Cloning and expression of murine CD27: comparison with 4-1BB, another lymphocyte-specific member of the nerve growth factor receptor family

Fundamental Characterization of Antibody Fusion-Single-Chain TNF Recombinant Proteins Directed against Costimulatory TNF Receptors Expressed by T-Lymphocytes

The costimulatory signal regulated by the members of the tumor necrosis factor receptor (TNFR) superfamily expressed by T cells plays essential roles for T cell responses and has emerged as a promising target for cancer immunotherapy. However, it is unclear how the difference in TNFR costimulation contributes to T cell responses. In this study, to clarify the functional significance of four different TNFRs, OX40, 4-1BB, CD27 and GITR, we prepared corresponding single-chain TNF ligand proteins (scTNFLs) connected to IgG Fc domain with beneficial characteristics, i.e., Fc-scOX40L, Fc-sc4-1BBL, Fc-scCD27L (CD70) and Fc-scGITRL. Without intentional cross-linking, these soluble Fc-scTNFL proteins bound to corresponding TNFRs induced NF-kB signaling and promoted proliferative and cytokine responses in CD4⁺ and CD8⁺ T cells with different dose-dependencies in vitro. Mice injected with one of the Fc-scTNFL proteins displayed significantly augmented delayed-type hypersensitivity responses, showing in vivo activity. The results demonstrate that each individual Fc-scTNFL protein provides a critical costimulatory signal and exhibits quantitatively distinct activity toward T cells. Our findings provide important insights into the TNFR costimulation that would be valuable for investigators conducting basic research in cancer immunology and also have implications for T cell-mediated immune regulation by designer TNFL proteins.

Siva 1 Inhibits Cervical Cancer Progression and Its Clinical Prognosis Significance

Background

Cervical cancer is the second most common female malignancies. But the exact etiology of cervical cancer is still under investigation. Recent observations revealed that the loss expression of Siva 1 was related to several different types of tumors. It could play an indispensable role in both exogenous and endogenous apoptotic signaling pathways. Nevertheless, the relationship between Siva 1 expression and cervical cancer progression has not yet been fully clarified. This study aimed to explore the functional role of Siva1 in cervical cancer.

Materials and Methods

In this present experiment, expression of Siva 1 was detected in 87 cervical cancer, 34 CIN and 20 normal samples by immunohistochemistry. The correlation of Siva 1 expression and overall survival times (OS) was analyzed by Kaplan–Meier analysis. We up-regulated the expression of Siva 1 by plasmid pCMV3-Siva 1 in C33A cells. CCK8, flow cytometry, wound-healing, and transwell assays were performed to examine the influences of Siva 1 expression on cell proliferation, apoptosis, migration and invasion.

Results

The expression of Siva 1 was decreased in cervical cancer tissues compared with CIN and normal tissues. In addition, the Siva 1 immunoreactivity was significantly associated with tumor differentiation. Patients with Siva 1 negative staining exhibited a significantly decreased overall survival. Then, we established stable Siva 1 ectopic expression cells, and we found that elevated expression of Siva 1 promoted apoptosis, inhibited proliferation, and suppressed migration and invasion of cervical cancer cells.

Conclusion

The present study revealed a crucial role of Siva 1 in tumor progression and it may be a valuable prognostic indicator of cervical cancer.

Siva-1 emerges as a tissue-specific oncogene beyond its classic role of a proapoptotic gene

Siva-1 is a typical apoptotic protein commonly activated by the p53 tumor suppressor protein and should therefore participate in a barrier against the development of cancer. It has proapoptotic activities in various cell systems. Recent findings suggest that Siva-1 possesses several other apoptosis-independent functions and interacts with many other proteins not directly involved in apoptosis. It harbors the ARF E3 ubiquitin protein ligase activity, a property that is clearly prooncogenic and leads to p53 degradation through the upregulation of the Hdm2 protein level. Surprisingly, recent evidence shows that Siva-1 absence prevents the development of non-small cell lung carcinomas in a mouse model and reveals the oncogenic roles in the same types of human cells, indicating its unique function as an oncogene in the cell context-dependent manner. Herein, we review reported activities of Siva-1 in various experimental settings and comment on its ambiguous function in tumor biology.

Fundamental Mechanisms of Immune Checkpoint Blockade Therapy

Immune checkpoint blockade is able to induce durable responses across multiple types of cancer, which has enabled the oncology community to begin to envision potentially curative therapeutic approaches. However, the remarkable responses to immunotherapies are currently limited to a minority of patients and indications, highlighting the need for more effective and novel approaches. Indeed, an extraordinary amount of preclinical and clinical investigation is exploring the therapeutic potential of negative and positive costimulatory molecules. Insights into the underlying biological mechanisms and functions of these molecules have, however, lagged significantly behind. Such understanding will be essential for the rational design of next-generation immunotherapies. Here, we review the current state of our understanding of T-cell costimulatory mechanisms and checkpoint blockade, primarily of CTLA4 and PD-1, and highlight conceptual gaps in knowledge.Significance: This review provides an overview of immune checkpoint blockade therapy from a basic biology and immunologic perspective for the cancer research community. Cancer Discov; 8(9); 1069-86. ©2018 AACR.

