Human HT-1080 Fibrosarcoma Cell Lines Research Articles

Abstract 2135: Complex roles of discoidin domain receptors (DDRs) in tumor growth and experimental metastasis: role of collagen I in DDR-mediated tumor growth

Abstract DDR1 and DDR2 constitute a unique set of receptor tyrosine kinases that signal in response to collagen. Evidence indicates that DDRs play key roles in cancer progression. However, a comparison of the effects of DDR1 and DDR2 on tumor growth and metastasis within the same cellular context has not been done. To accomplish this goal, we developed a doxycycline (DOX) regulated system (Tet-Off) to express human DDR1b or DDR2 in the human HT1080 fibrosarcoma cell line. The cells were then examined for their ability to form subcutaneous (s.c.) tumors, or experimental lung metastases after intravenous (i.v.) injection in SCID mice. To induce or repress DDR expression in vivo, mice were fed a regular diet or a diet with DOX, respectively. Because collagen I (COL I) is a ligand for both DDR1 and DDR2, a set of mice were inoculated s.c. with HT1080 cells suspended in COL I with or without DDR induction in –DOX and +DOX mice, respectively. Growth of s.c. tumors was evaluated by measuring tumor volumes and lung metastases were quantitated by Alu qPCR and histological examination. In the absence of COL I, expression of either DDR1b or DDR2 had no impact on s.c. tumor growth rate, when compared to cells without DDR induction (+DOX). However, in the presence of COL I, tumor growth rates were significantly higher only in HT1080 cells with induced expression of DDR1b or DDR2 (p<0.001 for both), when compared to control cells inoculated with COL I into +DOX mice (no DDR induction). This suggests that a pro-oncogenic effect of DDR1b and DDR2 can be readily uncovered only in tumors growing within a COL I-rich environment. Because the Hippo tumor suppressor pathway has been shown to be regulated by extracellular matrix, homogenates of COL I tumors generated by cells with or without DDR induction were examined for levels and activation of Hippo pathway components. These analyses were consistent with Hippo pathway inactivation in tumors generated by DDR1b- and DDR2-expressing cells in a COL I matrix, consistent with their higher rate of tumor growth. Experimental metastasis assays revealed that induction of DDR2 expression had no impact on lung metastatic burden. In contrast, induction of DDR1b expression dramatically suppressed HT1080 lung metastasis formation, compared to control cells (no DDR1b induction). Collectively, these results suggest that: 1. Ectopic expression of DDRs in HT1080 cells accelerates tumor growth only when co-inoculated with COL I, consistent with a pro-tumorigenic effect of activated receptors within a collagen matrix. 2. A DDR/COL I axis supports HT1080 tumor growth, in part, by inactivation of the Hippo tumor suppressor pathway, suggesting that COL I-initiated DDR signaling regulates the Hippo pathway in vivo. 3. DDR1b, but not DDR2, is a potent suppressor of lung metastasis in the HT1080 model. Taken together, these studies provide novel insights into the complex roles of DDRs in cancer. Citation Format: Benjamin D. Wasinski, R. Daniel Bonfil, Anjum Sohail, Seong Ho Kim, Lisa Polin, Allen-Dexter Saliganan, Mohamad Bouhamdan, Sayed Nabi, Hyeong-Reh C. Kim, Marco Prunotto, Rafael A. Fridman. Complex roles of discoidin domain receptors (DDRs) in tumor growth and experimental metastasis: role of collagen I in DDR-mediated tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2135.

Target irradiation induced bystander effects between stem-like and non stem-like cancer cells

Tumors are heterogeneous in nature and consist of multiple cell types. Among them, cancer stem-like cells (CSCs) are suggested to be the principal cause of tumor metastasis, resistance and recurrence. Therefore, understanding the behavior of CSCs in direct and indirect irradiations is crucial for clinical radiotherapy. Here, the CSCs and their counterpart non stem-like cancer cells (NSCCs) in human HT1080 fibrosarcoma cell line were sorted and labeled, then the two cell subtypes were mixed together and chosen separately to be irradiated via a proton microbeam. The radiation-induced bystander effect (RIBE) between the CSCs and NSCCs was measured by imaging 53BP1 foci, a widely used indicator for DNA double strand break (DSB). CSCs were found to be less active than NSCCs in both the generation and the response of bystander signals. Moreover, the nitric oxide (NO) scavenger c-PTIO can effectively alleviate the bystander effect in bystander NSCCs but not in bystander CSCs, indicating a difference of the two cell subtypes in NO signal response. To our knowledge, this is the first report shedding light on the RIBE between CSCs and NSCCs, which might contribute to a further understanding of the out-of-field effect in cancer radiotherapy.

