Staurosporine induces the cell surface expression of both forms of human tumor necrosis factor receptors on myeloid and epithelial cells and modulates ligand-induced cellular response

Downregulation of uridine-cytidine kinase like-1 decreases proliferation and enhances tumor susceptibility to lysis by apoptotic agents and natural killer cells

Natural killer (NK) cells target and kill tumor cells by direct anti-tumor cytotoxicity. NK lytic-associated molecule (NKLAM) is a protein involved in this cytolytic function. Acting as an E3 ubiquitin ligase, NKLAM binds to and ubiquitinates a novel protein, uridine-cytidine kinase like-1 (UCKL-1), targeting it for degradation. However, UCKL-1's function in tumor cell survival and NK cell cytotoxicity is unknown. UCKL-1's homology to uridine kinases and over expression in tumor cells suggests a role for UCKL-1 in tumor growth and/or survival. We propose that NKLAM and UCKL-1 interact in the tumor cell, where degradation of UCKL-1 leads to increased tumor cell apoptosis. Here we use RNA interference to downregulate UCKL-1 expression in K562 erythroleukemia cells. It was seen that downregulation of UCKL-1 initiated apoptosis and slowed the cell cycle, resulting in lower growth in the small interfering UCKL-1 RNA treated K562 cell culture. In addition, the chemotherapeutic agent staurosporine was seen to be more effective in inducing cell death by apoptosis in UCKL-1 depleted K562 cells compared with controls. We also found that UCKL-1 depleted K562 cells were more susceptible to NK mediated cytolysis than controls. These results indicate a role for UCKL-1 in tumor cell survival and suggest possible therapeutic potential of UCKL-1 inhibitors in cancer treatment.

Interleukin-1beta up-regulates tumor necrosis factor receptors in the mouse airways

Cytokines like interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha), released during the inflammatory process, play important roles in the development of airway hyperresponsiveness. The effects of these cytokines are mediated by cell surface receptors, specific for each cytokine. The expression of cytokine receptors is a dynamic process, where receptors can be up- or down-regulated in response to changes in the environment. One such environmental factor is the presence of cytokines per se. The present study was designed to evaluate the effects of IL-1beta on the expression of its corresponding receptor IL-1 RI, as well as on the closely related TNFalpha receptors TNF RI and TNF RII in airways using a mouse organ culture assay and intranasal inoculation model. Immunohistochemical staining was used to quantify expressional differences between fresh and cultured tracheal segments. In the fresh, uncultured, segments, IL-1 RI and TNF RI were seen in the epithelial layer and TNF RI in the smooth muscle layer. After 4 days of culture, the expression of TNF RI decreased in the epithelial layer, whereas the corresponding expression of IL-1 RI and TNF RI in the smooth muscle remained unchanged. When culture was performed in the presence of IL-1beta, the expression of IL-1 RI and TNF RI in the epithelial cells and TNF RI in the smooth muscle cells increased. TNF RII was not detected in either fresh or cultured trachea, but after treatment with IL-1beta an expression was found in both the epithelial layer and in the smooth muscle cells. The IL-1beta-induced increased expression, on TNF RI and TNF RII in the smooth muscle ex vivo and in the lung parenchyma after intranasal challenge in vivo, was verified at the mRNA level using real-time RT PCR. To summarize, presence of IL-1beta increases the expression of IL-1 R1 and TNF RI and induces expression of TNF RII in the airway wall. It is not inconceivable that these alterations of the IL-1 and TNF receptors may have important functional implications for the development of hyperresponsiveness in inflammatory airway diseases like asthma.

TNF receptor-associated factor 6-dependent CD40 signaling primes macrophages to acquire antimicrobial activity in response to TNF-alpha

IFN-gamma is considered an essential stimulus that allows macrophages to acquire activity against intracellular pathogens in response to a second signal such as TNF-alpha. However, protection against important pathogens can take place in the absence of IFN-gamma through mechanisms that are still dependent on TNF-alpha. Engagement of CD40 modulates antimicrobial activity in macrophages. However, it is not known whether CD40 can replace IFN-gamma as priming signal for induction of this response. We show that CD40 primes mouse macrophages to acquire antimicrobial activity in response to TNF-alpha. The effect of CD40 was not caused by modulation of IL-10 and TGF-beta production or TNFR expression and did not require IFN-alphabeta signaling. Induction of antimicrobial activity required cooperation between TNFR-associated factor 6-dependent CD40 signaling and TNFR2. These results support a paradigm where TNFR-associated factor 6 signaling downstream of CD40 alters the pattern of response of macrophages to TNF-alpha leading to induction of antimicrobial activity.

