First Report of Iris yellow spot virus on Garlic in India

Garlic (Allium sativum) is a spice crop of prime importance in India as well as other parts of the world. Iris yellow spot virus (IYSV; genus Tospovirus, family Bunyaviridae) is an important pathogen of onion bulb and seed crops in many parts of the world (3). The virus is also known to infect garlic and other Allium spp. (2-4). IYSV infection of garlic was reported from Reunion Island (4) and the United States (1). In February 2010, straw-colored, spindle-shaped spots with poorly defined ends were observed on the leaves of a garlic crop at the research farm of the Directorate of Onion and Garlic Research in the Pune District of Maharashtra State, India, 105 days after planting. The spots coalesced to form larger patches on the leaves, suggesting possible IYSV infection. Symptoms were visible on older leaves and more prevalent on cv. G-41, G-282, AC50, AC200, AC283, and Godavari than on other cultivars. The incidence of symptomatic plants was estimated at 5% for G-41 and AC-200, 8% for G-282 and AC283, and 10% for AC50. Leaves were sampled from 40 symptomatic plants per cultivar with each sample composited from young, middle, and older (basal) leaves of the plant. Samples were assayed by double-antibody sandwich-ELISA (Loewe Biochemica GmbH, Sauerlach, Germany) and each tested positive for the virus. Total RNA was extracted from the leaves of ELISA-positive plants using the RNAeasy Plant Mini kit (Qiagen GmbH, Hilden, Germany) and tested by reverse transcription-PCR assay using primers IYSV-F (5'-TCAGAAATCGAGAAACTT-3') and IYSV-R (5'-TAATTATATCTATCTTTCTTGG-3') (2) designed to amplify 797 bp of the nucleocapsid (N) gene of IYSV. Amplicons of expected size were obtained and cloned into a pDrive vector (Qiagen GmbH). The recombinant clone was sequenced (GenBank Accession No. HM173691). Sequence comparisons showed 98 to 100% nt identity with other IYSV N gene sequences in GenBank (Nos. EU310294 and EU310286). A phylogenetic analysis of the deduced amino acid sequences of the N gene showed that the garlic isolate of IYSV grouped most closely with onion IYSV isolates from India (GenBank Nos. EU310294, EU310286, EU310300, and EU310296). To our knowledge, this is the first report of natural infection of garlic by IYSV in India. Additional surveys and evaluations are needed to obtain a better understanding of the potential impact of IYSV on garlic production in India. References: (1) S. Bag et al. Plant Dis. 93:839, 2009. (2) A. Bulajic et al. Plant Dis. 93:976, 2009. (3) D. Gent et al. Plant Dis. 90:1468, 2006. (4) I. Robène-Soustrade et al. Plant Pathol. 55:288, 2006.

Differential gene expression during apoptosis induced by a serum factor: role of mitochondrial F0-F1 ATP synthase complex

The number of genes that are up regulated or down regulated during apoptosis is large and still increasing. In an attempt to characterize differential gene expression during serum factor induced apoptosis in AK-5 cells (a rat histiocytoma), we found subunit 6 and subunit 8 of the transmembrane proton channel and subunit alpha of the catalytic core of the mitochondrial F(0)-F(1) ATP synthase complex to be up regulated during apoptosis. The increase in the expression levels of these subunits was concomitant with a transient increase in the intracellular ATP levels, suggesting that the increase in cellular ATP content is a result of the increase in the expression of ATP synthase subunits' gene and de novo protein synthesis. Depleting the cellular ATP levels with oligomycin inhibited apoptosis significantly, pointing to the requirement of ATP during apoptosis. Caspase 1 and caspase 3 activity and the loss of mitochondrial membrane potential were also inhibited by oligomycin during apoptosis in these cells, suggesting that the oligomycin induced inhibition of apoptosis could be due to inhibition of caspase activity and inhibition of mitochondrial depolarization. However, cytochrome C release during apoptosis was found to be completely independent of intracellular ATP content. Besides the ATP synthase complex genes, other mitochondrial genes like cytochrome C oxidase subunit II and III also showed elevated levels of expression during apoptosis. This kind of a mitochondrial gene expression profile suggests that in AK-5 cells, these genes are upregulated in a time-linked manner to ensure sufficient intracellular ATP levels and an efficient functioning of the mitochondrial respiratory chain for successful completion of the apoptotic pathway.

Activation of NFkappaB and Ub-proteasome pathway during apoptosis induced by a serum factor is mediated through the upregulation of the 26S proteasome subunits

We have been investigating differential gene expression associated with apoptosis in AK-5 cells (a spontaneously regressing rat histiocytoma) and have observed catalytic subunits beta 7 and alpha 5 of the 26S proteasome and ubiquitin to be upregulated during apoptosis induced by a variety of agents. The observed elevation in gene expression was parallel to a comparable increase in the cytosolic protein expression of the proteasome and ubiquitin and a markedly amplified increase in the proteasome activity. Inhibition of the increase in gene expression resulted in the inhibition of the rise in the proteasome activity subsequently leading to an inhibition of apoptosis. Similarly, pretreatment with proteasome inhibitors, MG132 and lactacystin, resulted in a significant inhibition of apoptosis pointing to the requirement of a highly active protein degradation machinery during apoptosis. The apoptosis inhibitory effect of the proteasome inhibitors involved an inhibition of the activation of various initiator and effector caspases but was independent of any changes in the mitochondrial membrane depolarization and cytochrome c release associated with apoptosis. Inhibition of proteasome activity or its upstream PI3 kinase activity inhibited NFkappaB translocation thereby suppressing apoptosis, which highlights the requirement of NFkappaB activation for completion of apoptosis in AK-5 cells. Hence, the apoptosis associated induction of the Ub-proteasome pathway components and the proteasome activity suggests that the proteasome, in its capacity as an efficient protein degradation complex, plays an important role in the successful execution of apoptosis.

Cytokine-induced production of NO by macrophages induces apoptosis and immunological rejection of AK-5 histiocytic tumor

The immunological rejection of the AK-5 histiocytoma in syngeneic hosts involves the participation of NK cells and the upregulation of Th1 type cytokine response. The tumor cells are killed by necrosis and apoptosis. We have studied the role of host peritoneal macrophages in tumor regression. Activated macrophages from tumor- bearing animals produce cytokines like IL-1 beta, TNF-alpha, IL-12 and free radicals like nitric oxide during tumor regression. IL-12 and IFN-gamma played a crucial role in the induction of NO production by the host macrophages, since administration of anti IL-12 and anti IFN-gamma antibodies in AK-5 tumor-bearing animals suppressed NO production by the macrophages. Similarly the cytotoxic activity of the host macrophages which is dependent on NO production was also affected in antibody injected animals. These studies indicate an important role for cytokines in the activation of host macrophages which in turn produce nitric oxide that is involved in the induction of apoptosis in AK-5 cells, leading to the regression of the tumor.

