Establishment and phenotypic characterization of human U937 cells with inducible P210 BCR/ABL expression reveals upregulation of CEACAM1 (CD66a)

Generation and characterization of U937-TR: a platform cell line for inducible gene expression in human macrophages

Monocytes and macrophages are involved in a wide range of biological processes and parasitic diseases. The characterization of the molecular mechanisms governing such processes usually requires precise control of the expression of genes of interest. We implemented a tetracycline-controlled gene expression system in the U937 cell line, one of the most used in vitro models for the research of human monocytes and macrophages. Here we characterized U937-derived cell lines in terms of phenotypic (morphology and marker expression) and functional (capacity for phagocytosis and for Leishmania parasite hosting) changes induced by phorbol-12-myristate-13-acetate (PMA). Finally, we provide evidence of tetracycline-inducible and reversible Lamin-A gene silencing of the PMA-differentiated U937-derived cells.

CEACAM1 long isoform has opposite effects on the growth of human mastocytosis and medullary thyroid carcinoma cells

Carcinoembryonic antigen‐related cell adhesion molecule 1 (CEACAM1) is expressed in a number of tumor cell types. The immunoreceptor tyrosine‐based inhibitory motif (ITIM)‐containing isoforms of this molecule which possess a long cytoplasmic tail (CEACAM1‐L) generally play inhibitory roles in cell function by interacting with Src homology 2 domain‐containing tyrosine phosphatase (SHP)‐1 and/or SHP‐2. Src family kinases (SFKs) are also known to bind to and phosphorylate CEACAM1‐L isoforms. Here, we report that CEACAM1 was uniquely expressed at high levels in both human neoplastic mast cells (mastocytosis) and medullary thyroid carcinoma cell (MTC) lines, when compared with their expression in nonneoplastic mast cells or nonneoplastic C cells. This expression was mainly derived from CEACAM1‐L isoforms based upon assessment of CEACAM1 mRNA expression. CEACAM1 knockdown upregulated cell growth of HMC1.2 cells harboring KIT mutations detected in clinical mastocytosis, whereas downregulated the growth of TT cells harboring RET mutations detected in clinical MTCs. Immunoblotting, ELISA and immunoprecipitaion analysis showed that activated SHP‐1 is preferentially associated with CEACAM1 in HMC1.2 cells harboring KIT mutations, whereas Src family kinases (SFKs) are preferentially associated with CEACAM1 in TT cells harboring RET mutations. These studies suggest that the dominantly interacting proteins SHP1 or SFK determine whether CEACAM1‐L displays a positive or negative role in tumor cells.

Imatinib therapy of chronic myeloid leukemia restores the expression levels of key genes for DNA damage and cell-cycle progression

BACKGROUND

Chronic myeloid leukemia (CML) is a malignant clonal disorder of the hematopoietic system caused by the expression of the BCR/ABL fusion oncogene. It is well known that CML cells are genetically unstable. However, the mechanisms by which these cells acquire genetic alterations are poorly understood. Imatinib mesylate is the standard therapy for newly diagnosed CML patients. Imatinib mesylate targets the oncogenic kinase activity of BCR-ABL.

OBJECTIVE

To study the gene expression profile of bone marrow hematopoietic cells in the same patients with CML before and 1 month after imatinib therapy.

METHODS

Samples from patients with CML were analyzed using Affymetrix GeneChip Expression Arrays.

RESULTS

A total of 594 differentially expressed genes, most of which (393 genes) were downregulated, as a result of imatinib therapy were observed.

CONCLUSION

The blockade of oncoprotein Bcr-Abl by imatinib could cause a decrease in the expression of key DNA repair genes and substantially modify the expression profile of the bone marrow cells in the first days of therapy.

Antigens in chronic myeloid leukemia: implications for vaccine development

Treatment with imatinib mesylate and other tyrosine kinase inhibitors (TKI) revolutionized the therapy of chronic myeloid leukemia (CML). However, it alone does not cure this disease. Moreover, some patients develop resistance or adverse effects to this therapy. As successful treatment of a portion of CML patients by hematopoietic stem cell transplantation (HSCT) suggests the importance of immune mechanisms in the elimination of leukemic cells, including leukemia stem cells, TKI administration or HSCT might be combined with vaccination to cure CML patients. However, antigens implicated in the immune responses have not yet been sufficiently identified. Therefore, in this report, we compiled and characterized a list of 165 antigens associated with CML (CML-Ag165) and analyzed the expression of the corresponding genes in CML phases, subpopulations of leukemic cells, and CML-derived cell lines using available datasets from microarray transcriptional-profiling studies. From the CML-Ag165 list, we selected antigens most suitable for vaccine development and evaluated their appropriate characteristics.