HIV type 1 Tat inhibits tumor necrosis factor alpha-induced repression of tumor necrosis factor receptor p55 and amplifies tumor necrosis factor alpha activity in stably tat-transfected HeLa Cells

The human immunodeficiency virus type 1 (HIV-1) Tat protein is a key regulatory protein in the HIV-1 replication cycle. Tat interacts with cellular transcriptional factors and cytokines, such as tumor necrosis factor (TNF-alpha), and alters the expression of a variety of genes in HIV-1-infected and noninfected cells. To further elucidate the mechanisms by which HIV-1 Tat amplifies the activity of TNF-alpha, we transfected the HIV-1 tat gene into an epithelial (HeLa) cell line. We observed that Tat-expressing cells had increased NF-kappa B-dependent trans-activational activity due to enhanced NF-kappa B--DNA binding in response to TNF-alpha treatment. Tumor necrosis factor receptor (TNFR) p55 was the prominent receptor, as neutralizing antibodies to TNFR p55, but not to TNFR p75, blocked TNF-alpha-mediated NF-kappa B activation. Furthermore, tat-transfected cells were more sensitive to TNF-alpha-induced cytotoxicity and only the neutralizing antibodies to TNFR p55 completely protected the cells. To determine whether TNFR p55 was involved in amplification of cellular response to TNF-alpha by HIV-1 Tat, we investigated the effect of TNF-alpha on TNFR p55 expression in the tat-transfected cells. TNF-alpha treatment resulted in a reduction in both TNFR p55 mRNA and protein levels in the control cells but not in the tat-transfected cells as determined with Northern blot and Western blot analyses, respectively. Our results indicate that HIV-1 Tat may inhibit TNF-alpha-induced repression of TNFR p55 and thereby amplify TNF-alpha activity in these stably transfected cells.

Regulation of PDGFR-alpha in rat pulmonary myofibroblasts by staurosporine

Upregulation of the platelet-derived growth factor (PDGF) receptor-alpha (PDGFR-alpha) is a mechanism of myofibroblast hyperplasia during pulmonary fibrosis. We previously identified interleukin (IL)-1beta as a major inducer of the PDGFR-alpha in rat pulmonary myofibroblasts in vitro. In this study, we report that staurosporine, a broad-spectrum kinase inhibitor, upregulates PDGFR-alpha gene expression and protein. A variety of other kinase inhibitors did not induce PDGFR-alpha expression. Staurosporine did not act via an IL-1beta autocrine loop because the IL-1 receptor antagonist protein did not block staurosporine-induced PDGFR-alpha expression. Furthermore, staurosporine did not activate a variety of signaling molecules that were activated by IL-1beta, including nuclear factor-kappaB, extracellular signal-regulated kinase, and c-Jun NH2-terminal kinase. However, both staurosporine- and IL-1beta-induced phosphorylation of p38 mitogen-activated protein kinase and upregulation of PDGFR-alpha by these two agents was inhibited by the p38 inhibitor SB-203580. Finally, staurosporine inhibited basal and PDGF-stimulated mitogenesis over the same concentration range that induced PDGFR-alpha expression. Collectively, these data demonstrate that staurosporine is a useful tool for elucidating the signaling mechanisms that regulate PDGFR expression in lung connective tissue cells and possibly for evaluating the role of the PDGFR-alpha as a growth arrest-specific gene.

