Epidermal growth factor regulates protein kinase A activity in murine fibrosarcoma cells: differences between metastatic and nonmetastatic tumor cell variants

The interplay between cyclic AMP (cAMP)-dependent protein kinase A (PKA)- and p21ras-mediated signaling pathways is expected to determine further loss, maintenance, or modulation of differentiation and proliferation of a particular cell. Therefore, the relationship and nature of the cross-talk between these two major signaling systems are of utmost importance to the understanding of these processes in both normal and neoplastic cells. In view of their paramount physiological importance, one would expect the existence of a well-controlled bidirectional interaction between these pathways, which would be more appropriate and in agreement with basic principles of cellular homeostasis. However, based on the discovery that activated PKA may inhibit ras-mediated translocation of c-Raf-1 to the plasma membrane, it is generally accepted that the cross-talk between cAMP/PKA and p21ras-mediated signal transduction pathways is unilateral, i.e., that the activation of PKA regulates growth factor receptor protein tyrosine kinase-mediated signaling. To challenge the validity of a unilateral approach, we decided to test the possible existence of cross-talk of a bidirectional nature between the aforementioned signaling pathways at different stages of malignant differentiation. For that purpose, we investigated the nature of the cross-talk existing between a known receptor protein tyrosine kinase-epidermal growth factor receptor (EGFR) and PKA in highly metastatic and nonmetastatic cloned variants of a murine fibrosarcoma (T-10). Our study revealed the existence of principal differences in PKA activity between metastatic and nonmetastatic cloned fibrosarcoma variants that may be due to the differential expression and membrane translocation of the p21(Ki-ras) small mass G-protein. Most importantly, our experiments have demonstrated the existence of a novel character of interactions between EGFR and PKA, because the ligation of the EGFR by epidermal growth factor in the metastatic variant induced a high activity of PKA. These findings are of prime importance, because they reveal the existence of a new relationship between two major signal transduction pathways in mammalian cells, i.e., the existence of a bilateral interaction between the ras- and cAMP/PKA-mediated signal transduction pathways. Furthermore, the fact that two tumor cell variants originating in the same tumor and differing in their metastatic capacity differ as well in the nature of the cross-talk between major signal generation systems imposes new challenges for the future use of biological response modulators to cure cancer and restrict metastatic spread.

Urokinase plasminogen activator and gelatinases are associated with membrane vesicles shed by human HT1080 fibrosarcoma cells

Membrane vesicles are shed by tumor cells both in vivo and in vitro. Although their functions are not well understood, it has been proposed that they may play multiple roles in tumor progression. We characterized membrane vesicles from human HT1080 fibrosarcoma cell cultures for the presence of proteinases involved in tumor invasion. By gelatin zymography and Western blotting, these vesicles showed major bands corresponding to the zymogen and active forms of gelatinase B (MMP-9) and gelatinase A (MMP-2) and to the MMP-9. tissue inhibitor of metalloproteinase 1 complex. Both gelatinases appeared to be associated with the vesicle membrane. HT1080 cell vesicles also showed a strong, plasminogen-dependent fibrinolytic activity in 125I fibrin assays; this activity was associated with urokinase plasminogen activator, as shown by casein zymography and Western blotting. Urokinase was bound to its high affinity receptor on the vesicle membrane. Addition of plasminogen resulted in activation of the progelatinases associated with the vesicles, indicating a role of the urokinase-plasmin system in MMP-2 and MMP-9 activation. We propose that vesicles shed by tumor cells may provide a large membrane surface for the activation of membrane-associated proteinases involved in extracellular matrix degradation and tissue invasion.

Hepatic glutaminase gene expression in the tumor-bearing rat

Previous studies have documented an increase in hepatic plasma membrane glutamine transport in the tumor-bearing rat, but the effects of tumor burden on hepatic glutaminase expression have not been carefully studied. The purpose of this study was to examine the effects of tumor burden and food intake on hepatic glutaminase expression. Rats were implanted with syngeneic methylcholanthrene-induced fibrosarcoma tumor tissue; control rats were sham operated and pair-fed every 24 hr. Northern blotting was used to assay the effect of tumor burden and fasting on hepatic glutaminase mRNA levels, using beta-actin mRNA as a control. Hepatic glutaminase mRNA levels in livers of pair-fed controls were found to be 4-fold greater than levels in livers of tumor-bearing animals. Examination of food intake patterns in these animals indicated that pair-fed controls ate their allotted chow quickly while tumor-bearing rats ate small amounts throughout each 24 hr period. This observation suggested that the differences in glutaminase mRNA levels may be due to a period of fasting by pair-fed animals which was not experienced by the tumor-bearing group. Hepatic glutaminase mRNA levels rapidly increased in normal rats during acute fasting to levels 5.5-fold greater than fed animals. Glucose feeding and insulin injection rapidly reversed the effect of fasting on hepatic glutaminase mRNA levels in normal rats. Tumor-bearing rats also exhibited upregulation of hepatic glutaminase mRNA levels in response to fasting.

