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Biomedical subjects

E Hofsli

Publications and source records attributed to E Hofsli.

17 recordsLinked to original sources
PubMed2005

Identification of novel growth factor-responsive genes in neuroendocrine gastrointestinal tumour cells.

Targeting growth-regulatory pathways is a promising approach in cancer treatment. A prerequisite to the development of such therapies is characterisation of tumour growth regulation in the particular tumour cell type of interest. In order to gain insight into molecular mechanisms underlying proliferative responses in neuroendocrine (NE) gastrointestinal (GI) tumours, we investigated gene expression in human carcinoid BON cells after exposure to gastrin, hepatocyte growth factor (HGF), pituitary adenylate cyclase-activating polypeptide or epidermal growth factor. We particularly focused on gastrin- and HGF-induced gene expression, and identified 95 gastrin- and 101 HGF-responsive genes. The majority of these genes are known mediators of processes central in tumour biology, and a number of them have been associated with poor prognosis and metastasis in cancer patients. Furthermore, we identified 12 genes that were regulated by all four factors, indicating that they may be universally regulated during NE GI tumour cell proliferation. Our findings provide useful hypotheses for further studies aimed to search for new therapeutic targets as well as tumour markers in NE GI tumours.

Carcinoid Tumor↗
PubMed2001

Molecular mechanisms involved in gastrin-mediated regulation of cAMP-responsive promoter elements.

In the present study, we explore the role of cAMP-responsive (CRE) promoter elements in gastrin-mediated gene activation. By using the minimal CRE promoter reporter plasmid, pCRELuc, we show that gastrin can activate CRE. This activation is blocked by H-89 and GF 109203x, which inhibit protein kinases A and C, respectively. Moreover, Ca(2+)-activated pathways seem to be involved, because the calmodulin inhibitor W-7 reduced gastrin-mediated activation of pCRELuc. Deletion of CRE from the c-fos promoter rendered this promoter completely unresponsive to gastrin, indicating that CRE plays a central role in c-fos transactivation. Interestingly, gastrin-induced expression of the inducible cAMP early repressor (ICER), a gene that is known to be regulated by CRE promoter elements, was not reduced by H-89, W-7, or GF 109203x. Furthermore, bandshift analyses indicated that the region of the ICER promoter containing the CRE-like elements CARE 3-4 binds transcription factors that are not members of the CRE-binding protein-CRE modulator protein-activating transcription factor, or CREB/CREM/ATF-1, family. Our results underline the significance of the CRE promoter element in gastrin-mediated gene regulation and indicate that a variety of signaling mechanisms are involved, depending on the CRE promoter context.

Animals↗
PubMed2000

Regulation of inducible cAMP early repressor expression by gastrin and cholecystokinin in the pancreatic cell line AR42J.

The CREM gene encodes both activators and repressors of cAMP-induced transcription. Inducible cAMP early repressor (ICER) isoforms are generated upon activation of an alternative, intronic promoter within the CREM gene. ICER is proposed to down-regulate both its own expression and the expression of other genes that contain cAMP-responsive elements such as a number of growth factors. Thus, ICER has been postulated to play a role in proliferation and differentiation. Here we show that ICER gene expression is induced by gastrin, cholecystokinin (CCK), and epidermal growth factor in AR42J cells. The time course of gastrin- and CCK-mediated ICER induction is rapid and transient, similar to forskolin- and phorbol 12-myristate 13-acetate-induced ICER expression. The specific CCK-B receptor antagonist L740,093 blocks the gastrin but not the CCK response, indicating that both the CCK-B and the CCK-A receptor can mediate ICER gene activation. Noteworthy, CREB is constitutively phosphorylated at Ser-133 in AR42J cells, and ICER induction proceeds in the absence of increased CREB Ser(P)-133. Gastrin-mediated ICER induction was not reduced in the presence of the protein kinase A inhibitor H-89, indicating a protein kinase A-independent mechanism. This is the first report on ICER inducibility via G(q)/G(11) protein-coupled receptors.

Animals↗
PubMed1992

[Multiple drug resistance--theoretical and clinical aspects].

A major problem in the treatment of cancer is clinical resistance to chemotherapeutic drugs. Multi-drug resistance (MDR) is a well-studied experimental phenomenon which seems to play an important role in clinical resistance to drugs. Tumour cells selected for resistance to a "natural product" anticancer drug display crossresistance to a variety of structurally and functionally unrelated anticancer drugs. Such resistant cells accumulate and retain less drug than retained by their drug sensitive counterparts. This lower grade of accumulation is most likely mediated by P-glycoprotein, an integral membrane protein which functions as an energy-dependent efflux pump. It has now become clear that several lipophilic agents can reverse MDR both in vitro and in vivo. Clinical trials with such modulators (chemosensitizers) have already given promising results.

