The aryl hydrocarbon receptor controls mesenchymal stromal cell-mediated immunomodulation via ubiquitination of eukaryotic elongation factor-2 kinase

Mesenchymal stem cells (MSCs) have great therapeutic advantages due to their immunosuppressive properties. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor whose signaling plays an important role in the immune system. AHR may be involved in the regulation of MSC-associated immunomodulatory functions. However, the mechanisms by which AHR controls the immunosuppressive functions of MSCs are not well understood. Here, we report that Ahr-deficient MSCs show decreased therapeutic efficacy against graft-versus-host disease (GVHD) compared to wild-type (WT)-MSCs. This was probably due to decreased iNOS protein expression, which is a key regulatory enzyme in MSC immunomodulation. The expression of eukaryotic elongation factor 2 kinase (eEF2K), which inhibits the elongation stage of protein synthesis, is significantly increased in the Ahr-deficient MSCs. Inhibition of eEF2K restored iNOS protein expression. AHR is known to act as an E3 ligase together with CUL4B. We observed constitutive binding of AHR to eEF2K. Consequently, ubiquitination and degradation of eEF2K were inhibited in Ahr-deficient MSCs and by the AHR antagonist CH223191 in WT-MSCs. In summary, AHR regulates the immunomodulatory functions of MSCs through ubiquitination of eEF2K, thereby controlling iNOS protein synthesis and its product, nitric oxide levels.

Prunus cerasoides Extract and Its Component Compounds Upregulate Neuronal Neuroglobin Levels, Mediate Antioxidant Effects, and Ameliorate Functional Losses in the Mouse Model of Cerebral Ischemia

Prunus cerasoides (PC) has been reported to have antimicrobial and anti-inflammatory properties, but its potential as a neuroprotective agent in a mouse model of cerebral ischemia has not been explored. Considering neuroglobin (Ngb), an endogenous neuroprotective factor, as a novel approach to neuroprotection, in this study, Ngb promoter activity, Ngb expression changes, and antioxidant protection by PC extract (PCE) and PC component compounds (PCCs) were analyzed in oxygen–glucose deprivation (OGD)-treated neurons. In vivo analysis involved transient middle cerebral artery occlusion (tMCAO) in mice with pre- and post-treatment exposure to PCE. Following ischemic stroke induction, neurological behavior scores were obtained, and cellular function-related signals were evaluated in the ischemic infarct areas. In addition to PCE, certain component compounds from PCE also significantly increased Ngb levels and attenuated the intracellular ROS production and cytotoxicity seen with OGD in primary neurons. Administration of PCE reduced the infarct volume and improved neurological deficit scores in ischemic stroke mice compared with the vehicle treatment. Increased Ngb levels in infarct penumbra with PCE treatment were also accompanied by decreased markers of apoptosis (activated p38 and cleaved caspase-3). Our findings point to the benefits of Ngb-mediated neuroprotection via PCE and its antioxidant activity in an ischemic stroke model.

Long-term efficacy and safety of intravenous injection of clonal mesenchymal stem cells derived from bone marrow in five adults with moderate to severe atopic dermatitis

Atopic dermatitis is a chronic and relapsing inflammatory skin disease that is treated with immunosuppressants. However, long-term use of immunosuppressants may cause toxicity and severe side-effects. To confirm the long-term efficacy and safety of clonal mesenchymal stem cell therapy, we performed investigator-initiated clinical trials and long-term observation in five adult patients with moderate to severe atopic dermatitis that was refractory to conventional treatments. The clinical response assessment values such as Eczema Area and Severity Index (EASI) improved significantly at 16 weeks, and 80% (4/5) of the patients achieved EASI-50 after one or two treatment cycles. Patients were observed for long-term efficacy and safety for an average of 38 weeks (range, 16-86) and showed no serious side-effects. Among the cytokines tested, CCL-17, interleukin (IL)-13, and IL-22 significantly decreased at the end-point of the five participants, two patients who maintained good clinical response over 84 weeks showed increased IL-17 cytokine levels in the blood.

A role of aryl hydrocarbon receptor (AhR) in mesenchymal stem cells

Aryl hydrocarbon receptor (AhR), a ligand-induced transcription factor, is known to be involved in the balance between inflammatory and suppressive/regulatory T cell activity. Mesenchymal stem cells (MSCs) possess immunomodulatory activities, including suppression of T- and B-cell activation. MSC-mediated immunosuppression occurs via nitric oxide (NO) in mice. Here, we isolated MSCs from Ahr−/− bone marrow in mice and found less immunosuppressive function compared to the wild type (WT)-MSCs. When MSCs are co-cultured with T cells in the presence of anti-CD3 and anti-CD28 antibodies, the AhR-deficient MSCs less inhibited T-cell proliferation, CD25 and CD122 expression and cytokine productions such as IFN-γ, IL-17A compared with wild type MSCs. In addition, we found AhR-deficient MSCs produce less inducible nitric oxide synthase (iNOS) and NO compared with wild type MSCs, when MSCs were stimulated with IFN-γ, TNF-α, and IL-1β. Since MSCs has been used for the treatment of graft-vs-host disease (GvHD), we injected the WT and AhR-deficient MSCs into the GvHD mice. The AhR-deficient MSCs showed less therapeutic efficacy compared to the WT MSCs. We think that the AhR is involved in the production of NO via regulating iNOS expression which is required for the therapeutic efficacy of MSCs.