Emerging targets in cancer immunotherapy

The first generation of immune checkpoint inhibitors (anti-CTLA-4 and anti-PD-1/PD-L1) targeted natural immune homeostasis pathways, co-opted by cancers, to drive anti-tumor immune responses. These agents led to unprecedented results in patients with previously incurable metastatic disease and may become first-line therapies for some advanced cancers. However, these agents are efficacious in only a minority of patients. Newer strategies are becoming available that target additional immunomodulatory mechanisms to activate patients' own anti-tumor immune responses. Herein, we present a succinct summary of emerging immune targets with reported pre-clinical efficacy that have progressed to active investigation in clinical trials. These emerging targets include co-inhibitory and co-stimulatory markers of the innate and adaptive immune system. In this review, we discuss: 1) T lymphocyte markers: Lymphocyte Activation Gene 3 [LAG-3], T-cell Immunoglobulin- and Mucin-domain-containing molecule 3 [TIM-3], V-domain containing Ig Suppressor of T cell Activation [VISTA], T cell ImmunoGlobulin and ITIM domain [TIGIT], B7-H3, Inducible T-cell Co-stimulator [ICOS/ICOS-L], CD27/CD70, and Glucocorticoid-Induced TNF Receptor [GITR]; 2) macrophage markers: CD47/Signal-Regulatory Protein alpha [SIRPα] and Indoleamine-2,3-Dioxygenase [IDO]; and 3) natural killer cell markers: CD94/NKG2A and the Killer Immunoglobulin-like receptor [KIR] family. Finally, we briefly highlight combination strategies and potential biomarkers of response and resistance to these cancer immunotherapies.

p53 target Siva regulates apoptosis in ischemic kidneys

The role of p53 in inducing apoptosis following acute kidney injury is well-established; however, the molecular mechanisms remain largely unknown. We report here that the p53 proapoptotic target Siva and its receptor CD27, a member of the tumor necrosis factor receptor family, are upregulated following renal ischemia-reperfusion injury (IRI). Inhibition of Siva using antisense oligonucleotides conferred functional and morphological protection, and it prevented apoptosis postrenal IRI in mice. Renal IRI in CD27-deficient mice displayed functional protection and partial inhibition of apoptosis, suggesting an incomplete role for CD27 in Siva-mediated apoptosis. To further elucidate mechanisms by which Siva elicits apoptosis, in vitro studies were performed. In Siva-transfected LLC-PK(1)cells, Siva is persistently expressed in the nucleus at 3 h onwards and its translocation to mitochondria and the plasma membrane occurred at 6 h. Moreover, Siva overexpression induced mitochondrial permeability, cytochrome c release, caspase-8 and -9 activation, translocation of apoptosis-inducing factor (AIF) to the nucleus, and apoptosis. Inhibition of Siva in ischemic kidneys prevented mitochondrial release of cytochrome c and AIF. These data indicate that Siva function is pivotal in regulating apoptosis in the pathology of renal IRI. Targeting Siva may offer a potential therapeutic strategy for renal IRI.

PERP, a p53 proapoptotic target, mediates apoptotic cell death in renal ischemia

The p53 tumor suppressor gene plays a crucial role in mediating apoptotic cell death in renal ischemia-reperfusion injury (IRI). To further elucidate the p53-dependent pathway, we investigated the role of the p53 apoptosis effector related to PMP-22 (PERP), an apoptosis-associated p53 transcriptional target. PERP mRNA and protein are highly induced in the outer medullary proximal tubular cells (PTC) of ischemic kidneys postreperfusion at 3, 12, and 24 h in a p53-dependent manner. In PTC, overexpression of PERP augmented the rate of apoptosis following hypoxia by inducing mitochondrial permeability and subsequent release of cytochrome c, apoptosis-inducing factor (AIF), and caspase 9 activation. In addition, silencing of the PERP gene with short hairpin RNA prevented apoptosis in hypoxia-mediated injury by precluding mitochondrial dysfunction and consequent cytochrome c and AIF translocation. These data suggest that PERP is a key effector of p53-mediated apoptotic pathways and is a potential therapeutic target for renal IRI.

Eradication of lymphoma by CD8 T cells following anti-CD40 monoclonal antibody therapy is critically dependent on CD27 costimulation

Growing evidence points to the potential of agonistic anti-CD40 mAbs as adjuvants for vaccination against cancer. These appear to act by maturing dendritic cells (DCs) and allowing them to prime CD8 cytotoxic T lymphocytes (CTLs). Although it is well established that optimal T-cell priming requires costimulation via B7:CD28, recent studies emphasize the contribution of TNF receptors to this process. To understand how anti-CD40 mAbs trigger effective antitumor immunity, we investigated the role of TNFR superfamily members CD27 and 4-1BB in the generation of this immunity and showed that, although partially dependent on 4-1BB:4-1BBL engagement, it is completely reliant on CD27:CD70 interactions. Importantly, blocking CD70, and to some extent 4-1BBL, during anti-CD40 treatment prevented accumulation of tumor-reactive T cells and subsequent tumor protection. However, it did not influence changes in DC number, phenotype, nor the activity of CTLs once immunity was established. We conclude that CD27:CD70 and 4-1BB:4-1BBL interactions are needed for DC-driven accumulation of antitumor CTLs following anti-CD40 mAb treatment. Finally, in support of the critical role for CD70:CD27, we show for the first time that agonistic anti-CD27 mAbs given without a DC maturation signal completely protect tumor-bearing mice and provide a highly potent reagent for boosting antitumor T-cell immunity.