Antineoplastic Agents↗
PubMed1992

Effect of pyridoxine on tumor necrosis factor activities in vitro.

Clinical trials with tumor necrosis factor (TNF) as an antitumor agent have so far given rather disappointing results. In this study we show that the naturally occurring vitamin B6 compound, pyridoxine, enhances TNF-induced cytolysis of three subclones of a mouse fibrosarcoma cell line (WEHI 164). The degree of pyridoxine-induced enhancement of TNF cytotoxicity seems to be dependent on the cells sensitivity to TNF, as the enhancement was much more pronounced in the relatively TNF resistant subclone act-R(cl.12)-WEHI 164, than in the very TNF sensitive subclone WEHI 164 clone 13. Furthermore, our study shows that pyridoxine, in contrast to its enhancing effect on TNF-induced cytotoxicity, rather inhibits TNF-induced growth of human FS-4 fibroblasts. Pyridoxine also enhances lymphotoxin (LT)-induced tumor cell killing and inhibits LT-induced fibroblast growth. Pyridoxine is a relatively non-toxic agent in vivo. Our results suggest that a combination of TNF and pyridoxine may be more efficient than TNF alone, in the treatment of cancer patients.

Animals↗
PubMed1991

[Interleukins--important signal substances for T-lymphocytes].

The immune system plays an important role in defence against infections, and probably also in defence against cancer. The various white blood cells are the actors in the immune system. Important effector cells are the T-lymphocytes, which are responsible for the cellular immune response. Interleukins are proteins which act as signal substances between leukocytes. Many of the interleukins play an important role in the activation, growth, proliferation and differentiation of T-lymphocytes. This article describes the various interleukins and their effects on the T-lymphocytes.

Humans↗
PubMed1991

[Therapeutic failure of antineoplastic agents. Extracellular and cellular causes].

Chemotherapy plays an important role in the treatment of cancer. However, the drug regimens used today can only offer a cure to a small fraction of cancer patients. The article reviews the factors that limit the effect of chemotherapeutic treatment of cancer. The major cause of failure of chemotherapeutic treatment is the presence of resistant tumour cells. In addition to the various changes that may occur in tumour cells, various other factors may limit the "effective concentration" of a drug delivered to the site of the tumour, and thereby affect the overall clinical response to therapy.

Antineoplastic Agents↗
PubMed1990

Reversal of multidrug resistance by lipophilic drugs.

The phenomenon of multidrug resistance implies that a wide spectrum of structurally and functionally unrelated chemotherapeutic drugs are recognized and processed by the molecular system which protects multidrug-resistant (MDR) cells against lipophilic cytotoxic drugs. This suggests that lipophilic agents with low toxicity may also be recognized and processed by this molecular system. At high concentrations these agents might saturate the system, thereby reversing multidrug resistance. In support of this hypothesis, 19 (73%) of 26 arbitrarily chosen lipophilic drugs were in this study found to increase the accumulation of actinomycin D in MDR WEHI 164 cells. The most potent of these drugs were also shown to sensitize these cells to the cytotoxic effect of actinomycin D and doxorubicin. There was a good correlation between the ability of the lipophilic drugs to induce an increased accumulation of actinomycin D in MDR cells and their ability to sensitize these cells to the cytotoxic effect of chemotherapeutic drugs. The ability to reverse drug resistance appeared to be additive, since increased accumulation of actinomycin D was also obtained by combining low concentrations of various lipophilic drugs. This may be a way to reduce the in vivo toxic effect of the lipophilic drugs yet still obtain a reversal of drug resistance. When MDR cells were exposed to lipophilic drugs which reversed drug resistance, the synergistic cytotoxic effect of actinomycin D and tumor necrosis factor was obtained at reduced actinomycin D concentrations.

Animals↗
PubMed1989

Reversal of drug resistance by erythromycin: erythromycin increases the accumulation of actinomycin D and doxorubicin in multidrug-resistant cells.

Development of resistance to one type of lipophilic chemotherapeutic drug often leads to resistance to other, structurally unrelated, lipophilic drugs. This suggests that non-toxic lipophilic agents may interfere with and reverse drug resistance by saturating the pathway through which multidrug-resistant (MDR) cells protect themselves against cytotoxic drugs. The lipophilic antibiotic, erythromycin, can significantly reverse the resistance of MDR WEHI 164 murine fibrosarcoma cells to the chemotherapeutic drugs, doxorubicin and actinomycin-D. The MDR cells showed an approximately 10-fold higher expression of the P-glycoprotein than the drug-sensitive parental cells from which the resistant cells were derived. The accumulation of actinomycin-D and doxorubicin was much lower in the drug-resistant cells than in the sensitive parental cells. The concentrations of erythromycin which reversed the drug resistance of the MDR cells increased the accumulation of actinomycin-D and doxorubicin in these cells to a level comparable to that observed in the sensitive parental cells. Our data suggest that erythromycin reverses drug resistance by saturating the drug-binding sites on the P-glycoprotein, thereby reducing the capacity of this protein to pump drugs out of resistant cells. Some of our MDR cells have also become more resistant to tumour necrosis factor (TNF). However, erythromycin did not reverse TNF resistance, suggesting that the mechanisms of multi-drug and TNF resistance are different. TNF did not influence drug accumulation in MDR cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

Effect of erythromycin and tumour necrosis factor on the drug resistance of multidrug-resistant cells: reversal of drug resistance by erythromycin.

