The role of the c-mos gene in the 8;21 translocation in human acute myeloblastic leukemia

Trisomy 8 in leukemia: A GCRI experience

Trisomy of chromosome 8 is frequently reported in myeloid lineage disorders and also detected in lymphoid neoplasms as well as solid tumors suggesting its role in neoplastic progression in general. It is likely to be a disease-modulating secondary event with underlying cryptic aberrations as it has been frequently reported in addition to known abnormalities contributing to clinical heterogeneity and modifying prognosis. Here, we share our findings of trisomy 8 in leukemia patients referred for diagnostic and prognostic cytogenetic assessment. Total 60 cases of trisomy 8, as a sole anomaly or in addition to other chromosomal aberrations, were reported (January 2005–September 2008). Unstimulated bone marrow or blood samples were cultured, followed by GTG banding and karyotyping as per the ISCN 2005. Patients with +8 were chronic myeloid leukemia (CML) (36), acute myeloid leukemia (AML) (17), and acute lymphoblastic leukemia (ALL) (7). In 7 patients, trisomy 8 was the sole anomaly, whereas in 6 patients +8 was in addition to normal clone, in 47 patients, the +8 was in addition to t(9;22), t(15;17), and others, including 3 with tetrasomy 8. Only one patient showed constitutional +8. The present study will form the basis of further cumulative studies to correlate potential differential effects of various karyotypic anomalies on disease progression and survival following a therapeutic regime. To unravel the role of extra 8 chromosome, constitutional chromosomal analysis and uniparental disomy will be considered.

Acute myelogenous leukemia with tetrasomy 8 is a disease with a poor prognosis

Tetrasomy 8 is an extremely rare chromosome abnormality, one that has been reported in only a few cases with myeloid malignancies. The majority of reported cases consist of acute myelogenous leukemias (AML) of monocytic lineage. In slightly more than half of the patients, tetrasomy 8 was the single cytogenetic abnormality. Fluorescence in situ hybridization revealed tetrasomy 8 and trisomy 8 concurrently in all but one of the bone marrow samples. The clonal relationship between trisomy 8 and tetrasomy 8 in these cases remains to be clarified. Patients with tetrasomy 8 have a poor prognosis, and only 1 out of 33 patients was free of disease 3 years after autologous bone marrow transplantation. Here, we report the case of a 25-year-old female patient with monocytic leukemia and tetrasomy 8.

Clonal evolution from trisomy into tetrasomy of chromosome 8 associated with the development of acute myeloid leukemia from myelodysplastic syndrome

Tetrasomy 8, though rare, is usually associated with trisomy 8, a far more common chromosomal abnormality in acute myeloid leukemia (AML). Yet the clonal relationship between trisomy 8 and tetrasomy 8 in the cases with these chromosomal abnormalities has been unclear. Here, we report a case of a 17-year-old male, diagnosed as having a myelodysplastic syndrome (MDS). Chromosome analysis showed the presence of trisomy 8. Five years later, he developed overt AML exhibiting tetrasomy 8 only. After chemotherapy, the blast cells in the bone marrow decreased to 3.4%, and the karyotype showed trisomy 8 alone. Fluorescence in situ hybridization using a probe specific for chromosome 8 showed that the percentages of cells exhibiting 2/ 3 /4 signals were 7.8/89.2/2.0 at the MDS stage, 20.5/36.1/41.0 when overt AML developed and 24.0/72.1/2.4 after chemotherapy. These results suggested that tetrasomy 8 is derived from the AML clone, possibly evolved from the MDS clone with trisomy 8. To our knowledge, this is the first detailed case report of clonal evolution from trisomy 8 into tetrasomy 8 associated with the development of AML from MDS.

Molecular analysis and breakpoint definition of a set of human chromosome 21 somatic cell hybrids

Rodent-human somatic cell hybrids containing single human chromosomes or chromosome fragments are extremely valuable in physical mapping, marker analysis, and disease mapping. Chromosome 21 has been extensively studied in this fashion, and a single set of hybrids has been utilized in mapping the majority of chromosome 21 markers. The utility of a set of hybrids depends upon the definition of the human chromosome content. Recently, Chumakov and coworkers (1) utilized 198 chromosome 21 markers in the preliminary analysis of YACs spanning chromosome 21q. We have used these same markers to evaluate the STS content of a set of 27 chromosome 21 somatic cell hybrids, resulting in the description of the breakpoints at the molecular level, as well as the definition of 35 "bins. " The detailed molecular definition of chromosome 21 content of the hybrids, in combination with the further analysis of chromosome 21 YACs (2), has resulted in the most detailed picture of chromosome 21 to date.