CONCLUSIONS

(1) Tumor burden itself does not alter hepatic glutaminase expression, at least at the pre-translational level. Instead, differences in hepatic glutaminase mRNA content are due to differences in food intake patterns. (2) Hepatic glutaminase mRNA levels are rapidly upregulated in response to fasting, an effect which appears to be linked to a decrease in plasma insulin concentrations. Because tumor-bearing rats eat regularly over a 24 hr period (albeit in small increments), thereby maintaining the plasma insulin concentration, hepatic glutaminase mRNA may not rise as it does in pair-fed controls whose daily chow intake is complete within hours of food allocation. (3) This study indicates that differences in the timing of food intake between tumor-bearing rats and pair-fed controls can alter the expression of genes that are influenced by nutrient availability. These differences should be taken into account when designing studies which involve pair-feeding to control nutrient intake.

Activity of lysosomal and nonlysosomal proteases and contents of protein and its degradation products in the blood serum of rats with fibrosarcoma induced by methylcholanthrene

Activity of lysosomal and nonlysosomal proteases and contents of protein and its degradation products in the blood serum of rats with methylcholantrene fibrosarcoma were evaluated. Activity of lysosomal proteases and prolidase and prolinase as well in the blood serum of rats with methylcholanthrene tumour did not differ from the activity of these enzymes in the blood serum of control rats. Only the activity of elastase and collagenase in the blood serum of rats with methylcholanthrene tumour especially with tumour of intermediate and big mass was increased. Content of total protein was decreased in the blood serum of rats with tumour of intermediate and big mass and contents of glycoproteins and alfa-amin nitrogen were increased in comparison to the blood serum of control rats.

Expression of membrane-type matrix metalloproteinase 1 (MT1-MMP) in tumor cells enhances pulmonary metastasis in an experimental metastasis assay

Membrane-type matrix metalloproteinase 1 (MT1-MMP) is a member of the recently identified unique membrane-type subgroup in the matrix metalloproteinase (MMP) family. MT1-MMP has proteolytic activity against components in the extracellular matrix and activates progelatinase A (72-kDa type IV procollagenase/proMMP-2) on the cell surface. Because MT1-MMP is frequently expressed in a variety of tumors, we examined its contribution to their metastatic potential. The mouse lung carcinoma cell line Madison 109 was transiently transfected with a MT1-MMP expression plasmid and inoculated into the tail vein of BALB/c mouse. Fate of the transfected cells was monitored by the neo(r) gene in the plasmid using the quantitative PCR method. The survival rate of the parental cells in lung was 0.7% of the inoculated cells. It was increased by 3-fold with the MT1-MMP transfected cells and the number of the lung nodules increased accordingly. Immunostaining of the consecutive tissue sections revealed that lung nodules expressing MT1-MMP were positive for gelatinase A as well, whereas MT1-MMP-negative cells were not stained for gelatinase A at all. Thus, MT1-MMP-expressing cells acquire specific ability to bind exogenous progelatinase A.

Nuclear matrix bound DNA polymerase-beta in mouse fibrosarcoma: effect of gamma-radiation

Nuclear matrices isolated from the mouse fibrosarcoma tumour cells contain the eukaryotic replicative enzyme DNA polymerase-alpha and the presumptive repair enzyme DNA polymerase-beta. Exposure of tumors to various doses of gamma-radiation (1.95 to 6.5 Gy) causes a 2-fold increase in the levels of only DNA polymerase-beta in the nuclear matrix. The increase in the levels of this enzyme is not discernible if the matrices are isolated 24 hr after irradiation. The rise in the levels of the repair enzyme DNA polymerase-beta could be indicative of radiation stress response of the tumour cells and their repair ability.

