Molecular cytogenetic characterization of a critical region in bands 7q35-q36 commonly deleted in malignant myeloid disorders

Loss of chromosome 7 (-7) or deletion of the long arm (7q-) are recurring chromosome abnormalities in myeloid leukemias. The association of - 7/7q- with myeloid leukemia suggests that these regions contain novel tumor suppressor gene(s), whose loss of function contribute to leukemic transformation or tumor progression. Based on chromosome banding analysis, two critical regions have been identified, one in band q22 and another in bands q32-q35. Presently there are no data available on the molecular delineation of the distal critical region. In this study we analyzed bone marrow and blood samples from 13 patients with myeloid leukemia (de novo myelodysplastic syndrome [MDS], n=3; de novo acute myeloid leukemia [AML], n=9; therapy-related (t-) AML, n=1) which, on chromosome banding analysis, exhibited deletions (n=12) or in one case a balanced translocation involving bands 7q31-qter using fluorescence in situ hybridization (FISH). As probes we used representative clones from a contig map of yeast artificial chromosome (YAC) clones that spans chromosome bands 7q31.1-qter. In the 12 cases with loss of 7q material, we identified a commonly deleted region of approximately 4 to 5 megabasepairs in size encompassing the distal part of 7q35 and the proximal part of 7q36. Furthermore, the breakpoint of the reciprocal translocation from the patient with t-AML was localized to a 1,300-kb sized YAC clone that maps to the proximal boundary of the commonly deleted region. Interestingly, in this case both homologs of chromosome 7 were affected: one was lost (-7) and the second exhibited the t(7q35). The identification and delineation of translocation and deletion breakpoints provides the first step toward the identification of the gene(s) involved in the pathogenesis of 7q35-q36 aberrations in myeloid disorders.link_to_OA_fulltex

Stochastic modeling of cargo transport by teams of molecular motors

Many different types of cellular cargos are transported bidirectionally along microtubules by teams of molecular motors. The motion of this cargo-motors system has been experimentally characterized in vivo as processive with rather persistent directionality. Different theoretical approaches have been suggested in order to explore the origin of this kind of motion. An effective theoretical approach, introduced by M\"uller et al., describes the cargo dynamics as a tug-of-war between different kinds of motors. An alternative approach has been suggested recently by Kunwar et al., who considered the coupling between motor and cargo in more detail. Based on this framework we introduce a model considering single motor positions which we propagate in continuous time. Furthermore, we analyze the possible influence of the discrete time update schemes used in previous publications on the system's dynamic.Comment: Cenference proceedings - Traffic and Granular Flow 1

Molecular cytogenetic delineation of deletions and translocations involving chromosome band 7q22 in myeloid leukemias

Loss of chromosome 7 (-7) or deletion of its long arm (7q-) are recurring chromosome abnormalities in myeloid disorders, especially in therapy-related myelodysplastic syndrome (t-MDS) and acute myeloid leukemia (t-AML). The association of -7/7q- with myeloid leukemia suggests that these regions contain a novel tumor suppressor gene(s) whose loss of function contributes to leukemic transformation or tumor progression. Based on chromosome banding analysis, two critical regions have been identified: one in band 7q22 and a second in bands 7q32-q35. We analyzed bone marrow and blood samples from 21 patients with myeloid leukemia (chronic myeloid leukemia, n = 2; de novo MDS, n = 4; de novo AML, n = 13: t-AML, n = 2) that on chromosome banding analysis exhibited deletions (n = 19) or reciprocal translocations (n = 2) of band 7q22 using fluorescence in situ hybridization. As probes, we used Alu-polymerase chain reaction products from 22 yeast artificial chromosome (YAC) clones that span chromosome bends 7q21.1-q32, including representative clones from a panel of YACs recognizing a contiguous genomic DNA fragment of 5 to 6 Mb in band 7q22. In the 19 cases with deletions, we identified two distinct commonly deleted regions: one region within band 7q22 was defined by the two CML cases; the second region encompassed a distal part of band 7q22 and the entire band 7q31 and was defined by the MDS/AML cases. The breakpoint of one of the reciprocal translocations was mapped to 7q21.3, which is centromeric to both of the commonly deleted regions. The breakpoint of the second translocation, which was present in unstimulated bone marrow and phytohemagglutinin-stimulated blood of an MDS patient, was localized to a 400-kb genomic segment in 7q22 within the deletion cluster of the MDS/AML cases. In conclusion, our data show marked heterogeneity of 7q22 deletion and translocation breakpoints in myeloid leukemias, suggesting the existence of more than one pathogenetically relevant gene.link_to_OA_fulltex

A one-mutation mathematical model can explain the age incidence of acute myeloid leukemia with mutated nucleophosmin (NPM1).