The zinc containing pro-apoptotic protein siva interacts with the peroxisomal membrane protein pmp22

Host answers to pathogen attacks define the course of pathogenic events and decide about the fate of the host organism. Infection with coxsackievirus B3 (CVB3) can induce severe myocarditis and pancreatitis. The interplay between host factors and virus components is crucial for the fate of the infected host. As we have shown before, expression of the pro-apoptotic host protein Siva is significantly increased after CVB3 infection, and infected cells are removed by programmed cell death. Analysis of Siva expressed in Escherichia coli revealed that this protein binds three zinc ions, suggesting a rather complex three-dimensional structure. By screening a human heart cDNA library we found a new interaction partner of Siva. The peroxisomal membrane protein PMP22 may be involved in the host response against CVB3. Previous investigations showed that Siva interacts with the cytoplasmic C-terminus of CD27, a member of the tumor necrosis factor receptor group, and transmits an apoptotic signal. With the help of directed two-hybrid assays we determined the N-terminal part of Siva as the binding region for CD27.

Properties of murine CD8+CD27- T cells

In humans, loss of CD27 expression is associated with the stable acquisition of effector functions by CD8+ T cells. We found that murine (CD8+)CD27- T cells were confined to the primed CD62L(dull/-)CD44(bright)CCR7- T cell population. (CD8+)CD27- T cells were absent from lymph nodes but could be found in blood, spleen and in non-lymphoid organs such as lung and liver. Late after primary influenza virus infection, low percentages of antigen-specific CD27- cells emerged in the lung and spleen. After recovery from secondary influenza virus infection, high percentages of influenza-specific CD27- T cells were found in the lung and the loss of CD27 on lung CD8+ T cells coincided with high granzyme B expression. After murine cytomegalovirus infection, loss of CD27 expression on virus-specific CD8+ T cell populations was sustained and especially marked in liver and lung. We suggest that in mice, CD27 is lost from CD8+ T cells only after repetitive antigenic stimulation. Moreover, the high expression of both granzyme B and perforin in the CD27- T cells suggests that the lack of CD27 on murine CD8+ T cells can be used to identify memory T cells with expression of cytotoxic effector molecules.

Stimulation by soluble CD70 promotes strong primary and secondary CD8+ cytotoxic T cell responses in vivo

Identification of the signals required for optimal differentiation of naive CD8(+) T cells into effector and memory cells is critical for the design of effective vaccines. In this study we demonstrate that CD27 stimulation by soluble CD70 considerably enhances the magnitude and quality of the CD8(+) T cell response. Stimulation with soluble CD70 in the presence of Ag significantly enhanced the proliferation of CD8(+) T cells and their ability to produce IL-2 and IFN-gamma in vitro. Administration of Ag and soluble CD70 resulted in a massive (>300-fold) expansion of Ag-specific CD8(+) T cells in vivo, which was due to the enhanced proliferation and survival of activated T cells. In mice that received Ag and soluble CD70, CD8(+) T cells developed into effectors with direct ex vivo cytotoxicity. Furthermore, unlike peptide immunization, which resulted in a diminished response after rechallenge, CD27 stimulation during the primary challenge evoked a strong secondary response upon rechallenge with the antigenic peptide. Thus, in addition to increasing the frequency of primed Ag-specific T cells, CD27 signaling during the primary response instills a program of differentiation that allows CD8(+) T cells to overcome a state of unresponsiveness. Taken together these results demonstrate that soluble CD70 has potent in vivo adjuvant effects for CD8(+) T cell responses.

The Proapoptotic Gene SIVA Is a Direct Transcriptional Target for the Tumor Suppressors p53 and E2F1

The p53 tumor suppressor gene is believed to play an important role in neuronal cell death in acute neurological disease and in neurodegeneration. The p53 signaling cascade is complex, and the mechanism by which p53 induces apoptosis is cell type-dependent. Using DNA microarray analysis, we have found a striking induction of the proapoptotic gene, SIVA. SIVA is a proapoptotic protein containing a death domain and interacts with members of the tumor necrosis factor receptor family as well as anti-apoptotic Bcl-2 family proteins. SIVA is induced following direct p53 gene delivery, treatment with a DNA-damaging agent camptothecin, and stroke injury in vivo. SIVA up-regulation is sufficient to initiate the apoptotic cascade in neurons. Through isolation and analysis of the SIVA promoter, we have identified response elements for both p53 and E2F1. Like p53, E2F1 is another tumor suppressor gene involved in the regulation of apoptosis, including neuronal injury models. We have identified E2F consensus sites in the promoter region, whereas p53 recognition sequences were found in intron1. Sequence analysis has shown that these consensus sites are also conserved between mouse and human SIVA genes. Electrophoretic mobility shift assays reveal that both transcription factors are capable of binding to putative consensus sites, and luciferase reporter assays reveal that E2F1 and p53 can activate transcription from the SIVA promoter. Here, we report that the proapoptotic gene, SIVA, which functions in a broad spectrum of cell types, is a direct transcriptional target for both tumor suppressors, p53 and E2F1.

Costimulation of CD8 T Cell Responses by OX40

The persistence of functional CD8 T cell responses is dependent on checkpoints established during priming. Although naive CD8 cells can proliferate with a short period of stimulation, CD4 help, inflammation, and/or high peptide affinity are necessary for the survival of CTL and for effective priming. Using OX40-deficient CD8 cells specific for a defined Ag, and agonist and antagonist OX40 reagents, we show that OX40/OX40 ligand interactions can determine the extent of expansion of CD8 T cells during responses to conventional protein Ag and can provide sufficient signals to confer CTL-mediated protection against tumor growth. OX40 signaling primarily functions to maintain CTL survival during the initial rounds of cell division after Ag encounter. Thus, OX40 is one of the costimulatory molecules that can contribute signals to regulate the accumulation of Ag-reactive CD8 cells during immune responses.

