Hiraku Mori

Frequent pathway mutations of splicing machinery in myelodysplasia.

Myelodysplastic syndromes and related disorders (myelodysplasia) are a heterogeneous group of myeloid neoplasms showing deregulated blood cell production with evidence of myeloid dysplasia and a predisposition to acute myeloid leukaemia, whose pathogenesis is only incompletely understood. Here we report whole-exome sequencing of 29 myelodysplasia specimens, which unexpectedly revealed novel pathway mutations involving multiple components of the RNA splicing machinery, including U2AF35, ZRSR2, SRSF2 and SF3B1. In a large series analysis, these splicing pathway mutations were frequent (∼45 to ∼85%) in, and highly specific to, myeloid neoplasms showing features of myelodysplasia. Conspicuously, most of the mutations, which occurred in a mutually exclusive manner, affected genes involved in the 3′-splice site recognition during pre-mRNA processing, inducing abnormal RNA splicing and compromised haematopoiesis. Our results provide the first evidence indicating that genetic alterations of the major splicing components could be involved in human pathogenesis, also implicating a novel therapeutic possibility for myelodysplasia.

Frequent inactivation of A20 in B-cell lymphomas

A20 is a negative regulator of the NF-κB pathway and was initially identified as being rapidly induced after tumour-necrosis factor-α stimulation. It has a pivotal role in regulation of the immune response and prevents excessive activation of NF-κB in response to a variety of external stimuli; recent genetic studies have disclosed putative associations of polymorphic A20 (also called TNFAIP3) alleles with autoimmune disease risk. However, the involvement of A20 in the development of human cancers is unknown. Here we show, using a genome-wide analysis of genetic lesions in 238 B-cell lymphomas, that A20 is a common genetic target in B-lineage lymphomas. A20 is frequently inactivated by somatic mutations and/or deletions in mucosa-associated tissue lymphoma (18 out of 87; 21.8%) and Hodgkin’s lymphoma of nodular sclerosis histology (5 out of 15; 33.3%), and, to a lesser extent, in other B-lineage lymphomas. When re-expressed in a lymphoma-derived cell line with no functional A20 alleles, wild-type A20, but not mutant A20, resulted in suppression of cell growth and induction of apoptosis, accompanied by downregulation of NF-κB activation. The A20-deficient cells stably generated tumours in immunodeficient mice, whereas the tumorigenicity was effectively suppressed by re-expression of A20. In A20-deficient cells, suppression of both cell growth and NF-κB activity due to re-expression of A20 depended, at least partly, on cell-surface-receptor signalling, including the tumour-necrosis factor receptor. Considering the physiological function of A20 in the negative modulation of NF-κB activation induced by multiple upstream stimuli, our findings indicate that uncontrolled signalling of NF-κB caused by loss of A20 function is involved in the pathogenesis of subsets of B-lineage lymphomas.

Gain-of-function of mutated C-CBL tumour suppressor in myeloid neoplasms

Acquired uniparental disomy (aUPD) is a common feature of cancer genomes, leading to loss of heterozygosity. aUPD is associated not only with loss-of-function mutations of tumour suppressor genes, but also with gain-of-function mutations of proto-oncogenes. Here we show unique gain-of-function mutations of the C-CBL (also known as CBL) tumour suppressor that are tightly associated with aUPD of the 11q arm in myeloid neoplasms showing myeloproliferative features. The C-CBL proto-oncogene, a cellular homologue of v-Cbl, encodes an E3 ubiquitin ligase and negatively regulates signal transduction of tyrosine kinases. Homozygous C-CBL mutations were found in most 11q-aUPD-positive myeloid malignancies. Although the C-CBL mutations were oncogenic in NIH3T3 cells, c-Cbl was shown to functionally and genetically act as a tumour suppressor. C-CBL mutants did not have E3 ubiquitin ligase activity, but inhibited that of wild-type C-CBL and CBL-B (also known as CBLB), leading to prolonged activation of tyrosine kinases after cytokine stimulation. c-Cbl-/- haematopoietic stem/progenitor cells (HSPCs) showed enhanced sensitivity to a variety of cytokines compared to c-Cbl+/+ HSPCs, and transduction of C-CBL mutants into c-Cbl-/- HSPCs further augmented their sensitivities to a broader spectrum of cytokines, including stem-cell factor (SCF, also known as KITLG), thrombopoietin (TPO, also known as THPO), IL3 and FLT3 ligand (FLT3LG), indicating the presence of a gain-of-function that could not be attributed to a simple loss-of-function. The gain-of-function effects of C-CBL mutants on cytokine sensitivity of HSPCs largely disappeared in a c-Cbl+/+ background or by co-transduction of wild-type C-CBL, which suggests the pathogenic importance of loss of wild-type C-CBL alleles found in most cases of C-CBL-mutated myeloid neoplasms. Our findings provide a new insight into a role of gain-of-function mutations of a tumour suppressor associated with aUPD in the pathogenesis of some myeloid cancer subsets.

