Evidence for functional inter-relationships between FOXP3, leukaemia inhibitory factor, and axotrophin/MARCH-7 in transplantation tolerance

USP7 - a crucial regulator of cancer hallmarks

Over the course of three decades of study, the deubiquitinase Herpesvirus associated Ubiquitin-Specific Protease/Ubiquitin-Specific Protease 7 (HAUSP/USP7) has gradually come to be recognized as a crucially important molecule in cellular physiology. The fact that USP7 is overexpressed in a number of cancers, including breast, prostate, colorectal, and lung cancers, supports the idea that USP7 is also an important regulator of tumorigenesis. In this review, we discuss USP7's function in relation to the cancer hallmarks described by Hanahan and Weinberg. This post-translational modifier can support increased proliferation, block unfavorable growth signals, stop cell death, and support an unstable cellular genome by manipulating key players in the pertinent signalling circuit. It is interesting to note that USP7 also aids in the stabilization of molecules that support angiogenesis and metastasis. Targeting USP7 has now emerged as a crucial component of USP7 research because pharmacological inhibition of USP7 supports p53-mediated cell cycle arrest and apoptosis. Efficacious USP7 inhibition is currently being investigated in both synthetic and natural compounds, but issues with selectivity and a lack of co-crystal structure have hindered USP7 inhibition from being tested in clinical settings. Moreover, the development of new, more effective USP7 inhibitors and their encouraging implications by numerous groups give us a glimmer of hope for USP7-targeting medications as effective substitutes for hazardous cancer chemotherapeutics.

Association of MARCH7 with tumor progression and T-cell infiltration in esophageal cancer

MARCH7 is an E3 ubiquitin ligase known to regulate neuronal development,T-cell proliferation, and cell and tissue differentiation. But, the altered expression of MARCH7 has been observed in various malignancies. Herein, the cellular localization and role of MARCH7 have been elucidated in esophageal squamous cell carcinoma (ESCC), the information regarding which is currently limited. To check the expression of MARCH7 and its correlation with immune cells infiltration in ESCC, immunohistochemical analysis was performed. RNAi approach was used to investigate the role of MARCH7 in esophageal cancer cells. Interestingly, we found a significantly higher expression of MARCH7 protein in 84% of ESCC tissues than in distant matched non-malignant tissues (p ≤ 0.001). In addition to this, immunohistochemistry results have shown a negative correlation between MARCH7 protein expression and tumor-infiltrating immune cells such as CD8 + T cells (r = - 0.633, p = 0.001) and PD1 + T cells (r = - 0.560, p = 0.005). Furthermore, MARCH7 silencing inhibited the ESCC cell growth and reduced the clonogenic and invasion/migration potential of ESCC cells. MARCH7 silencing also significantly increased E-cadherin protein levels in ESCC cells relative to those in negative control cells (p < 0.05). Thus, MARCH7 is oncogenic and might have a possible role in esophageal carcinogenesis. Moreover, E-cadherin may be a downstream target of MARCH7 in ESCC.

Autophagy Regulation by Crosstalk between miRNAs and Ubiquitination System

MicroRNAs (miRNAs) are non-coding single-stranded RNA molecules encoded by endogenous genes with ~22 nucleotides which are involved in the regulation of post-transcriptional gene expression. Ubiquitination and deubiquitination are common post-translational modifications in eukaryotic cells and important pathways in regulating protein degradation and signal transduction, in which E3 ubiquitin ligases and deubiquitinases (DUBs) play a decisive role. MiRNA and ubiquitination are involved in the regulation of most biological processes, including autophagy. Furthermore, in recent years, the direct interaction between miRNA and E3 ubiquitin ligases or deubiquitinases has attracted much attention, and the cross-talk between miRNA and ubiquitination system has been proved to play key regulatory roles in a variety of diseases. In this review, we summarized the advances in autophagy regulation by crosstalk between miRNA and E3 ubiquitin ligases or deubiquitinases.