Molecular analysis of 12 patients with the t(8;21) translocation and M2 acute myelogenous leukemia

The t(8;21)(q22;q22) is a nonrandom cytogenetic abnormality associated with acute myelogenous leukemia of the M2 subtype (FAB classification). The 8q- and 21q+ derivative chromosomes have previously been isolated in somatic cell hybrids and used to map the anonymous sequences D21S65 and D21S17, which were proximal and distal, respectively, to the breakpoint on chromosome 21. DNA from a series of 12 t(8;21) patients and 7 controls was analyzed by pulsed field gel electrophoresis. Physical linkage of probes D21S65 and D21S17 on a 2100 kb NruI fragment was established by partial digestion experiments. In all the patients, the translocation generated a rearranged D21S65 NruI fragment of 650 to 750 kb, suggesting heterogeneity in the breakpoints. This heterogeneity was confirmed by using BssHII, SacII, and EagI enzymes. Our results are consistent with the presence of a 100 Kb breakpoint cluster region on chromosome 21 encompassing the AML1 gene. Interestingly, in half of the patients, demethylation of an NruI site located 7 kb proximal to the last exon of the AML1 gene occurred on the nontranslocated chromosome 21.

DNA sequences of chromosome 21-specific YAC detect the t(8;21) breakpoint of acute myelogenous leukemia

The t(8;21)(q22;q22) is a nonrandom translocation specifically marking blasts of acute myelogenous leukemia (AML) with undifferentiated phenotype. The breakpoint on chromosome 21 involved by this rearrangement has been precisely localized relative to cloned DNA markers by physical and genetic linkage analysis enabling the use of positional cloning for its isolation. Yeast artificial chromosome (YAC) clones for loci proximal (D21S65) and distal (ERG) to the (21q22) breakpoint have been developed and their chromosome 21 origin and location relative to the breakpoint has been established. By using in situ hybridization analysis, a 240 kb YAC clone for the D21S65 locus clearly identified both derivative chromosomes of the (8;21) translocation in metaphase spreads of leukemia blasts with the rearrangement. The characterization of the DNA sequences contained in this 240 kb YAC can reveal the functional consequences of their derangement in leukemia with abnormalities of the (21q22) region.

Isolation of a yeast artificial chromosome spanning the 8;21 translocation breakpoint t(8;21)(q22;q22.3) in acute myelogenous leukemia

The 8;21 translocation is one of the most common specific rearrangements in acute myelogenous leukemia. We have identified markers (D21S65 and a Not I boundary clone, Not-42, referred to as probe B) flanking the chromosome 21 translocation breakpoint (21q22.3) that demonstrate physical linkage in normal genomic DNA, by using at least three restriction endonucleases (Not I, Sac II, and BssHII), and that are located not more than 250-280 kilobases apart. Pulsed-field gel analysis of DNA from somatic cell hybrids containing the 8;21 translocation chromosomes demonstrates rearrangement of these markers. A 470-kilobase yeast artificial chromosome, YAC-Not-42, has been isolated that contains both probes. Mapping of lambda subclones constructed from YAC-Not-42 suggests that greater than 95% (25/26 probes tested) of the yeast artificial chromosome DNA is located on the proximal (D21S65) side of the breakpoint. In situ hybridization studies using metaphase chromosomes from five acute myelogenous leukemia patients with the 8;21 translocation confirmed these results and demonstrated the translocation of probe B to the derivative chromosome 8. A chromosome walk of approximately 39 kilobases from probe B has allowed identification of the breakpoint in DNA from a somatic cell hybrid containing the derivative chromosome 8. Since probe B contains conserved DNA sequences and is in close proximity to the translocation breakpoint, it may represent a portion of the involved gene on chromosome 21.