The shedding of membrane-anchored heparin-binding epidermal-like growth factor is regulated by the Raf/mitogen-activated protein kinase cascade and by cell adhesion and spreading

Heparin-binding epidermal-like growth factor (HB-EGF) is synthesized as a transmembrane precursor (HB-EGF(TM)). The addition of phorbol ester (PMA, phorbol 12-myristate 13-acetate) to cells expressing HB-EGF(TM) results in the metalloproteinase-dependent release (shedding) of soluble HB-EGF. To analyze mechanisms that regulate HB-EGF shedding, a stable cell line was established expressing HB-EGF(TM) in which the ectodomain and the cytoplasmic tail were tagged with hemagglutinin (HA) and Myc epitopes, respectively (HB-EGF(TM)HA/Myc). HB-EGF(TM)HA/Myc cleavage was followed by the appearance of soluble HB-EGFHA in conditioned medium, the loss of biotinylated cell-surface HB-EGF(TM)HA/Myc, and the appearance of a Myc-tagged cytoplasmic tail fragment in cell lysates. By using this approach, several novel metalloproteinase-dependent regulators of HB-EGF(TM) shedding were identified as follows. (i) HB-EGF(TM)HA/Myc shedding induced by PMA was blocked by the mitogen-activated protein (MAP) kinase kinase inhibitor, PD98059. PMA activated MAP kinase within 5 min, but HB-EGF(TM)HA/Myc shedding did not occur until 20 min, suggesting that MAP kinase activation was a necessary step in the pathway of PMA-induced HB-EGF(TM) cleavage. (ii) Activation of an inducible Raf-1 kinase, DeltaRaf-1:estrogen receptor, resulted in a rapid MAP kinase activation within 10 min and shedding of HB-EGF(TM)HA/Myc within 20-40 min. (iii) Serum induced MAP kinase activation and HB-EGF(TM)HA/Myc shedding that were inhibited by PD98059. (iv) Whereas PMA induced HB-EGF(TM)HA/Myc shedding in attached cells, no shedding occurred when the cells were placed in suspension. Shedding was fully restored shortly after cells were allowed to spread on fibronectin, and the extent of PMA-induced shedding increased with the extent of cell spreading. PMA induced the same level of MAP kinase activation whether the cells were attached or in suspension suggesting that although MAP kinase activation might be necessary for shedding, it was not sufficient. Taken together, these results suggest that there are two components of cell regulation that contribute to the shedding process, not previously recognized, the Raf-1/MAP kinase signal transduction pathway and cell adhesion and spreading.

Differential regulation of eotaxin expression by TNF-alpha and PMA in human monocytic U-937 cells

Regulation of eotaxin expression was investigated in U-937 cells, a human monocyte-like cell line. Eotaxin mRNA was induced by tumor necrosis factor-alpha (TNF-alpha; 0.1-100 ng/ml) and phorbol 12-myristate 13-acetate (PMA; 0.01-1 microM). PMA-induced eotaxin mRNA expression was of greater magnitude and was maximal at a later time point than TNF-alpha-induced expression (16 h vs. 2 h after stimulation), which was consistent with eotaxin protein expression detected by immunocytochemistry. Dexamethasone (0.01-10 microM) decreased eotaxin mRNA expression in both TNF-alpha- and PMA-stimulated U-937 cells. PMA-induced eotaxin mRNA expression was inhibited by cycloheximide (10 microg/ml), whereas TNF-alpha-induced expression was not. The protein kinase C (PKC) inhibitor staurosporine (10-50 nM) inhibited PMA-induced eotaxin mRNA expression, whereas TNF-alpha-induced expression was enhanced by this reagent. These results suggest that eotaxin expression can be induced by more than one mechanism: the PMA-triggered pathway is mediated by PKC activation and requires new protein synthesis, whereas the TNF-alpha-triggered pathway is independent of PKC and protein synthesis. TNF-alpha- and PMA-induced pathways are both associated with nuclear factor-kappaB, because its binding activity was enhanced in the presence of these stimuli, and both pathways were limited by its inhibitor, diethyldithiocarbamate.

