L-myc and N-myc in hematopoietic malignancies

N-MYC regulates cell survival via eIF4G1 in inv(16) acute myeloid leukemia

N-MYC (encoded by MYCN) is a critical regulator of hematopoietic stem cell function. While the role of N-MYC deregulation is well established in neuroblastoma, the importance of N-MYC deregulation in leukemogenesis remains elusive. Here, we demonstrate that N-MYC is overexpressed in acute myeloid leukemia (AML) cells with chromosome inversion inv(16) and contributes to the survival and maintenance of inv(16) leukemia. We identified a previously unknown MYCN enhancer, active in multiple AML subtypes, essential for MYCN mRNA levels and survival in inv(16) AML cells. We also identified eukaryotic translation initiation factor 4 gamma 1 (eIF4G1) as a key N-MYC target that sustains leukemic survival in inv(16) AML cells. The oncogenic role of eIF4G1 in AML has not been reported before. Our results reveal a mechanism whereby N-MYC drives a leukemic transcriptional program and provides a rationale for the therapeutic targeting of the N-MYC/eIF4G1 axis in myeloid leukemia.

Mouse models of pediatric high-grade gliomas with MYCN amplification reveal intratumoral heterogeneity and lineage signatures

Pediatric high-grade gliomas of the subclass MYCN (HGG-MYCN) are highly aggressive tumors frequently carrying MYCN amplifications, TP53 mutations, or both alterations. Due to their rarity, such tumors have only recently been identified as a distinct entity, and biological as well as clinical characteristics have not been addressed specifically. To gain insights into tumorigenesis and molecular profiles of these tumors, and to ultimately suggest alternative treatment options, we generated a genetically engineered mouse model by breeding hGFAP-cre::Trp53Fl/Fl::lsl-MYCN mice. All mice developed aggressive forebrain tumors early in their lifetime that mimic human HGG-MYCN regarding histology, DNA methylation, and gene expression. Single-cell RNA sequencing revealed a high intratumoral heterogeneity with neuronal and oligodendroglial lineage signatures. High-throughput drug screening using both mouse and human tumor cells finally indicated high efficacy of Doxorubicin, Irinotecan, and Etoposide as possible therapy options that children with HGG-MYCN might benefit from.

CD47-Dependent Regulation of Immune Checkpoint Gene Expression and MYCN mRNA Splicing in Murine CD8 and Jurkat T Cells

Elevated expression of CD47 in some cancers is associated with poor survival related to its function as an innate immune checkpoint when expressed on tumor cells. In contrast, elevated CD47 expression in cutaneous melanomas is associated with improved survival. Previous studies implicated protective functions of CD47 expressed by immune cells in the melanoma tumor microenvironment. RNA sequencing analysis of responses induced by CD3 and CD28 engagement on wild type and CD47-deficient Jurkat T lymphoblast cells identified additional regulators of T cell function that were also CD47-dependent in mouse CD8 T cells. MYCN mRNA expression was upregulated in CD47-deficient cells but downregulated in CD47-deficient cells following activation. CD47 also regulated alternative splicing that produces two N-MYC isoforms. The CD47 ligand thrombospondin-1 inhibited expression of these MYCN mRNA isoforms, as well as induction of the oncogenic decoy MYCN opposite strand (MYCNOS) RNA during T cell activation. Analysis of mRNA expression data for melanomas in The Cancer Genome Atlas identified a significant coexpression of MYCN with CD47 and known regulators of CD8 T cell function. Thrombospondin-1 inhibited the induction of TIGIT, CD40LG, and MCL1 mRNAs following T cell activation in vitro. Increased mRNA expression of these T cell transcripts and MYCN in melanomas was associated with improved overall survival.