CD27 promotes survival of activated T cells and complements CD28 in generation and establishment of the effector T cell pool

CD27, like CD28, acts in concert with the T cell receptor to support T cell expansion. Using CD27(-/-) mice, we have shown earlier that CD27 determines the magnitude of primary and memory T cell responses to influenza virus. Here, we have examined the relative contributions of CD27 and CD28 to generation of the virus-specific effector T cell pool and its establishment at the site of infection (the lung), using CD27(-/-), CD28(-/-), and CD27/CD28(-/-) mice. We find that primary and memory CD8+ T cell responses to influenza virus are dependent on the collective contribution of both receptors. In the primary response, CD27 and CD28 impact to a similar extent on expansion of virus-specific T cells in draining lymph nodes. CD27 is the principle determinant for accumulation of virus-specific T cells in the lung because it can sustain this response in CD28(-/-) mice. Unlike CD28, CD27 does not affect cell cycle activity, but promotes survival of activated T cells throughout successive rounds of division at the site of priming and may do so at the site of infection as well. CD27 was found to rescue CD28(-/-) T cells from death at the onset of division, explaining its capacity to support a T cell response in absence of CD28.

Co-stimulatory members of the TNFR family: keys to effective T-cell immunity?

Interactions between co-stimulatory ligands and their receptors are crucial for the activation of T cells, the prevention of tolerance and the development of T-cell immunity. It is now evident that members of the immunoglobulin-like CD28-B7 co-stimulatory family cannot fully account for an effective long-lasting T-cell response or the generation of memory T cells. Several members of the tumour-necrosis factor receptor (TNFR) superfamily--OX40, 4-1BB, CD27, CD30 and HVEM (herpes-virus entry mediator)--are poised to deliver co-stimulatory signals both early and late after encounter with antigen. The roles of these molecules in initiating and sustaining the T-cell response and in promoting long-lived immunity are discussed.

Costimulation of T cells by OX40, 4-1BB, and CD27

Costimulatory signals have been defined as signals brought about by ligation of membrane bound molecules that synergize with, or modify, signals provided when the T cell receptor engages peptide-MHC complexes. In large part, costimulatory signals are essential for many facets of a T cell response, and the general rule is that without these signals, a T cell is ineffective and may often succumb to death or become unresponsive. Until recently, costimulation has been dominated by studies of the Ig superfamily member, CD28, a constitutively expressed molecule that is required to initiate a majority of T cell responses. However, growing evidence over the past few years has now shown that several members of the TNFR family, OX40 (CD134), 4-1BB (CD137), and CD27, are equally important to the effective generation of many types of T cell response. In contrast to CD28, these molecules are either induced or highly upregulated on the T cell surface a number of hours or days after recognition of antigen, and appear to provide signals to allow continued cell division initially regulated by CD28 and/or to prevent excessive cell death several days into the response. An argument can be made that these molecules control the absolute number of effector T cells that are generated at the peak of the immune response and dictate the frequency of memory T cells that subsequently develop. The exact relationship between OX40, 4-1BB, and CD27, is at present unknown, including whether these molecules act together, or sequentially, or control differing types of T cell response. This review will focus on recent studies of these molecules and discuss their implications.

CD70/CD27 ligand, a member of the TNF family, is expressed in human brain tumors

CD70 (CD27 ligand) has been implicated in proapoptotic signals mediated by its receptor CD27 in lymphocytes as well as in proliferative effects induced by reverse signaling in CD70-positive hematopoetic tumor cells. We were able to show that CD70 is expressed at the mRNA and protein level in human meningioma cells, glioma cells from solid human gliomas as well as glioma cell lines and 1 ependynoma. The intensity of CD70 expression varies considerably between different samples from 1 tumor type. In the U343 glioma cell line, CD70 was preferentially localized in the cell processes. Thus, our studies identify CD70 as a new marker molecule in brain tumors that are of nonhematopoetic origin.

CD27 is required for generation and long-term maintenance of T cell immunity

The Traf-linked tumor necrosis factor receptor family member CD27 is known as a T cell costimulatory molecule. We generated CD27-/- mice and found that CD27 makes essential contributions to mature CD4+ and CD8+ T cell function: CD27 supported antigen-specific expansion (but not effector cell maturation) of naïve T cells, independent of the cell cycle-promoting activities of CD28 and interleukin 2. Primary CD4+ and CD8+ T cell responses to influenza virus were impaired in CD27-/- mice. Effects of deleting the gene encoding CD27 were most profound on T cell memory, reflected by delayed response kinetics and reduction of CD8+ virus-specific T cell numbers to the level seen in the primary response. This demonstrates the requirement for a costimulatory receptor in the generation of T cell memory.

Expression of CD27 on murine hematopoietic stem and progenitor cells

Hematopoietic stem cells (HSC) are defined by self-renewal and multilineage differentiation potentials. In order to uncover the genetic program of HSC, we utilized high-density arrays to compare gene expression in highly purified mouse HSC and their mature progeny. One molecule specifically expressed in immature cells is CD27, a member of the TNF receptor family previously shown to play roles in lymphoid proliferation, differentiation, and apoptosis. We show here that the CD27 protein is expressed by about 90% of cells in a purified HSC population. Interestingly, the CD27pos cells are enriched for cells with short-term hematopoietic activities (colony forming potential in vivo and in vitro), while the minority CD27neg population is more effective in clonal long-term transplantation.

