Myelomonocytic Tumor Research Articles

Histone deacetylase HDAC1 downregulates transcription of the serotonin transporter (5-HTT) gene in tumor cells

Serotonin (5-HT) has been reported to be involved in cancer progression by stimulating angiogenesis and cell growth. In this study, we examined the expression of the serotonin transporter (5-HTT) and the role of histone deacetylases (HDACs) in regulating the 5-HTT gene in tumor cells. The 5-HTT gene expression was almost silenced in chicken lymphoma DT40, myelomonocytic tumor HD11 and hepatoma DU249 cells, compared to their physiological counterpart. In contrast, HDAC1 mRNA expression was increased in these cell lines. Indeed, the pan-HDAC inhibitor trichostatin A (TSA) enhanced the 5-HTT mRNA expression in several tumor cell lines including the human cell lines HepG2 and THP-1 and increased the 5-HT uptake in HD11 cells. In addition, treatment with parthenolide, which is capable of depleting HDAC1, and knockdown of HDAC1 using siRNA resulted in increased 5-HTT mRNA expression, confirming the role of HDAC1 in the down-regulation of 5-HTT in the tumor cells. Deletion analysis of the 5-HTT promoter and site-directed mutagenesis revealed that the transcription factor CCAAT/enhancer binding protein beta (C/EBPß), in interacting with the 5-HTT promoter, mediated both the inhibition of the 5-HTT expression by HDAC1 and the activation by CREB-binding protein (CBP). Using a chromatin immunoprecipitation assay, we found increased acetylation of histone H4 associated with the 5-HTT promoter in cells treated with TSA. Our results suggest that the 5-HTT gene is epigenetically downregulated by HDAC1 in several types of cancer.

387. Myeloid Sarcoma Associated with Gene Marking of Hematopoietic Stem Cells in a Rhesus Macaque

Replication defective retroviruses are attractive tools for hematopoietic stem cell (HSC) gene therapy because of their ability to integrate into genomic DNA. Reports of neoplasia related to vector insertional proto-oncogene activation have raised safety concerns, however in these instances the vector itself carried a potentially cooperating transforming gene. We report for the first time a replication-defective vector-associated neoplasia in a non-human primate. Six years after autologous transplantation with G-CSF/SCF mobilized CD34+ cells transduced with a MSCV RD114 pseudotyped retroviral vector expressing eGFP and a drug resistant variant of the human dihydrofolate reductase gene (L22Y), a rhesus macaque developed a fatal myeloid sarcoma. Of note, this animal had high level transient marking during the first year following transplantation derived from a single transduced clone containing two vector insertions, over the next five years 1-3% GFP+ blood cells and was clinically well (Kelly et al, 2003). The animal received one cycle of trimextrexate and NBMP with transient increase in GFP+ blood cells 2001 (Persons et al, 2004). In 9/04 the animal developed abdominal distress and had a renal mass. Blood showed 30% GFP+ granulocytes, but no leukemia. Following surgery the animal died of pancreatitis and sepsis. Necroscopy revealed myelomonocytic tumor cell infiltrates with large round nuclei and variable amount of cytoplasm (MPO+, CD45+/-, CD68+, CD3-, CD20-, -/-, GFP+/-) in both kidneys, liver, pancreas, spleen, lymph nodes and in the choroid plexus. Taqman demonstrated a vector copy number of at least 1/cell in the tumor, suggesting association with vector. There was no detectable replication-competent helper virus in the tumor or the blood, based on PCR for helper gag/pol sequences. Blood cells and enriched tumor cells (>95%) have been analyzed via LAM-PCR identification of integration sites. A vector insertion in the first intron of the BCL2-A1 gene was found in the tumor, along with a second valid integration site that could not be mapped unequivocally using the human genome. PCR analysis using primers specific for the BCL2-A1 insertion suggested very high level contribution from the clone in the first year following transplantation, which then became undetectable and increased in the blood concurrent with the development of the myeloid sarcoma. Thus a single clone containing the vector insertion into the BCL2-A1 gene made a major multilineage contribution to hematopoieses during the first six months after reconstitution, became dormant and then re-emerged as a myeloid neoplasm after six years. The BCL2-A1 protein blocks apoptosis and is associated with a poor prognosis in human acute myeloid leukemia. Further research is required for risk assessment of current available vector systems, especially when targeting long-lived HSC.

