Interleukins and colony stimulating factors in human myeloid leukemia cell lines

Inhibition of the interleukin-6 signaling pathway: a strategy to induce immune tolerance

Interleukin-6 (IL-6) is a proinflammatory cytokine that is multifunctional, with multifaceted effects. IL-6 signaling plays a vital role in the control of the differentiation and activation of T lymphocytes by inducing different pathways. In particular, IL-6 controls the balance between Th17 cells and regulatory T (Treg) cells. An imbalance between Treg and Th17 cells is thought to play a pathological role in various immune-mediated diseases. Deregulated IL-6 production and signaling are associated with immune tolerance. Therefore, methods of inhibiting IL-6 production, receptors, and signaling pathways are strategies that are currently being widely pursued to develop novel therapies that induce immune tolerance. This survey aims to provide an updated account of why IL-6 inhibitors are becoming a vital class of drugs that are potentially useful for inducing immune tolerance as a treatment for autoimmune diseases and transplant rejection. In addition, we discuss the effect of targeting IL-6 in recent experimental and clinical studies on autoimmune diseases and transplant rejection.

Gene of the month: Interleukin 6 (IL-6)

The Interleukin 6 (IL-6) gene encodes the classic proinflammatory cytokine IL-6. It is also known as interferon-β2 (IFN-β2), B cell stimulatory factor-2 and hybridoma/plasmacytoma growth factor. IL-6 is a multifunctional cytokine with a central role in many physiological inflammatory and immunological processes. Due to its major role in initiation as well as resolving inflammation, deregulation of IL-6 is a mainstay of chronic inflammatory and autoimmune diseases. Additionally, IL-6 has been shown to be implicated in pathogenesis of many human malignancies. Thus, a better understanding of IL-6 and its role in various pathological conditions could enable the development of strategies to use it as a therapeutic target. This short review focuses on the structure, regulation and biological activities of IL-6. In addition we discuss the role of IL-6 in diseases with inflammatory background and cancer and also the therapeutic applications of anti-IL-6 agents.

Inhibition of the IL-6 signaling pathway: a strategy to combat chronic inflammatory diseases and cancer

Interleukin (IL)-6 is a pro-inflammatory cytokine that produces multifunctional effects. Deregulated IL-6 production and signaling are associated with chronic inflammatory diseases, auto-immunity and cancer. On this basis, inhibition of IL-6 production, its receptors or the signaling pathways are strategies currently being widely pursued to develop novel therapies for a wide range of diseases. This survey aims to provide an updated account of why IL-6 inhibitors are shaping up to become an important class of drugs potentially useful in the treatment of ailments and in particular in inflammation and cancer. In addition we discuss the role of different agents in modulating IL-6 and also recent clinical studies targeting IL-6 in inflammation-mediated diseases and cancer.

A fluorescent biomarker of the polyamine transport system to select patients with AML for F14512 treatment

The polyamine transport system (PTS), hyperactive in cancer cells, can constitute a gate to deliver F14512, a novel spermine epipodophyllotoxin conjugate recently selected for clinical development in AML phase I. We investigated in vitro the high antiproliferative effect of F14512 against 13 leukemia cell lines, and demonstrated a statistically significant correlation with the level of PTS activity, using a novel fluorescent marker F96982. This labelling protocol was then adapted for clinical applications for blood, bone marrow and AML samples with CD45 gating. Within the patient samples, the PTS activity varied significantly in AML cells, as compared to normal lymphocytes. In conclusion, the identification of PTS-positive AML with F98982 probe offers new perspectives to select patients prone to respond to F14512.

Nuclear organization of PML bodies in leukaemic and multiple myeloma cells

The nuclear arrangement of promyelocytic leukaemia nuclear bodies (PML NBs) was studied in vitro after the cell treatment by clinically used agents such as all-trans retinoic acid (RA) in human leukaemia and cytostatics or gamma radiation in multiple myeloma cells. In addition, the influence of phorbol ester (PMA) on PML NBs formation was analyzed. A reduced number of PML bodies, which led to relocation of PML NBs closer to the nuclear interior, mostly accompanied RA- and PMA-induced differentiation. Centrally located PML NBs were associated with transcriptional protein RNAP II and SC35 regions, which support importance of PML NBs in RNA processing that mostly proceeds within the nuclear interior. Conversely, the quantity of PML NBs was increased after cytostatic treatment, which caused re-distribution of PML NBs closer to the nuclear envelope. Here we showed correlations between the number of PML NBs and average Centre-to-PML distances. Moreover, a number of cells in S phase, especially during differentiation, influenced number of PML NBs. Studying the proteins involved in PML compartment, such as c-MYC, cell-type specific association of c-MYC and the PML NBs was observed in selected leukaemic cells undergoing differentiation, which was accompanied by c-MYC down-regulation.