miR-27b-3p/MARCH7 regulates invasion and metastasis of endometrial cancer cells through Snail-mediated pathway

Ubiquitin E3 ligase membrane-associated RING-CH-type finger 7 (MARCH7), also known as axotrophin, was originally identified in mouse embryonic stem cells. MARCH7 is involved in T-cell proliferation, neuronal development, and the immune system. However, its role in endometrial cancer (EC) remains unclear. This study aimed to investigate the role of MARCH7 in EC. Quantitative polymerase chain reaction, immunohistochemistry, and western blot analysis were used to examine the expression of MARCH7, E-cadherin, Snail, and Vimentin in EC cell lines or clinical specimens. The role of MARCH7 in maintaining EC cell malignant phenotype was determined by transwell assay and using xenograft tumor model. Dual-luciferase reporter gene assay was performed to determine whether MARCH7 is an authentic target of miR-27b-3p. Our data showed that the expression level of MARCH7 in EC tissues was higher than that in normal endometrium tissues. The level of MARCH7 was positively associated with that of Snail and Vimentin, clinical stage, and histological grade, while negatively associated with that of E-cadherin. Knockdown of MARCH7 inhibited the invasion and metastasis of EC cells in vitro and in vivo. The opposite effect was observed after overexpressing MARCH7. MARCH7 promoted invasion and metastasis of EC cells via the Snail-mediated pathway. Furthermore, MARCH7 was demonstrated to be an authentic target of miR-27b-3p, and miR-27b-3p decreased the stimulus effect induced by MARCH7. These data indicate that MARCH7 may be an oncogenic factor and a therapeutic target for EC. miR-27b-3p/MARCH7 may also regulate EC cell invasion and metastasis via the Snail-mediated pathway.

The Secretome Derived From 3D-Cultured Umbilical Cord Tissue MSCs Counteracts Manifestations Typifying Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disorder whose treatment is mostly restricted to pain and symptom management and to the delay of joint destruction. Mesenchymal stem/stromal cells from the umbilical cord tissue (UC-MSCs) have previously been proven to be immunomodulatory and more efficient than bone marrow-derived MSCs in causing remission of local and systemic arthritic manifestations in vivo. Given the paracrine nature of UC-MSC activity, their application as active substances can be replaced by their secretome, thus avoiding allogeneic rejection and safety issues related to unwanted grafting. In this work, we aimed at demonstrating the viability of applying the 3D-primed UC-MSC secretome for the amelioration of arthritic signs. A proteomic analysis was performed to both, media conditioned by UC-MSC monolayer (CM2D) and 3D cultures (CM3D). The analysis of relevant trophic factors confirmed secretome profiles with very significant differences in terms of therapeutic potential. Whereas, CM3D was characterised by a prevailing expression of anti-inflammatory cytokines such as IL-10 and LIF, along with trophic factors involved in different mechanisms leading to tissue regeneration, such as PDGF-BB, FGF-2, I-309, SCF, and GM-CSF; CM2D presented relatively higher levels of IL-6, MCP-1, and IL-21, with recognised pro-inflammatory roles in joint disease and pleiotropic effects in the progression of rheumatoid arthritis (RA). Accordingly, different motogenic effects over mouse chondrocytes and distinct capacities of inducing glycosaminoglycan synthesis in vitro were observed between CM3D and CM2D. Finally, the evaluation of arthritic manifestations in vivo, using an adjuvant-induced model for arthritis (AIA), suggested a significantly higher therapeutic potential of CM3D over CM2D and even UC-MSCs. Histological analysis confirmed a faster remission of local and systemic arthritic manifestations of CM3D-treated animals. Overall, the results show that the use of UC-MSC CM3D is a viable and better strategy than direct UC-MSC administration for counteracting AIA-related signs. This strategy represents a novel MSC-based but nonetheless cell-free treatment for arthritic conditions such as those characterising RA.

