Tumor counterattack: fact or fiction?

Tumor necrosis factor superfamily signaling: life and death in cancer

Immune checkpoint inhibitors have shaped the landscape of cancer treatment. However, many patients either do not respond or suffer from later progression. Numerous proteins can control immune system activity, including multiple tumor necrosis factor (TNF) superfamily (TNFSF) and TNF receptor superfamily (TNFRSF) members; these proteins play a complex role in regulating cell survival and death, cellular differentiation, and immune system activity. Notably, TNFSF/TNFRSF molecules may display either pro-tumoral or anti-tumoral activity, or even both, depending on tumor type. Therefore, TNF is a prototype of an enigmatic two-faced mediator in oncogenesis. To date, multiple anti-TNF agents have been approved and/or included in guidelines for treating autoimmune disorders and immune-related toxicities after immune checkpoint blockade for cancer. A confirmed role for the TNFSF/TNFRSF members in treating cancer has proven more elusive. In this review, we highlight the cancer-relevant TNFSF/TNFRSF family members, focusing on the death domain-containing and co-stimulation members and their signaling pathways, as well as their complicated role in the life and death of cancer cells.

Current and Future Trends of Colorectal Cancer Treatment: Exploring Advances in Immunotherapy

Cancer of the colon and rectum (CRC) has been identified among the three most prevalent types of cancer and cancer-related deaths for both sexes. Even though significant progress in surgical and chemotherapeutic techniques has markedly improved disease-free and overall survival rates in contrast to those three decades ago, recent years have seen a stagnation in these improvements. This underscores the need for new therapies aiming to augment patient outcomes. A number of emerging strategies, such as immune checkpoint inhibitors (ICIs) and adoptive cell therapy (ACT), have exhibited promising outcomes not only in preclinical but also in clinical settings. Additionally, a thorough appreciation of the underlying biology has expanded the scope of research into potential therapeutic interventions. For instance, the pivotal role of altered telomere length in early CRC carcinogenesis, leading to chromosomal instability and telomere dysfunction, presents a promising avenue for future treatments. Thus, this review explores the advancements in CRC immunotherapy and telomere-targeted therapies, examining potential synergies and how these novel treatment modalities intersect to potentially enhance each other's efficacy, paving the way for promising future therapeutic advancements.

The dual role of the CD95 and CD95L signaling pathway in glioblastoma

Binding of CD95, a cell surface death receptor, to its homologous ligand CD95L, transduces a cascade of downstream signals leading to apoptosis crucial for immune homeostasis and immune surveillance. Although CD95 and CD95L binding classically induces programmed cell death, most tumor cells show resistance to CD95L-induced apoptosis. In some cancers, such as glioblastoma, CD95-CD95L binding can exhibit paradoxical functions that promote tumor growth by inducing inflammation, regulating immune cell homeostasis, and/or promoting cell survival, proliferation, migration, and maintenance of the stemness of cancer cells. In this review, potential mechanisms such as the expression of apoptotic inhibitor proteins, decreased activity of downstream elements, production of nonapoptotic soluble CD95L, and non-apoptotic signals that replace apoptotic signals in cancer cells are summarized. CD95L is also expressed by other types of cells, such as endothelial cells, polymorphonuclear myeloid-derived suppressor cells, cancer-associated fibroblasts, and tumor-associated microglia, and macrophages, which are educated by the tumor microenvironment and can induce apoptosis of tumor-infiltrating lymphocytes, which recognize and kill cancer cells. The dual role of the CD95-CD95L system makes targeted therapy strategies against CD95 or CD95L in glioblastoma difficult and controversial. In this review, we also discuss the current status and perspective of clinical trials on glioblastoma based on the CD95-CD95L signaling pathway.

Hot or cold: Bioengineering immune contextures into in vitro patient-derived tumor models

In the past decade, immune checkpoint inhibitors (ICI) have proven to be tremendously effective for a subset of cancer patients. However, it is difficult to predict the response of individual patients and efforts are now directed at understanding the mechanisms of ICI resistance. Current models of patient tumors poorly recapitulate the immune contexture, which describe immune parameters that are associated with patient survival. In this Review, we discuss parameters that influence the induction of different immune contextures found within tumors and how engineering strategies may be leveraged to recapitulate these contextures to develop the next generation of immune-competent patient-derived in vitro models.

Luminal Breast Cancer: Risk of Recurrence and Tumor-Associated Immune Suppression

Hormone-receptor positive (HR+) breast cancer (BC) (including the luminal A and the luminal B subtypes) is the most common type of tumor in women diagnosed with early-stage BC (EBC). It represents a highly heterogeneous subgroup that is characterized by different risks of relapse. The aim of this review is to discuss the possible role played by the immune response in predicting this risk, along with the most common clinical and pathological factors and molecular tools that have been developed and are already in use. As opposed to what has previously been observed in the most aggressive human epidermal growth factor receptor 2 (HER2)-positive and triple-negative breast cancer (TNBC) subtypes, a high proportion of tumor-infiltrating lymphocytes (TILs)-reflecting a spontaneous and pre-existing immune response to the tumor-has been linked to a worse prognosis in HR+ EBC. This work provides some immune biological rationale explaining these findings and provides the basics to understand the principal clinical trials that are testing immunotherapy in HR+ (luminal) BC.

Fish natural killer enhancing factor-A (NKEF-A) enhance cytotoxicity of nonspecific cytotoxic cells against bacterial infection

Natural killer enhancing factor (NKEF)-A/B is a member of Peroxiredoxin (Prxs) family, which is named for the function of enhancing NK cells activity. NKEF also plays essential roles in multiple physiology/pathology processes including inflammation regulation, cancer development and redox reactions. However, the regulatory effects of fish NKEF on immune cells remain largely unknown. In this study, the full-length cDNA of NKEF-A (Accession No. MK584553, designated as On-NKEF-A) was identified from Nile tilapia (Oreochromis niloticus). On-NKEF-A encoded a 198 amino acid peptide with molecular mass of 22.085 kDa. On-NKEF-A protein contained a typical 2-Cys family domain, two active sites (51aa and 172aa) that were conserved in mammals, birds, amphibians and fish. Phylogenetic analysis showed that On-NKEF-A had the closest relationship with Zebra mbuna (Maylandia zebra) NKEF. The On-NKEF-A transcription was present in all examined tissues or organs. And the relative high expression levels of On-NKEF-A was found in head kidney leucocytes and nonspecific cytotoxic cells (NCC). After Streptococcus agalactiae stimulation, On-NKEF-A was significantly up-regulated in head kidney, spleen, gill and skin. Also, On-NKEF-A was markedly induced post S. agalactiae, LPS and poly I:C stimulation in head kidney-derived NCC. Moreover, On-NKEF-A was mainly distributed in cytoplasm of fathead minnow cells (FHM cells). The further in vitro analysis found that the recombinant protein of On-NKEF-A (rOn-NKEF-A) could induce the expression of various molecular markers of B cells, macrophages and NCC, enhanced the cytotoxicity of NCC via increasing the effectors expression. The present data collectively indicate that On-NKEF-A participates in anti-bacterial immune response via regulating NCC activity, which will provide new ideas to further explore the defense mechanism of fish against bacteria.