MYCN Drives a Tumor Immunosuppressive Environment Which Impacts Survival in Neuroblastoma

A wide range of malignancies presents MYCN amplification (MNA) or dysregulation. MYCN is associated with poor prognosis and its over-expression leads to several dysregulations including metabolic reprogramming, mitochondria alteration, and cancer stem cell phenotype. Some hints suggest that MYCN overexpression leads to cancer immune-escape. However, this relationship presents various open questions. Our work investigated in details the relationship of MYCN with the immune system, finding a correlated immune-suppressive phenotype in neuroblastoma (NB) and different cancers where MYCN is up-regulated. We found a downregulated Th1-lymphocytes/M1-Macrophages axis and upregulated Th2-lymphocytes/M2-macrophages in MNA NB patients. Moreover, we unveiled a complex immune network orchestrated by N-Myc and we identified 16 genes modules associated to MNA NB. We also identified a MYCN-associated immune signature that has a prognostic value in NB and recapitulates clinical features. Our signature also discriminates patients with poor survival in non-MNA NB patients where MYCN expression is not discriminative. Finally, we showed that targeted inhibition of MYCN by BGA002 (anti-MYCN antigene PNA) is able to restore NK sensibility in MYCN-expressing NB cells. Overall, our study unveils a MYCN-driven immune network in NB and shows a therapeutic option to restore sensibility to immune cells.

Molecular Mechanisms of MYCN Dysregulation in Cancers

MYCN, a member of MYC proto-oncogene family, encodes a basic helix-loop-helix transcription factor N-MYC. Abnormal expression of N-MYC is correlated with high-risk cancers and poor prognosis. Initially identified as an amplified oncogene in neuroblastoma in 1983, the oncogenic effect of N-MYC is expanded to multiple neuronal and nonneuronal tumors. Direct targeting N-MYC remains challenge due to its "undruggable" features. Therefore, alternative therapeutic approaches for targeting MYCN-driven tumors have been focused on the disruption of transcription, translation, protein stability as well as synthetic lethality of MYCN. In this review, we summarize the latest advances in understanding the molecular mechanisms of MYCN dysregulation in cancers.

Suppression of ABCE1-Mediated mRNA Translation Limits N-MYC-Driven Cancer Progression

The ability of the N-MYC transcription factor to drive cancer progression is well demonstrated in neuroblastoma, the most common extracranial pediatric solid tumor, where MYCN amplification heralds a poor prognosis, with only 11% of high-risk patients surviving past 5 years. However, decades of attempts of direct inhibition of N-MYC or its paralogues has led to the conclusion that this protein is "undruggable." Therefore, targeting pathways upregulated by N-MYC signaling presents an alternative therapeutic approach. Here, we show that MYCN-amplified neuroblastomas are characterized by elevated rates of protein synthesis and that high expression of ABCE1, a translation factor directly upregulated by N-MYC, is itself a strong predictor of poor clinical outcome. Despite the potent ability of N-MYC in heightening protein synthesis and malignant characteristics in cancer cells, suppression of ABCE1 alone selectively negated this effect, returning the rate of translation to baseline levels and significantly reducing the growth, motility, and invasiveness of MYCN-amplified neuroblastoma cells and patient-derived xenograft tumors in vivo. The growth of nonmalignant cells or MYCN-nonamplified neuroblastoma cells remained unaffected by reduced ABCE1, supporting a therapeutic window associated with targeting ABCE1. Neuroblastoma cells with c-MYC overexpression also required ABCE1 to maintain cell proliferation and translation. Taken together, ABCE1-mediated translation constitutes a critical process in the progression of N-MYC-driven and c-MYC-driven cancers that warrants investigations into methods of its therapeutic inhibition. SIGNIFICANCE: These findings demonstrate that N-MYC-driven cancers are reliant on elevated rates of protein synthesis driven by heightened expression of ABCE1, a vulnerability that can be exploited through suppression of ABCE1.