Lymphocyte survival--the struggle against death

Cell proliferation and cell death must be closely regulated to maintain the integrity of the immune system during the lifetime of multicellular organisms. Proliferative expansion of lymphoid cells is required for effective immune responses against invading microorganisms. However, following infection eradication, expanded effector cells must be eliminated to prevent non-adaptive accumulation of cells. Therefore, higher vertebrates have developed an extensive network of signal transduction pathways that allow integration of cell survival and cell death stimuli. This network functions to ensure the controlled activation and expansion of cells during an immune response and the deletion of lymphoid cells that are no longer needed at the end of an immune response. Extracellular signals appear to control both mechanisms. Ultimate responses are integrated through cell surface receptors that are linked to intracellular signaling cascades. These signal transduction pathways converge to regulate cell fate at both transcriptional and post-transcriptional levels. In this review, the role of pathways triggered by TNFR-related molecules that determine the fate of lymphoid cells during development and activation is summarized.

Murine Siva-1 and Siva-2, alternate splice forms of the mouse Siva gene, both bind to CD27 but differentially transduce apoptosis

CD27, a member of the TNFR family known to provide essential co-stimulatory signals for T cell growth and B cell Ig synthesis, can also mediate cell death. Using the CD27 cytoplasmic tail as the bait in yeast two hybrid assay, we previously cloned human Siva, a pro-apoptotic molecule. Here we report the characterization of the mouse Siva gene as a 4 kb sequence containing 4 exons and 3 introns. RT-PCR has revealed the presence of two forms of mouse Siva mRNA, the longer full length form Siva-1 and the shorter Siva-2 lacking the sequence coded by exon 2. Immunoblotting with anti-Siva (human) antibodies clearly demonstrate the presence of both Siva-1 and Siva-2. Cotransfection experiments in 293T cells reveal that mouse CD27 receptor can interact with both forms of Siva. Although mouse Siva-1 can trigger apoptosis in Rat-1 cells and in some of the mouse cell lines in transient transfection experiments, similar to the observation made with human Siva, intriguingly its alternate splice form, Siva-2 appears to be much less toxic. It is therefore likely that Siva-2 could regulate the function of Siva-1.

Compromised OX40 function in CD28-deficient mice is linked with failure to develop CXC chemokine receptor 5-positive CD4 cells and germinal centers

Mice rendered deficient in CD28 signaling by the soluble competitor, cytotoxic T lymphocyte-associated molecule 4-immunoglobulin G1 fusion protein (CTLA4-Ig), fail to upregulate OX40 expression in vivo or form germinal centers after immunization. This is associated with impaired interleukin 4 production and a lack of CXC chemokine receptor (CXCR)5 on CD4 T cells, a chemokine receptor linked with migration into B follicles. Germinal center formation is restored in CTLA4-Ig transgenic mice by coinjection of an agonistic monoclonal antibody to CD28, but this is substantially inhibited if OX40 interactions are interrupted by simultaneous injection of an OX40-Ig fusion protein. These data suggest that CD28-dependent OX40 ligation of CD4 T cells at the time of priming is linked with upregulation of CXCR5 expression, and migration of T cells into B cell areas to support germinal center formation.

Expression of CD27 and ischemia/reperfusion-induced expression of its ligand Siva in rat kidneys

BACKGROUND

Studies identifying genes that are differentially expressed following induction of acute ischemic injury have been useful in delineating the pathophysiology of acute renal failure.

METHODS

A differential cDNA library screening technique was used to identify genes that are differentially expressed in rat kidney following induction of acute ischemic renal injury.

RESULTS

Levels of mRNA with a high homology to that coding for Siva, a human proapoptotic protein, were increased approximately 4.5-fold in kidneys obtained from rats within 12 hours following ischemia, compared to kidneys from sham-operated rats. A partial cDNA sequence for the rat protein (rat Siva) was determined that overlaps 92% of the human open reading frame. The cDNA sequence predicts a protein 177 amino acids in length with 76% homology to human Siva. Levels of rat Siva in kidneys were elevated at one, five and seven days post-ischemia were not different from those in kidneys from sham-operated controls. In situ hybridization demonstrated that rat Siva mRNA was expressed in cells lining damaged sections in the S3 segment of the proximal tubule at 12 hours and one day post-ischemia. At five and seven days, Siva mRNA was located in epithelial cells of regenerating tubules including in papillary proliferations. TdT-mediated dUTP-biotin nick end-labeling (TUNEL)-positive cells colocalized with cells containing Siva mRNA. CD27, the receptor for Siva was localized by immunohistochemistry to sloughed cells in the lumens of damaged S3 segments at 12 hours post-ischemia and to cells within papillary proliferations at five days post-injury.

CONCLUSIONS

Siva that is produced within the kidney could be a mediator of apoptosis post-ischemia via an interaction with CD27.

NF-κB Activation in CD27 Signaling: Involvement of TNF Receptor-Associated Factors in Its Signaling and Identification of Functional Region of CD27

CD27 belongs to TNF receptor family, and it is unique in this family for its disulfide-linked homodimerization of 55-kDa monomers. In the present study we demonstrate that overexpression of CD27 in 293 cells induces a low level of NF-κB activation, and the ligation of the receptor by its corresponding ligand (CD70) augments this signal dramatically. Either TNF receptor-associated factor-2 (TRAF2) or TRAF3 binds to the CD27 molecule from the coimmunoprecipitation experiment. This NF-κB activation signal is inhibited by dominant negative TRAF2 or intact TRAF3, indicating that TRAF2 and TRAF3 works as a mediator and an inhibitor, respectively. The activated NF-κB complex contains at least two components, p50 and p65, but not p52. All these phenomena have also been observed in the TNF receptor type II, CD30 and CD40 signaling system, indicating that this receptor family uses the common or similar molecules for this signal. Finally, we identified the 13-amino acid alignment in the cytoplasmic region of the CD27 molecule (residues 238–250 amino acids), which is critical for the NF-κB activation signal and also for its association with TRAFs. This amino acid alignment contains the EEEG sequence, which is essential for interaction of CD30 or CD40 with TRAFs (TRAF1 and TRAF2, but not TRAF3), and also contains the PIQED sequence, which is similar to PXQXT that is known to be necessary for interaction of TNF receptor II and CD30 with TRAFs (TRAF1, 2, and 3).