Malignant hematopoietic cell lines: in vitro models for the study of erythroleukemia

A panel of leukemia cell lines has been assembled over the last 30 years representing a spectrum of erythroid cells arrested at various stages of differentiation. The oldest cell line is K-562 which is one of the most prolific in use. Most cell lines have been established from acute myeloid leukemia M6 or chronic myeloid leukemia in blast crisis and generally express immunoprofiles typically seen in immature erythroid cells. Several cell lines are constitutively growth factor-dependent, responding proliferatively to a variety of cytokines. The predominant cytogenetic abnormalities are the t(9;22)(q34;q11) found exclusively in CML-derived cell lines, and rearrangements of chromosomes 5 and 7 which occur in all disease subtypes. Ph+ve cell lines consistently displayed structural and numerical changes associated with disease evolution, including +8, -17/17p-/i(17q), and +19. It is striking that many cell lines though committed to either the erythroid or megakaryocytic lineage tend to co-express features of the other lineage, consistent with the concept of a common erythroid-megakaryocytic progenitor. Several cell lines may be induced to differentiate along the erythroid, megakaryocytic or monocytic pathway by treatment with pharmacological or physiological reagents. Notable functional features include expression of various globin chains or the complete hemoglobins as erythroid attributes. Taken together, this class of cell lines is relatively well characterized and affords useful model systems for immature erythroid cells.

HL-60 cell growth-conditioned medium is an effective inducer of myeloperoxidase expression in K-562 human leukemia cells

K-562 cells were cultured in HL-60 cell growth-conditioned medium (GCM) for up to 96h. Myeloperoxidase (MPO) mRNA was transiently detected by reverse transcription-polymerase chain reaction (RT-PCR) techniques at 12, 24, and 48h. The de novo expression of MPO protein was subsequently detectable by intracellular flow cytometry at 24, 48, 72 and 96h. Immunogold staining and cytochemical analysis demonstrated granularly-sequestered MPO in approximately 40% of HL-60 GCM-cultured cells after 48h of culture. The sequential detection of MPO mRNA and MPO biosynthesis is considered an indicator of serial maturation evocative of myeloblastic cells, and suggest that K-562 cells maintain the ability to differentiate along this lineage.

Continuous hematopoietic cell lines as model systems for leukemia-lymphoma research

Along with other improvements, the advent of continuous human leukemia-lymphoma (LL) cell lines as a rich resource of abundant, accessible and manipulable living cells has contributed significantly to a better understanding of the pathophysiology of hematopoietic tumors. The first LL cell lines, Burkitt's lymphoma-derived lines, were established in 1963. Since then, more than 1000 cell lines have been described, although not all of them in full detail. The major advantages of continuous cell lines is the unlimited supply and worldwide availability of identical cell material, and the infinite viable storability in liquid nitrogen. LL cell lines are characterized generally by monoclonal origin and differentiation arrest, sustained proliferation in vitro under preservation of most cellular features, and specific genetic alterations. The most practical classification of LL cell lines assigns them to one of the physiologically occurring cell lineages, based on their immunophenotype, genotype and functional features. Truly malignant cell lines must be discerned from Epstein-Barr virus (EBV)-immortalized normal cells, using various distinguishing parameters. However, the picture is not quite so straightforward, as some types of LL cell lines are indeed EBV+, and some EBV+ normal cell lines carry also genetic aberrations and may mimic malignancy-associated features. Apart from EBV and human T-cell leukemia virus in some lines, the majority of wild-type LL cell lines are virus-negative. The efficiency of cell line establishment is rather low and the deliberate establishment of new LL cell lines remains by and large an unpredictable random process. Difficulties in establishing continuous cell lines may be caused by the inappropriate selection of nutrients and growth factors for these cells. Clearly, a generally suitable microenvironment for hematopoietic cells, either malignant or normal, cannot yet be created in vitro. The characterization and publication of new LL cell lines should provide important and informative core data, attesting to their scientific significance. Large percentages of LL cell lines are contaminated with mycoplasma (about 30%) or are cross-contaminated with other cell lines (about 15-20%). Solutions to these problems are sensitive detection, effective elimination and rigorous prevention of mycoplasma infection, and proper, regular authentication of cell lines. The underlying cause, however, appears to be negligent cell culture practice. The willingness of investigators to make their LL cell lines available to others is all too often limited. There is a need in the scientific community for clean and authenticated high-quality LL cell lines to which every scientist has access. These are offered by various institutionalized public cell line banks. It has been argued that LL cell lines are genetically unstable (both cytogenetically and molecular genetically). For instance, cell lines are supposed to acquire numerical and structural chromosomal alterations and various types of mutations (e.g. point mutations) in vitro. We present evidence that while nearly 100% of all LL cell lines indeed carry genetic alterations, these alterations appear to be stable rather than unstable. As an example of the practical utility of LL cell lines, the recent advances in studies of classical and molecular cytogenetics, which in large part were made possible by cell lines, are highlighted. A list of the most useful, robust and publicly available reference cell lines that may be used for a variety of experimental purposes is proposed. Clearly, by opening new avenues for investigation, studies of LL cell lines have provided seminal insights into the biology of hematopoietic neoplasia. Over a period of nearly four decades, these initially rather exotic cell cultures, known only to a few specialists, have become ubiquitous powerful research tools that are available to every investigator.

