A critical role for Fas ligand in the active suppression of systemic immune responses by ultraviolet radiation.

Induction of antigen-specific suppression elicited by environmental insults, such as ultraviolet (UV)-B radiation in sunlight, can inhibit an effective immune response in vivo and may contribute to the outgrowth of UV-induced skin cancer. Although UV-induced DNA damage is known to be an initiating event in the immune suppression of most antigen responses, the underlying mechanism(s) of such suppression remain undefined. In this report, we document that Fas ligand (FasL) is critical for UV-induced systemic immune suppression. Normal mice acutely exposed to UV exhibit a profound suppression of both contact hypersensitivity and delayed type hypersensitivity (DTH) reactions and the development of transferable antigen-specific suppressor cells. FasL-deficient mice exposed to UV lack both transferable suppressor cell activity and primary suppression to all antigens tested, with the exception of the DTH response to allogeneic spleen cells. Interestingly, suppression of this response is also known to occur independently of UV-induced DNA damage. Delivery of alloantigen as protein, rather than intact cells, restored the requirement for FasL in UV-induced immune suppression of this response. These results substantiate that FasL/Fas interactions are essential for systemic UV-induced suppression of immune responses that involve host antigen presentation and suggest an interrelationship between UV-induced DNA damage and FasL in this phenomenon. Collectively, our results suggest a model whereby UV-induced DNA damage disarms the immune system in a manner similar to that observed in immunologically privileged sites.

Fas and Fas ligand interactions suppress melanoma lung metastasis.

Apoptosis induced by Fas (CD95) ligation is frequently lost during tumor progression; however, there is no direct evidence to support an association of Fas loss-of-function with metastatic tumor behavior. To determine whether Fas loss-of-function is critical for acquisition of the metastatic phenotype, we have compared the ability of Fas-sensitive K1735 murine melanomas to form spontaneous lung metastases in wild-type and Fas ligand-deficient mice. Fas-sensitive melanoma clones are highly tumorigenic but rarely metastatic in wild-type syngeneic mice. However, in Fas ligand-deficient mice, both the incidence and number of metastases are increased. These findings provide the first evidence that Fas-Fas ligand interactions can suppress metastasis and that tumor Fas loss-of-function may be causally linked to metastatic progression.

Fas ligand: a sensor for DNA damage critical in skin cancer etiology.

DNA-damaged cells can either repair the DNA or be eliminated through a homeostatic control mechanism termed "cellular proofreading." Elimination of DNA-damaged cells after ultraviolet radiation (UVR) through sunburn cell (apoptotic keratinocyte) formation is thought to be pivotal for the removal of precancerous skin cells. Sunburn cell formation was found to be dependent on Fas ligand (FasL), a pro-apoptotic protein induced by DNA damage. Chronic exposure to UVR caused 14 of 20 (70 percent) FasL-deficient mice and 1 of 20 (5 percent) wild-type mice to accumulate p53 mutations in the epidermis. Thus, FasL-mediated apoptosis is important for skin homeostasis, suggesting that the dysregulation of Fas-FasL interactions may be central to the development of skin cancer.

Activation-dependent transcriptional regulation of the human Fas promoter requires NF-kappaB p50-p65 recruitment.