The TNF receptor family member CD27 signals to Jun N-terminal kinase via Traf-2

CD27 is a lymphocyte-specific member of the TNF receptor (TNFR) family. It is a costimulatory molecule for peripheral T cells, as defined by its ability to enhance the TCR-induced proliferative response. We show here that CD27 augments TCR-induced Jun N-terminal kinase (JNK) activity in primary murine lymph node T cells. To investigate how CD27 couples to JNK, we performed a yeast two hybrid screen with the CD27 cytoplasmic tail. This revealed that CD27 directly associates with Traf-2. Transfection experiments using dominant negative Traf-2 indicated that CD27 communicates with JNK via Traf-2. These findings group CD27 together with other members of the TNFR family, TNFR-1, -2, CD30 and CD40, which have all been shown to couple to Traf proteins. Since Traf proteins have been reported to initiate an anti-apoptotic signaling pathway, our data suggest that CD27 not only regulates proliferation, but also survival of T lymphocytes.

A new member of the tumor necrosis factor/nerve growth factor receptor family inhibits T cell receptor-induced apoptosis

By comparing untreated and dexamethasone-treated murine T cell hybridoma (3DO) cells by the differential display technique, we have cloned a new gene, GITR (glucocorticoid-induced tumor necrosis factor receptor family-related gene) encoding a new member of the tumor necrosis factor/nerve growth factor receptor family. GITR is a 228-amino acids type I transmembrane protein characterized by three cysteine pseudorepeats in the extracellular domain and similar to CD27 and 4-1BB in the intracellular domain. GITR resulted to be expressed in normal T lymphocytes from thymus, spleen, and lymph nodes, although no expression was detected in other nonlymphoid tissues, including brain, kidney, and liver. Furthermore, GITR expression was induced in T lymphocytes upon activation by anti-CD3 mAb, Con A, or phorbol 12-myristate 13-acetate plus Ca-ionophore treatment. The constitutive expression of a transfected GITR gene induced resistance to anti-CD3 mAb-induced apoptosis, whereas antisense GITR mRNA expression lead to increased sensitivity. The protection toward T cell receptor-induced apoptosis was specific, because other apoptotic signals (Fas triggering, dexamethasone treatment, or UV irradiation) were not modulated by GITR transfection. Thus, GITR is a new member of tumor necrosis factor/nerve growth factor receptor family involved in the regulation of T cell receptor-mediated cell death.

CD27, a member of the tumor necrosis factor receptor family, induces apoptosis and binds to Siva, a proapoptotic protein

Members of the tumor necrosis factor receptor (TNFR) superfamily are important for cell growth and survival. In addition to providing costimulatory signals for cell proliferation, ligation of both TNFR1 and Fas can result in programmed cell death or apoptosis. The underlying mechanism requires an intact 80-aa stretch present in the cytoplasmic tails of both TNFR1 and Fas, termed the death domain (DD). Here we show that CD27, a member of the TNFR family, expressed on discrete subpopulations of T and B cells and known to provide costimulatory signals for T and B cell proliferation and B cell Ig production, can also induce apoptosis. Co-crosslinking of surface Ig receptors along with ligation of CD27 augments CD27-mediated apoptosis. Unlike TNFR1 and Fas, the cytoplasmic tail of CD27 is relatively short and lacks the DD. Using the yeast two-hybrid system, we have cloned a novel protein (Siva) that binds to the CD27 cytoplasmic tail. It has a DD homology region, a box-B-like ring finger, and a zinc finger-like domain. Overexpression of Siva in various cell lines induces apoptosis, suggesting an important role for Siva in the CD27-transduced apoptotic pathway.

CD40/CD40 ligand interactions in normal, reactive and malignant lympho-hematopoietic tissues

CD40 is a 48 Kd integral membrane protein expressed by cells of B cells, origin, dentritic cells, monocytes, epithelial cells, endothelial cells and tumor cells including carcinomas, B cell lymphomas/leukemias and Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin's disease (HD). CD40 has been clustered as a member of the nerve growth factor (NGF)/tumor necrosis factor (TNF) receptor superfamily with the corresponding counterstructure, the CD40 ligand (L) being mainly expressed by activated CD4+ T cells, but also some activated CD8+ T cells, basophils, eosinophils, mast cells and stromal cells. CD40L shares significant amino acid homology with TNF particularly in its extracellular domain ("TNF homology region") and is therefore viewed as a member of the TNF ligand superfamily. Binding of CD40L+ T cells to CD40+ B cells is thought to play a major role in T cell-dependent B cell activation, B cell proliferation, Ig isotype switching, memory B cell formation and rescue of B cells from apoptotic death in germinal centers. Mutations of the CD40L gene have been associated with the X-linked hyper-IgM immunodeficiency syndrome, pointing to the critical role of the CD40/CD40L interaction in the T cell-B cell interplay. Accordingly, expression of CD40 by human lympho-hematopoietic tumors has been shown in most of the B cell neoplasias, H-RS cells and HD and some carcinomas. In contrast, CD40L+ tumor cells are almost invariably restricted to CD4+/CD8- T cell lymphomas. Overall, functional CD40/CD40L interactions appear to be critical for cellular activation signals during immune responses and neoplastic tumor cell growth. The understanding of the biology of CD40L has improved our diagnostic and therapeutic repertoire in the management of several human diseases, including CD40+ tumors.