Malignant hematopoietic cell lines: in vitro models for the study of multiple myeloma and plasma cell leukemia

Multiple myeloma (MM) is a neoplasm of a terminally differentiated B-cell. The disease is progressive and always lethal characterized by the slow proliferation of malignant plasma cells in the bone marrow. Much of our current understanding of the biology of MM has been obtained by studying MM-derived cell lines. Human myeloma cell lines were shown to be suitable model systems for use in various fields of the biological sciences. However, it has proved very difficult to establish cell lines from plasma cell dyscrasias. Most reported MM cell lines have been derived from patients with advanced disease and from extramedullary sites. Nevertheless, within the last 20 years more than 100 cell lines have been established. A significant portion of this panel is partially or well characterized with regard to their cell culture, clinical, immunophenotypic, cytogenetic and functional features. Distinct immunoprofiles could be assigned to MM cell lines. All MM cell lines display chromosomal aberrations; in more than 80% of the cell lines analyzed, chromosome 14 band q32 (immunoglobulin heavy chain locus) is affected; the various types of 14q+ chromosomes showed different distributions among the MM cell lines. A large percentage of MM cell lines is constitutively interleukin-6-dependent or responsive to various cytokines. It is important to realize that not every cell line established from a patient with myeloma is a neoplastic cell line. So-called 'myeloma cell lines' have been previously reported and are still widely used which are in reality Epstein-Barr virus (EBV)-positive B-lymphoblastoid cell lines. The presence of the EBV-genome in residual normal B-cells provides them with a selective growth advantage after explantation. In summary, a significant number of authentic and well-characterized MM cell lines has been established and described. The availability of these bona fide MM cell lines is of great importance for the study of the biology, etiology and treatment of the disease.

Induction of gp130 and LIF by differentiation inducers in human myeloid leukemia K562 cells

It has been previously shown that phorbol 12-myristate 13-acetate (PMA), a potent differentiation inducer, induced the expression of both interleukin-6 (IL-6) and IL-6 receptor alpha component (IL-6Ralpha) in K562 leukemia cells. In the present study, we examined the ability of several differentiation inducers to regulate the expression of the signal-transducing receptor component for IL-6, gp130, and cytokine leukemia inhibitory factor (LIF) in K562 cells. We found that the expression of gp130 was dramatically induced at both the mRNA and protein levels by the two megakaryocytic inducers sodium butyrate (NaBut) and PMA. In contrast, the mRNA expression of LIF was induced by the two erythroid inducers 1-beta-D-arabinofuranosyl cytosine (Ara-C) and hemin. Furthermore, activation of the PMA-induced gp130 receptor by exogenous IL-6 potentiated the differentiating effects of PMA. Our findings suggest that IL-6/gp130 signaling may be involved in the regulation of the megakaryocytic differentiation of K562 cells.

