Nitric oxide-dependent activation of p53 suppresses bleomycin-induced apoptosis in the lung.

Chronic inflammation leading to pulmonary fibrosis develops in response to environmental pollutants, radiotherapy, or certain cancer chemotherapeutic agents. We speculated that lung injury might be mediated by p53, a proapoptotic transcription factor widely implicated in the response of cells to DNA damage. Intratracheal administration of bleomycin led to caspase-mediated DNA fragmentation characteristic of apoptosis. The effects of bleomycin were associated with translocation of p53 from the cytosol to the nucleus only in alveolar macrophages that had been exposed to the drug in vivo, suggesting that the lung microenvironment regulated p53 activation. Experiments with a thiol antioxidant (N-acetylcysteine) in vivo and nitric oxide (NO) donors in vitro confirmed that reactive oxygen species were required for p53 activation. A specific role for NO was demonstrated in experiments with inducible nitric oxide synthase (iNOS)(-/)- macrophages, which failed to demonstrate nuclear p53 localization after in vivo bleomycin exposure. Strikingly, rates of bleomycin-induced apoptosis were at least twofold higher in p53(-/)- C57BL/6 mice compared with heterozygous or wild-type littermates. Similarly, levels of apoptosis were also twofold higher in the lungs of iNOS(-/)- mice than were observed in wild-type controls. Consistent with a role for apoptosis in chronic lung injury, levels of bleomycin-induced inflammation were substantially higher in iNOS(-/)- and p53(-/)- mice compared with wild-type controls. Together, our results demonstrate that iNOS and p53 mediate a novel apoptosis-suppressing pathway in the lung.

The CD3 zeta cytoplasmic domain mediates CD2-induced T cell activation.

CD2-mediated T lymphocyte activation requires surface expression of CD3-Ti, the T cell receptor (TCR) for antigen major histocompatibility complex protein. Given the importance of CD3 zeta in TCR signaling, we have directly examined the ability of the CD3 zeta cytoplasmic domain to couple CD2 to intracellular signal transduction pathways. A cDNA encoding a chimeric protein consisting of the human CD3 zeta cytoplasmic domain (amino acid residues 31-142) fused to the CD8 alpha extracellular and transmembrane domains (amino acid residues 1-187) was transfected into a CD2+CD3-CD8- variant of the human T cell line Jurkat. The resulting transfectants expressed the CD8 alpha/CD3 zeta chimeric receptor at the cell surface in the absence of other TCR subunits. Stimulation of these transfectants with anti-T11(2) + anti-T11(3) monoclonal antibodies (mAbs) initiated both a prompt cytosolic free calcium ([Ca2+]i) rise and protein tyrosine kinase activation. Stimulation with either intact anti-T11(2) + anti-T11(3) mAbs or purified F(ab')2 fragments resulted in interleukin 2 (IL-2) secretion. In contrast, control cell lines transfected with a cDNA encoding wild-type CD8 alpha, and thus lacking surface expression of the CD3 zeta cytoplasmic domain, failed to show any [Ca2+]i rise, protein tyrosine kinase activation, or IL-2 secretion after identical stimulation. These data directly establish the CD3 zeta cytoplasmic domain as a necessary and sufficient component of the CD3-Ti complex involved in T lymphocyte activation through CD2. Moreover, they show that CD2 signaling can function in the absence of Fc receptors.

Signal transduction pathways to apoptosis.

Recent work has demonstrated that a number of signalling events, including cytosolic Ca(2+) rises, cAMP accumulation, activation of protein kinase C, activation of protein tyrosine kinases, and production of ceramide, regulate apoptosis in diverse model systems. However, in some cells these signals promote apoptosis, whereas in others they block the response. This review discusses these observations and proposes explanations for how a given set of signal transduction systems might be involved in multiple cellular responses.

2,3,7,8-Tetrachlorodibenzo-p-dioxin kills immature thymocytes by Ca2+-mediated endonuclease activation.

Suspensions of thymocytes from young rats were incubated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which resulted in a sustained increase in cytosolic free Ca2+ concentration followed by DNA fragmentation and loss of cell viability. Both the Ca2+ increase and DNA fragmentation were prevented in cells treated with the inhibitor of protein synthesis, cycloheximide, and DNA fragmentation and cell killing were not detected when cells were incubated in a "Ca2+-free" medium or pretreated with high concentrations of the calcium probe, quin-2 tetraacetoxymethyl ester. These results indicate that TCDD can kill immature thymocytes by initiating a suicide process similar to that previously described for glucocorticoid hormones.