Dynamics of T Lymphocyte between the Periphery and the Brain from the Acute to the Chronic Phase Following Ischemic Stroke in Mice

Stroke causes systemic immunosuppression. T lymphocytes are involved in infarct size in the early stages of stroke. However, the phenotypes of T lymphocytes and their functions in peripheral immune organs and the brain have not been well analyzed in the acute and chronic phases of stroke. Here, we investigated pathological phenotypic alterations in the systemic immune response, especially changes in T lymphocytes, from one day to six months after ischemic stroke in mice. Impairment in thymocyte numbers, development, proliferation, and apoptosis were observed for up to two weeks. The number of mature T cells in the spleen and blood decreased and showed reduced interferon-γ production. Increased numbers of CD4^-CD8^-CD3⁺ double-negative T cells were observed in the mouse brain during the early stages of stroke, whereas interleukin (IL)-10⁺Foxp3⁺ regulatory T lymphocytes increased from two weeks during the chronic phase. These phenotypes correlated with body weight and neurological severity scores. The recovery of T lymphocyte numbers and increases in IL-10⁺Foxp3⁺ regulatory T lymphocytes may be important for long-term neurological outcomes. Dynamic changes in T lymphocytes between the acute and chronic phases may play different roles in pathogenesis and recovery. This study provides fundamental information regarding the T lymphocyte alterations from the brain to the peripheral immune organs following stroke.

A Novel Immunomodulatory Mechanism Dependent on Acetylcholine Secreted by Human Bone Marrow-derived Mesenchymal Stem Cells

Background and Objectives

Mesenchymal stem cells (MSCs) are used to treat autoimmune or inflammatory diseases. Our aim was to determine the immunomodulatory mechanisms elicited by MSCs during inflammation.

Methods and Results

We cocultured MSCs with peripheral blood mononuclear cells for a mixed lymphocyte reaction or stimulated them by phytohemagglutinin. Morphological changes of MSCs and secretion of acetylcholine (ACh) from MSCs were measured. The effects of an ACh antagonist and ACh agonist on lymphocyte proliferation and proinflammatory-cytokine production were determined. The inflammatory milieu created by immune-cell activation caused MSCs to adopt a neuronlike phenotype and induced them to release ACh. Additionally, nicotinic acetylcholine receptors (nAChRs) were upregulated in activated peripheral blood mononuclear cells. We observed that ACh bound to nAChR on activated immune cells and led to the inhibition of lymphocyte proliferation and of proinflammatory-cytokine production. MSC-mediated immunosuppression through ACh activity was reversed by an ACh antagonist called α-bungarotoxin, and lymphocyte proliferation was inhibited by an ACh agonist, ACh chloride.

Conclusions

Our findings point to a novel immunomodulatory mechanism in which ACh secreted by MSCs under inflammatory conditions might modulate immune cells. This study may provide a novel method for the treatment of autoimmune diseases by means of MSCs.

Comparable Immune Function Inhibition by the Infliximab Biosimilar CT-P13: Implications for Treatment of Inflammatory Bowel Disease

BACKGROUND AND AIMS

CT-P13 is the first biosimilar monoclonal antibody to infliximab, and was recently approved in the European Union, Japan, Korea, and USA for all six indications of infliximab. However, studies directly assessing the biologic activity of CT-P13 versus inflximab in the context of inflammatory bowel disease [IBD] are still scanty. In the present study, we aimed to compare the biological activities of CT-P13 and infliximab with specific focus on intestinal cells so as to gain insight into the potential biosimilarity of these two agents for treatment of IBD.

METHODS

CT-P13 and infliximab were investigated and compared by in vitro experiments for their neutralisation ability of soluble tumour necrosis factor alpha [sTNFα] and membrane-bound tumour necrosis factor alpha [mTNFα], suppression of cytokine release by reverse signalling, induction of regulatory macrophages and wound healing, and antibody-dependent cell cytotoxicity [ADCC].

RESULTS

CT-P13 showed similar biological activities to infliximab as gauged by neutralisation of soluble TNFα, as well as blockade of apoptosis and suppression of pro-inflammatory cytokines in intestinal Caco-2 cells. Infliximab and CT-P13 equally induced apoptosis and outside-to-inside signals through transmembrane TNFα [tmTNFα]. Moreover, regulatory macrophage induction and ensuing wound healing were similarly exerted by CT-P13 and infliximab. However, neither CT-P13 nor infliximab exerted any significant ADCC of ex vivo-stimulated peripheral blood monocytes or lamina propria mononuclear cells from IBD patients.

CONCLUSIONS

These findings indicate that CT-P13 and infliximab exert highly similar biological activities in intestinal cells, and further support a mechanistic comparability of these two drugs in the treatment of IBD.

