A novel function of CD40: induction of cell death in transformed cells

Expression of CD40 and growth-inhibitory activity of CD40 ligand in ovarian cancer cell lines

OBJECTIVE

Soluble recombinant human CD40 ligand trimer (rhuCD40Lt) has shown antitumor activity in preclinical and clinical studies. We evaluated the effect of rhuCD40Lt on epithelial ovarian carcinoma (EOC) cell lines.

METHODS

Expression of the receptor, CD40, was determined by reverse transcriptase-polymerase chain reaction and flow cytometry, and antiproliferative effects of rhuCD40Lt, either alone or in combination with recombinant interferon-gamma (rIFN-gamma), were examined in 8 EOC lines.

RESULTS

Expression of CD40 was elevated in 5 out of 8 EOC cell lines examined by flow cytometry, and the presence of CD40 transcripts was detected by RT-PCR in all 8 cell lines. CD40 expression was increased by rIFN-gamma, but treatment with rhuCD40Lt decreased CD40 expression in 4 of the 5 lines that had shown elevated CD40 expression. rhuCD40Lt had a growth-inhibitory effect on 2774 cells, which also exhibited the highest level of CD40 expression. Growth-inhibitory effect of rhuCD40Lt was additive with rIFN-gamma on 2774, NMP-1, a cisplatin-resistant subline of OVCAR3, and HEY cell lines. The number of apoptotic tumor cells was increased following treatment with rhuCD40Lt.

CONCLUSIONS

CD40 is expressed on EOC cell lines, and expression was found at the transcript level in all of the EOC lines examined. rIFN-gamma enhances CD40 expression, though a decrease in CD40 expression was observed following treatment with rhuCD40Lt. Growth-inhibitory activity of rhuCD40Lt on EOC lines that express CD40 could be enhanced when rhuCD40Lt treatment was combined with rIFN-gamma. These results suggest that future studies of the combination of rhuCD40Lt and rIFN-gamma might warrant consideration.

Preclinical pharmacokinetics, pharmacodynamics, and activity of a humanized anti-CD40 antibody (SGN-40) in rodents and non-human primates

1. Cell-surface expression of CD40 in B-cell malignancies and multiple solid tumors has raised interest in its potential use as a target for antibody-based cancer therapy. SGN-40, a humanized monoclonal anti-CD40 antibody, mediates antibody-dependent cytotoxicity and inhibits B-cell tumor growth in vitro, properties of interest for the treatment of cancers, and is currently in Phase I clinical trials for B-cell malignancies. In this study, we determined in vivo activity and pharmacokinetics properties of SGN-40. 2. Effect of SGN-40 in xenograft model of CD40-expressing B-cell lymphoma in severe-combined immune deficiency mice and its in vivo pharmacokinetics properties in normal mice, rats and cynomolgus monkeys were studied. 3. Treatment with SGN-40 significantly increased the survival of mice xenografted with human B-cell lymphoma cell line. SGN-40 exhibited nearly 100% bioavailability in mice and it cleared faster when given at a low dose. In monkeys, clearance of SGN-40 was also much faster at low dose, suggesting nonlinear pharmacokinetics in these species. In rats, however, SGN-40 clearance at all tested doses was similar, suggesting that pharmacokinetics were linear in this dose range in rats. Administration of SGN-40 to monkeys also produced marked, dose-dependent, and persistent depletion of peripheral CD20(+) B lymphocytes. 4. Data presented in this report suggest that SGN-40 is active in in vivo, and based upon interspecies scaling, SGN-40 clearance in humans is predicted to be similar to observed SGN-40 clearance in monkeys. These data suggest that SGN-40 has appropriate pharmacokinetic properties that support its clinical use.

The Sjögren’s Syndrome-Associated Autoantigen Ro52 Is an E3 Ligase That Regulates Proliferation and Cell Death

Patients affected by Sjögren's syndrome and systemic lupus erythematosus (SLE) carry autoantibodies to an intracellular protein denoted Ro52. Although the serologic presence of Ro52 autoantibodies is used clinically for diagnostic purposes, the function of the protein or why it is targeted as an autoantigen in several rheumatic conditions has not been elucidated. In this study, we show that the expression of Ro52 is significantly increased in PBMC of patients with Sjögren's syndrome and SLE, and demonstrate that Ro52 is a RING-dependent E3 ligase involved in ubiquitination. Overexpression of Ro52, but not of Ro52 lacking the RING domain, in a mouse B cell line lead to decreased growth in steady state and increased cell death after activation via the CD40 pathway. The role of Ro52 in activation-mediated cell death was further confirmed as a reduction in Ro52 expression restored cell viability. These findings suggest that the increased expression of the Ro52 autoantigen in patients may be directly involved in the reduced cellular proliferation and increased apoptotic cell death observed in Sjögren's syndrome and SLE, and may thus contribute to the autoantigenic load and induction of autoimmune B and T cell responses observed in rheumatic patients.

Analysis of apoptosis-associated genes and pathways in oral cancer cells

BACKGROUND

Cancer cells can resist apoptosis that is induced by stimuli such as detachment or differentiation, but may be more susceptible to apoptosis when exposed to chemotherapeutic drugs. The pattern of gene expression that produces this phenotype is unknown.

METHODS

We compared gene expression patterns of normal human epidermal keratinocytes (NHEK cells) and the oral cancer cell line Tu183 when the cells were exposed to different apoptosis-inducing stimuli.

RESULTS

Pathway analysis revealed that the phenotype difference could be best explained by the simultaneous existence of both proapoptosis and antiapoptosis signals in the cancer cells. Microarray analysis, supported by immunoblotting, showed that one gene that was likely to be involved in the proapoptosis signal was TNFRSF5, which encodes the receptor CD40. When Tu183 cells were exposed to the CD40 ligand they showed apoptosis, while NHEK cells did not.

CONCLUSIONS

The effects of different apoptotic stimuli on normal cells and oral cancer cells can be explained by expression of proapoptosis genes, including the gene that encodes CD40.

Constitutive activation of the CD40 pathway promotes cell transformation and neoplastic growth

CD40, a tumour necrosis factor (TNF) receptor family member, is expressed in a variety of cell types, including B lymphocytes, macrophages, fibroblasts, endothelial and epithelial cells, and this widespread expression is likely to account for its central role in normal physiology and disease pathogenesis. In this study, we provide evidence to support a role for constitutive CD40 signalling in cell transformation. We show that the ligand for CD40 (CD40L/CD154) is expressed in CD40-positive human breast tumour biopsies, suggesting that the constitutive activation of the CD40 receptor in vivo may contribute to the oncogenic process. Coexpression of CD40 and CD40L confers oncogenic effects on immortalized human epithelial cells in vitro, increasing their proliferation, motility and invasion. Expression of LMP:CD40, a hybrid molecule comprising the N-terminus and transmembrane domains of the Epstein-Barr virus-encoded latent membrane protein-1 (LMP1) fused to the cytoplasmic tail of CD40, mimics a constitutively active CD40 receptor and promotes the transformation of immortalized rodent fibroblasts in vitro and their oncogenicity in vivo. The observed effects of aberrant CD40 activation on cell transformation are largely diminished upon suppression of the oncogenic NF-kappaB signalling pathway. Taken together, our results suggest a role for the constitutive engagement of the CD40L/CD40/NF-kappaB activation pathway in cell transformation and neoplastic growth. Strategies that neutralize this pathway may therefore be useful in cancer treatment and prevention.

TRAF6 is required for TRAF2-dependent CD40 signal transduction in nonhemopoietic cells

The emerging role of CD40, a tumor necrosis factor (TNF) receptor family member, in immune regulation, disease pathogenesis, and cancer therapy necessitates the analysis of CD40 signal transduction in a wide range of tissue types. In this study we present evidence that the CD40-interacting proteins TRAF2 and TRAF6 play an important physiological role in CD40 signaling in nonhemopoietic cells. Using mutational analysis of the CD40 cytoplasmic tail, we demonstrate that the specific binding of TRAF2 to CD40 is required for efficient signaling on the NF-kappaB, Jun N-terminal protein kinase (JNK), and p38 axis. In fibroblasts lacking TRAF2 or in carcinoma cells in which TRAF2 has been depleted by RNA interference, the CD40-mediated activation of NF-kappaB and JNK is significantly reduced, and the activation of p38 and Akt is severely impaired. Interestingly, whereas the TRAF6-interacting membrane-proximal domain of CD40 has a minor role in signal transduction, studies utilizing TRAF6 knockout fibroblasts and RNA interference in epithelial cells reveal that the CD40-induced activation of NF-kappaB, JNK, p38, and Akt requires the integrity of TRAF6. Furthermore, we provide evidence that TRAF6 regulates CD40 signal transduction not only through its direct binding to CD40 but also indirectly via its association with TRAF2. These observations provide novel insight into the mechanisms of CD40 signaling and the multiple roles played by TRAF6 in signal transduction.