Influence of Microgravity on Apoptosis in Cells, Tissues, and Other Systems In Vivo and In Vitro

All life forms have evolved under the constant force of gravity on Earth and developed ways to counterbalance acceleration load. In space, shear forces, buoyance-driven convection, and hydrostatic pressure are nullified or strongly reduced. When subjected to microgravity in space, the equilibrium between cell architecture and the external force is disturbed, resulting in changes at the cellular and sub-cellular levels (e.g., cytoskeleton, signal transduction, membrane permeability, etc.). Cosmic radiation also poses great health risks to astronauts because it has high linear energy transfer values that evoke complex DNA and other cellular damage. Space environmental conditions have been shown to influence apoptosis in various cell types. Apoptosis has important functions in morphogenesis, organ development, and wound healing. This review provides an overview of microgravity research platforms and apoptosis. The sections summarize the current knowledge of the impact of microgravity and cosmic radiation on cells with respect to apoptosis. Apoptosis-related microgravity experiments conducted with different mammalian model systems are presented. Recent findings in cells of the immune system, cardiovascular system, brain, eyes, cartilage, bone, gastrointestinal tract, liver, and pancreas, as well as cancer cells investigated under real and simulated microgravity conditions, are discussed. This comprehensive review indicates the potential of the space environment in biomedical research.

Circulating Plasma Gelsolin: A Predictor of Favorable Clinical Outcomes in Head and Neck Cancer and Sensitive Biomarker for Early Disease Diagnosis Combined with Soluble Fas Ligand

Head and neck cancer (HNC) accounts for more than 330,000 cancer deaths annually worldwide. Despite late diagnosis being a major factor contributing to HNC mortality, no satisfactory biomarkers exist for early disease detection. Cytoplasmic gelsolin (cGSN) was discovered to predict disease progression in HNC and other malignancies, and circulating plasma gelsolin (pGSN) levels are significantly correlated with infectious and inflammatory disease prognoses. Here, the plasma levels of five candidate biomarkers (circulating pGSN, squamous cell carcinoma antigen, cytokeratin 19 fragment, soluble Fas, and soluble Fas ligand (sFasL)) in 202 patients with HNC and 45 healthy controls were measured using enzyme-linked immunosorbent assay or Millipore cancer multiplex assay. The results demonstrated that circulating pGSN levels were significantly lower in patients with HNC than in healthy controls. Moreover, circulating pGSN outperformed other candidate biomarkers as an independent diagnostic biomarker of HNC in both sensitivity (82.7%) and specificity (95.6%). Receiver operating characteristic curves indicated that combined pGSN and sFasL levels further augmented this sensitivity (90.6%) for early disease detection. Moreover, higher pGSN levels predicted improved prognosis at both 5-year overall survival and progression-free survival. In conclusion, circulating pGSN could be an independent predictor of favorable clinical outcomes and a novel biomarker for the early HNC detection in combination with sFasL.

Differential in vivo biodistribution of 131I-labeled exosomes from diverse cellular origins and its implication for theranostic application

Exosomes are critical mediators of intercellular crosstalk and are regulator of the cellular/tumor microenvironment. Exosomes have great prospects for clinical application as a theranostic and prognostic probe. Nevertheless, the advancement of exosomes research has been thwarted by our limited knowledge of the most efficient isolation method and their in vivo trafficking. Here we have shown that a combination of two size-based methods using a 0.20 μm syringe filter and 100 k centrifuge membrane filter followed by ultracentrifugation yields a greater number of uniform exosomes. We also demonstrated the visual representation and quantification of the differential in vivo distribution of radioisotope 131I-labeled exosomes from diverse cellular origins, e.g., tumor cells with or without treatments, myeloid-derived suppressor cells and endothelial progenitor cells. We also determined that the distribution was dependent on the exosomal protein/cytokine contents. The applied in vivo imaging modalities can be utilized to monitor disease progression, metastasis, and exosome-based targeted therapy.

Reverse Signaling of Tumor Necrosis Factor Superfamily Proteins in Macrophages and Microglia: Superfamily Portrait in the Neuroimmune Interface

The tumor necrosis factor (TNF) superfamily (TNFSF) is a protein superfamily of type II transmembrane proteins commonly containing the TNF homology domain. The superfamily contains more than 20 protein members, which can be released from the cell membrane by proteolytic cleavage. Members of the TNFSF function as cytokines and regulate diverse biological processes, including immune responses, proliferation, differentiation, apoptosis, and embryogenesis, by binding to TNFSF receptors. Many TNFSF proteins are also known to be responsible for the regulation of innate immunity and inflammation. Both receptor-mediated forward signaling and ligand-mediated reverse signaling play important roles in these processes. In this review, we discuss the functional expression and roles of various reverse signaling molecules and pathways of TNFSF members in macrophages and microglia in the central nervous system (CNS). A thorough understanding of the roles of TNFSF ligands and receptors in the activation of macrophages and microglia may improve the treatment of inflammatory diseases in the brain and periphery. In particular, TNFSF reverse signaling in microglia can be exploited to gain further insights into the functions of the neuroimmune interface in physiological and pathological processes in the CNS.

Stromal Cell PD-L1 Inhibits CD8+ T-cell Antitumor Immune Responses and Promotes Colon Cancer

Stromal cells of mesenchymal origin reside below the epithelial compartment and provide structural support in the intestine. These intestinal stromal cells interact with both the epithelial cell compartments, as well as infiltrating hematopoietic immune cells. The importance of these cells in regulating immune homeostasis during inflammation is well recognized. However, little is known about their function and phenotype in the inflammatory tumor microenvironment. Using a syngeneic, immunogenic model of colorectal cancer, we showed that TNFα-initiated inflammatory signaling in CT26 colorectal cancer cells selectively induced PD-L1 expression in stromal cells. Using CD274 shRNA and antibody-mediated approaches, we showed that stromal cell PD-L1 potentiated enhanced immunosuppression, characterized by inhibition of activated CD8⁺ granzyme B-secreting T cells in vitro, and the inhibition of CD8⁺ effector cells was associated with enhanced tumor progression. Stromal cell immunosuppressive and tumor-promoting effects could be reversed with administration of anti-PD-1 in vivo We validated our findings of stromal cell CD274 expression in two cohorts of clinical samples and also observed PD-L1 induction on human stromal cells in response to exposure to the inflammatory secretome from human colon cancer cells, irrespective of microsatellite instability. Collectively, our data showed that tumor-associated stromal cells support T-cell suppression by PD-L1 induction, which is dependent on colon cancer inflammatory signaling. Our findings reveal a key role of mesenchymal stromal cells PD-L1 in suppression of CD8⁺ antitumor immune responses and potentiation of colorectal cancer progression. Cancer Immunol Res; 6(11); 1426-41. ©2018 AACR.