Fas (CD95) and Fas ligand (CD95L) are an interacting receptor-ligand pair required for immune homeostasis. Lymphocyte activation results in the upregulation of Fas expression and the acquisition of sensitivity to FasL-mediated apoptosis. Although Fas upregulation is central to the preservation of immunologic tolerance, little is known about the molecular machinery underlying this process. To investigate the events involved in activation-induced Fas upregulation, we have examined mRNA accumulation, fas promoter activity, and protein expression in the Jurkat T-cell line treated with phorbol myristate acetate and ionomycin (P/I), pharmacological mimics of T-cell receptor activation. Although resting Jurkat cells express Fas, Fas mRNA was induced approximately 10-fold in 2 h upon P/I stimulation. Using sequential deletion mutants of the human fas promoter in transient transfection assays, we identified a 47-bp sequence (positions -306 to -260 relative to the ATG) required for activation-driven fas upregulation. Sequence analysis revealed the presence of a previously unrecognized composite binding site for both the Sp1 and NF-kappaB transcription factors at positions -295 to -286. Electrophoretic mobility shift assay (EMSA) and supershift analyses of this region documented constitutive binding of Sp1 in unactivated nuclear extracts and inducible binding of p50-p65 NF-kappaB heterodimers after P/I activation. Sp1 and NF-kappaB transcription factor binding was shown to be mutually exclusive by EMSA displacement studies with purified recombinant Sp1 and recombinant p50. The functional contribution of the kappaB-Sp1 composite site in P/I-inducible fas promoter activation was verified by using kappaB-Sp1 concatamers (-295 to -286) in a thymidine kinase promoter-driven reporter construct and native promoter constructs in Jurkat cells overexpressing IkappaB-alpha. Site-directed mutagenesis of the critical guanine nucleotides in the kappaB-Sp1 element documented the essential role of this site in activation-dependent fas promoter induction.

Wild-type human p53 and a temperature-sensitive mutant induce Fas/APO-1 expression.

Fas/APO-1 is a cell surface protein known to trigger apoptosis upon specific antibody engagement. Because wild-type p53 can activate transcription as well as induce apoptosis, we queried whether p53 might upregulate Fas/APO-1. To explore this possibility, we examined human p53-null (H358 non-small-cell lung adenocarcinoma and K562 erythroleukemia) and wild-type p53-containing (H460 non-small-cell lung adenocarcinoma) cell lines. When H358 or H460 cells were transduced with a replication-deficient adenovirus expression construct containing the human wild-type p53 gene but not with vector alone, a marked upregulation (approximately a three-to fourfold increase) of cell surface Fas/APO-1 was observed by flow cytometry. Similarly, K562, cells stably transfected with a plasmid vector containing the temperature-sensitive human p53 mutant Ala-143 demonstrated a four- to sixfold upregulation of Fas/APO-1 by flow-cytometric analysis at the permissive temperature of 32.5 degrees C. Temperature-sensitive upregulation of Fas/APO-1 in K562 Ala-143 cells was verified by immunoprecipitation and demonstrated to result from enhanced mRNA production by nuclear run-on and Northern (RNA) analyses. Stably transfected K562 cells expressing temperature-insensitive, transcriptionally inactive p53 mutants (His-175, Trp-248, His-273, or Gly-281) failed to upregulate Fas/APO-1 at either 32.5 degrees or 37.5 degrees C. The temperature-sensitive transcription of Fas/APO-1 occurred in the presence of cycloheximide, indicating that de novo protein synthesis was not required and suggested a direct involvement of p53. Collectively, these observations argue that Fas/APO-1 is a target gene for transcriptional activation by p53.

Elevated soluble Fas (sFas) levels in nonhematopoietic human malignancy.

Fas is a widely expressed membrane-anchored protein that induces apoptosis. Soluble Fas (sFas), generated by alternative mRNA splicing, can antagonize cell-surface Fas function. We have investigated sFas in 104 cancer patients with nonhematopoietic malignancies using a Fas-specific ELISA and immunoprecipitation. Our studies demonstrate an elevated 40-42-kDa sFas species in both patient serum and tumor explants. These observations provide the first evidence that sFas is increased in patients with solid tumors in a manner reflective of disease stage and tumor burden and argue that sFas can be synthesized and released both systemically and locally within the tumor microenvironment.

Synergy of tumor necrosis factor and interleukin 2 in the activation of human cytotoxic lymphocytes: effect of tumor necrosis factor alpha and interleukin 2 in the generation of human lymphokine-activated killer cell cytotoxicity.