Phase II trial of imatinib mesylate in patients with metastatic melanoma.

Metastatic melanoma cells express a number of protein tyrosine kinases (PTKs) that are considered to be targets for imatinib. We conducted a phase II trial of imatinib in patients with metastatic melanoma expressing at least one of these PTKs. Twenty-one patients whose tumours expressed at least one PTK (c-kit, platelet-derived growth factor receptors, c-abl, or abl-related gene) were treated with 400 mg of imatinib twice daily. One patient with metastatic acral lentiginous melanoma, containing the highest c-kit expression among all patients, had dramatic improvement on positron emission tomographic scan at 6 weeks and had a partial response lasting 12.8 months. The responder had a substantial increase in tumour and endothelial cell apoptosis at 2 weeks of treatment. Imatinib was fairly well tolerated: no patient required treatment discontinuation because of toxicity. Fatigue and oedema were the only grade 3 or 4 toxicities that occurred in more than 10% of the patients. Imatinib at the studied dose had minimal clinical efficacy as a single-agent therapy for metastatic melanoma. However, based on the characteristics of the responding tumour in our study, clinical activity of imatinib, specifically in patients with melanoma with certain c-kit aberrations, should be examined.

Adenoviral-mediated interferon alpha overcomes resistance to the interferon protein in various cancer types and has marked bystander effects.

We have previously shown that intravesical administration of adenovirus encoding human interferon alpha-2b (Ad-IFN) induced a marked regression of superficial human bladder tumors derived from cells that are resistant to over 1 million units/ml of IFNalpha protein in vitro. In addition, Ad-IFN appeared to produce strong bystander effects. In this study, we show that Ad-IFN causes marked inhibition of cell growth and apoptosis in cells of various tumor types, all of which are resistant to IFNalpha protein. In addition, strong perinuclear IFN staining was seen in all cell lines following Ad-IFN transfection and was never observed after exposure to the IFN protein. Ad-IFN induced proteolytic processing of caspases 3, 8 and 9, indicative of enzymatic activation. However, the caspase-8-selective inhibitor, IETDfmk, blocked apoptosis only in the cell lines that were sensitive to the IFNalpha protein and had minimal effect on Ad-IFN-induced caspase-3 or -9 processing and cell death, indicating that death receptor-independent mechanism(s) were involved in the cytotoxic effects observed for cancer cell lines resistant to the IFNalpha protein. Moreover, we document that a yet to be identified soluble factor(s) is responsible for causing the bystander effect observed following Ad-IFN treatment in IFN protein-resistant cancer cells.

Apoptosis resistance increases with metastatic potential in cells of the human LNCaP prostate carcinoma line.

The aim of this study was to determine whether stable differences in apoptosis sensitivity were selected for in nonmetastatic and metastatic variants of the LNCaP human prostate carcinoma line that had been isolated from tumors grown orthotopically in the prostate glands and regional lymph nodes of nude mice. The nonmetastatic LNCaP-Pro5 cells were significantly more sensitive to thapsigargin-induced apoptosis than were the metastatic LNCaP-LN3 cells, as measured by viability, DNA fragmentation, and interleukin 1beta-converting enzyme family-mediated cleavage of the DNA repair enzyme, poly(ADP-ribose) polymerase. Apoptosis resistance in the metastatic cells was associated with higher levels of expression of the cell death suppressor BCL-2 and lower levels of the death promoters BAX and BAK than were detected in the nonmetastatic LNCaP-Pro5 cells, whereas levels of two other BCL-2 family members (BCL-X(L) and BAD) were indistinguishable. Our data support the hypothesis that apoptosis resistance contributes to prostate cancer metastasis and that elevated expression of BCL-2 is involved.

Cardiac glycosides stimulate Ca2+ increases and apoptosis in androgen-independent, metastatic human prostate adenocarcinoma cells.

