Pathogenic ‘germline’ variants associated with myeloproliferative disorders in apparently normal individuals: inherited or acquired genetic alterations?

We developed a real-time copy number polymerase chain reaction assay for deletions on chromosome 20q (del20q), screened peripheral blood granulocytes from 664 patients with myeloproliferative disorders, and identified 19 patients with del20q (2.9%), of which 14 (74%) were also positive for JAK2-V617F. To examine the temporal relationship between the occurrence of del20q and JAK2-V617F, we performed colony assays in methylcellulose, picked individual burst-forming units–erythroid (BFU-E) and colony-forming units–granulocyte (CFU-G) colonies, and genotyped each colony individually for del20q and JAK2-V617F. In 2 of 9 patients, we found that some colonies with del20q carried only wild-type JAK2, whereas other del20q colonies were JAK2-V617F positive, indicating that del20q occurred before the acquisition of JAK2-V617F. However, in colonies from 3 of 9 patients, we observed the opposite order of events. The lack of a strict temporal order of occurrence makes it doubtful that del20q represents a predisposing event for JAK2-V617F. In 2 patients with JAK2-V617F and 1 patient with MPL-W515L, microsatellite analysis revealed that del20q affected chromosomes of different parental origin and/or 9pLOH occurred at least twice. The fact that rare somatic events, such as del20q or 9pLOH, occurred more than once in subclones from the same patients suggests that the myeloproliferative disorder clone carries a predisposition to acquiring such genetic alterations.

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Identification of the Involvement of the Tyrosine Kinase C-Ros in the Pathogenesis of Chronic Myelomonocytic Leukemia (CMML)

Blood ◽

10.1182/blood.v112.11.687.687 ◽

2008 ◽

Vol 112 (11) ◽

pp. 687-687

Author(s):

Daniela Cilloni ◽

Sonia Carturan ◽

Enrico Bracco ◽

Ilaria Defilippi ◽

Chiara Maffè ◽

...

Keyword(s):

Tyrosine Kinase ◽

Tyrosine Kinases ◽

Growth Factor Receptor ◽

Annexin V ◽

Myeloproliferative Disorders ◽

Genetic Alterations ◽

Chronic Myelomonocytic Leukemia ◽

Common Finding ◽

Chimeric Receptor ◽

Myelomonocytic Leukemia

Abstract The abnormal activation of tyrosine kinases are a common finding in chronic myeloproliferative disorders. Perturbation of RTK signalling by genetic alterations results into an abnormal proliferation advantage and finally into a malignant transformation. c-Ros is an orphan RTK displaying transforming activity whose role has been established in the development of neuronal neoplasia. The aim of this study was to evaluate the involvement of c-Ros in the pathogenesis of chronic myelomonocytic leukemia (CMML) and to establish the effects of c-Ros activation. c-Ros expression was evaluated by RQ-PCR in 133 samples collected from 96 CMML patients at diagnosis (96 BM and 37 PB) and 60 healthy donors (30 PB and 30 BM). The protein amount and localization was analyzed by westen blot and immunofluorescence assay. In order to establish the effects of c-Ros activation we generated a chimeric receptor containing the extracellular domain derived from epidermal growth factor receptor (EGFR) and the transmembrane and cytoplasmic domains from c-ros (ER). The chimeric receptor was then transfected in NIH3T3 and HEK293T cells. Transfected and control cells were then stimulated with 100 nM EGF ligand and proliferation and apoptosis evaluated by incorporation of 3H timidine and MTT assay and by FACS for the detection of annexin V, respectively. We found that Ros is undetectable in healthy subjects but it is overexpressed in CMML (p<0,0001) in both BM and PB cells with a median value of 2−ΔΔCt in BM of 380 (range 10–63303) and 212 in PB (range 6–30012). WB confirmed the presence of c-Ros protein in CMML cells but not in normal controls. Immunofluorescence staining localized the protein within the cytoplasm. We found that ROS is highly expressed in CD34+ cells and monocytes from CMML patients but not in their normal counterparts. Sequence analysis revealed the absence of mutations of c-Ros promoter. SNPs analysis exclude the presence of duplications or deletions of the gene. Moreover we found that the EGF induced activation of c-Ros affects proliferation by increasing of 3.5 folds the proliferation rate as compared to cells transfected with the empty vector and stimulated with EGF under the same conditions. Furthermore cell adhesion was 4 folds decreased as compared to control. By contrast apoptosis is not affected by c-ROS activity (p=0,2). This study demonstrates that c-Ros is abnormally expressed in patients with CMML. The abnormal activation of c-Ros is responsible for loss of adhesion and increased proliferation. In conclusion, we identified a new tyrosine kinase which may be responsible for the proliferation defect typical of CMML cells and could represent a target for molecular therapies.