F-MuLV acceleration of myelomonocytic tumorigenesis in SV40 large T antigen transgenic mice is accompanied by retroviral insertion at Fli1 and a novel locus, Fim4.

We describe here the development of a murine system for the identification of genes involved in myelomonocytic neoplasms. Transgenic C57BL/6J mice expressing SV40 early region under a myelomonocytic promoter develop histiocytic sarcomas with a latency of 167 days. We used retroviral proviral tagging to accelerate tumorigenesis and to uncover genetic changes that contribute to tumor development. Infection of transgenic mice with Friend murine leukemia virus (F-MuLV) shortened the latency of morbidity to 103 days (P< 0.001); this was associated with clonal proviral integrations in tumor DNA. As expected for F-MuLV, proviral insertions occurred at Fli1 in both transgenic and nontransgenic tumors. Four insertions were found at a novel locus, termed Fim4, on chromosome 6. This region is syntenic to human 7q32, a region that is commonly deleted in human myelodysplastic syndrome and acute myeloid leukemia. A murine BAC containing Fim4 was sequenced and analyzed, and while there was significant human-mouse homology in the area of the insertions, no candidate gene has been identified. Thus we have established a system to identify genes involved in myelomonocytic tumors, and have used it to identify Fim4, a new common site of proviral insertion. Study of this locus may provide insight into genes involved in AML-associated 7q32 deletions in humans.

Reactivity of Murine Cytokine Fusion Toxin, Diphtheria Toxin390-Murine Interleukin-3 (DT390-mIL-3), With Bone Marrow Progenitor Cells

Myeloid leukemias can express interleukin-3 receptors (IL-3R). Therefore, as an antileukemia drug, a fusion immunotoxin was synthesized consisting of the murine IL-3 (mIL-3) gene spliced to a truncated form of the diphtheria toxin (DT390) gene coding for a molecule that retained full enzymatic activity, but excluded the native binding domain. The DT390-mIL-3 hybrid gene was cloned into a vector under the control of an inducible promote. The fusion protein was expressed in Escherichia coli and then purified from inclusion bodies. The fusion toxin was potent because it inhibited FDC-P1, an IL-3R-expressing murine myelomonocytic tumor line (IC50 = 0.025 nmol/L or 1.5 ng/mL). Kinetics were rapid and cell-free studies showed that DT390-mIL-3 was as toxic as native DT. DT390-mIL-3 was selective because anti-mIL-3 monoclonal antibody, but not irrelevant antibody, inhibited its ability to kill. Cell lines not expressing IL-3R were not inhibited by the fusion protein. Because the use of DT390-mIL-3 as an antileukemia agent could be restricted by its reactivity with committed and/or primitive progenitor cells, bone marrow (BM) progenitor assays were performed. DT390-mIL-3 selectively inhibited committed BM progenitor cells as measured by in vitro colony-forming unit-granulocyte-macrophage and in vivo colony-forming unit-spleen colony assays. To determine if this fusion protein was reactive against BM progenitor cells required to rescue lethally irradiated recipients, adoptive transfer experiments were performed. Eight million DT390-mIL-3-treated C57BL/6 Ly5.2 BM cells, but not 4 million, were able to rescue lethally irradiated congenic C57BL/6 Ly5.1 recipients, suggesting that progenitor cells might be heterogenous in their expression of IL-3R. This idea was supported in competitive repopulation experiments in which DT390-mIL-3 treated C57BL/6 Ly5.2 BM cells were mixed with nontreated C57BL/6 Ly5.1 BM cells and used to reconstitute C57BL/6 Ly5.1 mice. A significant reduction, but not elimination, of Ly5.2-expressing cells 95 days post-BM transplantation and secondary transfer experiments indicated that IL-3R is not uniformly expressed on all primitive progenitor cells. The fact that some early progenitor cells survived DT390-mIL-3 treatment indicates that this fusion toxin may be useful in the treatment of myeloid leukemias that express the IL-3R.