Construction and expression of a eukaryotic expression plasmid containing human CD40 ligand in human hepatocellular carcinoma cell line HepG2 and its effect on apoptosis

AIM: To construct and express a eukaryotic expression plasmid containing human CD40 ligand (CD40L) in human hepatocellular carcinoma cell line HepG2 for the biological function study of CD40L on HepG2 cells.

METHODS: Human CD40L cDNA was synthesized by reverse transcription-polymerase chain reaction (RT-PCR) with the specific primers from the RNA of human peripheral blood monocyte (PBMC) and directly ligated into the eukaryotic expression vector pcDNA^TM3.1/myc-His(-)A through digestion with specific restriction endonuclease. The recombined plasmid was transformed into the E. coli DH5α to amplify CD40L gene. Then HepG2 cells were divided into 4 groups. The cells in group A were transfected with the recombined plasmid, and group B with the blank plasmid (not containing CD40L cDNA). The cells in group C were just normally cultured, and the ones in group D weren't transfected but added G418 as the control for transfection. The expression of CD40L and CD40 were detected by RT-PCR and fluorescent activated cell sorter (FACS) in HepG2 cells, and the apoptosis, cell cycle, as well as Fas expression, were measured by FACS.

RESULTS: The full-length human CD40L cDNA was successfully cloned into the eukaryotic vector pcDNA^TM3.1/myc-His(-)A. The recombinant plasmid was stably transfected into group A and the rate of CD40L expression was 39.7%. There was no CD40L expression in group B and C. The rates of CD40 expression in group A, B and C were 15.4%, 31.7% and 28.5%, respectively. The apoptotic rate of group A was 45.0±0.3%, but neither group B or C showed obvious apoptosis (P <0.01). Compared with group C, a larger proportion of cells in group A was restrained at G0/G1 phase (90.4±1.3% vs 60.6±1.5%, P <0.01), while the proportions of the cells in S phase (6.32±1.0% vs 12.0±0.7%) and G2/M phase (3.3±0.7% vs 27.3±1.2%) were reduced (both P <0.01). The expression of Fas in group A showed marked increase as compared with that in group B and C (27.8±1.5% vs 3.2±0.8%, 4.2±1.0%, respectively, both P <0.01).

CONCLUSION: The eukaryotic expression plasmid pcDNA^TM3.1/myc-His(-)A can be stably expressed in HepG2 cell line. CD40L-induced apoptosis of HepG2 is correlated with the increased expression of Fas and cell cycle arrest.

Preclinical antilymphoma activity of a humanized anti-CD40 monoclonal antibody, SGN-40

SGN-40 is a humanized IgG1 antihuman CD40 that is currently in a phase I clinical trial for the treatment of multiple myeloma. As surface CD40 expression on B-lineage cells is maintained from pro-B cells to plasma cells, SGN-40 may be applicable to treatment of other B-cell neoplasias, including non-Hodgkin's lymphoma. In this study, we examined potential in vitro and in vivo anti-B-lineage lymphoma activity of SGN-40. Recombinant SGN-40 was expressed and purified from Chinese hamster ovary cells and characterized based on binding affinity, specificity, and normal B-cell stimulation. The ability of SGN-40 to target neoplastic B cells was examined in vitro by proliferation inhibition, cytotoxicity, and antibody-dependent cell cytotoxicity assays and in vivo by human lymphoma xenograft models. Recombinant SGN-40 showed high affinity, Kd of approximately 1 nmol/L, and specific binding to CD40. Whereas SGN-40 was a weak agonist in stimulating normal B-cell proliferation in the absence of IL-4 and CD40L, it delivered potent proliferation inhibitory and apoptotic signals to, and mediated antibody-dependent cytotoxicity against, a panel of high-grade B-lymphoma lines. These in vitro antilymphoma effects were extended to disseminated and s.c. xenograft CD40 tumor models. In these xenograft models, the antitumor activity of SGN-40 was comparable with that of rituximab. The preclinical in vitro and in vivo antilymphoma activity of SGN-40 observed in this study provides a rationale for the clinical testing of SGN-40 in the treatment of CD40+ B-lineage lymphomas.

Death receptor-mediated apoptosis in human malignant glioma cells: modulation by the CD40/CD40L system

CD40, a TNF-R-related cell surface receptor, is shown here to be expressed by glioma cells in vitro and in vivo. Glioma cell lines expressing low levels of CD40 at the cell surface resist cytotoxic effects of CD40L. CD40 gene transfer sensitizes glioma cells to CD40L. Inhibition of protein synthesis potentiates cell death which involves CD40 clustering and caspases 8 and 3 processing. CD40-transfected LN-18 cells acquire resistance to CD95L. In contrast, subtoxic concentrations of CD40L strongly sensitize these cells for TNF-alpha-induced apoptosis. Bispecific CD40xCD95 antibodies specifically kill glioma cells, disclosing the property of endogenous CD40 to facilitate death signalling.

Human T cell leukemia virus type I Tax activates CD40 gene expression via the NF-kappa B pathway

The human T cell leukemia virus type I (HTLV-I) is an oncogenic retrovirus that is etiologically linked to the genesis of adult T cell leukemia (ATL) as well as HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Emerging evidence suggests that the pathogenicity of HTLV-I involves deregulated activation of immune cells, especially T lymphocytes, although the underlying mechanism remains unclear. In this study, we demonstrate that HTLV-I Tax induces the aberrant expression of CD40, a member of the tumor necrosis factor receptor (TNFR) family that plays an important role in lymphocyte activation and differentiation. In a panel of HTLV-I-transformed T cell lines analyzed, CD40 expression was highly elevated compared to HTLV-I-negative T cells. Using Tax mutants and a genetically manipulated T cell system, we demonstrated that Tax-induced CD40 expression required the NF-kappaB signaling pathway. In addition, ligation of CD40 on T cells with recombinant CD40L elicited NF-kappaB activation, suggesting that the CD40 pathway is intact and may participate in a positive regulatory loop in T cells. CD40 ligation strongly synergized with Tax to activate NF-kappaB, suggesting that CD40 signals may costimulate Tax-mediated NF-kappaB activation, particularly when Tax is expressed at low levels. Collectively, these results indicate that CD40 is a novel Tax-regulated gene, and the regulation of CD40 by Tax may play a role in cellular activation and HTLV-I-induced disease pathogenesis.

The role of CD40-CD154 interaction in cell immunoregulation

CD40, a member of the nerve growth factor/tumor necrosis factor receptor superfamily, and its ligand, CD154, play essential roles in cell immune responses. The results of many studies have indicated that CD40-CD154 interaction can upregulate costimulatory molecules, activate antigen-presenting cells (APCs), influence T-cell priming and T-cell-mediated effector functions as well as participate in the pathogenic processing of chronic inflammatory diseases, such as autoimmune diabetes, graft rejection, atherosclerosis, and cancer. Ligation of CD40 on cancer cells was also found to produce a direct growth-inhibitory effect through cell cycle blockage and/or apoptosis with no overt side effects on normal cells and treatment with CD154 can heighten tumor rejection immune response as well. However, systemic treatment with CD154 has some potential risks. Therefore, searching for efficient and safe strategies of CD154-based cancer therapy has been a hot topic in human cancer research. This review focuses on the latest discovered functions of CD40-CD154 interaction in cell immune responses and on the new findings of CD154-based human cancer therapy.

Novel role of CD40 in Fas-dependent apoptosis of cultured salivary epithelial cells from patients with Sjögren's syndrome

OBJECTIVE

To determine the role of Fas and CD40 in the molecular mechanism of salivary epithelial cell death in Sjogren's syndrome (SS).

METHODS

The expression of Fas and CD40 in SS salivary epithelial cells was analyzed by flow cytometry. Induction of apoptosis with anti-Fas and/or anti-CD40 monoclonal antibodies (mAb) was examined by morphologic analysis, DNA fragmentation, and TUNEL assay. Expression of c-FLIP, Fas-associated phosphatase 1, FADD, Bcl-2, Bcl-x(L), and Bcl-x(S) was determined by Western blot analysis.

RESULTS

Expression of Fas and CD40 was significantly higher in SS salivary epithelial cells than in normal cells after interferon-gamma (IFNgamma) stimulation (P < 0.001 for both Fas and CD40). Although neither anti-Fas (CH11) nor anti-CD40 mAb alone could induce typical apoptosis, the two together and preincubation with IFNgamma efficiently induced apoptosis in SS salivary epithelial cells. This apoptosis was almost completely blocked by neutralizing anti-Fas mAb (ZB4), whereas an antagonistic mAb to CD40 (ch5D12) partially inhibited anti-Fas/anti-CD40-induced apoptosis. Also, c-FLIP, an important inhibitory molecule in the Fas death pathway, was strongly expressed in SS salivary epithelial cells, but its expression was down-regulated at the protein level by anti-CD40 mAb.

CONCLUSION

CD40 signals promote Fas-dependent death of SS salivary epithelial cells by down-regulating c-FLIP expression. The presence of c-FLIP in these cells may explain their resistance to undergoing apoptosis in response to either anti-Fas or anti-CD40 mAb, despite their surface expression of both proteins. These findings suggest that SS salivary epithelial cell death requires the cooperation of both Fas and CD40.

