Biomedical subjects

A Villunger

Publications and source records attributed to A Villunger.

29 records · Page 2Linked to original sources

PubMed1998

Functional granulocyte/macrophage colony stimulating factor receptor is constitutively expressed on neoplastic plasma cells and mediates tumour cell longevity.

It has been shown that granulocyte/macrophage colony stimulating factor (GM-CSF) is able to support myeloma cell propagation in cooperation with interleukin (IL)-6, the major growth factor for malignant plasma cells, although the biological mechanisms involved remain unknown. Therefore we investigated (i) the expression levels of the GM-CSF receptor (GM-CSFR) constituents in three malignant plasma cell lines and in native malignant plasma cells, (ii) the ability of the receptor to mediate common signalling pathways regulating proliferation and cell survival in malignant plasma cell lines, and (iii) the effects of GM-CSF on tumour cell biology. The GM-CSFRalpha subunit was detected in the malignant plasma cell lines RPMI-8226, MC/CAR, IM-9 as well as 6/6 native myeloma cell samples derived from the bone marrow of patients with overt disease. Furthermore, GM-CSFR expression was also detected in the CD19+ fraction from 2/3 bone marrow samples and 5/8 peripheral blood samples derived from patients with malignant plasma cell disorders, but not in the CD19+ fraction of peripheral blood from healthy donors. The expressed cytokine receptor alpha-subunit was able to constitute a functional signalling complex with the ubiquitously expressed GM-CSFRbeta subunit, as demonstrated by the fact that GM-CSF induced the p21-ras/mitogen-activated protein kinase (MAPK) signalling cascade in malignant plasma cell lines. Since this signalling cascade plays an essential role in the mediation of both proliferation and cell survival, we investigated the impact of GM-CSF on these two events. Application of GM-CSF led to an increase of DNA-synthesis in MC/CAR, IM-9 and RPMI-8226 cells. Furthermore, it increased longevity of these malignant plasma cell lines by reducing the rates of spontaneous apoptosis. We conclude that (i) the functional GM-CSFR is commonly expressed on malignant plasma cells and that (ii) GM-CSF promotes the clonal expansion of myeloma cells by inhibiting spontaneous apoptosis and promoting DNA synthesis.

Aged↗

PubMed1998

On the role and significance of Fas (Apo-1/CD95) ligand (FasL) expression in immune privileged tissues and cancer cells using multiple myeloma as a model.

Our knowledge in immunology has been dramatically increased by several excellent investigations elucidating the role of the Fas (Apo-1/CD95) receptor/ligand (FasL) system in complex immunological processes such as the acquisition of self tolerance in T cells, progression of autoimmunity, clonal deletion of activated T cells, B-cell regulation and the establishment of "immune privileged" sites such as testis or retina. In addition to these regulatory immunological activities, Fas/FasL interaction was also shown to participate in active defense mechanisms of the host against infected or transformed cells thereby inducing apoptosis in target cells. However, the same mechanism seems also to be part of an escape strategy utilized by tumor cells in various neoplastic malignancies of both hematopoetic as also non-hematopoetic origin. We ourselves were able to demonstrate that neoplastic plasma cell lines, as well as native malignant myeloma cells constitutively express FasL mRNA and protein. The FasL molecule is functionally active and able to induce programmed cell death in Fas sensitive target T cells in vitro. These target T cells were protected from programmed cell death by preincubation of T cells with a Fas-blocking monoclonal antibody (mAb) or of myeloma cells with a FasL-neutralizing mAb. respectively. Furthermore, overexpression of the caspase inhibitor, cowpoxvirus protein CrmA, also protected target T cells from being killed by myeloma cells, identifying Fas/FasL mediated signaling as the effector pathway utilized by malignant plasma cells. Our observations strongly suggest the engagement of Fas/FasL interaction in the escape strategy of this malignancy. The molecular basis of this evasive mechanism differs in essential respects from those described in melanoma, lung cancer, hepatocellular carcinoma, or astrocytoma, since downregulation of Fas or instrinsic insensitivity towards Fas-mediated signaling were not prerequisites for the occurrence of this phenomenon in Fas-sensitive multiple myeloma cell lines. However, myeloma cell lines resisted cocultivation with FasL-expressing target T cells in vitro. The aim of this review is to discuss the role of Fas/FasL interaction in the establishment of malignant disease, in the light of our findings on myeloma cells and also by drawing upon similar observations of other investigators on different kinds of tumor cells and cell lines and further to consider its possible relevance in formulating novel approaches to cancer therapy.