Expression of USP7 and MARCH7 Is Correlated with Poor Prognosis in Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is one of the worst malignancies in females with poor overall survival due to the rapid metastasis and the absence of ideal biomarkers. Ubiquitin-specific protease 7 (USP7), an important deubiquitinating enzyme, was reported to be upregulated in several cancers, including liver, prostate and colon cancers. Membrane associated RING-CH protein 7 (MARCH7) belongs to the member of the E3 ubiquitin ligases. In addition, MARCH7 regulates T cell proliferation and the neuronal development and participates in the membrane trafficking and protein degradation. Importantly, MARCH7 itself is ubiquitinated and acts as a potential substrate of USP7. However, the roles of USP7 and MARCH7 in EOC remain to be investigated. We collected 121 EOC patients and analyzed the expression levels of USP7 and MARCH7 in tumor tissues with immunohistochemical staining. We found that the high expression of the two proteins was correlated with lymph node metastasis in EOC patients. Univariate and multivariate analyses revealed that the patients with high expression of the two proteins showed poorer prognosis compared with other patients. Subsequently, using SKOV3 human ovarian adenocarcinoma cells, we showed that either USP7 or MARCH7 enhanced the proliferation and invasion abilities. Moreover, USP7 could regulate the expression levels of E-cadherin and β-catenin through the MARCH7 signaling pathway. Our findings indicate that USP7 and MARCH7 are involved in the progression of EOC. In conclusion, analyzing the expression of USP7 and MARCH7 has high prognostic value in predicting EOC prognosis.

Ubiquitin E3 ligase MARCH7 promotes ovarian tumor growth

Ubiquitin E3 ligase MARCH7 is involved in T cell proliferation and neuronal development. We found that expression of MARCH7 was higher in ovarian cancer tissues than normal ovarian tissues. Silencing MARCH7 decreased cell proliferation, migration, and invasion. Ectopic expression of MARCH7 increased cell proliferation, migration and invasion. Silencing MARCH7 prevented ovarian cancer growth in mice. Silencing MARCH7 inhibited NFkB and Wnt/β-catenin pathway. In agreement, ectopically expressed MARCH7 activated NFkB and Wnt/β-catenin pathways. Finally, MARCH7 was regulated by miR-101. Thus, MARCH7 is oncogenic and a potential target (oncotarget) for ovarian cancer therapy.

The Membrane Associated RING-CH Proteins: A Family of E3 Ligases with Diverse Roles through the Cell

Since the discovery that conjugation of ubiquitin to proteins can drive proteolytic degradation, ubiquitination has been shown to perform a diverse range of functions in the cell. It plays an important role in endocytosis, signal transduction, trafficking of vesicles inside the cell, and even DNA repair. The process of ubiquitination-mediated control has turned out to be remarkably complex, involving a diverse array of proteins and many levels of control. This review focuses on a family of structurally related E3 ligases termed the membrane-associated RING-CH (MARCH) ubiquitin ligases, which were originally discovered as structural homologs to the virals E3s, K3, and K5 from Kaposi's sarcoma-associated herpesvirus (KSHV). These proteins contain a catalytic RING-CH finger and are typically membrane-bound, with some having up to 14 putative transmembrane domains. Despite several lines of evidence showing that the MARCH proteins play a complex and essential role in several cellular processes, this family remains understudied.

Axotrophin/MARCH7 acts as an E3 ubiquitin ligase and ubiquitinates tau protein in vitro impairing microtubule binding