A functional CD40 receptor is expressed in pancreatic beta cells

AIMS/HYPOTHESIS

Despite differences in function and embryonic origin, pancreatic islet cells and neurons express proteins belonging to the tumour necrosis factor receptor superfamily. While neurons express the CD40 receptor, it is unknown whether islet cells also express it. We investigated CD40 expression in human and mouse pancreatic islets as well as in NIT-1 insulinoma cells.

METHODS

CD40 expression was studied by reverse transcriptase polymerase chain reaction, flow cytometry, immunohistochemistry and western blot. Responses mediated by CD40 were assessed by a luciferase gene reporter assay following stimulation with a CD40 agonist antibody.

RESULTS

We found that CD40 is expressed in mouse and human pancreatic islet cells. CD40 is expressed by beta cells, and its expression is upregulated by proinflammatory cytokines (IL-1beta, IFN-gamma and TNF-alpha). CD40 signalling in NIT-1 insulinoma cells activates nuclear factor kappa-B, demonstrating that CD40 is functional.

CONCLUSIONS/INTERPRETATION

We present evidence that, in addition to immune cell types, mouse and human pancreatic beta cells express CD40. Its expression is upregulated by proinflammatory stimuli, and signalling through this receptor activates NF-kappaB. We suggest that the effects of inflammatory stimuli that affect beta cell function and survival may be also mediated by signalling through the CD40 receptor. Thus, CD40 may have a role in processes associated with islet autoimmunity and transplantation.

A novel blocking monoclonal antibody recognizing a distinct epitope of human CD40 molecule

CD40, a member of the tumor necrosis factor receptor superfamily, is an important costimulatory molecule during the immune response. Here, we report a blocking mouse antihuman CD40 monoclonal antibody, mAb 3G3, of which the specificity was verified by flow cytometry and Western blot. It was shown by competition test that 3G3 bound to a different site (epitope) of CD40 from the reported CD40 mAbs, including clone mAb89, 3B2, and 5C11. It was also found that mAb 3G3 could inhibit homotypic aggregation of Daudi cells induced by the agonistic anti-CD40 mAb 5C11. Furthermore, mAb 3G3 effectively inhibited the proliferation of peripheral blood mononuclear cells in mixed lymphocyte reaction assay. Finally, a sensitive and specific soluble CD40 (sCD40) ELISA kit was established by matching mAb 3G3 with 5C11, and it was found that the levels of sCD40 in sera from patients with immune disorders such as hyperthyroidism, chronic nephritis, and rheumatoid arthritis were obviously higher than those from normal individuals. Thus, this blocking anti-CD40 mAb provides a novel tool for the study of CD40.

Activation of CD40 in Cervical Carcinoma Cells Facilitates CTL Responses and Augments Chemotherapy-Induced Apoptosis

In this study, we describe the expression and function of CD40, a TNF receptor family member, in cervical carcinomas. CD40 was present at very low levels in normal cervical epithelium but was overexpressed in human papillomavirus-infected lesions and advanced squamous carcinomas of the cervix. The stimulation of CD40-positive cervical carcinoma cell lines with soluble CD40L (CD154) resulted in activation of the NF-kappaB and MAPK signaling pathways and up-regulation of cell surface markers and intracellular molecules associated with Ag processing and presentation. Concomitantly, the CD154-induced activation of CD40 in carcinoma cells was found to directly influence susceptibility to CTL-mediated killing. Thus, CD40 stimulation in cervical carcinoma cell lines expressing a TAP-dependent human papillomavirus 16 E6 Ag epitope resulted in their enhanced killing by specific CTLs. However, CD154 treatment of carcinoma cells expressing proteasome-dependent but TAP-independent Ags from the EBV-encoded BRLF1 and BMLF1 failed to increase tumor cell lysis by specific CTLs. Moreover, we demonstrate that chemotherapeutic agents that suppress protein synthesis and reverse the CD40-mediated dissociation of the translational repressor eukaryotic initiation factor 4E-binding protein from the initiation factor eukaryotic initiation factor 4E, such as 5-fluorouracil, etoposide, and quercetin, dramatically increase the susceptibility of cervical carcinoma cells to CD40L-induced apoptosis. Taken together, these observations demonstrate the functional expression of CD40 in epithelial tumors of the cervix and support the clinical exploitation of the CD40 pathway for the treatment of cervical cancer through its multiple effects on tumor cell growth, apoptosis, and immune recognition.

NF-kappaB overrides the apoptotic program of TNF receptor 1 but not CD40 in carcinoma cells

The activation of NF-kappaB and phosphatidylinositol-3 (PI3) kinase by TNF-alpha and TRAIL overrides the pro-apoptotic effects of these ligands in carcinoma cells and hinders their therapeutic application. In this report we show that CD40 ligand, another member of the TNF superfamily, also triggers the activation of these signalling pathways but, importantly, utilises only the PI3 kinase cascade for anti-apoptotic responses, inasmuch as suppression of PI3 kinase but not NF-kappaB sensitises carcinoma cells to CD40L-induced apoptosis. Therefore, NF-kappaB activation does not always confer anti-apoptotic effects. Moreover, no cross-talk between the two pathways was observed, as the specific suppression of PI3 kinase with chemical inhibitors did not influence CD40-mediated IkappaBalpha phosphorylation and degradation or NF-kappaB binding and transactivation. Similarly, whilst suppression of Akt expression by RNA interference sensitised tumour cells to CD40L-induced apoptosis, it had no effect on CD40-mediated IkappaBalpha degradation. These data provide new evidence for the role of NF-kappaB and PI3 kinase/Akt in phenotypic effects mediated by CD40 ligation and highlight differences in the mechanisms by which TNF family members regulate apoptosis in carcinoma cells.

Novel immunosuppressive properties of interleukin-6 in dendritic cells: inhibition of NF-kappaB binding activity and CCR7 expression

Interleukin-6 (IL-6) is produced during bacterial and viral infections and by various malignant tumors. Here, we describe novel immunosuppressive properties of IL-6 in dendritic cells (DC). In the presence of GM-CSF, IL-4, and a maturation stimulus, IL-6 skewed monocyte differentiation into phenotypically mature but functionally impaired DC. In DC matured with the toll-like receptor (TLR)4 stimulus lipopolysaccharide (LPS) or other pro-inflammatory stimuli, IL-6 inhibited CCR7 chemokine receptor up-regulation. As demonstrated for LPS-stimulated DC, IL-6 impaired chemotaxis to CCR7-activating chemokines required for recruiting DC to lymphoid tissues in vivo. Moreover, IL-6 inhibited production of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma inducible protein-10 (IP-10) in DC, and DC-driven allogeneic T cell proliferation in mixed lymphocyte reactions. CCR7 expression was blocked at the transcriptional level. IL-6 led to inhibition of nuclear factor-kappaB (NF-kappaB) binding activity, regulating CCR7 transcription. Neutralization experiments revealed that autocrine IL-10 partially contributed to CCR7 suppression in IL-6-treated DC. Thus IL-6, a cytokine once labeled as "pro-inflammatory" can mediate immunosuppressive functions, which may involve induction of the classical "anti-inflammatory" cytokine IL-10. Because IL-6 is expressed in response to various pro-inflammatory stimuli in vivo, this mechanism may contribute to down-regulating the immune response initiated by pathogens, in persistent infections or tumors.

Transcriptional regulation of TNF family receptors and Bcl-2 family by chemotherapeutic agents in murine CT26 cells

Various chemotherapeutic agents have been shown to sensitize cancer cells to members of the tumor necrosis factor (TNF) family. However, it is unclear whether sensitization by chemotherapeutic agents involves the transcriptional regulation of apoptosis-related genes. In this study, we investigated mRNA regulation of TNF family receptors and Bcl-2 family members after treating the murine colon cancer cell line, CT26, with various apoptosis inducers. We found that treatment with cycloheximide, a protein synthesis inhibitor, remarkably increased CD40 mRNA levels by semi-quantitative RT-PCR. Other protein synthesis inhibitors, such as anisomycin and emetine, also enhanced CD40 mRNA expression, which was significantly blocked by a NF-kappaB antagonist and a p38 MAP kinase antagonist. After treatment with cycloheximide, and further cultivation in fresh medium, CD40 protein levels were found to increase by flow cytometry. Additionally, we found that cycloheximide treatment appeared to downregulate the Bcl-xL mRNA level but not the Bax mRNA level by RNase protection assay. Because the upregulation of CD40 mRNA and the downregulation of Bcl-xL correlated with CT26 cell death, our results suggest that chemotherapeutic agents, including cycloheximide, may exert their synergistic effects on the TNF family treatment of cancer cells by regulating the mRNA levels of apoptosis-related genes.