ICOSL expression in human bone marrow-derived mesenchymal stem cells promotes induction of regulatory T cells

Mesenchymal stem cells (MSCs) can modulate lymphocyte proliferation and function. One of the immunomodulatory functions of MSCs involves CD4⁺CD25⁺FoxP3⁺ regulatory T cells (Tregs), which negatively regulate inflammatory responses. MSC-mediated Treg induction is supposed to be regulated by mechanisms requiring both soluble and cell contact-dependent factors. Although the involvement of soluble factors has been revealed, the contact-dependent mechanisms in MSC-mediated Treg induction remain unclear. We attempted to identify molecule(s) other than secreted factors that are responsible for MSC-mediated Treg induction and to uncover the underlying mechanisms. Under in vitro Treg-inducing conditions, ICOSL expression in MSCs coincided with Treg induction in co-cultures of MSCs with CD4⁺ T cells. When cultured in a transwell plate, MSCs failed to induce Tregs. Neutralization or knockdown of ICOSL significantly reduced Tregs and their IL-10 release. ICOSL overexpression in MSCs promoted induction of functional Tregs. ICOSL-ICOS signaling promoted Treg differentiation from CD4⁺ T cells through activation of the phosphoinositide 3-kinase-Akt pathway. MSCs primed with Interleukin-1β significantly induced Tregs through ICOSL upregulation. We demonstrated that the Treg-inducing activity of MSCs is proportionate to their basal ICOSL expression. This study provides evidence that ICOSL expression in human MSCs plays an important role in contact-dependent regulation of MSC-mediated Treg induction.

Manufacture of Clinical-Grade Human Clonal Mesenchymal Stem Cell Products from Single Colony Forming Unit-Derived Colonies Based on the Subfractionation Culturing Method

Stem cell products derived from mesenchymal stem cells (MSCs) have been widely used in clinical trials, and a few products have been already commercialized. However, the therapeutic effects of clinical-grade MSCs are still controversial owing to mixed results from recent clinical trials. A potential solution to overcome this hurdle may be to use clonal stem cells as the starting cell material to increase the homogeneity of the final stem cell products. We have previously developed an alternative isolation and culture protocol for establishing a population of clonal MSCs (cMSCs) from single colony forming unit (CFU)-derived colonies. In this study, we established a good manufacturing practice (GMP)-compatible procedure for the clinical-grade production of human bone marrow-derived cMSCs based on the subfractionation culturing method. We optimized the culture procedures to expand and obtain a clonal population of final MSC products from single CFU-derived colonies in a GMP facility. The characterization results of the final cMSC products met our preset criteria. Animal toxicity tests were performed in a good laboratory practice facility, and showed no toxicity or tumor formation in vivo. These tests include single injection toxicity, multiple injection toxicity, biodistribution analysis, and tumorigenicity tests in vivo. No chromosomal abnormalities were detected by in situ karyotyping using oligo-fluorescence in situ hydridization (oligo-FISH), providing evidence of genetic stability of the clinical-grade cMSC products. The manufacture and quality control results indicated that our GMP methodology could produce sufficient clonal population of MSC products from a small amount of bone marrow aspirate to treat a number of patients.

Disruption of CTCF/cohesin-mediated high-order chromatin structures by DNA methylation downregulates PTGS2 expression

The CCCTC-binding factor (CTCF)/cohesin complex regulates gene transcription via high-order chromatin organization of the genome. De novo methylation of CpG islands in the promoter region is an epigenetic hallmark of gene silencing in cancer. Although the CTCF/cohesin complex preferentially targets hypomethylated DNA, it remains unclear whether the CTCF/cohesin-mediated high-order chromatin structure is affected by DNA methylation during tumorigenesis. We found that DNA methylation downregulates the expression of prostaglandin-endoperoxide synthase 2 (PTGS2), which is an inducible, rate-limiting enzyme for prostaglandin synthesis, by disrupting CTCF/cohesin-mediated chromatin looping. We show that the CTCF/cohesin complex is enriched near a CpG island associated with PTGS2 and that the PTGS2 locus forms chromatin loops through methylation-sensitive binding of the CTCF/cohesin complex. DNA methylation abolishes the association of the CTCF/cohesin complex with the PTGS2 CpG island. Disruption of chromatin looping by DNA methylation abrogates the enrichment of transcriptional components, such as positive elongation factor b, at the transcriptional start site of the PTGS2 locus. These alterations result in the downregulation of PTGS2. Our results provide evidence that CTCF/cohesin-mediated chromatin looping of the PTGS2 locus is dynamically influenced by the DNA methylation status.

Galectin-9 is Involved in Immunosuppression Mediated by Human Bone Marrow-derived Clonal Mesenchymal Stem Cells

Bone marrow-derived mesenchymal stem cells (MSCs) have immunomodulatory properties and can suppress exaggerated pro-inflammatory immune responses. Although the exact mechanisms remain unclear, a variety of soluble factors are known to contribute to MSC-mediated immunosuppression. However, functional redundancy in the immunosuppressive properties of MSCs indicates that other uncharacterized factors could be involved. Galectin-9, a member of the β-galactoside binding galectin family, has emerged as an important regulator of innate and adaptive immunity. We examined whether galectin-9 contributes to MSC-mediated immunosuppression. Galectin-9 was strongly induced and secreted from human MSCs upon stimulation with pro-inflammatory cytokines. An in vitro immunosuppression assay using a knockdown approach revealed that galectin-9-deficient MSCs do not exert immunosuppressive activity. We also provided evidence that galectin-9 may contribute to MSC-mediated immunosuppression by binding to its receptor, TIM-3, expressed on activated lymphocytes, leading to apoptotic cell death of activated lymphocytes. Taken together, our findings demonstrate that galectin-9 is involved in MSC-mediated immunosuppression and represents a potential therapeutic factor for the treatment of inflammatory diseases.