Abstract 5112: Traditional Chinese medicine formula LQ inhibits spontaneous and cyclophosphamide-enhanced metastasis.

Abstract TCM (Traditional Chinese Medicine) formula LQ, an herbal cocktail, has shown anti-metastasis and anti-tumor efficacy without overt side-effects. In the present study, the human HT1080 fibrosarcoma cell line was labeled with both red fluorescent protein (RFP) in the cytoplasm and green fluorescent protein (GFP) in the nucleus. Dual-color HT1080 cells were injected into the footpad of mice following LQ treatment. Dual-color HT1080 cells were also injected into epigastric cranialis vein of the mice pre-treated with cyclophosphamide (CYC) or a combination of CYC and LQ. The efficacy was monitored through dynamic subcellular imaging of trafficking of cancer cells in lymph nodes and blood vessels in live mice. LQ significantly inhibited HT1080 spontaneous metastases to their local lymph nodes in the foot pad injection model. In the control group, 100% of mice had lymph node metastasis, compared to 12.5% of the mice in the LQ group. LQ also inhibited cyclophosphamide-enhanced experimental metastasis in the epigastric cranialis vein injection model. LQ prolonged the overall survival of mice in the spontaneous lymph node metastatic model. LQ therefore shows promise as an antimetastatic agent. Citation Format: Lei Zhang, Chengyu Wu, Yong Zhang, Robert M. Hoffman. Traditional Chinese medicine formula LQ inhibits spontaneous and cyclophosphamide-enhanced metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5112. doi:10.1158/1538-7445.AM2013-5112

Epigenetic regulation of proMMP-1 expression in the HT1080 human fibrosarcoma cell line

The matrix metalloproteinase (MMP) family members play an important role in various physiological and pathological processes. Although MMP-1 (collagenase-1) has been shown to be involved in tumor invasiveness, the regulation of its expression is still not fully elucidated and could implicate epigenetic mechanisms. The aim of this study was to analyze the effects of the Histone Deacetylase Inhibitor (HDI) trichostatin A (TSA) and the inhibitor of DNA methylation 5-aza-2'-deoxycytidine (5-azadC) on the proMMP-1 expression in the human HT1080 fibrosarcoma cell line. Real-time RT-PCR revealed that 5-azadC or 5-azadC + TSA but not TSA alone, despite global histone H4 hyperacetylation, increased proMMP-1 mRNA levels. This transcription activation was correlated with chromatin decondensation determined by nuclear texture image analysis technique. Western blot analysis of cell culture conditioned media revealed a significant increase in proMMP-1 secretion after 5-azadC or 5-azadC + TSA treatment compared to untreated cells. These results suggested that epigenetic mechanisms could be involved in proMMP-1 gene expression including chromatin supra-organization changes. Indeed, although the proMMP-1 gene promoter does not appear to contain CpG islands, its expression can be induced by the demethylating agent 5-azadC. Further experiments revealed that inhibition of protein neosynthesis by cycloheximide decreased 5-azadC-induced proMMP-1 mRNA, suggesting that epigenetically regulated intermediate molecules could be involved in proMMP-1 expression regulation in these cells.