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A multi-institutional investigation assessing prevalence of germline genetic alterations in Chinese patients with gastric carcinoma.

Journal of Clinical Oncology ◽

10.1200/jco.2019.37.15_suppl.e13020 ◽

2019 ◽

Vol 37 (15_suppl) ◽

pp. e13020-e13020

Author(s):

Yinjie Zhang ◽

Xicheng Wang ◽

Changbin Zhu ◽

Xiaotian Zhang ◽

Qing Wei ◽

...

Keyword(s):

Gastric Cancer ◽

Family History ◽

Gastric Carcinoma ◽

Familial Cancer ◽

Germline Mutations ◽

Genetic Alterations ◽

Chinese Patients ◽

Multiple Primary Cancers ◽

Cancer History ◽

Germline Variants

e13020 Background: Gastric carcinoma is one of the most common malignancies in east asian. Previous studies demonstrated around 10% of patients with gastric cancer were found to have pathogenic germline variants. While, predisposition genes of gastric cancer in Chinese patients are still largely unknown. Thus, we aim to delineate prevalence of deleterious germline mutations in Chinese gastric patients with hereditary high-risk familial cancer history. We also aim to analyze clinical relevance of deleterious germline mutations. Methods: Forty index cases were recruited from 7 institutions in China. DNA samples extracted from blood specimens were captured using a 171-cancer predisposition gene panel and then sequenced by MGI-SEQ 2000 platform. Germline variants were determined to be deleterious according to the ACMG 2015 guidelines. Pathogenic and Likely pathogenic germline variants were further validated by Sanger sequencing. Results: 12 of 40 (30%) probands had 13 pathogenic/likely pathogenic germline variants involving 11 different genes: CHEK2 (n = 2), SPINK1 (n = 2), BLM (n = 1), CDH1(n = 1), EXT2 (n = 1), MLH1 (n = 1), MSH2(n = 1), MUTYH (n = 1), PALB2 (n = 1), NF1 (n = 1), ERCC2 (n = 1). For patients with multiple primary cancers, pathogenic germline alterations were exclusively presented (5 out of 12) (P=0.003). Besides,27 germline variants (like EPCAM, RAD54B, FANCD2, FANCA) with uncertain significance in 15 patients were predicated to be deleterious via in silico predictors. Conclusions: This multi-institutional study identified 30% (12/40) of Chinese gastric cancer patients with family history to have deleterious germline alterations. And potential deleterious variants were also identified. Our data illustrates a significantly distinguished spectrum of germline variants compared with Caucasian ones. This may indicate unique carcinogenesis of gastric cancer in Chinese patients. Since patients with pathogenic or likely pathogenic germline variants have dismal clinical outcome and higher rate of multi-cancer occurrence, genetic counseling of gastric cancer should be considered for individuals with family history at their early age.

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JAK2 Gene Is Mutated in Patients with Myeloproliferative Disorders and Spontaneous Erythroid Colony Formation but Not in Patients with Spontaneous Megakaryocyte Growth Only.

Blood ◽

10.1182/blood.v108.11.3600.3600 ◽

2006 ◽

Vol 108 (11) ◽

pp. 3600-3600

Author(s):

Satu Mustjoki ◽

Ioana Borze ◽

Riitta Alitalo ◽

Sakari Knuutila ◽

Eeva Juvonen

Keyword(s):