Induction of apoptosis in breast cancer cells in vitro by Fas ligand reverse signaling

PURPOSE

The Fas-antigen is a cell surface receptor that transduces apoptotic signals into cells. The purpose of this study was to evaluate FasL expression in breast cancer and to elucidate the role of its signaling in different breast cancer cell lines.

METHODS

T47D and MCF7 cells were used and cultured in Dulbecco's modified Eagle's medium. FasL translocation to the membrane was achieved by culturing the cells in the presence of human interferon-γ (IFNγ). Translocation was detected by immunofluorescence. The ability of a Fas:Fc fusion protein to trigger apoptosis in these cells was investigated by cell death detection ELISA. After incubation with IFNγ for 4 h and 18 h, apoptosis was assessed in response to treatment with Fas:Fc.

RESULTS

Immunofluorescence revealed that the used cell lines were positive for FasL which was increased and changed to more membrane-bound FasL expression after IFNγ stimulation. After stimulation with 50 IU/ml IFNγ, Fas:Fc significantly increased MCF7 apoptosis (1.39 ± 0.06-fold, p = 0.0004) after 18 h. After stimulation with 100 IU/ml, Fas:Fc significantly increased apoptosis both after 4 h (1.49 ± 0.15-fold, p = 0.018) and 18 h (1.30 ± 0.06-fold, p = 0.013). In T47D cells this effect was seen after 4 h of stimulation with 50 IU/ml and addition of Fas:Fc (1.6 ± 0.08-fold, p = 0.03).

CONCLUSION

Membrane-bound FasL expression could be induced by IFNγ in a breast cancer cell model. More importantly, in the presence of IFNγ the Fas:Fc fusion protein was able to transmit pro-apoptotic signals to T47D and MCF7 cells, significantly inducing apoptosis. The current findings support further in vivo studies regarding FasL activation as a potential target for therapeutic intervention in breast cancer.

FasR and FasL in colorectal cancer

Colorectal cancer (CRC) is one of the most common solid organ cancers prevalent worldwide causing, in spite of advancing therapeutic methodology, high rate of patient mortality, especially due to metastasis development. The cancer stem cell (CSC) theory of tumor growth indicates that CSCs within the tumor mass have great capacity to initiate and sustain tumor growth. Following the suggestion that Fas signaling can be engaged in apoptosis, tumor maintenance, senescence or DICE (death induced by CD95 or CD95L elimination), the attempts to broaden the knowledge concerning the relationships between CSCs features and FasR/FasL appeared to be necessary. The most important advantage of our study was the simultaneously analysis of CSCs from commonly used CRC lines (HCT116 and HT29) and tumor fragments collected from CRC patients. Moreover, the sphere-promoting expansion of CRC lines brought a specific three-dimensional specific environment for CSC exploration. We further investigated the function of Fas signaling in CRC lines depending on the culture mode as we incubated HCT116 and HT29 cells with anti-FasR agonistic antibodies. It appeared to act in a line-dependent and culture mode-dependent manner and influenced some particular features of CSCs such as spherogenicity, proliferation and phenotype. Additionally, the analysis of mRNA level showed that disease progression is associated with significantly increased expression of FasR and/or FasL. In conclusion, our observation seems to confirm that spherical model of cancer lines is more reliable for some sophisticated analysis because of their greater resemblance to the CSCs from human CRC samples in comparison to commonly used adherent cells, at least according to aspects of their biology analyzed in this study. That can be extended to the resemblance of in vitro sphere forming conditions to the in vivo environment. However, the greatest difference concerns the level of apoptosis, thus, this issue require further experiments.

Liposomal prednisolone phosphate potentiates the antitumor activity of liposomal 5-fluorouracil in C26 murine colon carcinoma in vivo

The antitumor efficacy of 5-fluorouracil (5-FU) in advanced colorectal cancer (CRC) is hindered not only by the low therapeutic index, but also by tumor cell resistance to this cytotoxic drug. Therefore, to enhance the 5-FU antitumor activity, the present research used a novel tumor-targeted therapy based on the co-administration of 5-FU encapsulated in long-circulating liposomes (LCL-5-FU) together with liposomal prednisolone phosphate (LCL-PLP), a formulation with known anti-angiogenic actions on C26 murine colon carcinoma cells. Thus, we assessed the in vivo effects of the combined liposomal drug therapy on C26 carcinoma growth as well as on the production of molecular markers with key roles in tumor development such as angiogenic, inflammatory, and oxidative stress molecules. To get further insight into the polarization state of tumor microenvironment after the treatment, we determined the IL-10/IL-12p70 ratio in tumors. Our results showed that combined liposomal drug therapy inhibited almost totally tumor growth and was superior as antitumor activity to both single liposomal drug therapies tested. The antitumor efficacy of the combined therapy was mainly related to the anti-angiogenic and anti-inflammatory actions on C26 carcinoma milieu, being favored by its controlling effect on intratumor oxidative stress and the skewing of polarization of tumor microenvironmental cells toward their antineoplastic phenotypes. Thus, our study unveils a promising treatment strategy for CRC that should be furthermore considered.

Immune surveillance in melanoma: From immune attack to melanoma escape and even counterattack

Pharmacologic inhibition of the cytotoxic T lymphocyte antigen 4 (CTLA4) and the programmed death receptor-1 (PD1) has resulted in unprecedented durable responses in metastatic melanoma. However, resistance to immunotherapy remains a major challenge. Effective immune surveillance against melanoma requires 4 essential steps: activation of the T lymphocytes, homing of the activated T lymphocytes to the melanoma microenvironment, identification and episode of melanoma cells by activated T lymphocytes, and the sensitivity of melanoma cells to apoptosis. At each of these steps, there are multiple factors that may interfere with the immune surveillance machinery, thus allowing melanoma cells to escape immune attack and develop resistance to immunotherapy. We provide a comprehensive review of the complex immune surveillance mechanisms at play in melanoma, and a detailed discussion of how these mechanisms may allow for the development of intrinsic or acquired resistance to immunotherapeutic modalities, and potential avenues for overcoming this resistance.