Tau is the major microtubule-associated protein in neurons involved in microtubule stabilization in the axonal compartment. Changes in tau gene expression, alternative splicing and posttranslational modification regulate tau function and in tauopathies can result in tau mislocalization and dysfunction, causing tau aggregation and cell death. To uncover proteins involved in the development of tauopathies, a yeast two-hybrid system was used to screen for tau-interacting proteins. We show that axotrophin/MARCH7, a RING-variant domain containing protein with similarity to E3 ubiquitin ligases interacts with tau. We defined the tau binding domain to amino acids 552–682 of axotrophin comprising the RING-variant domain. Co-immunoprecipitation and co-localization confirmed the specificity of the interaction. Intracellular localization of axotrophin is determined by an N-terminal nuclear targeting signal and a C-terminal nuclear export signal. In AD brain nuclear localization is lost and axotrophin is rather associated with neurofibrillary tangles. We find here that tau becomes mono-ubiquitinated by recombinant tau-interacting RING-variant domain, which diminishes its microtubule-binding. In vitro ubiquitination of four-repeat tau results in incorporation of up to four ubiquitin molecules compared to two molecules in three-repeat tau. In summary, we present a novel tau modification occurring preferentially on 4-repeat tau protein which modifies microtubule-binding and may impact on the pathogenesis of tauopathies.

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We search for tau-interacting proteins using a cytotrap yeast two-hybrid assay.

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MARCH7 was identified as a tau-binding protein and confirmed by several methods.

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Recombinant MARCH7 Ring-variant domain uses Ubc5 for E3 self-ubiquitinating activity.

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MARCH7 Ring-variant domain mono-ubiquitinates tau protein at multiple sites including the microtubule-binding domain.

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Mono-ubiquitination of tau protein diminishes its microtubule-binding.

MARCH7 E3 ubiquitin ligase is highly expressed in developing spermatids of rats and its possible involvement in head and tail formation

Spermatogenesis is a highly complicated metamorphosis process of male germ cells. Recent studies have provided evidence that the ubiquitin-proteasome system plays an important role in sperm head shaping, but the underlying mechanism is less understood. In this study, we localized membrane-associated RING-CH (MARCH)7, an E3 ubiquitin ligase, in rat testis. Northern blot analysis showed that March7 mRNA is expressed ubiquitously but highly in the testis and ovary. In situ hybridization of rat testis demonstrated that March7 mRNA is expressed weakly in spermatogonia and its level is gradually increased as they develop. Immunohistochemical analysis detected MARCH7 protein expression in spermiogenic cells from late round spermatids to elongated spermatids and in epididymal spermatozoa. Moreover, MARCH7 was found to be localized to the caudal end of the developing acrosome of late round and elongating spermatids, colocalizing with β-actin, a component of the acroplaxome. In addition, MARCH7 was also detected in the developing flagella and its expression levels were prominent in elongated spermatids. We also showed that MARCH7 catalyzes lysine 48 (K48)-linked ubiquitination. Immunolocalization studies revealed that K48-linked ubiquitin chains were detected in the heads of elongating spermatids and in the acrosome/acroplaxome, neck, midpiece and cytoplasmic lobes of elongated spermatids. These results suggest that MARCH7 is involved in spermiogenesis by regulating the structural and functional integrity of the head and tail of developing spermatids.

Membrane-associated RING-CH 10 (MARCH10 protein) is a microtubule-associated E3 ubiquitin ligase of the spermatid flagella

Spermiogenesis is a complex and dynamic process of the metamorphosis of spermatids into spermatozoa. There is a great deal that is still unknown regarding the regulatory mechanisms for the formation of the sperm flagellum. In this study, we determined that the membrane-associated RING-CH 10 (March10) gene is predominantly expressed in rat testis. We isolated two March10 isoforms encoding MARCH10a and MARCH10b, which are generated by alternative splicing. MARCH10a is a long RING finger protein, and MARCH10b is a short RING finger-less protein. Immunohistochemical staining revealed that the MARCH10 proteins are specifically expressed in elongating and elongated spermatids, and the expression is absent in epididymal spermatozoa. MARCH10 immunoreactivity was observed in the cytoplasmic lobes as well as the principal piece and annulus of the flagella. When overexpressed in COS7 cells, MARCH10a was localized along the microtubules, whereas MARCH10b was distributed throughout the cytoplasm. An in vitro microtubule cosedimentation assay showed that MARCH10a is directly associated with microtubules. An in vitro ubiquitination assay demonstrated that the RING finger domain of MARCH10a exhibits an E3 ubiquitin ligase activity along with the E2 ubiquitin-conjugating enzyme UBE2B. Moreover, MARCH10a undergoes proteasomal degradation by autoubiquitination in transfected COS7 cells, but this activity was abolished upon microtubule disassembly. These results suggest that MARCH10 is involved in spermiogenesis by regulating the formation and maintenance of the flagella in developing spermatids.