Mutation Analysis ◽

Colony Formation ◽

Myeloproliferative Disorders ◽

Colony Growth ◽

Genetic Alterations ◽

Diagnostic Tools ◽

Diagnostic Laboratory ◽

Jak2 Mutation ◽

Specific Pcr

Abstract In the past two decades spontaneous erythroid (BFU-E) and megakaryocytic (CFU-Meg) colony formation have proved to be useful diagnostic tools in diagnosing myeloproliferative disorders (MPD). Recently a point mutation in the JAK2-gene was discovered to be a pathogenetic event in polycythemia vera (PV) and essential thrombocythemia (ET). JAK2 mutation analysis has been recommended to be used as a primary diagnostic method for these disorders. However, so far only a few studies comparing the in vitro growth pattern of hematopoietic progenitors and JAK2 mutation status have been published and, to the best of our knowledge, no studies describing the association between spontaneous CFU-Meg growth and the JAK2 status have been conducted. Therefore, the aim of this study was to compare the results obtained with these methods in PV and ET. 52 ET and 33 PV patients were studied. Allele-specific PCR based JAK2 mutation analysis and hematopoietic colony forming assays were done from bone marrow (BM) aspirate samples. Morphology of BM aspirates was analyzed in our routine diagnostic laboratory. 30/33 (91%) PV patients and 35/52 (67%) ET patients showed spontaneous BFU-E growth. Spontaneous CFU-Meg growth was found in 23/33 (70%) of PV patients and in 29/52 (56%) of ET patients. JAK2 mutation was seen in 26 (79%) PV patients and in 31 (60 %) ET patients. All JAK2 mutated PV and ET patients were found to have spontaneous BFU-E growth. In addition, 4 of 7 (57%) JAK2 mutation negative PV patients and 4 of 21 (19%) JAK2 mutation negative ET patients had spontaneous BFU-E colony formation. JAK2 mutated ET patients had spontaneous CFU-Meg growth more often than JAK2 mutation negative patients (71% vs. 33%), while in PV patients there was no clear difference between the two groups (JAK2 mutation positive 69% vs. negative 71%). Interestingly, 9 patients (6 with ET, 3 with PV) had only spontaneous CFU-Meg growth but no spontaneous BFU-E growth. They were all JAK2 mutation negative. In addition, 11/52 ET patients (21%) were JAK2 mutation negative and had neither spontaneous BFU-E nor spontaneous CFU-Meg growth. BM morphology was considered suggestive of ET or PV in 83% and 70% of the cases respectively. No significant differences in BM morphology were found between JAK2 mutation negative and positive patients. In conclusion, in this group of 88 MPD patients spontaneous BFU-E colony growth was the most sensitive diagnostic assay. All patients with JAK2 mutation also had spontaneous BFU-E growth and an additional 8 patients without the mutation also had spontaneous BFU-E growth. Although recently the JAK2 mutation has been described in megakaryocytes as well, none of the present patients with spontaneous CFU-Meg growth but without spontaneous BFU-E growth were JAK2 mutation positive. This suggests that JAK2 mutation may not be the only pathogenetic event causing spontaneous CFU-Meg growth and further studies are needed to define genetic alterations behind this phenomenon.

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A multicenter study assessing the prevalence of germline genetic alterations in Chinese gastric cancer patients

10.21203/rs.3.rs-15940/v1 ◽

2020 ◽

Author(s):

Yinjie Zhang ◽

Yang Yang ◽

Qing Wei ◽

Ting Xu ◽

Xiaotian Zhang ◽

...

Keyword(s):

Risk Factors ◽

Gastric Cancer ◽

High Risk ◽

Gene Mutations ◽

Genetic Alterations ◽

Chinese Patients ◽

Germline Variants ◽

High Risk Factors ◽

Uncertain Significance ◽

Gastric Cancer Patients

Abstract Background: Approximately 10% of patients with gastric cancer (GC) have a genetic predisposition for the disease. To date, knowledge regarding germline mutations in predisposing genes in the Chinese GC population is scarce. The aim of this study was to determine the spectrum and distribution of predisposing gene mutations among Chinese GC patients known to have hereditary high-risk factors for cancer. Methods: Forty patients from among ten families were recruited from seven medical institutions in China. Next-generation sequencing was performed on 171 genes associated with cancer predisposition. For probands with pathogenic/likely pathogenic germline variants, Sanger sequencing was used to validate the variants in the probands and their relatives. Results: Sequencing indicated that 25% (10/40) of the patients carried a combined total of ten pathogenic or likely pathogenic germline variants involving nine different genes: CDH1 (n = 1), MLH1 (n = 1), MSH2 (n = 1), CHEK2 (n = 1), BLM (n = 1), EXT2 (n = 1), PALB2 (n = 1), ERCC2 (n = 1), and SPINK1 (n = 2). Five of these variants have not previously been reported. In addition, a total of 129 variants of uncertain significance were identified in 27 patients. Conclusions: This study found that 25% of Chinese GC patients with hereditary high-risk factors have deleterious germline alterations. This result may indicate a unique genetic background of GC among Chinese patients.

