Poly(ADP-ribosylation) at successive stages of rooster spermatogenesis. Levels of polymeric ADP-ribose in vivo and poly(ADP-ribose) polymerase activity and turnover of ADP-ribosyl residues in vitro

Assessment of PARP-1 Distribution in Tissues of Cynomolgus Monkeys

The poly(ADP-ribose) polymerase 1 (PARP-1) enzyme has received much attention in the last decade due to its promising role in cancer therapeutics. Despite the expanding use of PARP inhibitors in cancer therapy, little is known about PARP-1 tissue distribution. Our study provides a detailed survey of PARP-1 tissue and cellular distribution using well-preserved cynomolgus monkey organs and a well-characterized, highly specific monoclonal PARP-1 antibody. Overall, PARP-1 was detected in most organs, but its distribution was restricted to specific cells within each tissue, suggesting that PARP-1 expression is tightly regulated. The strongest expression was in the pituitary, the ovary, the male adrenal gland, and the thymus. One of the key findings of this study was the stronger expression of PARP-1 in proliferating cells rather than mature cells. This observation not only provides clues to the importance of PARP-1 in processes such as DNA replication and transcription in these cell types, but it also provides the basis for further investigation into the effects of its inhibition in the context of malignancy. Overall, this study greatly expands the current knowledge of PARP-1 tissue expression, enabling the identification of tissues where PARP inhibition may be most efficacious.

Alteration of poly(ADP-ribose) metabolism affects murine sperm nuclear architecture by impairing pericentric heterochromatin condensation

The mammalian sperm nucleus is characterized by unique properties that are important for fertilization. Sperm DNA retains only small numbers of histones in distinct positions, and the majority of the genome is protamine associated, which allows for extreme condensation and protection of the genetic material. Furthermore, sperm nuclei display a highly ordered architecture that is characterized by a centrally located chromocenter comprising the pericentromeric chromosome regions and peripherally positioned telomeres. Establishment of this unique and well-conserved nuclear organization during spermiogenesis is not well understood. Utilizing fluorescence in situ hybridization (FISH), we show that a large fraction of the histone-associated sperm genome is repetitive in nature, while a smaller fraction is associated with unique DNA sequences. Coordinated activity of poly(ADP-ribose) (PAR) polymerase and topoisomerase II beta has been shown to facilitate DNA relaxation and histone to protamine transition during spermatid condensation, and altered PAR metabolism is associated with an increase in sperm histone content. Combining FISH with three-dimensional laser scanning microscopy technology, we further show that altered PAR metabolism by genetic or pharmacological intervention leads to a disturbance of the overall sperm nuclear architecture with a lower degree of organization and condensation of the chromocenters formed by chromosomal pericentromeric heterochromatin.

Testis-specific novel transcripts in chicken: in situ localization and expression pattern profiling during sexual development

Tissue-specific novel transcripts expressed during sexual development were examined by RT-PCR, quantitative RT-PCR (qRT-PCR), and in situ hybridization to provide data for chicken genomics. Public databases for transcript data have been constructed with known and unknown sequences of various tissues from different animals. However, the expression patterns and functions of the transcripts are less known. From the The Institute for Genomics Research Gallus gallus library, we examined 291 tentative consensus (TC) sequences that assembled 100% with transcripts by RT-PCR during male and female sexual development from Embryonic Day 6 to 25 wk of age. We found 85 TC sequences that were specific to testicular development; of these, 43 TC sequences were exclusively upregulated in 25-wk-old testis. Another 52 TC sequences were not specific to one tissue, but occurred in the testis and ovary at different developmental ages. Twelve testis-specific TC sequences upregulated in 25-wk-old testis were randomly selected and further examined with qRT-PCR. For precise localization, these 12 testis-specific TC sequences were examined by in situ hybridization with 25-wk-old adult testis. Six TC sequences were strongly expressed in secondary spermatocytes and haploid spermatids until spermatozoa release. Another six TC sequences were differentially expressed in the adluminal compartment of seminiferous tubules. Among the testis-specific TC sequences, TC120901 is a known gene, phospholipase C, zeta (PLCZ1). Our data provide potential insight into gene expression and genomic information on novel transcripts that are important to avian reproduction.