Interferon-gamma-dependent expression of inducible nitric oxide synthase, interleukin-12, and interferon-gamma-inducing factor in macrophages elicited by allografted tumor cells

We have examined the mechanisms of activation of macrophages (Møs) induced by i.p. allografted Meth A tumor cells (Meth A-Møs) during the rejection of the cells by C57BL/6 mice. Inducible nitric oxide (NO) synthase (iNOS), interleukin-12 (IL-12), and interferon-gamma (IFN-gamma)-inducing factor (IGIF) were transiently expressed in Meth A-Møs during the rejection. The expression was impaired in mice in which the gene encoding IFN-gamma had been disrupted (IFN-gamma-/-). In vitro studies showed that Meth A-Møs from IFN-gamma +/+ mice induced an apoptotic type of cell death in P815 cells, without cell-to-cell contact, in an NO-dependent manner, whereas Meth A-Møs from IFN-gamma-/- mice could not lyse these cells. The iNOS, IL-12, and IGIF expression was also impaired in bacteria-activated Møs from IFN-gamma-/-mice, indicating that IFN-gamma, but not IGIF, would be the initial signal that leads to the activation of Møs in vivo.

Tumor cell autocrine motility factor is the neuroleukin/phosphohexose isomerase polypeptide

To date, the structure of the autocrine motility factor (AMF), a tumor-secreted cytokine which stimulates cell migration in vitro and metastasis in vivo, is unknown. Here, AMF secreted by Gc-4 PF murine fibrosarcoma into a protein-free conditioned media was isolated, purified, and microsequenced. The results demonstrate that AMF is the previously cloned cytokine and enzyme designated as neuroleukin, and phosphohexose isomerase (PHI), which has been independently implicated in cell motility, and to be a cancer progression marker. PHI catalyzes isomerization of glucose 6-phosphate to fructose 6-phosphate and is specific for both sugars. Murine AMF exhibits the enzymatic properties of PHI and rabbit heart PHI-stimulated mouse fibrosarcoma cells' motility similar to those of the endogenous AMF. Specific PHI inhibitors (carbohydrate phosphates) inhibited enzymatic activity and AMF-induced cell motility.

Phenethyl isothiocyanate, a natural chemopreventive agent, activates c-Jun N-terminal kinase 1

Phenethyl isothiocyanate (PEITC) and other structurally related compounds are potent chemopreventive agents in a number of experimental models of cancer in animals. The mechanisms of cancer protection by these agents are not clear but may involve the regulation of gene expression, such as that by Phase II detoxifying enzymes. To unveil the upstream signaling events that lead to the potential transcriptional activation of genes, we studied the involvement of mitogen-activated protein kinase, c-Jun N-terminal kinase 1 (JNK1), and extracellular signal-regulated kinase 1 and 2 cascades, which have been shown to mediate numerous types of extracellular signals. On treatment of human ovarian HeLa cells with PEITC, JNK1 activity was strongly induced in a dose- and time-dependent manner, whereas the activation of extracellular signal-regulated kinase 1 and 2 was not substantial. Furthermore, activation of JNK1 by PEITC was inhibited by pro-oxidants hydrogen peroxide and diamide, although these two pro-oxidants by themselves had opposing effects on JNK1 activity. Pretreatment with an antioxidant, N-acetyl-L-cysteine, had no effects on PEITC activation of JNK1. When comparing the kinetics of JNK1 activation by different isothiocyanates, PEITC elicited a sustained activation, whereas 3-phenylpropyl isothiocyanate and 4-phenylbutyl isothiocyanate stimulated transient activations. The responsiveness of JNK1 to PEITC, 3-phenylpropyl isothiocyanate, and 4-phenylbutyl isothiocyanate suggests the involvement of JNK1 in the regulation of Phase II detoxifying enzyme gene expression. Furthermore, different patterns of JNK1 induction by these isothiocyanates may contribute to their distinct chemopreventive efficacies in some animal tumor model studies.

Molecular mechanisms underlying IFN-gamma-mediated tumor growth inhibition induced during tumor immunotherapy with rIL-12