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A multicenter study assessing the prevalence of germline genetic alterations in Chinese gastric cancer patients

10.21203/rs.2.18927/v1 ◽

2019 ◽

Author(s):

Yinjie Zhang ◽

Yang Yang ◽

Qing Wei ◽

Ting Xu ◽

Xiaotian Zhang ◽

...

Keyword(s):

Risk Factors ◽

Gastric Cancer ◽

High Risk ◽

Gene Mutations ◽

Genetic Alterations ◽

Chinese Patients ◽

Germline Variants ◽

High Risk Factors ◽

Uncertain Significance ◽

Gastric Cancer Patients

Abstract BackgroundApproximately 10% of patients with gastric cancer (GC) have a genetic predisposition for the disease. To date, knowledge regarding germline mutations in predisposing genes in the Chinese GC population is scarce. The aim of this study was to determine the spectrum and distribution of predisposing gene mutations among Chinese GC patients known to have hereditary high-risk factors for cancer. Forty patients from among ten families were recruited from seven medical institutions in China. Next-generation sequencing was performed on 171 genes associated with cancer predisposition. For probands with pathogenic/likely pathogenic germline variants, Sanger sequencing was used to validate the variants in the probands and their relatives.ResultsSequencing indicated that 25% (10/40) of the patients carried a combined total of ten pathogenic or likely pathogenic germline variants involving nine different genes: CDH1 (n = 1), MLH1 (n = 1), MSH2 (n = 1), CHEK2 (n = 1), BLM (n = 1), EXT2 (n = 1), PALB2 (n = 1), ERCC2 (n = 1), and SPINK1 (n = 2). Five of these variants have not previously been reported. In addition, a total of 129 variants of uncertain significance were identified in 27 patients.ConclusionsThis study found that 25% of Chinese GC patients with hereditary high-risk factors have deleterious germline alterations. This result may indicate a unique genetic background of GC among Chinese patients.

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Novel Role of Activated Ras in Leukaemogenesis: Induction of Angiogenesis.

Blood ◽

10.1182/blood.v108.11.1313.1313 ◽

2006 ◽

Vol 108 (11) ◽

pp. 1313-1313

Author(s):

Robert J. Knight ◽

Tracey A. O’Brien ◽

Robert Lindeman ◽

Alla Dolnikov

Keyword(s):

Bone Marrow ◽

Extracellular Matrix ◽

Progenitor Cells ◽

Myeloproliferative Disorders ◽

Genetic Alterations ◽

Angiogenic Factors ◽

Ras Genes ◽

Cell Engraftment ◽

Normal Human ◽

Microarray Expression

Abstract Mutations in Ras genes are among the most frequent genetic alterations found in leukaemia. Our previous results have indicated that mutant N-ras (N-rasm) expression in the murine haematopoietic progenitor cells results in the development of myeloproliferative disorders that resemble human leukaemia. Our group has recently established a ‘humanised’ NOD/SCID mouse model of Ras-induced leukaemogenesis. N-rasm was transduced into normal human primitive haematopoietic progenitor cells (HPC) using recombinant GFP-expressing retrovirus to initiate the leukaemogenic transformation. When injected in NOD/SCID mice, N-rasm/GFP-expressing HPCs induce a pre-leukaemic condition characterised by the increased expansion of human N-rasm/GFP-positive cells with concomitant myeloid lineage expansion in the bone marrow of the recipient mice. In long-term culture N-rasm induces expansion of primitive CD34+/CD117+ and CD34+CXCR4+ progenitor cells enriched with NOD/SCID repopulating cells as well as myelomonocytic CD34−/CD14+ cells within the expanse of erythroid and lymphoid lineages. Microarray expression analysis revealed the induction of a number of the angiogenic factors and extracellular matrix proteins including VEGF, SDF-1, IL3, PDGF 1 and 2, metalloproteinases 9, 11, 12 and 14 that promote angiogenesis. The expansion of the primitive endothelial (CD34+VEGFR2+) and lymphatic (CD34+VEGFR3+) progenitor cells was consistently observed in N-rasm-transduced cultures. In addition, myelomonocytic CD34−CD14+ cells expanded by N-rasm also appear to contribute to neo-angiogenesis. N-rasm-induced pro-angiogenic factors also act as mitogenic and survival factors for pre-leukaemia HPCs by inhibiting apoptosis and promoting leukaemia-inititating-cell engraftment into the bone marrow of the recipient mice. N-rasm acts to modulate the interaction of leukaemia-initiating-cells with the bone marrow stroma by the induction of extracellular matrix degradation. We propose that the induction of pro-angiogenic factors by N-rasm acts to promote leukaemogenic transformation of leukaermia-inititating stem cells and needs to be investigated as a new candidate therapeutic target for leukaemia.

