in the cellular response to a variety of stimuli.

TAK1-binding protein 2 facilitates ubiquitination of TRAF6 and assembly of TRAF6 with IKK in the IL-1 signaling pathway

TAK1 mitogen-activated protein kinase kinase kinase participates in the Interleukin-1 (IL-1) signaling pathway by mediating activation of JNK, p38, and NF-kappaB. TAK1-binding protein 2 (TAB2) was previously identified as an adaptor that links TAK1 to an upstream signaling intermediate, tumor necrosis factor receptor-associated factor 6 (TRAF6). Recently, ubiquitination of TRAF6 was shown to play an essential role in the activation of TAK1. However, the mechanism by which IL-1 induces TRAF6 ubiquitination remains to be elucidated. Here we report that TAB2 functions to facilitate TRAF6 ubiquitination and thereby mediates IL-1-induced cellular events. A conserved ubiquitin binding domain in TAB2, the CUE domain, is important for this function. We also found that TAB2 promotes the assembly of TRAF6 with a downstream kinase, IkappaB kinase (IKK). These results show that TAB2 acts as a multifunctional signaling molecule, facilitating both IL-1-dependent TRAF6 ubiquitination and assembly of the IL-1 signaling complex.

The roles of two IkappaB kinase-related kinases in lipopolysaccharide and double stranded RNA signaling and viral infection

Viral infection and stimulation with lipopolysaccharide (LPS) or double stranded RNA (dsRNA) induce phosphorylation of interferon (IFN) regulatory factor (IRF)-3 and its translocation to the nucleus, thereby leading to the IFN-beta gene induction. Recently, two IkappaB kinase (IKK)-related kinases, inducible IkappaB kinase (IKK-i) and TANK-binding kinase 1 (TBK1), were suggested to act as IRF-3 kinases and be involved in IFN-beta production in Toll-like receptor (TLR) signaling and viral infection. In this work, we investigated the physiological roles of these kinases by gene targeting. TBK1-deficient embryonic fibroblasts (EFs) showed dramatic decrease in induction of IFN-beta and IFN-inducible genes in response to LPS or dsRNA as well as after viral infection. However, dsRNA-induced expression of these genes was residually detected in TBK1-deficient cells and intact in IKK-i-deficient cells, but completely abolished in IKK-i/TBK1 doubly deficient cells. IRF-3 activation, in response not only to dsRNA but also to viral infection, was impaired in TBK1-deficient cells. Together, these results demonstrate that TBK1 as well as, albeit to a lesser extent, IKK-i play a crucial role in the induction of IFN-beta and IFN-inducible genes in both TLR-stimulated and virus-infected EFs.

Role of adaptor TRIF in the MyD88-independent toll-like receptor signaling pathway

Stimulation of Toll-like receptors (TLRs) triggers activation of a common MyD88-dependent signaling pathway as well as a MyD88-independent pathway that is unique to TLR3 and TLR4 signaling pathways leading to interferon (IFN)-beta production. Here we disrupted the gene encoding a Toll/IL-1 receptor (TIR) domain-containing adaptor, TRIF. TRIF-deficient mice were defective in both TLR3- and TLR4-mediated expression of IFN-beta and activation of IRF-3. Furthermore, inflammatory cytokine production in response to the TLR4 ligand, but not to other TLR ligands, was severely impaired in TRIF-deficient macrophages. Mice deficient in both MyD88 and TRIF showed complete loss of nuclear factor kappa B activation in response to TLR4 stimulation. These findings demonstrate that TRIF is essential for TLR3- and TLR4-mediated signaling pathways facilitating mammalian antiviral host defense.

TAB2 is essential for prevention of apoptosis in fetal liver but not for interleukin-1 signaling

The proinflammatory cytokine interleukin-1 (IL-1) transmits a signal via several critical cytoplasmic proteins such as MyD88, IRAKs and TRAF6. Recently, serine/threonine kinase TAK1 and TAK1 binding protein 1 and 2 (TAB1/2) have been identified as molecules involved in IL-1-induced TRAF6-mediated activation of AP-1 and NF-kappa B via mitogen-activated protein (MAP) kinases and I kappa B kinases, respectively. However, their physiological functions remain to be clarified. To elucidate their roles in vivo, we generated TAB2-deficient mice. The TAB2 deficiency was embryonic lethal due to liver degeneration and apoptosis. This phenotype was similar to that of NF-kappa B p65-, IKK beta-, and NEMO/IKK gamma-deficient mice. However, the IL-1-induced activation of NF-kappa B and MAP kinases was not impaired in TAB2-deficient embryonic fibroblasts. These findings demonstrate that TAB2 is essential for embryonic development through prevention of liver apoptosis but not for the IL-1 receptor-mediated signaling pathway.