All-trans retinoic acid and hematopoietic growth factors regulating the growth and differentiation of blast progenitors in acute promyelocytic leukemia

Although acute leukemia is generally thought to be characterized by maturation arrest, it has been shown that differentiation occurs in blast cells of acute myelogenous leukemia (AML) in vitro as well as in vivo, and that morphologically abnormal mature polymorphonuclear neutrophils (PMNs) often seen in patients with AML are possibly derived from spontaneously differentiating leukemic cells. Acute promyelocytic leukemia (APL) is an unique example in which these features of AML are evident in an almost complete form; administration of all-trans retinoic acid (ATRA) induces differentiation of neoplastic cells into mature neutrophils and successfully induce complete remission in most patients. However, PMNs appearing during ATRA treatment are morphologically abnormal, as indicated not only by the presence of Auer rods but also by neutrophil secondary-granule deficiency that is commonly seen in AML. Moreover, ATRA has heterogeneous effects on the growth of blast progenitors in APL in different patients, being inhibitory, stimulatory or ineffective, which might account in part for the leukemia relapse in patients treated with ATRA alone. Hematopoietic growth factors regulate the growth of blast progenitors in APL. Among them, granulocyte colony-stimulating factor (G-CSF) is unique in that it preferentially stimulates clonal growth, but not self-renewal, in many APL cases, and synergistically enhances the differentiation-inducing effect of ATRA when used in combination. Many other compounds also exert such synergistic effects with ATRA, for which a variety of mechanisms have been suggested. It is crucial to precisely elucidate the functions of these molecules governing the growth/differentiation balance of AML blast progenitors and the mechanisms underlying their deregulated differentiation program in order to achieve effective differentiation therapy for patients with AML, not restricted to APL.

Differential regulation of interleukin-1alpha and interleukin-1beta in K-562 cells

Interleukin (IL)-1alpha and IL-1beta are encoded by two separate genes, but both function as comitogens for lymphocyte activation. In this study, we observed K-562 cells to express constitutively mRNA for IL-1alpha, although IL-1alpha was not detected in the growth-conditioned medium (GCM). However, IL-1beta mRNA was not expressed unless the cells had been treated with phorbol myristate acetate (PMA). Both IL-1alpha and IL-1beta were detected in the GCM after the cells had been cultured with PMA, suggesting that IL-1 elaboration required PMA treatment. The K-562 cells treated with PMA differentiated to the myeloblastic stage, as observed by nuclear morphologic properties by electron microscopy. PMA treatment induced de novo expression of CD61 or gpIIIa, a marker associated with megakaryoblasts. These results showed that although K-562 cells constitutively expressed IL-1alpha mRNA, PMA treatment was required for secretion. On the other hand, both the expression and secretion of IL-1beta required treatment with PMA. This study showed that K-562 cells treated with PMA differentiated to the myeloblastic stage and expressed and secreted IL-1alpha and IL-1beta.

Growth-inhibitory effects of transforming growth factor-beta 1 on myeloid leukemia cell lines

Transforming growth factor-beta1 is a pleiotropic cytokine involved in a variety of biological processes in both transformed and normal cells, including regulation of cellular proliferation and differentiation; its predominant action on hematopoietic cells is to inhibit cell growth. We used growth factor-dependent cell lines to assess TGF-beta1 effects on human myeloid leukemia cell growth. While four lines were completely or predominantly resistant, TGF-beta1 inhibited effectively, albeit to various extents, the growth of 12 other cell lines. This effect was dose dependent and specific, because a neutralizing anti-TGF-beta1 antibody prevented TGF-beta1-induced growth suppression. In the present system, basic fibroblast growth factor, known as an antagonist of TGF-beta1 counteracting its inhibitory effects, did not abrogate the suppressive effects of TGF-beta1. Other growth-stimulatory cytokines negated the TGF-beta1-induced inhibition in several cell lines, again to various extents. When proliferation was enhanced by growth-promoting cytokines (e.g. granulocyte-macrophage colony-stimulating factor, GM-CSF, stem cell factor, SCF, or PIXY-321), some previously TGF-beta1-sensitive cell lines acquired cellular resistance toward TGF-beta1-mediated growth suppression, whereas four other cell lines remained susceptible to TGF-beta1 growth inhibition despite possible counteraction by other cytokines. Thus, three growth response patterns to TGF-beta1 were seen: (1) constitutive resistance; (2) factor-dependent relative resistance; and (3) sensitivity to growth inhibition indifferent to counteracting cytokines. In the latter case, TGF-beta1 did not downregulate expression of one specific growth factor receptor. These studies indicate that human myeloid leukemia cells, represented here by leukemia cell lines as model systems, exhibit heterogeneous growth responses to TGF-beta1; its inhibitory effects can be modulated or completely alleviated by positive antagonistic cytokines. The availability of TGF-beta1-susceptible and -refractory cell lines allows for detailed investigations on the mechanisms of these regulatory pathways, the nature of TGF-beta1-resistance, and the possible contribution of acquired TGF-beta1-resistance to disease progression.