Cardiac glycosides are used clinically to increase contractile force in patients with cardiac disorders. Their mechanism of action is well established and involves inhibition of the plasma membrane Na+/K+-ATPase, leading to alterations in intracellular K+ and Ca(2+) levels. Here, we report that the cardiac glycosides oleandrin, ouabain, and digoxin induce apoptosis in androgen-independent human prostate cancer cell lines in vitro. Cell death was associated with early release of cytochrome c from mitochondria, followed by proteolytic processing of caspases 8 and 3. Oleandrin also promoted caspase activation, detected by cleavage poly(ADP-ribose) polymerase and hydrolysis of a peptide substrate (DEVD-pNA). Comparison of the rates of apoptosis in poorly metastatic PC3 M-Pro4 and highly metastatic PC3 M-LN4 subclones demonstrated that cell death was delayed in the latter because of a delay in mitochondrial cytochrome c release. Single-cell imaging of intracellular Ca(2+) fluxes demonstrated that the proapoptotic effects of the cardiac glycosides were linked to their abilities to induce sustained Ca(2+) increases in the cells. Our results define a novel activity for cardiac glycosides that could prove relevant to the treatment of metastatic prostate cancer.

In vivo intracellular signaling as a marker of antiangiogenic activity.

Alterations in endothelial cell (EC) signaling could serve as a marker of effective antiangiogenic therapy. We determined the effect of an antiangiogenic tyrosine kinase inhibitor, SU6668, on tumor EC signaling in liver metastases in mice. In vitro immunofluorescence verified that pretreatment of ECs with SU6668 before exposure to VEGF decreased in vitro phosphorylation of Erk and Akt. Using double-fluorescence immunohistochemistry, phosphorylated Erk and Akt were constitutively expressed in ECs in liver metastases in untreated mice, but SU6668 blocked activation of these signaling intermediates. Determining the activation status of the Erk and Akt signaling pathways in tumor ECs may serve as a surrogate marker for the effectiveness of antiangiogenic regimens.

Expression of vascular endothelial growth factor is necessary but not sufficient for production and growth of brain metastasis.

We investigated the molecular mechanisms of angiogenesis in experimental brain metastasis. Cells from six different human cancer cell lines (proven to produce visceral metastasis) were injected into the internal carotid artery of nude mice. Colon carcinoma (KM12SM) and lung adenocarcinoma (PC14PE6 and PC14Br) cells produced large, fast-growing parenchymal brain metastases, whereas lung squamous cell carcinoma (H226), renal cell carcinoma (SN12PM6), and melanoma (TXM13) cells produced only a few slow-growing brain metastases. Rapidly progressing brain metastases contained many enlarged blood vessels. The expression of VEGF mRNA and protein by the tumor cells directly correlated with angiogenesis and growth of brain metastasis. Causal evidence for the essential role of VEGF in this process was provided by transfecting PC14PE6 and KM12SM cells with antisense-VEGF165 gene, which significantly decreased the incidence of brain metastasis. In contrast, transfection of H226 human lung squamous carcinoma cells with sense-VEGF121 or sense-VEGF165 neither enhanced nor inhibited formation of brain metastases. Collectively, the results indicate that VEGF expression is necessary but not sufficient for the production of brain metastasis and that the inhibition of VEGF represents an important therapeutic target.

Therapy of human pancreatic carcinoma implants by irinotecan and the oral immunomodulator JBT 3002 is associated with enhanced expression of inducible nitric oxide synthase in tumor-infiltrating macrophages.

We determined the therapeutic effect of irinotecan (CPT-11) combined with the immunomodulator JBT 3002, a synthetic bacterial lipopeptide (N-acylated derivative of psi-amino-C1-C3-alkane-sulfonic acid), against highly metastatic human pancreatic carcinoma cells injected into the pancreas of athymic nude mice. Mice received four courses consisting of three daily oral doses of JBT 3002, followed by once weekly i.p. injection of CPT-11. Control mice were treated with CPT-11 alone, JBT 3002 alone, or saline. Tumor growth and metastasis were assessed by gross pathology and confirmed by histological examination. Treatment with CPT-11 alone significantly decreased the median volume of pancreatic tumors and the incidence of metastasis, whereas treatment with only JBT 3002 did not. The combination therapy of CPT-11 plus JBT 3002 decreased tumor volume and incidence of metastasis significantly more than CPT-11 alone. The number of apoptotic cells (terminal deoxynucleotidyl transferase-mediated nick end labeling assay), the number of scavenger-receptor-positive macrophages, and expression level of inducible nitric oxide synthase (iNOS) within lesions directly correlated with therapeutic effects. Indeed, the in vitro incubation of tumor cells with macrophages activated by JBT 3002 plus IFN-gamma produced a significant lysis of tumor cells that could be blocked by a specific inhibitor of iNOS. Collectively, these data demonstrate that the oral administration of the immunomodulator JBT 3002 combined with i.p. injection of CPT-11 can decrease the growth of human pancreatic carcinoma and the incidence of metastasis in nude mice by both a direct antitumor effect and the activation of iNOS in infiltrating macrophages.