Therapeutic effects of mouse bone marrow-derived clonal mesenchymal stem cells in a mouse model of inflammatory bowel disease

Mouse bone marrow-derived clonal mesenchymal stem cells (mcMSCs), which were originated from a single cell by a subfractionation culturing method, are recognized as new paradigm for stem cell therapy featured with its homogenous cell population. Next to proven therapeutic effects against pancreatitis, in the current study we demonstrated that mcMSCs showed significant therapeutic effects in dextran sulfate sodium (DSS)-induced experimental colitis model supported with anti-inflammatory and restorative activities. mcMSCs significantly reduced the disease activity index (DAI) score, including weight loss, stool consistency, and intestinal bleeding and significantly increased survival rates. The pathological scores were also significantly improved with mcMSC. We have demonstrated that especial mucosal regeneration activity accompanied with significantly lowered level of apoptosis as beneficiary actions of mcMSCs in UC models. The levels of inflammatory cytokines including TNF-α, IFN-γ, IL-1β, IL-6, and IL-17 were all significantly concurrent with significantly repressed NF-κB activation compared to the control group and significantly decreased infiltrations of responsible macrophage and neutrophil. Conclusively, our findings provide the rationale that mcMSCs are applicable as a potential source of cell-based therapy in inflammatory bowel diseases, especially contributing either to prevent relapse or to accelerate healing as solution to unmet medical needs in IBD therapy.

Molecular Characterization of Neurally Differentiated Human Bone Marrow-derived Clonal Mesenchymal Stem Cells

Bone marrow-derived mesenchymal stem cells (MSCs) are multipotent, with the ability to differentiate into different cell types. Additionally, the immunomodulatory activity of MSCs can downregulate inflammatory responses. The use of MSCs to repair injured tissues and treat inflammation, including in neuroimmune diseases, has been extensively explored. Although MSCs have emerged as a promising resource for the treatment of neuroimmune diseases, attempts to define the molecular properties of MSCs have been limited by the heterogeneity of MSC populations. We recently developed a new method, the subfractionation culturing method, to isolate homogeneous human clonal MSCs (hcMSCs). The hcMSCs were able to differentiate into fat, cartilage, bone, neuroglia, and liver cell types. In this study, to better understand the properties of neurally differentiated MSCs, gene expression in highly homogeneous hcMSCs was analyzed. Neural differentiation of hcMSCs was induced for 14 days. Thereafter, RNA and genomic DNA was isolated and subjected to microarray analysis and DNA methylation array analysis, respectively. We correlated the transcriptome of hcMSCs during neural differentiation with the DNA methylation status. Here, we describe and discuss the gene expression profile of neurally differentiated hcMSCs. These findings will expand our understanding of the molecular properties of MSCs and contribute to the development of cell therapy for neuroimmune diseases.

Mesenchymal Stem Cell Lines Isolated by Different Isolation Methods Show Variations in the Regulation of Graft-versus-host Disease

Since the discovery of the immunomodulation property of mesenchymal stem cells (MSCs) about a decade ago, it has been extensively investigated whether MSCs can be used for the treatment of immune-related diseases, such as graft-versus-host disease (GvHD). However, how to evaluate the efficacy of human MSCs for the clinical trial is still unclear. We used an MHC-mismatched model of GvHD (B6 into BALB/c). Surprisingly, the administration of the human MSCs (hMSCs) could reduce the GvHD-related mortality of the mouse recipients and xenogeneically inhibit mouse T-cell proliferation and IFN-γ production in vitro. We recently established a new protocol for the isolation of a homogeneous population of MSCs called subfractionation culturing methods (SCM), and established a library of clonal MSC lines. Therefore, we also investigated whether MSCs isolated by the conventional gradient centrifugation method (GCM) and SCM show different efficacy in vivo. Intriguingly, clonal hMSCs (hcMSCs) isolated by SCM showed better efficacy than hMSCs isolated by GCM. Based on these results, the MHC-mismatched model of GvHD may be useful for evaluating the efficacy of human MSCs before the clinical trial. The results of this study suggest that different MSC lines may show different efficacy in vivo and in vitro.

Treatment of Atopic Dermatitis by Bone Marrow-derived Clonal Mesenchymal Stem Cells (119.3)

Mesenchymal stem cells (MSCs) can perform immunomodulatory activities, including suppression of T- and B-cell proliferation. MSCs have been primarily studied for their suppression of pro-inflammatory Th1 responses, but their therapeutic effects on atopic dermatitis (AD), which is a Th2-dominant disease, have not been reported. In this study, using an ovalbumin-induced mouse AD model, we investigated whether MSCs reduce the allergic inflammation in AD. We used mouse bone marrow-derived clonal mesenchymal stem cells (mcMSCs) isolated by our newly established isolation protocol termed the subfractionation culturing method (SCM). When injected intravenously into animals between antigen challenges, mcMSCs were found to inhibit the majority of AD-specific pathological changes by decreasing cell infiltration in skin lesions and reducing serum level of IgE. To explore the mechanism of this effect, we investigated the effects of mcMSCs on IgE production in B cells. We found that mcMSCs significantly inhibited IgE production when B cells were stimulated either by lipopolysaccharide (LPS) or anti-CD40 antibodies in the presence of interleukin (IL)-4. In addition, allogeneic mcMSCs can inhibit both isotype class switching and terminal differentiation of B cells probably by inhibiting NF-κB activation. These results suggest that mcMSC-based cell therapy is a promising therapeutic modality for AD treatment.

