Several chromosomes involved in translocations with chromosome 5 shown with fluorescence in situ hybridization in patients with malignant myeloid disorders

Molecular cytogenetic studies characterizing a novel complex karyotype with an uncommon 5q22 deletion in childhood acute myeloid leukemia

Deletions in the long arm of chromosome 5 or loss of the whole chromosome are rare in childhood Acute Myeloid Leukemia (AML) patients. It is also unknown if the wide variety of breakpoints have diverging implications in the patient’s outcome. Despite -5/5q- abnormalities have usually been described as a poor prognostic feature, however, the low frequency of -5/5q- in pediatric AML patients limits a full knowledge about this cytogenetic and clinical category, which is an intriguing factor for further research and new findings. Here, we report an AML child showing an uncommon deletion in 5q associated with 2 new abnormalities involving chromosome 2 within a complex karyotype well-characterized by several molecular cytogenetic approaches. Our work stimulates upcoming studies with more detailed descriptions about 5q abnormalities to better define its role in the stratification risk of such cytogenetic subgroup in childhood AML.

Isochromosome 5p and related anomalies: a novel recurrent chromosome abnormality in myeloid disorders

Loss of material from chromosome arm 5q is a common finding in patients with myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML). Fluorescence in situ hybridization with a panel of different types of probes, used as a complement to conventional cytogenetics, revealed that 7 of 148 patients (4.7%) with abnormalities of chromosome 5 had an i(5)(p10), an idic(5)(q11), or a structurally rearranged i(5)(p10). Three patients had MDS and four had AML. Six of the patients were female, and one was male; age at diagnosis ranged from 56 to 85 years. All patients but one had a complex karyotype. Isochromosome of the short arm of chromosome 5 and its related abnormalities such as idic(5)(q11) and structurally rearranged i(5)(p10) are rare but recurrent abnormalities; their identification requires a combination of conventional and molecular cytogenetic techniques. The biological and clinical significance cannot yet be assessed, not only because too few cases have been described but also because these abnormalities are usually part of a complex karyotype.

Dicentric chromosomes and 20q11.2 amplification in MDS/AML with apparent monosomy 20

FISH analysis of 41 previously karyotyped cases of MDS and AML with apparent monosomy of chromosome 20 revealed a variety of dicentric abnormalities involving chromosome 20. These usually, but not always, involved a breakpoint in the long arm of chromosome 20 and loss of the common deleted region at 20q12. Not one case of true monosomy 20 was confirmed. We found evidence for dicentric chromosome formation in 21 of 24 unbalanced translocations containing chromosome 20 and that were studied in more detail. Subsequent loss of one of the centromeres had occurred in eight of these 24 cases, and was more frequent than centromere inactivation as a means of resolving the inherent instability of a dicentric chromosome. In the three cases with dicentric chromosomes from which proximal 20q had been excised along with the 20 centromere, the excised segment was retained, and in two of these it was amplified. Proximal 20q was clearly retained in all but three cases, and present in three or more copies in 17 of 41 cases. The retention and amplification of proximal 20q provides support for the hypothesis that there is an oncogene located in this region of 20q that is activated in cases of MDS/AML with del(20q). Apparent monosomy 20 in MDS/AML should be treated as evidence of unidentified chromosome 20 abnormalities, and familiarity with the typical G-banded morphology of these derivatives can help with their identification. The reported incidence of dicentric chromosomes is clearly an under-estimate but is increasing in myeloid disorders as more cases are studied with methods allowing their detection.

Egr-1 abrogates the E2F-1 block in terminal myeloid differentiation and suppresses leukemia

Deregulated growth and blocks in differentiation collaborate in the multistage process of leukemogenesis. Previously, we have shown that ectopic expression of the zinc finger transcription factor Egr-1 in M1 myeloblastic leukemia cells promotes terminal differentiation with interleukin-6 (IL-6). In addition, we have shown that deregulated expression of the oncogene E2F-1 blocks the myeloid terminal differentiation program, resulting in proliferation of immature cells in the presence of IL-6. Here it is shown that the positive regulator of differentiation Egr-1 abrogates the E2F-1-driven block in myeloid terminal differentiation. The M1E2F-1/Egr-1 cells underwent G(0)/G(1) arrest and functional macrophage maturation following treatment with IL-6. Furthermore, Egr-1 diminished the aggressiveness of M1E2F-1 leukemias and abrogated the leukemic potential of IL-6-treated M1E2F-1 cells. Previously, we reported that Egr-1 abrogated the block in terminal myeloid differentiation imparted by deregulated c-myc, which blocks differentiation at a later stage than E2F-1, resulting in cells that have the characteristics of functionally mature macrophages that did not undergo G(0)/G(1) arrest. Taken together, this work extends and highlights the tumor suppressor role of Egr-1, with Egr-1 behaving as a tumor suppressor against two oncogenes, each blocking myeloid differentiation by a different mechanism. These findings suggest that Egr-1 and/or Egr-1 target genes may be useful tools to treat or suppress oncogene-driven hematological malignancies.

Redefining monosomy 5 by molecular cytogenetics in 23 patients with MDS/AML

Deletion of the long arm of chromosome 5 [del(5q)] or loss of a whole chromosome 5 (-5) is a common finding, arising de novo in 10% of patients with myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML) and in 40% of patients with therapy-related MDS or AML. We investigated by molecular cytogenetics 23 MDS/AML patients for whom conventional cytogenetics detected a monosomy 5. Monosomy 5 was redefined as unbalanced or balanced translocation and ring of chromosome 5. Loss of 5q material was identified in all 23 patients, but one. One copy of EGR1(5q31) or CSF1R(5q33-34) genes was lost in 22 of the 23 patients. Chromosome 5p material was a constant chromosomal component of derivative chromosomes or rings in all patients, but one. Sequential fluorescent in situ hybridization studies with whole chromosome paints and region-specific probes, used as a complement to conventional cytogenetic analysis, allow a better interpretation of karyotypes in MDS/AML patients.

Finer delineation and transcript map of the 7q31 locus deleted in myeloid neoplasms

Acquired complete and partial deletions of chromosome 7 are associated with several malignancies. In acute myelogenous leukemia (AML) and preleukemic myelodysplasia (MDS), loss of chromosome 7 portends a poor clinical outcome. The identity of a classical leukemia suppressor gene, however, has been elusive. Previously, we defined a candidate suppressor locus of approximately 6 Mb in the 7q31 interval. Here we report an island of retention of heterozygosity within this interval in a case of monosomy 7. Allelotyping of AML cell lines revealed that ML3 and HEL cells, karyotypically diploid for chromosome 7, are hemizygous for all the 7q31 loci, implicating loss of the wild type and duplication of the remaining chromosome 7. Based on the completed genomic sequence of chromosome 7, we have generated a transcript map of the critical region of loss (between the D7S525 and D7S2502 loci). Notably, a recently characterized tumor suppressor gene, DOCK4, and an evolutionarily conserved zinc finger gene, ZNF277, localize to this interval, head to head, within <0.5 kb of each other. Thus, the reagents generated in this study will be valuable in elucidating the role of loss of 7q31 loci in the pathogenesis of AML.