Human lymphocytes can respond to interleukin 2 (IL-2) under serum-free conditions with generation of major histocompatibility locus-unrestricted oncolytic activity. This function has been named lymphokine activated killing (LAK). Although IL-2 is sufficient for the development of LAK, this function can be regulated positively by the addition of tumor necrosis factor alpha or beta (TNF-alpha or -beta). The cytotoxic synergy observed with TNF enables production of optimal LAK function at a 10-fold lower IL-2 concentration. Neither TNF-alpha nor -beta is able to induce LAK function in the absence of IL-2. Using TNF-alpha as a model, we demonstrate that (a) the cytotoxic synergy occurs with both fresh human tumors and cell lines; (b) the degree of IL-2/TNF-alpha synergy, for most peripheral blood lymphocyte donors, is dependent upon the IL-2 concentration used for activation with the most striking synergy observed at lower IL-2 doses; (c) synergy is specific for TNF-alpha and can be abrogated by neutralizing antibody against this cytokine; (d) addition of high-dose neutralizing antibody to IL-2 alone-stimulated peripheral blood lymphocytes can reduce the cytotoxicity capacity of these effectors suggesting an immunoregulatory role for endogenous TNF-alpha; and (e) TNF-alpha addition to IL-2-stimulated peripheral blood lymphocytes does not increase proliferation or cell recovery but does result in enhanced IL-2 receptor expression. Collectively, our results suggest that TNF-alpha (and -beta) have immunopotentiating roles in the amplification of non-major histocompatibility locus-restricted lymphocyte effector function.

Anti-Fas on nonhematopoietic tumors: levels of Fas/APO-1 and bcl-2 are not predictive of biological responsiveness.

Fas/APO-1 is a cell surface protein known to trigger apoptosis in a variety of cell types upon specific antibody binding. Although extensively studied on normal and malignant hematopoietic cells, little is known about Fas/APO-1 on nonhematopoietic cells. In the study presented here, we have examined Fas/APO-1 expression and function on 11 human tumors of nonhematopoietic origin. By flow cytometric analysis, Fas/APO-1 was expressed on 10 of the 11 tumors at levels comparable to those previously reported for lymphoid cells sensitive to the cytolytic effects of anti-Fas. Despite abundant cell surface expression, only 4 of the 10 Fas-positive tumors were sensitive to the cell-killing effects of anti-Fas. Moreover, anti-Fas enhanced the growth of 2 of 10 Fas-positive tumors. Additional studies using cycloheximide demonstrated that de novo protein synthesis was required for anti-Fas-triggered growth stimulation and, at least in one case, was responsible for the resistance to antibody-induced apoptosis. The biological effects initiated by anti-Fas engagement, however, were not correlated with endogenous bcl-2 expression. This report documents that: (a) Fas/APO-1 is widely expressed on cultured nonhematopoietic tumors; (b) the inherent susceptibility to anti-Fas-induced apoptosis is not correlated with expression of the Fas/APO-1 protein; (c) Fas/APO-1 engagement can result in growth enhancement; and (d) protective/growth-promoting proteins other than bcl-2 may contribute to the diverse spectrum of biological effects induced by anti-Fas engagement of the Fas/APO-1 protein.

Synergy of human recombinant interleukin 1 with interleukin 2 in the generation of lymphokine-activated killer cells.

Peripheral blood mononuclear cells cultured in vitro with interleukin 2 (IL-2) become cytolytic towards both autologous and allogeneic tumor cells. We report here that IL-1 synergizes with IL-2 in serum-free conditions to produce increased (1.3-286-fold) lymphokine-activated killer (LAK) activity. The most dramatic synergy is seen with low IL-2 concentrations (10 U/ml, 222 pM) and 50-250 U/ml IL-1 alpha or beta. Kinetics of addition experiments demonstrate a specific requirement for IL-1 at or before addition of IL-2 to the culture. We postulate that one of the mechanisms whereby IL-1 augments LAK activity is by rendering LAK-precursors more responsive to IL-2. Up-regulation of the IL-2 receptor beta chain (Tac) and increased [3H]thymidine incorporation in cultures containing IL-1 and IL-2 support this view. In some instances, IL-1 alone is capable of maintaining/generating a small degree of cytolytic activity. Collectively, our data demonstrate that IL-1 is capable of interacting with low dose IL-2 to significantly augment LAK activity, potentially playing an important role in the early stages of LAK activation and differentiation. Because synergy is observed with dramatically reduced IL-2 concentrations, this system may offer an alternative approach to high dose IL-2 therapy for the treatment of neoplastic disease.