ras mutations in human leukemia and related disorders

The clinical association of an increased incidence of acute myelogenous leukemia (AML) with previous chemoradiotherapy, the detection of specific karyotypic changes in these secondary (therapy-induced) cases of AML and the discovery of increasing levels of oncogene-specific RNA in leukemia cells suggest that one potential site of action of environmental agents might be the proto-oncogenes in human hematopoietic stem cells. The location of human proto-oncogenes at the sites of chromosome breaks and/or translocations in cells from some patients with leukemia or lymphoma is a striking observation. These data stimulated research into the mechanism of activation of specific oncogenes that change the biology of human hematopoietic cells. Recent investigations have focused upon several areas that might alter cell biology including: 1) translocation and/or inversion of chromosome fragments containing a proto-oncogene to a location where other gene sequences can stimulate oncogene activation, 2) replication of copy number of proto-oncogenes or increased transcriptional activity and 3) point mutation in proto-oncogenes leading to a structurally altered protein. The third area of research has recently received significant attention with respect to the potential role of three ras genes (c-Harvey-ras, c-Kirsten-ras and N-ras) in human leukemias and myelodysplastic syndromes. Recent studies have proposed a model for leukemogenic transformation of human hematopoietic cells by the product of a mutated ras oncogene. Mutations at codons 12, 13 or 61 of the first exon of its 4.7 Kb of DNA (for c-Ha-ras) have been described. Other data revealing an absence of such mutations in the ras genes of many human leukemias and the absence of detectable transcription of ras genes in many alkylating agent-associated cases of AML, suggest that while ras mutations may be involved in some settings, there are probably multiple genetic pathways to leukemogenic transformation of human hematopoietic cells.

Localization of human c-mos to chromosome band 8q11 in leukemic cells with the t(8;21) (q22;q22)

Chromosome in situ hybridization studies locate c-mos to chromosome band 8q11 in leukemic cells carrying the t(8;21) (q22;q22). This amends the previous assignment of c-mos to chromosome band 8q22 and conforms with its recent assignment to 8q11 in normal cells and in a cell line with a structurally abnormal chromosome 8. C-mos lies proximally to, and distant from, the breakpoint at 8q22 in the t(8;21) and is unlikely to have a role in the onset of acute myeloid leukemia characterized by this translocation.

Translocation of the MOS gene in a rare t(8;16) associated with acute myeloblastic leukemia and Down syndrome

Cytogenetic analysis of an infant with Down syndrome with concomitant acute myelogenous leukemia revealed a unique t(8;16)(q22;q24). In situ chromosomal hybridization was used to demonstrate that the protooncogene MOS was translocated from chromosome 8 to chromosome 16. This is the first report of the transposition of MOS in association with acute leukemia.

Trisomy 8 mosaicism syndrome. Two cases demonstrating variability in phenotype

The paper presents clinical manifestations and results of cytogenetic examination of two patients with trisomy 8 mosaicism syndrome. The findings confirm the extreme phenotype variability of this syndrome. Both the first patient, a mentally retarded child with multiple dysmorphic changes, and the second, a 31-year-old woman with normal IQ and hypogammaglobulinemia as a predominant sign, revealed osteoarticular anomalies. Dermatoglyphic studies in both patients were typical for trisomy 8, and correlated with deep skin furrows. The chromosomal analysis was based on two types of lymphocyte cultures: 3-day and 2-day. A decreased percentage of trisomic cells in 3-day cultures in comparison to 2-day cultures may suggest the influence of environmental factors on spontaneous elimination of trisomic cells in vitro.

Human chromosome 8

The role of human chromosome 8 in genetic disease together with the current status of the genetic linkage map for this chromosome is reviewed. Both hereditary genetic disease attributed to mutant alleles at gene loci on chromosome 8 and neoplastic disease owing to somatic mutation, particularly chromosomal translocations, are discussed.

The cytogenetics of childhood leukemia: clinical and biologic implications

Cytogenetic studies have revealed a broad spectrum of abnormalities in the chromosomal make-up of human leukemic cells. These abnormalities are acquired during the process of malignant transformation within the neoplastic clone and reflect the genetic lesions and ablations that have occurred. Because cytogenetic abnormalities are tightly linked to the molecular events that lead to leukemogenesis, it is not surprising that these features correlate with immunophenotypic and morphologic features of the leukemic cells, as well as with the clinical characteristics of children at diagnosis and their responsiveness to therapy. Molecular analysis of the disordered structure or disrupted regulation of genes located at critical chromosomal breakpoints in leukemic cells should continue to provide important insight into normal and aberrant hematopoietic cell function.