Inhibition of phosphatidylinositol 3-kinase- and ERK MAPK-regulated protein synthesis reveals the pro-apoptotic properties of CD40 ligation in carcinoma cells

CD40, a member of the tumor necrosis factor receptor superfamily, is frequently expressed in carcinomas where its stimulation results in induction of apoptosis when de novo protein synthesis is inhibited. The requirement of protein synthesis inhibition for efficient killing suggests that CD40 transduces potent survival signals capable of suppressing its pro-apoptotic effects. We have found that inhibition of CD40 signaling on the phosphatidylinositol 3-kinase (PI3K) and ERK MAPK but not on the p38 MAPK axis disrupts this balance and sensitizes carcinoma cells to CD40-mediated cell death. The CD40-mediated PI3K and ERK activities were found to converge on the regulation of protein synthesis in carcinoma cells via a pathway involving the activation of p90 ribosomal S6 kinase (p90Rsk) and p70S6 kinases, upstream of the translation elongation factor eEF2. In addition, CD40 ligation was found to mediate a PI3K- and mammalian target of rapamycin (mTOR)-dependent phosphorylation of 4E-BP1 and its subsequent dissociation from the mRNA cap-binding protein eIF4E as well as an ERK-dependent phosphorylation of eIF4E, thus promoting translation initiation. Concomitantly, the antiapoptotic protein cFLIP was found to be induced in CD40 ligand-stimulated carcinoma cells in a PI3K-, ERK-, and mammalian target of rapamycin (mTOR)-dependent manner and down-regulation of cFLIPS expression sensitized to CD40-mediated carcinoma cell death. These data underline the significance of the PI3K and ERK pathways in controlling the balance between CD40-mediated survival and death signals through the regulation of the protein synthesis machinery. Pharmacological agents that target this machinery or its upstream kinases could, therefore, be exploited for CD40-based tumor therapy.

Differential induction of nuclear factor-kappaB and activator protein-1 activity after CD40 ligation is associated with primary human hepatocyte apoptosis or intrahepatic endothelial cell proliferation

CD40, a tumor necrosis factor receptor superfamily member, is up-regulated on intraheptatic endothelial cells (IHEC) and epithelial cells during inflammatory liver disease, and there is evidence that the functional outcome of CD40 ligation differs between cell types. Ligation of CD40 on cholangiocytes or hepatocytes results in induction of Fas-mediated apoptosis, whereas ligation of IHEC CD40 leads to enhanced chemokine secretion and adhesion molecule expression. We now report that differential activation of two transcription factors, nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1), in primary human hepatocytes or IHEC, is associated with and may explain, in part, the different responses of these cell types to CD40 ligation. CD40 ligation induced a rise in NF-kappaB activity in hepatocytes,which peaked at 2 h and returned to baseline by 24 h; however, IHEC CD40 ligation resulted in a sustained up-regulation of NF-kappaB (>24 h). In hepatocytes, CD40 ligation led to sustained up-regulation of AP-1 activity >24 h associated with increased protein levels of RelA (p65), c-Jun, and c-Fos, whereas no induction of AP-1 activity was observed in IHECs. Analysis of mitogen-activated protein kinase phosphorylation (phospho-extracellular signal-regulated kinase 1/2 and phospho-c-Jun NH(2)-terminal kinase 1/2) and expression of inhibitor kappaBalpha were entirely consistent, and thus confirmed the profiles of NF-kappaB and AP-1 signaling and the effects of the selective inhibitors assessed using electrophoretic mobility shift assay or Western immunoblotting. CD40 ligation resulted in induction of apoptosis in hepatocytes after 24 h, but on IHECs, CD40 ligation resulted in proliferation. Inhibition of (CD40-mediated) NF-kappaB activation prevented IHEC proliferation and led to induction of apoptosis. Selective extracellular signal-regulated kinase and c-Jun NH(2)-terminal kinase inhibitors reduced levels of apoptosis in (CD40-stimulated) hepatocytes by approximately 50%. We conclude that differential activation of these two transcription factors in response to CD40 ligation is associated with differences in cell fate. Transient activation of NF-kappaB and sustained AP-1 activation is associated with apoptosis in hepatocytes, whereas prolonged NF-kappaB activation and a lack of AP-1 activation in IHECs result in proliferation.

Heterogeneous expression and regulation of CD40 in human hepatocellular carcinoma

OBJECTIVE

CD40, a member of the tumour necrosis factor receptor family, plays a major role in adaptive immune responses and contributes to cancer surveillance. Conflicting results have been reported recently on the expression and function of CD40 in carcinomas. The aim of the present study was to investigate the role of CD40 in human hepatoma.

DESIGN/METHODS

CD40 expression was examined in hepatomas and derived cell lines by immunohistochemistry, flow cytometry and reverse transcriptase polymerase chain reaction. We investigated in hepatoma cell lines the regulation of CD40 by pro-inflammatory cytokines and the effects of its ligation with soluble CD40L on the expression of co-stimulatory and pro-apoptotic cell-surface molecules and survival.

RESULTS

CD40 was detected with a similar frequency of about 40% in hepatoma specimens and derived cell lines but not in normal hepatocytes. Tumour necrosis factor alpha and its combination with interferon gamma upregulated CD40 only in intrinsically positive cell lines. CD40 ligation had no effect on cell viability or surface expression of CD54, CD80, CD86 or CD95.

CONCLUSIONS

CD40 is expressed variably in human hepatoma and enhanced by distinct pro-inflammatory cytokines. The lack of detectable effects of CD40 ligation does not support a major role of this molecule in hepatocellular carcinoma biology.

Prospects for CD40-directed experimental therapy of human cancer

CD40, a member of the tumor necrosis factor receptor (TNF-R) family, is a surface receptor best known for its capacity to initiate multifaceted activation signals in normal B cells and dendritic cells (DCs). CD40-related treatment approaches have been considered for the experimental therapy of human leukemias, lymphomas, and multiple myeloma, based on findings that CD40 binding by its natural ligand (CD40L), CD154, led to growth modulation of malignant B cells. Recent studies also exploited the selective expression of the CD40 receptor on human epithelial and mesenchymal tumors but not on most normal, nonproliferating epithelial tissues. Ligation of CD40 on human breast, ovarian, cervical, bladder, non small cell lung, and squamous epithelial carcinoma cells was found to produce a direct growth-inhibitory effect through cell cycle blockage and/or apoptotic induction with no overt side effects on their normal counterparts. CD154 treatment also heightened tumor rejection immune responses through DC activation, and by increasing tumor immunogenicity through up-regulation of costimulatory molecule expression and cytokine production of epithelial cancer cells. These immunopotentiating features can produce a "bystander effect" through which the CD40-negative tumor subset is eliminated by activated tumor-reactive cytotoxic T cells. However, the potential risk of systemic inflammation and autoimmune consequences remains a concern for systemic CD154-based experimental therapy. The promise of CD154 as a tumor therapeutic agent to directly modulate tumor cell growth, and indirectly activate antitumor immune response, may depend on selective and/or restricted CD154 expression within the tumor microenvironment. This may be achieved by inoculating cancer vaccines of autologous cancer cells that have been transduced ex vivo with CD154, as documented by recently clinical trials. This review summarizes recent findings on CD154 recombinant protein- and gene therapy-based tumor treatment approaches, and examines our understanding of the multifaceted molecular mechanisms of CD154-CD40 interactions.

Death of HT29 adenocarcinoma cells induced by TNF family receptor activation is caspase-independent and displays features of both apoptosis and necrosis

The HT29 adenocarcinoma is a common model of epithelial cell differentiation and colorectal cancer and its death is an oft-analyzed response to TNF family receptor signaling. The death event itself remains poorly characterized and here we have examined the involvement of caspases using pan-caspase inhibitors. zVAD-fmk did not block death of HT29 cells in response to activation of the Fas, TRAIL, TNF, TWEAK and LTbeta receptors. The secondary induction of TNF or the other known bona fide death inducing ligands did not account for death following LTbeta receptor activation indicating that TNF family receptors can trigger a caspase-independent death pathway regardless of the presence of canonical death domains in the receptor. To provide a frame of reference, the phenotype of HT29 death was compared to four other TNF family receptor triggered death events; Fas induced Jurkat cell apoptosis, TNF/zVAD induced L929 fibroblast necrosis, TNF induced death of WEHI 164 fibroblastoid cells and TNF/zVAD induced U937 death. The death of HT29 and U937 cells under these conditions is an intermediate form with both necrotic and apoptotic features. The efficient coupling of TNF receptors to a caspase-independent death event in an epithelial cell suggests an alternative approach to cancer therapy.

In vitro activation of cancer patient-derived dendritic cells by tumor cells genetically modified to express CD154

PURPOSE

Triggering of CD40 on antigen-presenting cells via its ligand CD154 is an important event in the initial phase of an immune response against cancer cells. In this study, we investigated the effects of adenoviral CD154 immunomodulatory gene therapy on the activation of human dendritic cells (DCs) in a well-defined in vitro system.

EXPERIMENTAL DESIGN

Human bladder cancer cell lines and tumor cells from patients with renal cell carcinoma (RCC) were transduced with Ad-CD154 vectors or control vectors. Activation of human in vitro generated DCs after coculture with transduced tumor cells was analyzed. Therapeutic efficacy and cytotoxic T-lymphocyte (CTL) activity were assessed in a subcutaneous (s.c.) murine bladder cancer model.