The present study investigates the molecular mechanisms by which IFN-gamma produced as a result of in vivo IL-12 administration exerts its anti-tumor effects. rIL-12 was administered three or five times into mice bearing CSA1M fibrosarcoma, OV-HM ovarian carcinoma or MCH-1-A1 fibrosarcoma. This regimen induced complete regression of CSA1M and OV-HM tumors but only transient growth inhibition of MCH-1-A1 tumors. The anti-tumor effects of IL-12 were associated with enhanced induction of IFN-gamma because these effects were abrogated by pretreatment of hosts with anti-IFN-gamma antibody. Exposure in vitro of the three types of tumor cells to rRFN-gamma resulted in moderate to potent inhibition of tumor cell growth. IFN-gamma stimulated the expression of mRNAs for an inducible type of NO synthase (iNOS) in CSA1M cells and indoleamine 2,3-dioxygenase (IDO), an enzyme capable of degrading tryptophan, in OH-HM cells, but induced only marginal levels of these mRNAs in MCH-1-A1 cells. In association with iNOS gene expression, IFN-gamma-stimulated CSA1M cells produced a large amount of NO which functioned to inhibit their own growth in vitro. Although OV-HM and MCH-1A1 cells did not produce NO, they also exhibited NO susceptibility. Whereas the tumor masses from IL-12-treated CSA1M-bearing or OV-HM-bearing mice induced higher levels of iNOS (for CSA1M) or IDO and iNOS (for OV-HM) mRNAs, the MCH-1-A1 tumor mass expressed lower levels of iNOS mRNA alone. Moreover, massive infiltration of CD4(+) and CD8(+) T cells and Mac-1(+) cells was seen only in the CSA1M and OV-HM tumors. Thus, these results indicate that IFN-gamma produced after IL-12 treatment induces the expression of various genes with potential to modulate tumor cell growth by acting directly on tumor cells or stimulating tumor-infiltrating lymphoid cells and that the effectiveness of IL-12 therapy is associated with the operation of these mechanisms.

Retention of unmethylated CpG island alleles in human diploid fibroblast x fibrosarcoma hybrids expressing high levels of DNA methyltransferase

The mechanisms underlying ectopic methylation of CpG islands in neoplastic cells are poorly understood. One determinant may be the increased expression of DNA methyltransferase (DNA MTase) observed frequently in neoplastic cells. To evaluate the role of DNA MTase overexpression in aberrant CpG island methylation, we assessed methylation of fibroblast-derived CpG islands in human diploid fibroblast x fibrosarcoma hybrid cell lines. Each of six independently derived, immortalized hybrid cell lines exhibited a high level of DNA MTase expression, comparable to that of the fibrosarcoma parental line. The methylation status of five CpG island loci, each of which was methylated extensively in the fibrosarcoma parental cells but not in the fibroblasts, was then determined in the hybrid cell lines. The patterns of methylation were consistent and highly locus dependent among the hybrid lines. Unmethylated alleles were retained stably at three loci. The parental origin of alleles could be determined at two other loci in the hybrid cells. Whereas no methylation of parental fibroblast-derived alleles of the HIC-1 locus was noted in hybrid cell lines, a marked increase in methylation of fibroblast-derived alleles of the estrogen receptor was observed in all hybrid cell lines. Therefore, despite high-level DNA MTase expression, widespread loss of unmethylated CpG islands was not observed in the hybrid cell lines. The nonrandom pattern of increased CpG island methylation in the hybrid cell lines suggests that locus-specific features and/or clonal selection, and not just DNA MTase expression, affect the evolution of ectopic methylation in neoplastic cells. Somatic cell hybrids may provide useful models for studying aberrant epigenetic events in neoplastic cells.

Independent regulation of matrix metalloproteinases and plasminogen activators in human fibrosarcoma cells

Serine proteases and matrix metalloproteinases have been shown to often cooperate in multiple physiological and pathological processes associated with changes in the extracellular matrix (ECM). We have examined the interaction between the plasminogen activator (PA)-plasmin system and matrix metalloproteinases (MMPs) in HT1080 human fibrosarcoma cells treated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA). While TPA treatment evoked a temporary increased expression of urokinase type PA (uPA), the production of both types of human plasminogen activator inhibitors (PAI) was induced and sustained over 12 h by TPA treatment shifting the protease-protease inhibitors balance in favor of the inhibitors. TPA treatment of HT1080 cells induced the expression of interstitial collagenase (MMP-1) and increased the expression of gelatinase B (MMP-9), tissue inhibitor of metalloproteinases-1 (TIMP-1), and MT-MMP, a membrane-bound activator of progelatinase A (proMMP-2), while MMP-2 and TIMP-2 expression were decreased. Increased MT-MMP expression by TPA treatment was associated with increased activation of proMMP-2. These data show that the regulation of PA-plasmin and metalloproteinase and their specific inhibitors is uncoordinated. In addition, inhibition of the PA-plasmin system by PAI-2 or aprotinin did not prevent the activation of proMMP-2 by TPA, suggesting that plasmin is not involved in MT-MMP-mediated activation of proMMP-2.