Genetic analysis of Karnal bunt (Neovossia indica) resistance in wheat

Embryos excised from seeds of six generations (P1, P2, F1, BC1, BC2 and F2) of a cross WH 283 WH 533 were cultured on modified MS medium already inoculated with secondary sporidia of Neovossia indica. Significant variations for callusing response (CR) (54 55-75 55%) were observed among generations but the presence or absence of N. indicia did not affect callusing response. A clear inhibition zone (IZ) was formed around each embryo showing callusing. The diameter of IZ varied significantly among generations and was maximum in the resistant genotype, WH 283 (3 60 cm). Fresh weight and dry weight of calli, initiated from embryo cultured and inoculated with N. indica, varied significantly among generations. Coefficient of infection as well as percentage of infection reflected the overdominance of susceptibility. Generation mean analysis showed that the three parameter model was adequate for diameter of IZ only. Six-parameter model showed that additive (in presence of N. indica), additive and additive dominance (in absence of N. indica) effects were also significant. Complementary type of epistasis for fresh weight of calli and dominance, and dominance dominance effects for dry weight of calli were observed in the presence of N. indica. Magnitude of additive effects was higher for diameter of IZ in three parameter model. Therefore, selection might assist in improving this trait and thus indirectly help in attaining the resistance towards N. indica.

Induction of apoptosis in a human erythroleukemic cell line K562 by tylophora alkaloids involves release of cytochrome c and activation of caspase 3

Tylophora alkaloids are plant products known for their antiasthamatic and antiproliferative activities. The underlying cellular changes resulting from inhibition of proliferation were investigated. Tylophora alkaloids induced apoptosis in K562 cells with characteristic apoptotic features like nuclear condensation, apoptotic body formation, flipping of membrane phosphatidylserine, activation of caspase 3 and release of mitochondrial cytochrome c. These studies suggest that the Tylophora alkaloids, in addition to their antiproliferative effects also induce apoptosis in erythroleukemic cells. These observations imply that Tylophora alkaloids could be useful molecules for their antiproliferative activity and for induction of apoptosis in tumor cells.

Host-tumor interactions during the regression of a rat histiocytoma, AK-5

An efficient immune response comprises a highly intricate, integrated circuitry involving both the cellular and the humoral arms of the immune system of the host interacting with the rapidly proliferating microcosm of the tumor The mechanism of tumor rejection involving multiple arms of the immune system was reviewed in a spontaneously regressing rat histiocytoma, AK-5, an autologous tumor-host system. Intraperitoneal tumor transplantation leads to death in all animals, whereas subcutaneously (s.c.) transplanted tumor undergoes regression in 70% of animals. Regression of the tumor occurs by both apoptosis and necrosis, and natural killer (NK) cells were identified as the chief effectors mediating tumor cell death in vivo. A type 1 helper T cell (Th1)-driven cytokine cascade played a crucial role in enhancing cellular functions at the tumor site and obtaining a sufficient immune response for tumor rejection. The s.c. tumor-bearing hosts were shown to produce a factor which induced apoptosis in tumor cells, mediating tumor rejection. This review emphasizes the daunting complexities and interesting liaisons between the host immune system and the tumor, highlighting the work from our laboratory, and stressing that it is the interaction of several factors in concert or antagonizing each other that is responsible for the spontaneous regression of a tumor.

An immunosuppressive tryptophan-derived alkaloid from Lepidagathis cristata

An immunosuppressive, tryptophan-derived alkaloid cristatin A (1), and two known compounds, cycloartenol and stigmasta-5,11(12)-diene-3 beta-ol, were isolated from the whole plant Lepidagathis cristata Willd. The structures of the isolates were established by interpretation of their spectral data.

Induction of stress response renders human tumor cell lines resistant to curcumin-mediated apoptosis: role of reactive oxygen intermediates

Curcumin, a well-known dietary pigment derived from Curcuma longa, has been shown to be a potent antiinflammatory, antioxidant, and anticarcinogenic compound. The present study was designed to investigate the cytotoxic potential of curcumin against a range of human tumor cell lines in an attempt to understand its mechanism of action, which may lead to its possible therapeutic applications. We have shown that different cancer cell lines differ in their sensitivity to curcumin. Cell lines established from malignancies like leukemia, breast, colon, hepatocellular, and ovarian carcinomas underwent apoptosis in the presence of curcumin, whereas cell lines from lung, kidney, prostate, cervix, CNS malignancies, and melanomas showed resistance to the cytotoxic effects of curcumin. Sensitivity of the cancer cell lines to curcumin correlated with the generation of superoxide radicals as determined by the reduction of ferricytochrome C. Curcumin-resistant tumor cell lines showed significantly higher production of Hsp70, thus mounting a stress response and protecting the cells from the apoptotic cell death. These observations yield clues toward understanding the regulation of the cell death machinery by the stress proteins. Interestingly, curcumin had no effect on nontransformed cell lines, which showed neither superoxide generation nor the induction of a stress response. These observations demonstrate that curcumin is an interesting molecule with varied actions, depending on the cell type.

Induction of apoptosis in AK-5 tumor cells by a serum factor from tumor rejecting animals: cytochrome c release independent of Bcl-2 and caspases

The ability to selectively induce apoptosis in tumor cells is the prime goal in cancer immunotherapy and aims at identifying potential molecular targets, regulating this process. Here we show that the sera from the animals which had spontaneously rejected the AK-5 tumor (a rat histiocytoma) had an effective and potent ability to counteract and kill tumor cells by inducing apoptosis, with a high degree of specificity. Apoptosis induced by the serum factor involved the activation of caspases and cytochrome c release to the cytosol. A reduction in mitochondrial transmembrane potential (Delta psi(m)) occurred considerably later than cytochrome c translocation. The anti-apoptotic protein Bcl-2 and the pancaspase inhibitor zVAD-fmk did not prevent cytochrome c release, but completely blocked the reduction in Delta psi(m), DNA fragmentation and apoptosis. Cyclosporin A (CsA), an inhibitor of the mitochondrial permeability transition (MPT) pore had no effect on cytochrome c release and apoptosis mediated by serum factor in AK-5 cells, suggesting that apoptosis was independent of MPT. Taken together these results suggest that the serum factor in conjunction with the immune cells may be participating in the efficient rejection of the tumor in syngeneic hosts and Delta psi(m) disruption but not cytochrome c release, is a critical and decisive event to trigger apoptotic cell death induced by the serum factor in AK-5 tumor cells.

Target cell induced activation of NK cells in vitro: cytokine production and enhancement of cytotoxic function

This study examines the effect of fixed AK-5 tumour cells on rat NK cells. Co-culture of NK cells with fixed tumour cells augmented the cytotoxicity of NK cells against NK-sensitive targets, YAC-1 and AK-5, and induced the secretion of IFN-gamma by NK cells. Antibody against IFN-gamma suppressed the anti-tumour activity of NK cells, whereas the addition of T cells during co-culture enhanced this activity. However, macrophages and B cells had no significant effect when present during co-culture with NK cells. All the inducible cytotoxicity was contained within the NK (CD161+) and NKT (CD3+, CD161+) subsets of lymphocytes. However, in the presence of T cells, the cytolytic potential of NKT cells was higher than that of NK cells alone. The augmentation of cytotoxic activity of NK cells by AK-5 cells in presence of T cells was dependent on IL-2 and IFN-gamma secretion. NK cell activation was blocked by specific antibodies to IL-2 and IFN-gamma in the presence of T cells. Interaction between fixed AK-5 cells with NK and T cell populations induced the expression of Fas-L and perforin in NK cells. These data demonstrate that fixed AK-5 cells initiated cytokine synthesis by NK cells, and the enhanced cytotoxic activity in the presence of T cells was induced as a consequence of the products secreted by activated T lymphocytes. The present observations reflect the possible interactions taking place in vivo after the transplantation of AK-5 tumour in animals. They also suggest direct activation of NK cells after their interaction with the tumour cells.