Characterization of mouse clonal mesenchymal stem cell lines established by subfractionation culturing method

AIM

To characterize single-cell-derived mouse clonal mesenchymal stem cells (mcMSCs) established with bone marrow samples from three different mouse strains.

METHODS

We established mcMSC lines using subfractionation culturing method from bone marrow samples obtained from long bones. These lines were characterized by measuring cell growth, cell surface epitopes, differentiation potential, lineage-specific gene expression and T-cell suppression capability. Nonclonal MSCs isolated by the conventional gradient centrifugation method were used as controls.

RESULTS

All mcMSC lines showed typical nonclonal MSC-like spindle shape morphology. Lines differed in optimal growth density requirement. Cell surface epitope profiles of these mcMSC lines were similar to those of nonclonal MSCs. However, some lines exhibited different expression levels in a few epitopes, such as CD44 and CD105. Differentiation assays showed that 90% of the mcMSC lines were capable of differentiating into adipogenic and/or chondrogenic lineages, but only 20% showed osteogenic lineage differentiation. T-cell suppression analysis showed that 75% of the lines exhibited T-cell suppression capability.

CONCLUSION

mcMSC lines have similar cell morphology and cell growth rate but exhibit variations in their cell surface epitopes, differentiation potential, lineage-specific gene expression and T-cell suppression capability.

Human bone marrow-derived clonal mesenchymal stem cells inhibit inflammation and reduce acute pancreatitis in rats

BACKGROUND & AIMS

Acute pancreatitis (AP) has a high mortality rate; repetitive AP induces chronic AP and pancreatic adenocarcinoma. Mesenchymal stem cells (MSCs) have immunoregulatory effects and reduce inflammation. We developed a protocol to isolate human bone marrow-derived clonal MSCs (hcMSCs) from bone marrow aspirate and investigated the effects of these cells in rat models of mild and severe AP.

METHODS

Mild AP was induced in Sprague-Dawley rats by 3 intraperitoneal injections of cerulein (100 μg/kg), given at 2-hour intervals; severe AP was induced by intraparenchymal injection of 3% sodium taurocholate solution. hcMSCs were labeled with CM-1,1'-dioctadecyl-3,3,3'-tetramethylindo-carbocyanine perchloride and administered to rats through the tail vein.

RESULTS

hcMSCs underwent self-renewal and had multipotent differentiation capacities and immunoregulatory functions. Greater numbers of infused hcMSCs were detected in pancreas of rats with mild and severe AP than of control rats. Infused hcMSCs reduced acinar-cell degeneration, pancreatic edema, and inflammatory cell infiltration in each model of pancreatitis. The hcMSCs reduced expression of inflammation mediators and cytokines in rats with mild and severe AP. hcMSCs suppressed the mixed lymphocyte reaction and increased expression of Foxp3(+) (a marker of regulatory T cells) in cultured rat lymph node cells. Rats with mild or severe AP that were given infusions of hcMSCs had reduced numbers of CD3(+) T cells and increased expression of Foxp3(+) in pancreas tissues.

CONCLUSIONS

hcMSCs reduced inflammation and damage to pancreatic tissue in a rat model of AP; they reduced levels of cytokines and induced numbers of Foxp3(+) regulatory T cells. hcMSCs might be developed as a cell therapy for pancreatitis.

K33-linked polyubiquitination of T cell receptor-zeta regulates proteolysis-independent T cell signaling

Tagging the cell surface receptor with ubiquitin is believed to provide a signal for the endocytic pathway. E3 ubiquitin ligases such as Cbl-b and Itch have been implicated in T cell activation and tolerance induction. However, the underlying mechanisms remain unclear. We describe that in mice deficient in the E3 ubiquitin ligases Cbl-b and Itch, T cell activation was augmented, accompanied by spontaneous autoimmunity. The double-mutant T cells exhibited increased phosphorylation of the T cell receptor-zeta (TCR-zeta) chain, whereas the endocytosis and stability of the TCR complex were not affected. TCR-zeta was polyubiquitinated via a K33-linkage, which affected its phosphorylation and association with the zeta chain-associated protein kinase Zap-70. The juxtamembrane K54 residue in TCR-zeta was identified to be a primary ubiquitin conjugation site, whose mutation increased its phosphorylation and association of TCR-zeta and Zap-70. Thus, the present study reveals unconventional K33-linked polyubiquitination in nonproteolytic regulation of cell-surface-receptor-mediated signal transduction.