A novel nonviral cytoplasmic gene expression system and its implications in cancer gene therapy

We recently have developed a unique cytoplasmic transient gene expression system based on cotransfection of target cells with bacteriophage T7 RNA polymerase (RNAP) and plasmid DNA vectors containing a T7 autogene. Because this T7 system is self-initiating, self-maintaining, and requires no cellular factors for transcription, it is therefore likely to function in any mammalian cell with any gene both in vitro and, more importantly, in vivo. In this study we demonstrate that the T7 DNA vector and T7 RNAP could be efficiently codelivered to cultured cells by lipofection. Different target genes were expressed by the T7 system in a wide variety of mammalian cells including several tumor cell lines. Gene expression could be detected in more than 30% of the cells of some tumor cell lines transiently transfected by the T7 vector. Average activity of the reporter enzyme (luciferase) expressed by a transfected cell was relatively constant regardless of the cell line used. When a T7-luciferase vector was directly injected into various tissues of mice without the use of liposomes, luciferase activity could be found in the injected liver, muscle, brain and tail connective tissues. The luciferase levels expressed by the T7 system were found to be up to 200-fold higher, depending upon the injected tissues, than levels achieved with a traditional nuclear gene expression vector. Direct tumor injection with a T7-beta-galactosidase (beta-gal) construct resulted in beta-gal gene expression in tumor cells near the injection sites. In addition, direct injection of the T7 system in mice did not generate detectable quantities of antibodies against the T7 RNAP. These results suggest that this gene expression system may be useful in many different medical applications such as cancer gene therapies and DNA vaccination, where transient but rapid and efficient gene expression is required.

Clonal heterogeneity in plasminogen activator activity produced by two murine tumor cell lines

Secretion of plasminogen activators (PA) has been shown to be an important method by which cells can initiate degradation of the extracellular matrix (ECM). In this study we have examined the PA production of two murine cell lines, KHT-LP1, a fibrosarcoma and SCC-VII, a squamous cell carcinoma, and have found a high degree of clonal heterogeneity. Our method for assaying PA activity measures the PA activity of small colonies of cells derived from single cells, using an in vitro fibrin/agarose PA assay in which colonies with PA activity form discernable 'halos' in the fibrin/agarose semisolid growth medium. When these small colonies of cells were disassociated and the component cells were reassayed for PA activity it was again found to be heterogeneous, suggesting that this property can be generated during the growth of the colonies. KHT-LP1 cells derived from single cell clones were assayed for PA activity to determine the rate at which this phenotype was produced. It was found that the rate of formation of the PA activity phenotype was 6.5 x 10(-6) events per cell generation. The component cells of colonies which initially demonstrated high PA activity produced more PA activity than the component cells of the colonies that had low PA activity. This suggests that some aspects of the phenotype may be more stable than others. To examine whether the addition of lethally irradiated cells could stabilize the phenotype we determined whether fibrin/agarose PA assays supplemented with lethally irradiated cells would reduce the heterogeneity of PA activity. The results indicated that the heterogeneity was not reduced, and there was an increase in the average amount of PA activity.

Synthesis and structure-activity relationships of gelatinase inhibitors derived from matlystatins

To investigate a series of new inhibitors of gelatinases based on matlystatin B (1b), extensive structure-activity relationship studies were performed. The new derivatives were evaluated in vitro for the ability to inhibit gelatinases. The inhibitory activities against thermolysin were also assayed to test the compounds' selectivity. Among the compounds modified at the P'3 moiety, the N-methylamide derivative 5 g was virtually twice as effective on gelatinase B as the parent compound 1b (5g, IC50 = 0.27 microM vs. 1b, IC50 = 0.57 microM). Other derivatives, including 1) esters 7a and 7b having the ester portions P'2 and P'3, 2) the cyclic amino acids, L-proline or L-pipecolinic acid (13a and 13b) bearing P'2, and 3) compounds 29a and 29b representing an attachment of the pentyl side chain at C3' (P'1 side chain) instead of C2', all showed decreased potencies. The key discovery was the observation that the introduction of a nonyl group at the P'1 position yielded a compound (31f, IC50 = 0.0012 microM) with high inhibitory activity against gelatinases and high selectivity over thermolysin. This result suggested that the S'1 subsites of the gelatinases have a locally deep hydrophobic structure, since on the basis of the optimum inhibitory activity in the alkyl series, the nonyl group seems to fit best into this hydrophobic pocket. Thus 31f exhibited a 475-fold more potent inhibitory activity than 1b towards gelatinase B.