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Genetic Profiling of BCR/ABL Negative Myeloproliferative Disorders Using High-Resolution Microarrays

Blood ◽

10.1182/blood.v110.11.1538.1538 ◽

2007 ◽

Vol 110 (11) ◽

pp. 1538-1538

Author(s):

Frank Stegelmann ◽

Martin Griesshammer ◽

Sandra Ruf ◽

Susanne Kuhn ◽

Frank G. Rücker ◽

...

Keyword(s):

High Resolution ◽

Array Cgh ◽

Snp Array ◽

Uniparental Disomy ◽

Myeloproliferative Disorders ◽

Genetic Alterations ◽

Comparative Genomic ◽

Snp Analysis ◽

Genomic Imbalances ◽

Trisomy 9

Abstract Recently, the identification of the gain of function mutation JAK2V617F delivered important insights into the pathogenesis of BCR/ABL negative myeloproliferative disorders (MPD). JAK2V617F is detectable in more than 90% of polycythemia vera (PV) patients (pts) and in approximately 50% of pts with essential thrombocythemia (ET) or primary myelofibrosis (PMF), representing the genetic hallmark of BCR/ABL negative disease. However, about 30% of MPD pts lack the JAK2V617F mutation and previous studies on ET and PV demonstrated that clonality exceeds the percentage of V617F mutated cells. These findings suggest that additional genetic alterations are involved in the pathogenesis of MPD, in both JAK2 mutated and unmutated pts. To identify novel genetic aberrations and to determine whether specific lesions are associated with disease phenotype, genomic DNA from granulocytes of 72 MPD pts classified according to the WHO criteria was analyzed using high-resolution, genome-wide microarray techniques [disease, number analyzed, JAK2 mutation status: PMF, n=14, 9/14; post-ET MF, n=5, 3/5; post-PV MF, n=5, 5/5; PV, n=37, 37/37; ET, n=11, 11/11]. In a first approach, all cases were investigated by comparative genomic hybridization to 8k arrays (array CGH) with an average probe spacing of less than 1 Mb. While no genomic imbalances were found in ET, 11% of PV pts (n=4) exhibited large (>10 Mb) deletions on 20q (n=2) or gains on 9p and 1q (n=1, each). In addition, small (<1 Mb) recurrent gains in 1q21.1 (n=2) and 22q11.23 (n=2) were identified. In MF pts the incidence of large genomic imbalances was 25% (n=6) with trisomy 9 (n=3) being the most frequent aberration followed by loss of 20q, 5q, and 13q in single cases. Furthermore, in one pt with post-PV MF small genomic losses in 17q11.2 (2 Mb) and 17p13.2 (0.8 Mb) were identified harbouring NF1 but not TP53. Deletion of the NF1 allele without concomitant loss of TP53 was confirmed by FISH. To further increase resolution and to investigate the role of uniparental disomy (UPD), single nucleotide polymorphism (SNP) analysis using the Affymetrix 250k Nsp SNP array was performed in all MF cases. Copy number estimation and loss of heterozygosity probability were analyzed using a set of 117 remission samples from acute myeloid leukemia pts as a common reference. SNP analysis confirmed all anomalies detected by array CGH. In addition, SNP analysis revealed small genomic losses (1.6–2.6 Mb) in 1q21.2 (n=3), 5q13.2, and 3p13 (n=1, each), and in one secondary MF pt another microdeletion in 17q11.2 (1.2 Mb). UPDs recurrently affected 9p (n=5) in a region harbouring the JAK2 locus. In single cases, large UPDs of 1q (25 Mb), 2p (14 Mb), 5q (4 Mb), 6p (11 Mb), and 7q (11 Mb) were identified. Of note, all JAK2V617F mutated post-PV and post-ET MF cases exhibited 9p abnormalities represented either by trisomy 9 or UPD of 9p. In conclusion, using a combined microarray approach we were able to detect novel submicroscopic alterations in addition to known abnormalities. Parallel analysis of both techniques clearly demonstrated the superiority of array-SNP mapping. Further analyses on larger pt populations and correlation with global gene expression data will facilitate the identification of disease-related genes that are involved in the pathogenesis of BCR/ABL negative MPD.