Dual role of macrophages in the response of C26 colon carcinoma cells to 5-fluorouracil administration

Previous studies have demonstrated that tumor-associated macrophages (TAMs) are pivotal players in tumor progression via modulation of tumor angiogenesis, inflammation, metastasis and oxidative stress, as well as of the response of cancer cells to cytotoxic drugs. Nevertheless, the role of TAMs in the prognosis of colorectal cancer remains controversial. Therefore, the present study aimed to investigate how TAMs mediate the response of C26 colon carcinoma cells to the cytotoxic drug 5-fluorouracil (5-FU), upon TAM co-cultivation with these cancer cells in vitro. In this respect, 5-FU cytotoxicity was assessed in C26 cells in standard culture and in a co-culture with peritoneal macrophages, the production of NF-κB was determined by western blot analysis, and the production of angiogenic/inflammatory proteins in each experimental model was evaluated by protein array analysis. To gain further evidence of the effect of TAMs on oxidative stress, malondialdehyde was measured through high-performance liquid chromatography, and the total nonenzymatic antioxidant levels and the production of nitrites were measured through colorimetric assays. The results demonstrated that TAMs exerted a dual role in the response of C26 cells to 5-FU administration in the co-culture model. Thus, on one side, TAMs sensitized C26 cells to 5-FU administration through inhibition of the production of inflammatory and angiogenic proteins in these cancer cells; however, they also protected cancer cells against 5-FU-induced oxidative stress. Collectively, the present findings suggest that the combined administration of 5-FU with pharmacological agents that prevent TAMs to maintain the physiological range of tumor cell oxidative stress may highly improve the therapeutic potential of this drug.

In vivo Effects in Melanoma of ROCK Inhibition-Induced FasL Overexpression

Ectopic Fas-ligand (FasL) expression in tumor cells is responsible for both tumor escape through tumor counterattack of Fas-positive infiltrating lymphocytes and tumor rejection though inflammatory and immune responses. We have previously shown that RhoA GTPase and its effector ROCK negatively control FasL membrane expression in murine melanoma B16F10 cells. In this study, we found that B16F10 treatment with the ROCK inhibitor H1152 reduced melanoma development in vivo through FasL membrane overexpression. Although H1152 treatment did not reduce tumor growth in vitro, pretreatment of tumor cells with this inhibitor delayed tumor appearance, and slowed tumor growth in C57BL/6 immunocompetent mice. Thanks to the use of mice-bearing mutated Fas receptors (B6/lpr), we found that reduced tumor growth, observed in immunocompetent mice, was linked to FasL overexpression induced by H1152 treatment. Tumor growth analysis in immunosuppressed NUDE and IFN-γ-KO mice highlighted major roles for T lymphocytes and IFN-γ in the H1152-induced tumor growth reduction. Histological analyses of subcutaneous tumors, obtained from untreated versus H1152-treated B16F10 cells, showed that H1152 pretreatment induced a strong intratumoral infiltration of leukocytes. Cytofluorometric analysis showed that among these leukocytes, the number of activated CD8 lymphocytes was increased. Moreover, their antibody-induced depletion highlighted their main responsibility in tumor growth reduction. Subcutaneous tumor growth was also reduced by repeated intravenous injections of a clinical ROCK inhibitor, Fasudil. Finally, H1152-induced ROCK inhibition also reduced pulmonary metastasis implantation independently of T cell-mediated immune response. Altogether, our data suggest that ROCK inhibitors could become interesting pharmacological molecules for melanoma immunotherapy.

Reprogramming the tumor microenvironment: tumor-induced immunosuppressive factors paralyze T cells

It has become evident that tumor-induced immuno-suppressive factors in the tumor microenvironment play a major role in suppressing normal functions of effector T cells. These factors serve as hurdles that limit the therapeutic potential of cancer immunotherapies. This review focuses on illustrating the molecular mechanisms of immunosuppression in the tumor microenvironment, including evasion of T-cell recognition, interference with T-cell trafficking, metabolism, and functions, induction of resistance to T-cell killing, and apoptosis of T cells. A better understanding of these mechanisms may help in the development of strategies to enhance the effectiveness of cancer immunotherapies.

The role of CD95 and CD95 ligand in cancer

CD95 (Fas/APO-1) and its ligand, CD95L, have long been viewed as a death receptor/death ligand system that mediates apoptosis induction to maintain immune homeostasis. In addition, these molecules are important in the immune elimination of virus-infected cells and cancer cells. CD95L was, therefore, considered to be useful for cancer therapy. However, major side effects have precluded its systemic use. During the last 10 years, it has been recognized that CD95 and CD95L have multiple cancer-relevant nonapoptotic and tumor-promoting activities. CD95 and CD95L were discovered to be critical survival factors for cancer cells, and were found to protect and promote cancer stem cells. We now discuss five different ways in which inhibiting or eliminating CD95L, rather than augmenting, may be beneficial for cancer therapy alone or in combination with standard chemotherapy or immune therapy.

Clinical implications of Fas/Fas ligand expression in patients with esophageal squamous cell carcinoma following neoadjuvant chemoradiotherapy

Recent epidemiological studies demonstrated that the incidence of esophageal squamous cell carcinoma (ESCC) is on the increase. Although neoadjuvant chemoradiotherapy (CRT) followed by surgery may improve long-term survival and reduce local recurrence in patients with esophageal cancer, the overall cure rate of esophageal cancer is low. Fas/Fas ligand (FasL) signaling initiates the cell death pathway. The roles of FasL in tumor growth, progression and resistance to treatment have been demonstrated in several malignancies. The aim of this preliminary study was to evaluate Fas/FasL expression in ESCC with neoadjuvant CRT. A total of 20 patients who received neoadjuvant CRT (30-40 Gy; 5-fluorouracil plus cisplatin followed by surgery) were enrolled. We evaluated the expression of Fas, FasL and Ki67 (a proliferative marker) using immunohistochemistry and analyzed the correlations between their expression and clinical outcomes. Additionally, we investigated the association of Fas/FasL expression with peritumoral immune CD8-positive and Foxp3-positive cells. High FasL expression was significantly correlated with disease recurrence (P=0.0134). Patients with high FasL expression exhibited poorer recurrence-free and overall survival (P=0.0102 and 0.0385, respectively). Patients with low Fas and high FasL exhibited significantly poorer recurrence-free survival (P=0.0035). Although statistical significance was not reached, Fas expression appeared to be inversely correlated with Foxp3-positive cells and FasL expression appeared to be inversely correlated with CD8-positive cells. In conclusion, FasL expression was associated with tumor relapse and poor prognosis in patients with ESCC following CRT. Pharmacological control of Fas/FasL signaling may improve therapeutic efficacy and outcome in ESCC patients receiving preoperative CRT.

Apolipoprotein A1 as a potential biomarker in the ascitic fluid for the differentiation of advanced ovarian cancers

CONTEXT

Primary ovarian cancer and ovarian metastasis from non-ovarian cancers in advanced stage are closely mimicking conditions whose therapeutics and prognosis are different.

