Takahiko Yasuda

Phosphorylated high molecular weight neurofilament protein in lower motor neurons in amyotrophic lateral sclerosis and other neurodegenerative diseases involving ventral horn cells

SummaryLower motor neurons of the spinal cord of patients with amyotrophic lateral sclerosis (ALS), Werdnig-Hoffmanns disease (WH), X-linked recessive bulbospinal neuronopathy (X-BSNP) and multiple system atrophy (MSA), all of which were known to involve the lower motor neurons, were immunohistochemically examined by using a monoclonal antibody (Ta-51) specific to phosphorylated epitopes of high molecular weight subunits of neurofilaments. The incidence of Ta-51-positive neurons was significantly increased in ALS, WH and MSA, but not in X-BSNP. Ta-51-positive neurons showed a wide variety of morphological appearances, including neurons with normal appearance, central chromatolysis, simple atrophy and neurons containing massive neurofilamentous accumulation. In aged-control cases, similar Ta-51-positive neurons were observed, although to a much lesser extent. In ALS, spheroids and globules, which were strongly positive for Ta-51, were also significantly increased. Ta-51-positive motor neurons, spheroids and globules appeared in proportional to the number of remaining large motor neurons in ALS.

Transforming mutations of RAC guanosine triphosphatases in human cancers

Members of the RAS superfamily of small guanosine triphosphatases (GTPases) transition between GDP-bound, inactive and GTP-bound, active states and thereby function as binary switches in the regulation of various cellular activities. Whereas HRAS, NRAS, and KRAS frequently acquire transforming missense mutations in human cancer, little is known of the oncogenic roles of other small GTPases, including Ras-related C3 botulinum toxin substrate (RAC) proteins. We show that the human sarcoma cell line HT1080 harbors both NRAS(Q61K) and RAC1(N92I) mutant proteins. Whereas both of these mutants were able to transform fibroblasts, knockdown experiments indicated that RAC1(N92I) may be the essential growth driver for this cell line. Screening for RAC1, RAC2, or RAC3 mutations in cell lines and public databases identified several missense mutations for RAC1 and RAC2, with some of the mutant proteins, including RAC1(P29S), RAC1(C157Y), RAC2(P29L), and RAC2(P29Q), being found to be activated and transforming. P29S, N92I, and C157Y mutants of RAC1 were shown to exist preferentially in the GTP-bound state as a result of a rapid transition from the GDP-bound state, rather than as a result of a reduced intrinsic GTPase activity. Activating mutations of RAC GTPases were thus found in a wide variety of human cancers at a low frequency; however, given their marked transforming ability, the mutant proteins are potential targets for the development of new therapeutic agents.

Recurrent DUX4 fusions in B cell acute lymphoblastic leukemia of adolescents and young adults

The oncogenic mechanisms underlying acute lymphoblastic leukemia (ALL) in adolescents and young adults (AYA; 15–39 years old) remain largely elusive. Here we have searched for new oncogenes in AYA-ALL by performing RNA-seq analysis of Philadelphia chromosome (Ph)-negative AYA-ALL specimens (n = 73) with the use of a next-generation sequencer. Interestingly, insertion of D4Z4 repeats containing the DUX4 gene into the IGH locus was frequently identified in B cell AYA-ALL, leading to a high level of expression of DUX4 protein with an aberrant C terminus. A transplantation assay in mice demonstrated that expression of DUX4-IGH in pro-B cells was capable of generating B cell leukemia in vivo. DUX4 fusions were preferentially detected in the AYA generation. Our data thus show that DUX4 can become an oncogenic driver as a result of somatic chromosomal rearrangements and that AYA-ALL may be a clinical entity distinct from ALL at other ages.

Leukemic evolution of donor-derived cells harboring IDH2 and DNMT3A mutations after allogeneic stem cell transplantation.

Leukemic evolution of donor-derived cells harboring IDH2 and DNMT3A mutations after allogeneic stem cell transplantation

MicroRNA-31 is a positive modulator of endothelial-mesenchymal transition and associated secretory phenotype induced by TGF-β.