A retroviral wild-type p53 expression vector penetrates human lung cancer spheroids and inhibits growth by inducing apoptosis.

Multicellular tumor spheroids approximate the three-dimensional configuration of primary and metastatic tumors. The effects of retrovirus-mediated transduction of wild-type p53 (wt-p53) were studied on multicellular tumor spheroids of human non-small cell lung cancer cell lines H322a, the p53 gene of which is homozygously mutated at codon 248, and WT226b, which has endogenous wt-p53. The growth of WT226b spheroids was not affected by exogenous wt-p53 transduction; the growth of H322a spheroids, however, was significantly inhibited by the addition of wt-p53 virus stocks. Transduction of cells by the wt-p53 retroviral vector and penetration of multiple cell layers in H322a spheroids was demonstrated by in situ polymerase chain reaction/hybridization with the neomycin-resistant neo probe. Apoptotic changes indicating programmed cell death were observed in H322a spheroids treated with the wt-p53 virus. These results suggest that retroviral vectors can penetrate into multiple cell layers of three-dimensional tumor masses and induce potentially therapeutic effects.

Characterization of OKT3-initiated lymphokine-activated effectors expanded with interleukin 2 and tumor necrosis factor alpha.

Synergistic and cooperative effects in vitro of OKT3, interleukin 2 (IL-2), and tumor necrosis factor alpha (TNF) as stimuli in generating effectors with lymphokine-activated killer activity were studied. Activation of human peripheral blood mononuclear cells with OKT3 (10 ng/ml) for 48 h, followed by culture in low concentrations of IL-2 (10 units/ml) and TNF (250 units/ml) resulted in higher cell recovery (50- to 3300-fold) compared to the number of cells in the initial culture and enhanced lytic activity against both Raji and fresh lung tumor targets (mean 100-fold) by day 30 compared to those expanded with higher concentrations of IL-2 (100 units/ml) alone. Immunofluorescence analysis of peripheral blood mononuclear cells initiated with OKT3 and expanded with IL-2 plus TNF revealed a selective increase in CD8+ cells and a decrease in CD4+ by day 28; the opposite effect was observed when cells were incubated with 100 units/ml of IL-2 alone, resulting in a greater proportion of CD4+ cells. Almost all cells were CD3+. Studies of cytokine receptor expression indicated that OKT3 plus IL-2 plus TNF caused an earlier up-regulation of the IL-2 receptor beta chain (Tac) and higher TNF receptor expression by day 6 compared to 100 units/ml IL-2 alone. Significant TNF levels (greater than 17 units/ml) were measured in culture supernatants from peripheral blood mononuclear cells initiated with OKT3 alone. Collectively, our data demonstrate that induction of lymphokine-activated killer activity with OKT3, followed by culture in low concentrations of IL-2 plus TNF is an alternative to the use of high-dose IL-2 alone and suggest that this combination may provide potential advantages in long-term generation of cytolytic cells.

Induction of chemosensitivity in human lung cancer cells in vivo by adenovirus-mediated transfer of the wild-type p53 gene.

Recombinant adenovirus-mediated transfer of the wild-type p53 gene into monolayer cultures or multicellular tumor spheroids of human non-small cell lung cancer cell line H358, which has a homozygous deletion of p53, markedly increased the cellular sensitivity of these cells to the chemotherapeutic drug cisplatin. Treated cells underwent apoptosis with specific DNA fragmentation. Direct injection of the p53-adenovirus construct into H358 tumors s.c. implanted into nu/nu mice, followed by i.p. administration of cisplatin, induced massive apoptotic destruction of the tumors. These results support the clinical application of a regimen combining gene replacement using replication-deficient wild-type p53 adenovirus and DNA-damaging drugs for treatment of human cancer.