Antiangiogenic therapy targeting the tyrosine kinase receptor for vascular endothelial growth factor receptor inhibits the growth of colon cancer liver metastasis and induces tumor and endothelial cell apoptosis.

Increased vascular endothelial growth factor (VEGF) expression is associated with colon cancer metastases. We hypothesized that inhibition of VEGF receptor activity could inhibit colon cancer liver metastases. BALB/c mice underwent splenic injection with CT-26 colon cancer cells to generate metastases. Mice received daily i.p. injections of vehicle, tyrosine kinase inhibitor for Flk-1/KDR (SU5416) or tyrosine kinase inhibitor for VEGF, basic fibroblast growth factor, and platelet-derived growth factor receptors (SU6668). SU5416 and SU6668 respectively inhibited metastases (48.1% and 55.3%), microvessel formation (42.0% and 36.2%), and cell proliferation (24.4% and 27.3%) and increased tumor cell (by 2.6- and 4.3-fold) and endothelial cell (by 18.6- and 81.4-fold) apoptosis (P<0.001). VEGF receptor inhibitors increased endothelial cell apoptosis, suggesting that VEGF may serve as an endothelial survival factor.

Tyrosine kinase inhibition of multiple angiogenic growth factor receptors improves survival in mice bearing colon cancer liver metastases by inhibition of endothelial cell survival mechanisms.

Redundant mechanisms mediate colon cancer angiogenesis. Targeting multiple angiogenic factors simultaneously may improve survival of mice with colon cancer metastases. BALB/c mice underwent splenic injection with CT-26 colon cancer cells to generate liver metastases and received administration of either vehicle alone or a tyrosine kinase inhibitor for vascular endothelial growth factor, basic fibroblast growth factor, and platelet-derived growth factor receptors (SU6668). Mice were sacrificed when they became moribund as determined by a blinded observer. In a parallel experiment, groups of mice were sacrificed at earlier time points to better define the kinetics of the effect of SU6668 on angiogenic parameters over time. SU6668 increased median survival by 58% (P < 0.001) and led to a progressive increase in tumor cell and endothelial cell apoptosis that increased over time. In addition, pericyte vessel coverage and tumor vascularity were significantly decreased in mice treated with SU6668. Based on current knowledge of endothelial cell survival, these data suggest that SU6668 may prevent tumor endothelial cell survival directly (vascular endothelial growth factor) and indirectly (pericyte coverage) by affecting endothelial cell survival mechanisms.

The human retinoblastoma gene product suppresses ceramide-induced apoptosis in human bladder tumor cells.

The retinoblastoma gene product, Rb, has previously been implicated as an obligatory component in the antiproliferative effects mediated by the lipid second messenger, ceramide. We have evaluated both the apoptotic effects and the effects on cell cycle distribution of the exogenous cell-permeable ceramide, N-hexanoyl-D-sphingosine, in an Rb-null human bladder tumor cell line, 5637, as well as in retrovirally infected, Rb(+) clones derived therefrom. These cell lines demonstrated comparable sensitivity to N-hexanoyl-D-sphingosine in a neutral red dye uptake assay. Exposure of the Rb-null parental cell line to 20 microM N-hexanoyl-D-sphingosine for 24 h resulted in a classical pattern of DNA fragmentation that was accompanied by apoptotic nuclear morphological alterations. In contrast, the Rb(+) clones demonstrated suppression of DNA fragmentation in response to N-hexanoyl-D-sphingosine. Similarly, the frequency and degree of alteration of nuclear morphology in Rb(+) cells was also suppressed. Flow cytometric analysis of the parental and infected clones indicated that expression of Rb was without effect on their cell cycle distribution, with or without exposure to N-hexanoyl-D-sphingosine for 25 h; tunel assay confirmed that in this time frame apoptotic cells were far less frequent in the Rb(+) clones than in the parental 5637 cells. Human tumor cell lines derived from three other histological origins, breast and prostatic carcinomas and osteogenic sarcoma, also demonstrated very similar cytotoxic sensitivities to N-hexanoyl-D-sphingosine, irrespective of the expression of Rb. We conclude that Rb is not required for ceramide-induced apoptosis and that Rb can actually inhibit the DNA fragmentation and nuclear morphological changes associated with classical apoptosis.