RESULTS

Human bladder cancer cell lines expressing CD154 showed a decreased growth rate, increased apoptosis, and modulated expression of molecules important for recognition by cytotoxic lymphocytes. Further, CD154-expressing allogeneic bladder tumor cell lines and autologous tumor cells from patients with renal cell cancer induced maturation of DCs and stimulated IFN-gamma production from lymphocytes cocultured with mature DCs. In vivo studies showed that CD154 gene therapy was highly effective in wild-type mice but only minimally effective in nude mice. Consequently, strong tumor-specific CTL activity was detected in mice vaccinated with tumor cells expressing CD154.

CONCLUSIONS

Using tumor cell lines as well as patient-derived material, we could show that tumor cells expressing CD154 efficiently induce maturation and activation of DCs as well as activation of lymphocytes. Our murine in vivo studies demonstrate that lymphocytes contribute to the observed antitumor effect in a s.c. bladder tumor model. These studies should stimulate CD154 gene therapy approaches for the treatment of urologic malignancies.

Expression of CD154 on renal cell carcinomas and effect on cell proliferation, motility and platelet-activating factor synthesis

CD40 activation by CD154 may trigger diverse cellular responses, ranging from proliferation and differentiation to growth suppression and cell death, in normal and malignant cells. However, the pathophysiologic role of CD154 expressed by tumor cells remains unclear. We have investigated the expression of the CD40-CD154 system in 24 primary cultures derived from renal cell carcinomas, its correlation with tumor stage and its potential functional significance. We found coexpression of CD40 and CD154 in most of the renal carcinoma cell lines. CD154, but not CD40 expression, significantly correlated with tumor stage. Moreover, renal carcinoma cell lines also released the soluble form of CD154 into the supernatant. CD40 engagement by CD154 did not affect apoptosis or survival. On the contrary, CD154 stimulated cell proliferation, motility and production of PAF, a phospholipid mediator of inflammation with angiogenic properties. Furthermore, the renal carcinoma cell lines expressed PAF-R. Blockade of PAF-R by WEB-2170, a PAF-R antagonist, abolished the CD154-dependent motility, indicating a role for PAF synthesized after CD154 stimulation in renal carcinoma cell motility. In conclusion, this study identifies new functional properties for CD154, which are potentially relevant for the growth and dissemination of renal carcinoma cells.

Apoptotic crosstalk of TNF receptors: TNF-R2-induces depletion of TRAF2 and IAP proteins and accelerates TNF-R1-dependent activation of caspase-8

We have recently shown that stimulation of TNF-R2 selectively enhances apoptosis induction by the death receptor TNF-R1. Here, we demonstrate that stimulation of CD30 or CD40 also leads to selective enhancement of TNF-R1-induced cell death. Enhancement of apoptosis was correlated with the depletion of endogenous TRAF2 within 1 to 6 hours. Selective prestimulation of TNF-R2 for several hours inhibited TNF-R2-induced activation of the anti-apoptotic NF-κB pathway up to 90% and dramatically enhanced apoptosis induction by this receptor. When both TNF-receptors were stimulated simultaneously, TNF-R1-induced NF-κB activation remained unaffected but TNF-R1-induced apoptosis was still significantly enhanced. Compared with FasL-induced cell death TNF-R1-induced activation of caspase-8 was significantly weaker and delayed. Costimulation or prestimulation of TNF-R2 enhanced caspase-8 processing. Life cell imaging and confocal microscopy revealed that both TNF-R1 and TNF-R2 recruited the anti-apoptotic factor cIAP1 in a TRAF2-dependent manner. Thus, TNF-R2 may compete with TNF-R1 for the recruitment of newly synthesized TRAF2-bound anti-apoptotic factors, thereby promoting the formation of a caspase-8-activating TNF-R1 complex. Hence,TNF-R2 triggering can interfere with TNF-R1-induced apoptosis by inhibition of NF-κB-dependent production of anti-apoptotic factors and by blocking the action of anti-apoptotic factors at the post-transcriptional level.

In vitro expression of fas and CD40 and induction of apoptosis in human cystic fibrosis airway epithelial cells

Cystic fibrosis is characterized by a damaged airway epithelium with inflammation and chronic infection. The aim of this study was to investigate the process of apoptosis in this disease. To evaluate the effects of interferon gamma and the Fas apoptotic pathway on cystic fibrosis airway epithelial cells, we used immortalized cystic fibrosis (CFT-1 and CFT-2) and normal (NT-1) human tracheal epithelial cell lines. Cell death was determined usingannexin-V/propidium iodide labelling and electron microscopy. In vitro expression of Fas and CD40 surface antigens was analysed by immunofluorescence staining and flow cytometry. Normal and cystic fibrosis cells constitutively express these antigens. CD40, but not Fas expression, was upregulated by interferon gamma. Treatment of interferon gamma-stimulated cells with anti-Fas resulted in apoptosis for about 80% of CFT-2 (homozygous for delta F508 deletion) cells and for 35-40% of CFT-1 (heterozygous) or normal cells. Our results suggest that Fas may mediate apoptosis in cystic fibrosis airway epithelium.

CD40 activation in epithelial ovarian carcinoma cells modulates growth, apoptosis, and cytokine secretion

BACKGROUND/AIMS

CD40, a member of the tumour necrosis factor (TNF) receptor family, is expressed on a variety of haematopoietic cells and is crucial in orchestrating both humoral and cellular immune responses. CD40 is also expressed on some carcinoma cells, where its function remains largely unknown. This study investigated the effects of CD40 ligation on ovarian carcinoma cell growth and apoptosis and on cytokine production, in addition to the role of the NF-kappa B and JNK signalling pathways.

METHODS

CD40 expression was measured in epithelial ovarian carcinoma (EOC) biopsies by immunohistochemistry and in EOC cell lines by flow cytometry. To examine the effects of CD40 ligation on cell growth recombinant soluble CD40 ligand was used to stimulate EOC cell lines and growth was measured by MMT assays. Cytokine production was measured by enzyme linked immunosorbent assays interleukin 8 (IL-8) gene transcription was estimated by means of reverse transcription polymerase chain reaction. The integrity of the CD40 signalling pathway in those cell lines that did not produce cytokines in response to CD40 ligation was assessed by the detection of the transcription factor NF-kappa B by an electrophoretic mobility shift assay. To investigate the defect in the NF-kappa B pathway the phosphorylation status of I kappa B alpha was determined by an antibody specific to phosphorylated I kappa B alpha and dissociation of the I kappa B alpha-p65 complex was assessed by co-immunoprecipitation.

RESULTS

CD40 is expressed in primary ovarian carcinoma biopsies and EOC cell lines. CD40 ligation resulted in growth inhibition in most of these carcinoma cell lines and was also found to promote apoptosis, with this last effect only being evident in early passage EOC cells. CD40 ligation also induced significant IL-6 and IL-8 production in most of the EOC cell lines examined and it was confirmed for IL-8 that this effect was regulated at the transcriptional level. NF-kappa B activation in response to CD40 ligation was found in three of the EOC cell lines and specific defects in the CD40 induced NF-kappa B pathway were identified in two cell lines. However, CD40 engagement induced JNK activation in all the EOC cell lines.

CONCLUSIONS

These data suggest that the CD40 pathway is functional in ovarian carcinoma cells and highlight the need for further studies to provide insight into the role of CD40 in the carcinogenic process and the possible exploitation of this pathway for novel therapeutic approaches.

CD40 on salivary gland epithelial cells: high constitutive expression by cultured cells from Sjögren's syndrome patients indicating their intrinsic activation

CD40 has been identified in an expanding list of haematopoietic and non-haematopoietic cells and has received an increased interest based on its role in a variety of cell-mediated responses and its potential to participate in the pathogenesis of chronic inflammatory disorders. Sjögren's syndrome (SS) is an autoimmune exocrinopathy, which is characterized by chronic lymphocytic infiltration of exocrine glands and aberrant activation of epithelial tissues. We studied the expression of CD40 protein in cultured non-neoplastic salivary gland epithelial cell (SGEC) lines as well as in minor SG biopsies obtained from 17 SS patients and 12 controls. Immunocytochemical and flow cytometric analyses had revealed the occurrence of constitutively expressed CD40 molecules on the surface of long-term cultured SGEC lines, which could be further induced by interferon-gamma (IFN-gamma) and IL-1beta cytokines, but not tumour necrosis factor-alpha (TNF-alpha), IL-4, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF) or IFN-alpha. Triggering of SGEC through CD40 enhanced the surface expression of the adhesion molecule intercellular adhesion molecule-1 (ICAM-1)/CD54, but not MHC class I and class II (HLA-DR) molecules. Spontaneous CD40 expression was significantly higher in SGEC lines derived from SS patients, compared with controls (P < 0.001), which is suggestive of their intrinsically activated status. In SG biopsies, CD40 was constitutively expressed by lymphocytes, ductal epithelial cells and endothelial cells but not by other glandular cell types, such as acinar cells, myoepithelial cells and fibroblasts. In addition, CD40L staining was also detected in 30--50% of the infiltrating lymphocytes in the biopsies of SS patients. Our findings indicate the immunoregulatory potential of SGEC and lend further support to a model of intrinsic activation in salivary epithelia in SS, whereby these cells actively participate in the induction and maintenance of lymphocytic infiltrates of patients.