Essential role for TIRAP in activation of the signalling cascade shared by TLR2 and TLR4

Signal transduction through Toll-like receptors (TLRs) originates from their intracellular Toll/interleukin-1 receptor (TIR) domain, which binds to MyD88, a common adaptor protein containing a TIR domain. Although cytokine production is completely abolished in MyD88-deficient mice, some responses to lipopolysaccharide (LPS), including the induction of interferon-inducible genes and the maturation of dendritic cells, are still observed. Another adaptor, TIRAP (also known as Mal), has been cloned as a molecule that specifically associates with TLR4 and thus may be responsible for the MyD88-independent response. Here we report that LPS-induced splenocyte proliferation and cytokine production are abolished in mice lacking TIRAP. As in MyD88-deficient mice, LPS activation of the nuclear factor NF-kappaB and mitogen-activated protein kinases is induced with delayed kinetics in TIRAP-deficient mice. Expression of interferon-inducible genes and the maturation of dendritic cells is observed in these mice; they also show defective response to TLR2 ligands, but not to stimuli that activate TLR3, TLR7 or TLR9. In contrast to previous suggestions, our results show that TIRAP is not specific to TLR4 signalling and does not participate in the MyD88-independent pathway. Instead, TIRAP has a crucial role in the MyD88-dependent signalling pathway shared by TLR2 and TLR4.

Small anti-viral compounds activate immune cells via the TLR7 MyD88-dependent signaling pathway

The imidazoquinoline compounds imiquimod and R-848 are low-molecular-weight immune response modifiers that can induce the synthesis of interferon-alpha and other cytokines in a variety of cell types. These compounds have potent anti-viral and anti-tumor properties; however, the mechanisms by which they exert their anti-viral activities remain unclear. Here we show that the imidazoquinolines activate immune cells via the Toll-like receptor 7 (TLR7)-MyD88-dependent signaling pathway. In response to the imidazoquinolines, neither MyD88- nor TLR7-deficient mice showed any inflammatory cytokine production by macrophages, proliferation of splenocytes or maturation of dendritic cells. Imidazoquinoline-induced signaling events were also abolished in both MyD88- and TLR7-deficient mice.

A Toll-like receptor recognizes bacterial DNA

DNA from bacteria has stimulatory effects on mammalian immune cells, which depend on the presence of unmethylated CpG dinucleotides in the bacterial DNA. In contrast, mammalian DNA has a low frequency of CpG dinucleotides, and these are mostly methylated; therefore, mammalian DNA does not have immuno-stimulatory activity. CpG DNA induces a strong T-helper-1-like inflammatory response. Accumulating evidence has revealed the therapeutic potential of CpG DNA as adjuvants for vaccination strategies for cancer, allergy and infectious diseases. Despite its promising clinical use, the molecular mechanism by which CpG DNA activates immune cells remains unclear. Here we show that cellular response to CpG DNA is mediated by a Toll-like receptor, TLR9. TLR9-deficient (TLR9-/-) mice did not show any response to CpG DNA, including proliferation of splenocytes, inflammatory cytokine production from macrophages and maturation of dendritic cells. TLR9-/- mice showed resistance to the lethal effect of CpG DNA without any elevation of serum pro-inflammatory cytokine levels. The in vivo CpG-DNA-mediated T-helper type-1 response was also abolished in TLR9-/- mice. Thus, vertebrate immune systems appear to have evolved a specific Toll-like receptor that distinguishes bacterial DNA from self-DNA.

A Toll-like receptor recognizes bacterial DNA

DNA from bacteria has stimulatory effects on mammalian immune cells, which depend on the presence of unmethylated CpG dinucleotides in the bacterial DNA. In contrast, mammalian DNA has a low frequency of CpG dinucleotides, and these are mostly methylated; therefore, mammalian DNA does not have immuno-stimulatory activity. CpG DNA induces a strong T-helper-1-like inflammatory response. Accumulating evidence has revealed the therapeutic potential of CpG DNA as adjuvants for vaccination strategies for cancer, allergy and infectious diseases. Despite its promising clinical use, the molecular mechanism by which CpG DNA activates immune cells remains unclear. Here we show that cellular response to CpG DNA is mediated by a Toll-like receptor, TLR9. TLR9-deficient (TLR9-/-) mice did not show any response to CpG DNA, including proliferation of splenocytes, inflammatory cytokine production from macrophages and maturation of dendritic cells. TLR9-/- mice showed resistance to the lethal effect of CpG DNA without any elevation of serum pro-inflammatory cytokine levels. The in vivo CpG-DNA-mediated T-helper type-1 response was also abolished in TLR9-/- mice. Thus, vertebrate immune systems appear to have evolved a specific Toll-like receptor that distinguishes bacterial DNA from self-DNA.