Glucose availability in hypoxia regulates the selection of chronic myeloid leukemia progenitor subsets with different resistance to imatinib-mesylate

BACKGROUND

Incubation of chronic myeloid leukemia cells in hypoxia inhibits growth and selects BCR/Abl-independent cells with stem cell properties which are refractory to imatinib-mesylate. This study aimed to characterize the relationship of this refractoriness with glucose availability in the environment.

DESIGN AND METHODS

K562 or primary chronic myeloid leukemia cells were cultured at 0.1% O(2), different cell densities and glucose concentrations. The stem and progenitor cell potential of these cultures at different times of incubation in relation to BCR/Abl(protein) expression and sensitivity to imatinib-mesylate was explored by transferring cells to growth-permissive secondary cultures in normoxia, according to the Culture-Repopulating Ability assay methodology.

RESULTS

Hypoxia-resistant cells maintained BCR/Abl(protein) expression until glucose was no longer available in primary hypoxic cultures, where glucose availability appeared to regulate cell number and the balance between the enrichment of cells with kinetic properties typical of stem or progenitor cells. Cells surviving merely hypoxic conditions were, upon transfer to secondary cultures, immediately available for numerical expansion due to the maintained BCR/Abl(protein) expression, and were consequently sensitive to imatinib-mesylate. Instead, BCR/Abl(protein)-negative cells selected in primary cultures under oxygen/glucose shortage underwent a delayed numerical expansion in secondary cultures, which was completely refractory to imatinib-mesylate. Cells with the latter properties were also found in primary chronic myeloid leukemia explants.

CONCLUSIONS

Glucose shortage in hypoxia was shown to represent the condition selecting BCR/Abl(protein)-negative cells refractory to imatinib-mesylate from either chronic myeloid leukemia lines or patients. These cells, exhibiting stem cell properties in vitro, are metabolically suited to home to stem cell niches in vivo and so may represent the chronic myeloid leukemia cell subset responsible for minimal residual disease.

Tetracycline regulator expression alters the transcriptional program of mammalian cells

Background

Tetracycline regulated ectopic gene expression is a widely used tool to study gene function. However, the tetracycline regulator (tetR) itself has been reported to cause certain phenotypic changes in mammalian cells. We, therefore, asked whether human myeloid U937 cells expressing the tetR in an autoregulated manner would exhibit alterations in gene expression upon removal of tetracycline.

Methodology/Principal Findings

Microarray analyses revealed that 172 and 774 unique genes were significantly differentially expressed by at least 2- or 1.5-fold, respectively, when tetR expressing U937 cells were maintained in media with or without the antibiotic.

Conclusions/Significance

These alterations in gene expression are likely to contribute to the phenotypic consequences of tetR expression. In addition, they need to be taken into consideration when using the tetR system for the identification of target genes of transcription factors or other genes of interest.

The t(X;7)(q22;q34) in paediatric T-cell acute lymphoblastic leukaemia results in overexpression of the insulin receptor substrate 4 gene through illegitimate recombination with the T-cell receptor beta locus

The t(X;7)(q22;q34), a translocation not previously reported in a neoplastic disorder, was identified and molecularly characterised in a paediatric T-cell acute lymphoblastic leukaemia (T-ALL), subsequently shown also to harbour a deletion of 6q, a STIL/TAL1 fusion and an activating NOTCH1 mutation. The t(X;7) was further investigated using fluorescence in situ hybridisation (FISH), real-time quantitative polymerase chain reaction (RQ-PCR) and Western blot analyses. FISH revealed a breakpoint at the T-cell receptor beta locus at 7q34 and mapped the corresponding breakpoint to Xq22.3. The latter region contains only two known genes, namely insulin receptor substrate 4 (IRS4) and collagen, type IV, alpha 5 (COL4A5), the expressions of which were analysed by the use of RQ-PCR. COL4A5 was not differentially expressed in the t(X;7)-positive sample compared to five T-ALL controls. However, a marked, 1000-fold overexpression of IRS4 was identified. Western blot analysis with a monoclonal antibody against IRS4 showed overexpression also at the protein level. Considering that forced expression of several members of the IRS family has been shown to result in increased cell proliferation, for example in haematopoietic cells, we hypothesise that the IRS4 up-regulation in T-ALL is pathogenetically important as a mitogenic stimulus.