Overexpression of the p80 TNF Receptor Leads to TNF-Dependent Apoptosis, Nuclear Factor-κB Activation, and c-Jun Kinase Activation

Because they have distinct intracellular domains, it has been proposed that the p60 and p80 forms of the TNF receptor mediate different signals. Several signaling proteins have been isolated that associate with either the p60 or the p80 receptor. By using TNF muteins specific to the p60 and p80 receptors, we have previously shown that cytotoxicity and nuclear factor-κB (NF-κB) activation are mediated through the p60 form of the endogenous receptor. What signals are mediated through the p80 receptor is less clear. This study was an effort to answer that question. HeLa cells, which express only p60 receptors, were transfected with p80 receptor cDNA and then examined for apoptosis, NF-κB activation, and c-Jun kinase activation induced by TNF and by p60 or p80 receptor-specific muteins. The p80 mutein, like TNF and the p60 mutein, induced apoptosis and activation of NF-κB and c-Jun kinase in cells overexpressing recombinant p80 receptor but had no effect on cells expressing a high level of endogenous p80 receptor. The apoptosis mediated through the p60 receptor was also potentiated after overexpression of the p80 receptor, suggesting a synergistic relationship between the two receptors. Interestingly, Abs to the p80 receptor blocked apoptosis induced by all ligands but by itself activated NF-κB in the p80-transfected cells. Overall, our results show that the p80 receptor, which lacks the death domain, mediated apoptosis, NF-κB activation, and c-Jun kinase activation, but only when it was overexpressed, whereas endogenous p60 receptor mediated similar signals without overexpression.

The involvement of novel protein kinase C isozymes in influencing sensitivity of breast cancer MCF-7 cells to tumor necrosis factor-alpha

Protein kinase C (PKC) has been implicated in tumor necrosis factor-alpha (TNF) signaling. Structurally and functionally distinct PKC activators and selective inhibitors of PKC were used to investigate the involvement of PKC isozymes in influencing TNF sensitivity in MCF-7 cells. Activators of PKC, such as phorbol-12, 13-dibutyrate (PDBu) (1.0 microM), indolactam V (10 microM), and bryostatin 1 (1.0 microM) decreased the sensitivity of MCF-7 cells to TNF by 5-, 10-, and 1.7-fold, respectively. The PKC-specific inhibitor bisindolylmaleimide II (BIM) (> or = 1 microM) antagonized the effect of PDBu in protecting MCF-7 cells against TNF cytotoxicity. High concentrations of BIM (> or = 10 microM) also significantly enhanced the sensitivity of MCF-7 cells to TNF. In contrast, Gö 6976, a specific inhibitor of cPKCs, did not potentiate TNF sensitivity and failed to reverse the effect of PDBu. In addition, BIM but not Gö 6976 blocked PDBu-mediated down-regulation of TNF receptors. There was no correlation between down-regulation of PKC alpha, -delta, and -epsilon, and protection against TNF cytotoxicity by PKC activators. A 6-hr exposure to 1.0 microM PDBu, 10 microM indolactam V, and 1.0 microM bryostatin 1 caused a 1.8-, 3.5- and 1.2-fold induction, respectively, of nPKC eta in MCF-7 cells. Similar exposure to BIM but not Gö 6976 led to a significant down-regulation of nPKC eta. This novel regulation of PKC eta implicates this isozyme in PDBu-mediated protection of MCF-7 cells against TNF cytotoxicity.

Modulation of tumor necrosis factor (TNF) receptor expression during monocytic differentiation by glucocorticoids

OBJECTIVE AND DESIGN

Regulation of tumor necrosis factor receptors by glucocorticoids was investigated during phorbol ester-induced monocytic differentiation.

MATERIALS AND TREATMENT

As model system the human monocytic cell lines U937 and THP-1, which express both types of TNF receptors (TNF-R60 and TNF-R80), were differentiated with tetradecanoyl phorbol-13-acetate (TPA, 5 x 10(-9) M) in the presence or absence of dexamethasone (10(-9) - 10(-6) M).

METHODS

Expression of TNF receptors was determined at the mRNA level by Northern blot analysis and at the protein level by FACS analysis.

RESULTS

During differentiation, TNF-R60 mRNA was down-regulated, whereas TNF-R80 mRNA levels were increased. Dexamethasone had no effect on TNF-R60 mRNA expression but attenuated TNF-R80 mRNA expression in both cell lines. Cell surface expression of TNF-R60 protein remained essentially unchanged during differentiation of THP-1 cells, whereas a rapid down-regulation of TNF-R80 was observed that was followed by a slow recovery. Surface expression of TNF-R80 was not affected by dexamethasone, whereas TNF-R60 expression was reduced by about 25%.