Effect of administering cyclophosphamide and vitamin E on the levels of tumor-marker enzymes in rats with experimentally induced fibrosarcoma

Cyclophosphamide, and antineoplastic drug, and vitamin E, the common antioxidant present in the diet, were administered in separate dosages and in combination to animals (rats) with fibrosarcoma, metastatic tumor of the connective tissues, induced. The anticancer drug (20 mg/kg body weight) and the vitamin-E (400 mg/kg body weight) was administered for a period of 28 days from the day of tumor transplantation. The individual and the combined effects of these two substances were investigated by checking the growth of the tumor. Tumor markers like lactate dehydrogenase (LDH), serum glutamate pyruvate transminase (SGPT), serum glutamate oxaloacetate transaminase (SGOT), acid phosphatase, and alkaline phosphatase were analyzed for the changes in their concentration in serum, liver, and kidney to assess the success of the therapy. The increased level of the enzymes in the fibrosarcoma-suffering rats (GPII) was reduced by cyclophosphamide treatment (GP III) and vitamin E administration (GP IV). Among the treated groups, the combination therapy (GP V) showed greater efficacy in the treatment of fibrosarcoma than did individual administration, as there was more reduction in the levels of enzymes in Group V than those in to Groups III and IV. The enzyme levels were brought to near the normal level.

Altered topoisomerase I and II activities in suramin-resistant lung fibrosarcoma cells

To better understand the molecular basis for the cytotoxic effects of suramin, we have developed suramin-resistant DC-3F/SU 1000 cells by continuous exposure of fibrosarcoma cells to increasing concentrations of suramin. The suramin resistance (approximately 10-fold) is not associated with changes in uptake or intracellular distribution of the drug. The sensitivity to actinomycin D, cytarabine, aphidicolin, hydroxyurea, vincristine, and 5-fluorouracil is unaltered. In contrast, DC-3F/SU 1000 cells are about 2-fold resistant to classical DNA topoisomerase II inhibitors such as doxorubicin, amsacrine, and etoposide, whereas the cells are 1.5-fold more sensitive to the topoisomerase I inhibitor camptothecin. The cross-resistance to topoisomerase II inhibitors occurred earlier than the collateral sensitivity to camptothecin. Amsacrine- and etoposide-induced DNA-protein complex formation is reduced about 2-fold in DC-3F/SU 1000 cells, compared with DC-3F cells, whereas camptothecin-induced DNA-protein complex formation is increased 1.5-fold. Western blot analysis of cellular lysates from the two cell lines shows no significant differences in the level of topoisomerase II, whereas the level of topoisomerase I is increased 2.5-fold in DC-3F/SU 1000 cells. The catalytic activities of topoisomerases I and II in nuclear extracts from DC-3F/SU 1000 cells are both about 2-fold higher than those in extracts from DC-3F cells, whereas amsacrine- and etoposide-induced DNA-protein complex formation is comparable between the two cell lines. Taken together, our results support the involvement of DNA topoisomerases in the cytotoxic activity of suramin. We further believe that the DC-3F/SU 1000 cells may be a useful model for the elucidation of factors that lead to low, clinically relevant, levels of resistance to topoisomerase II inhibitors.

Effect of intralipid infusion on serum high- and low-density lipoprotein cholesterol, lecithin:cholesterol acyltransferase, and lipoprotein lipase in tumor-bearing rats

We compared the effects of 0.45% normal saline (NS), 5% Intralipid (IL), and 16.7% glucose (Glu) infusions on total serum triglycerides and cholesterol, serum high-(HDL-c) and low-density lipoprotein cholesterol (LDL-c), and activity of serum lecithin:cholesterol acyltransferase (LCAT), and serum lipoprotein lipase (LPL) in rats implanted with a fibrosarcoma. In tumor-bearing rats given NS, a two-fold increase in total serum cholesterol, a four-fold increase in LDL-c, and a five-fold decrease in the HDL-c/LDL-c ratio were observed compared to tumor-free rats. In tumor-bearing rats administered IL, a two-fold increase in total serum triglyceride and cholesterol, a three-fold increase in HDL-c and HDL-c/LDL-c ratio, and a two-fold increase in LPL activity were observed compared to tumor-bearing rats administered NS. In tumor-bearing rats administered Glu, a two-fold decrease in total serum cholesterol, a two-fold decrease in HDL-c, and a three-fold decrease in LDL-c were observed compared to tumor-bearing rats administered NS. Tumor weights and LCAT activity did not differ significantly between treatment groups. Previous results have demonstrated that lipophilic compounds that interact with plasma lipoproteins have altered pharmacological effects when administered with IL. Therefore, this study suggests that IL infusions alter the HDL-c/LDL-c ratio and could affect the pharmacological behavior of anticancer compounds that predominantly distribute into the LDL fraction upon entrance into the bloodstream.