High expression of CEACAM6 and CEACAM8 mRNA in acute lymphoblastic leukemias

CEACAM family members are a set of widely expressed proteins involved in several biological functions, including cell adhesion, migration, signal transduction, and the regulation of gene expression. Abnormal overexpression and downregulation of some CEACAMs have been described in tumor cells. Monoclonal antibodies grouped in the CD66 cluster recognize CEACAM members. Ectopic CD66 expression is commonly detected in B-cell lineage acute lymphoblastic leukemia (ALL). To investigate the CEACAM messenger RNA (RNA) expression in leukemic blasts, we performed a quantitative polymerase chain reaction (RQ-PCR) analysis in purified RNA samples from a consecutive series of acute leukemias (135 patients). Most B-cell lineage ALL expressed CD66 (79.5%), whereas no single case of T-cell lineage ALL disclosed CD66 reactivity (0%). All the BCR-ABL+ ALL cases showed CD66 expression. CD66 was positive even in cases without CD10 expression (72.7%) and/or with MLL rearrangements. Despite the sharp contrast between T-ALL and B-ALL in CD66 reactivity, CEACAM patterns were comparable, and only minor differences for CEACAM1 and CEACAM8 were detected. All the leukemic samples showed overexpression of CEACAM6 and 8 when compared with normal granulocytes. These results were confirmed by dilutional experiments. The leukemic pattern paralleled the normal regenerating bone marrow with lower values for CEACAM1. In line with the results for CD66 reactivity, neoplastic cell lines had a uniform low expression of CEACAM family members. It remains to be investigated whether these CEACAM disturbances provide growth advantages to tumoral cells by inhibiting the anoikis process.

Deregulation of the Wilms' tumour gene 1 protein (WT1) by BCR/ABL1 mediates resistance to imatinib in human leukaemia cells

The Wilms' tumour gene 1 (WT1) protein is highly expressed in most leukaemias. Co-expression of WT1 and the fusion protein AML1-ETO in mice rapidly induces acute myeloid leukaemia (AML). Mechanisms behind expression of WT1, as well as consequences thereof, are still unclear. Here, we report that the fusion protein BCR/ABL1 increases expression of WT1 mRNA and protein via the phosphatidylinositol-3 kinase (PI3K)-Akt pathway. Inhibition of BCR/ABL1 or PI3K activity strongly suppressed transcription from WT1 promoter/enhancer reporters. Forced expression of BCR/ABL1 in normal human progenitor CD34+ cells increased WT1 mRNA and protein, further supporting the notion of BCR/ABL1-driven expression of WT1 in human haematopoietic cells. Forced expression of WT1 in K562 cells provided protection against cytotoxic effects of the ABL1 tyrosine kinase inhibitor imatinib, as judged by effects on viability measured by trypan blue exclusion, metabolic activity, annexin V and DAPI (4', 6-diamidino-2-phenylindole) staining. None of the isoforms provided any detectable protection against apoptosis induced by arsenic trioxide and only very weak protection against etoposide, indicating that WT1 interferes with specific apoptotic signalling pathways. Our data demonstrate that WT1 expression is induced by oncogenic signalling from BCR/ABL1 and that WT1 contributes to resistance against apoptosis induced by imatinib.

Expression of the p210BCR-ABL oncoprotein drives centrosomal hypertrophy and clonal evolution in human U937 cells

Centrosomes play fundamental roles in mitotic spindle organization, chromosome segregation and maintenance of genetic stability. Recently, we have shown that centrosome aberrations occur early in chronic myeloid leukemia (CML) and are induced by imatinib in normal fibroblasts in vitro. To investigate the influence of BCR-ABL on centrosomes, we performed long-term in vitro experiments employing the conditionally p210BCR-ABL-expressing (tetracycline-inducible promoter) human monocytic cell line U937p210BCR-ABL/c6 as a model of CML chronic phase. Centrosome hypertrophy was detectable after 4 weeks of transgene expression onset, increasing up to a rate of 25.7% aberrant cells within 13 weeks of propagation. This concurred with clonal expansion of aneuploid cells displaying a hyperdiploid phenotype with 57 chromosomes. Partial reversibility of centrosome aberrations (26-8%) was achieved under prolonged propagation (14 weeks) after abortion of induction and bcr-abl silencing using small interfering RNA. Therapeutic doses of imatinib did not revert the aberrant phenotype, but counteracted the observed reverting effect of bcr-abl gene expression switch off. Suggesting a mechanistic model that features distinct abl-related tyrosine kinase activity levels as essential determinants of centrosomal integrity, this is the first report mechanistically linking p210BCR-ABL oncoprotein activity to centrosomal hypertrophy.