Capsiate inhibits ultraviolet B-induced skin inflammation by inhibiting Src family kinases and epidermal growth factor receptor signaling

Capsiate, one of the major capsaicinoids, is nonpungent and present in sweet pepper. We investigated the effects of capsiate on the ultraviolet B (UVB)-induced inflammatory response in skin and its molecular mechanisms. Capsiate-pretreated human keratinocytes inhibited intracellular reactive oxygen species (ROS), which activate the mitogen-activated protein kinase and nuclear factor-kappaB (NF-kappaB) pathways. Therefore, we determined the effects of capsiate on these pathways. Capsiate inhibited UVB-induced cyclooxygenase-2 (COX-2) expression, extracellular signal-related kinase 1/2 phosphorylation, nuclear translocation of NF-kappaB, and the expression of proinflammatory cytokines and potent angiogenic factors, including vascular endothelial cell growth factor and matrix metalloproteinase-2 (MMP-2) and MMP-9. In addition, capsiate inhibited UVB-induced epidermal growth factor receptor (EGFR) activation, which reduces the levels of proinflammatory cytokines and angiogenic factors. We also investigated the photoprotective effects of capsiate in vivo. Topical treatment with capsiate significantly decreased UVB-induced skin damage and inhibited the expression of COX-2, proinflammatory cytokines, and angiogenic factors, including platelet/endothelial cell adhesion molecule-1 and intercellular adhesion molecule-1. Inhibition of Src kinase activity and ROS may inhibit the EGFR activation. Therefore, capsiate may protect the skin from UVB-induced adverse effects and these results provide a molecular basis for understanding its effects on inflammation and angiogenesis.

Xenoreactivity of human clonal mesenchymal stem cells in a major histocompatibility complex-matched allogeneic graft-versus-host disease mouse model

Effects of mesenchymal stem cells (MSCs) on graft-versus-host disease (GVHD) have been actively investigated since the discovery of the immunomodulation property of MSCs about a decade ago. Human clonal MSCs (hcMSCs) were isolated from human bone marrow aspirate according to our newly established isolation protocol called subfractionation culturing method, and were evaluated for their efficacy on GVHD treatment, using a mouse MHC-matched B6-->BALB.B GVHD model system. Although the hcMSCs can suppress the allogeneic proliferation of human peripheral blood mononuclear cells in in vitro, the administration of the hcMSCs failed to reduce the GVHD-related mortality of the murine recipients. One of the reasons might be that murine cytokines such as IFN-gamma and TNF-alpha cannot activate the hcMSCs. Based on these results, we suggest that xenogeneic MSCs may not be used for the treatment of GVHD.

Reciprocal regulation of 12- and 15-lipoxygenases by UV-irradiation in human keratinocytes

The 12/15-lipoxygenase (12/15-LOX) pathways of arachidonate metabolism have been implicated in the pathogenesis of psoriasis. Since UV photo-therapy is a commonly used technique for inhibiting cell proliferation and inflammation in skin diseases, we hypothesized that UV-irradiation may affect 12/15-LOX expression which might regulate cell proliferation. In this study, we showed that UV-irradiation suppressed 12-LOX expression, whereas up-regulated 15-LOX expression. Treatment with the 15-LOX metabolites sufficiently suppressed insulin-like growth factor II-induced 12-LOX expression and blocked cell cycle progression. On the basis of our findings, we think that the 15-LOX metabolites may inhibit epidermal hyperplasia in psoriasis by regulating 12-LOX expression.

Impaired Activation and Localization of LAT in Anergic T Cells as a Consequence of a Selective Palmitoylation Defect

The molecular basis of T cell anergy is not completely understood. We show that in antigen-primed anergic murine CD4(+) T cells the linker for activation of T cells (LAT) is hypophosphorylated upon CD3/CD28 restimulation. Signaling events downstream of LAT (PLCgamma1 phosphorylation and p85 [PI3-K] association) were impaired, whereas upstream events (CD3zeta and ZAP-70 phosphorylation) remained intact. LAT recruitment to the immunological synapse and its localization in detergent-resistant membrane (DRM) fractions were defective in anergic T cells. These defects resulted from impaired palmitoylation of LAT and were selective since the DRM localization and palmitoylation of Fyn were intact. This LAT defect was independent of Cbl-b and did not reflect enhanced LAT degradation. These results identify LAT as the most upstream target of anergy induction; moreover, they suggest that regulation of the amount of LAT in the immunological synapse and DRM by posttranslational palmitoylation contributes to the induction of T cell anergy.

Negative Regulation of the E3 Ubiquitin Ligase Itch via Fyn-Mediated Tyrosine Phosphorylation

Conjugation of ubiquitin (Ub) to a protein substrate targets the substrate for degradation or functional modification, which is tightly controlled by diverse mechanisms including phosphorylation of the substrate. An emerging mechanism involves regulation of the E3 Ub ligase, for example, the JNK-dependent phosphorylation and activation of Itch E3 ligase, which controls the turnover of Jun proteins and T cell differentiation. Here we show that Itch is also modulated by an Src kinase Fyn via tyrosine phosphorylation at the Tyr371 residue. Fyn associates with Itch, and loss of Fyn results in reduced Itch phosphorylation. Importantly, tyrosine phosphorylation of Itch appears to reduce its interaction with its substrate JunB. The turnover of JunB is accelerated in Fyn-deficient T cells, which is further reconstituted by Itch Tyr371 mutation. Thus, in contrast to the activation pathway mediated by serine/threonine phosphorylation, tyrosine phosphorylation of Itch plays a negative role in modulating Itch-promoted ubiquitination.