OBJECTIVE

To identify biomarkers that can differentiate the two variants of advanced ovarian cancers.

METHODS

Gel-based proteomics and antibody-based assays were used to study the differentially expressed proteins in the ascitic fluid of fourteen patients with advanced ovarian cancers.

RESULTS

Programmed Cell Death 1-Ligand 2, apolipoprotein A1, apolipoprotein A4 and anti-human fas antibody are differentially expressed proteins.

CONCLUSIONS

Apolipoprotein A1 with a 61.8 ng/ml cut-off is a potential biomarker with the best differentiating statistical parameters.

Stimulation of FasL induces production of proinflammatory mediators through activation of mitogen-activated protein kinases and nuclear factor-κB in THP-1 cells

FasL is a member of the tumor necrosis factor (TNF) superfamily involved in the various immune reactions such as activation-induced cell death, cytotoxic effector function, and establishment of immune privileged sites through its interaction with Fas. On the other hand, FasL is known to transmit a reverse signal that serves as a T cell co-stimulatory signal. However, the role of FasL-mediated reverse signaling in macrophage function has not been investigated. In order to investigate the presence of FasL-mediated signaling in macrophages, the human macrophage-like cell line THP-1 was analyzed after treatment with FasL ligating agents such as recombinant Fas:Fc fusion protein or anti-FasL monoclonal antibody. Stimulation of FasL induced the expression of proinflammatory mediators such as matrix metalloproteinase-9, TNF-α, and IL-8. The specificity of the reaction was confirmed by the transfection of the FasL-specific siRNAs, which suppressed FasL expression as well as the production of proinflammatory mediators. Utilization of various inhibitors of signaling adaptors and ELISA-base nuclear factor (NF)-κB binding assay demonstrated that the signaling initiated from FasL is mediated by mitogen-activated protein kinases including extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase which induce subsequent activation of NF-κB. These data indicate that membrane expression of FasL and its interaction with its counterpart may contribute to the inflammatory activation of macrophages during immune reactions or pathogenesis of chronic inflammatory diseases.

CD95 signaling in colorectal cancer

CD95 and its ligand (CD95L) are widely expressed in colorectal tumors, but their role in shaping tumor behavior is unclear. CD95 activation on tumor cells can lead to apoptosis, while CD95L attracts neutrophils, suggesting a function in tumor suppression. However, CD95 can also promote tumorigenesis, at least in part by activating non-apoptotic signaling pathways that stimulate tumor cell proliferation, invasion and survival. In addition, CD95 signaling in stromal cells and tumor-infiltrating inflammatory cells has to be taken into account when addressing the function of CD95 and its ligand in colorectal tumor biology. We present a model in which the tumor-suppressing and tumor-promoting activities of CD95/CD95L together determine colorectal tumor behavior. We also discuss how these multiple activities are changing our view of CD95 and CD95L as potential therapeutic targets in the treatment of colorectal cancer. We conclude that locking CD95 in apoptosis-mode may be a more promising anti-cancer strategy than simply inhibiting or stimulating CD95.

Fas expression in renal cell carcinoma accurately predicts patient survival after radical nephrectomy

OBJECTIVES

To investigate Fas, Fas ligand (FasL) and Bcl-2 expression, which are considered to be important apoptotic regulatory factors in renal cell carcinomas (RCCs).

PATIENTS AND METHODS

mRNA quantification and immunohistochemistry allowed for the determination of the expression of these three factors in surgically resected tumors from 82 patients with RCC. The correlation of protein and gene expression with more than 10 years of survival data following nephrectomy (along with clinical and pathologic parameters) was analyzed using uni- and multivariate statistical models.

RESULTS

A significantly poorer outcome was observed in patients with tumors expressing high levels of Fas mRNA in the multivariate analysis (p = 0.0002). In addition, patient survival was significantly worse in FasL mRNA-positive tumor cases when compared with FasL mRNA-negative cases (p = 0.0345). Ten cases relapsed more than 5 years after nephrectomy. Among them, the tumors of 8 cases (80%) did not express FasL mRNA. Analysis of Bcl-2 did not show statistical significance of Bcl-2 expression as a prognostic indicator.

CONCLUSIONS

The data suggest that pronounced Fas expression is a surrogate biomarker of active cancer cell proliferation. Given the FasL tumor counterattack theory, FasL overexpression in RCC may be one of the host immune deficiencies, consequently leading to poor prognosis.

The significant immunological characteristics of peripheral blood neutrophil-to-lymphocyte ratio and Fas ligand expression incidence in nephrectomized tumor in late recurrence from renal cell carcinoma

OBJECTIVE

In order to characterize the significance of immune system function in patients with advanced renal cell carcinoma (RCC), we investigated the interactive relationships among the following parameters: metastatic characteristics, expression of Fas ligand (FasL) in nephrectomized specimens, immunological parameters, and patient's prognosis.

MATERIALS AND METHODS

Thirty-five patients with advanced RCC were stratified into 3 groups according to the characteristics of metastasis timing, at first presentation (mFP), within 5 years of nephrectomy (early-recurrence), after 5 years (late-recurrence). Immunological parameters [hemoglobin, lymphocyte count, neutrophil/lymphocyte ratio (NLR), serum albumin, Eastern Cooperative Oncology Group (ECOG) performance status (PS), and Charlson Comorbidity Index], FasL expression in RCC, and patient prognosis from occurrence of metastasis were compared among the groups. Thirty-five patients were also stratified into 2 groups according to FasL positivity and individual parameters. Patient's prognosis and the remaining immunological parameters were compared between groups.

RESULTS

The NLRs of the late-recurrence group were significantly lower than those of the mFP (P = 0.0004) and early-recurrence (P = 0.013) groups. The FasL mRNA positivity of the late-recurrence group was significantly lower than those of the mFP (P = 0.001) and early-recurrence (P = 0.0277) groups. The prognosis of the late-recurrence group was significantly better than that of the early-recurrence group (P = 0.0255). NLRs were significantly lower in the FasL-negative group than in the -positive group (P = 0.0182). The cause-specific survival rates of the ECOG PS 0 group were significantly higher than that of the ECOG PS > 0 group (P < 0.0001).

CONCLUSIONS

Our results suggest the associations of the prognosis in advanced RCC with peripheral blood NLR and FasL expression in nephrectomized tumor. The characteristics of lower values of NLR and FasL expression positivity in late-recurrence compared with other metastatic timings suggest strong host immune activity, and may imply relatively long survival. On the other hand, elucidation of the patient's general condition obtained not only by chemical data but also by ECOG PS is crucial in the management of patients with advanced RCC.