History and classification of human leukemia-lymphoma cell lines

Continuous human leukemia-lymphoma cell lines have become indispensable tools in hematological research since the establishment of the first human lymphoma cell line Raji in 1963. We summarize here historical landmarks in the establishment of unique leukemia-lymphoma-derived cell lines from the various cell lineages; their special importance in hematopoietic research is emphasized. The first cell lines were derived from African Burkitt lymphomas and were found to integrate the Epstein-Barr virus in their genome leading to the discovery and isolation of this virus. However, it was later recognized that not every cell line derived from a patient with leukemia-lymphoma represents a malignant cell line as residual normal B-lymphocytes can also be immortalized by EBV infection. During the following 20-30 years many other types of hematopoietic cell lines, commonly derived from hematopoietic neoplasms, were established. These panels of cell lines now span almost the whole spectrum of hematopoietic cell lineages (except for dendritric cells) and the various distinct stages of differentiation along the respective cell axes. From early on, cell lines became important tools for basic and clinical hematological research, initially mainly in the field of immunology, but later expanding to other areas also. It became apparent that leukemia-lymphoma cell lines are of monoclonal origin, are arrested at a discrete maturational stage during differentiation in each lineage, and show sustained and growth factor-independent or -dependent unlimited proliferation. Categorization of cell lines might best be based on the physiological stages of hematopoietic differentiation in the various cell lineages. For an adequate classification, detailed characterizations of both the cell lines and the primary cells from which the cell lines originated are absolutely mandatory. In summary, the availability of large numbers of continuous leukemia-lymphoma cell lines has greatly facilitated clinical and immunobiological studies of normal and malignant hematopoiesis. Human leukemia-lymphoma cell lines will continue to provide exquisite model systems for many biomedical disciplines.

Hoxa9 transforms primary bone marrow cells through specific collaboration with Meis1a but not Pbx1b

Hoxa9, Meis1 and Pbx1 encode homeodomaincontaining proteins implicated in leukemic transformation in both mice and humans. Hoxa9, Meis1 and Pbx1 proteins have been shown to physically interact with each other, as Hoxa9 cooperatively binds consensus DNA sequences with Meis1 and with Pbx1, while Meis1 and Pbx1 form heterodimers in both the presence and absence of DNA. In this study, we sought to determine if Hoxa9 could transform hemopoietic cells in collaboration with either Pbx1 or Meis1. Primary bone marrow cells, retrovirally engineered to overexpress Hoxa9 and Meis1a simultaneously, induced growth factor-dependent oligoclonal acute myeloid leukemia in <3 months when transplanted into syngenic mice. In contrast, overexpression of Hoxa9, Meis1a or Pbx1b alone, or the combination of Hoxa9 and Pbx1b failed to transform these cells acutely within 6 months post-transplantation. Similar results were obtained when FDC-P1 cells, engineered to overexpress these genes, were transplanted to syngenic recipients. Thus, these studies demonstrate a selective collaboration between a member of the Hox family and one of its DNA-binding partners in transformation of hemopoietic cells.