Localization of the proto-oncogene MOS to 8q11-q12 by in situ chromosomal hybridization

The human MOS proto-oncogene has been mapped previously to two different sites on chromosome 8 (8q22 and 8q11). Here we report in situ hybridization data from two different laboratories which confirm the localization of MOS to the proximal region of the long arm of chromosome 8, at 8q11-q12.

Familial fragile 8q22 involved as a cancer breakpoint in cells of a large bowel tumor

A familial fragile 8q22 and an interferon-induced fragile 16q22 were found in two sisters. Eight years previously, both sisters developed an endometrial adenocarcinoma and now one of them presented with an adenocarcinoma of the colon. An 8q22 deletion was found in all the cells of the colonic tumor and seemed to be the primary initiating change. Other nonrandom and possibly promoting aberrations were also present, among others, a 16q22 deletion. The possibility exists that a familial fragile 8q22 may predispose to cancer and a fragile 16q22 may have promoting capacities.

Oncogenes in human leukemias

Eukaryotic cells contain a family of genes termed cellular oncogenes or proto-oncogenes thought to regulate normal cell growth and development. In some abnormal circumstances, such as following transduction by retroviruses, activation of these genes causes leukemias in animals. Possible mechanisms of activation of cellular oncogenes include: point mutation, deletion, or insertion; amplification; activation by internal rearrangement, chromosomal translocation, or promoter insertion; recombinatorial events resulting in the formation of novel chimeric genes; among others. In this review, we consider data implicating activation of cellular oncogenes in the pathogenesis of leukemia in humans. We discuss possible mechanisms whereby oncogene activation may induce leukemias, as well as potential diagnostic and therapeutic implications.

Oncogenes and human leukemias

Eukaryotic cells contain a family of genes termed "cellular oncogenes" or "proto-oncogenes," thought to regulate normal cell growth and development. In some circumstances, such as following transduction by retroviruses, activation of these genes causes tumors and leukemias in animals. Possible mechanisms of cellular oncogene activation include: 1) DNA point mutation, deletion or insertion, 2) gene amplification, 3) gene activation by internal rearrangement, chromosomal translocation or promoter insertion, 4) recombinative events resulting in the formation of novel chimeric genes, and others. In this review, we consider data which implicates cellular oncogene activation in the pathogenesis of leukemia in humans. We discuss possible mechanisms by which oncogene activation may induce leukemias, as well as potential diagnostic and therapeutic implications.

Chromosome marker and enhanced expression of c-Ha-ras in a DMBA-induced erythroleukemia cell line (D5A1)

Oncogene activation induced by chromosomal changes is now regarded as one of the most important phenomena during carcinogenesis. We have reported c-abl activation in a rat leukemia cell line K3D, caused by a secondary chromosomal translocation. Another erythroblastic leukemia cell line D5A1, originally derived from a leukemia induced by 7,12-dimethylbenz(a)anthracene (DMBA) in a Long-Evans rat, is characterized by a marker chromosome 1q+, which also probably occurred as a secondary change. In this cell line, the transcription level of Ha-ras related mRNA increased compared with other cell lines. By the in situ hybridization technique, the c-Ha-ras locus was assigned to 1q43 and the breakpoint 1q+. Because the breakpoint was so near the c-Ha-ras locus on the chromosome, the present system may provide a model of activation of the c-Ha-ras gene brought about by chromosomal translocation.

Localization of the human c-mos gene by in situ hybridization in two cases of acute nonlymphocytic leukemia type M2

The t(8;21)(q22.1;q22.3) is specific for the FAB-M2 subtype of acute nonlymphocytic leukemia (ANLL). The human c-mos protooncogene is located near the site of rearrangement on chromosome #8, at a position corresponding to band 8q22. The present in situ hybridization studies were performed in order to establish if c-mos is transposed from chromosome #8 to chromosome #21, in two cases of M2-ANLL showing the typical t(8;21). A statistical analysis of the results revealed that the c-mos oncogene was definitely not translocated from chromosome #8 to #21 in one of these patients, and was inconclusive in the other patient. The findings in the former patient suggest that either c-mos is not involved in the etiology of M2-ANLL or, alternatively, if c-mos is important in the pathogenesis of this disease, it must be activated by some mechanism other than transposition of this oncogene to an aberrant position.