Deoxyribonucleic acid repair and apoptosis in testicular germ cells of aging fertile men: the role of the poly(adenosine diphosphate-ribosyl)ation pathway

OBJECTIVE

To explore the relationship between men's age and DNA damage repair proteins related to apoptosis in human testicular germ cells.

DESIGN

Retrospective case-control study.

SETTING

Academic institutions.

PATIENT(S)

Testicular specimens were obtained from 22 fertile volunteers aged 20-82 years.

INTERVENTION(S)

Deoxyribonucleic acid repair markers were assessed using immunohistochemical staining for the cell proliferation marker [proliferating cell nuclear antigen (PCNA)]; DNA repair markers [poly(adenosine diphosphate-ribose) polymerase-1 (PARP-1), poly(adenosine diphosphate-ribose) (PAR), X-ray repair cross-complementing1(XRCC1), and apurinic/apyrimidinic endonuclease 1 (APE1)]; and apoptosis-associated markers (caspase 9, active caspase 3, and cleaved PARP-1).

MAIN OUTCOME MEASURE(S)

The prevalence and cellular localization of the above markers in testicular tissues of young, middle aged, and old men.

RESULT(S)

Statistically significant differences in DNA damage repair-associated proteins (PARP-1, PAR, XRCC1, and APE1), and apoptosis markers (caspase 9, active caspase 3, and cleaved PARP-1) were observed in testicular samples from older men. These differences were most marked in spermatocytes.

CONCLUSION(S)

The study demonstrates that there is an age-related increase in human testicular germ cell DNA break repair and apoptosis with age.

Poly(ADP-ribosyl)ation during chromatin remodeling steps in rat spermiogenesis

In spermiogenesis, spermatid differentiation is marked by dramatic changes in chromatin density and composition. The extreme condensation of the spermatid nucleus is characterized by an exchange of histones to transition proteins and then to protamines as the major nuclear proteins. Alterations in DNA topology that occur in this process have been shown to require the controlled formation of DNA strand breaks. Poly(ADP-ribosyl)ation is a posttranslational modification of proteins mediated by a family of poly(ADP-ribose) polymerase (PARP) proteins, and two family members, PARP-1 and PARP-2, are activated by DNA strand breaks that are directly detected by the DNA-binding domains of these enzymes. Here, we show for the first time that poly(ADP-ribose) formation, mediated by poly(ADP-ribose) polymerases (PARP-1 and presumably PARP-2), occurs in spermatids of steps 11-14, steps that immediately precede the most pronounced phase of chromatin condensation in spermiogenesis. High levels of ADP-ribose polymer were observed in spermatid steps 12-13 in which the highest rates of chromatin nucleoprotein exchanges take place. We also detected gamma-H2AX, indicating the presence of DNA double-strand breaks during the same steps. Thus, we hypothesize that transient ADP-ribose polymer formation may facilitate DNA strand break management during the chromatin remodeling steps of sperm cell maturation.

Formation of native-like mammalian sperm cell chromatin with folded bull protamine

The DNA of most vertebrate sperm cells is packaged by protamines. The primary structure of mammalian protamine I can be divided into three domains, a central DNA binding domain that is arginine-rich and amino- and carboxyl-terminal domains that are rich in cysteine residues. In native bull sperm chromatin, intramolecular disulfide bonds hold the terminal domains of bull protamine folded back onto the central DNA binding domain, whereas intermolecular disulfide bonds between DNA-bound protamines help stabilize the chromatin of mature mammalian sperm cells. Folded bull protamine was used to condense DNA in vitro under various solution conditions. Using transmission electron microscopy and light scattering, we show that bull protamine forms particles with DNA that are morphologically similar to the subunits of native bull sperm chromatin. In addition, the stability provided by intermolecular disulfide bonds formed between bull protamine molecules within in vitro DNA condensates is comparable with that observed for native bull sperm chromatin. The importance of the bull protamine terminal domains in controlling the bull sperm chromatin morphology is indicated by our observation that DNA condensates formed under identical conditions with a fish protamine, which lacks cysteine-rich terminal domains, do not produce as uniform structures as bull protamine. A model is also presented for the bull protamine.DNA complex in native sperm cell chromatin that provides an explanation for the positions of the cysteine residues in bull protamine that form intermolecular disulfide bonds.