Resistance to radiation-induced apoptosis in Bcl-2-expressing cells is reversed by depleting cellular thiols.

The mechanism by which Bcl-2 oncogene expression inhibits radiation-induced apoptosis has been investigated in two mouse lymphoma cell lines: line LY-as is radiation sensitive, displays substantial radiaton-induced apoptosis, and expresses low levels of Bcl-2; line LY-ar is radiation-resistant, displays a low apoptosis propensity, and expresses 30-fold higher amount of Bcl-2 protein than does the sensitive line. We observed that upon incubation in cystine/methionine-free (C/M-) medium, radiation-induced apoptosis in the LY-ar cells was restored to levels comparable to that seen in the LY-as cells. lntracellular glutathione (GSH) concentrations in LY-ar cells incubated in C/M- medium plummeted to 50% of control values within 2 h. LY-ar cells treated with diethyl maleate (DEM) or diamide, agents that deplete cellular thiols, had increased susceptibility to radiation-induced apoptosis in a manner similar to C/M- medium. These results are consistent with the general idea that Bcl-2 expression blocks apoptosis through an antioxidant pathway that involves cellular thiols. That Bcl-2-expressing tumor cells can be sensitized by exogeneous agents that modify cellular thiols offers strategies for overcoming such resistance.

Nitric oxide-mediated apoptosis of K-1735 melanoma cells is associated with downregulation of Bcl-2.

Recent studies have shown that the treatment of nonmetastatic K-1735 murine melanoma cells with cytokines induces the production of nitric oxide (NO) and hence cell death. The purpose of this study was to determine the mechanism of this cytokine-induced NO-mediated apoptosis. Incubation of nonmetastatic K-1735 cells with interleukin-1 alpha (IL-1alpha) and interferon-gamma (IFN-gamma) induced high NO production, Bcl-2 downregulation, and apoptotic cell death. In contrast, incubation of metastatic K-1735 cells with IL-1alpha and IFN-gamma did not induce significant production of NO, downregulation of Bcl-2, or cell death. The exposure to exogenous NO derived from the NO donors, sodium nitroprusside (SNP), or GEA5024 produced a dose-dependent apoptotic cell death in both the metastatic and nonmetastatic K-1735 cells, which was associated with downregulation of Bcl-2 at the mRNA level and, to a lesser extent, at the protein level. Nonmetastatic and metastatic K-1735 cells transfected with the Bcl-2 gene were more resistant to apoptosis mediated by both endogenous and exogenous NO. Subsequent to intravenous injection, the tumor cells transfected with the Bcl-2 gene had an increased survival rate in the lungs of nude mice and produced a higher number of experimental lung metastases. These data suggest that NO-induced apoptosis in K-1735 melanoma cells is associated with downregulation of Bcl-2.

Enforced c-KIT expression renders highly metastatic human melanoma cells susceptible to stem cell factor-induced apoptosis and inhibits their tumorigenic and metastatic potential.

Expression of the tyrosine-kinase receptor encoded by the c-KIT proto-oncogene progressively decreases during local tumor growth and invasion of human melanomas. To provide direct evidence that c-KIT plays a role in metastasis of human melanoma, we transfected the c-KIT gene into the c-KIT negative highly metastatic human melanoma cell line A375SM and subsequently analysed its tumorigenic and metastatic potential. A375SM parental cells, A375SM-NOT (neo, control), and A375SM-KIT-positive cells were injected s.c. and i.v. into nude mice. A375SM-KIT cells produced significantly slower growing s.c. tumors and fewer lung metastases than control cells. Exposure of c-KIT-positive melanoma cells in vitro and in vivo to stem cell factor (SCF), the ligand for c-KIT, triggered apoptosis of these cells but not of c-KIT-negative melanoma cells or normal melanocytes. Since SCF is produced by keratinocytes and other dermal cells in the skin, these results suggest that the loss of c-KIT receptor expression may allow malignant melanoma cells to escape SCF/c-KIT-mediated apoptosis, hence contributing to tumor growth and eventually metastasis. The antitumor and antimetastatic properties of SCF may be useful in treating human melanomas in early stages.