Tumor necrosis factor receptor-associated factor (TRAF)-1, TRAF-2, and TRAF-3 interact in vivo with the CD30 cytoplasmic domain; TRAF-2 mediates CD30-induced nuclear factor kappa B activation

CD30 is a member of the tumor necrosis factor receptor superfamily, which can transduce signals for proliferation, death, or nuclear factor kappa B (NF-kappa B) activation. Investigation of CD30 signaling pathways using a yeast two-hybrid interaction system trapped a cDNA encoding the tumor necrosis factor receptor-associated factor (TRAF)-2 TRAF homology domain. TRAF-1 and TRAF-3 also interacted with CD30, and > 90% of in vitro-translated TRAF-1 or -2, or 50% of TRAF-3, bound to the CD30 cytoplasmic domain. TRAF-1, -2, and -3 bound mostly, but not exclusively, to the carboxyl-terminal 36 residues of CD30. The binding was strongly inhibited by a CD30 oligopeptide centered around a PXQXT (where X is any amino acid) motif shared with CD40 and the Epstein-Barr virus transforming protein LMP1, indicating that this motif in CD30 is an important determinant of TRAF-1, -2 or -3 interaction. At least 15% of TRAF-1, -2, or -3 associated with CD30 when coexpressed in 293 cells. The association was not affected by CD30 cross-linking. However, cross-linking of CD30 activated NF-kappa B. NF-kappa B activation was dependent on the carboxyl-terminal 36 amino acids of CD30 that mediate TRAF association. TRAF-2 has been previously shown to have a unique role in TRAF-mediated NF-kappa B activation, and NF-kappa B activation following CD30 cross-linking was blocked by a dominant negative TRAF-2 mutant. These data indicate that CD30 cross-linking-induced NF-kappa B activation is predominantly TRAF-2-mediated.

Molecular, structural, and biological characteristics of the tumor necrosis factor ligand superfamily

The tumor necrosis factor receptor superfamily at present consists of ten different transmembrane (type I) glycoproteins with characteristic limited sequence homology for the cysteine-rich repeats in the extracellular domain. In parallel the tumor necrosis factor ligand super-family has been recognized by discovery of ligands for all members of the receptor superfamily. These molecules are also transmembrane (type II) glycoproteins, with the exception of lymphotoxin-alpha which is the only entirely secreted protein of the tumor necrosis factor-like proteins. Several members of the ligand superfamily, including tumor necrosis factor and CD95L also exist in a biologically active soluble form. The tumor necrosis factor ligand superfamily contains at present ten different proteins. In addition, NGFR p75 binds to a second family of proteins (neurotrophins). These nerve growth factor-like dimeric soluble molecules are basic neurotrophic factors and the five members (NGF, BDNF, NT-3, NT-4, NT-5) are not related to the tumor necrosis factor superfamily ligands. The members of the tumor necrosis factor ligand superfamily (TNF, LT-alpha, LT-beta, CD27L, CD30L, CD40L, CD95L, 4-IBB, OX40L, TRAIL) share common biological activities, but some properties are shared by only some ligands, while others are unique. The diverse biological activities triggered through tumor necrosis factor receptors have been linked to the regulation of cellular activation, including immune responses and inflammatory reactions, but also with the pathology of a series of human diseases.

CD27 cooperates with the pre-T cell receptor in the regulation of murine T cell development

CD27 is a lymphocyte-specific member of the TNF receptor family and has a TNF-related transmembrane ligand, CD70. The CD27/CD70 receptor-ligand pair cooperates with the TCR in the regulation of the peripheral T cell response. The study presented here reveals that CD27 may play a similar role in thymic pre-T cell development. We have previously cloned the cDNA encoding murine CD27, prepared specific mAbs and observed that murine CD27 is expressed on virtually all thymocytes, with the exception of a subpopulation of CD4-8- precursor T cells. It is shown here that induction of murine CD27 expression occurs at the transition from the CD4-8-25+ to the CD4-8-25- precursor T cell stage and is regulated by the pre-TCR. Therefore, we investigated whether CD27 contributes to pre-TCR-mediated thymocyte development. Pre-TCR function was mimicked by the induction of CD3 signaling in thymocytes of recombination activating gene (RAG)-deficient mice. This in vivo anti-CD3 epsilon mAb treatment induces an about fifty fold numerical expansion of CD4-8-25+ thymocytes and their differentiation to the CD4+8+25- stage. Co-injection of anti-CD27 mAb inhibited the CD3-mediated expansion and differentiation of the CD4-8-25+ precursor population. Also, injection of anti-CD27 mAb in TCR alpha-/- mutant mice led to a reduction in the absolute number of CD4+8+25- thymocytes. We present evidence that in these in vivo systems, anti-CD27 mAb inhibits CD27-ligand interaction. Therefore, we conclude that CD27 may contribute to normal murine T cell development by synergizing with the pre-TCR-mediated signal.