Targeting cancer stem cell pathways for cancer therapy

Since cancer stem cells (CSCs) were first identified in leukemia in 1994, they have been considered promising therapeutic targets for cancer therapy. These cells have self-renewal capacity and differentiation potential and contribute to multiple tumor malignancies, such as recurrence, metastasis, heterogeneity, multidrug resistance, and radiation resistance. The biological activities of CSCs are regulated by several pluripotent transcription factors, such as OCT4, Sox2, Nanog, KLF4, and MYC. In addition, many intracellular signaling pathways, such as Wnt, NF-κB (nuclear factor-κB), Notch, Hedgehog, JAK-STAT (Janus kinase/signal transducers and activators of transcription), PI3K/AKT/mTOR (phosphoinositide 3-kinase/AKT/mammalian target of rapamycin), TGF (transforming growth factor)/SMAD, and PPAR (peroxisome proliferator-activated receptor), as well as extracellular factors, such as vascular niches, hypoxia, tumor-associated macrophages, cancer-associated fibroblasts, cancer-associated mesenchymal stem cells, extracellular matrix, and exosomes, have been shown to be very important regulators of CSCs. Molecules, vaccines, antibodies, and CAR-T (chimeric antigen receptor T cell) cells have been developed to specifically target CSCs, and some of these factors are already undergoing clinical trials. This review summarizes the characterization and identification of CSCs, depicts major factors and pathways that regulate CSC development, and discusses potential targeted therapy for CSCs.

A Critical Review of Animal Models Used in Acute Myeloid Leukemia Pathophysiology

Acute myeloid leukemia (AML) is one of the most frequent, complex, and heterogeneous hematological malignancies. AML prognosis largely depends on acquired cytogenetic, epigenetic, and molecular abnormalities. Despite the improvement in understanding the biology of AML, survival rates remain quite low. Animal models offer a valuable tool to recapitulate different AML subtypes, and to assess the potential role of novel and known mutations in disease progression. This review provides a comprehensive and critical overview of select available AML animal models. These include the non-mammalian Zebrafish and Drosophila models as well as the mammalian rodent systems, comprising rats and mice. The suitability of each animal model, its contribution to the advancement of knowledge in AML pathophysiology and treatment, as well as its advantages and limitations are discussed. Despite some limitations, animal models represent a powerful approach to assess toxicity, and permit the design of new therapeutic strategies.

N-Myc-mediated epigenetic reprogramming drives lineage plasticity in advanced prostate cancer

Despite recent therapeutic advances, prostate cancer remains a leading cause of cancer-related death. A subset of castration resistant prostate cancers become androgen receptor (AR) signaling-independent and develop neuroendocrine prostate cancer (NEPC) features through lineage plasticity. These NEPC tumors, associated with aggressive disease and poor prognosis, are driven, in part, by aberrant expression of N-Myc, through mechanisms that remain unclear. Integrative analysis of the N-Myc transcriptome, cistrome and interactome using in vivo, in vitro and ex vivo models (including patient-derived organoids) identified a lineage switch towards a neural identity associated with epigenetic reprogramming. N-Myc and known AR-co-factors (e.g., FOXA1 and HOXB13) overlapped, independently of AR, at genomic loci implicated in neural lineage specification. Moreover, histone marks specifically associated with lineage-defining genes were reprogrammed by N-Myc. We also demonstrated that the N-Myc-induced molecular program accurately classifies our cohort of patients with advanced prostate cancer. Finally, we revealed the potential for EZH2 inhibition to reverse the N-Myc-induced suppression of epithelial lineage genes. Altogether, our data provide insights on how N-Myc regulates lineage plasticity and epigenetic reprogramming associated with lineage-specification. The N-Myc signature we defined could also help predict the evolution of prostate cancer and thus better guide the choice of future therapeutic strategies.

Upregulated heme biosynthesis, an exploitable vulnerability in MYCN-driven leukemogenesis