A Murine Cytokine Fusion Toxin Specifically Targeting the Murine Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) Receptor on Normal Committed Bone Marrow Progenitor Cells and GM-CSF-Dependent Tumor Cells

Abstract A fusion protein was synthesized consisting of the murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) gene spliced to a truncated form of the diphtheria toxin (DT390) gene coding for a molecule that retained full enzymatic activity, but excluded the native binding domain. The DT390-mGM-CSF hybrid gene was cloned into a vector under the control of an inducible promoter and the protein expressed in Escherichia coli. After induction, a protein was purified from inclusion bodies in accord with the deduced molecular weight of DT390 mGM-CSF. Cell-free studies of the adenosine diphosphate-ribosylating activity of DT390 mGM-CSF showed results that were similar to those of native DT. The DT390 mGM-CSF immunotoxin inhibited FDCP2.1d, a murine myelomonocytic tumor line expressing the GM-CSF receptor with an IC50 (concentration inhibiting 50% activity) of 5 x 10(-11) mol/L. The fusion toxin was specifically cytotoxic and directed by the GM-CSF portion of the molecule because addition of a monoclonal antibody directed against GM-CSF inhibited its ability to kill the cell line. Cell lines that do not express GM-CSF receptor were not inhibited by the fusion toxin. DT390 mGM-CSF was also able to specifically inhibit normal committed bone marrow (BM) progenitor cells as measured in clonal colony-forming unit granulocyte-macrophage assays. Together, these findings indicate that DT390 mGM-CSF may be useful as a novel tool for purging BM of contaminating leukemia cells or in vivo for eliminating residual leukemia cells. Also, it can be used to determine whether committed and/or noncommitted BM progenitor cells express the GM-CSF receptor.

A murine cytokine fusion toxin specifically targeting the murine granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor on normal committed bone marrow progenitor cells and GM-CSF-dependent tumor cells

A fusion protein was synthesized consisting of the murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) gene spliced to a truncated form of the diphtheria toxin (DT390) gene coding for a molecule that retained full enzymatic activity, but excluded the native binding domain. The DT390-mGM-CSF hybrid gene was cloned into a vector under the control of an inducible promoter and the protein expressed in Escherichia coli. After induction, a protein was purified from inclusion bodies in accord with the deduced molecular weight of DT390 mGM-CSF. Cell-free studies of the adenosine diphosphate-ribosylating activity of DT390 mGM-CSF showed results that were similar to those of native DT. The DT390 mGM-CSF immunotoxin inhibited FDCP2.1d, a murine myelomonocytic tumor line expressing the GM-CSF receptor with an IC50 (concentration inhibiting 50% activity) of 5 x 10(-11) mol/L. The fusion toxin was specifically cytotoxic and directed by the GM-CSF portion of the molecule because addition of a monoclonal antibody directed against GM-CSF inhibited its ability to kill the cell line. Cell lines that do not express GM-CSF receptor were not inhibited by the fusion toxin. DT390 mGM-CSF was also able to specifically inhibit normal committed bone marrow (BM) progenitor cells as measured in clonal colony-forming unit granulocyte-macrophage assays. Together, these findings indicate that DT390 mGM-CSF may be useful as a novel tool for purging BM of contaminating leukemia cells or in vivo for eliminating residual leukemia cells. Also, it can be used to determine whether committed and/or noncommitted BM progenitor cells express the GM-CSF receptor.

Characterization of the epitope recognized by a mAb that reacts differentially with murine suppressor T cells.

Although reliable antibodies are available that distinguish human suppressor T (Ts) cells from CTL and other T cells, few are available for murine Ts cells. We have developed a mAb (984D4.6.5) that, in the presence of complement, depletes alloantigen-specific Ts cells but not CTL. This antibody recognizes activated Ts cells but not their precursors. In these studies, flow cytometric analysis demonstrates that 984D4.6.5 reacts with several Ts cell hybridomas, cloned Ts cell lines and WEHI-3 (a myelomonocytic tumor cell line). Reactivity was not detected with BW5147, Th cell hybridomas, cloned Th cells, CTL lines and hybridomas, B cell lines, thymocytes, splenocytes, bone marrow cells nor a variety of tumor cells. Among 984D4.6.5 positive lines, expression is heterogeneous and the number of cells expressing high levels of the epitope is increased when the hybridomas are maintained at a relatively high cell density. Neuriminidase and pronase deplete the epitope recognized by mAb 984D4.6.5. Protein synthesis and glycosylation inhibitors also reduce expression of this epitope. These observations suggest that the epitope recognized by 984D4.6.5 is a carbohydrate linked to a polypeptide. This antibody was tested by ELISA for binding to a large panel of carbohydrates and glycolipids coupled to BSA. The only one that bound 984D4.6.5 was LS tetrasaccharide c (NeuNAc alpha 2-6Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc), an O-linked carbohydrate. Comparative analysis shows that both the sequence and the linkage of these sugars are essential to the reactivity with the 984D4.6.5 antibody. This epitope is expressed by a glycoprotein of approximately 200 kDa, as shown by Western blots. The identity of this glycoprotein remains to be determined, but indirect evidence suggests that it is not CD45.