Differential regulation of apoptosis in AK-5 tumor cells by the proto-oncogene Bcl-2: presence of Bcl-2 dependent and independent pathways

The anti-apoptotic protein Bcl-2 functions as a crucial negative regulator of apoptosis. Bcl-2 has been shown to prevent the efflux of apoptogenic factors from mitochondria to cytosol, thus inhibiting cell death. Here, we show the susceptibility of a spontaneously regressing, rat histiocytic tumor cell line, AK-5, to the apoptotic effects of diverse stimuli and the ability of Bcl-2 overexpression to block cell death. Bcl-2 overexpression selectively inhibits apoptosis induced by ceramide and serum factor from AK-5 tumor regressing animals but not actinomycin D and curcumin, whereas the pancaspase inhibitor z-Val-Ala-Asp fluoromethylketone completely blocks apoptosis, irrespective of the inducer used. The ability of Bcl-2 overexpression to block cell death does not depend on its ability to prevent cytochrome c release but correlates with its ability to prevent the dissipation of mitochondrial transmembrane potential. The results demonstrate that there are inducer dependent redundant activation pathways in a single cell, which may either be Bcl-2 dependent or independent.

Activated macrophages migrate to the subcutaneous tumor site via the peritoneum: a novel route of cell trafficking

Spontaneous regression of AK-5 tumor in syngeneic hosts reported earlier involves the interplay of Th1-type cytokines and cell-mediated immunity. Upon subcutaneous transplantation of AK-5 cells, there was accumulation of immune cells in the peritoneum, of which macrophages were the predominant type and were found to be in a hyperactive state. They released macrophage-derived tumoricidal mediators like NO, O2(-), and ONOO(-) which exhibited potent cytotoxic activity against AK-5 cells in vitro. Interestingly, there was a dramatic disappearance of these hyperactive cells from the peritoneal cavity which correlated well with the onset of tumor regression at the subcutaneous site. Direct labeling of these cells in the peritoneum by the tracking dye PKH26 showed their migration to the tumor site. Similarly, frozen tumor sections when scanned under confocal microscope clearly exhibited fluorescent macrophages embedded into the tumor. Immunohistochemical sections of these intratumoral macrophages showed nitrotyrosine residues, indicating their contribution in the free-radical-mediated AK-5 cell death, thereby leading to successful tumor remission. These observations suggest a directional migration of the hyperactivated peritoneal population to the tumor site. We have also confirmed the influx of macrophages and other immune cells into the peritoneum after sc transplantation of Meth A tumor cells in Balb/c mice. Our studies suggest a role for the peritoneal compartment in imparting appropriate stimulus to the immune cells prior to their participation in the antitumor immune response. These studies suggest a novel route of macrophage trafficking via the peritoneum.

Differential modulation of nitric oxide production by curcumin in host macrophages and NK cells

Curcumin, the yellow pigment from Curcuma longa, has been shown to possess tumoricidal activity. We have earlier reported the induction of apoptosis in AK-5, rat histiocytic cells by curcumin leading to the inhibition of tumor growth in vivo. In this study we have observed differential activation status in host macrophages and NK cells induced by curcumin during the spontaneous regression of subcutaneously transplanted AK-5 tumors. Closer scrutiny of the cytokine profile and nitric oxide (NO) production by immune cells showed an initial downregulation of Th1 cytokine response and NO production by macrophages, and their upregulation in NK cells, which picked-up upon prolonged treatment with curcumin, culminating in a stronger tumoricidal effect. These studies suggest that the host macrophages and NK cells play an important modulatory role in the remission of AK-5 tumor.

Interleukin-2-induced nitric oxide synthase and nuclear factor-kappaB activity in activated natural killer cells and the production of interferon-gamma

We have previously shown that inducible nitric oxide synthase (iNOS) was up-regulated in natural killer (NK) cells when AK-5 tumour cells were transplanted subcutaneously into syngeneic Wistar rats. This study was designed to investigate the role of interleukin (IL)-2 during the induction of iNOS and to understand the subsequent events involved in NK cell activation. There was up-regulation of iNOS expression when naïve NK cells were cultured in the presence of recombinant IL-2. These NK cells produced a higher nitrite content and possessed cytotoxic activity against YAC-1 and AK-5 tumour cells. Induction of iNOS enhanced nuclear factor (NF)-kappaB binding activity in IL-2 activated NK cells, which was confirmed using L-NAME, an NO synthesis inhibitor. Addition of L-NAME along with rIL-2 significantly blocked NF-kappaB activity and also down-regulated the production of NO and the cytotoxic activity of NK cells. Furthermore, injection of anti-IL-2 antibody in subcutaneous tumour transplanted animals abrogated significantly the expression of iNOS and NF-kappaB activity, leading to reduced NO production and cytotoxic activity of NK cells against YAC-1 and AK-5 cells. In addition, the expression of interferon (IFN)-gamma by NK cells was also inhibited in anti-IL-2 antibody injected animals compared with the control animals. Finally, there was enhanced tumour growth and delayed regression in anti-IL-2 injected animals compared with control animals.

Heat induced expression of CD95 and its correlation with the activation of apoptosis upon heat shock in rat histiocytic tumor cells

The heat shock response is a universal phenomenon and is among the most highly conserved cellular responses. However, BC-8, a rat histiocytoma, fails to mount a heat shock response unlike all other eukaryotic cells. In the absence of induction of heat shock proteins, apoptotic cell death is activated in BC-8 tumor cells upon heat shock. We demonstrate here that stable transformants of BC-8 tumor cells transfected with hsp70 cDNA constitutively express hsp70 protein and are transiently protected from heat induced apoptosis for 6-8 h. In addition heat stress induces CD95 gene expression in these tumor cells. There is a delay in CD95 expression in hsp70 transfected cells suggesting a correlation between the cell surface expression of CD95 and the time of induction of apoptosis in this tumor cell line. Also expression of CD95 antigen appears to inhibit the interaction between heat shock factors and heat shock elements in these cells resulting in the lack of heat shock response.

Risk assessment in first degree female relatives of breast cancer patients using the alkaline Comet assay

First degree female relatives (FDFRs) of breast cancer patients have been reported to have a 2- to 3-fold increase in breast cancer risk as compared with the general population. Assessment of genetic instability (DNA damage and repair efficiency) is an important parameter concerning mutagenesis and carcinogenesis. In an attempt to identify individuals at high risk of breast cancer in the FDFRs of breast cancer patients, two tests were used: the alkaline Comet assay on leucocytes and the micronucleus test (MNT) on buccal epithelial cells. In addition to FDFRs, two other categories of subjects were included: breast cancer patients and controls. The Comet assay was used to study basal DNA damage, DNA susceptibility to a mutagen (N-methyl N-nitro N-nitrosoguanidine) and DNA repair efficiency. In addition, the MNT served as an indicator of chromosome breakage/aneuploidy. A significant increase in DNA damage (basal and after treatment with a mutagen, as well as after allowing repair to take place) and micronucleus frequency was observed from controls to FDFRs and from FDFRs to breast cancer patients. There was considerable variability in the subjects with respect to both of these parameters. Outliers identified among the FDFRs based on 3 SD limits of DNA damage and micronucleus frequency were considered as high risk individuals.