Animals↗

PubMed1998

Does "death receptor" signaling play a role in tumorigenesis and cancer therapy?

Physiological cell death, known as apoptosis, is an evolutionarily conserved process that is required for normal development and function of multicellular organisms. Abnormalities in cell death control are implicated as a cause or contributing factor in a range of diseases, including cancer, autoimmunity, and degenerative disorders. Importantly, the propensity of a cell to undergo apoptosis is one of the determinants of the sensitivity of tumor cells to antineoplastic therapy. Apoptosis can be triggered by stress-induced signals that arise from within the doomed cell or by signals that are elicited by binding of extracellular "death ligands" to their "death receptors." Cysteine proteases have been recognized as essential effectors of all pathways to apoptosis. Experiments with transgenic mice and gene knockout mice have shown that different caspases and their adaptor molecules are needed for "death receptor" signaling and apoptotic pathways elicited by cytokine withdrawal, DNA damage, or corticosteroids. These differences allow the pathways to be regulated by distinct inhibitors. It has been published that chemotherapeutic drugs and gamma-radiation induce apoptosis by "death ligand"-mediated activation of "death receptors," but this model has been challenged. Our review discusses this controversy in the light of current knowledge of the molecular control of apoptosis.

Animals↗

PubMed1997

Drug-induced apoptosis is associated with enhanced Fas (Apo-1/CD95) ligand expression but occurs independently of Fas (Apo-1/CD95) signaling in human T-acute lymphatic leukemia cells.

Induction of apoptosis is considered to be the underlying mechanism that accounts for the efficiency of chemotherapeutic drugs. It has recently been proposed that induction of Fas ligand (FasL) expression with subsequent autocrine and/or paracrine induction of cell death through binding to the Fas (Apo-1/CD95) membrane accounts for chemotherapy-associated apoptosis. In the present study, we analyzed the significance of FasL expression in the mediation of drug-induced apoptosis in the T-acute lymphatic leukemia model CEM. In particular, we examined the potential of the tumor drugs fludarabine, doxorubicin, and cisplatin to induce FasL expression. We also raised the question of whether apoptosis induced by these drugs occurs through the Fas pathway and hence can be blocked by the cowpox virus protein CrmA, a specific inhibitor of this pathway. All tumor drugs examined led to an increase in FasL protein. However, overexpression of CrmA had no effect on drug-induced apoptosis. Moreover, neither incubation with inhibitory monoclonal antibodies against Fas that completely prevented Fas-induced apoptosis in these cells nor pretreatment with a monoclonal antibody to FasL affected drug-induced cell death. Our observations suggest a Fas/FasL-independent mechanism for drug-induced apoptosis and exclude the involvement of caspase 1 and caspase 8 in this process in T-acute lymphatic leukemia cells.

Antineoplastic Agents↗

PubMed1997

Constitutive expression of Fas (Apo-1/CD95) ligand on multiple myeloma cells: a potential mechanism of tumor-induced suppression of immune surveillance.