Modulation of CD4+ T lymphocyte lineage outcomes with targeted, nanoparticle-mediated cytokine delivery

Within the immune system there is an exquisite ability to discriminate between "self" and "non-self" that is orchestrated by antigen-specific T lymphocytes. Genomic plasticity enables differentiation of naive CD4+ T lymphocytes into either regulatory cells (Treg) that express the transcription factor Foxp3 and actively prevent autoimmune self-destruction or effector cells (Teff) that attack and destroy their cognate target. An example of such plasticity is our recent discovery that leukemia inhibitory factor (LIF) supports Treg maturation in contrast to IL-6, which drives development of the pathogenic Th17 effector phenotype. This has revealed a LIF/IL6 axis in T cell development which can be exploited for modulation using targeted cytokine delivery. Here we demonstrate that LIF-loaded nanoparticles (NPs) directed to CD4+ T cells (i) oppose IL6-driven Th17 development; (ii) prolong survival of vascularized heart grafts in mice; and (iii) expand FOXP3+ CD4+ T cell numbers in a non-human primate model in vitro. In contrast, IL-6 loaded nanoparticles directed to CD4+ T cells increase Th17 development. Notably, nanoparticle-mediated delivery was demonstrated to be critical: unloaded nanoparticles and soluble LIF or IL-6 controls failed to recapitulate the efficacy of cytokine-loaded nanoparticles in induction and/or expansion of Foxp3+ cells or Th17 cells. Thus, this targeted nanoparticle approach is able to harness endogenous immune-regulatory pathways, providing a powerful new method to modulating T cell developmental plasticity in immune-mediated disease indications.

A LIF/Nanog axis is revealed in T lymphocytes that lack MARCH-7, a RINGv E3 ligase that regulates the LIF-receptor

Nanog is a stem cell transcription factor required for self-renewal and for maintaining pluripotency, and Nanog itself is regulated at least in part by leukaemia inhibitory factor (LIF)--a pluripotent cytokine of the IL6 family. MARCH-7 is an E-3 ligase linked to regulation of the LIF-receptor in T lymphocytes and T cells from mice that lack expression of MARCH-7 are hyper-responsive to activation signals and show a five-fold increase in LIF activity. Here we ask, does MARCH-7 influence the expression profile of Nanog during the synchronized entry of T cells into the cell cycle? We discovered that lack of MARCH-7 was permissive for Nanog expression at both transcript and protein levels during G₁/S: moreover, addition of exogenous LIF to the MARCH-7 null cells caused a further 13-fold induction of Nanog; other measured transcripts including TGFβ, p53 and STAT3 were relatively unchanged. Since lack of MARCH-7 altered responsiveness to activation signals we sought evidence for pre-existing regulatory miR's that might correlate with MARCH-7 gene dose using head-to-head comparisons between MARCH-7 null, heterozygous and wt spleen cells. 34 miRs were found including miR-346 that is known to target LIF transcripts and miR-346 is one of 16 miRs differentially expressed between hESCs and induced hiPSCs. Of the 34 miRs, 12 were known to be temporally regulated in embryonic nerve cells. In summary, in the absence of MARCH-7 a new signaling pathway is unmasked that involves Nanog expression in the T cell lineage. This is the first demonstration that T cells retain responsiveness to a LIF/Nanog axis and that this axis is linked to MARCH-7.