Role of phospholipase D in laminin-induced production of gelatinase A (MMP-2) in metastatic cells

Metastatic spread depends critically upon the invasiveness of tumor cells, i.e. their ability to breach basement membranes by elaborating and secreting specific proteolytic enzymes such as gelatinase A (MMP-2). Laminin is a major constituent of the extracellular matrix that can trigger production of MMP-2 in metastatic cells, but not in non-metastatic cells. The present study was designed to examine the role of phospholipase D (PLD) and its product, phosphatidic acid, in the intracellular signal transduction mechanisms that mediate induction of MMP-2 by laminin. Here we show that stimulation of tumor cells with laminin results in a time- and dose-dependent activation of PLD. Laminin-induced production of MMP-2 is attenuated by 1-butanol, a competitive substrate of PLD that reduces PLD-catalyzed production of PA. Moreover, phosphatidic acid itself can induce production of MMP-2 in metastatic tumor cells. MMP-2 can also be induced by exposing the cells to exogenous bacterial PLD. Elevated cellular phosphatidic acid induces MMP-2 in metastatic ras-transformed 3T3 fibroblasts but, like laminin, fails to do so in normal cells. These data indicate that laminin-induced activation of PLD and consequent generation of phosphatidic acid are involved in a signal propagation pathway leading to induction of MMP-2 and enhanced invasiveness of metastatic tumor cells.

Malignant transformation by H-ras results in aberrant regulation of ribonucleotide reductase gene expression by transforming growth factor-beta 1

Ribonucleotide reductase is a key rate-limiting and regulatory step in DNA synthesis and plays a crucial role in the coordination of DNA synthesis, DNA repair, and cell proliferation. The present study demonstrates a link between alterations in TGF-beta 1 regulation during malignant conversion and the expression of ribonucleotide reductase. H-ras-transformed mouse 10T1/2 cell lines exhibiting malignant potential were examined for possible TGF-beta 1-mediated alterations in ribonucleotide reductase expression. Selective induction of ribonucleotide reductase gene expression occurred, since only H-ras-transformed highly metastatic cells exhibited marked elevations in ribonucleotide reductase expression, whereas nontransformed normal 10T1/2 cells were unaffected by TGF-beta 1 treatment. These changes occurred without any detectable modifications in DNA synthesis rates, suggesting that these changes were regulated by a novel mechanism independent of the S-phase of the cell cycle. Furthermore, this TGF-beta 1-mediated regulation of ribonucleotide reductase expression was shown to occur through an autocrine mechanism. TGF-beta 1-modulated regulation of ribonucleotide reductase expression requires de novo protein synthesis and involves, at least in part, transcriptional and post-transcriptional events. Furthermore, evidence is presented to suggest a possible role for protein kinase C-mediated events, protein phosphatases, and G-protein-coupled events in the TGF-beta 1-mediated regulation of ribonucleotide reductase expression in H-ras-transformed malignant cells. TGF-beta 1 regulation of ribonucleotide reductase in highly malignant cells appears to be complex and multifaceted and constitutes an integral part of an altered growth regulatory program.

Quantitative distinction of cisplatin-sensitive and -resistant mouse fibrosarcoma cells grown in multicell tumor spheroids

As a suitable model to study the growth behavior and therapeutic response of drug-resistant and -sensitive cells in three-dimensional coculture we have established multicellular spheroids generated from both cisplatin-sensitive and -resistant cells of a murine fibrosarcoma cell line. A drug resistant clone was derived from the parent cisplatin-sensitive cells by intermittent drug exposure in vitro. As a prerequisite for analysis of differential growth and treatment response of spheroid subpopulations, two efficient methods to discriminate between the two morphologically indistinguishable subpopulations in mixed spheroids were established. In the cisplatin-resistant cell line chosen for the present study, resistance is mainly due to an increased cellular metallothionein content and is therefore associated with increased resistance to CdCl2. Exposure of colonies to high concentrations of CdCl2 thus allowed selective elimination of sensitive colonies. Permanent labeling of either resistant or sensitive cells was achieved by introduction of the Escherichia coli beta-galactosidase marker gene with a retroviral vector system. The transformation of an uncolored galactose derivative by this enzyme into an indigo stain allowed detection of cells carrying and expressing the marker gene. The marker gene and CdCl2 method led to identical results when used simultaneously to distinguish quantitatively between resistant and sensitive colonies grown from plated cells of untreated or irradiated mixed spheroids. The retroviral labeling method was also used successfully in the study of intact spheroids, showing that in 1:1 mixed spheroids, cisplatin-sensitive parent cells accumulate in the spheroid periphery, outgrowing resistant cells and displacing them into the metabolically restricted spheroid center. Only when sensitive and resistant cells are initially mixed at a ratio of 1:9 are the resulting spheroids composed of equal proportions of the 2 cell types throughout 10-20 days after spheroid initiation.