Induction of nitric oxide production by natural killer cells: its role in tumor cell death

It has been recognized that natural killer (NK) cells destroy AK-5 tumor cells, largely by cytolysis and apoptosis. The objective of this study was to elucidate the existence and the role of nitric oxide (NO) during this killing. The target cell killing ability of NK cells was associated with an increased production of NO with higher expression of inducible nitric oxide synthase. In part, the production of NO was confirmed by significant increase in cell lysis in the presence of l-arginine and attenuation of cell lysis, DNA fragmentation, and apoptosis by N(omega)-nitro-l-arginine methyl ester (L-NAME). An increased oxidation of intracellularly trapped dichlorofluorescein was observed in NK cells, which was effectively prevented by L-NAME. Exposure of AK-5 cells to chemically generated NO also induced DNA fragmentation in AK-5 cells. Further evidence for the involvement of NO in apoptosis was provided by the inhibition of specific cleavage of PARP and activation of CPP32 by L-NAME. Increased production of NO with simultaneous enhancement of the cytotoxic activity of NK cells from sc tumor-transplanted animals has been implicated in tumor regression when compared to the ip tumor-bearing animals. Overall, these observations suggest an important role for NO during NK cell-mediated apoptosis and lysis of AK-5 cells.

Regulation of effector cell functions through the ligation of lymphocyte function-associated antigen-1 and intracellular adhesion molecule-1 leads to spontaneous regression of a rat histiocytoma

Cell adhesion molecules mediate cell-to-cell interactions, thereby regulating effective immune response against target cells. We have investigated the intercellular cross-talk between lymphocyte function-associated antigen-1 (LFA-1) and its counter-receptor, intercellular adhesion molecule-1 (ICAM-1). This interaction regulates the postadhesion events leading to the regression of a rat histiocytoma, AK-5, which is mediated by natural killer (NK) cells through antibody-dependent cell cytotoxicity (ADCC). Repeated systemic administration of anti-cell adhesion molecule (anti-CAM) monoclonal antibodies (MoAbs), i.e. anti-LFA-1 and anti-intracellular adhesion molecule-1 (anti-ICAM-1), in AK-5 tumour-bearing animals enhanced tumour growth and caused delayed regression. The immune suppression achieved after the administration of these antibodies could be attributed to the diminished cytotoxic, as well as apoptotic, activity of NK cells. The MoAbs selectively reduced the adhesion of NK cells to the tumour cells in vitro. Flow cytometric analysis showed down-regulation of Fas-ligand expression on NK and T cells following MoAb administration in vivo. Marked reduction in the lymphokine-activated killer (LAK) activity of NK cells was also observed after in vitro blocking of LFA-1 and ICAM-1 molecules. In addition, continuous MoAb administration induced suppression of the cytokine response. These results underline the importance of ligand binding between LFA-1 and ICAM-1, which could provide co-stimulation for the effector-cell functions via signalling events to induce cytotoxicity, apoptosis and cytokine production, resulting in the efficient regression of AK-5 tumour in syngeneic hosts.

Curcumin mediated apoptosis in AK-5 tumor cells involves the production of reactive oxygen intermediates

Curcumin, the active ingredient of the rhizome of Curcuma longa has anti-inflammatory, antioxidant and antiproliferative activities. Although its precise mode of action remains elusive, studies have shown that chemopreventive action of curcumin might be due to its ability to induce apoptosis in cancer cells. Curcumin was shown to be responsible for the inhibition of AK-5 tumor (a rat histiocytoma) growth by inducing apoptosis in AK-5 tumor cells via caspase activation. This study was designed to investigate the mechanism leading to the induction of apoptosis in AK-5 tumor cells. Curcumin treatment resulted in the hyperproduction of reactive oxygen species (ROS), loss of mitochondrial membrane potential (delta psi(m)) and cytochrome c release to the cytosol, with the concomitant exposure of phosphatidylserine (PS) residues on the cell surface. This study suggests redox signalling and caspase activation as the mechanisms responsible for the induction of curcumin mediated apoptosis in AK-5 tumor cells.

Lack of heat shock response triggers programmed cell death in a rat histiocytic cell line

Stress response is a universal phenomenon. However, a rat histiocytic cell line, BC-8, showed no heat shock response and failed to synthesize heat shock protein 70 (hsp70) upon heat shock at 42 degrees C for 30 min. BC-8 is a clone of AK-5, a rat macrophage tumor line that is adapted to grow in culture and has the same chromosome number and tumorigenic potential as AK-5. An increase in either the incubation temperature or time or both to BC-8 cells leads to loss of cell viability. In addition, heat shock conditions activated apoptotic cell death in these cells as observed by cell fragmentation, formation of nuclear comets, apoptotic bodies, DNA fragmentation and activation of ICE-like cysteine proteases. Results presented here demonstrate that BC-8 cells cannot mount a typical heat shock response unlike all other eukaryotic cells and that in the absence of induction of hsps upon stress, these cells undergo apoptosis at 42 degrees C.

Role of IFN-gamma produced after intraperitoneal transplantation of AK-5 cells in the induction of Fas ligand expression by tumor cells leading to immune evasion

AK-5 tumor cells expressed Fas-L on their surface after intraperitoneal transplantation in syngeneic animals. Fas-L expression by AK-5 cells is involved in the killing of the effector cells. Thus, the tumor has developed an escape mechanism from immune attack. In the present study, we showed that Fas-L expression on AK-5 cells is regulated by interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha), as injection of antibodies against IFN-gamma downregulated the expression of Fas-L by tumor cells as determined by immunostaining and Northern hybridizations. Fas-L present on the tumor cells is biologically functional, as it induced DNA fragmentation in Fas+ YAC-1 cells. We have also shown shedding of Fas-L in cell-free ascitic fluid from tumor-bearing animals. These observations suggest that such cytokines as IFN-gamma and TNF-alpha play an important role in regulating the expression of Fas-L by AK-5 cells.

Interaction between B.7 and CD28 costimulatory molecules is essential for the activation of effector function mediating spontaneous tumour regression

The spontaneous regression of a rat histiocytoma, AK-5, is mediated by activated natural killer cells through antibody-dependent cellular cytotoxicity. In addition to the Fc-FcR interaction between the target and the effector cells demonstrated previously, we show the participation of costimulatory molecules B7 and CD28 in the efficient killing of the tumour cell. Blockade of the costimulatory interaction in vivo using anti-CD28 led to increased tumour growth and a suppressed cytokine response. Anti-CD28 antibody administration in vivo also diminished the cytotoxic potential of NK cells against AK-5 cells in vitro. Our studies also demonstrate the expression of B7.1 and B7.2 antigen on AK-5 tumour cells. The cytotoxic activity of natural killer cells was significantly inhibited when the effector/target cells were cultured in the presence of antibodies raised against B7.1, B7.2 and CD28. Administration of anti-CD28 in vivo also affected the efficiency of the formation of effector/target conjugates in vitro. Similarly, anti-CD28 injections affected expression of the adhesion molecules LFA 1 and ICAM 1 by splenocytes. Administration of anti-B7.1 and B7. 2 antibodies in AK-5 tumour-bearing animals showed a differential response. The cytotoxicity of natural killer cells was significantly inhibited after anti-B7.2 administration, suggesting the preferential participation of B7.2 molecules in vivo. These observations suggest an important role for B7-CD28 interaction in AK-5 tumour regression.