The Fas (Apo-1/CD95) ligand (FasL) plays a central role in the elimination of target cells by effector T lymphocytes and in the suppression of cellular immune responses against nonmalignant and malignant cells. We show the expression of FasL on the surface of neoplastic plasma cells. We provide evidence that the FasL is functionally active because five of five neoplastic plasma cell lines tested killed CEM-C7H2 T-acute lymphoblastic leukemia (T-ALL) cells. The effect was mediated via the Fas (Apo-1/CD95) receptor molecule because blocking of Fas on the target cells or the FasL on the tumor cells by receptor- and ligand-specific monoclonal antibodies (MoAbs), respectively, protected T cells from being killed by myeloma cells. In addition, overexpression of the cowpox virus protein CrmA, a molecule with inhibitory potential on caspase-1 and caspase-8, specifically involved in Fas-induced signaling, protected T cells from being destroyed by the neoplastic cells or the agonistic anti-Fas MoAb. The potential of the malignant plasma cells to extinguish target T cells was independent of their own sensitivity to the agonistic anti-Fas MoAb, and FasL-positive (FasL+) CEM-C7H2 T cells were incapable of killing myeloma cells. Our results suggest that tumor cell-induced suppression of the immune system may be exerted via the FasL active on malignant plasma cells. Furthermore, loss of Fas expression or insensitivity to the agonistic anti-Fas MoAb do not seem to be prerequisites for myeloma cells to defeat T cells via Fas/FasL interaction.

Aged↗

PubMed1997

The interleukin 1beta-converting enzyme inhibitor CrmA prevents Apo1/Fas- but not glucocorticoid-induced poly(ADP-ribose) polymerase cleavage and apoptosis in lymphoblastic leukemia cells.

Glucocorticoids (GC) induce programmed cell death (apoptosis) in immature lymphocytes and are an essential component in the therapy of acute lymphatic leukemia. The mechanism underlying GC-induced apoptosis particularly in leukemia cells is, however, not well understood. Most forms of apoptosis seem to employ a common final effector pathway characterized by specific proteolytic events mediated by interleukin 1beta-converting enzyme (ICE) and/or other ICE-like cysteine proteases. These events may result in the morphologic changes characteristic of apoptosis. To determine whether a similar proteolytic pathway is activated during GC-induced leukemia cell apoptosis, we investigated poly(ADP-ribose) polymerase (PARP), a typical target of ICE-like proteases, during GC-induced apoptosis of the human acute T-cell leukemic cell line CEM-C7H2. Our studies showed proteolytic PARP cleavage suggestive of activation of ICE-like proteases that preceeded morphologic signs of apoptosis. We further established stably transfected CEM-C7H2 sublines expressing the cowpox virus protein CrmA that inhibits some, but not all, ICE-like proteases. GC-induced PARP cleavage and apoptosis were neither inhibited nor delayed in crmA-expressing cell lines. In contrast, crmA expression rendered the same lines resistant to Apo1/Fas-induced PARP cleavage and apoptosis. Thus, different proteases might be activated during the effector phases of GC-and Apo1/Fas-induced apoptosis in human leukemia cells.

Apoptosis↗

PubMed1997

Expression of Apo-1/Fas (CD95), Bcl-2, Bax and Bcl-x in myeloma cell lines: relationship between responsiveness to anti-Fas mab and p53 functional status.

The down-regulation of apoptosis may be an essential mechanism for tumour cell expansion in slowly proliferating tumours such as multiple myeloma. We studied eight myeloma cell lines for the presence of Bcl-2, which inhibits apoptosis, of Bax, which counteracts Bcl-2, of Bcl-x(L) and Bcl-x(S), which act in an anti- and pro-apoptotic fashion, respectively, and of Apo-1/Fas, which induces programmed cell death, when activated by the Apo-1/Fas ligand or the relevant monoclonal antibody (mab). All cell lines constitutively expressed homogenous amounts of Bcl-2, but displayed different amounts of Bax and Bcl-x proteins. The Apo-1/Fas antigen could be detected in seven out of eight myeloma lines, but expression levels varied considerably. The relative expression levels of Apo-1/Fas correlated with that of Bax, but not with that of Bcl-2 or Bcl-x subtypes. Furthermore, the effectiveness of the Apo-1/Fas mab was associated with the relative expression levels of the Apo-1/Fas and with that of the Bax antigen, but not with that of the Bcl-2 and Bcl-x antigens. We further showed that wild-type p53 function is not required for Apo-1/Fas-induced apoptosis, nor is it necessary for the expression of Bax or Apo-1/Fas antigens in myeloma. In conclusion, our results suggest a p53-independent co-regulation of Apo-1/Fas and Bax, as well as a role for Bax in Apo-1/Fas-induced apoptosis in myeloma.