Recurrent mutations in multiple components of the cohesin complex in myeloid neoplasms

Cohesin is a multimeric protein complex that is involved in the cohesion of sister chromatids, post-replicative DNA repair and transcriptional regulation. Here we report recurrent mutations and deletions involving multiple components of the cohesin complex, including STAG2, RAD21, SMC1A and SMC3, in different myeloid neoplasms. These mutations and deletions were mostly mutually exclusive and occurred in 12.1% (19/157) of acute myeloid leukemia, 8.0% (18/224) of myelodysplastic syndromes, 10.2% (9/88) of chronic myelomonocytic leukemia, 6.3% (4/64) of chronic myelogenous leukemia and 1.3% (1/77) of classical myeloproliferative neoplasms. Cohesin-mutated leukemic cells showed reduced amounts of chromatin-bound cohesin components, suggesting a substantial loss of cohesin binding sites on chromatin. The growth of leukemic cell lines harboring a mutation in RAD21 (Kasumi-1 cells) or having severely reduced expression of RAD21 and STAG2 (MOLM-13 cells) was suppressed by forced expression of wild-type RAD21 and wild-type RAD21 and STAG2, respectively. These findings suggest a role for compromised cohesin functions in myeloid leukemogenesis.

Somatic SETBP1 mutations in myeloid malignancies

Here we report whole-exome sequencing of individuals with various myeloid malignancies and identify recurrent somatic mutations in SETBP1, consistent with a recent report on atypical chronic myeloid leukemia (aCML). Closely positioned somatic SETBP1 mutations encoding changes in Asp868, Ser869, Gly870, Ile871 and Asp880, which match germline mutations in Schinzel-Giedion syndrome (SGS), were detected in 17% of secondary acute myeloid leukemias (sAML) and 15% of chronic myelomonocytic leukemia (CMML) cases. These results from deep sequencing demonstrate a higher mutational detection rate than reported with conventional sequencing methodology. Mutant cases were associated with advanced age and monosomy 7/deletion 7q (–7/del(7q)) constituting poor prognostic factors. Analysis of serially collected samples indicated that SETBP1 mutations were acquired during leukemic evolution. Transduction with mutant Setbp1 led to the immortalization of mouse myeloid progenitors that showed enhanced proliferative capacity compared to cells transduced with wild-type Setbp1. Somatic mutations of SETBP1 seem to cause gain of function, are associated with myeloid leukemic transformation and convey poor prognosis in myelodysplastic syndromes (MDS) and CMML.