Characterization of the evolution of immune phenotype during the development and progression of squamous cell carcinoma of the head and neck

While studies have indicated that squamous cell carcinoma of the head and neck (HNSCC) is associated with immune suppression, these studies did not analyze the immune response at the dysplastic stage. The present study utilized a mouse model of 4-nitroquinoline 1-oxide-induced oral carcinogenesis to examine the alterations in immune phenotype at the premalignant and malignant stages of HNSCC. Cervical lymph nodes of HNSCC-bearing mice were found to contain a greater number of cells, including a greater number of conventional (Tconv) and regulatory (Treg) T cells, compared to cervical lymph nodes of control and premalignant lesion-bearing mice, though the Tconv cells appear to be less proliferative and the Treg cells appear to be less suppressive at the HNSCC stage. Premalignant lesion-bearing mouse lymph nodes consist of a greater percentage of Tconv cells expressing markers for activation, memory, and exhaustion compared to both control and HNSCC-bearing mice. Also, lymph nodes' cells from both premalignant lesion-bearing and HNSCC-bearing mice include increased levels of Th1, Tc1, and Th17 cells, with no differences in levels of Th2 cells, compared to control mice. The data show that while there is the expected increase in immunosuppressive Tregs in lymph nodes when HNSCC is present, there is also an unexpected increase in immune populations usually associated with a beneficial antitumor response, including Tconv cells and Th1 and Tc1 cells. In addition, the results demonstrate that the premalignant stage of HNSCC development is associated with a robust immune response involving an increase in inflammatory Th1, Tc1, and Th17 cells.

Cytomegalovirus and tumors: two players for one goal-immune escape

Cytomegalovirus (CMV) and the human tumor cell share the same objectives: escape the recognition and destruction by the immune system and establish a state of immune tolerance conducive for their development. For early tumor development, the escape of the first lines of defense of the immune surveillance is a critical step which determines survival or destruction. The presence of CMV on the tumor site and its involvement in carcinogenesis as initiator or promoter is increasingly documented. In this article, we highlight the similarity between mechanisms used by tumors and CMV to circumvent the immune defenses and evade from immune surveillance. We suggest that CMV and tumors help one another for their common objective. CMV gets shelter in immunologically poor environment of the tumor cells. In return CMV, by acting directly on the cancer cell and/or on the tumor microenvironment, provides the tumor cell the ways to promote its immune escape and development of immune tolerance.

TRAIL receptor signaling regulation of chemosensitivity in vivo but not in vitro

Background

Signaling by Tumor Necrosis Factor-Related Apoptosis Inducing Ligand (TRAIL) and Fas ligand (FasL) has been proposed to contribute to the chemosensitivity of tumor cells treated with various other anti-cancer agents. However, the importance of these effects and whether there are differences in vitro and in vivo is unclear.

Methodology/Principal Findings

To assess the relative contribution of death receptor pathways to this sensitivity and to determine whether these effects are intrinsic to the tumor cells, we compared the chemosensitivity of isogenic BJAB human lymphoma cells where Fas and TRAIL receptors or just TRAIL receptors were inhibited using mutants of the adaptor protein FADD or by altering the expression of the homeobox transcription factor Six1. Inhibition of TRAIL receptors did not affect in vitro tumor cell killing by various anti-cancer agents indicating that chemosensitivity is not significantly affected by the tumor cell-intrinsic activation of death receptor signaling. However, selective inhibition of TRAIL receptor signaling caused reduced tumor regression and clearance in vivo when tested in a NOD/SCID mouse model.

Conclusions

These data show that TRAIL receptor signaling in tumor cells can determine chemosensitivity in vivo but not in vitro and thus imply that TRAIL resistance makes tumors less susceptible to conventional cytotoxic anti-cancer drugs as well as drugs that directly target the TRAIL receptors.

Insights into the molecular regulation of FasL (CD178) biology

Fas ligand (FasL, CD95L, APO-1L, CD178, TNFSF6, APT1LG1) is the key death factor of receptor-triggered programmed cell death in immune cells. FasL/Fas-dependent apoptosis plays a pivotal role in activation-induced cell death, termination of immune responses, elimination of autoreactive cells, cytotoxic effector function of T and NK cells, and the establishment of immune privilege. Deregulation or functional impairment of FasL threatens the maintenance of immune homeostasis and defense and results in severe autoimmunity. In addition, FasL has been implicated as an accessory or costimulatory receptor in T cell activation. The molecular mechanisms underlying this reverse signaling capacity are, however, poorly understood and still controversially discussed. Many aspects of FasL biology have been ascribed to selective protein-protein interactions mediated by a unique polyproline region located in the membrane-proximal intracellular part of FasL. Over the past decade, we and others identified a large number of putative FasL-interacting molecules that bind to this polyproline stretch via Src homology 3 or WW domains. Individual interactions were analyzed in more detail and turned out to be crucial for the lysosomal storage, the transport and the surface appearance of the death factor and potentially also for reverse signaling. This review summarizes the work in the framework of the Collaborative Research Consortium 415 (CRC 415) and provides facts and hypotheses about FasL-interacting proteins and their potential role in FasL biology.

Role of apoptosis resistance in immune evasion and metastasis of colorectal cancer

The host immune system functions as a guardian against tumor development. It has been demonstrated that cytotoxic T lymphocyte (CTL)-mediated cytotoxic pathways function to inhibit or delay human colorectal cancer development. However, the host anti-tumor immune responses also 'edit' the tumor and select for more aggressive variants, resulting in immune evasion and tumor escape. Fas is a death receptor that mediates one of the major cytotoxic effector mechanisms of the CTLs. Fas is highly expressed in normal human colon epithelial cells but is frequently silenced in colorectal carcinoma, especially in metastatic colorectal carcinoma, suggesting that loss of Fas expression and function may be an immune evasion and tumor escape mechanism. In addition, recent studies indicated that Fas also mediates cellular proliferation signaling pathways to promote tumor development. Therefore, the death receptor Fas may not only transduce death signals to suppress tumor development but also activate cellular proliferation and the migration process to promote tumor growth and progression. Thus, understanding the mechanisms by which the Fas receptor and its associated protein complex transduces the death and survival signals may identify molecular targets for the development of therapeutic strategy to enhance the Fas-mediated death signals to increase the efficacy of cancer immunotherapy.

Cellular automata modeling of FASL-initiated apoptosis

Two strategies for fighting cancer by modulating FASL-induced apoptosis were modeled by 2D-cellular automata. Our models predict that cancer cells can be killed by maximizing the apoptosis via joint suppression of FLIP and IAP inhibitors by siRNA and SMAC proteins, respectively. It was also predicted that the presumed feedback loop CASP3-->CASP9-->|IAP in the intrinsic pathway accelerates the apoptosis, but does not change significantly the concentration of DFF40, the protein that decomposes DNA. The alternative strategy of preventing the killing of the immune system's T-cells, via minimizing their tumor-induced FAS-L apoptosis by overexpression of FLIP and IAP, was also shown to be promising with a predicted considerable synergy action of the two inhibitors. Dual suppression or overexpression of apoptosis inhibitors emerges thus as promising approach in the fight against cancer. Our modeling has also brought some light on the process of turning type-I cells into type-II ones, which emerges as compensatory mechanism in case of damaged or silenced FASL pathway by preserving about the same self-death level at only 10-12% lower performance rate.