Apoptosis↗

PubMed1996

Constituents of autocrine IL-6 loops in myeloma cell lines and their targeting for suppression of neoplastic growth by antibody strategies.

We examined the constitution and biological relevance of an autocrine IL-6/IL6-receptor (r) loop in 7 multiple myeloma and plasma-cell leukemia lines in order to determine its biological role and potential therapeutic impact on antibody strategies. The expression and constitution of the IL-6r [i.e. membrane-bound gp-80, soluble (s)gp-55 and the gp-130 IL-6 signal-transducing element (str)], the binding capacity of the membrane-associated receptor(s) for IL-6, the production and secretion of IL-6 by neoplastic plasma cells, and the effect of IL-6 on tumor-cell proliferation were investigated. In the U-266 cell line, the growth-inhibitory effects of antibodies (Abs) against IL-6 and IL-6-binding subunit of its receptor were compared with each other. From our results the following conclusions may be drawn: (i) Substantial differences in the quantificative assembly of the IL-6r constituents and in the response to recombinant (r) human (h) IL-6 became evident in the 7 myeloma cell lines. (ii) The components of an autocrine IL-6 loop may be regulated in an independent and, in the case of IL-6 and sgp-55, probably counteractive manner. (iii) The level of endogenous IL-6 and the reservoir of recruitable sgp-55 were important for the response to exogenous rhIL-6. (iv) Apart from IL-6, other growth factors are important for the propagation of myeloma cells but at least some of them exert their effect through an IL-6-dependent pathway. Their growth-promoting activity, as well as that of IL-6, may be successfully targeted by immunological means, with Abs against the IL-6r being more efficient than those against the ligand.

Antibodies↗

PubMed1996

Modulation of Apo-1/Fas (CD95)-induced programmed cell death in myeloma cells by interferon-alpha 2.

The Apo-1/Fas (CD95) antigen is known to be involved in the process of T cell-mediated target cell killing and has recently been shown to be expressed on myeloma cell lines and native malignant plasma cells. Several cytokines have been reported to interfere with spontaneous and even Apo-1/Fas-induced apoptosis, but no attempt has been made yet to investigate these interactions and the possible underlying mechanisms in myeloma cells. Since in myeloma patients Interferon (IFN)-alpha2 displays a profound therapeutic effect in vivo, which is usually attributed to its growth inhibitory and/or immunomodulatory capacity, we set out to study the potential interference of IFN-alpha2 with Apo-1/Fas-induced apoptosis. Contrary to expectations, IFN-alpha2 reduced the degree of apoptosis caused by the treatment of five Apo-1/Fas-sensitive myeloma cell lines with a Fas monoclonal antibody (mAb). Simultaneous application of IFN-alpha2 and Fas mAb was superior to the prolonged (i.e. >8 h) preincubation with the cytokine as far as inhibition of Apo-1/Fas-induced apoptosis was concerned. This effect of IFN-alpha2 was neither explained by a down-regulation of the Apo-1/Fas receptor nor caused by modulation of the expression levels of c-myc, bcl-2-, bcl-xL, bax- or p53 genes. IFN-alpha2 did not alter the Apo-1/Fas-induced activity of Mitogen-activated protein kinase (MAPK) 1 and did not inhibit the Apo-1/Fas-mediated proteolytic cleavage of ADP-ribosyltransferase, a substrate of Interleukin-beta1 converting enzyme (ICE) and homologues. However, activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) mimicked the effects of IFN-alpha2. Furthermore, the bis-indolylmaleimide GF 109203X, a specific inhibitor of PKC, inhibited the effect of PMA as well as that of IFN-alpha2 on Apo-1/Fas-induced apoptosis. These results point to a PKC-dependent mechanism of transient interaction between the intracellular signaling along the IFN-alpha2 and the Apo-1/Fas pathway (downstream of MAPK signaling as well as of ICE homologues), which becomes exhausted by prolonged stimulation with the cytokine. According to our data IFN-alpha2, applied continuously and in high doses resembling the therapeutic situation in vivo, inhibits myeloma growth. However, based on the observed inhibitory effect of IFN-alpha2 on Apo-1/Fas-induced apoptosis, a partial inhibition of the natural immune surveillance on myeloma cells by endogenous IFN-alpha2 present in the bone marrow microenvironment of this malignancy should be investigated.