Induction of nitric oxide production by the peritoneal macrophages after intraperitoneal or subcutaneous transplantation of AK-5 tumor

We have investigated the role of host macrophages in the activation of effector functions in addition to their direct role in the induction of tumor cell death. Peritoneal macrophages from s.c. tumor-bearing animals were in an activated state and induced NO-mediated apoptotic death in AK-5 tumor cells. They also showed overexpression of inducible nitric oxide synthase both at the transcript and at the enzyme levels. However, macrophages from the i.p. tumor-bearing animals showed suppression of activation especially when the tumor load was high, suggesting thereby tumor-induced suppression of macrophage activation in i.p. tumor-transplanted hosts. Suppression of macrophage activation was also observed upon coculture of peritoneal macrophages with tumor cells in vitro. These studies suggest an important role played by the host peritoneal macrophages in the regression of AK-5 tumor. They also indicate suppression of macrophage activation by the tumor cells.

Induction of apoptosis in AK-5 cells by rotenone involves participation of caspases

AK-5 tumour cells undergo apoptosis after treatment with rotenone an electron transport inhibitor and oligomycin which inhibits mitochondrial ATPases. Apoptotic process involves the induction of caspases 2 and 3, whereas caspase 1 does not seem to be participating in rotenone/oligomycin induced apoptosis. DEVD which is a specific inhibitor of caspase 3, inhibited apoptosis in AK-5 cells. We have also observed a significant lowering of intracellular pH in AK-5 cells which are induced into the apoptotic process by rotenone. These results suggest an important role for mitochondrial electron transport in the induction of apoptosis in AK-5 tumour cells.

Upregulation of antitumor immunity by IL-12 gene-transfected AK-5 tumor cells in vivo

We have earlier demonstrated a significant role for IL-12 in the regression of a rat histiocytic tumor, AK-5. In order to analyze further the antitumor immunity induced by interleukin (IL)-12, we have established IL-12-secreting tumor cell clones by gene transfection. Significant enhancement in the lytic potential of splenocytes by the culture supernatants containing IL-12 demonstrated retention of biological activity by the tumor-cell-derived cytokine. Athymic nude mice transplanted subcutaneously with tumor cells engineered to secret IL-12 showed a significant reduction in tumor size, with enhanced antibody-dependent cellular cytotoxicity. Analysis of the serum samples from animals injected with the IL-12 gene-transfected AK-5 cells on different days revealed a significant increase in circulatory IL-12, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and antitumor antibodies, all of which contributed to the reduction in tumor mass. The enhanced proliferative capacity of splenocytes from these animals indicated the presence of highly activated immune cells in vivo. Similarly, intraperitoneal transplantation of IL-12 gene-transfected tumor cells in syngeneic Wistar rats induced a significant increase in cellular cytotoxicity, with a concomitant reduction in circulatory IL-12 (p40) protein. Administration of antibodies to IL-12 and IFN-gamma reduced the expression of the costimulatory molecules B7.1 and B7.2 and the cytolytic effectors granzyme B and Fas-L, suggesting their involvement in IFN-gamma-dependent antitumor immune response induced by IL-12. The present study thus demonstrates that IL-12 gene therapy could be among the promising approaches for an effective cancer therapy.

Antitumor activity of curcumin is mediated through the induction of apoptosis in AK-5 tumor cells

Curcumin, the yellow pigment of turmeric (Curcuma longa), used commonly as a spice, has been shown to possess anticarcinogenic activity. Curcumin inhibited AK-5 tumor growth and induced apoptosis in AK-5 cells. Curcumin induced apoptosis is mediated through the activation of caspase-3, which is specifically inhibited by the tetrapeptide Ac-DEVD-CHO. In addition, curcumin induced tumor cell death is caused through the generation of reactive oxygen intermediates which is inhibited by N-acetyl-L-cysteine. Our studies suggest that the apoptotic process induced by curcumin is the mechanism mediating AK-5 tumor cell death.

Selective involvement of caspase-3 in ceramide induced apoptosis in AK-5 tumor cells

Ceramide, a product of sphingomyelin metabolism, is a novel lipid second messenger that mediates diverse cellular functions. The present study demonstrates the activation of caspase-3/CPP-32beta, during apoptosis induced by cell permeable exogenous ceramides, in AK-5 tumor, a spontaneously regressing rat histiocytoma. The apoptotic events were suppressed by the caspase-3 specific tetrapeptide inhibitor DEVD-CHO but not by the caspase-1 inhibitor YVAD-CMK. In cells overexpressing Bcl-2, a significant decrease in cell death was observed after exogenous addition of ceramides. Furthermore the processing of caspase-3 to its active form upon apoptotic stimulus, and the subsequent cleavage of the substrate PARP, suggested a central role for caspase-3 in the ceramide mediated apoptosis in AK-5 tumor cells.

Depletion of the natural killer cell population in the peritoneum by AK-5 tumor cells overexpressing fas-ligand: a mechanism of immune evasion

AK-5 tumor kills 100% hosts when injected ip and only 20-30% of animals die when the tumor cells are transplanted sc. Seventy percent of animals regress the subcutaneous tumor and exhibit total immunity against subsequent challenges of AK-5 cells by either route. Initially the 100% killing in ip-injected animals was attributed to the rapid growth of the tumor cells in the peritoneum thereby not giving enough time for the host immune system to mount an antitumor response. In the present report we have demonstrated overexpression of Fas-L by day 3 and day 4 ascitic tumor cells which depletes the peritoneum of Fas+ lymphocytes. In addition the effector cells from the ascites are ineffective in inducing cytotoxicity against tumor cells in vitro. However, splenocytes from animals bearing ip tumors possessed cytotoxicity against YAC-1 as well as AK-5 cells. We have also shown the presence of soluble Fas-L in the ascitic fluid, which induced DNA fragmentation in Fas+ Jurkat cells. Fas-L present in the tumor cells is able to induce apoptosis in activated lymphocytes and Jurkat cells, suggesting retention of its biological function. These studies implicate Fas-L in the depletion of the effector cell number and inhibition of their functional activity. They also suggest differential regulation of Fas-L expression by the tumor cells depending upon the site of transplantation.

Role of cytokines in the maintenance of the memory immune response induced by a rat histiocytoma in syngeneic hosts

The nature of immune memory induced by a rat histiocytoma, AK-5, in syngeneic hosts was studied. AK-5 tumor when transplanted intraperitoneally (i.p.) into naive animals grows as ascites and is 100% fatal. However, spontaneous regression of AK-5 tumor was observed in 60% of animals upon s.c. transplantation. Interestingly, all the tumor-rejected animals (immune) were found to resist further i.p. challenges with AK-5 cells. The immunity thus developed is specific for AK-5 tumor, since other tumors grow in these animals. In order to understand the tumor-specific immune memory induced after AK-5 tumor transplantation, we have evaluated circulatory-cytokine profiles of i.p. tumor-transplanted naive and immune animals. Our results show an increase in the levels of IL-2, IL-12 and IL-4 in tumor-injected immune animals compared with normal animals, whereas the interferon-gamma levels were totally reversed in these two sets of animals. We also found elevated levels of circulating immune complexes in the sera from AK-5-rechallenged immune animals. We have also evaluated the cytotoxic potential of splenocytes and pure natural killer cells from immune animals rechallenged with AK-5 cells, and have found a significant increase in antibody-dependent cellular cytotoxicity. Similarly, in vitro proliferation of total splenocytes and nylon-wool non-adherent cells from immune animals was much higher compared with the normal animals. The present study thus suggests antigen-independent maintenance of clonal burst size, which could be the form of immune memory induced by AK-5 tumor in the syngeneic host.