Enhanced cytotoxicity of IL-24 gene-modified dendritic cells co-cultured with cytokine-induced killer cells to hepatocellular carcinoma cells

As a novel human cytokine found recently, IL-24 could selectively kill tumor cells by multiple ways. Dendritic cells (DCs) are the major antigen-presenting cells. Recent studies have revealed that IL-24 can promote the antigen-presenting function of DCs. In this study, we evaluated the antitumor effect and mechanism of co-cultured cytokine-induced killer (CIK) cells and autologous DCs modified with IL-24 gene on hepatocellular carcinoma (HCC) cells. DCs and CIK cells were prepared routinely from human peripheral blood mononuclear cells. Recombinant adenovirus AdVGFP/IL-24 (Ad-IL24) was constructed expressing IL-24. IL-24 gene was transduced into DCs via Ad-IL24, the cells obtained were named DC-IL-24. We demonstrated that the expression rates of CD80, CD83, CD1a, HLA-DR, CD40, CXCR4 on DC-IL-24 were significantly increased compared with those of the control group. DC-IL-24 produced markedly higher levels of IL-24, IL-12 and TNF-alpha as compared with those of DCs. On comparison with non-transfected DCs co-cultured with CIK cells, transfected DCs co-cultured with CIK cells had a significant higher lytic activity against SMMC7721 cells, a HCC cell line.

Enhanced cytotoxicity of IL-24 gene-modified dendritic cells co-cultured with cytokine-induced killer cells to hepatocellular carcinoma cells

As a novel human cytokine found recently, IL-24 could selectively kill tumor cells by multiple ways. Dendritic cells (DCs) are the major antigen-presenting cells. Recent studies have revealed that IL-24 can promote the antigen-presenting function of DCs. In this study, we evaluated the antitumor effect and mechanism of co-cultured cytokine-induced killer (CIK) cells and autologous DCs modified with IL-24 gene on hepatocellular carcinoma (HCC) cells. DCs and CIK cells were prepared routinely from human peripheral blood mononuclear cells. Recombinant adenovirus AdVGFP/IL-24 (Ad-IL24) was constructed expressing IL-24. IL-24 gene was transduced into DCs via Ad-IL24, the cells obtained were named DC-IL-24. We demonstrated that the expression rates of CD80, CD83, CD1a, HLA-DR, CD40, CXCR4 on DC-IL-24 were significantly increased compared with those of the control group. DC-IL-24 produced markedly higher levels of IL-24, IL-12 and TNF-alpha as compared with those of DCs. On comparison with non-transfected DCs co-cultured with CIK cells, transfected DCs co-cultured with CIK cells had a significant higher lytic activity against SMMC7721 cells, a HCC cell line.

[Dissecting the pathways of tumour escape: " question of life and death?"]

Apoptotic pathways are providing important saveguard mechanisms in protection from cancer by eliminating altered and often harmful cells. The disturbances of cell proliferation, differentiation and apoptosis are also found on specific signal-transduction pathways within the tumour cells and between these and the immune system. The article focuses attention on the evolution of the melanocytic naevi in the direction of a dysplastic or tumour cell. The determination of single molecules as prognostic parameters within cancer genesis seems to be problematic. New hopes are being placed on the treatment with TW-37, ABT-737 and TAT-Bim, which, to an extent, are able to support the programmed cell death. The clinical importance of these innovative therapies remains to be seen and should therefore, be viewed with considerable criticism.

Control of death receptor ligand activity by posttranslational modifications

The death receptor ligands are involved in many physiological and pathological processes involving triggering of apoptosis, inflammation, proliferation, and activation. The expression of these molecules is reported to be tightly regulated at the transcriptional level. However, over the last few years, an increasing number of data demonstrated that the control of transcription is only one of the mechanisms that manage the expression of the death receptor ligands. Thus, this review is focused on posttranslational regulation of the three main members of this family, namely FasL, TNF-alpha, and TRAIL. We discuss here the importance of distribution, storage, and degranulation of these molecules, as well as their shedding by proteases on the control of death receptor ligands expression and activity.

Mutant PIK3CA licenses TRAIL and CD95L to induce non-apoptotic caspase-8-mediated ROCK activation

Constitutively active PI3K catalytic subunit alpha (PIK3CA) interfered with apoptosis induction downstream of death receptor-signaling complex formation allowing robust caspase-8 activation without triggering the execution steps of apoptosis. In mutant PIK3CA-expressing cells, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and CD95L stimulated nuclear factor kappaB (NFkappaB) activation, invasion, and transition to an amoeboid-like morphology. NFkappaB activation and adoption of amoeboid shape were inhibited by caspase-8 knockdown or FLIP-S expression, but only the cell morphology alterations required caspase-8 activity. Furthermore, we identified caspase-8-mediated, caspase-3-independent cleavage of the protein kinase rho-associated, coiled-coil containing protein kinase 1 as a novel mechanism for acquiring amoeboid shape and enhanced invasiveness in response to TRAIL and CD95L. Taken together, we provide evidence that mutated PIK3CA converts the 'tumor surveillance' activity of cancer cell-expressed death receptors and caspase-8 toward tumor promotion.

The expression of p53, bcl-2, bax, fas and fasL in the primary tumour and lymph node metastases of breast cancer

PURPOSE. It is unknown to what extent lymph node metastases differ from primary tumours of breast cancer. Our aim was to investigate the similarity between primary breast tumours and the matching lymph node metastases in 59 breast cancer patients. EXPERIMENTAL DESIGN. Immunohistochemical stainings of p53, bax, bc-l2, fas and fasL were performed in primary tumours and the parallel lymph node metastases. RESULTS. When using a cut point of 10%, the concordance between primary tumours and parallel lymph node metastases in the expression of p53 was 85%, bcl-2 79%, bax 69%, fas 59% and fasL 43%. In most tumours the staining status of p53, bcl-2 and bax in the primary tumour and the corresponding lymph node did not change more than 20%. However, these variables could fluctuate in both directions. In 15-25% of the cases, nodal expression was more than 20% lower than in the primary tumours, while in 10-17% of the cases, nodal expression was more than 20% higher than in the primary tumours. In half of the tumours, fas status did not change. Most fasL positive tumours lost positivity in the lymph node metastases or showed positively staining cancer cells only in the peripheral region of the node. A phenotype analysis of combined information of tumour fas/tumour fasL/nodal fas/nodal fasL expression (+/ - ) was assessed. The most frequently observed phenotype was tumour fas - /tumour fasL + /nodal fas - /nodal fasL- (22% of the tumours), although almost all combinations were seen. CONCLUSIONS. The expression of p53, bax, bcl - 2, fas and fasL is not maintained in the matching lymph node metastases of breast cancer. Large studies comparing the expression of relevant tumour biology factors in primary tumours and parallel lymph node metastases and their impact on therapy outcome, especially in the adjuvant setting, are warranted.