The E3 ligase axotrophin/MARCH-7: protein expression profiling of human tissues reveals links to adult stem cells

Axotrophin/MARCH-7 was first identified in mouse embryonic stem cells as a neural stem cell gene. Using the axotrophin/MARCH-7 null mouse, we discovered profound effects on T lymphocyte responses, including 8-fold hyperproliferation and 5-fold excess release of the stem cell cytokine leukemia inhibitory factor (LIF). Our further discovery that axotrophin/MARCH-7 is required for targeted degradation of the LIF receptor subunit gp190 implies a direct role in the regulation of LIF signaling. Bioinformatics studies revealed a highly conserved RING-CH domain in common with the MARCH family of E3-ubiquitin ligases, and accordingly, axotrophin was renamed "MARCH-7." To probe protein expression of human axotrophin/MARCH-7, we prepared antibodies against different domains of the protein. Each antibody bound its specific target epitope with high affinity, and immunohistochemistry cross-validated target specificity. Forty-eight human tissue types were screened. Epithelial cells stained strongly, with trophoblasts having the greatest staining. In certain tissues, specific cell types were selectively positive, including neurons and neuronal progenitor cells in the hippocampus and cerebellum, endothelial sinusoids of the spleen, megakaryocytes in the bone marrow, crypt stem cells of the small intestine, and alveolar macrophages in the lung. Approximately 20% of central nervous system neuropils were positive. Notably, axotrophin/MARCH-7 has an expression profile that is distinct from that of other MARCH family members. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

The trafficking and regulation of membrane receptors by the RING-CH ubiquitin E3 ligases

Ubiquitylation of membrane receptors is recognised as a critical post-translational modification, governing their regulation and function. Following ubiquitylation, membrane proteins may be internalised, recycled or degraded via lysosomal or proteasomal pathways. Viruses have appropriated these cellular pathways as a mechanism of immune evasion. RING (really interesting new gene)-CH ubiquitin E3 ligases were initially identified from the Kaposi's associated herpesvirus (KSHV) and their founding members, K3 and K5, downregulate several critical immunoreceptors to prevent detection by the host immune system. K3 promotes formation of lysine-63 linked polyubiquitin chains on MHC Class I, signalling Class I internalisation and endolysosomal degradation. K5 targets multiple immunoreceptors, including MHC Class I, CD86, intracellular adhesion molecule (ICAM) 1 and MHC Class I-related chain (MIC)-A/B, thereby preventing detection from cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. The cellular homologues of K3 and K5, the Membrane Associated RING-CH (MARCH) genes, represent eleven proteins that also appear to be important in the downregulation of membrane receptors. While overexpression of several MARCH genes downregulate cell surface receptors such as MHC Class I, MHC Class II, CD86 and ICAM 1, determining their physiological roles has proved difficult. Elucidating the transcriptional regulation, localisation and trafficking of MARCH genes may provide insights into their cellular functions.

Viral and cellular MARCH ubiquitin ligases and cancer

Covalent conjugation of proteins with ubiquitin is one the most important post-translational modifications because it controls intracellular protein trafficking typically resulting in protein degradation. Frequently ubiquitinated proteins are targeted to the proteasome for degradation in the cytosol. However, ubiquitinated membrane bound proteins can also be targeted for endocytosis and degradation in the lysosome. Ubiquitin-dependent degradation pathways have clear cancer relevance due to their integral involvement in protein quality control, regulation of immune responses, signal transduction, and cell cycle regulation. In spite of its fundamental importance, little is known regarding how proteins are specifically identified for ubiquitin-dependent degradation. In this article we review a newly discovered family of viral and cellular ubiquitin ligases called MARCH proteins. Recent studies of MARCH proteins define new paradigms showing how ubiquitin E3 ligases determine the intracellular location and fate of proteins.