Molecular cloning and characterization of a tumor rejection antigen from rat histiocytoma, AK-5

We have cloned and sequenced a tumor rejection antigen from a highly immunogenic rat histiocytoma, AK-5. Recombinant antigen induced an antibody response in syngeneic hosts, and the immunized animals showed significant resistance to AK-5 tumor challenge, where growth of the tumor was retarded. Autologous anti-AK-5 antibody, as well as the specific monoclonal antibodies raised against whole AK-5 cells, recognized the recombinant protein. Similarly, recombinant antigen was able to neutralize antitumor antibody in a complement-mediated lysis assay. Antibodies raised against the fusion protein recognized a 60-kDa protein from AK-5 cell extracts. A cDNA sequence analysis revealed significant homology with mouse thymus (81%), lymph node (83%), and human brain (71%) cDNAs; however, the function of these genes is not known. These observations suggest the recombinant protein to be a strong candidate for the tumor rejection antigen that is involved in the spontaneous regression of the AK-5 tumor in syngeneic hosts.

Stress induced shedding of a tumor antigen by a rat histiocytic cell line AK-5: a possible mechanism of immune evasion

AK-5 is a highly immunogenic tumor which stimulates multiple arms of the host immune system. Tumor cells when transplanted subcutaneously grow as solid tumors which are regressed in about 70% of animals, whereas 100% i.p. transplanted animals succumb to the tumor growth. In the present study we demonstrate shedding of an antigen by AK-5 cells when subjected to stress such as low cell number transplantation in vivo, heat shock and serum starvation in vitro. The shed antigen is able to neutralize antitumor antibody in a complement fixation assay. The antigen is also detected in the cell-free ascitic fluid. The size of the shed antigen as recognized by anti-AK-5 antibody is approximately 45 kDa. We have also studied some of the biochemical characteristics of the purified shed antigen. These observations suggest a positive role for the AK-5 antigen in immune recognition which is lost in i.p. transplanted tumor cells due to the shedding of the antigen, thereby escaping the immune invasion.

Early expression of interleukin-12, p40 subunit and IFN-gamma inhibits regression of AK-5 tumor

Differential immune response of syngeneic animals to a rat histiocytoma AK-5 based on the route of transplantation was investigated. Spontaneous regression of subcutaneous tumor was observed in 55-60% of animals. On the other hand, when the tumor cells were injected intraperitoneally, none of the animals survived. Earlier studies from this laboratory indicated upregulation of Th-1-type cytokines, leading to early tumor regression when the tumor was transplanted subcutaneously. Hence we evaluated and compared the circulatory-cytokine profiles in both s.c. and i.p. tumor-injected animals. Our results show an early increase in the p40 subunit of IL-12, prolific increase in IFN-gamma and lower levels of IL-2 in i.p. tumor-injected animals. However, there were no significant differences in the levels of transcripts for these cytokines in either of the groups. Significantly, a lower level of cytotoxicity was observed with splenocytes from i.p. tumor-transplanted animals. Moreover, the cytotoxicity of IL-12-activated but not IL-2-activated NK cells was inhibited by sera (rich in IL-12, p40 subunit) from i.p. tumor-transplanted animals, suggesting the participation of p40 subunit in the regulation of tumor regression. Thus the present study suggests a possible translational regulation of Th-1-type cytokines in AK-5 tumor-host interaction.

Administration of anti-IL-12 antibody in vivo inhibits rejection of a rat histiocytoma and suppresses cytokine response in a tumour-bearing host

Activated macrophages are the major producers of heterodimeric cytokine interleukin-12 (IL-12). Earlier evidence suggested that early rejection of AK-5 tumours is mediated by IL-12 through interferon-gamma (IFN-gamma) production, involving activation of natural killer (NK) cells and upregulation of T-helper 1 (Th1)-type cytokine response. Injection of anti-IL-12 antibody into AK-5 tumour-bearing animals resulted in a large number of changes in the host immune response towards the tumour. These animals showed diminished NK-mediated antibody-dependent cell-mediated cellular cytotoxicity (ADCC) activity, down-regulation of Th1-type cytokine response, decreased anti-tumour antibody response ultimately leading to either delay or inhibition of the tumour-regression process. There was also increased production of IL-10 in the animals that had received anti-IL-12 antibody thereby resulting in the down-regulation of IL-2 and IFN-gamma production. IL-12 plays a major role in the activation of the different immune parameters responsible for early rejection of AK-5 tumour. We also studied the activation status of macrophages from tumour-transplanted animals and their ability to produce IL-12. Monocytes/macrophages from antibody-injected animals were less active and produced lower quantities of IL-12, IL-1 beta and tumour necrosis factor-alpha (TNF-alpha) as compared with the macrophages from AK-5 tumour-bearing animals.

Caspase-mediated apoptosis in AK-5 tumor cells: a cell-free study using peptide inhibitors and antisense strategy

An in vitro system has been employed to study the apoptotic mechanisms in the AK-5 tumor which is a spontaneously regressing rat histiocytoma. Cytosolic extracts of tumor cells primed for apoptosis using dexamethasone and immune serum from tumor-regressing animals were able to induce apoptosis in intact nuclei and reproduce the classical morphological and biochemical features typical of apoptotic cells. The cleavage of lamin A and PARP to signature fragments by these extracts and the inhibition of the same using peptide inhibitors signify the pivotal role of ICE and ICE-related proteases in apoptosis. Lamin A cleavage was insensitive to YVAD but PARP cleavage was blocked by both YVAD and DEVD. Cell extracts derived from cells overexpressing the Bcl-2 gene and Nedd-2 antisense gene, respectively, failed to induce apoptosis in exogenously added nuclei, suggesting that Bcl-2 gene product is downregulating a key event in apoptotic cascade. The study also demonstrates the coherent action of different ICE-related proteases in apoptosis and their functional redundancy. This system may prove useful for analyzing complex molecular mechanisms underlying apoptosis in tumor cells.

High intratumoural level of cytokines mediates efficient regression of a rat histiocytoma

We have studied the role of cytokines in the spontaneous regression of AK-5 histiocytoma in syngeneic rats. Animals in which the tumour regresses show high levels of cytokines in the serum compared with animals which succumb to the tumour, and levels of IL-2, IL-4, IL-12, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) are significantly higher in tumour tissue of the former. Thus there is an association between rejection of the tumour and the levels of cytokines present in the tumour mass. Our results also suggest a predominant Th1-type of response in those rats that display early tumour rejection.