A novel LPS-inducible C-type lectin is a transcriptional target of NF-IL6 in macrophages

C-type lectins serve multiple functions through recognizing carbohydrate chains. Here we report a novel C-type lectin, macrophage-inducible C-type lectin (Mincle), as a downstream target of NF-IL6 in macrophages. NF-IL6 belongs to the CCAAT/enhancer binding protein (C/EBP) of transcription factors and plays a crucial role in activated macrophages. However, what particular genes are regulated by NF-IL6 has been poorly defined in macrophages. Identification of downstream targets is required to elucidate the function of NF-IL6 in more detail. To identify downstream genes of NF-IL6, we screened a subtraction library constructed from wild-type and NF-IL6-deficient peritoneal macrophages and isolated Mincle that exhibits the highest homology to the members of group II C-type lectins. Mincle mRNA expression was strongly induced in response to several inflammatory stimuli, such as LPS, TNF-alpha, IL-6, and IFN-gamma in wild-type macrophages. In contrast, NF-IL6-deficient macrophages displayed a much lower level of Mincle mRNA induction following treatment with these inflammatory reagents. The mouse Mincle proximal promoter region contains an indispensable NF-IL6 binding element, demonstrating that Mincle is a direct target of NF-IL6. The Mincle gene locus was mapped at 0.6 centiMorgans proximal to CD4 on mouse chromosome 6.

A Novel LPS-Inducible C-Type Lectin Is a Transcriptional Target of NF-IL6 in Macrophages

C-type lectins serve multiple functions through recognizing carbohydrate chains. Here we report a novel C-type lectin, macrophage-inducible C-type lectin (Mincle), as a downstream target of NF-IL6 in macrophages. NF-IL6 belongs to the CCAAT/enhancer binding protein (C/EBP) of transcription factors and plays a crucial role in activated macrophages. However, what particular genes are regulated by NF-IL6 has been poorly defined in macrophages. Identification of downstream targets is required to elucidate the function of NF-IL6 in more detail. To identify downstream genes of NF-IL6, we screened a subtraction library constructed from wild-type and NF-IL6-deficient peritoneal macrophages and isolated Mincle that exhibits the highest homology to the members of group II C-type lectins. Mincle mRNA expression was strongly induced in response to several inflammatory stimuli, such as LPS, TNF-α, IL-6, and IFN-γ in wild-type macrophages. In contrast, NF-IL6-deficient macrophages displayed a much lower level of Mincle mRNA induction following treatment with these inflammatory reagents. The mouse Mincle proximal promoter region contains an indispensable NF-IL6 binding element, demonstrating that Mincle is a direct target of NF-IL6. The Mincle gene locus was mapped at 0.6 centiMorgans proximal to CD4 on mouse chromosome 6.

Differential roles of TLR2 and TLR4 in recognition of gram-negative and gram-positive bacterial cell wall components

Toll-like receptor (TLR) 2 and TLR4 are implicated in the recognition of various bacterial cell wall components, such as lipopolysaccharide (LPS). To investigate in vivo roles of TLR2, we generated TLR2-deficient mice. In contrast to LPS unresponsiveness in TLR4-deficient mice, TLR2-deficient mice responded to LPS to the same extent as wild-type mice. TLR2-deficient macrophages were hyporesponsive to several Gram-positive bacterial cell walls as well as Staphylococcus aureus peptidoglycan. TLR4-deficient macrophages lacked the response to Gram-positive lipoteichoic acids. These results demonstrate that TLR2 and TLR4 recognize different bacterial cell wall components in vivo and TLR2 plays a major role in Gram-positive bacterial recognition.

TLR6: A novel member of an expanding toll-like receptor family

Drosophila Toll protein is shown to activate the innate immune system in adult and regulate the dorsoventral patterning in the developing embryo. Recently, five human homologs of Drosophila Toll, designated as Toll-like receptors (TLRs), have been identified and shown to play a role in the innate immune response. We report here the molecular cloning and characterization of a new member of Toll-like receptor family, Toll-like receptor 6 (TLR6). Human and murine TLR6 are type-I transmembrane receptors that contain both an extracellular leucine-rich repeat (LRR) domain and a cytoplasmic Toll/IL-1 receptor (IL-1R)-like region. The amino acid sequence of human TLR6 (hTLR6) is most similar to that of hTLR1 with 69% identity. RT-PCR analysis revealed that murine TLR6 is expressed predominantly in spleen, thymus, ovary and lung. Like other TLR family members, constitutively active TLR6 activates both NF-kappaB and c-Jun N-terminal kinase (JNK). The TLR6 gene, as well as the TLR1 gene, mapped to the proximal region of murine chromosome 5 within 1.7cM of each other. These results suggest that TLR6 is a novel member of an expanding TLR family.