Identification and selection of human lymphokine activated killer cell effectors and novel recycling intermediates by unique light-scattering properties.

When peripheral blood lymphocytes (PBL) are incubated with interleukin 2 (IL 2), a novel cytotoxic lymphocyte subpopulation, termed lymphokine activated killers (LAK), arises. LAK are functionally defined as IL 2 responsive cells demonstrating major histocompatibility antigen-unrestricted cell-mediated cytotoxicity against fresh solid tumors and other natural killer cell-resistant and -sensitive tumor targets in the absence of prior antigen priming. Flow cytometric analysis of IL 2 activated PBL using forward and right angle light scatter and fluorescence intensity identified the emergence of a large, optically dense, autofluorescent cell population which paralleled the generation of LAK activity. These unique IL 2 induced lymphocytes have been named giant autofluorescent lymphocytes (GAL). These cells are readily distinguished from the small nonfluorescent lymphocytes (SNL) observed in fresh PBL, unstimulated cultured PBL, and those cells remaining after incubation with IL 2 which have not acquired GAL characteristics. In this investigation, LAK cultures were sorted on days 4, 5, and 6 into GAL and SNL populations and were tested for oncolytic activity against the natural killer-resistant Daudi and RC-1 tumor targets. Against these targets, lymphocytes from non-IL 2 activated PBL or the sorted SNL population expressed less than 2% of the oncolytic activity (measured in lytic units) exhibited by GAL effectors. The SNL and GAL populations were cultured in IL 2 for up to 48 h following the sorting procedure and then reassayed for tumor cytolytic activity. During this culture period, GAL but not SNL continued to express LAK killing against natural killer-resistant tumor targets. Using gamma-irradiation to prevent further cell cycling, it was shown that the functional half-life of the LAK effector was approximately 8.5 h. Therefore, the cytotoxicity expressed by the sorted GAL population after 48 h in culture (equivalent to five functional half-lives) must be expressed by progeny of the originally plated lymphocytes. These results indicate that in addition to the LAK effector, the GAL population contains a self-sustaining, recycling intermediate responsible for generating new LAK. Our data indicate that analysis of IL 2 activated PBL using GAL light-scattering properties has application in phenotyping LAK, monitoring of cellular kinetics, cell sorting, and enrichment of the LAK effector population, and in the clinical monitoring of IL 2 therapy.

Interleukin (IL)-12 and IL-12 gene transfer up-regulate Fas expression in human osteosarcoma and breast cancer cells.

Expression of Fas (CD95, APO-1), a cell surface receptor capable of inducing ligand-mediated apoptosis, is involved in tissue homeostasis and elimination of targeted cells by natural killer and T cells. Corruption of this pathway, such as reduced Fas expression, can allow tumor cells to escape elimination and promote metastatic potential. In this study, the status of Fas expression has been examined in the parental SAOS human osteosarcoma cells that do not metastasize and in selected variants that cause lung metastases in 16 weeks (LM2) or 8 weeks (LM6) after i.v. injection into nude mice. Fas expression correlated with the metastatic potentials of the three cell lines. Northern and fluorescence-activated cell-sorting analyses indicated that LM6 cells expressed Fas at a lower level than seen in the parental cells. Infection of the LM6 cells with an adenoviral vector containing the murine interleukin (IL)-12 gene (AD:mIL-12) or treatment with recombinant murine IL-12 resulted in a dose-dependent up-regulation of FAS: The up-regulation of Fas by IL-12 was also demonstrated in human etoposide-resistant MDA-MB-231 breast cancer cells. [(3)H]Thymidine growth inhibition studies indicated that the cell surface Fas induced after IL-12 exposure was functional and able to mediate cell death on cross-linking with anti-FAS: We also demonstrate that this effect is independent of IFN-gamma. Whereas these cell lines are sensitive to IFN-gamma, incubation with IFN-gamma does not increase susceptibility to Fas-mediated cell death, nor do these cells produce IFN-gamma with or without IL-12 treatment. We hypothesize that expression of Fas may play a role in the elimination of metastatic tumor cells in the lung, an organ in which Fas ligand is expressed. The antitumor activity of IL-12 may be secondary in part to its ability to up-regulate Fas expression on tumor cells, which subsequently increases immune-mediated destruction of osteosarcoma cells.