The increased heme biosynthesis long observed in leukemia was previously of unknown significance. Heme, synthesized from porphyrin precursors, plays a central role in oxygen metabolism and mitochondrial function, yet little is known about its role in leukemogenesis. Here, we show increased expression of heme biosynthetic genes, including UROD, only in pediatric AML samples that have high MYCN expression. High expression of both UROD and MYCN predicts poor overall survival and unfavorable outcomes in adult AML. Murine leukemic progenitors derived from hematopoietic progenitor cells (HPCs) overexpressing a MYCN cDNA (MYCN-HPCs) require heme/porphyrin biosynthesis, accompanied by increased oxygen consumption, to fully engage in self-renewal and oncogenic transformation. Blocking heme biosynthesis reduced mitochondrial oxygen consumption and markedly suppressed self-renewal. Leukemic progenitors rely on balanced production of heme and heme intermediates, the porphyrins. Porphyrin homeostasis is required because absence of the porphyrin exporter, ABCG2, increased death of leukemic progenitors in vitro and prolonged the survival of mice transplanted with Abcg2-KO MYCN-HPCs. Pediatric AML patients with elevated MYCN mRNA display strong activation of TP53 target genes. Abcg2-KO MYCN-HPCs were rescued from porphyrin toxicity by p53 loss. This vulnerability was exploited to show that treatment with a porphyrin precursor, coupled with the absence of ABCG2, blocked MYCN-driven leukemogenesis in vivo, thereby demonstrating that porphyrin homeostasis is a pathway crucial to MYCN leukemogenesis.

The MYCN Protein in Health and Disease

MYCN is a member of the MYC family of proto-oncogenes. It encodes a transcription factor, MYCN, involved in the control of fundamental processes during embryonal development. The MYCN protein is situated downstream of several signaling pathways promoting cell growth, proliferation and metabolism of progenitor cells in different developing organs and tissues. Conversely, deregulated MYCN signaling supports the development of several different tumors, mainly with a childhood onset, including neuroblastoma, medulloblastoma, rhabdomyosarcoma and Wilms’ tumor, but it is also associated with some cancers occurring during adulthood such as prostate and lung cancer. In neuroblastoma, MYCN-amplification is the most consistent genetic aberration associated with poor prognosis and treatment failure. Targeting MYCN has been proposed as a therapeutic strategy for the treatment of these tumors and great efforts have allowed the development of direct and indirect MYCN inhibitors with potential clinical use.

MYCN is a novel oncogenic target in pediatric T-cell acute lymphoblastic leukemia

MYCN is an oncogene frequently overexpressed in pediatric solid tumors whereas few evidences suggest his involvement in the pathogenesis of haematologic malignancies. Here we show that MYCN is overexpressed in a relevant proportion (40 to 50%) of adult and pediatric T-cell acute lymphoblastic leukemias (T-ALL). Focusing on pediatric T-ALL, MYCN-expressing samples were found almost exclusively in the TAL1-positive subgroup. Moreover, TAL1 knockdown in T-ALL cell lines resulted in a reduction of MYCN expression, and TAL1 directly binds to MYCN promoter region, suggesting that TAL1 pathway activation could sustain the up-regulation of MYCN. The role of MYCN in T-ALL was investigated by peptide nucleic acid (PNA-MYCN)-mediated transcriptional silencing of MYCN and by siRNAs. MYCN knockdown in T-ALL cell lines resulted in a reduction of cell viability, up to 50%, while no effect was elicited with a mismatch PNA. The inhibitory effect of PNA-MYCN on cell viability was due to a significant increase in apoptosis. PNA-MYCN treatment in pediatric T-ALL samples reduced cell viability of leukemic cells from patients with high MYCN expression, while no effect was obtained in MYCN-negative blast cells. These results showed that MYCN is frequently overexpressed in pediatric T-ALL and suggested his role as a candidate for molecularly-directed therapies.

A distinct expression of various gene subsets in CD34+ cells from patients with early and advanced myelodysplastic syndrome

Gene expression profiles of CD34+ cells were compared between 51 MDS patients and 7 controls. The most up-regulated genes in patients included HBG2, HBG1, CYBRD1, HSPA1B, ANGPT, and MYC, while 13 genes related to B-lymphopoiesis showed down-regulation. We observed in advanced MDS patients decreased expression of genes involved in cell cycle control, DNA repair and increased expression of proto-oncogenes, angiogenic and anti-apoptic genes. The results suggest that increased cell proliferation and resistance to apoptosis together with a loss of cell cycle control, damaged DNA repair and altered immune response may play an important role in malignant clone expansion in MDS.