CONCLUSIONS

These results indicate differential regulation of the two types of TNF receptors at the mRNA and protein level during monocytic differentiation. Glucocorticoids interfered with mRNA expression of TNF-R80 and protein expression of TNF-R60, but the rather limited effect leaves the question of its functional relevance open. In contrast to other cytokine systems, TNF receptors do not appear to be major targets of glucocorticoid action.

TNF alpha receptor expression in rat cardiac myocytes: TNF alpha inhibition of L-type Ca2+ current and Ca2+ transients

Tumor necrosis factor-alpha (TNF alpha) is a potentially powerful anti-neoplastic agent; however, its therapeutic usefulness is limited by its cardiotoxic and negative inotropic effects. Accordingly, studies were undertaken to gain a better understanding of the mechanisms of TNF alpha-mediated cardiodepression. Single cell RT-PCR, [125I]TNF alpha ligand binding and Western immunoblotting experiments demonstrated that rat cardiac cells predominantly express type I TNF alpha receptors (TNFRI or p60). TNF alpha inhibited cardiac L-type Ca2+ channel current (ICa) and contractile Ca2+ transients. Thus, it is possible that the negative inotropic effects of TNF alpha are the result of TNFRI-mediated blockade of cardiac excitation-contraction coupling.

Effect of cell cycle on the regulation of the cell surface and secreted forms of type I and type II human tumor necrosis factor receptors

The cell cycle has been shown to regulate the biological effects of human tumor necrosis factor (TNF), but to what extent that regulation is due to the modulation of TNF receptors is not clear. In the present report we investigated the effect of the cell cycle on the expression of surface and soluble TNF receptors in human histiocytic lymphoma U-937. Exposure to hydroxyurea, thymidine, etoposide, bisbensimide, and demecolcine lead to accumulation of cells primarily in G1/S, S, S/G2/M, G2/M, and M stages of the cell cycle, respectively. While no significant change in TNF receptors occurred in cells arrested in G1/S or S/G2 stages, about a 50% decrease was observed in cells at M phase of the cycle. Scatchard analysis showed a reduction in receptor number rather than affinity. In contrast, cells arrested at S phase (thymidine) showed an 80% increase in receptor number. The decrease in the TNF receptors was not due to changes in cell size or protein synthesis. The increase in receptors, however, correlated with an increase in total protein synthesis (to 3.8-fold of the control levels). A proportional change was observed in the p60 and p80 forms of the TNF receptors. A decrease in the surface receptors in cells arrested in M phase correlated with an increase in the amount of soluble receptors. The cellular response to TNF increased to 8- and 2-fold in cells arrested in G1 and S phase, respectively; but cells at G2/M phase showed about 6-fold decrease in response. In conclusion, our results demonstrate that the cell cycle plays an important role in regulation of cell-surface and soluble TNF receptors and also in the modulation of cellular response.

Transfection of cells with basic fibroblast growth factor and Kaposi fibroblast growth factor genes induce resistance to and receptor modulation of tumor necrosis factor

Tumor necrosis factor (TNF) has been shown to inhibit the growth of some cell types and stimulate the proliferation of others by a mechanism that is not understood. In the present study, we investigated the effect of transfection of NIH-3T3 cells with either the basic fibroblast growth factor gene (bFGF) or the kaposi FGF gene (K-fgf) on the growth-modulatory effects of TNF. Our results show that transformation of cells with either gene leads to resistance to the growth-inhibitory effects of TNF. The K-fgf gene was found to be a more potent inducer of cellular resistance than the bFGF gene. The cellular resistance correlated with the inhibition of TNF-induced activation of phospholipase A2 and down-modulation of TNF receptors. Overall, our results indicate that both K-fgf and bFGF play an important role in suppression of antiproliferative effects of TNF.