Clinical and immunomodulatory effects of combination immunotherapy with low-dose interleukin 2 and tumor necrosis factor alpha in patients with advanced non-small cell lung cancer: a phase I trial.

Sixteen patients with metastatic non-small cell lung cancer were treated with a combination of simultaneous low-dose interleukin 2 (IL-2) and tumor necrosis factor alpha. The purpose of this phase I dose escalation trial was to assess the clinical toxicities, immunomodulatory effects, and antitumor efficacy of this combination. Patients received a continuous daily i.v. infusion of 6 x 10(6) IU/m2 of IL-2 for 5 days and a concomitant daily i.m. dose of tumor necrosis factor alpha on each day of IL-2 administration. Tumor necrosis factor alpha administration started at a dose of 25 micrograms/m2/day (level I) for seven patients, 50 micrograms/m2/day (level II) for seven patients, and 100 micrograms/m2/day (level III) for two patients. Treatment was given at 3-week intervals. Only one patient required monitoring by an intensive care unit during therapy. Major toxic effects included fever, local skin reaction at the i.m. injection site, pancytopenia, and general malaise, all of which were reversible within 48 h of cessation of therapy. Dose level II was determined to be the maximum tolerated dose, with the dose-limiting toxicity being thrombocytopenia (less than 50,000/microliters). In 12 evaluable patients, one partial and three minor tumor regressions were observed. Seven patients with progressive disease before entry into this study had radiographic stabilization of their disease (median, 12 weeks) before termination of therapy due to progression. All patients exhibited biological responses including augmented lymphokine-activated killer and natural killer cell activities while receiving therapy, as assessed by the cytolysis of Raji- and K562 targets in vitro. Enhanced lysis of autologous tumor during therapy was demonstrated for four patients with available tumor samples. Serum levels of IL-2 were detected by enzyme-linked immunosorbent assay 2 weeks after cessation of therapy. This serum IL-2 had biological activity, which was evident from the ability to induce proliferation of NK-8 cells (an IL-2-dependent cell line) which was abrogated by anti-IL-2 antibody.

Differential involvement of the CD95 (Fas/APO-1) receptor/ligand system on apoptosis induced by the wild-type p53 gene transfer in human cancer cells.

The CD95 (Fas/APO-1) system regulates a number of physiological and pathological processes of cell death. The ligand for CD95 induces apoptosis in sensitive target cells by interacting with a transmembrane cell surface CD95 receptor. We previously reported that the recombinant adenovirus-mediated transfer of the wild-type p53 gene caused apoptotic cell death in a variety of human cancer cells. To better understand the mechanism responsible for this cell death signaling, we have investigated the potential involvement of the CD95 receptor/ligand system in p53-mediated apoptosis. The transient expression of the wild-type p53 gene upregulated the CD95 ligand mRNA as well as protein expression in H1299 human lung cancer cells deficient for p53 and in DLD-1 and SW620 human colon cancer cells with mutated p53, all of which constitutively expressed CD95 receptor as shown by a flow cytometric analysis, and induced rapid apoptotic cell death as early as 24 h after gene transfer. However, the sensitivity to the cytolytic effect of agonistic anti-CD95 antibody (CH11) varied among these cell lines: CH11 induced apoptosis in H1299 cells, but not in DLD-1 and SW620 cells despite their abundant CD95 receptor expression, suggesting that the CD95 receptors on DLD-1 and SW620 cells might be inactivated. In addition, an antagonistic anti-CD95 ligand antibody (4H9) that interfered with the CD95-receptor-ligand interaction partially reduced the apoptosis induced by the wild-type p53 gene transfer in H1299 cells, whereas apoptosis of DLD-1 and SW620 cells occurred in the presence of 4H9. Taken together, these findings led us to conclude that the CD95 receptor/ligand system is differentially involved in p53-mediated apoptosis, suggesting that the restoration of the wild-type p53 function may mediate apoptosis through CD95 receptor/ligand interactions as well as an alternative pathway.