Overexpression of N-Myc rapidly causes acute myeloid leukemia in mice

N-MYC encodes a basic helix-loop-helix/leucine zipper (bHLH/LZ) transcription factor that is frequently overexpressed in human neuroblastoma. N-MYC overexpression has also been reported in human acute myeloid leukemias (AML), which we show here is a frequent event. Myeloid cells in N-Myc-overexpressing mouse bone marrow hyperproliferate but those in c-MYC-overexpressing bone marrow do not. The NH(2)-terminal transactivation domain, nuclear localization signal, and bHLH/LZ domain of N-Myc are essential for this effect. Microarray analysis revealed 969 differentially expressed genes between N-Myc- and c-MYC-overexpressing myeloid cells. N-Myc-overexpressing cells showed decreased transforming growth factor beta signaling and increased c-Jun-NH(2)-kinase signaling, both of which are associated with proliferation and leukemic transformation of myeloid cells. Mice transplanted with bone marrow expressing wild-type N-Myc developed clonal and transplantable AML after approximately 1 month; those transplanted with bone marrow expressing mutant N-Myc did not. Twist, a known suppressor of the p19Arf/p53 pathway, was up-regulated in all tumors. These results show that N-Myc overexpression is highly oncogenic in mouse myeloid cells and suggest that N-MYC up-regulation contributes to human myeloid leukemogenesis.

Conditional MN1-TEL knock-in mice develop acute myeloid leukemia in conjunction with overexpression of HOXA9

The chromosomal translocation t(12; 22)(p13;q11) in human myeloid leukemia generates an MN1-TEL (meningioma 1-translocation-ETS-leukemia) fusion oncoprotein. This protein consists of N-terminal MN1 sequences, a transcriptional coactivator fused to C-terminal TEL sequences, an ETS (E26 transformation-specific) transcription factor. Enforced expression of MN1-TEL in multipotent hematopoietic progenitors in knock-in mice perturbed growth and differentiation of myeloid as well as lymphoid cells. Depending on obligatory secondary mutations, these mice developed T-cell lympholeukemia. Here we addressed the role of MN1-TEL in myeloid leukemogenesis using the same mouse model. Expression of MN1-TEL enhanced the growth of myeloid progenitors in an interleukin 3/stem cell factor (IL-3/SCF)-dependent manner in vitro whereas 10% of MN1-TEL-expressing mice developed altered myelopoiesis with severe anemia after long latency. Coexpression of MN1-TEL and IL-3, but not SCF, rapidly caused a fatal myeloproliferative disease rather than acute myeloid leukemia (AML). Because MN1-TEL+ AML patient cells overexpress HOXA9 (homeobox A9), we tested the effect of coexpression of MN1-TEL and HOXA9 in mice and found that 90% of MN1-TEL+/HOXA9+ mice developed AML much more rapidly than control HOXA9+ mice. Thus, the leukemogenic effect of MN1-TEL in our knock-in mice is pleiotropic, and the type of secondary mutation determines disease outcome.

Insertion of Retroviral Vectors in NOD/SCID Repopulating Human Peripheral Blood Progenitor Cells Occurs Preferentially in the Vicinity of Transcription Start Regions and in Introns

Reports on insertional "genotoxicity" in patients have created intense interest in characterizing retroviral vector integrations on the genomic level. The retroviral vector SF91m3 was used for transduction of human peripheral blood progenitor cells (PBPC). These PBPC were transplanted into nonobese diabetic/severe combined immunodeficient mice. A total of 186 retroviral vector integration sites were isolated by ligation-mediated PCR from chimeric mouse bone marrow of five PBPC donors, sequenced, and blasted against the human genome. Preferred integration near the transcription start regions, within CpG islands, and within Alu regions was observed. Detailed analysis of targeted RefSeq genes showed a favored integration within the first intron. Integrations were most common in genes coding for signaling proteins, transcription factors, and kinases. In all genes targeted independently multiple times the respective orientation of the provirus within the gene was identical, indicating integration hot spot regions and similar steric determinants for integration sites. Possible explanations for these findings could be nonrandom vector integration, clonal selection due to gene expression interference, or engraftment issues related to gene insertion in signaling and cell cycle genes. The low frequency of integrations in exons may be reassuring as to the safety of retroviral gene therapy with normal human PBPC.