Transforming growth factor‐β (TGF‐β) plays central roles in endothelial–mesenchymal transition (EndMT) involved in development and pathogenesis. Although EndMT and epithelial–mesenchymal transition are similar processes, roles of microRNAs in EndMT are largely unknown. Here, we report that constitutively active microRNA‐31 (miR‐31) is a positive regulator of TGF‐β‐induced EndMT. Although the expression is not induced by TGF‐β, miR‐31 is required for induction of mesenchymal genes including α‐SMA, actin reorganization and MRTF‐A activation during EndMT. We identified VAV3, a regulator of actin remodeling and MRTF‐A activity, as a miR‐31 target. Global transcriptome analysis further showed that miR‐31 positively regulates EndMT‐associated unique secretory phenotype (EndMT‐SP) characterized by induction of multiple inflammatory chemokines and cytokines including CCL17, CX3CL1, CXCL16, IL‐6 and Angptl2. As a mechanism for this phenomenon, TGF‐β and miR‐31 suppress Stk40, a negative regulator of NF‐κB pathway. Interestingly, TGF‐β induces alternative polyadenylation (APA)‐coupled miR‐31‐dependent Stk40 suppression without concomitant miR‐31 induction, and APA‐mediated exclusion of internal poly(A) sequence in Stk40 3′UTR enhances target efficiency of Stk40. Finally, miR‐31 functions as a molecular hub to integrate TGF‐β and TNF‐α signaling to enhance EndMT. These data confirm that constitutively active microRNAs, as well as inducible microRNAs, serve as phenotypic modifiers interconnected with transcriptome dynamics during EndMT.

B Cell Receptor-ERK1/2 Signal Cancels PAX5-Dependent Repression of BLIMP1 through PAX5 Phosphorylation: A Mechanism of Antigen-Triggering Plasma Cell Differentiation

Plasma cell differentiation is initiated by Ag stimulation of BCR. Until BCR stimulation, B lymphocyte-induced maturation protein 1 (BLIMP1), a master regulator of plasma cell differentiation, is suppressed by PAX5, which is a key transcriptional repressor for maintaining B cell identity. After BCR stimulation, upregulation of BLIMP1 and subsequent suppression of PAX5 by BLIMP1 are observed and thought to be the trigger of plasma cell differentiation; however, the trigger that derepresses BLIMP1 expression is yet to be revealed. In this study, we demonstrated PAX5 phosphorylation by ERK1/2, the main component of the BCR signal. Transcriptional repression on BLIMP1 promoter by PAX5 was canceled by PAX5 phosphorylation. BCR stimulation induced ERK1/2 activation, phosphorylation of endogenous PAX5, and upregulation of BLIMP1 mRNA expression in B cells. These phenomena were inhibited by MEK1 inhibitor or the phosphorylation-defective mutation of PAX5. These data imply that PAX5 phosphorylation by the BCR signal is the initial event in plasma cell differentiation.

Eosinophilia predicts better overall survival after acute graft-versus-host-disease

The prognostic significance of eosinophilia after allogeneic hematopoietic SCT (HSCT) and the relationship between eosinophilia and acute GVHD are not well studied. We retrospectively analyzed 201 adult patients who underwent their first allogeneic HSCT. Seventy-three (36%) patients developed eosinophilia within the first 100 days after HSCT. Eosinophilia was observed more frequently among those patients with acute GVHD than those without it (48 vs 25%, P=0.009). However, it was associated with milder acute GVHD and lower incidence of gut and liver acute GVHD. Among patients with acute GVHD, the 3-year OS for patients with and without eosinophilia was 63.4 and 47.2% (P=0.02), respectively, and 3-year nonrelapse mortality (NRM) was 20.2 and 37.5% (P=0.01), respectively. Multivariate analysis confirmed that eosinophilia was associated with a better OS (P=0.03) and lower NRM (P=0.046) in patients with acute GVHD, whereas it was not associated with a higher relapse rate (P=0.45). In contrast, eosinophilia was not associated with outcomes in those patients without acute GVHD. In conclusion, eosinophilia was associated with milder acute GVHD and better prognosis among patients with acute GVHD. The pathophysiology behind eosinophilia after allogeneic HSCT remains to be investigated.