Adjuvants, Immunologic↗

PubMed1996

2',2'-Difluorodeoxycytidine (gemcitabine) induces apoptosis in myeloma cell lines resistant to steroids and 2-chlorodeoxyadenosine (2-CdA).

The paucity of effective cytotoxic agents for the treatment of steroid resistant multiple myeloma explains the ongoing search for alternative substances for chemotherapy of this disease. In the present study, the purine antagonist 2-chlorodeoxyadenosine (2-CdA, cladribine) and the pyrimidine antagonist 2',2'-difluorodeoxycytidine (gemcitabine) were tested on four myeloma cell lines (i.e., U 266, OPM 2, RPMI 8226, IM 9), one plasma cell leukemia cell line (HS Sultan) and a myeloid control cell line (HL 60), all of which are resistant to 10-6 M dexamethasone. Gemcitabine has been found to be promising in the chemotherapy of other tumors with low proliferative activity, but its effectiveness against myeloma cells has not been analyzed so far. In our tests, gemcitabine induced a significant degree of apoptosis in all cell lines investigated. After incubation for 48 h with 10 microM gemcitabine, the median numbers of apoptotic cells were in the range of 45% in the OPM 2 and 79% in the U 266 cell line. All of the investigated cell lines were responsive to concentrations of 10 microM gemcitabine even after an exposure of only 30 min, three of them (U 266, HS Sultan, IM 9) also responded to a concentration of 10 nM. Higher concentrations and longer exposure times were necessary to suppress the growth of normal hematopoietic bone marrow progenitor cells. In contrast to gemcitabine, standard concentrations of 2-CdA (i.e., 30 and 300 nM) failed to induce a significant degree of apoptosis in the cell lines investigated but inhibited the growth of myeloid progenitor cells. The results suggest that gemcitabine induces apoptosis in myeloma and plasma cell leukemia lines resistant to steroids and 2-CdA. The fact that tumor cell apoptosis was achieved at concentrations clinically achievable and tolerable, which at the same time do not inhibit the growth of normal CFU-GM progenitor cells, favors the initiation of phase I trials with this drug for the treatment of multiple myeloma.

2-Chloroadenosine↗

PubMed1991

Lactogenic hormone and cell type-specific control of the whey acidic protein gene promoter in transfected mouse cells.

The whey acidic protein (WAP) is a major milk protein. It is abundantly expressed in mammary epithelial cells, and its gene is controlled by lactogenic hormones. The identification of regulatory cis-acting sequences of the mouse WAP gene was so far dependent on the analysis of transgenic animals. We report here the possibility of analyzing regulatory sequences by gene transfer experiments using the lactogenic hormone-dependent mammary epithelial cell line HC11. A WAP-chloramphenicol acetyltransferase construct containing 2.5 kilobases of the 5'-flanking sequence of the WAP gene was stably transfected into HC11 cells. High chloramphenicol acetyltransferase activity was induced in pools of transfected cells cultured in the presence of the lactogenic hormones glucocorticoid, PRL, and insulin. A lower induction was observed by glucocorticoid hormone alone. PRL by itself was not able to induce the WAP gene promoter above the level observed in the absence of lactogenic hormones. A time course of hormone induction showed a weak initial response with a steady increase over at least 4 days of hormone treatment. Induction was not observable in the mammary epithelial cell line NOG-8 and NIH3T3 fibroblasts, despite the presence of functional glucocorticoid receptor in these cells. This indicates the requirement for a cell type-specific transcription factor present in the mammary epithelial cell line HC11, but not in NOG-8 epithelial cells or NIH3T3 fibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