A family of ligands for the TNF receptor superfamily

Recent progress in the definition of molecules involved in immune regulation has led to the discovery of a number of type I membrane glycoproteins with a distinctive, cysteine-rich, repetitive domain structure within their extracellular regions. Because the prototype members of this family are receptors for cytokines (tumor necrosis factor [TNF] and nerve growth factor [NGF]), it was expected that the ligands for the other receptors would possess cytokine-like activities. This prediction has been fulfilled by the cloning of cDNA encoding a series of type II membrane glycoproteins, with homology to TNF, that bind to, and signal through, their cognate receptors. While the biological role of some of these ligand-receptor pairs remains obscure, at least two members of the family, CD40 and Fas, have proven their importance. The human X-linked immunodeficiency, hyper IgM syndrome, is the result of mutations in the CD40 ligand gene, and the Fas and Fas ligand genes are mutated in two mouse strains, lpr and gld, that develop autoimmune disease. These findings, together with other evidence, point to key roles of CD40/CD40 ligand interactions in immune activation, particularly in T-dependent B cell responses, and of Fas/Fas ligand in apoptosis and peripheral tolerance. These molecules, as well as the other ligands of the family, share the property of costimulation of T cell proliferation and are all expressed by activated T cells. More detailed analysis of the expression patterns of ligands and receptors on lymphocyte subpopulations will be necessary to define their different roles in immune activation and suppression.

CD27: marker and mediator of T-cell activation?

CD27 is a lymphocyte-specific member of the tumour necrosis factor receptor (TNF-R) family, expression of which is tightly regulated during T-cell ontogeny. Recently, the ligand for CD27 was identified and was shown to be identical to CD70, a novel member of the TNF family. Functional experiments show that the interaction between CD27 and its ligand generates a co-stimulatory signal for T-cell activation. Here, Rogier Hintzen and colleagues integrate the phenotypic and functional data available on CD27 and its ligand, and propose a role for CD27 in the amplification of T-cell responses.

Tumor necrosis factor receptor superfamily members and their ligands

The tumor necrosis factor (TNF) receptor family comprises a number of type I integral membrane glycoproteins which exhibit sequence homology in their cysteine-rich extracellular domains. Recently, ligands for many of these receptors have been identified. These molecules all display sequence identity with TNF and lymphotoxin beta, prototype ligands for this receptor family, and have the conformation of type II transmembrane molecules. While certain biological activities are common to many members of this TNF-like family, other activities appear to be shared only by some ligands, or are unique. The identification of the TNF superfamily of ligands has provided the opportunity to compare and contrast the diverse biological effects mediated through the interaction of these related molecules with their receptors.

The human OX40 homolog: cDNA structure, expression and chromosomal assignment of the ACT35 antigen

Tissue distribution and expression on mitogen and virally stimulated lymphocytes render the ACT35 molecule a human lymphocyte activation antigen which as yet could not be clustered. Expression cloning of the ACT35 antigen from a pCDM8 library of the HUT-102 cell line revealed strong homology of the cDNA and its encoded protein sequence with the formerly described rat OX40 antigen. The 1.4-kb nucleotide sequence and the deduced 277-amino acid sequence of the single transmembrane protein were 65% and 63% identical, in human and in rat, respectively. Conservation included one N-linked glycosylation site and one protein kinase C phosphorylation site. When expressed in COS-1 cells, the cDNA presented properties comparable to the native ACT35 antigen and the rat OX40 molecule (relative molecular mass 48,000). Thus, the ACT35 protein corresponds to the hitherto unknown human OX40 antigen and is, therefore, another member of the tumor necrosis factor/nerve growth factor receptor (TNFR/NGFR) family. After applying fluorescence in situ hybridization, the human ACT35/OX40 gene could be mapped to chromosome band 1p36 and is, thus, linked to the genes for TNFR II and CD30.

Tumor necrosis factors protect neurons against metabolic-excitotoxic insults and promote maintenance of calcium homeostasis

Emerging data indicate that neurotrophic factors and cytokines utilize similar signal transduction mechanisms. Although neurotrophic factors can protect CNS neurons against a variety of insults, the role of cytokines in the injury response is unclear. We now report that TNF beta and TNF alpha (1-100 ng/ml) can protect cultured embryonic rat hippocampal, septal, and cortical neurons against glucose deprivation-induced injury and excitatory amino acid toxicity. The elevation of intracellular calcium concentration ([Ca2+]i) induced by glucose deprivation, glutamate, NMDA, or AMPA was attenuated in neurons pretreated with TNF beta. The mechanism whereby TNFs stabilize [Ca2+]i may involve regulation of the expression of proteins involved in maintaining [Ca2+]i homeostasis, since both TNF beta and TNF alpha caused a 4- to 8-fold increase in the number of neurons expressing the calcium-binding protein calbindin-D28k. These data suggest a neuroprotective role for TNFs in the brain's response to injury.

CELL-SURFACE ANTIGENS

The cell surface is covered with protein molecules that are held in the membrane by hydrophobic transmembrane segments or glycosyl–phosphatidylinositol (GPI) anchors. Antigens found on cell surfaces comprise not only those encoded by the cell itself but also the products of intracellular parasites. Soluble ligands may be bound to receptor structures on the cell membrane or lectin-like molecules bound to cell-surface carbohydrate structures. The molecules that form an integral part of the cell surface may be proteins, glycoproteins, or glycolipids. They subserve one of three major functions: adhesion, antigen recognition, or receptors for soluble mediators. However, many cell-surface molecules possess more than one function—for example, molecules involved in cell–cell or cell–extracellular matrix adhesion can also themselves be involved in signal transduction. The cell-surface antigens of leukocytes have been intensively studied because of ease of access to this cellular compartment.