Differential pattern of oncogene and beta-actin expression in leukaemic cells from AML patients

The presence of mRNA hybridizing to five oncogene (fos, mos, myc, sis, abl) and a beta-actin probe(s) was studied with a semiquantitative dot-blot procedure in eight AML patients. Around 10(7) leucocytes, corresponding to 1-10 ml blood, sufficed for the analysis. Each patient, regardless of the FAB group, exhibited a distinct pattern of oncogene or beta-actin expression. Especially strong signals were obtained with the beta-actin probe in two patients and with the fos probe in three patients. The findings underscore the heterogeneity of AML, either present from the first step towards malignancy or arising during the progression of the disease. The pattern of oncogene expression in leukaemic cells studied in routine blood samples may become an additional means for classification and follow-up of AML patients.

New variant translocation (1;8;21) in a case of acute myeloblastic leukemia (M2)

A new translocation involving chromosome #1, #8, and #21 in a patient with type M2 acute myeloblastic leukemia is reported. The breakpoint of #1 in this case was at band p13 and differed from that in two previously reported cases of t(1;8;21) involving the long arm of #1. A key event leading to the development of the M2 phenotype appears to be a break at band q22 of #8 with associated translocation of the terminal end of the long arm of #21.

Hu-ets-2 is translocated to chromosome 8 in the t(8;21) in acute myelogenous leukemia

The human genome contains two distinct loci with homology to the viral ets gene, the transforming sequence of the E26 avian erythroblastosis virus; these loci, Hu-ets-1, and Hu-ets-2, have been mapped to 11q23 and 21q22, respectively. Using in situ chromosomal hybridization, we have demonstrated that Hu-ets-2 is translocated to chromosome #8, the chromosome containing the critical or conserved junction, as a result of the t(8;21) (q22;q22) in acute myelogenous leukemia. Another protooncogene, c-mos, is also retained at the conserved junction, suggesting that one or both of these genes may play a role in the pathogenesis of acute myelogenous leukemia.

t(4;21) (p16;q22) in blastic crisis of a chronic myeloid leukemia with variant Philadelphia translocation

A chronic myeloid leukemia (CML) patient who had presented a t(2;9;22) translocation during the chronic phase developed an unusual t(4;21) (p16;q22) translocation during the M2 type FAB classification blastic crisis. The role of these two recombinant chromosomes in the genesis of the terminal phase is discussed, particularly as the breakpoint on chromosome 21 near to the ets-2 oncogene locus, seems to be the same as that described in the t(8;21) (q22;q22) translocation specific of type M2 AML.

In situ hybridization--application to gene localization and RNA detection

In situ hybridization offers a direct approach for localization and quantitation of nucleic acid sequences in cellular preparations. Recent improvements in technology and methodology make possible the detection of DNA and RNA of relatively low copy number. For example, development of in situ hybridization methods for detection of single copy DNA sequences on mitotic chromosomes has led to general use of this technique for gene mapping of the human genome. More recently, improvements in methodology for detection of low abundancy RNA make possible a facilitated analysis of gene expression, both from cellular genes and exogenous sequences, such as viral genomes. In situ hybridization is now a powerful method for studying nucleic acid organization and function in normal cells, as well as in malignant cells, which should contribute to better understanding of the cell transformation process.

Trisomy 8 in human hematologic neoplasia and the c-myc and c-mos oncogenes

The c-mos and c-myc proto-oncogenes have been assigned to bands q22 and q24, respectively, of human chromosome No. 8. A gain of chromosome No. 8 is the most common abnormality observed in myeloproliferative diseases. By using probes specific for the c-mos and c-myc genes, we have analysed the genomic DNA from peripheral blood and bone marrow samples from 15 patients with various malignant myeloid diseases, including leukemia and myelodysplasia, and from one patient with non-Hodgkin's lymphoma, all of whom have trisomy for chromosome No. 8. Except for one patient, the c-mos and c-myc genes were found in restriction fragments of germline size. In one patient with myelodysplasia, one c-myc allele was rearranged in a Hind III fragment, the other allele being normal. Thus, trisomy 8 associated with human hematologic neoplasia is generally not related to gross rearrangements of the c-mos or c-myc genes.