Activation of naïve CD4 T cells by anti-CD3 reveals an important role for Fyn in Lck-mediated signaling

Although there was no impairment in IL-2 secretion and proliferation of Fyn-deficient naïve CD4 cells after stimulation with antigen and antigen-presenting cells, stimulation of these cells with anti-CD3 and anti-CD28 revealed profound defects. Crosslinking of purified wild-type naïve CD4 cells with anti-CD3 activated Lck and initiated the signaling cascade downstream of Lck, including phosphorylation of ZAP-70, LAT, and PLC-gamma1; calcium flux; and dephosphorylation and nuclear translocation of the nuclear factor of activated T cells (NFAT)p. All of these signaling events were diminished severely in Fyn-deficient naïve cells activated by CD3 crosslinking. Coaggregation of CD3 and CD4 reconstituted this Lck-dependent signaling pathway in Fyn(-/-) T cells. These results suggest that when signaling of naïve T cells is restricted to the T cell antigen receptor, Fyn plays an essential role by positive regulation of Lck activity.

Activation of arterial wall dendritic cells and breakdown of self-tolerance in giant cell arteritis

Giant cell arteritis (GCA) is a granulomatous and occlusive vasculitis that causes blindness, stroke, and aortic aneurysm. CD4(+) T cells are selectively activated in the adventitia of affected arteries. In human GCA artery-severe combined immunodeficiency (SCID) mouse chimeras, depletion of CD83(+) dendritic cells (DCs) abrogated vasculitis, suggesting that DCs are critical antigen-presenting cells in GCA. Healthy medium-size arteries possessed an indigenous population of DCs at the adventitia-media border. Adoptive T cell transfer into temporal artery-SCID mouse chimeras demonstrated that DCs in healthy arteries were functionally immature, but gained T cell stimulatory capacity after injection of lipopolysaccharide. In patients with polymyalgia rheumatica (PMR), a subclinical variant of GCA, adventitial DCs were mature and produced the chemokines CCL19 and CCL21, but vasculitic infiltrates were lacking. Human histocompatibility leukocyte antigen class II-matched healthy arteries, PMR arteries, and GCA arteries were coimplanted into SCID mice. Immature DCs in healthy arteries failed to stimulate T cells, but DCs in PMR arteries could attract, retain, and activate T cells that originated from the GCA lesions. We propose that in situ maturation of DCs in the adventitia is an early event in the pathogenesis of GCA. Activation of adventitial DCs initiates and maintains T cell responses in the artery and breaks tissue tolerance in the perivascular space.

Essential Role of the E3 Ubiquitin Ligase Cbl-b in T Cell Anergy Induction

Antigen-specific immunotolerance limits the expansion of self-reactive T cells involved in autoimmune diseases. Here, we show that the E3 ubiquitin ligase Cbl-b is upregulated in T cells after tolerizing signals. Loss of Cbl-b in mice results in impaired induction of T cell tolerance both in vitro and in vivo. Importantly, rechallenge of Cbl-b mutant mice with the tolerizing antigen results in massive lethality. Moreover, ablation of Cbl-b resulted in exacerbated autoimmunity. Mechanistically, loss of Cbl-b rescues reduced calcium mobilization of anergic T cells, which was attributed to Cbl-b-mediated regulation of PLCgamma-1 phosphorylation. Our results show a critical role for Cbl-b in the regulation of peripheral tolerance and anergy of T cells.

Negative regulation of T cell antigen receptor-mediated Crk-L-C3G signaling and cell adhesion by Cbl-b

It was previously reported that Cbl-b associates with Crk-L in Jurkat T cells. However, the physiological significance of such association remains unclear. Here we examined a regulatory role of Cbl-b in Crk-L-C3G signaling pathway. We found that Cbl-b associates with, and induces, ubiquitin conjugation to Crk-L, which requires a functional RING finger. Cbl-b deficiency does not affect Crk-L stability, but its association with C3G. In Cbl-b-/- T cells, the interaction between Crk-L and C3G, and the activity of the small GTPase Rap1, are increased. Cbl-b-/- T cells also display increased adhesion and cell surface binding to ICAM-1, a finding that is supported by the enhanced clustering of LFA-1 in Cbl-b-/- T cells in response to TCR stimulation. Thus, Cbl-b plays a negative role in Crk-L-C3G-mediated Rap1 and LFA-1 activation in T cells.

Trapping of misdirected dendritic cells in the granulomatous lesions of giant cell arteritis

Immature dendritic cells (DCs) are scattered throughout peripheral tissues and act as sentinels that sample the antigenic environment. After activation, they modify their chemokine receptor profile and migrate toward lymphoid tissues. On arrival, they have matured into chemokine-producing DCs that express co-stimulatory molecules and can prime naive T cells. Normal temporal arteries contain immature DCs that are located at the media-adventitia border. In temporal arteries affected by giant cell arteritis, DCs are highly enriched and activated and have matured into fully differentiated cells producing the chemokines, CCL18, CCL19, and CCL21. In keeping with their advanced maturation, DCs in the granulomatous lesions possess the chemokine receptor, CCR7. CCR7 binds CCL19 and CCL21, causing the highly activated DCs to be trapped in the peripheral tissue site. The co-stimulatory molecule, CD86, which is critical for DC/T-cell interaction, is expressed by a subset of DCs captured in the arterial wall. DC/T-cell interaction does not involve interleukin-12; transcripts for interleukin-12 p40 are absent in the vasculitic infiltrates. We propose that differentiation of DCs and the autocrine and paracrine actions of chemokines in granulomatous lesions misdirect DCs away from their usual journey to lymphoid organs and are critical in maintaining T-cell activation and granuloma formation in giant cell arteritis.