Inhibitory effect of caffeic acid on cancer cell proliferation by oxidative mechanism in human HT-1080 fibrosarcoma cell line

Caffeic acid (3,4-dihydroxy cinnamic acid) (CA) is naturally found in fruits, vegetables, olive oil, and coffee. This study was undertaken to evaluate the anticancer effect of caffeic acid on HT-1080 human fibrosarcoma cell line. The antiproliferative effect of caffeic acid was determined by MTT assay, and the oxidative stress was determined by lipid peroxidation, changes in the enzymatic, and non-enzymatic antioxidant status. To understand the mode of antiproliferative effect of CA, the authors observed intracellular ROS levels by DCFH-DA method, mitochondrial membrane potential alterations by Rh-123 staining, oxidative DNA damage by comet assay, and apoptotic morphological changes by AO/EtBr-staining method. The results show that caffeic acid enhances lipid peroxidative markers such as TBARS, CD, and LHP in HT-1080 cell line. Caffeic acid enhances the ROS levels, which is evidenced by the increased DCF fluorescence. Further, caffeic acid treatment altered the mitochondrial membrane potential in HT-1080 cells. Similarly, the authors observed increased oxidative DNA damage (% Tail DNA, % Tail length, Tail moment, and olive tail moment), and apoptotic morphological changes in caffeic acid-treated groups. These data suggest that caffeic acid exhibits potent anticancer effect in HT-1080 cell line, and that it may be used as an anticancer agent.

Canthin-6-one Alkaloids and a Tirucallanoid from Eurycoma longifolia and Their Cytotoxic Activity against a Human HT-1080 Fibrosarcoma Cell Line

Phytochemical investigation of the stems of Eurycoma longifolia Jack led to the isolation of two new canthin-6-one alkaloids, 4,9-dimethoxycanthin-6-one (1) and 10-hydroxy-11-methoxycanthin-6-one (2), and a new tirucallane-type triterpenoid, 23,24,25-trihydroxytirucall-7-en-3,6-dione (3), along with 37 known compounds. Among these, an oxasqualenoid (4) was isolated as a natural product for the first time. The structures of the isolates were elucidated by spectroscopic and mass spectrometric means. All the isolates were evaluated for their cytotoxic activity against a HT-1080 human fibrosarcoma cell line. Among them, 9,10-dimethoxycanthin-6-one (14, IC50 = 5.0 microM), 10-hydroxy-9-methoxycanthin-6-one (15, IC50 = 7.2 microM), dihydroniloticin (18, IC50 = 8.2 microM), and 14-deacetyleurylene (34, IC50 = 3.2 microM) displayed stronger activity than the positive control 5-FU (IC50 = 9.2 microM).

Tumor cells expressing tissue factor influence the migration of smooth muscle cells in a catalytic activity-dependent way

The expression of tissue factor (TF) in tumors reportedly exacerbates the aggressiveness of several types of cancers. The shedding of TF-containing membrane particles is believed to influence the ability of tumors to expand and metastasize, and these microparticles may also be harmful in the onset of disseminated intravascular coagulation in specific cancers. Furthermore, the intracellular signaling that is elicited after the formation of the TF / coagulation factor VIIa complex at the cell membrane modulates the activity of adhesion molecules and mitogen-activated protein (MAP) kinases. To evaluate whether TF overexpression in tumor cells modulates its shedding and neighboring stromal cells by its catalytic or intracellular activity, TF-GFP (green fluorescent protein) and a tailless form (TFDeltaC-GFP) were stably expressed in the rat Morris hepatoma and human HT1080 fibrosarcoma cell lines. Both TF proteins were efficiently produced by tumor cells and functionally active, and their clotting activity could be blocked by the active site-inhibited factor VIIa (ASIS). TF-expressing tumorigenic cells produced a soluble factor that increased the migration of arterial smooth muscle cells in vitro. This effect was abrogated by ASIS and the PAR-1 receptor antagonist ATAP-2, showing that it is dependent on the proteolytic activity of the TF ligand factor VIIa and the thrombin-activated cell membrane receptor. We propose that TF-containing microparticles that are released in the culture medium by tumor cells influence the migratory behavior of neighboring stromal cells, thus aiding the cancer cell's tumorigenic potential.