Acute myeloid leukemia with mutated NPM1 gene and aberrant cytoplasmic expression of nucleophosmin (NPMc(+) acute myeloid leukemia) shows distinctive biological and clinical features. Experimental evidence of the oncogenic potential of the nucleophosmin mutant is, however, still lacking, and it is unclear whether other genetic lesion(s), e.g. FLT3 internal tandem duplication, cooperate with NPM1 mutations in acute myeloid leukemia development. An analysis of age-specific incidence, together with mathematical modeling of acute myeloid leukemia epidemiology, can help to uncover the number of genetic events needed to cause leukemia. We collected data on age at diagnosis of acute myeloid leukemia patients from five European Centers in Germany, The Netherlands and Italy, and determined the age-specific incidence of AML with mutated NPM1 (a total of 1,444 cases) for each country. Linear regression of the curves representing age-specific rates of diagnosis per year showed similar slopes of about 4 on a double logarithmic scale. We then adapted a previously designed mathematical model of hematopoietic tumorigenesis to analyze the age incidence of acute myeloid leukemia with mutated NPM1 and found that a one-mutation model can explain the incidence curve of this leukemia entity. This model fits with the hypothesis that NPMc(+) acute myeloid leukemia arises from an NPM1 mutation with haploinsufficiency of the wild-type NPM1 allele

Analysis of NPM1 splice variants reveals differential expression patterns of prognostic value in acute myeloid leukemia

Mutations of the nucleophosmin-1 (NPM1) gene in cytogenetically normal (CN) acute myeloid leukemia (AML) identify a group of patients with more favorable prognosis. NPM1 encodes three main alternatively spliced isoforms R1(B23.1), R2(B23.2), and R3(B23.3). The expression of splice variants R1, R2 and R3 were higher in AML patients compared to normal cells of healthy volunteers (HVs), although RNA-seq analysis revealed enhanced R2 expression also in less differentiated cells of HVs as well as in AML cells. The variant R2, which lacks exons 11 and 12 coding for the nucleolar localization domain, might behave similar to the mutant form of NPM1 (NPM1mut). In accordance, in CN-AML high R2 expression was associated with favorable impact on outcome. Moreover, functional studies showed nucleolar localization of the eGFP-NPM1 wildtype and cytoplasmic localization of the eGFP-NPM1 mut protein. While the eGFP-NPM1 R2 splice variant localized predominantly in the nucleoplasm, we also could detect cytoplasmic expression for the R2 variant. These results support a unique biological consequence of R2 overexpression and in part explain our clinical observation, where that high R2 variant expression was associated with a better prognosis in CN-AML patients

Circular RNAs of the nucleophosmin (NPM1) gene in acute myeloid leukemia

In acute myeloid leukemia, there is growing evidence for splicing pattern deregulation, including differential expression of linear splice isoforms of the commonly mutated gene nucleophosmin (NPM1). In this study, we detect circular RNAs of NPM1 and quantify circRNA hsa_circ_0075001 in a cohort of NPM1 wild-type and mutated acute myeloid leukemia (n=46). Hsa_circ_0075001 expression correlates positively with total NPM1 expression, but is independent of the NPM1 mutational status. High versus low hsa_circ_0075001 expression defines patient subgroups characterized by distinct gene expression patterns, such as lower expression of components of the Toll-like receptor signaling pathway in high hsa_circ_0075001 expression cases. Global evaluation of circRNA expression in sorted healthy hematopoietic controls (n=10) and acute myeloid leukemia (n=10) reveals circRNA transcripts for 47.9% of all highly expressed genes. While circRNA expression correlates globally with parental gene expression, we identify hematopoietic differentiation-associated as well as acute myeloid leukemia subgroup-specific circRNA signatures

Cryo Electron Tomography of Herpes Simplex Virus during Axonal Transport and Secondary Envelopment in Primary Neurons

During herpes simplex virus 1 (HSV1) egress in neurons, viral particles travel from the neuronal cell body along the axon towards the synapse. Whether HSV1 particles are transported as enveloped virions as proposed by the ‘married’ model or as non-enveloped capsids suggested by the ‘separate’ model is controversial. Specific viral proteins may form a recruitment platform for microtubule motors that catalyze such transport. However, their subviral location has remained elusive. Here we established a system to analyze herpesvirus egress by cryo electron tomography. At 16 h post infection, we observed intra-axonal transport of progeny HSV1 viral particles in dissociated hippocampal neurons by live-cell fluorescence microscopy. Cryo electron tomography of frozen-hydrated neurons revealed that most egressing capsids were transported independently of the viral envelope. Unexpectedly, we found not only DNA-containing capsids (cytosolic C-capsids), but also capsids lacking DNA (cytosolic A-/B-capsids) in mid-axon regions. Subvolume averaging revealed lower amounts of tegument on cytosolic A-/B-capsids than on C-capsids. Nevertheless, all capsid types underwent active axonal transport. Therefore, even few tegument proteins on the capsid vertices seemed to suffice for transport. Secondary envelopment of capsids was observed at axon terminals. On their luminal face, the enveloping vesicles were studded with typical glycoprotein-like spikes. Furthermore, we noted an accretion of tegument density at the concave cytosolic face of the vesicle membrane in close proximity to the capsids. Three-dimensional analysis revealed that these assembly sites lacked cytoskeletal elements, but that filamentous actin surrounded them and formed an assembly compartment. Our data support the ‘separate model’ for HSV1 egress, i.e. progeny herpes viruses being transported along axons as subassemblies and not as complete virions within transport vesicles