Establishment and characterization of human B cell precursor-leukemia cell lines

A large number of continuous human leukemia cell lines have been established over the last three decades. Clearly, leukemia cell lines have become important research tools. Here, we have summarized the immunological, molecular and standard cytogenetic features of a panel of well characterized B cell precursor (BCP)-leukemia cell lines which were derived from patients with acute lymphoblastic/undifferentiated leukemia (ALL/AUL) or chronic myeloid leukemia (CML) in blast crisis. Following the recently proposed immunological EGIL classification, we assigned our panel of 27 BCP-cell lines to one of the following categories: B-I pro-B cell line; B-II common-B cell line; and B-III pre-B cell line. All cell lines express general B-lineage associated surface markers (HLA-DR, CD22, CD79a) being negative for surface immunoglobulin (Ig); the differences between the subgroups reside in expression of CD10 and cytoplasmic Ig. Several BCP-cell lines show the myelomonocytic cell-associated markers CD13 and/or CD33. These immunologically 'biphenotypic' BCP-cell lines are generally TdT+ CD10+ CD13+ CD19+ CD22+ CD34+ and carry the Philadelphia (Ph) translocation. The BCP-cell lines display surface receptors for interferon-gamma (CD119), interleukin-7 (CD127) and FLT-3 ligand (CD135). All BCP-cell lines examined have complex numerical and structural chromosomal alterations including translocations commonly seen in BCP-ALL such as t(4;11), t(9;22), t(11;19), t(12;21), and t(17;19) involving the fusion genes MLL-AF4, BCR-ABL, ENL-MLL, TEL/ETV6-AML1 and E2A-HLF, respectively. Besides the expected rearrangement of the Ig heavy chain receptor gene, several cell lines also have rearrangements of the T cell receptor genes beta, gamma or delta. While some BCP-cell lines express (aberrantly) myeloperoxidase at the mRNA level, most lines are negative in the immunological or cytochemical staining. Several large series documented the difficulty in establishing such BCP cell lines with success rates in the range of 10-20% (on average 15%). Still, since the establishment of the first bonafide BCP-cell line in 1974 (cell line REH), some 150 cell lines have been established of which, however, only a small percentage have been sufficiently well characterized and described. A higher success rate for immortalizing any given leukemia cell might depend on a closer emulation of the physiological in vivo microenvironment. The possibility to grow in vitro leukemia cells at will would represent ideal experimental systems permitting basic research and patient-specific investigations. In summary, the use of well-characterized BCP-cell lines provide unprecedented opportunities for studying a multitude of biological aspects related to normal and neoplastic B-lymphocytes.

Bladder carcinoma cell line KU-19-19-derived cytokines support proliferation of growth factor-dependent hematopoietic cell lines: modulation by phorbol ester, interferon-gamma and interleukin-1 beta

The human bladder carcinoma cell line KU-19-19 synthesizes and secretes hematopoietic growth factors. Conditioned medium (CM) from KU-19-19 stimulated the [3H]thymidine incorporation of growth factor-dependent hematopoietic cell lines. ELISA documented high amounts of granulocyte colony-stimulating factor (G-CSF; > 5 ng/ml); also granulocyte-macrophage CSF (GM-CSF), macrophage-CSF (M-CSF), stem cell factor (SCF), IL-6, and IL-8 were detected in KU-19-19 CM. Pretreatment with phorbol ester, IL-1 beta, or IFN-gamma increased the level of G-CSF, GM-CSF, and M-CSF in KU-19-19 CM. Thus, KU-19-19 represents a reliable source for purification of G-CSF and can easily be used to support proliferation of growth factor-dependent cell lines. The ability to respond to different stimuli suggests that several regulatory pathways may be involved in cytokine production of this bladder carcinoma cell line.

Transforming growth factor beta1 attenuates ceramide-induced CPP32/Yama activation and apoptosis in human leukaemic HL-60 cells

Ceramide, a product of sphingomyelin turnover, is a novel lipid second messenger that mediates important cellular functions including proliferation, differentiation and apoptosis. This study demonstrates that the CPP32/Yama protease was activated during apoptosis induced by the membrane-permeable second messenger C2-ceramide in HL-60 cells. We also found that the addition of a specific tetrapeptide inhibitor of CPP32/Yama, Ac-DEVD-CHO, provided an effective protection against ceramide-induced cell death. These results suggested that CPP32/Yama has a central role in ceramide-mediated apoptosis. Furthermore a wide variety of cytokines were examined for their effect on ceramide-induced apoptosis. Only transforming growth factor beta1 (TGF-beta1) (1 ng/ml) exerted significant prevention of apoptosis induced by C2-ceramide, or by sphingomyelinase (increases intracellular ceramide). Consistently, TGF-beta1 abrogated the cleavage of poly(ADP-ribose) polymerase and the production of the CPP32/Yama active subunit, p17. However, TGF-beta1 treatment did not cause growth inhibition or alter the level of cyclin-dependent kinase inhibitor p27. It suggests that the preventive effect of TGF-beta1 is not mediated by growth arrest. Interestingly, we found that TGF-beta1 prevented the C2-ceramide-caused decrease of Bcl-2 protein. We thus propose that TGF-beta1 rescues ceramide-induced cell death, possibly by maintaining the constant level of Bcl-2, thereby abolishing CPP32/Yama protease activation.