The ubiquitin E3 ligase MARCH7 is differentially regulated by the deubiquitylating enzymes USP7 and USP9X

Protein modification by one or more ubiquitin chains serves a critical signalling function across a wide range of cellular processes. Specificity within this system is conferred by ubiquitin E3 ligases, which target the substrates. Their activity is balanced by deubiquitylating enzymes (DUBs), which remove ubiquitin from both substrates and ligases. The RING-CH ligases were initially identified as viral immunoevasins involved in the downregulation of immunoreceptors. Their cellular orthologues, the Membrane-Associated RING-CH (MARCH) family represent a subgroup of the classical RING genes. Unlike their viral counterparts, the cellular RING-CH proteins appear highly regulated, and one of these in particular, MARCH7, was of interest because of a potential role in neuronal development and lymphocyte proliferation. Difficulties in detection and expression of this orphan ligase lead us to search for cellular cofactors involved in MARCH7 stability. In this study, we show that MARCH7 readily undergoes autoubiquitylation and associates with two deubiquitylating enzymes - ubiquitin-specific protease (USP)9X in the cytosol and USP7 in the nucleus. Exogenous expression and short interfering RNA depletion experiments demonstrate that MARCH7 can be stabilized by both USP9X and USP7, which deubiquitylate MARCH7 in the cytosol and nucleus, respectively. We therefore demonstrate compartment-specific regulation of this E3 ligase through recruitment of site-specific DUBs.

In primed allo-tolerance, TIM-3-Ig rapidly suppresses TGFbeta, but has no immediate effect on Foxp3

T-cell immunoglobulin mucin-3 (TIM-3) is only expressed by differentiated TH1 cells following their proliferative response to antigen, functioning to terminate TH1-mediated immunity upon binding to the TIM-3 ligand, galectin-9. This critical regulatory process involves Treg cells via their stable expression of galectin-9. Soluble TIM-3-Ig blocks galectin-9 and prevents induction of peripheral tolerance. Here we have looked for evidence that TIM-3-Ig might also break established regulatory tolerance. Using allo-primed spleen cells cultured ex vivo and challenged with irradiated donor-type stimulator cells either alone or together with 20 microg/ml TIM-3-Ig, we measured daily cytokine release [IL2, inferon gamma (INFgamma), transforming growth factor beta (TGFbeta), IL6, IL10] and cellular Foxp3 protein. In allo-tolerance, a specific effect of TIM-3-Ig was some fourfold reduction in TGFbeta. Foxp3 was induced in the allo-tolerant response to donor and this was not altered by TIM-3-Ig over the 5-day culture period. No Foxp3 was detected in either rejected or donor stimulator cells at any time. Thus, in an ex vivo model of in vivo tolerance to heart allografts, TIM-3-Ig therapy appears to reduce the stable tolerogenic environment by a rapid and specific repression of TGFbeta release.

Regulatory transplantation tolerance and "stemness": evidence that Foxp3 may play a regulatory role in SOCS-3 gene transcription

Immune self-tolerance is controlled by a subset of T lymphocytes that are regulatory (Treg) and epigenetically programmed to suppress autoreactive immune effector cells in vivo. Treg require expression of Foxp3, a transcription factor that not only represses the interleukin-2 gene promoter, but also sequesters key mediators of T-cell signal transduction by complexing with cytoplasmic NFAT and NFkappaB. We have discovered that expression of Foxp3 is linked to two stem cell-related factors, namely leukemia inhibitory factor (LIF) and axotrophin. Because both LIF and axotrophin each influence Foxp3, we now ask if reciprocal cross-talk occurs; for example, does Foxp3 in turn influence LIF and/or axotrophin? We compared the effect of wt-Foxp3 versus mutant DeltaE251-Foxp3, which lacks transcriptional activity, on transcript levels of axotrophin, LIF, and suppressor of cytokine signaling-3 (SOCS-3; a feedback inhibitor of LIF) in the Jurkat human T-cell line. Unexpectedly, a 50-fold increase in SOCS-3 transcripts occurred in the DeltaE251-Foxp3 cells, coincident with a dramatic decrease in LIF transcription. This implies that, either directly or indirectly, transcription of SOCS-3 is negatively regulated by wt-Foxp3. Suppression of SOCS-3 by Foxp3 would support a model wherein Foxp3 promotes LIF signaling in Treg and is further evidence of reciprocity between Foxp3, LIF, and axotrophin.