Functional characterization of BRCC3 mutations in acute myeloid leukemia with t(8;21)(q22;q22.1)

BRCA1/BRCA2-containing complex 3 (BRCC3) is a Lysine 63-specific deubiquitinating enzyme (DUB) involved in inflammasome activity, interferon signaling, and DNA damage repair. Recurrent mutations in BRCC3 have been reported in myelodysplastic syndromes (MDS) but not in de novo AML. In one of our recent studies, we found BRCC3 mutations selectively in 9/191 (4.7%) cases with t(8;21)(q22;q22.1) AML but not in 160 cases of inv(16)(p13.1q22) AML. Clinically, AML patients with BRCC3 mutations had an excellent outcome with an event-free survival of 100%. Inactivation of BRCC3 by CRISPR/Cas9 resulted in improved proliferation in t(8;21)(q22;q22.1) positive AML cell lines and together with expression of AML1-ETO induced unlimited self-renewal in mouse hematopoietic progenitor cells in vitro. Mutations in BRCC3 abrogated its deubiquitinating activity on IFNAR1 resulting in an impaired interferon response and led to diminished inflammasome activity. In addition, BRCC3 inactivation increased release of several cytokines including G-CSF which enhanced proliferation of AML cell lines with t(8;21)(q22;q22.1). Cell lines and primary mouse cells with inactivation of BRCC3 had a higher sensitivity to doxorubicin due to an impaired DNA damage response providing a possible explanation for the favorable outcome of BRCC3 mutated AML patients

Endogenous tumor suppressor microRNA-193b: Therapeutic and prognostic value in acute myeloid leukemia

Purpose Dysregulated microRNAs are implicated in the pathogenesis and aggressiveness of acute myeloid leukemia (AML). We describe the effect of the hematopoietic stem-cell self-renewal regulating miR-193b on progression and prognosis of AML. Methods We profiled miR-193b-5p/3p expression in cytogenetically and clinically characterized de novo pediatric AML (n = 161) via quantitative real-time polymerase chain reaction and validated our findings in an independent cohort of 187 adult patients. We investigated the tumor suppressive function of miR-193b in human AML blasts, patient-derived xenografts, and miR-193b knockout mice in vitro and in vivo. Results miR-193b exerted important, endogenous, tumor-suppressive functions on the hematopoietic system. miR-193b-3p was downregulated in several cytogenetically defined subgroups of pediatric and adult AML, and low expression served as an independent indicator for poor prognosis in pediatric AML (risk ratio 6 standard error, 20.56 6 0.23; P = .016). miR-193b-3p expression improved the prognostic value of the European LeukemiaNet risk-group stratification or a 17-gene leukemic stemness score. In knockout mice, loss of miR-193b cooperated with Hoxa9/Meis1 during leukemogenesis, whereas restoring miR-193b expression impaired leukemic engraftment. Similarly, expression of miR-193b in AML blasts from patients diminished leukemic growth in vitro and in mouse xenografts. Mechanistically, miR-193b induced apoptosis and a G1/S-phase block in various human AML subgroups by targeting multiple factors of the KIT-RAS-RAF-MEK-ERK (MAPK) signaling cascade and the downstream cell cycle regulator CCND1. Conclusion The tumor-suppressive function is independent of patient age or genetics; therefore, restoring miR-193b would assure high antileukemic efficacy by blocking the entire MAPK signaling cascade while preventing the emergence of resistance mechanisms

Functional classification of TP53 mutations in acute myeloid leukemia

Mutations of the gene occur in a subset of patients with acute myeloid leukemia (AML) and confer an exceedingly adverse prognosis. However, whether different types of mutations exert a uniformly poor outcome has not been investigated yet. Here, we addressed this issue by analyzing data of 1537 patients intensively treated within protocols of the German-Austrian AML study group. We classified mutations depending on their impact on protein structure and according to the evolutionary action (EAp53) score and the relative fitness score (RFS). In 98/1537 (6.4%) patients, 108 mutations were detected. While the discrimination depending on the protein structure and the EAp53 score did not show a survival difference, patients with low-risk and high-risk AML-specific RFS showed a different overall survival (OS; median, 12.9 versus 5.5 months, = 0.017) and event-free survival (EFS; median, 7.3 versus 5.2 months, = 0.054). In multivariable analyses adjusting for age, gender, white blood cell count, cytogenetic risk, type of AML, and TP53 variant allele frequency, these differences were statistically significant for both OS (HR, 2.14; 95% CI, 1.15-4.0; = 0.017) and EFS (HR, 1.97; 95% CI, 1.06-3.69; = 0.033). We conclude that the AML-specific RFS is of prognostic value in patients with TP53-mutated AML and a useful tool for therapeutic decision-making