Participation of CED-3/ICE and YAMA proteinases in the execution of apoptosis in AK-5 tumor cells leading to spontaneous tumor regression

AK-5, which is a spontaneously regressing rat histiocytoma, is killed by necrosis (perforin mediated) and apoptosis. We have studied the induction of apoptosis in AK-5 tumor cells by each of the following: a factor from anti-AK-5 antiserum, dexamethasone, and natural killer cells. Partial inhibition in apoptosis was observed when AK-5 cells were transfected with Crm A gene, a specific inhibitor of ICE protease. Similarly peptide inhibitors Ac-YVAD-cmk and Ac-DEVD-CHO inhibited partially the formation of nuclear bodies and DNA fragmentation induced by each of the above-mentioned apoptotic inducers. Although NK cells were able to kill Crm A and bcl-2 transfected clones by cytotoxic action, they failed to induce DNA fragmentation in these clones, suggesting a dual mode of action by NK cells in the induction of target cell death. We were unable to detect ICE and YAMA/CPP32 transcripts in control AK-5 cells, but upon induction of the apoptotic process, there was significant expression of these transcripts in AK-5 cells. When bcl-2 gene was introduced into AK-5 cells there was complete inhibition of apoptosis, suggesting its affect to be upstream of ICE and YAMA proteases. These results suggest an important role for cysteine proteases in the execution of apoptosis, leading to tumor cell death and the regression of AK-5 tumor in syngeneic hosts.

Effect of anti-apoptotic genes and peptide inhibitors on cytoplasmic acidification during apoptosis

Cytoplasmic acidification has been shown to occur during the apoptotic process of cell death although its relation with other events in the process are not yet clear. AK-5 tumor cells have been shown to undergo apoptosis upon treatment with stimuli like dexamethasone (1 microM) or with serum from animals that reject AK-5 tumor. The current study was designed to measure the extent of cytoplasmic acidification during apoptosis in AK-5 cells and to study the effect of antiapopoptic genes and peptide inhibitors on cytoplasmic acidification. Our results show that AK-5 cells when triggered into apoptosis show intracellular acidification by about 0.2 pH units and this is prevented when cells are treated with peptide inhibitors. In addition cytoplasmic acidification does not occur when AK-5 cells are transfected with anti-apoptotic genes Nedd-2 A.S, Crm A or bcl-2 which inhibit apoptosis.

Natural killer cell as the effector which mediates in vivo apoptosis in AK-5 tumor cells

AK-5 tumor cell death is mediated by natural killer cells through necrosis (perforin mediated) and apoptosis. Apoptosis is the mechanism which operates in immune animals in vivo. We have identified natural killer (NK) cell as the effector cell which induces apoptosis leading to tumor cell death in vivo. Naive NK cell which is unable to kill the AK-5 tumor cell can be activated with IL-2/IL-12 to make it capable of inducing apoptosis in tumor cells. NK cells from tumor-rejected animals show higher expression of Fas ligand and serine esterase granzyme B. In addition, NK cell-mediated apoptosis in AK-5 cells is totally abolished when effector cells are treated with anti-NKR-P1 mAb 3.2.3 and complement. NK cell-mediated apoptotic activity is inhibited in bcl-2 transfected tumor cells; however, the cytotoxic activity (perforin-mediated) remains unaffected. These observations suggest an important role for activated NK cells in inducing tumor cell death through necrosis (ADCC) and apoptosis leading to spontaneous regression of the AK-5 tumor in syngeneic animals.

Differential modulation of LAK and ADCC functions of natural killer cells from AK-5 tumor-bearing rats by IL-2, IL-12 and IFN-gamma

Modulation of NK cell activity by various lymphokines is well documented. Freshly isolated NK cells exhibit natural cytotoxicity (NC) and antibody-dependent cellular cytotoxicity (ADCC) against certain targets. Upon stimulation with IL-2, the NK cells acquire lymphokine-activated killer (LAK) activity, which enables them to kill a wide variety of targets. Our results demonstrate that freshly isolated NK cells from tumor-bearing rats exhibit NK activity towards YAC-1, and ADCC activity towards AK-5 targets. Fresh NK cells did not lyse AK-5 targets in the absence of anti AK-5 antibody. However, in vitro culture of fresh NK cells in the presence of rat recombinant IL-2 (r-IL-2) over a period of 7 days resulted in complete loss of ADCC activity with concomitant acquisition of LAK activity on AK-5 tumor targets. The LAK and ADCC activities could be effectively distinguished based on our observation that monoclonal anti-rat ICAM-1 and anti-rat LFA-1 antibodies inhibited only LAK activity, but not ADCC activity, in addition, anti-AK-5 antiserum, but not purified anti-AK-5 antibody, inhibited LAK activity, suggesting that soluble ICAM-1 present in hyperimmune serum could be responsible for inhibition of LAK activity. The loss of ADCC activity upon culture of NK cells with rIL-2 was not observed when the cultures were grown on a macrophage feeder layer. In addition, NK cells retained their ADCC activity when cultures were supplemented with a combination of recombinant IL-2 and IL-12. However IL-2, IFN-gamma or IL-12 alone did not prevent the loss of ADCC activity, suggesting the requirement of a combination of these lymphokines for the maintainance of ADCC activity.

Caspase-2/NEDD-2 protease mediates execution of apoptosis in AK-5 tumor cells

AK-5 tumour cells have been shown to undergo apoptosis in vitro and in vivo. The efficient killing of tumour cells by necrosis and apoptosis leads to spontaneous regression of the tumour. To investigate a possible involvement of caspase-2/Nedd-2 protease in AK-5 apoptosis, we introduced Nedd-2 gene in antisense orientation and showed inhibition of tumour cell apoptosis. Similarly introduction of the bcl-2 gene in tumour cells also inhibited the apoptotic programme. NK cells which have previously been shown to be the effector cells also fail to induce apoptosis in Nedd-2 antisense and bcl-2 transfected clones whereas NK mediated cytotoxic activity is not altered in the transfectants. These results suggest participation of Nedd-2 protease in the induction of apoptosis in AK-5 cells leading to tumour regression.

Increased apoptosis in AK-5 tumor cells after transfection with wild type p53 gene

AK-5 tumor cell death is mediated through necrosis and apoptosis. The apoptotic activity in AK-5 cells has been studied after introduction of wild-type p53 gene. Apoptotic activity both in vitro and in vivo is significantly increased in p53 transfected cells. Similarly there is fragmentation of tumor cell DNA after undergoing apoptosis. These observations suggest an active participation of p53 in inducing apoptosis in AK-5 tumor cells.

AK-5 tumor-induced modulation of host immune function: upregulation of Th-1-type cytokine response mediates early tumor regression

AK-5, a rat histiocytoma, grows as ascites and undergoes spontaneous regression upon subcutaneous transplantation. Earlier studies from this laboratory have demonstrated that immunogenic rejection of AK-5 tumor is mediated through ADCC involving CD8+ NK cells and anti-AK-5 antibody. Upon subcutaneous transplantation, 55-60% of animals initiated tumor regression between 12-15 days after tumor transplantation (early rejectors), while 40-45% did not evoke regression up to 20-25 days (late rejectors). In order to delineate this differential response among syngeneic animals to the same tumor, we have evaluated the cytokine profiles in circulation of both early and late rejecting animals. Our results show that an increase in IL-2, IFN-gamma, IL-4, IL-12 and TNF-alpha contributed to early regression, suggesting a predominantly Th-1 type of cytokine function being evoked against AK-5 tumor. Hosts with lower circulating levels of these cytokines showed delayed tumor regression. In addition, administration of anti-IL-4/anti-IL-4 + anti-IL-10 lead to a decreased antibody response to AK-5 surface antigens in vivo. Neutralization of IFN-gamma in tumor-bearing animals resulted in inhibition of NK-cell-mediated cytotoxicity against AK-5 cells and delayed the regression process. The present study suggests that early regression of AK-5 tumor depends primarily on the higher levels of circulating Th-1-type cytokines; however, the role of IL-4 and anti-AK-5 antibody in tumor regression cannot be ruled out.