Expression of histone acetyltransferases was down-regulated in poly(ADP-ribose) polymerase-1-deficient murine cells

NF-kappaB-dependent, as well as human immunodeficiency virus type-1 (HIV-1) long terminal repeat (LTR)-dependent, reporter gene expression was significantly impaired in cells derived from poly(ADP-ribose) polymerase-1 (PARP-1)-knockout (PARP-1 -/-) mice. In addition, the level of protein acetylation was markedly lower in PARP-1 -/- cells than control (PARP-1 +/+) cells. Surprisingly, the expression levels of histone acetyltransferases (HATs), p300, cAMP response element-binding protein-binding protein (CBP), and p300/CBP-associated factor (PCAF), were significantly reduced in PARP-1 -/- cells, as compared with PARP-1 +/+ cells. These results suggest that PARP-1 is required for the proper expression of particular HATs. Since p300 and CBP are coactivators of NF-kappaB, we propose here that PARP-1 participates in NF-kappaB-dependent transcription by means of maintaining the expression of HATs.

Evidence of poly(ADP-ribosylation) in the cockroach Periplaneta americana

Poly(ADP-ribosylation) is a post-translational modification of nuclear proteins typical of most eukaryotic cells. This process participates in DNA replication and repair and is mainly regulated by two enzymes, poly(ADP-ribose) polymerase, which is responsible for the synthesis of polymers of ADP-ribose, and poly(ADP-ribose) glycohydrolase, which performs polymer degradation. The aim of this work was to investigate in the cockroach Periplaneta americana L. (Blattaria: Blattidae) the behaviour of poly(ADP-ribosylation). In particular, we addressed: (i) the possible modulation of poly(ADP-ribosylation) during the embryonic development; (ii) the expression of poly(ADP-ribose) polymerase and glycohydrolase in different tissues; and (iii) the role of poly(ADP-ribosylation) during spermatogenesis. In this work we demonstrated that: (i) as revealed by specific biochemical assays, active poly(ADP-ribose) polymerase and glycohydrolase are present exclusively in P. americana embryos at early stages of development; (ii) an activity carrying out poly(ADP-ribose) synthesis was found in extracts from testes; and (iii) the synthesis of poly(ADP-ribose) occurs preferentially in differentiating spermatids/spermatozoa. Collectively, our results indicate that the poly(ADP-ribosylation) process in P. americana, which is a hemimetabolous insect, displays catalytical and structural features similar to those described in the holometabolous insects and in mammalian cells. Furthermore, this process appears to be modulated during embryonic development and spermatogenesis.

Metabolic changes in the poly(ADP-ribosyl)ation pathway of differentiating rat germinal cells

Endogenous levels of poly(ADP-ribose) and betaNAD+ have been determined in rat male germinal cells at different stages of differentiation. The levels of both metabolites decreased progressively from primary spermatocytes to secondary spermatocytes and especially in spermatids. We have also determined the size and complexity of the ADP-ribose polymers synthesized in permeabilized germ cells. Polymers of different chain length and complexity were observed in cells incubated with different concentrations of [32P]betaNAD+; short polymers characterized primary spermatocytes incubated with low betaNAD+ concentration. In all cell fractions, polymers of over 20 residues in size were observed at high betaNAD+ levels. Long polymers were associated with the sulfuric acid-insoluble proteins (nonhistone proteins such as PARP itself). By contrast, oligomers of 20 ADP-ribose units or less were found in the sulfuric acid-soluble proteins (histone proteins). We have also identified the main ADP-ribose protein acceptors formed in each cell type. In all cells examined, PARP appears to be extensively automodified. However, by far, the H1t variant of histone H1 appeared to be the preferred ADP-ribose target among the acid-soluble proteins separated by reverse-phase HPLC. Therefore, we conclude that an active protein-poly(ADP-ribosyl)ation system is concentrated in primary spermatocytes, based on a high level of PARP automodification accompanied by the preferential heteromodification of the histone H1 variant specifically expressed in the cells undergoing the pachytene phase of the meiotic division.