A novel mechanism for BCR-ABL action: stimulated secretion of CCN3 is involved in growth and differentiation regulation

Chronic myeloid leukemia (CML) is characterized by the presence of the constitutively active BCR-ABL protein tyrosine kinase. Using a multipotent hemopoietic cell line, FDCP-Mix, expressing BCR-ABL tyrosine kinase, we investigated the initial effects of this kinase in primitive hematopoietic stem cells. We identified down-regulation of a novel gene, CCN3, as a direct consequence of BCR-ABL kinase activity. CCN3 has been reported to function as a tumor suppressor gene in solid tumors. Northern and Western blotting plus immunocytochemical analysis confirmed CCN3 expression is decreased and is tyrosine-phosphorylated in BCR-ABL kinase active FDCP-Mix cells. Decreased cellular CCN3 correlated with increased CCN3 secretion in BCR-ABL kinase active cells. In vitro treatment of human CML cell lines with imatinib or siRNA directed against BCR-ABL significantly reduced BCR-ABL while increasing CCN3 expression. Cells from patients responding to imatinib showed a similar decrease in BCR-ABL and increase in CCN3. CML CD34+ cells treated with imatinib in vitro demonstrated increased CCN3 protein. Transfecting CCN3 into BCR-ABL+ cells inhibited proliferation and decreased clonogenic potential. CCN3 plays an important role in internal and external cell-signaling pathways. Thus, BCR-ABL can regulate protein levels by governing secretion, a novel mechanism for this tyrosine kinase.

Identification of transcriptional targets associated with the expression of p210 Bcr-Abl

OBJECTIVES

Chronic myeloid leukaemia is caused by the expression of the p210 Bcr-Abl fusion protein which results from the Philadelphia translocation, t(9;22). This oncogene has been the focus of extensive research. However, the molecular mechanisms responsible for the haematological malignancy are not fully understood. The main objective of the current study was to identify novel transcriptional targets of Bcr-Abl.

METHODS

In order to achieve this, microarrays were employed in order to conduct a genome-wide expression analysis comparing 32D cells with a transfected clone expressing high levels of p210 Bcr-Abl. Quantitative RT-PCR was employed in order to confirm the observed increase/decrease in expression for a number of the deregulated genes.

RESULTS AND CONCLUSIONS

This comparison identified 138 genes of known function showing altered expression in response to Bcr-Abl-mediated signalling. Among the genes found to be upregulated in response to p210 Bcr-Abl were aldolase 1A and phosphofructokinase, both of which encode key enzymes in the glycolytic pathway. As a consequence of this, we demonstrate that the rate of glycolysis is significantly increased in Bcr-Abl expressing cells in a PI3K-dependent manner. Our results also indicate altered expression of genes involved in cell proliferation, cell adhesion and cell signalling.

Identification of genes differentially regulated by the P210 BCR/ABL1 fusion oncogene using cDNA microarrays

OBJECTIVE

The t(9;22) translocation is associated with more than 95% of cases of chronic myeloid leukemia. The resulting fusion of the BCR and ABL1 loci produces the constitutively active BCR/ABL1 tyrosine kinase. A wide range of signal transduction molecules are activated by BCR/ABL1, including MYC, PI-3 kinase, and different STAT molecules. In contrast, relatively few genes are known to be regulated by BCR/ABL1 at the level of transcription.

MATERIALS AND METHODS

In an effort to better understand the transcriptional program activated by BCR/ABL1, we used cDNA microarrays to evaluate the relative expression of approximately 6450 human genes in U937 myelomonocytic cells expressing P210 BCR/ABL1 via a tetracycline-inducible promoter.

RESULTS

We confirmed the previously reported up-regulation of the PIM1 and JUN oncogenes by BCR/ABL1. In addition, we identified 59 more genes up-regulated by BCR/ABL1. Interestingly, roughly one third of these were genes previously reported to be interferon (IFN)-responsive, including the OAS1, IFIT1, IFI16, ISGF3G, and STAT1 genes. An additional seven BCR/ABL1-regulated genes were found to be IFN-responsive in U937 cells. The expression profile also included genes encoding transcription factors, kinases, and signal transduction molecules, as well as genes regulating cell growth, differentiation, apoptosis, and cell adhesion, features previously suggested to be affected by BCR/ABL1.

CONCLUSION

These observations shed novel insight into the mechanism of BCR/ABL1 action and provide a range of targets for further investigation.