WEHI 164 murine fibrosarcoma cells were rendered multidrug-resistant (MDR) by culture in the presence of actinomycin D. In addition to resistance to actinomycin D, the cells acquired resistance to doxorubicin, mitomycin, vincristine and cycloheximide. The fact that development of resistance to one type of lipophilic chemotherapeutic drug also results in resistance to other structurally unrelated lipophilic drugs suggests that non-toxic lipophilic agents may interfere with drug resistance by saturating the pathway by which MDR-cells inhibit drug cytotoxicity. We show that the antibiotic erythromycin significantly reverses the resistance of MDR WEHI 164 cells to doxorubicin and actinomycin D. In addition to cross-resistance to chemotherapeutic drugs, 3 out of 4 actinomycin D-resistant WEHI 164 cell lines also showed higher resistance to tumour necrosis factor (TNF) than the parental WEHI 164 cells. However, whereas verapamil, a calcium antagonist known to reverse multidrug-resistance, rendered resistant cells more sensitive to chemotherapeutic drugs, it protected the cells from killing by TNF, suggesting that drug resistance and TNF resistance may not be directly connected. A synergistic cytotoxic effect of TNF and actinomycin D was obtained on both the parental and the MDR cells. However, higher concentrations of TNF and actinomycin D were required to obtain a cytotoxic effect in the MDR cells, reflecting actinomycin D and TNF resistance in these cells.

Animals↗
PubMed1989

A flow cytometric and immunofluorescence microscopic study of tumor necrosis factor production and localization in human monocytes.

The production and localization of tumor necrosis factor (TNF) in human monocytes were investigated by using monoclonal and polyclonal antibodies against recombinant human TNF together with flow cytometry and immunofluorescence microscopy. Lipopolysaccharide (LPS) induced a rapid and transient accumulation of TNF in perinuclear vesicles which was detected 20 min after the addition of LPS. The fluorescence intensity of the vesicles peaked at 40 min of LPS exposure, concomitantly with the release of TNF into the medium. Thus, our results indicate that the secretion of TNF is typical for secretory proteins as it involves passage through the secretory apparatus. Additional studies demonstrated that plasma membrane-associated TNF could not be detected in live monocytes not exposed to LPS. However, after 90 min with LPS, a small population of monocytes expressed membrane-associated TNF, and by 24 hr approximately 50% of the monocytes displayed TNF on the plasma membrane. Furthermore, our results indicate that plasma membrane-associated TNF does not represent released TNF bound back to its own receptor. Thus, our findings support the view that TNF exists as a surface trans-membrane protein in LPS-stimulated monocytes.

Cell Compartmentation↗
PubMed1989

Tumor necrosis factor-induced expression of platelet-derived growth factor A-chain messenger RNA in fibroblasts.

Recombinant tumor necrosis factor (rTNF) induced a transient increase in the expression of the PDGF A-chain mRNA in FS-4 fibroblasts, as determined by Northern blot hybridization. The mRNA transcripts were of the expected sizes 1.9, 2.3, and 2.8 kb. Increased levels of the PDGF A-chain mRNA were detected 1, 2, and 4 h after addition of rTNF, the highest level being detected after 2 h. After 8 h the mRNA level was similar to that in control cultures. No PDGF B-chain mRNA (c-sis) could be detected following addition of rTNF. There was also an accumulation of PDGF receptor-competing activity in the medium of rTNF-exposed fibroblasts, suggesting that rTNF also induced the synthesis and release of functional PDGF A-chain homodimers (PDGF-AA). The fibroblast growth stimulatory activity in supernatants from rTNF-exposed fibroblasts could be neutralized by antiserum against rTNF, and thus rTNF seemed to be able to act as a direct mitogen. Hence rTNF-induced PDGF-AA is not the main mediator of rTNF's mitogenicity under the conditions investigated.

Binding, Competitive↗
PubMed1989

Recombinant tumour necrosis factor (TNF) fixed to cell monolayers retains its cytotoxic and growth-stimulatory activity. Evidence that internalization of TNF is not necessary for induction of biological effects.

