Absence of allelic loss on chromosome 5q by RFLP analysis in preleukemia

NPM1 ablation induces HSC aging and inflammation to develop myelodysplastic syndrome exacerbated by p53 loss

Myelodysplastic syndrome (MDS) is characterized by ineffective hematopoiesis with morphologic dysplasia and a propensity to transform into overt acute myeloid leukemia (AML). Our analysis of two cohorts of 20 MDS and 49 AML with multi-lineage dysplasia patients shows a reduction in Nucleophosmin 1 (NPM1) expression in 70% and 90% of cases, respectively. A mouse model of Npm1 conditional knockout (cKO) in hematopoietic cells reveals that Npm1 loss causes premature aging of hematopoietic stem cells (HSCs). Mitochondrial activation in Npm1-deficient HSCs leads to aberrant activation of the NLRP3 inflammasome, which correlates with a developing MDS-like phenotype. Npm1 cKO mice exhibit shortened survival times, and expansion of both the intra- and extra-medullary myeloid populations, while evoking a p53-dependent response. After transfer into a p53 mutant background, the resulting Npm1/p53 double KO mice develop fatal leukemia within 6 months. Our findings identify NPM1 as a regulator of HSC aging and inflammation and highlight the role of p53 in MDS progression to leukemia.

Cytogenetic deletion maps of hematologic neoplasms: circumstantial evidence for tumor suppressor loci

Research in oncogenetics has led to the identification of two major classes of tumor-associated genes, oncogenes and tumor suppressor genes. In a wide variety of solid tumor types, mutations of both groups of genes have been implicated in the tumorigenic process. In hematologic neoplasms, on the other hand, most attention has focused on illegitimate activation of oncogenes, e.g., deregulation leading to disturbed transcriptional activity and structural rearrangements resulting in hybrid genes. Whether loss or mutational inactivation of tumor suppressor genes also plays an essential role in the genesis of tumors of the hematopoietic system has received less attention. Because such inactivation can be the result of karyotypically detectable loss of chromosomal material, cytogenetic studies may prove helpful in pinpointing genomic sites that harbor tumor suppressor genes. The present study is based on a total of 12,473 cytogenetically abnormal hematologic neoplasms reported in the literature to date. Among these, we selected the 6,422 cases with sole clonal chromosomal abnormalities in order to include only aberrations of importance in the genesis, rather than in the progression, of these neoplasms. All tumors with monosomies or structural abnormalities resulting in loss of chromosomal material were compiled, and for every such structural aberration, i.e., deletion, unbalanced translocation, isochromosome, and ring chromosome, the chromosome bands lost were ascertained. This cytogenetic deletion mapping revealed that the most commonly lost chromosomes were Y and 7 in acute myeloid leukemia (AML), myelodysplastic syndromes (MDS), and chronic myeloproliferative disorders (MPD); X, Y, 7, 20, and 21 in acute lymphocytic leukemia (ALL); X, Y, and 17 in chronic lymphoproliferative disorders (LPD); and X and Y in non-Hodgkin's lymphoma (NHL). Chromosome segments/bands lost due to unbalanced structural abnormalities in at least 5% of the cases were 5q13-33, 7q22-36, 9q13-31, 11q23-25, 12p12-13, 17p11-13, and 20q11-13 in AML; 5q13-35 and 20q11-13 in MDS; 5q22-23, 7q22, 13q12-22, 17p11-13, and 20q11-13 in MPD; 6q15-27, 9p11-24, 12p12-13, and 19p13 in ALL; 6q16-27, 11q21-25, 13q13-14, and 14q32 in LPD; and 6q21-27, 11q13-25, and 14q24-32 in NHL. Based on these findings, three conclusions can be drawn. First, there is no good correspondence between total and partial monosomies, the only exception being -7 and 7q-, both of which are common in myeloid neoplasms. This indicates different pathogenetic effects of total and partial losses.(ABSTRACT TRUNCATED AT 400 WORDS)

Consistent interstitial chromosomal deletions in myeloid malignancies and their correlation with fragile sites

Chromosomal deletions occurring in myeloid malignancies have sometimes been reported either with no breakpoints or as terminal deletions. It is of importance to deduce whether these deletions are actually terminal or interstitial because this has implications for their biologic consequences and the mechanism of their development. Chromosomal deletions have been observed in 38 patients with myeloid malignancies. Two or more deletions occurred in six cases, and in seven cases this was part of a complex abnormality. In all, 45 deletions were observed. In all cases analyzed, the deletions consistently were interstitial. Of the 38 cases, 16 were myelodysplastic syndromes (MDS) [refractory anemia (RA), three; RA with ringed sideroblasts (RARS) three; RA with excess of blasts (RAEB) eight; RAEB in transformation (RAEB-t) one; and unclassified, one], 11 cases were acute nonlymphocytic leukemia (ANLL), and 11 were other myeloproliferative disorders [polycythemia rubra vera (PRV) seven; essential thrombocytopenia (ET), three; unclassified, one]. In general, no uniformity of breakpoints could be identified other than del(9)(q13q22.2) most of which occurred with t(8;21) and del(20)(q11.2q13.3 or 13.1). The breakpoints corresponded to or were adjacent to fragile sites in 49% (proximal 64%, distal 33%). These data emphasize that chromosomal deletions in myeloid malignancies are interstitial. The uniformity of breakpoints in del 9q and del 20q supports the concept that in some instances the exact breakpoints may be important through juxtaposition of genes rather than loss of critical regions. The data also suggest that there may be different mechanisms for the development of proximal and distal breakpoints.