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The Genetic Basis of Myeloproliferative Disorders

Hematology ◽

10.1182/asheducation-2007.1.1 ◽

2007 ◽

Vol 2007 (1) ◽

pp. 1-10 ◽

Cited By ~ 29

Author(s):

Radek Skoda

Keyword(s):

Jak2 V617f ◽

Myeloproliferative Disorders ◽

Genetic Alterations ◽

Erythropoietin Receptor ◽

Janus Kinase ◽

Jak2 Mutation ◽

Von Hippel Lindau ◽

Activating Mutations ◽

Diagnostic Work

AbstractFor many decades, myeloproliferative disorders (MPD) were largely neglected orphan diseases. The conceptual work of William Dameshek in 1951 provided the basis for understanding MPD as a continuum of related syndromes, possibly with a common pathogenetic cause. Recognition of the clonal origin of peripheral blood cells in MPD in 1976 and the ability to grow erythroid colonies in vitro in the absence of added growth factors in 1974 initiated the search for genetic alterations that might be responsible for myeloproliferation. Mutations in the genes for the erythropoietin receptor, thrombopoietin and the von Hippel–Lindau protein were found to cause familial syndromes resembling MPD, but despite their phenotypic similarities, none of these mutations were later found in patients with the sporadic form of MPD. The discovery of activating mutations in the Janus kinase 2 (JAK2) in most patients with MPD has fully transformed and energized the MPD field. Sensitive assays for detecting the JAK2-V617F mutation have become an essential part of the diagnostic work-up, and JAK2 now constitutes a prime target for developing specific inhibitors for the treatment of patients with MPD. Despite this progress, many questions remain unsolved, including how a single JAK2 mutation causes three different MPD phenotypes, what other genes might be involved in the pathogenesis, and what are the factors determining the progression to acute leukemia.

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Mutant N-ras Induces Myeloproliferative Disorders and Apoptosis in Bone Marrow Repopulated Mice

Blood ◽

10.1182/blood.v93.6.2043.406k17_2043_2056 ◽

1999 ◽

Vol 93 (6) ◽

pp. 2043-2056 ◽

Cited By ~ 79

Author(s):

K.L. MacKenzie ◽

A. Dolnikov ◽

M. Millington ◽

Y. Shounan ◽

G. Symonds

Keyword(s):

Bone Marrow ◽

Myeloid Leukemia ◽

Philadelphia Chromosome ◽

Myeloproliferative Disorders ◽

Genetic Alterations ◽

Myelogenous Leukemia ◽

In Vivo Model ◽

High Level

Mutations that activate the N-ras oncogene are among the most frequently detected genetic alterations in human acute myeloid leukemias (AMLs), Philadelphia chromosome-negative myeloproliferative disorders (MPDs), and myelodysplastic syndromes (MDSs). However, because N-ras has not been shown to induce these disorders in an in vivo model, the role of N-ras in the evolution of myeloid leukemia is unclear. To investigate the potential of N-ras to induce myeloid leukemia, lethally irradiated mice were reconstituted with bone marrow (BM) cells infected with a retroviral vector carrying activated N-ras. Approximately 60% of these mice developed hematopoietic disorders, including severe MPDs resembling human chronic myelogenous leukemia (CML) or AML with differentiation (French-American-British [FAB] classification M2). Other reconstituted mice succumbed to hematopoietic defects that were pathologically similar to human MDSs. The latter disorders appeared to be due to a myeloid impairment that was demonstrated by enumeration of day-12 colony-forming units-spleen (CFU-S) and by in vitro colony assays. A high level of apoptosis associated with thymic atrophy and peripheral blood (PB) lymphopenia was also evident in N-rasreconstituted mice. Our results are consistent with a model in which antiproliferative effects are a primary consequence of N-rasmutations and secondary transforming events are necessary for the development of myeloid leukemia. This is the first report of an in vivo model for N-ras induced MPD and leukemia.

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