Does CD40 ligation induce B cell negative selection?

Binding of CD154 to its receptor, CD40, provides costimulation for mature B cell activation and differentiation in response to Ag receptor signals. In mice, early B cell precursors express CD40, but its function at this stage is unknown. We examined the effects of CD40 ligation during B cell ontogeny in transgenic mice constitutively expressing CD154 on B cells (kappaEP-CD154). Precursors beyond pro-B cells were absent in adult bone marrow but were increased in the fetal liver. Newborn kappaEP-CD154 mice had largely increased numbers of peripheral B cells, which were CD154+, and that 36 h after birth expressed high surface levels of CD23 and MHC class II, resembling activated mature B cells. Nevertheless, kappaEP-CD154 mice were hypogammaglobulinemic, indicating that the expanded population of apparently activated B cells was nonfunctional. Further analysis revealed that soon after birth, kappaEP-CD154 mice-derived B cells became CD5+/Fas+, after which progressively decreased in the periphery in a CD154-CD40-dependent manner. These results indicate that CD40 ligation during B cell ontogeny induces negative selection characterized by either hyporesponsiveness or an arrest in maturation depending on the time of analysis and the anatomic site studied.

Significance of phosphotyrosine proteins, Bcl-2 and p53 for apoptosis in resting B-chronic lymphocytic leukemia (CLL) cells

Signal transduction and apoptosis in B-cell chronic lymphocytic leukemia (CLL) cells with a post-germinal center (GC) phenotype were studied. Specific activation of the cells was induced by a combination of soluble anti-CD40 monoclonal antibody and interleukin-4 (CD40/IL-4) and nonspecific activation with a combination of phytohemagglutinin, phorbol-12-myristate-13-acetate and ionomycin (chemical mixture). Less than 5% of these leukemia cells entered the cell cycle after activation, as indicated by the number of cells in G0/G1 phase. The protein tyrosine phosphorylation pattern and expression of the Bcl-2 protein were specific in ex vivo CLL cells of each individual patient. Expression of the p53 protein was not detectable in these leukemia cells. Cross-linking of the CD40/IL-4 receptors on CLL cells significantly upregulated phosphotyrosine proteins and the p53 protein. In the presence of chemical mixture, downregulated phosphotyrosine proteins were detected. Alterations in Bcl-2 expression were independent of cross-linking with CD40/IL-4 or chemical mixture. A high frequency of apoptotic cells was detected in cells that had downregulated phosphotyrosine proteins and Bcl-2 protein. There was no correlation between induction of apoptosis and expression of p53 protein. Our results suggest that apoptosis in resting leukemia cells could occur prior to the cell cycle progression. Alterations in phosphotyrosine proteins and Bcl-2 but not p53 might play an important role in the regulation of apoptosis in resting G0/G1 memory post-GC B-CLL cells.

CD40 activates NF-kappa B and c-Jun N-terminal kinase and enhances chemokine secretion on activated human hepatic stellate cells

Activated hepatic stellate cells (HSCs) are the main producers of extracellular matrix in the fibrotic liver and contribute to hepatic inflammation through the secretion of chemokines and the recruitment of leukocytes. This study assesses the function of CD40 on human HSCS: Activated human HSCs express CD40 in culture and in fibrotic liver, as determined by flow cytometry, RT-PCR, and immunohistochemistry. CD40 expression is strongly enhanced by IFN-gamma. Stimulation of CD40 with CD40 ligand (CD40L)-transfected baby hamster kidney cells induces NF-kappaB, as demonstrated by the activation of I-kappaB kinase (IKK), increased NF-kappaB DNA binding, and p65 nuclear translocation. CD40-activated IKK also phosphorylates a GST-p65 substrate at serine 536 in the transactivation domain 1. Concomitant with the activation of IKK, CD40L-transfected baby hamster kidney cell treatment strongly activates c-Jun N-terminal kinase. CD40 activation increases the secretion of IL-8 and monocyte chemoattractant protein-1 by HSCs 10- and 2-fold, respectively. Adenovirally delivered dominant negative (dn) IKK2 and TNFR-associated factor 2dn inhibit IKK-mediated GST-I-kappaB and GST-p65 phosphorylation, NF-kappaB binding, and IL-8 secretion, whereas IKK1dn and NF-kappaB-inducing kinase dominant negative do not have inhibitory effects. We conclude that the CD40-CD40L receptor-ligand pair is involved in a cross-talk between HSCs and immune effector cells that contributes to the perpetuation of HSC activation in liver fibrosis through TNFR-associated factor 2- and IKK2-dependent pathways.

CD40L induces matrix-metalloproteinase-9 but not tissue inhibitor of metalloproteinases-1 in cervical carcinoma cells: imbalance between NF-kappaB and STAT3 activation

Matrix-metalloproteinases (MMPs) are essentially required for tumor cell invasion and metastasis. Production of precursor enzymes is regulated on transcriptional level, while activation of the pro-enzymes is tightly controlled by posttranscriptional mechanisms. The enzyme activity can be blocked by specific tissue inhibitors of MMPs (TIMPs). In cervical carcinomas strong up-regulation of the type IV collagenase MMP-9 had been demonstrated. We show that activation of CD40, a receptor highly expressed on cervical carcinomas, induces MMP-9 in cervical carcinoma cells, whereas TIMP-1 production inhibiting MMP-9 activity was not affected. This gene induction pattern corresponded to the differential activation of the transcription factor nuclear factor kappaB (NF-kappaB) regulating MMP-9, but not signal transducer and activator of transcription 3 (STAT3), which is involved in TIMP-1 gene regulation. Transient expression of the CD40-inducible NF-kappaB subunit p65 was sufficient for MMP-9 induction. Agents that suppressed CD40-mediated NF-kappaB activation also reduced MMP-9 induction, further supporting an important role of NF-kappaB in CD40-mediated MMP-9 induction. Our data suggest that CD40 expression in carcinoma cells might convert a CD40L-dependent immunological defense signal into a tumor-promoting signal. Selective CD40-mediated signaling through NF-kappaB but not STAT3 correlates to a shift of the balance between MMP-9 and TIMP-1 toward the protease.

Apoptosis in liver disease

A variety of biological functions are regulated through extracellular signals. Amongst the best studied examples is growth control, which is achieved by the regulatory function of growth factors. In recent years it has become apparent that cell death (apoptosis) is controlled in a similar fashion.Apoptosis, firstly a morphologically defined process, is a highly controlled type of cell death that plays a critical role in embryonic development, deletion of autoreactive T-cells and adult tissue homoeostasis. There is increasing evidence that derangement of the apoptotic program is the underlying cause of a series of diseases including liver diseases. The deadly program can be initiated by ligand binding to membrane bound receptors such as CD95 (Fas), which is the most prominent cell death inducing member of the TNF receptor superfamily. The core of the subsequently activated intracellular machinery is formed by a set of proteases, namely caspases. Once activated, they orchestrate the complete destruction of the cellular skeleton leading to the typical apoptotic morphology. This review focuses on the underlying mechanism leading to derangement of the usually highly controlled apoptotic program in different liver diseases.

Phase I study of recombinant human CD40 ligand in cancer patients

PURPOSE

To determine the toxicity, maximum-tolerated dose (MTD), and pharmacokinetics of recombinant human CD40 ligand (rhuCD40L) (Avrend; Immunex Corp, Seattle, WA), suggested in preclinical studies to mediate cytotoxicity against CD40-expressing tumors and immune stimulation.

PATIENTS AND METHODS

Patients with advanced solid tumors or intermediate- or high-grade non-Hodgkin's lymphoma (NHL) received rhuCD40L subcutaneously daily for 5 days in a phase I dose-escalation study. Subsequent courses were given until disease progression.

RESULTS

Thirty-two patients received rhuCD40L at three dose levels. A total of 65 courses were administered. The MTD was 0.1 mg/kg/d based on dose-related but transient elevations of serum liver transaminases. Grade 3 or 4 transaminase elevations occurred in 14%, 28%, and 57% of patients treated at 0.05, 0.10, and 0.15 mg/kg/d, respectively. Other toxicities were mild to moderate. At the MTD, the half-life of rhuCD40L was calculated at 24.8 +/- 22.8 hours. Two patients (6%) had a partial response on study (one patient with laryngeal carcinoma and one with NHL). For the patient with laryngeal cancer, a partial response was sustained for 12 months before the patient was taken off therapy and observed on no additional therapy. Three months later, the patient was found to have a complete response and remains biopsy-proven free of disease at 24 months. Twelve patients (38%) had stable disease after one course, which was sustained in four patients through four courses.