Analysis of the TPA regulatory element in the genomic poly(ADP-ribose) synthetase gene in human leukemia U937 cells

The human leukemia U937 cells differentiate into monocyte/macrophage-like cells when treated with 12-O-tetradecanoylphorbol-13-acetate (TPA). We observed that during this process, both protein and mRNA levels for PARS markedly decreased in U937 cells. Through deletion analysis of the PARS regulatory gene, we found that the sequence within the first intron region was responsible for the TPA-dependent repression. Electrophoretic mobility shift assays (EMSAs) and Southwestern blot analysis indicate that this element bound specifically to a nuclear protein. TPA treatment abolished the binding of the protein in U937 cells but not in HeLa cells. DNase I footprinting data show that the cis regulatory element is located between residues 328 and 383. We further examined the function of this cis element (BS207) in a basal promoter regulatory reporter construct and found that this cis element (BS207) functions as an enhancer via the binding of an unknown trans-acting factor. TPA treatment diminished the binding activity of the factor in U937 cells, resulting in a decrease in the enhanced activity to the basal level. These results suggest that abolishment of the binding of a special nuclear protein to the first intron of the PARS gene is related to the TPA-responsive downregulation of PARS in U937 cells.

Interaction of Oct-1 and automodification domain of poly(ADP-ribose) synthetase

We isolated several clones from a matchmaker two-hybrid system human lymphocyte cDNA library using an automodification domain of poly(ADP-ribose) synthetase (PARS) as a probe. A DNA sequence (approximately 1 kbp) of the clone was identical to part of the Oct-1 DNA sequence. We then constructed either a His-tagged or GST fusion protein of the inserted cDNA from the clone and the fusion protein was shown to interact with PARS by far-Western blot analysis and co-precipitation with affinity resin. Furthermore, the His-tagged Oct-1/POU-homeo fusion protein interacted weakly with the octamer motif of the DRa promoter and the addition of PARS fusion protein greatly increased the DNA binding activity. These results suggest that PARS interacts with Oct-1 and stabilizes the binding of Oct-1 to the octamer motif.

Inhibition of interferon-gamma- and phorbol ester-induced HLA-DR and interleukin-1 production by the expression of a transfected poly(ADP-ribose) synthetase gene in human leukemia THP-1 cells

We have examined a correlation between an expression level of poly(ADP-ribose) synthetase gene and the stage of monocytic differentiation. We selected three human leukemia cell lines, U937, THP-1, and J111, whose differentiation stage was characterized by nitroblue tetrazolium reduction activity, non-specific esterase activity, phagocytic activity and a cell surface marker. Enzyme activity and mRNA level of the synthetase decreased in accompaniment with the progress of monocytic differentiation. When THP-1 cells were treated with either interferon-gamma or phorbol ester, mRNA level of the synthetase decreased and HLA-DR or interleukin-1 was induced, respectively. We transfected expression plasmid of the exogenous synthetase gene to examine whether the down-regulation of the synthetase is a necessary step to induce these proteins. An expression of the exogenous synthetase gene inhibited the interferon-gamma- and phorbol ester-dependent induction of HLA-DR and interleukin-1. The results suggest that down-regulation of the synthetase may be a signal mediator of immunological response such as HLA-DR or interleukin-1 production in monocytes.

Enhanced expression of poly(ADP-ribose) synthetase gene in malignant lymphoma

Over-expression of cellular protooncogenes has been proposed to function in the initiation and maintenance of malignancies. In order to distinguish malignant lymphoma from reactive proliferative diseases, we surveyed the expression levels of three protooncogenes(c-myc, c-fos and c-myb) in malignant lymphoma and reactive proliferative diseases. An increased level of c-myc or c-fos mRNA was observed in one case, respectively, out of three malignant lymphomata. The other cases exhibited no enhancement in protooncogenes. These oncogenes are critically regulated during differentiation, but the half-life of c-myc mRNA was very short, and the level of the mRNA decreased to the initial level very quickly. Thus, the high level of the expression of these oncogenes may not always be maintained in all malignant cells. We then examined the level of mRNA for poly(ADP-ribose) synthetase in those cases. An enhanced expression for the synthetase gene was observed in all five malignant lymphomata tested, but no increase in the level of the mRNA was observed in any reactive proliferative cases or normal lymph nodes. These results suggest that enhanced expression of poly(ADP-ribose) synthetase gene seems to be a common characteristic of protopathic malignant lymphoma. By using the characteristics of malignant lymphoma, the level of mRNA for the synthetase may be applicable for differential diagnosis of malignant lymphoma from several pathologically indistinguishable diseases.