Differential p53 phosphorylation and activation of apoptosis-promoting genes Bax and Fas/APO-1 by irradiation and ara-C treatment.

In this study, we examined the effects of radiation and ara-C on induction of apoptosis and on the apoptosis-promoting genes p53, Bax and Fas/APO-1, in BV173 human leukemia cells, which harbor the wild-type p53 gene. It has been reported that p53 upregulates Fas/APO-1 and Bax expression. Both irradiation and ara-C treatment resulted in apoptosis and induction of p53 proteins within hours. The Bax gene was activated in irradiated and ara-C-treated BV173 cells, but Fas/APO-1 was induced only in irradiated BV173 cells. Radiation and ara-C treatment did not induce Bax or Fas/APO-1 protein expression in p53-null HL60 cells. Radiation weakly induced Fas/APO-1 expression in KBM-7 cells, which harbor a partially defective p53 gene. Both HL60 and KBM-7 cells are more resistant to radiation- and ara-C-induced apoptosis than BV173 cells. These results suggest that functional p53 is necessary for the activation of Bax and Fas/APO-1 expression. However, elevated p53 protein is not sufficient to activate Fas/APO-1 gene expression in ara-C-treated cells. Using two-dimensional gel electrophoresis, we found that the p53 proteins in irradiated and ara-C-treated BV173 cells have different isoelectric points; they converged to a single isoelectric point after in vitro treatment with phosphatase. These results suggest that different genotoxic treatments cause different phosphorylations of p53, which may account for the different levels of activation of Fas/APO-1 expression.

Soluble Fas/APO-1 in tumor cells: a potential regulator of apoptosis?

Fas/APO-1, a member of the NGF/TNF receptor superfamily expressed on the cell-surface of normal and malignant cells, is known to induce cell death by apoptosis. In the present study, we have investigated Fas/APO-1 gene defects in a human osteosarcoma cell line resistant to the apoptosis-inducing effects of anti-Fas. cDNA cloning and sequencing revealed that these cells contained both 'authentic' and mutant Fas/APO-1 containing a 63 base pair in-frame deletion spanning the transmembrane domain, designated DFas/APO-1. Direct evidence for the existence of a soluble Fas/APO-1 protein was obtained by immunoprecipitation and Western blotting. Taken together with prior studies demonstrating a role for Fas/APO-1 and Fas ligand, respectively, in tumor target cell killing by cytotoxic T-lymphocytes, production of soluble Fas/APO-1 might have significant implications in malignant disease pathogenesis.

NG-methyl-L-arginine, an inhibitor of nitric oxide formation, reverses IL-2-mediated hypotension in dogs.

The effects of NG-methyl-L-arginine (L-NMA), an inhibitor of nitric oxide formation, were studied in dogs treated with interleukin-2 (IL-2). The administration of IL-2 to dogs resulted in hypotension within 3 days of treatment. The development of hypotension correlated with accumulation in the serum of nitrate, which is a stable breakdown product of nitric oxide. Administration of L-NMA decreased serum nitrate levels and increased the mean arterial pressure. The antihypotensive effect was dose dependent with a maximum effect observed at a dose of 20 mg/kg. Administration of a continuous infusion of L-NMA (5 mg.kg-1.h-1) maintained the mean arterial pressure for 48 h with concurrent administration of IL-2. Evaluation of IL-2-induced lymphokine-activated killer cell proliferation and tumoricidal activity toward a canine glioblastoma target cell line was unaffected by L-NMA. These studies imply that L-NMA may effectively ameliorate the dose-limiting hypotension associated with administration of IL-2 without adversely affecting the antitumor effects.