High frequency of myelomonocytic tumors in aging E mu L-myc transgenic mice.

Transgenic mice that contain constructs of the L-myc gene under the transcriptional control of the immunoglobulin heavy chain enhancer (E mu) develop thymic hyperplasia and are predisposed to T cell lymphomas. Here we describe a second form of malignancy that occurs in aging E mu L-myc transgenic mice. The mean latency period for the development of this malignancy is longer compared with the E mu L-myc T cell lymphomas but the overall incidence is increased threefold. The histopathological morphology is that of a highly malignant mesenchymal neoplasm that closely resembles human fibrous histiocytoma. The tumor cells were classified as myelomonocytic on the basis of several lineage-specific markers and the lack of rearrangements of the immunoglobulin heavy chain and the T cell receptor beta loci. Cultured tumor cells produce macrophage colony-stimulating factor (M-CSF) protein and express the M-CSF receptor, suggesting the involvement of an autocrine loop in this malignancy. Similar to the E mu L-myc T cell lymphomas, these tumors show high-level transgene expression but no detectable levels of endogenous c-myc mRNA, directly implicating the deregulated expression of L-myc in the generation of this malignancy. E mu L-myc myelomonocytic tumors show consistent trisomy of chromosome 16, implicating this as a secondary event in the development of this tumor. In the light of recent findings that L-myc is expressed in human myeloid leukemias and in several human myeloid tumor cell lines, the results described here might implicate L-myc in the development of naturally occurring myeloid neoplasias.

Mouse macrophage ? subunit (CD11b) cDNA for the CR3 complement receptor/Mac-1 antigen

The cDNA for the common beta Mac-1 subunit (CD11b) of the mouse LFA-1/Mac-1/p150,95 group of leukocyte cell adhesion receptors, formally designated integrin beta 2, has been cloned and sequenced. Clones were isolated from cDNA libraries made from J774 macrophage and WEHI-3B myelomonocytic tumor cells which express this subunit as a component of the macrophage activation antigen 1 (Mac-1), also known as complement receptor type 3 (CR3). This subunit is expressed as a single, abundant mRNA species approximately 2.7 kilobase (kb) in size. The 2422 base pair (bp) cDNA sequence obtained codes for a 771 amino acid protein organized with leader, extracellular, transmembrane, and cytoplamic domains of 23, 680, 23, and 46 amino acids, respectively, yielding an 82,700 mature protein of 747 amino acids. The mouse beta Mac-1 subunit is highly similar to its human counterpart with an overall sequence identity of 81% and identical positioning of 5 out of 6 potential N-linked glycosylation sites, as well as 56 Cys residues that are organized in repeating motifs characteristic of integrin beta subunits. The most highly conserved regions are the transmembrane and cytoplasmic domains where only 4 out of 69 amino acids differ, indicating that the functions associated with this domain in Mac-1-mediated processes, such as iC3b-triggered phagocytosis, have been evolutionarily conserved.

Moloney murine leukemia virus-induced myeloid tumors in adult BALB/c mice: requirement of c-myb activation but lack of v-abl involvement.

BALB/c mice treated with pristane and Abelson virus have been used as an animal model system for the rapid induction of plasmacytomas. Myelomonocytic tumors with helper Moloney murine leukemia virus clonally inserted into the c-myb locus were observed in about 10% of pristane-primed BALB/c mice infected with Abelson virus. However, v-abl was absent in almost all of those tumors. Since Moloney virus is thought to induce mostly T-cell lymphomas, we have carried out studies to investigate this alteration of disease specificity and to determine whether v-abl played an obligatory role in the development of these tumors. We found that, whereas lymphomas developed late (greater than 3 months) in both pristane-primed and unprinted control mice, the myelomonocytic tumors arose at a high frequency, within 3 months, but only in pristane-treated mice. Clonal Moloney virus insertion was again found in each of the seven myelomonocytic tumors examined. Northern blot analyses and S1 mapping studies revealed the presence of virally promoted chimeric mRNAs that lack the three 5'-most myb coding exons. Hence it appears that the requirement for the v-abl gene product in tumor induction is not obligatory. Our results also indicate that tumor-specific alteration at the 5' end of the myb gene plays an important role in the development of these tumors.