Fluctuation of gene expression for poly(ADP-ribose) synthetase during hemin-induced erythroid differentiation of human leukemia K562 cells and its reversion process

We have studied the regulation of gene expression for poly(ADP-ribose) synthetase during erythroid differentiation and its reversion process. When human leukemia K562 cells were incubated in the presence of 80 microM hemin, benzidine-positive cells appeared at day 2 and 90% of the cells became positive at day 6. However, RNA blot analysis reveals that mRNA for gamma-globin was already abundant in untreated K562 cells and the level of the message was slightly increased by hemin-treatment. Spectroscopic analysis and polyacrylamide gel electrophoresis of the induced cell extracts indicate that hemoglobin molecules were not detected in untreated cells, and increased successively up to day 6. The hemin-induced cells were thoroughly washed, and then recultured in the absence of hemin. The benzidine-positive cells mostly disappeared 3 days after the elimination of the inducer. During the hemin-induced erythroid differentiation, the activity and mRNA for poly(ADP-ribose) synthetase decreased to 50% and 20% of the initial level at day 3 and a low level of the gene expression was maintained afterwards, whereas the activity and mRNA returned to the initial value 1 day after hemin elimination. The results indicate that the hemin-induced erythroid differentiation of K562 cells is a reversible process and depression of the synthetase may be involved in the progress of differentiation.

Inhibitory effect of interferon-gamma-dependent induction of major histocompatibility complex class II antigen by expressing exogenous poly(ADP-ribose) synthetase gene

Ia antigen, one of class II major histocompatibility complexes, was induced by treatment of mouse macrophage P388D1 cells with interferon-gamma. During the process, expression of poly(ADP-ribose) synthetase gene was depressed. We examined whether or not down-regulation of the synthetase was required for the interferon-gamma-dependent induction of Ia antigen. We constructed expression plasmid harboring metallothionein promoter-regulated synthetase gene. The enzyme activity and mRNA level of the synthetase were increased in exogenous synthetase gene-transfected clones. Induction of Ia antigen gene was strongly inhibited by expressing the exogenous synthetase gene upon treatment of the transfected clones with interferon-gamma. The result suggests that interferon-gamma-dependent down-regulation of the synthetase may be involved in a step of the signal transduction to induce Ia antigen.

Requirement of down-regulation of NAD+ ADP-ribosyltransferase for the interferon-gamma-induced activation process of murine macrophage tumor cells

Expression of the NAD+ ADP-ribosyltransferase gene is depressed during interferon-gamma-induced activation of murine macrophage P388D1 tumor cells [Taniguchi, T., Yamauchi, K., Yamamoto, T., Tokushima, K., Harada, N., Tanaka, H., Takahashi, S., Yamamoto, H. & Fujimoto, S. (1988) Eur. J. Biochem. 171, 571-575]. In order to study the role(s) of NAD+ ADP-ribosyltransferase in interferon-gamma-induced activation of P388D1 cells, we transfected an cloned synthetase gene into P388D1 cells and examined the effect of exogenous transferase gene expression on the induction of the Ia antigen, one of the major histocompatibility gene products, by interferon-gamma. The transferase activity of the transfected cells was twice that of control cells, and Southern blot analysis revealed that characteristic restriction sizes of cDNA were detected in the clones. RNA blot analysis using a cDNA for the transferase as a probe showed that the level of mRNA for the transferase in transfected cells was higher than that in control cells, and mRNA for the exogenous transferase was still detectable 2 days after the transfected cells were treated with interferon-gamma. This indicates that the exogenous transferase gene was expressed in transfected cells. RNA blot analysis with a cDNA for the Ia antigen and flow-cytometric analysis showed that the Ia antigen was induced much less in the transfected cells by interferon-gamma, in terms of the mRNA and the Ia antigen. The results suggest that down-regulation of the transferase is required for the induction of the Ia antigen in P388D1 cells by interferon-gamma.