Inhibition of tumor growth and metastasis of human melanoma by intracellular anti-ATF-1 single chain Fv fragment.

Activating transcription factor-1 (ATF-1) and cAMP-responsive element (CRE)-binding protein (CREB) have been implicated in cAMP and Ca2+-induced transcriptional activation. The expression of the transcription factors CREB and ATF-1 is upregulated in metastatic melanoma cells. However, how overexpression of ATF-1/CREB contributes to the acquisition of the metastatic phenotype remains unclear. Here, the effect of disrupting ATF-1 activity was investigated using intracellular expression of an inhibitory anti-ATF-1 single chain antibody fragment (ScFv). Intracellular expression of ScFv anti-ATF-1 in MeWo melanoma cells caused significant reduction in CRE-dependent promoter activation. In addition, expression of ScFv anti-ATF-1 in melanoma cells suppressed their tumorigenicity and metastatic potential in nude mice. ScFv anti-ATF-1 rendered the melanoma cells susceptible to thapsigargin-induced apoptosis in vitro and caused massive apoptosis in tumors transplanted subcutaneously into nude mice, suggesting that ATF-1 and its associated proteins act as survival factor for human melanoma cells. This is the first report to demonstrate the potential of ScFv anti-ATF-1 as an inhibitor of tumor growth and metastasis of solid tumor in vivo. Oncogene (2000).

Differential regulation of endogenous endonuclease activation in isolated murine fibroblast nuclei by ras and bcl-2.

Transfection of a murine fibroblast cell line with an activated form of the Harvey ras oncogene conferred sensitivity to apoptosis induced by various agents. This intrinsic sensitivity to apoptosis correlated with the expression of endogenous endonuclease activity in isolated nuclei that was undetectable in the untransfected parental cell line. Subsequent transfection with the human bcl-2 oncogene prevented the morphological and biochemical features of apoptosis in whole cells, although it failed to confer complete protection against cell death. Furthermore, transfection of the bcl-2 oncogene also inhibited the enhanced endonuclease activity in isolated nuclei. Our results indicate that some of the effects of Ha-ras and bcl-2 and potentially other oncogenes, are exerted on the biochemical machinery of apoptosis at the level of the nucleus.

Apoptosis suppression by bcl-2 is correlated with the regulation of nuclear and cytosolic Ca2+.

Bcl-2 expression is associated with the progression of prostate cancer from androgen-dependence to androgen-independence. Bcl-2 is an integral membrane protein which localizes to mitochondria, endoplasmic reticulum, and the nuclear envelope. Using spectrofluorometry and laser confocal microscopy, the ability of bcl-2 to modulate intracellular Ca2+ was examined in the Dunning G prostate carcinoma cell line following apoptosis induction by adriamycin. Adriamycin and thapsigargin, an endoplasmic reticulum Ca2+-pump inhibitor, were effective inducers of apoptosis in control, but not bcl-2 transfected, cells. Treatment with adriamycin was accompanied by a sustained rise in cytoplasmic Ca2+ in control and bcl-2 transfected cells. An increase in intranuclear Ca2+ was observed in control cells only. Apoptosis induction by thapsigargin was associated with an increase in cytoplasmic Ca2+ in control cells that was not detected in the resistant bcl-2 transfectants. Ca2+ was excluded from nuclei isolated from bcl-2 expressing cells, but was sequestered in control nuclei, following the addition of ATP. These findings suggest that bcl-2 may regulate levels of intranuclear Ca2+ independently of cytosolic Ca2+ levels. The ability of bcl-2 to modulate, directly or indirectly, sustained increases in both cytosolic and intranuclear Ca2+ may provide a common basis for bcl-2 function in different subcellular compartments.