Natural killer cell activation-associated induction of target cell DNA fragmentation in a spontaneously regressing rat histiocytoma

The spontaneous regression of AK-5 histiocytoma is mediated by natural killer (NK) cells through antibody-dependent cell-mediated cellular cytotoxicity (ADCC) and the target cell death involves necrosis and apoptosis. We have studied the NK cell activation and the associated induction of apoptosis in the AK-5 tumour in rats. NK cells from immune animals expressed very low levels of CD16 and CD25 surface receptors, as revealed by Northern hybridization and flow cytometry. Interaction between NK cells and antibody-tagged AK-5 cells triggered the expression of these receptors to a higher level and affected AK-5 killing. Treatment of naive NK cells in vitro with interleukin-2 (IL-2), interferon-gamma (IFN-gamma) and IL-12 also enhanced the expression of these activation markers. Co-culture of NK cells from immune animals with antibody-tagged AK-5 cells induced formation of nuclear bodies in AK-5 and extensive fragmentation of AK-5 cell DNA. NK-mediated apoptosis was inhibited by zinc, actinomycin D and cycloheximide. The in vitro treatment of NK cells with cytokines enhanced their ability to induce apoptosis in AK-5 tumour. These results suggest that the NK cells acquire their ability to induce apoptosis in AK-5 tumour in association with their optimal activation.

Correlation of in vitro and in vivo effects of interferon-gamma with the spontaneous regression of a rat histiocytoma

Cytokines trigger activation of different lymphocyte populations, resulting in augmentation of humoral and cell-mediated immunity. We have examined the role of IFN-gamma in mediating AK-5 tumor regression. High levels of circulating IFN-gamma and IL-2 marked the process of regression. Moreover, interaction of immune NK cells with antibody-tagged AK-5 resulted in IFN-gamma secretion, providing in vitro evidence for the involvement of this cytokine. IFN-gamma and IL-2 potentiated the cytolytic activity of naive NK cells, suggesting their role in antitumor activity. Furthermore, pretreatment of immune NK cells with protein tyrosine kinase inhibitor downregulated the IFN-gamma release, suggesting that the secretion of IFN-gamma is phosphorylation dependent. Nonimmune cells could be induced to secrete IFN-gamma when exposed to rIL-12, demonstrating IL-12 dependence in inducing IFN-gamma release. In vivo administration of anti-IFN-gamma inhibited the cytotoxic activity and the process of tumor regression, further substantiating the role of IFN-gamma in regulating the rejection of AK-5 tumor. These observations suggest a definitive role for IFN-gamma in AK-5 regression. This cytokine in concert with IL-2 and IL-12 might aid in designing effective anticancer therapy.

AK-5 tumor-induced expression of interleukin-12: role of IL-12 in NK-mediated AK-5 regression

Spontaneous regression of AK-5, a histiocytic tumor, is mediated by CD3-, CD8+ NK cells through ADCC. The onset of AK-5 regression is associated with the induction of humoral immune response and the augmentation of effector function. The mechanism of tumor cell death involves both necrosis and apoptosis. Interleukin-12, a 75-kDa heterodimeric cytokine, has multiple effects on T and NK cells. We have investigated the role of IL-12 in the NK cell-mediated AK-5 tumor regression process. Subcutaneous transplantation of AK-5 tumor induced the expression of IL-12 (p35 and p40) message by Day 6-8 in the splenocytes of syngenic rats. Similarly, analysis of serum samples from tumor-bearing animals showed the presence of circulating IL-12 around the same time. Interaction of immune cells with antibody-tagged AK-5 cells in vitro also triggered the expression of IL-12 message and protein by 3 hr. The circulating IL-12 in the sera of tumor-rejecting animals, as well as rIL-12, stimulated NK cell proliferation, expression of CD16 and CD25, and the activation of NK cells function. These observations suggest that the ability of the AK-5 tumor to induce the endogenous production of IL-12 may be responsible for keeping the NK cells constantly in an activated state, thus demonstrating an efficient mechanism for the complete regression of the tumor.

Apoptosis: the in vivo mechanism which mediates spontaneous AK-5 tumor regression

We have studied the mechanism of induction of apoptosis in a rat histiocytoma in vivo. Tumor cells are killed by necrosis and apoptosis when injected into immune animals; however, naive animals are incapable of killing the tumor cells. Tumor cells show DNA fragmentation within 3 h after transplantation in the peritoneal cavity. Natural killer (NK) cells act as the effector in causing tumor cell death through apoptosis since animals depleted of their NK cell population did not show target cell DNA fragmentation. Herbimycin A inhibits the induction of apoptosis, suggesting the requirement for protein phosphorylation.

Multiple specific chromosomal alterations in a rat ascitic histiocytoma 'AK-5'

In the rat ascitic histiocytoma, AK-5, chromosome numbers vary between 33 and 41 with a peak at 40 chromosomes. None of the metaphase spreads showed double minute chromosomes. The karyotype of this tumor was characterized by hypodiploid chromosome constitution. Giemsa banding analysis revealed 12 clonal marker chromosomes (M1-M12). Tentative identification of these markers were: M1 = ins(1q); M2 = t(5;?); M3 = t(8;10); M4 = t(8;?); M5 = t(10;X); M6 - t(15;?); M7 = t(5;6); M8 = del(13p); M9-M12 = unidentified. M3 being a large near metacentric chromosome serves as a characteristic marker for this tumor. All marker chromosomes except M2 and M4 were present in single copy per cell. In some metaphases M2 was present in 2 copies while M4 was present in 2 or 3 copies per cell. The total cell cycle duration of AK-5 cells was 15.5 h and the different phases, G1, S, G2 + M were estimated as 1.2, 12.2, and 2 h, respectively.

Conjugate formation between effector and target as a function of cytotoxicity in antibody-dependent killing of AK-5 tumor

The present study was carried out to mechanistically view a possible correlation between the process of, conjugate formation and its relation to target cell death. AK-5 killing is mediated by CD8+ natural killer cells through ADCC. Immune effectors on exposure to antibody primed AK-5 tumor cells formed tight conjugates. Ability of various cell types (NK, T, monocytes and macrophages) to form conjugates was evaluated. Marked increase in the number of NK cells binding to the target as compared to the other cell types was observed. Cytotoxicity of free and bound effectors against antibody tagged AK-5 cells demonstrated a reduced cytotoxic ability of the former in contrast to a significantly high lytic potential of the bound effectors. The results highlight the requirement for priming of NK cells which mediate killing of AK-5 tumor and provide additional evidence that formation of stable conjugates acts as the first signal for triggering lymphocyte activation and effective target cell lysis.

Comet assay to measure DNA damage in apoptotic cells

We have used microelectrophoresis technique to study DNA fragmentation in tumor cells undergoing apoptosis induced by NK cells through ADCC. The DNA damage in target cells is proportionate to the time of co-culture with the effector cells. The assay is simple, rapid and inexpensive.