Poly(ADP-ribosylation) of nuclear proteins in rat testis correlates with active spermatogenesis

Poly(ADP-ribosylation) of nuclear proteins has been investigated in rat testis under different experimental conditions to determine whether it is associated with somatic or germinal cells. Isolated, intact nuclei were incubated with [14C]NAD and extracted sequentially with 5% HClO4 and 0.25 M HCl, and labelled soluble proteins were analysed by reverse-phase high-performance liquid chromatography and acetic acid-urea polyacrylamide gel electrophoresis (pH 2.9). Results show that in normal adult testis a major acceptor protein for poly(ADP-ribose) in HClO4 extracts is the tissue-specific histone, H1t. Core histones and three proteins (alpha, beta and gamma) with low mobility on acetic acid-urea gels were the major acceptors identified in HCl extracts. Poly(ADP-ribosylation) of all the aforementioned proteins is very low in isolated intact nuclei of testis from 8-day-old animals (only spermatogonia present in seminiferous tubules), increases significantly by 16-day (pachytene spermatocytes appear) and reaches adult proportions by 32 days (condensing spermatids present). In the nuclei from cryptorchid testes, poly(ADP-ribosylation) of nuclear proteins resembles 8-day-old testis. It is concluded that (a) poly(ADP-ribosylation) of nuclear proteins in rat testis is closely correlated with spermatogenesis and can be inferred that is particularly active in the early stages of meiosis; (b) testis-specific proteins (histone H1t and low mobility proteins, alpha, beta and gamma) are poly(ADP-ribosylated) to higher specific radioactivity than somatic histones.

Intracellular distribution of poly(ADP-ribose) synthetase in rat spermatogenic cells

The highest activity of poly(ADP-ribose) synthetase was found in the testis among several rat tissues tested. Subcellular fractionation of the testis demonstrated that the synthetase was localized primarily in the nucleus and partially in the microsomal-ribosomal fraction. This result was confirmed by immunocytochemical staining with the enzyme-specific antibody. The synthetase was localized in the nuclei of interstitial cells, Sertoli cells, spermatogonia, and spermatocytes. In addition, round spermatids showed a granular staining in the cytoplasm, which was comparable in intensity with that in the nucleus. The cytoplasmic synthetase had a molecular weight of 115,000 and synthesized oligomers of ADP-ribose on itself (automodification). The synthetase activity in the isolated cytoplasmic fraction was stimulated about threefold by the addition of DNA and depressed by treatment with DNase I, suggesting the presence of endogenous activator DNA. A candidate DNA for such an activator was isolated from the microsomal-ribosomal fraction, and identified tentatively as mitochondrial DNA on the basis of its size and restriction fragment patterns.

Decrease in the level of poly(ADP-ribose) synthetase during nerve growth factor-promoted neurite outgrowth in rat pheochromocytoma PC12 cells

We have studied the changes in the levels of the enzyme molecule and mRNA for poly(ADP-ribose) synthetase during nerve growth factor-promoted neurite outgrowth in rat pheochromocytoma PC12 cells. When the PC12 cells were cultured in the presence of nerve growth factor, the content of enzyme molecules decreased along with neurite outgrowth to 50% of the original amounts in 2 days and the content of mRNA for the enzyme also decreased to approximately 50% in 2 days. These results suggest that the decrease of the enzyme molecule may be due to depression of expression of the gene for synthetase during the process. Taken together with previous observations, the decrease of the synthetase seems to be required for some cellular differentiation.

Depression in gene expression for poly(ADP-ribose) synthetase during the interferon-gamma-induced activation process of murine macrophage tumor cells

A 2.7-kb cDNA clone coding for bovine poly(ADP-ribose) synthetase was isolated from a lambda gt11 expression library by direct immunological screening with an antiserum to the enzyme. The cDNA hybridizes to an approximately 3.8-kb bovine thymus polyadenylated RNA, which translates an immunoprecipitable 120-kDa protein with the antibody to the enzyme. The partial DNA sequence of the cDNA was determined and portions of the predicted amino acid sequence matched the sequence of 26 amino acids at the N terminal of the 41-kDa alpha-chymotryptic fragment and two cyanogen-bromide-cleaved peptides of the enzyme. A subcloned fragment from the coding region of the cDNA was used as a probe to estimate the level of mRNA for the enzyme during the interferon-gamma-induced activation process of the murine macrophage tumor P388D1 cell line. The amount of mRNA for the enzyme decreased nearly completely within 24 h after incubation in a medium containing interferon-gamma, while mRNA of the Ia antigen, one of the major histocompatibility gene products, was increased in the macrophage tumor cells by interferon-gamma as confirmed by the I-A beta cDNA as a probe. These results suggest that the gene expression for poly(ADP-ribose) synthetase is depressed during the interferon-gamma-induced activation process of macrophage tumor cells.