Calcium salicylate‐mediated apoptosis in human HT‐1080 fibrosarcoma cells

Salicylates are novel biologically active compounds that exhibit multiple therapeutic activities. The anti-cancer effectiveness of calcium salicylate has been investigated on human HT-1080 fibrosarcoma cell lines at relatively low concentrations (predominantly 0.4 mM) compared to those previously reported. Although low calcium salicylate concentrations did not retard tumour growth progression significantly, as measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and time-lapse assays, its cytotoxic characteristics were proven to be prominent by various morphological and immunocytological techniques. The results here demonstrate evidence for approximately 25% apoptosis after treatment with calcium salicylate, which up-regulatd the expression of p53, p21 and Bax, and down-regulated Bcl-2 in HT-1080 cells.

Constituents of the Vietnamese medicinal plant Streptocaulon juventas and their antiproliferative activity against the human HT-1080 fibrosarcoma cell line.

The methanolic extract of roots of Streptocaulon juventas, having shown strong antiproliferative activity against the highly metastatic human HT-1080 fibrosarcoma cell line, was subjected to activity-guided isolation to yield 16 cardenolides including five new ones, acovenosigenin A 3-O-beta-digitoxopyranoside (1), digitoxigenin gentiobioside (2), digitoxigenin 3-O-[O-beta-glucopyranosyl-(1-->6)-O-beta-glucopyranosyl-(1-->4)-3-O-acetyl-beta-digitoxopyranoside] (3), digitoxigenin 3-O-[O-beta-glucopyranosyl-(1-->6)-O-beta-glucopyranosyl-(1-->4)-O-beta-digitalopyranosyl-(1-->4)-beta-cymaropyranoside] (4), and periplogenin 3-O-(4-O-beta-glucopyranosyl-beta-digitalopyranoside) (5), and two new hemiterpenoids, (4R)-4-hydroxy-3-isopropylpentyl beta-rutinoside (6) and (R)-2-ethyl-3-methylbutyl beta-rutinoside (7), together with two known phenylpropanoids and a known phenylethanoid. The isolated cardenolides strongly inhibited the proliferation of the HT-1080 cell line (IC(50) values, 54-1600 nM).

Three new C-14 oxygenated taxanes from the wood of Taxus yunnanensis.

Three new C-14 oxygenated taxane-type diterpenes, hongdoushans A-C (1-3), were isolated from the wood of Taxus yunnanensis together with four known diterpenes and two lignans. The absolute stereochemistry of the 2-methylbutyryloxy group attached at C-14 of the taxane skeleton was determined to be S by GC analysis of the methyl ester of 2-methylbutyric acid obtained after alkaline hydrolysis of 1 and 4 followed by treatment with CH(2)N(2). The complete stereostructure of the known compound 2alpha,5alpha,10beta-triacetoxy-14beta-[(S)-2-methylbutyryloxy]-4(20),11-taxadiene (4) was established for the first time. The isolates obtained were evaluated for their antiproliferative activity toward murine colon 26-L5 carcinoma and human HT-1080 fibrosarcoma cell lines.

Four highly oxygenated isopimarane-type diterpenes of Orthosiphon stamineus.

Four highly oxygenated isopimarane-type diterpenes, named orthosiphols O, P and Q and nororthosiphonolide A, have been isolated from the aerial parts of Orthosiphon stamineus from Myanmar, together with three known diterpenes, orthosiphols D and E and orthosiphonone A. Their structures were determined on the basis of extensive spectral analysis. All the isolated compounds displayed mild antiproliferative activities against highly liver metastatic colon 26-L5 carcinoma and human HT-1080 fibrosarcoma cell lines.

Five novel highly oxygenated diterpenes of Orthosiphon stamineus from Myanmar.

Five novel highly oxygenated diterpenes, orthosiphols K (1), L (2), M (3), and N (4) and norstaminone A (5), were isolated from the aerial part of Orthosiphon stamineus, together with three known diterpenes, orthosiphols A (6) and B (7) and neoorthosiphol A (8). Orthosiphol L (2) is an isopimarane-type diterpene with a hydroxyl group at C-12, which supports the biogenesis of staminane-type diterpenes, i.e., migration of a vinylic group from C-13 of isopimarane to C-12. Norstaminone A (5) has a staminane carbon framework and supports the biosynthetic pathway from staminols to norstaminols via staminolactones. All the isolated compounds showed mild to weak antiproliferative activities toward highly liver metastatic colon 26-L5 carcinoma and human HT-1080 fibrosarcoma cell lines.