Autocrine amplification loop in statin-induced apoptosis of human melanoma cells

BACKGROUND AND PURPOSE

Beside their cholesterol lowering effect, statins exert pleiotropic effects, which include anti-inflammatory, immunosuppressive and anti-proliferative actions. In higher concentrations, statins trigger apoptosis in primary cells and tumour cells. In particular, melanoma cells have been found to be susceptible to statin-induced apoptosis, although only after longer incubation times. The molecular mechanisms behind this delayed drug-induced apoptosis are still unclear.

EXPERIMENTAL APPROACH

The human melanoma A375 and 518A2 cell lines were exposed to various statins in a time-dependent and dose-dependent manner, and indicators of apoptosis, caspase activity and individual apoptotic pathways were analysed for 3-hydroxy-3-methylglutaryl-coenzyme A reductase dependent and independent effects.

KEY RESULTS

Kinetic analysis of statin-induced apoptosis revealed an apoptotic burst for exposure times longer than 24 h. While the extrinsic pathway was not activated within 24 h, longer incubation times corroborated amplification of the mitochondrial pathway with significant activation of caspase 8. Continuous refreshing of the simvastatin-containing medium abrogated the mitochondrial amplification loop via caspase 8. Moreover, conditional medium, supplemented with mevalonic acid in order to nullify a possible contamination by statins, significantly triggered caspase 8 activity. Fas ligand was excluded as a possible candidate to account for the statin-induced autocrine amplification loop.

CONCLUSIONS AND IMPLICATIONS

Simvastatin and atorvastatin are capable of triggering an 'autocrine' suicide factor, which amplifies apoptosis via the extrinsic pathway in human melanoma cells. This pro-apoptotic stimulus implies possible therapeutic potential and may guide feasibility for more potent statins in anti-cancer strategies.

ProtEx technology for the generation of novel therapeutic cancer vaccines

Therapeutic vaccines present an attractive alternative to conventional treatments for cancer. However, tumors have evolved various immune evasion mechanisms to modulate innate, adaptive, and regulatory immunity for survival. Therefore, successful vaccine formulations may require a non-toxic immunomodulator or adjuvant that not only induces/stimulates innate and adaptive tumor-specific immune responses, but also overcomes immune evasion mechanisms. Given the paramount role costimulation plays in modulating innate, adaptive, and regulatory immune responses, costimulatory ligands may serve as effective immunomodulating components of therapeutic cancer vaccines. Our laboratory has developed a novel technology designated as ProtEx that allows for the generation of recombinant costimulatory ligands with potent immunomodulatory activities and the display of these molecules on the cell surface in a rapid and efficient manner as a practical and safe alternative to gene therapy for immunomodulation. Importantly, the costimulatory ligands not only function when displayed on tumor cells, but also as soluble proteins that can be used as immunomodulatory components of conventional vaccine formulations containing tumor-associated antigens (TAAs). We herein discuss the application of the ProtEx technology to the development of effective cell-based as well as cell-free conventional therapeutic cancer vaccines.

FasL expression and reverse signalling

FasL plays a central role in the induction of apoptosis within the immune system. It mediates activation-induced cell death (AICD) of T lymphocytes and contributes to the cytotoxic effector function of T and NK cells. Moreover, FasL is discussed as direct effector molecule for the establishment of immune privilege and tumour survival. Besides its death-promoting activity, FasL has been implicated in reverse signalling and might thus also play a role in T cell development and selection and the modulation of T cell activation. Considering these diverse functions, the overall FasL expression has to be tightly controlled to avoid unwanted damage. Based on an activation-associated transcriptional control, several post-transcriptional processes ensure a safe storage, a rapid mobilisation, a target-directed activity and a subsequent inactivation. Over the past years, the identification and characterisation of FasL-interacting proteins provided novel insight into the mechanisms of FasL transport, processing and reverse signalling, which might be exemplary also for the other members of the TNF family.

Death ligands designed to kill: development and application of targeted cancer therapeutics based on proapoptotic TNF family ligands

The identification of molecular markers associated with cancer development or progression, opened a new era in the development of therapeutics. The successful introduction of a few low molecular weight chemicals and recombinant protein therapeutics with targeted actions into clinical practice have raised great expectations to broadly improve cancer therapy with respect to both overall clinical responses and tolerability. Targeting the apoptotic machinery of malignant cells is an attractive concept to combat cancer, which is currently exploited for the proapoptotic members of the TNF ligand family at various stages of preclinical and clinical development. This review summarizes recent progress in this rapidly progressing field of "biologic" therapies targeting the death receptors of TNF, CD95L, and TRAIL by means of its cognate protein ligands, receptor specific antibodies, and gene therapeutic approaches. Preclinical data on newly derived variants and fusion proteins based on these death ligands, designed to act in a tumor restricted manner, thereby preventing a systemic, potentially harmful action, will also be discussed.

Posttranslational regulation of Fas ligand function

The TNF superfamily member Fas ligand acts as a prototypic death factor. Due to its ability to induce apoptosis in Fas (APO-1, CD95) expressing cells, Fas ligand participates in essential effector functions of the immune system. It is involved in natural killer cell- and T cell-mediated cytotoxicity, the establishment of immune privilege, and in termination of immune responses by induction of activation-induced cell death. In addition, Fas ligand-positive tumours may evade immune surveillance by killing Fas-positive tumour-infiltrating cells. Given these strong cytotoxic capabilities of Fas ligand, it is obvious that its function has to be strictly regulated to avoid uncontrolled damage. In hematopoietic cells, the death factor is stored in secretory lysosomes and is mobilised to the immunological synapse only upon activation. The selective sorting to and the release from this specific lysosomal compartment requires interactions of the Fas ligand cytosolic moiety, which mediates binding to various adapter proteins involved in trafficking and cytoskeletal reorganisation. In addition, Fas ligand surface expression is further regulated by posttranslational ectodomain shedding and subsequent regulated intramembrane proteolysis, releasing a soluble ectodomain cytokine into the extracellular space and an N-terminal fragment with a potential role in intracellular signalling processes. Moreover, other posttranslational modifications of the cytosolic domain, including phosphorylation and ubiquitylation, have been described to affect various aspects of Fas ligand biology. Since FasL is regarded as a potential target for immunotherapy, the further characterisation of its biological regulation and function will be of great importance for the development and evaluation of future therapeutic strategies.