The murine IL-2 promoter contains distal regulatory elements responsive to the Ah receptor, a member of the evolutionarily conserved bHLH-PAS transcription factor family

Signaling through the TCR and costimulatory signals primarily control transcription of the IL-2 gene in naive T cells. The minimal promoter necessary for this expression lies proximal, between -300 and the transcription start site. We had previously shown that activation of the arylhydrocarbon receptor (AHR), a member of the bHLH-PAS family of transcription factors, leads to increased mRNA expression of IL-2 in murine fetal thymocytes. The AHR is abundant in the thymus and may play a role for the development of the immune system. Moreover, its overactivation by chemicals such as dioxins leads to immunosuppression and thymic involution. Binding motifs for the liganded AHR can be identified in the distal region -1300 to -800 of the mouse IL-2 promoter. We show here that these DNA motifs, the so-called dioxin response elements, after binding to the liganded AHR are sufficient to transactivate luciferase expression in a reporter gene system. The IL-2 gene can be induced by the AHR also in thymocytes in vivo after injection of 2,3,7, 8-tetrachlorodibenzo-p-dioxin, a potent ligand of the AHR. The AHR mediates the IL-2 induction as shown with AHR-deficient mice. However, in spleen cells in vitro costimulation via the TCR is necessary for optimal IL-2 gene induction. Thus, the IL-2 promoter region contains novel distal regulatory elements that can be addressed by the AHR to induce IL-2 and can cooperate with the proximal promoter in this.

Constitutive expression in gal7 mutants of Kluyveromyces lactis is due to internal production of galactose as an inducer of the Gal/Lac regulon

The induction process of the galactose regulon has been intensively studied, but until now the nature of the inducer has remained unknown. We have analyzed a delta gal7 mutant of the yeast Kluyveromyces lactis, which lacks the galactotransferase activity and is able to express the genes of the Gal/Lac regulon also in the absence of galactose. We found that this expression is semiconstitutive and undergoes a strong induction during the stationary phase. The gal1-209 mutant, which has a reduced kinase activity but retains its positive regulatory function, also shows a constitutive expression of beta-galactosidase, suggesting that galactose is the inducer. A gal10 deletion in delta gal7 or gal1-209 mutants reduces the expression to under wild-type levels. The presence of the inducer could be demonstrated in both delta gal7 crude extracts and culture medium by means of a bioassay using the induction in gal1-209 cells. A mutation in the transporter gene LAC12 decreases the level of induction in gal7 cells, indicating that galactose is partly released into the medium and then retransported into the cells. Nuclear magnetic resonance analysis of crude extracts from delta gal7 cells revealed the presence of 50 microM galactose. We conclude that galactose is the inducer of the Gal/Lac regulon and is produced via UDP-galactose through a yet-unknown pathway.

Endosymbiosis in amoebae: recently established endosymbionts have become required cytoplasmic components

A strain of large, free-living amoeba that became dependent on bacterial endosymbionts which had infected the amoebae initially as intracellular parasites, was studied by micrurgy and electron microscopy. The results show that the infected host cells require the presence of live endosymbionts for their survival.Thus, the nucleus of an infected amoeba can form a viable cell with the cytoplasm of a noninfected amoeba only when live endosymbionts are present. The endosymbiotic bacteria are not digested by the host amoebae and are not themselves used as nutritional supplement. While the host amoebae are dependent specifically on the endosymbionts, the latter can live inside amoebae of different strains, indicating that their dependence on the host cells is not yet strain specific.

Scanning electron microscope observations of Amoeba proteus during phagocytosis

Phagocytosing Amoeba proteus at different stages of forming foodcups have been observed by scanning electron microscopy. A nonphagocytosing ameba is characterized by dorsal and lateral ridges running longitudinally over the posterior half of the cell and its attachment to the substrate over small areas. When stimulated by prey organisms, the ameba loses polarity and ridges, and adheres to the substrate more firmly over a wider area of contact. Then it forms broad pseudopods to surround its prey and this results in the formation of foodcups. The surface of all ameba is covered with small projections, and membranous blebs are often seen on the surface of phagocytosing organisms.

Cytoplasmic filaments and cellular wound healing in Amoeba proteus

The flexibility and self-healing properties of animal cell surface membranes are well known. These properties have been best exploited in various micrurgical studies on living cells (2, 3), especially in amoebae (7, 20). During nuclear transplantation in amoebae, the hole in the membrane through which a nucleus passes can have a diameter of 20-30 mum, and yet such holes are quickly sealed, although some cytoplasm usually escapes during the transfer. While enucleating amoebae in previous studies, we found that if a very small portion of a nucleus was pushed through the membrane and exposed to the external medium, the amoeba expelled such a nucleus on its own accord. When this happened, a new membrane appeared to form around the embedded portion of the nucleus and no visible loss of cytoplasm occurred during nuclear extrusion. In the present study, we examined amoebae that were at different stages of expelling partially exposed nuclei, to follow the sequence of events during the apparent new membrane formation. Unexpectedly, we found that a new membrane is not formed around the nucleus from inside but a hole is sealed primarily by a constriction of the existing membrane, and that cytoplasmic filaments are responsible for the prevention of the loss of cytoplasm.