Regulation of matrix metalloproteinase-2 (gelatinase A, MMP-2), membrane-type matrix metalloproteinase-1 (MT1-MMP) and tissue inhibitor of metalloproteinases-2 (TIMP-2) expression by elastin-derived peptides in human HT-1080 fibrosarcoma cell line.

Soluble kappa-elastin peptides were shown to stimulate the expression of MMP-2 (but not MMP-9) by human fibrosarcoma HT-1080 cells, both at the protein and mRNA levels; maximal effect being observed at a concentration of 25 microg/ml of kappa-elastin. The stimulatory effect could be reproduced using Val-Gly-Val-Ala-Pro-Gly (VGVAPG) peptide, an elastin-derived hydrophobic hexapeptide which represented the elastin receptor binding sequence of tropoelastin. Furthermore, treatment of cells with lactose (30 mM), which dissociated 67-kDa elastin binding protein (EBP) from cell surfaces, completely abolished this effect, suggesting that the elastin receptor could mediate such a response. Using a specific monoclonal antibody, 67-kDa EBP was detected in HT-1080 membrane preparations by Western immunoblotting. Following treatment with 25 microg/ml kappa-elastin or 200 microg/ml VGVAPG, increased levels of the active 62-kDa form of MMP-2 were found in HT-1080 cell extracts. Stimulation of MT1-MMP mRNA expression by treatment with elastin-derived peptides (EDPs) was shown by competitive polymerase chain reaction (PCR). A reverse zymography analysis revealed that EDPs also stimulated TIMP-2 (but not TIMP-1) production by HT-1080 cells. Competitive PCR confirmed increased TIMP-2 mRNA expression by such treatment. These results suggest that occupancy of the 67-kDa elastin receptor by elastin-derived peptides enhanced both expression and activation of proMMP-2 and consequently, could promote the invasive/metastatic ability of tumor cells expressing this receptor.

Effect of cyclin D1 overexpression on drug sensitivity in a human fibrosarcoma cell line.

Alterations in the expression of genes that control the cell cycle may be of critical importance in determining the sensitivity of cells and tumors to drugs (chemosensitivity) and radiation. Mutations and deletions of the p53 tumor suppressor gene in cell lines and tumors are associated with resistance to a variety of DNA-damaging agents. The effects of alterations in the cyclin genes and their products on drug action have not been studied. One of these genes, cyclin D1, is expressed in early G1 phase, and its protein product, together with the cyclin-dependent kinases CDK4 and CDK6, mediates the phosphorylation and functional inactivation of the retinoblastoma protein (pRb). Elevated levels of expression of cyclin D1 protein have been found in a variety of cancers, including breast cancer, head and neck cancer, non-small-cell lung cancer, and mantle cell lymphomas. This study was conducted to investigate the effect of increased expression of cyclin D1 protein on the chemosensitivity profile of a human fibrosarcoma cell line. Expression plasmids containing either the neomycin-resistance gene and the complementary DNA sequence encoding human cyclin D1 or the neomycin-resistance gene only (control) were transfected by lipofection into the human HT1080 fibrosarcoma cell line, and cell colonies resistant to the antibiotic neomycin (G418) were isolated. Cyclin D1 messenger RNA (mRNA) and protein levels were measured by ribonuclease protection and western blot analyses, respectively. Dihydrofolate reductase (DHFR) mRNA and protein levels were measured by northern blot and western blot analyses, respectively. The phosphorylation status of pRb was assessed by western blot analysis. Cell cycle analysis was performed by use of the technique of fluorescence-activated cell sorting. Cytotoxicity assays were carried out by use of the sulforhodamine blue assay. Of the 16 cyclin D1-transfected cell clones that were isolated, four were randomly selected for further study. Two cell clones expressed high levels of cyclin D1 mRNA and protein as compared with control cells transfected with plasmids containing the neomycin-resistance gene only. A relative increase in the phosphorylated form of pRb in cells expressing high versus low levels of cyclin D1 was also revealed by western blot analysis. There was an increased fraction of cells in the S and G2 phases of the cell cycle among cells expressing higher levels of cyclin D1. Transfectants with increased cyclin D1 expression also had increased DHFR mRNA and protein expression. Cytotoxicity assays revealed a statistically significant (P < .01) increase in resistance to methotrexate in cells expressing high levels of cyclin D1 compared with cells expressing lower levels. There was no difference in resistance to doxorubicin, paclitaxel (Taxol), and cytarabine. Alterations in the expression of cyclin D1 led to altered cell cycle distribution in a human sarcoma cell line. The associated increase in DHFR expression resulted in increased resistance to methotrexate but had no effect on other classes of anticancer agents. These results indicate that alterations in cell cycle genes may differ in their effects on cytotoxicity. It will be important to determine the effects of alterations of other cell cycle regulatory genes on the responses of cells to specific classes of drugs. Tumors with overexpression of cyclin D1 may be relatively refractory to methotrexate treatment.