Large-scale identification of disease genes involved in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of diseases in which chromosomal aberrations, small insertions or deletions, or point mutations in certain genes have profound consequences for prognosis. However, the majority of AML patients present without currently known genetic defects. Retroviral insertion mutagenesis in mice has become a powerful tool for identifying new disease genes involved in the pathogenesis of leukemia and lymphoma. Here we have used the Graffi-1.4 strain of murine leukemia virus, which causes predominantly AML, in a screen to identify novel genes involved in the pathogenesis of this disease. We report 79 candidate disease genes in common integration sites (CISs) and 15 genes whose family members previously were found to be affected in other studies. The majority of the identified sequences (60%) were not found in lymphomas and monocytic leukemias in previous screens, suggesting a specific involvement in AML. Although most of the virus integrations occurred in or near the 5' or 3' ends of the genes, suggesting deregulation of gene expression as a consequence of virus integration, 18 CISs were located exclusively within the genes, conceivably causing gene disruption.

Large-scale identification of novel potential disease loci in mouse leukemia applying an improved strategy for cloning common virus integration sites

The identification of common virus integration sites (cVIS) in retrovirally induced tumors in mice provides a powerful strategy to isolate novel transforming genes. Applying virus LTR-specific inverse-PCR and RT-PCR combined with automated sequencing on CasBr-M Murine Leukemia Virus (MuLV) induced myeloid leukemias, 126 virus integration sites were cloned. Using locus- and LTR-specific primers, a nested-PCR/Southern-blotting procedure was developed on genomic DNA from a large panel of MuLV-induced leukemias, to analyse whether a particular virus insertion represented a cVIS. In fact 39 out of 41 integrations analysed this way appeared to represent a common virus integration. We recognized six previously cloned cVISs, i.e. Evi1, Hoxa7, c-Myb, Cb2/Evi11, Evi12, and His1 and 33 novel common insertions, designated Cas-Br Virus Integration Site (Casvis). Among this group we found integrations in or near genes encoding nuclear proteins, e.g. Dnmt-2, Nm23-M2, Ctbp1 or Erg, within receptor genes, e.g. Cb2 or mrc1, novel putative signaling or transporter genes, the ringfinger-protein gene Mid1 and a panel of genes encoding novel proteins with unknown function. The finding that 39 out of 41 integrations analysed represented a cVIS, suggests that the majority of the other virus insertions that were not yet analysed by the PCR/Southern-blotting method are located in a cVIS as well and may therefore also harbor novel disease genes.

Phenotyping of Evi1, Evi11/Cb2, and Evi12 transformed leukemias isolated from a novel panel of cas-Br-M murine leukemia virus-infected mice

Cas-Br-M murine leukemia virus (MuLV) is a slow-transforming retrovirus that potently induces leukemias in mice and therefore is well suited for retroviral insertional mutagenesis. We used Cas-Br-M MuLV in NIH/Swiss mice to establish a new panel of mainly myeloid leukemias. All tumors found in leukemic animals were classified by gross pathology, morphology, and immunophenotype, as well as the incidence of known common virus integration sites (VISs) in MuLV-induced myeloid malignancies (i.e., Evi1, Evi11/Cb2, Evi12, Fli1, and c-Myb). Interestingly, male mice were more susceptible than females to the induction of leukemia by Cas-Br-M MuLV. Seventy-four of the Cas-Br-M MuLV-inoculated mice developed a severe splenomegaly, sometimes in association with a thymoma. Although most of the immunophenotyped Cas-Br-M MuLV tumors were of myeloid origin (58%), numerous T-cell leukemias (21%) and mixed myeloid/T-cell leukemias (21%) were found. The myeloid leukemias and myeloid compartment of the mixed leukemias were further characterized by immunophenotyping with stem cell-, myeloid-, and erythroid-specific antibodies. The known Cas-Br-M MuLV common VISs (Evi1, Evi11/Cb2, and Evi12) were demonstrated in 19%, 12%, and 20% of the cases, respectively, whereas no Fli1 and c-Myb rearrangements were found. Integrations into Evi1 were restricted to myeloid leukemias, whereas those in Evi11/Cb2 and Evi12 were identified in myeloid as well as T-lymphoid leukemias. This panel of well characterized Cas-Br-M MuLV-induced hematopoietic tumors may be useful for the isolation and characterization of new proto-oncogenes involved in myeloid or T-cell leukemias.