Alternative internal splicing in c-myb RNAs occurs commonly in normal and tumor cells.

Activation of the c-myb gene by viral transduction or proviral insertional mutagenesis that is likely to result in the production of structurally altered myb proteins has been shown to be predominantly associated with myelomonocytic tumors. An alternative splicing event in which a portion of the intron bounded by the vE6 and vE7 exons with v-myb homology is included as an additional 363-nucleotide coding exon has recently been identified in a mouse tumor that carries a provirus-activated myb gene. This alternative splicing was hypothesized to be a tumor-specific aberrant form of 3'-myb RNA processing as a consequence of the disruption of upstream 5'-sequences by proviral insertion. However, RNA blot analyses and RNase mapping studies presented here show that a significant portion (approximately 10%) of all myb transcripts examined, whether in normal or in clonal tumor cells, contains the additional exon. Hence the alternative splicing is a hitherto unrecognized common normal event that potentially increases the diversity of the myb proteins expressed in normal tissues including thymus and spleen, as well as in tumor cells with either normal or 5'-rearranged myb alleles. The lack of change in the ratio of the two spliced products expressed from either the normal or the 5'-rearranged myb further indicates that the insertion of the unique 121 amino acids in the larger myb transcripts is not a consequence of tumor-specific activation of the mouse myb oncogene.

Isolation from the spleen of myeloproliferative sarcoma virus-infected mice of a myelomonocytic tumor cell line secreting hematopoietic colony stimulating factors

Clonogenic tumor cells were detected in the spleen of DBA/2 mice infected with the myeloproliferative sarcoma virus (MPSV). These cells could be isolated because of their ability to proliferate on the greater omentum of sublethally irradiated isogenic recipient mice. We have established a permanent suspension myelomonocytic cell line in vitro (TE 8), from a tumor obtained after subcutaneous transplantation of the omental tumor masses. The TE 8 cells are clonogenic in semi-solid medium containing agarose. The colonies thus obtained gave rise to myelomonocytic cell lines growing in suspension in liquid medium. One of those cloned cell lines, C1 1011 was studied in details. It is exclusively composed of initial donor cells, it is tumorigenic in vivo, clonogenic in vitro and produces MPSV. It also secretes a colony stimulating activity (CSA), and an activity termed mixed colony promoting activity (MPA), which enables pluripotent hematopoietic stem cells to proliferate and differentiate. It differentiates through the granulomacrophage cell line independently of exogenous factors other than those which may be present in the serum.

Characterization and functional properties of tumor cell lines in accessory cell replacement assays.

This study reports the initial phenotypic and functional characterization of a series of cloned, murine, myelomonocytic tumors and their parent cell line WEHI-3, and a group of murine B lymphoma tumors. The tumor cell lines of the myelomonocytic lineage demonstrated the ability to reconstitute a macrophage-depleted, primary in vitro anti-SRBC PFC response, but only marginally enhanced an accessory cell-depleted, ova-primed, lymphocyte proliferation in vitro response. The B lymphoma tumors displayed exactly the reverse functional profile, being highly efficient in reconstitution of the proliferation response, but not supporting the SRBC PFC response. Detailed analysis of the cell surface phenotype of the various B lymphoma tumors used in this study show they display cell surface markers characteristic of normal B lymphocytes but are heterogeneous in their various stages of differential arrest. Future work will concentrate on the orchestration of Ia-mediated and soluble factor-mediated (IL 1) modalities of antigen-triggering of lymphocytes by these B lymphoma and myelomonocytic tumor cell lines.

Demonstration of migration inhibitory factor (MIF) in a murine system using myelomonocytic leukemia cells (WEHI-3)

Cells of the myelomonocytic tumor cell line, WEHI-3, were used as indicator cells in the indirect capillary test for the detection of migration inhibitory factor (MIF). A migration inhibition of about 50% was found and the results were highly reproducible. The indicator cells can be obtained in large quantities, as the myelomonocytic cells grow as an ascitic tumor in the peritoneal cavity of BALB/c mice.