Recombinant human tumour necrosis factor (rTNF) retained its cytotoxic activity after being fixed with paraformaldehyde to adherent cell monolayers. The cytotoxicity appeared to be mainly due to fixed rTNF and not to any free soluble rTNF that could have leaked out from the fixed rTNF cell preparations. The fixed rTNF cell preparations also stimulated the growth of human diploid fibroblasts, under conditions where little growth-stimulatory activity was found in suspension. These results indicate that TNF may exert its effect on target cells without internalization, perhaps through a receptor-mediated process that may alter the levels of a second messenger within the target cells. This signal transduction does not appear to involve cAMP or cGMP, since we were unable to detect significant changes in the levels of these two second messengers in TNF-exposed WEHI 164 clone 13 cells.

Cell Adhesion↗
PubMed1988

Evidence that tumour necrosis factor (TNF) is not constitutively present in vivo. The association of TNF with freshly isolated monocytes reflects a rapid in vitro production.

Tumour necrosis factor (TNF) cytotoxic activity has been shown not to be present in detectable amounts in the serum of healthy humans, but it may be found in some patients with meningococcal disease. In this study we investigated whether TNF is constitutively present in vivo on or within monocytes. TNF was detected on freshly isolated paraformaldehyde-fixed monocytes from both healthy individuals and cancer patients. No significant difference was found between the two groups. TNF appeared first 40-60 min after in vitro monocyte adherence, which is the same time as it took TNF to appear extracellularly after the exposure of in vitro cultured monocytes to lipopolysaccharide (LPS). This indicates that TNF associated with freshly isolated monocytes was synthesized in vitro. The inducing signal may be monocyte contact with plastic. Exposure of whole blood to LPS immediately after vein puncture was followed by about twice as rapid TNF release as that observed with in vitro cultured monocytes. The release was inhibited by cycloheximide but not by actinomycin D, indicating that the TNF detected did not represent TNF present in vivo. This is consistent with the fact that no TNF cytotoxic activity was detected in blood cell extracts. However, TNF-mRNA may have been present in vivo. Thus, the available evidence indicates that TNF is not constitutively expressed in vivo.

Cycloheximide↗
PubMed1988

Involvement of tumor necrosis factor in cytotoxicity mediated by human monocytes.

Human monocytes cultured in a specially prepared medium free of lipopolysaccharide (LPS) constitutively produced a small, though significant, amount of tumor necrosis factor (TNF). Upon addition of LPS, the amount produced remained constant until the LPS concentration reached 1-10 ng/ml, whereupon the production of TNF dramatically increased, eventually becoming 100-fold greater than when the LPS concentration was below 1 ng/ml. Priming the monocytes with recombinant interferon-gamma (rIFN-gamma) before LPS exposure resulted in a 2- to 10-fold increase in TNF production, the highest relative increase being obtained at lower LPS concentrations and in the absence of LPS. Monocyte-produced TNF appears to be the effector molecule in monocyte-mediated killing of some target cell types, since antiserum against recombinant TNF inhibited killing of both actinomycin D-treated and untreated WEHI 164 cells by human monocytes. However, it also appears that TNF may not in all cases be an effector molecule in monocyte-mediated killing, since cytolysis of K562 cells mediated by IFN-gamma/LPS-activated monocytes was not inhibited by antiserum against recombinant TNF. Antiserum which was raised against a monocyte-derived cytotoxic factor and which neutralized recombinant TNF did, however, inhibit monocyte-mediated cytolysis of K562 cells, suggesting that an extracellular factor, perhaps related to TNF, was also involved in monocyte-mediated killing of K562 cells. A TNF-like activity was associated with the monocyte surface membrane, since paraformaldehyde-fixed monocytes expressed cytotoxic activity which was neutralized by antiserum against recombinant TNF. Fixed monocytes activated with rIFN-gamma in addition to LPS before fixation were generally more cytotoxic than those exposed to LPS alone, and those exposed to LPS were much more cytotoxic than those not exposed to LPS. Thus it is possible that high local TNF concentrations may be generated near the target cell upon direct contact between effector and target cells, and that also monocyte-associated TNF may in this way be involved in monocyte-mediated cytotoxicity.

Animals↗
PubMed1987

Lymphotoxin-induced growth stimulation of diploid human fibroblasts in the presence and absence of gamma interferon.

In the present study we investigated the effect of lymphotoxin (LT) on the growth of human diploid fibroblasts, in the presence and absence of gamma interferon (IFN-gamma). Recombinant LT (rLT) had a growth stimulatory effect on diploid human FS-4 fibroblasts. This growth-stimulatory effect was reduced in the presence of recombinant IFN-gamma (rIFN-gamma). LT thus has a similar effect on diploid fibroblasts as tumour necrosis factor (TNF).

Cell Division↗