Cyclic AMP-independent up-regulation of the human serotonin transporter by staurosporine in choriocarcinoma cells

Treatment of confluent cultures of JAR human placental choriocarcinoma cells with staurosporine caused a marked stimulation of serotonin transport activity in these cells. The stimulatory effect was noticeable at nanomolar concentrations of staurosporine, and a treatment time of > 4 h was required for staurosporine to elicit the effect. At 40 nM and with a treatment time of 16 h, the stimulation of the transport activity was 3.5-6.0-fold. None of the several other protein kinase inhibitors tested had similar effect except KT 5720, a protein kinase A inhibitor, which showed a small but significant (approximately 1.4-fold) stimulatory effect at a concentration of 5 microM. Blockade of RNA synthesis and protein synthesis in the cells prevented completely the stimulation of the transport activity induced by staurosporine. The stimulation was observed not only in intact cells but also in plasma membrane vesicles prepared from staurosporine-treated cells. The stimulation was accompanied by a 5-7-fold increase in the steady state levels of the transporter-specific mRNAs, by a 7-fold increase in the maximal velocity of the transport process, and by a 6-fold increase in the transporter density in the plasma membrane. Even though both staurosporine and cholera toxin had similar effects on the serotonin transport activity in these cells, the effect was not additive when the cells were treated with both reagents together. While treatment of the cells with cholera toxin markedly elevated intracellular levels of cAMP, staurosporine did not have any effect on the cellular levels of this cyclic nucleotide. It is concluded that staurosporine up-regulates the serotonin transport activity in JAR cells by increasing the steady state levels of the serotonin transporter mRNA and by the consequent increase in the transporter density in the plasma membrane and that the process involves a cAMP-independent signaling pathway.

Staurosporine causes epidermal growth factor to induce differentiation in PC12 cells via receptor up-regulation

Although they all utilize tyrosine kinase receptors and activate signaling pathways characterized by a similar set of phosphoproteins, epidermal growth factor (EGF) promotes only cell division while fibroblast growth factor (FGF) and nerve growth factor (NGF) can induce division followed by differentiation in PC12 cells. EGF, in contrast to NGF and FGF, cannot maintain the sustained phosphorylation and activation of mitogen-activated protein (MAP) kinase kinase and MAP kinases, which may account for the difference in phenotypic response. The pretreatment of PC12 cells with staurosporine, a protein kinase inhibitor, causes a substantial increase in both receptor and MAP kinase phosphorylation that results in a differentiative response (neurite proliferation). However, neurites begin to disappear after 3 days, despite the continual presence of EGF, and are largely gone after 5 days, which is not the case with NGF and FGF. Thus, the effect of staurosporine is not permanent. Northern and Western blots indicate that the staurosporine response mainly results from a substantial up-regulation in EGF receptor synthesis, thus providing a much stronger cell surface signal and supporting the view that quantitative rather than qualitative differences distinguish the EGF versus NGF/FGF signaling pathways in these cells.

Characterization of the apoptotic effects of human tumor necrosis factor: development of highly rapid and specific bioassay for human tumor necrosis factor and lymphotoxin using human target cells

Currently available bioassays for most cytokines require several days and therefore must be performed under sterile conditions. In this report we describe a bioassay for tumor necrosis factor (TNF) and lymphotoxin (LT) that is extremely rapid and specific and does not require sterile conditions. Using tritiated thymidine release, we could conveniently monitor degradation of DNA into small fragments following the incubation of human myelogenous leukemia ML-1a cells with TNF. The assay showed that TNF-dependent DNA fragmentation was potentiated by cycloheximide and occurred within 90 min. Treatment of cells to TNF lead to apoptosis as indicated by thymidine release, DNA laddering on agarose gels and morphological alterations. Under these conditions, plasma membrane were not damaged as indicated by lack of chromium release. This effect was linear with TNF concentration. This assay had high throughput, did not require sterile conditions, could be carried out in the absence of serum, and was sensitive only to TNF and LT and not to interferon (IFN)-alpha, IFN-beta, IFN-gamma, transforming growth factor beta, interleukin-4, leukemia inhibitory factor and granulocyte-monocyte colony stimulating factor; all cytokines known to inhibit different cell types. Besides detection of TNF in biological fluids, this assay may prove useful for the identification of novel inhibitors of TNF action.