Superoxide dismutase (SOD) activity with Fe-chlorin e6-Na and suppression of malignant tumor growth in rats

Derivatives of porphyrin, specifically Fe-chlorin e6-Na (FeCNa), mimic superoxide dismutase (SOD). This SOD activity was determined by decrease in electron spin resonance (ESR) signals and increase in hydrogen peroxide (H2O2) as the intermediate of O2-. by the coloration using 4-aminoantipyrin. Chlorin e6-Na used for cancer photodynamic therapy (PDT)(1) does not show SOD mimicking activity. The specific activity of FeCNa, comparing with bovine RBC-SOD, was 1/7.5 as determined by ESR analysis. The iron element of Fe-chlorin e6-Na, being tightly encased in the molecule, did not participate in the Fenton reaction. The SOD mimetic activity of FeCNa was stable against physico-chemical treatment such as pH shock, heat and digestion by pronase. For cancer bearing rats with oxidative stress (OS), immediate relief of OS was possible by a single intraperitoneal injection of FeCNa and relief continued for 24 hours. The subsequent administration of FeCNa suppressed cancer growth in vivo.

A sensitive assay for the IFN-regulated 2-5A synthetase enzyme

2-5A synthetase is the central enzyme of the 2-5A system, an important mediator of interferon action. An assay capable of detecting low, yet biologically important levels of 2-5A synthetase enzyme activity is described. The purification of enzyme reaction products on SepPak C-18 cartridges resulted in a significant reduction in background, when a high specific activity substrate was used to label the 2-5A. Quantitation of labeled 2-5A by chromatography and scintillation counting provided a means of detecting femptomolar amounts of 2-5A. The combination of these procedures accounts for a 3-4 log increase in sensitivity over existing assays. This degree of sensitivity should permit a more accurate determination of the 2-5A synthetase activity in vivo leading to a better understanding of the role of the 2-5A system in virus infection and other cellular processes.

Okadaic acid-elicited transcriptional activation of collagenase gene expression in HT-1080 fibrosarcoma cells is mediated by JunB

Okadaic acid (OA) is a novel, non-phorbol ester-type tumor promoter, which is a specific inhibitor of protein phosphatases 1 and 2A. Treatment of human fibrosarcoma HT-1080 cells with OA resulted in induction of collagenase and stromelysin-1 mRNA levels, while mRNA levels for tissue inhibitor of metalloproteinases-1 were enhanced to a lesser extent. Induction of collagenase and stromelysin-1 mRNA levels was dependent on protein synthesis. Exposure of HT-1080 cells to OA resulted in marked and persistent induction of junB, junD, and c-fos mRNA levels up to 24 h, while c-jun mRNA levels were only slightly elevated. In transiently transfected HT-1080 cells, OA-elicited activation of a 3.8-kilobase collagenase promoter/reporter gene construct was entirely dependent on junB expression, as determined by cotransfection with a junB antisense expression construct. Overexpression of JunB in HT-1080 cells enhanced collagenase promoter activity by 10-fold, and OA augmented trans-activation of collagenase promoter by c-Jun and JunB. The results indicate that induction of collagenase gene expression by OA is mediated by enhanced JunB expression, as well as enhanced trans-activating capacity of AP-1 complexes containing c-Jun and JunB. These results also suggest that selective overexpression of junB may enhance invasive and metastatic potential of neoplastic cells.

Transfection of tissue transglutaminase into a highly malignant hamster fibrosarcoma leads to a reduced incidence of primary tumour growth

Reduced expression of the tissue transglutaminase in both murine and human tumours has been consistently associated with tumour growth and progression. To investigate the functional effects of transglutaminase expression we have transfected a constitutive human tissue transglutaminase expression construct into a highly malignant hamster fibrosarcoma cell line Met B. Met B clones expressing the exogenous tissue transglutaminase exhibited a reduced incidence of primary tumour formation and an increased adherence to tissue culture plastic and fibronectin coated surfaces when compared to transfected and non transfected control cells. Transglutaminase transfected clones exhibited no significant differences in their growth rates measured in vitro, cell morphology or levels of spontaneous apoptosis measured by the determination of detergent insoluble apoptotic envelopes. The data demonstrates a suppressive effect of tissue transglutaminase on tumour growth and confirms its importance in the phenotypic changes associated with the cancer process.