CONCLUSION

The MTD of rhuCD40L when administered subcutaneously daily for 5 days was defined by transient serum elevations in hepatic transaminases. Encouraging antitumor activity, including a long-term complete remission, was observed. Phase II studies are warranted.

Involvement of FAN in TNF-induced apoptosis

TNF-alpha is a pleiotropic cytokine activating several signaling pathways initiated at distinct intracellular domains of the TNF receptors. Although the C-terminal region is believed to be responsible for apoptosis induction, the functions of more membrane-proximal domains, including the domain that couples to neutral sphingomyelinase activation, are not yet fully elucidated. The roles of this region and of the associated adapter protein FAN (factor associated with neutral SMase activation) in the cytotoxic response to TNF have been investigated. We have now shown that stable expression in human fibroblasts of a dominant negative form of FAN abrogates TNF-induced ceramide generation from sphingomyelin hydrolysis and reduces caspase processing, thus markedly inhibiting TNF-triggered apoptosis. However, the cytotoxic responses to daunorubicin and exogenous ceramide remain unaltered, as do the TNF-induced p42/p44 MAPK activation and CD54 expression. Fibroblasts from FAN-knockout mice also proved to be resistant to TNF toxicity. These findings highlight the previously unrecognized role of the adapter protein FAN in signaling cell death induction by TNF.

Factors regulating the cytotoxic activity of the human natural killer cell line, NK-92

NK-92, a highly cytotoxic, interleukin-2 (IL-2)-dependent human natural killer (NK) cell line, has been of interest for basic and translational research. We report on a comprehensive analysis of NK-92 for factors implicated in NK cytotoxicity to elucidate factors underlying NK-92's high cytolytic activity and target range. Thus, we hope to develop a method to identify patients best suited to NK-92 immunotherapy. In addition, as a model system, we hope to increase understanding of the basis for the elevated activity exhibited by activated NK (ANK) cells. NK-92 exhibits an unusual receptor expression profile, expressing a relatively large number of activating (NKp30, NKp46, 2B4, NKGD, E, CD28) receptors. Conversely, it expresses few inhibitory receptors (NKGA/B, low levels of KIR2DL4, ILT-2), lacking most of the killer inhibitory receptors (KIRs) clonally expressed on normal NK cells. In addition, NK-92 expresses high levels of molecules involved in the perforin-granzyme cytolytic pathway as well as additional cytotoxic effector molecules including tumor necrosis factor (TNF)-superfamily members FasL, TRAIL, TWEAK, TNF-alpha, indicating the ability to kill via alternative mechanisms. NK-92 also expresses other molecules implicated immune effector cell regulation (CD80, CD86, CD40L, TRANCE) whose relevance in NK killing is unclear. This study provides initial data to develop a method to identify NK-92 susceptible cells (cells expressing ligands for NK-92 activating receptors ie CD48 for 2B4 and CD80/86 for CD28). Furthermore, this work suggests mechanisms that may contribute to ANK cell activity, including modulation of receptor expression to favor activation, up-regulation of cytotoxic effector molecules, and acquisition of new cytolytic pathways.

CD40-CD40 ligand (CD154) engagement is required but not sufficient for modulating MHC class I, ICAM-1 and Fas expression and proliferation of human non-small cell lung tumors

To determine the possible functional significance of CD40 expression on human non-small cell lung carcinomas and to assess the potential of CD40 as a therapeutic target, 18 lung tumor cell lines were established from biopsy tissues and were monitored for phenotypic changes on the cell surface and alterations in tumor cell proliferation after the ligation of CD40 with a trimeric fusion protein complex of CD40 ligand (CD40Lt). CD40 cross-linking resulted in up to a 6-fold increase in the surface expression of major histocompatibility complex (MHC) class I, Fas and intracellular adhesion molecule (ICAM)-1 in a subset of tumors expressing the highest levels of CD40. Suppression of tumor proliferation was seen after the ligation of CD40 on CD40Lt-responsive cell lines. The suppression was dose dependent, reversible and resulted from a delay of the tumor cells entering S-phase. No change in the cell phenotype or in proliferation were observed in CD40-negative tumors or in tumors expressing moderate-to-low levels of CD40 after incubation with CD40Lt. CD40-negative tumors transfected with the CD40 gene expressed high levels of CD40 on their surface, but were also unresponsive to CD40Lt cross-linking of CD40. Our data establish that CD40 is required (but not sufficient) for transducing a signal that results in phenotypic changes in human lung tumors and suppression in their proliferation. We conclude that CD40 on non-small cell lung tumors may represent a potential therapeutic target, but only on a subset of the CD40+ tumors.

CD45 is required for CD40-induced inhibition of DNA synthesis and regulation of c-Jun NH2-terminal kinase and p38 in BAL-17 B cells

Stimulation of B cell antigen receptor (BCR) may induce proliferation, differentiation, or apoptosis, depending upon the maturational stage of the cell and the presence or absence of signals transmitted via coreceptors. One such signal is delivered via CD40; for instance, ligation of CD40 rescues B cells from BCR-induced apoptosis. Here we show that, in contrast to WEHI-231 cells, CD40 ligation did not reverse BCR-induced growth inhibition in the BAL-17 mature B cell line and CD40 ligation itself inhibited proliferation. This inhibitory signaling was not observed in CD45-deficient cells. Further analyses demonstrate that transfection of dominant-negative form of SEK1 or treatment with SB203580 strongly reduced CD40-induced inhibition of BAL-17 proliferation, suggesting a requirement for c-Jun NH2-terminal kinase and p38 in CD40-induced inhibition of proliferation. Interestingly, CD40-initiated activation of c-Jun NH2-terminal kinase and p38 was enhanced and sustained in CD45-deficient cells, and these phenotypes were reversed by transfecting CD45 gene. However, CD40-mediated induction of cell surface molecules was not affected in CD45-deficient cells. Taken collectively, these results suggest that CD45 exerts a decisive effect on selective sets of CD40-mediated signaling pathways, dictating B cell fate.

Marrow-derived CD40-positive cells are required for mice to clear Cryptosporidium parvum infection

To clear a Cryptosporidium parvum infection, mice need CD4+ T cells, major histocompatibility complex class II, and an intact CD40-CD154 signaling pathway. CD40 is constitutively expressed on marrow-derived cells such as dendritic cells and B lymphocytes and is induced by gamma interferon (IFN-gamma) on most somatic cells. To determine whether the CD40 needed to clear a C. parvum infection has to be on marrow-derived mononuclear cells or on the epithelial cells that normally harbor the parasite, we transplanted CD40-/- mice with CD40+/- bone marrow and then infected them with C. parvum. These chimeras cleared the C. parvum infection, while CD40+/- controls transplanted with CD40-/- marrow cells remained infected. CD40 expression on marrow-derived cells therefore suffices for a C. parvum infection to be cleared, while CD40 expression on intestinal epithelial cells is not sufficient. There was no difference between the acquisition of CD69 and CD154 by mesenteric lymph node T cells of C. parvum-infected animals with intact or disrupted CD40-CD154 pathways. CD4 T cells entered the intestinal laminae propriae of C. parvum-infected animals whether or not the CD40 genes of these recipients were intact. These results suggest that, for a C. parvum infection to be cleared, CD40 is not necessary for T-cell activation but may instead contribute to an effector pathway of marrow-derived cells.

CD40 is not detected on human prostate cancer cells by immunohistologic techniques

OBJECTIVES

The CD40 antigen is expressed by antigen-presenting cells, many kinds of epithelium, and carcinomas. As signaling through CD40 modulates the differentiation state of CD40-expressing cells, we wanted to investigate whether benign or malignant prostate epithelium expressed CD40.

METHODS

Twenty-two paraffin-embedded and 10 snap-frozen human prostate tissue samples were analyzed by immunohistologic methods, using the basal cell-specific markers, high molecular weight cytokeratin (HMWCK) and keratin-14 (K14), and the luminal cell marker, low molecular weight cytokeratin (LMWCK), together with CD40. Fresh prostate tissue was cultured in vitro and analyzed by immunocytofluorescence.

RESULTS

The pattern of CD40 expression was continuous on basal epithelial cells of normal and hyperplastic prostate glands but discontinuous in glands that featured prostatic intraepithelial neoplasia. Coexpression of CD40 with the basal cell-specific cytokeratins, HMWCK and K14, was confirmed by double labeling. In contrast, glandular epithelial cells in prostate adenocarcinoma did not express CD40 or these cytokeratins. A luminal cell phenotype defined as CAM5.2-positive and HMWCK-negative K14-negative was identified among primary epithelial cells cultured in vitro. Most of the cultured cells (more than 99%) were also CD40-negative.

CONCLUSIONS

Together, our results support the hypothesis that CD40 expression correlates with the basal cell phenotype, which is lost upon malignant transformation of the prostate. Hence, CD40 may be useful diagnostically to distinguish benign from malignant prostate lesions in biopsy material.