The human bladder carcinoma cell line 5637 constitutively secretes functional cytokines

We have studied cytokine secretion by the human bladder carcinoma cell line 5637 using growth factor-dependent cell line bioassays and specific ELISA. The 5637 cell line-conditioned medium (5637 CM) stimulated proliferation of human growth factor-dependent leukemia cell lines in a dose-dependent fashion. Quantitation by specific ELISA and by bioassays detected high amounts of G-CSF and GM-CSF and smaller quantities of IL-1beta, M-CSF and SCF in 5637 CM; the concentration of IL-3 was below the detection level of the ELISA, if present at all. The G-CSF and GM-CSF activities secreted by 5637 cells could be inhibited specifically by neutralizing anti-G-CSF and anti-GM-CSF antibodies. In conclusion, 5637 bladder carcinoma cells constitutively produce and secrete several functionally active cytokines; 5637 CM is a valuable, reliable and inexpensive source for cytokines, for instance for the culture of growth factor-responsive or -dependent hematopoietic primary cells and cell lines.

Phorbol ester PMA induces expression of the thrombopoietin receptor MPL in leukemia cells

Thrombopoietin (TPO) is a major regulator of megakaryocytopoiesis both in vivo and in vitro. TPO initiates its biological effects by binding to the c-MPL receptor, which is a member of the hematopoietin receptor superfamily. To define the regulation of the MPL receptor, six continuous human leukemia cell lines with megakaryocytic properties were treated with the phorbol ester 12-myristate 13-acetate (PMA), TPO and transforming growth factor (TGF)-beta 1, a cytokine known to possess inhibitory effects. We used Northern blotting and flow cytometry analysis to determine MPL mRNA and protein levels. An increase of MPL mRNA and protein expression was observed in 2/6 PMA-exposed cell lines. There is no evidence from this study that TPO or TGF-beta 1 cause any decrease or increase in MPL expression. MPL upregulation triggered by PMA was accompanied by signs of induced differentiation such as increase in CD41, CD42 and CD61 expression, increase in cell size and cessation of proliferation. These data demonstrate that MPL can be upregulated in differentiating megakaryocytic cells via stimulation of protein kinase C, the intracellular target of PMA and a key kinase in one of the second messenger signal transduction pathways. These findings further the understanding of the regulation of this molecule, a cytokine receptor that, together with its ligand TPO, appears to represent a crucial element in megakaryocytopoiesis.

Expression of thrombopoietin and thrombopoietin receptor MPL in human leukemia-lymphoma and solid tumor cell lines

Thrombopoietin (TPO) is the major regulator of platelet production in vivo and is the ligand for the MPL receptor. In an effort to determine the distribution of TPO and MPL in the different hematopoietic cell types and in various types of tissue, we examined the mRNA expression of this ligand-receptor pair in two series of human leukemia-lymphoma cell lines and of solid tumor cancer cell lines using northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. At the northern blot mRNA level, 8/15 (53%) megakaryocytic and 3/11 (27%) erythroid leukemia cell lines expressed MPL mRNA; except for one positive monocytic cell line, the remaining 78 pre B-cell, B-cell, plasma cell, T-cell, NK cell, myeloid, monocytic and Hodgkin/anaplastic large cell lymphoma (ALCL)-derived cell lines were negative. No MPL message was detected in any of the 23 solid tumor cell lines established from 21 different tumors. In order to examine whether a low level of MPL expression could be detected, 51 leukemia cell lines were investigated with the RT-PCR technique. By this technique, MPL message was seen in many more cell types: 13/26 (50%) of non-erythromegakaryocytic cell lines and in nearly all megakaryocytic (14/15, 93%) and erythroid (10/11, 91%) cell lines. Thus, the highest expression of MPL clearly occurs in cells with megakaryocytic differentiation; furthermore, expression of MPL appears to be restricted to hematopoietic cell types. TPO mRNA expression was examined by RT-PCR and found in 9/11 (82%) of the solid tumor cell lines (derived from colon, endometrium, kidney, liver, ovary, retinoblastoma and urinary bladder cancers). Among the leukemia-lymphoma cell lines, TPO mRNA was detected by RT-PCR in most plasma cell, myeloid, megakaryocytic and erythroid cell lines, but not in pre B-cell, B-cell or T-/NK-cell lines. The results reported here extend the observations of MPL and TPO expression in normal cells to the whole spectrum of hematological cell types and to an array of different tissue types, both exemplified by their malignant counterparts.