Limb and skin abnormalities in mice lacking IKKalpha

The gene encoding inhibitor of kappa B (IkappaB) kinase alpha (IKKalpha; also called IKK1) was disrupted by gene targeting. IKKalpha-deficient mice died perinatally. In IKKalpha-deficient fetuses, limb outgrowth was severely impaired despite unaffected skeletal development. The epidermal cells in IKKalpha-deficient fetuses were highly proliferative with dysregulated epidermal differentiation. In the basal layer, degradation of IkappaB and nuclear localization of nuclear factor kappa B (NF-kappaB) were not observed. Thus, IKKalpha is essential for NF-kappaB activation in the limb and skin during embryogenesis. In contrast, there was no impairment of NF-kappaB activation induced by either interleukin-1 or tumor necrosis factor-alpha in IKKalpha-deficient embryonic fibroblasts and thymocytes, indicating that IKKalpha is not essential for cytokine-induced activation of NF-kappaB.

Cutting Edge: Toll-Like Receptor 4 (TLR4)-Deficient Mice Are Hyporesponsive to Lipopolysaccharide: Evidence for TLR4 as the Lps Gene Product

The human homologue of Drosophila Toll (hToll), also called Toll-like receptor 4 (TLR4), is a recently cloned receptor of the IL-1/Toll receptor family. Interestingly, the TLR4 gene has been localized to the same region to which the Lps locus (endotoxin unresponsive gene locus) is mapped. To examine the role of TLR4 in LPS responsiveness, we have generated mice lacking TLR4. Macrophages and B cells from TLR4-deficient mice did not respond to LPS. All these manifestations were quite similar to those of LPS-hyporesponsive C3H/HeJ mice. Furthermore, C3H/HeJ mice have, in the cytoplasmic portion of TLR4, a single point mutation of the amino acid that is highly conserved among the IL-1/Toll receptor family. Overexpression of wild-type TLR4 but not the mutant TLR4 from C3H/HeJ mice activated NF-κB. Taken together, the present study demonstrates that TLR4 is the gene product that regulates LPS response.

Cutting edge: Toll-like receptor 4 (TLR4)-deficient mice are hyporesponsive to lipopolysaccharide: evidence for TLR4 as the Lps gene product

The human homologue of Drosophila Toll (hToll), also called Toll-like receptor 4 (TLR4), is a recently cloned receptor of the IL-1/Toll receptor family. Interestingly, the TLR4 gene has been localized to the same region to which the Lps locus (endotoxin unresponsive gene locus) is mapped. To examine the role of TLR4 in LPS responsiveness, we have generated mice lacking TLR4. Macrophages and B cells from TLR4-deficient mice did not respond to LPS. All these manifestations were quite similar to those of LPS-hyporesponsive C3H/HeJ mice. Furthermore, C3H/HeJ mice have, in the cytoplasmic portion of TLR4, a single point mutation of the amino acid that is highly conserved among the IL-1/Toll receptor family. Overexpression of wild-type TLR4 but not the mutant TLR4 from C3H/HeJ mice activated NF-kappaB. Taken together, the present study demonstrates that TLR4 is the gene product that regulates LPS response.

Duet is a novel serine/threonine kinase with Dbl-Homology (DH) and Pleckstrin-Homology (PH) domains

We show here the identification of Duet, a novel molecule bearing serine/threonine kinase, Dbl-Homology (DH), and Pleckstrin-Homology (PH) domains. The kinase domain of Duet shows a homology to that of DAP kinase that is involved in apoptosis, and Duet is autophosphorylated by an in-vitro kinase assay. The DH- and PH-domains are closely related to those of Trio and Kalirin. Trad mRNA is specifically expressed in skeletal muscle. Duet protein was localized to actin-associated cytoskeletal elements. These data suggest a role of Duet in the cytoskeleton-dependent cell function.