Mycobacterial lipoarabinomannan recognition requires a receptor that shares components of the endotoxin signaling system.

Abstract Phagocytic leukocytes respond to a variety of bacterial products including Gram-negative bacterial LPS and mycobacterial lipoarabinomannan (LAM). Anti-CD14 mAbs have been shown to block LPS and LAM activation of myeloid cells, suggesting that CD14 is required for cellular recognition of both ligands. Activation of undifferentiated promonomyelocytic THP-1 cells with LAM or LPS under serum-free conditions was enhanced in the presence of recombinant soluble CD14 (rsCD14). LPS binding protein (LBP), which is present in normal serum, further enhanced the sensitivity of undifferentiated THP-1 cells to both ligands even in the absence of rsCD14. Although CD14-transfected Chinese hamster ovary and human HT1080 fibrosarcoma cell lines can be activated by LPS, neither cell line was activated by LAM. Furthermore, U373 astrocytoma cells, which respond to LPS using sCD14 and LBP, failed to be activated by LAM in the presence of rsCD14 and rLBP. We then tested the effects of lipid IVA and Rhodobacter sphaeroides lipid A, compounds that function as endotoxin inhibitors in human cells by interacting with a molecule thought to be a CD14-dependent LPS signal transducer. Both lipid IVA and R. sphaeroides lipid A inhibited the effects of LPS and LAM in THP-1 cells. Thus, the LPS and LAM receptors share CD14, LBP, and a putative endotoxin antagonist-inhibitable signal transducing component. However, the LAM signaling system appears to require an additional receptor component whose expression is restricted to cells of hemopoietic origin.

Nuclear c-Myc Plays an Important Role in the Cytotoxicity of Tumor Necrosis Factor Alpha in Tumor Cells

The phosphoprotein c-Myc has the potential to kill cells by apoptosis. To investigate whether c-Myc is involved in tumor necrosis factor alpha (TNF-alpha)-mediated cell killing, we have examined two HeLa cell lines (D98 and H21) which show dramatic differences in their susceptibilities to TNF-alpha cytotoxicity. Northern (RNA) blot analyses showed that there were no significant differences between these cell lines in basal or TNF-alpha-induced mRNA expression for a variety of proteins, including manganous superoxide dismutase, A20 zinc finger protein, plasminogen activator inhibitor type 2, and hsp70, all of which are known to influence the susceptibility of certain cells to TNF-alpha killing. On the other hand, there was a dramatic increase in c-Myc mRNA expression in TNF-alpha-sensitive D98 cells, but not in TNF-alpha-resistant H21 cells, which was only observed when the cells were treated with cycloheximide. Western blot (immunoblot) analyses revealed that even in the absence of TNF-alpha or cycloheximide, c-Myc was detectable only in nuclear extracts of TNF-alpha-sensitive D98 cells, implying a role for preexisting c-Myc in TNF-alpha killing. In support of this interpretation, a c-myc antisense oligonucleotide specifically inhibited the TNF-alpha killing of D98 cells, provided that the oligonucleotide was added 6 h prior to TNF-alpha treatment. Either dexamethasone treatment or transient expression of c-myc antisense cDNA fragments decreased nuclear c-Myc in D98 cells and rendered the cells more resistant to TNF-alpha cytotoxicity. Nuclear c-Myc was also detectable in a TNF-alpha-sensitive human HT-1080 fibrosarcoma cell line, but it was undetectable in a derivative of HT-1080 (SS-HT-1080) known to be resistant to TNF-alpha killing because of overexpression of plasminogen activator inhibitor type 2. HT-1080 cells transfected with antisense c-myc cDNA had significantly less nuclear c-Myc and were resistant to TNF-alpha cytotoxicity. Together, these data indicate that a nuclear transcription factor, c-Myc, plays an important role in sensitizing two different tumor cell types to TNF-alpha cytotoxicity.