Role of TNF in lymphocyte-mediated cytotoxicity

We now know that tumor necrosis factor (TNF) family ligands regulate development of lymphoid tissue and coordinate cellular differentiation to defend against intracellular pathogens. In particular, TNF provides essential signals for the formation of secondary lymphoid tissue structures and plays an important role in several physiological and pathological conditions that relate to its action in inflammation and leukocyte movement. The TNF-related family of membrane-anchored and secreted ligands also represents a major mechanism regulating cell death and cell survival. TNF was first described as an endotoxin-induced and macrophage secreted factor that caused haemorrhagic necrosis of tumor cells. Over the past two decades we have come to appreciate that T lymphocytes and natural killer (NK) cells also produce TNF, yet no clear single role for lymphocyte-derived TNF has emerged. This review describes the key molecular details of the action of TNF and discusses the evidence for TNF-mediated cytotoxicity being critical to lymphocyte function and immunoregulation.

CD40 induces apoptosis in carcinoma cells through activation of cytotoxic ligands of the tumor necrosis factor superfamily

CD40, a tumor necrosis factor (TNF) receptor (TNFR) family member, conveys signals regulating diverse cellular responses, ranging from proliferation and differentiation to growth suppression and cell death. The ability of CD40 to mediate apoptosis in carcinoma cells is intriguing given the fact that the CD40 cytoplasmic C terminus lacks a death domain homology with the cytotoxic members of the TNFR superfamily, such as Fas, TNFR1, and TNF-related apoptosis-inducing ligand (TRAIL) receptors. In this study, we have probed the mechanism by which CD40 transduces death signals. Using a trimeric recombinant soluble CD40 ligand to activate CD40, we have found that this phenomenon critically depends on the membrane proximal domain (amino acids 216 to 239) but not the TNFR-associated factor-interacting PXQXT motif in the CD40 cytoplasmic tail. CD40-mediated cytotoxicity is blocked by caspase inhibitors, such as zVAD-fmk and crmA, and involves activation of caspase 8 and caspase 3. Interestingly, CD40 ligation was found to induce functional Fas ligand, TRAIL (Apo-2L) and TNF in apoptosis-susceptible carcinoma cells and to up-regulate expression of Fas. These findings identify a novel proapoptotic mechanism which is induced by CD40 in carcinoma cells and depends on the endogenous production of cytotoxic cytokines and autocrine or paracrine induction of cell death.

CD40 expressed on human melanoma cells mediates T cell co-stimulation and tumor cell growth

CD40 is a 50 kDa molecule, a member of the tumor necrosis factor/nerve growth factor receptor family. It is expressed on B cells, monocytes, dendritic cells and various malignant cells. While the critical relevance of this molecule in T cell-dependent B cell activation is already established, the biological role of CD40-CD154 interaction in non-hematopoietic cells is still unknown. Here we show that CD40 is functionally expressed on human melanoma-derived cell lines. No correlation between surface CD40 expression and the origin of the cell line, primary versus metastatic, was observed. Melanoma cells were shown to be able to co-stimulate TCR-triggered human T cells; moreover, because they do not express CD80 or CD86 co-stimulatory structures, the involvement of additional pathways have to be postulated. We have identified CD40 as one of the molecules involved in melanoma cell-mediated co-stimulation of anti-CD3-triggered human CD4(+) T lymphocytes. In addition, a CD40-dependent pathway, able to enhance tumor cell proliferation at low serum concentrations, in vitro, has been shown to be functional in human melanoma cell lines.

T cell life and death signalling via TNF-receptor family members

An effective immune response requires the rapid and accurate mobilisation of millions of effector cells in an antigen driven fashion. These effector cells must be kept alive long enough to fulfil their function but the majority must then be eliminated, a process known as activation-induced cell death. Recent advances in the field of lymphocyte biology have shed light onto how this balance is maintained and onto the consequences for disease if the homeostatic mechanisms become disturbed.

CD40 ligation alters the cell cycle of differentiating keratinocytes

CD40 is expressed in normal human keratinocytes, especially in the basal cell layer. We have recently reported that CD40 ligation strongly inhibits keratinocyte proliferation and induces their differentiation. In this study, the CD40 pathway that prevents keratinocyte growth was investigated. We first reported that interferon-gamma treatment potentiated the CD40-mediated inhibition of keratinocyte proliferation. CD40-CD40 ligand interactions, in the presence or absence of interferon-gamma, neither enhanced spontaneous keratinocyte apoptosis, nor did it enhance apoptosis induced by various agents. More importantly, we showed that CD40 signaling altered the keratinocyte cell cycle, as demonstrated by a decreasing number of cells in the G1 and S phases and an accumulation in G2/M phase of the cell cycle. Furthermore, western blot analysis of cell cycle regulatory proteins, showed a decrease in cyclin A and E expression in CD40-activated keratinocytes. Collectively, these results indicate that CD40 ligation inhibits keratinocyte renewal by a mechanism independent of cell apoptosis and that modulation of the keratinocyte cell cycle is an additional outcome of CD40 signaling.

CD40 ligand-induced apoptosis is Fas-independent in human multiple myeloma cells

We and others previously demonstrated that human multiple myeloma (MM) cells express CD40 and have an active CD40-growth regulatory pathway. This study characterizes the growth outcome of soluble (gp39) or membrane-bound recombinant human CD40-ligand (rCD40L) and its relationship with Fas-dependent apoptosis. Contrary to the moderate growth-stimulatory effect of the CD40-MAb G28.5, gp39 inhibited 3H-thymidine uptake of the plasma dyscrasia lines ARH-77, U266, and HS-Sultan in a dose-dependent fashion by up to 82%. By comparison, RPMI 8226 cells were resistant to CD40L-growth modulation, which may be attributable to a single base substitution (TCA-->TTA, serine-->leucine) at the 3rd cysteine-rich extramembrane region of CD40. Gp39 similarly reduced myeloma clonogenic colony (MCC) formation in patient primary bone marrow cultures by 50% (40-76%; n=6). Studies using transfectant L cells that constitutively expressed CD40L showed that membrane-bound CD40L inhibited the growth of ARH-77, U266, and HS-Sultan cells (66%, 63%, and 32%, respectively), whereas untransfected L cells did not. Growth inhibition by gp39 or CD40L+ L cells was neutralized by coincubation with the CD40L antibodies 5c8 or LL48. CD40L-treatment increased apoptotic activity of MM cells, as defined by oligonucleosomal DNA fragmentation and an increased binding to annexin V (16-28%). All three untreated CD40-responsive MM lines expressed the Fas/Apo-1/CD95 antigen (65-92% CD95+). However, only ARH-77 cells responded to the growth inhibitory effect of the CD95-agonistic antibody CH-11. CD95 expression was not affected significantly by gp39 treatment, and growth inhibition by CH-11 was additive to gp39 (from 42% to 64% decrease in 3H-thmidine uptake). Conversely, the CD95 antagonist antibody ZB4 reversed the Fas-dependent growth inhibitory process but did not significantly alter gp39-mediated growth outcome. Gp39 treatment lowered the expression of TNFR-associated factors TRAF4 and TRAF6 by 38% and 32%, respectively, whereas detectable levels of TRAF1,2,3, and 5 levels remained unchanged. Our observations indicate that the CD40L-binding inhibits human MM cell growth and increases its apoptotic activity. This growth inhibitory effect corresponds to lower levels of cytoplasmic TRAF signaling elements, and appears independent of the Fas-signaling pathway. CD40 receptor mutation may lead to unresponsiveness to CD40 growth modulation in multiple myeloma cells.

Stress-induced apoptosis is not mediated by endolysosomal ceramide

A major lipid-signaling pathway in mammalian cells implicates the generation of ceramide from the ubiquitous sphingolipid sphingomyelin (SM). Hydrolysis of SM by a sphingomyelinase present in acidic compartments has been reported to mediate, via the production of ceramide, the apoptotic cell death triggered by stress-inducing agents. In the present study, we investigated whether the ceramide formed within or accumulated in lysosomes indeed triggers apoptosis. A series of observations strongly suggests that ceramide involved in stress-induced apoptosis is not endolysosomal: 1) Although short-chain ceramides induced apoptosis, loading cells with natural ceramide through receptor-mediated endocytosis did not result in cell death. 2) Neither TNF-alpha nor anti-CD95 induced the degradation to ceramide of a natural SM that had been first introduced selectively into acidic compartments. 3) Stimulation of SV40-transformed fibroblasts by TNF-alpha or CD40 ligand resulted in apoptosis equally well in cells derived from control individuals and from patients affected with Farber disease, having a genetic defect of acid ceramidase activity leading to lysosomal accumulation of ceramide. Also, induction of apoptosis using anti-CD95 (Fas) or anti-CD40 antibodies, TNF-alpha, daunorubicin, and ionizing radiation was similar in control and Farber disease lymphoid cells. In all cases, apoptosis was preceded by a comparable increase of intracellular ceramide levels. 4) Retroviral-mediated gene transfer and overexpression of acid ceramidase in Farber fibroblasts, which led to complete metabolic correction of the ceramide catabolic defect, did not affect the cell response to TNF-alpha and CD40 ligand.