DRAKs, novel serine/threonine kinases related to death-associated protein kinase that trigger apoptosis

The present study describes the cloning of two novel serine/threonine kinases termed DRAK1 and DRAK2, whose catalytic domains are related to that of death-associated protein kinase, a serine/threonine kinase involved in apoptosis. Both DRAKs are composed of the N-terminal catalytic domain and the C-terminal domain that is responsible for regulation of kinase activity. DRAK1 and DRAK2 show 59.7% identity and display ubiquitous expression. An in vitro kinase assay revealed that both DRAKs are autophosphorylated and phosphorylate myosin light chain as an exogenous substrate, although the kinase activity of DRAK2 is significantly lower than that of DRAK1. Both DRAKs are exclusively localized to the nucleus. Furthermore, overexpression of both DRAKs induces the morphological changes of apoptosis in NIH 3T3 cells, suggesting the role of DRAKs in apoptotic signaling.

Ig receptor binding protein 1 (alpha4) is associated with a rapamycin-sensitive signal transduction in lymphocytes through direct binding to the catalytic subunit of protein phosphatase 2A

Rapamycin is an immunosuppressant that effectively controls various immune responses; however, its action in the signal transduction of lymphocytes has remained largely unknown. We show here that a phosphoprotein encoded by mouse alpha4 (malpha4) gene transmitting a signal through B-cell antigen receptor (BCR) is associated with the catalytic subunit of protein phosphatase 2A (PP2Ac). The middle region of alph4, consisting of 109 amino acids (94-202), associates directly with PP2Ac, irrespective of any other accessory molecule. Rapamycin treatment disrupts the association of PP2Ac/alpha4 in parallel with the inhibitory effect of lymphoid cell proliferation. The effect of rapamycin was inhibited with an excess amount of FK506 that potentially completes the binding to FKBP. Rapamycin treatment also suppresses the phosphatase activity of cells measured by in vitro phosphatase assay. Introduction of the malpha4 cDNA into Jurkat cells or the increased association of PP2Ac/alpha4 by the culture with low serum concentration confers cells with rapamycin resistance. Moreover, glutathione S-transferase (GST)-alpha4 augments the PP2A activity upon myelin basic protein (MBP) and histone in the in vitro assay. These results suggest that alpha4 acts as a positive regulator of PP2A and as a new target of rapamycin in the activation of lymphocytes.

The gene structure and promoter analysis of mouse lymphocyte signal transduction molecule alpha 4 that is related to the yeast TAP42 involved in a rapamycin-sensitive pathway

The mouse alpha 4 phosphoprotein encoding a component associated with the B cell antigen receptor (BCR)-mediated signal transduction is suggested to be involved in a unique rapamycin-sensitive pathway. We studied the structure and the molecular mechanism of the expression of alpha 4 gene by isolating two phage clones, named #10 and #23, covering entire exons of the mouse alpha 4 gene. The alpha 4 gene is located within about 25 kb and composed of six exons. To analyze the regulation of alpha 4 gene expression, we determined the nucleotide sequence toward 2 kb upstream of the translation start site of the alpha 4 gene. The 5'-flanking region does not contain a typical TATA box or the initiation consensus sequence, but it contains a CCAAT box, E-boxes, and several DNA binding motifs such as c-Myc, c-Myb, and c-Ets. Transcription of the alpha 4 gene starts at four different sites, determined by primer extension analysis, that were surrounded by Y-rich sequences. We further characterized the functional promoter of the alpha 4 gene at the region between -263 and the transcription start site of alpha 4 gene by luciferase assay system and suggested that the 5' upstream region of alpha 4 gene contains the silencer element of MT repetitive sequence.

ZIP kinase, a novel serine/threonine kinase which mediates apoptosis

We have identified a novel serine/threonine kinase, designated ZIP kinase, which mediates apoptosis. ZIP kinase contains a leucine zipper structure at its C terminus, in addition to a kinase domain at its N terminus. ZIP kinase physically binds to ATF4, a member of the activating transcription factor/cyclic AMP-responsive element-binding protein (ATF/CREB) family, through interaction between their leucine zippers. The leucine zipper domain is necessary for the homodimerization of ZIP kinase as well as for the activation of kinase. Immunostaining study showed that ZIP kinase localizes in the nuclei. Overexpression of intact ZIP kinase but not catalytically inactive kinase mutants led to the morphological changes of apoptosis in NIH 3T3 cells, suggesting that the cell death-inducing activity of ZIP kinase depends on its intrinsic kinase activity. Interestingly, the catalytic domain of ZIP kinase is closely related to that of death-associated protein kinase (DAP kinase), which is a mediator of apoptosis induced by gamma interferon. Therefore, both ZIP and DAP kinases represent a novel kinase family, which mediates apoptosis through their catalytic activities.