Constitutive and Interleukin-7/Interleukin-15 Stimulated DNA Binding of Myc, Jun, and Novel Myc-Like Proteins in Cutaneous T-Cell Lymphoma Cells

Members of the Myc and Jun/Fos gene families have been found to be expressed in late stages of cutaneous T-cell lymphoma (CTCL) and may be responsible for the transition from low-grade to high-grade tumors. The composition of these complexes is an important parameter, as the different homo- and heterodimeric jun and myc complexes can have gene transcription activating or suppressing activities. We determined the composition of the jun and myc DNA-binding complexes in three CTCL cell lines and malignant cells of seven Sézary patients by electrophoretic mobility shift assays (EMSAs) and “supershift” assays in which specific antibodies against the different members of the tested gene families were included in the binding reactions. Complexes containing JunD were found in three cell lines and two patients. The three cell lines and one patient contained also c-Myc/Max heterodimers. Because c-Myc/Max heterodimers are strong gene transcription activators and are necessary for cell-cycle progression, they may play a role in the progression of CTCL. JunD may also promote cell-cycle progression and influence the expression of cell death survival genes. Interleukin-7 (IL-7) and IL-15, which have been identified as growth factors for CTCL cells, stimulated the DNA binding of JunD and two novel c-Myc recognition site (E-box) binding proteins, but not the DNA binding of c-Myc/Max heterodimers.

Constitutive and Interleukin-7/Interleukin-15 Stimulated DNA Binding of Myc, Jun, and Novel Myc-Like Proteins in Cutaneous T-Cell Lymphoma Cells

Members of the Myc and Jun/Fos gene families have been found to be expressed in late stages of cutaneous T-cell lymphoma (CTCL) and may be responsible for the transition from low-grade to high-grade tumors. The composition of these complexes is an important parameter, as the different homo- and heterodimeric jun and myc complexes can have gene transcription activating or suppressing activities. We determined the composition of the jun and myc DNA-binding complexes in three CTCL cell lines and malignant cells of seven Sézary patients by electrophoretic mobility shift assays (EMSAs) and “supershift” assays in which specific antibodies against the different members of the tested gene families were included in the binding reactions. Complexes containing JunD were found in three cell lines and two patients. The three cell lines and one patient contained also c-Myc/Max heterodimers. Because c-Myc/Max heterodimers are strong gene transcription activators and are necessary for cell-cycle progression, they may play a role in the progression of CTCL. JunD may also promote cell-cycle progression and influence the expression of cell death survival genes. Interleukin-7 (IL-7) and IL-15, which have been identified as growth factors for CTCL cells, stimulated the DNA binding of JunD and two novel c-Myc recognition site (E-box) binding proteins, but not the DNA binding of c-Myc/Max heterodimers.

A novel chromosomal abnormality involving chromosomes 2 and 18 in a patient with myelodysplastic syndrome

Cytogenetic analysis of bone marrow cells from a patient with myelodysplastic syndrome associated with eosinophilia showed a complex translocation with a 46,XY,t(2;18;2)(p23;q11;q32) karyotype. The patient has refractory anemia (RA) according to the French-American-British Cooperative Group (FAB) classification, and after 90 months of follow-up he shows no evidence of leukemic transformation. This chromosomal abnormality has not been previously described in myelodysplastic syndromes and may be associated with good prognosis as the patient has been stable for a long time.