BCOR and BCORL1 mutations in myelodysplastic syndromes and related disorders

Patients with low-risk myelodysplastic syndromes (MDS) that rapidly progress to acute myeloid leukemia (AML) remain a challenge in disease management. Using whole-exome sequencing of an MDS patient, we identified a somatic mutation in the BCOR gene also mutated in AML. Sequencing of BCOR and related BCORL1 genes in a cohort of 354 MDS patients identified 4.2% and 0.8% of mutations respectively. BCOR mutations were associated with RUNX1 (P = .002) and DNMT3A mutations (P = .015). BCOR is also mutated in chronic myelomonocytic leukemia patients (7.4%) and BCORL1 in AML patients with myelodysplasia-related changes (9.1%). Using deep sequencing, we show that BCOR mutations arise after mutations affecting genes involved in splicing machinery or epigenetic regulation. In univariate analysis, BCOR mutations were associated with poor prognosis in MDS (overall survival [OS]: P = .013; cumulative incidence of AML transformation: P = .005). Multivariate analysis including age, International Prognostic Scoring System, transfusion dependency, and mutational status confirmed a significant inferior OS to patients with a BCOR mutation (hazard ratio, 3.3; 95% confidence interval, 1.4-8.1; P = .008). These data suggest that BCOR mutations define the clinical course rather than disease initiation. Despite infrequent mutations, BCOR analyses should be considered in risk stratification.

EED mutants impair polycomb repressive complex 2 in myelodysplastic syndrome and related neoplasms

EED mutants impair polycomb repressive complex 2 in myelodysplastic syndrome and related neoplasms

Transition of Polycythemia Vera to Chronic Neutrophilic Leukemia

Two cases of polycythemia vera (PV) had transition to a hematological condition compatible with chronic neutrophilic leukemia (CNL) 17 and 8 years after diagnosis, respectively. One patient was treated with carboquone followed by hydroxyurea (HU) and the other with HU during PV phase. On transition, both had neutrophilia with white blood cell count above 40,000/microl, elevated neutrophil alkaline phosphatase activity, splenomegaly, normal karyotype without bcr-abl rearrangement. Busulfan was temporally effective in controlling the neutrophil count. However, one patient progressed to the so-called spent phase and the other subsequently had multiple transitions between PV and CNL. These cases may represent a form of uncommon evolution of PV and support the contention that CNL is a type of myeloproliferative disorder and that at least some CNL cases have derangement at the hematopoietic stem cell level.

Hypocomplementemia and Hematological Abnormalities in Immunoblastic Lymphadenopathy and Immunoblastic Lymphadenopathy-Like T Cell Lymphoma

Serum complement levels and hematological data were evaluated in five patients with immunoblastic lymphadenopathy (IBL) and four with IBL-like T cell lymphoma (IBL-T). Anemia with Hb values below 10.0 g/dl was seen in four patients. A direct Coombs test was positive in five patients and the bone marrow of two of these showed features of pure red cell aplasia. Seven patients were thrombocytopenic with platelet counts below 100 x 10(9)/l. Six of the seven patients had splenomegaly. Platelet-associated IgG was elevated in all three thrombocytopenic patients examined. Whole complement activity (CH50) was reduced in eight patients (89%) at presentation and subsequently normalized in five who were treated either with prednisolone (two patients with IBL) or with multidrug combination chemotherapy (three with IBL-T). One patient achieved complete remission and four partial remission. Remission was accompanied by normalization of hematological abnormalities and elevation of complement activity to the normal range in all cases. These results suggested that complement-mediated mechanisms are responsible, at least in part, for some of the hematological abnormalities observed in IBL and IBL-T and that hypocomplementemia is a common abnormality with significance as a laboratory marker for the disease activity.

CASE REPORT: Primary hepatic lymphoma associated with chronic liver disease

We report on a case of primary hepatic lymphoma that developed in a patient with chronic hepatitis C. Given that Japan is an area endemic for both hepatitis B and C viruses, we reviewed 51 Japanese cases of primary hepatic lymphoma, addressing the question as to whether the Japanese cases have unique characteristics and whether there is a causal relationship to the presence of chronic liver disease. Primary hepatic lymphoma most commonly affected middle‐aged males. Presenting symptoms and physical findings were non‐specific. Aminotransferases tended to stay in the low range compared with marked increases in lactate dehydrogenase. Sixteen patients (31%) had chronic liver disease, eight had liver cirrhosis and eight had chronic hepatitis, suggesting that there is a possible aetiological link between chronic liver disease and primary hepatic lymphoma.