Nuclear c-Myc plays an important role in the cytotoxicity of tumor necrosis factor alpha in tumor cells.

The phosphoprotein c-Myc has the potential to kill cells by apoptosis. To investigate whether c-Myc is involved in tumor necrosis factor alpha (TNF-alpha)-mediated cell killing, we have examined two HeLa cell lines (D98 and H21) which show dramatic differences in their susceptibilities to TNF-alpha cytotoxicity. Northern (RNA) blot analyses showed that there were no significant differences between these cell lines in basal or TNF-alpha-induced mRNA expression for a variety of proteins, including manganous superoxide dismutase, A20 zinc finger protein, plasminogen activator inhibitor type 2, and hsp70, all of which are known to influence the susceptibility of certain cells to TNF-alpha killing. On the other hand, there was a dramatic increase in c-Myc mRNA expression in TNF-alpha-sensitive D98 cells, but not in TNF-alpha-resistant H21 cells, which was only observed when the cells were treated with cycloheximide. Western blot (immunoblot) analyses revealed that even in the absence of TNF-alpha or cycloheximide, c-Myc was detectable only in nuclear extracts of TNF-alpha-sensitive D98 cells, implying a role for preexisting c-Myc in TNF-alpha killing. In support of this interpretation, a c-myc antisense oligonucleotide specifically inhibited the TNF-alpha killing of D98 cells, provided that the oligonucleotide was added 6 h prior to TNF-alpha treatment. Either dexamethasone treatment or transient expression of c-myc antisense cDNA fragments decreased nuclear c-Myc in D98 cells and rendered the cells more resistant to TNF-alpha cytotoxicity. Nuclear c-Myc was also detectable in a TNF-alpha-sensitive human HT-1080 fibrosarcoma cell line, but it was undetectable in a derivative of HT-1080 (SS-HT-1080) known to be resistant to TNF-alpha killing because of overexpression of plasminogen activator inhibitor type 2. HT-1080 cells transfected with antisense c-myc cDNA had significantly less nuclear c-Myc and were resistant to TNF-alpha cytotoxicity. Together, these data indicate that a nuclear transcription factor, c-Myc, plays an important role in sensitizing two different tumor cell types to TNF-alpha cytotoxicity.

Measurement of plasminogen activator activity from human fibrosarcoma cells by a new microassay.

Elevated levels of plasminogen activator (PA) activity have been correlated with neoplasia and may have an important role in tumor-cell invasion and metastasis. We have developed a new caseinolytic assay that uses an immunochemical approach to measure the activity of PA elaborated by malignant tumor cells. The highly sensitive assay consists in incubating a source of PA (viable tumor cells, cell extracts, or conditioned medium) with purified plasminogen in microtiter plates precoated with a suitable protein substrate such as casein. Clearance of the immobilized protein substrate by PA-generated plasmin is then measured by a technique based on the enzyme-linked immunosorbent assay. In experiments using urokinase as a source of PA, the assay displayed near linearity over several log units of urokinase activity and could detect as little as 10(-2) Ploug units of PA activity. Besides successfully measuring PA activity produced by the human HT 1080 fibrosarcoma cell line, the assay permitted detection of significant plasminogen-independent proteolytic activity generated by intact tumor cells cultured in direct contact with immobilized protein substrates.