Clinical significance of hemophagocytosis in BM clot sections during the peri-engraftment period following allogeneic hematopoietic SCT

The effects of macrophage activation on the outcome of allogeneic hematopoietic SCT (allo-HSCT) have yet to be fully examined. A total of 70 adult patients who received a first allo-HSCT for hematological diseases were studied. We counted the number of hemophagocytic cells in BM clot sections on day +14±7, and analyzed its impact on subsequent outcome. In all, 23 patients were diagnosed as having increased numbers of hemophagocytic cells (HP group), whereas 47 were not (non-HP group). The HP group was not associated with an increased incidence of acute or chronic GVHD, but was associated with worse hematopoietic recovery than the non-HP group. The 2-year OS for the HP group and the non-HP group was 30 and 65% (P<0.01), respectively, and 2-year non-relapse mortality was 48% and 27% (P<0.01), respectively. Multivariate analysis confirmed that the HP group was associated with a lower OS (hazard ratio (HR)=2.3; 95% confidence interval (CI), 1.0–5.4; P=0.048) and higher non-relapse mortality (HR=4.0; 95% CI, 1.6–9.9; P<0.01). The HP group had higher incidences of death due to graft failure (P<0.01) and endothelial complications, such as sinusoidal obstruction syndrome and transplant-associated microangiopathy (P=0.01). Macrophage activation is a previously unrecognized complication with negative impact on outcome of allo-HSCT.

Integrative analysis of genomic alterations in triple-negative breast cancer in association with homologous recombination deficiency

Triple-negative breast cancer (TNBC) cells do not express estrogen receptors, progesterone receptors, or human epidermal growth factor receptor 2. Currently, apart from poly ADP-ribose polymerase inhibitors, there are few effective therapeutic options for this type of cancer. Here, we present comprehensive characterization of the genetic alterations in TNBC performed by high coverage whole genome sequencing together with transcriptome and whole exome sequencing. Silencing of the BRCA1 gene impaired the homologous recombination pathway in a subset of TNBCs, which exhibited similar phenotypes to tumors with BRCA1 mutations; they harbored many structural variations (SVs) with relative enrichment for tandem duplication. Clonal analysis suggested that TP53 mutations and methylation of CpG dinucleotides in the BRCA1 promoter were early events of carcinogenesis. SVs were associated with driver oncogenic events such as amplification of MYC, NOTCH2, or NOTCH3 and affected tumor suppressor genes including RB1, PTEN, and KMT2C. Furthermore, we identified putative TGFA enhancer regions. Recurrent SVs that affected the TGFA enhancer region led to enhanced expression of the TGFA oncogene that encodes one of the high affinity ligands for epidermal growth factor receptor. We also identified a variety of oncogenes that could transform 3T3 mouse fibroblasts, suggesting that individual TNBC tumors may undergo a unique driver event that can be targetable. Thus, we revealed several features of TNBC with clinically important implications.

Transforming somatic mutations of mammalian target of rapamycin kinase in human cancer

Mammalian target of rapamycin (mTOR) is a serine–threonine kinase that acts downstream of the phosphatidylinositol 3‐kinase signaling pathway and regulates a wide range of cellular functions including transcription, translation, proliferation, apoptosis, and autophagy. Whereas genetic alterations that result in mTOR activation are frequently present in human cancers, whether the mTOR gene itself becomes an oncogene through somatic mutation has remained unclear. We have now identified a somatic non‐synonymous mutation of mTOR that results in a leucine‐to‐valine substitution at amino acid position 2209 in a specimen of large cell neuroendocrine carcinoma. The mTOR(L2209V) mutant manifested marked transforming potential in a focus formation assay with mouse 3T3 fibroblasts, and it induced the phosphorylation of p70 S6 kinase, S6 ribosomal protein, and eukaryotic translation initiation factor 4E–binding protein 1 in these cells. Examination of additional tumor specimens as well as public and in‐house databases of cancer genome mutations identified another 28 independent non‐synonymous mutations of mTOR in various cancer types, with 12 of these mutations also showing transforming ability. Most of these oncogenic mutations cluster at the interface between the kinase domain and the FAT (FRAP, ATM, TRRAP) domain in the 3‐D structure of mTOR. Transforming mTOR mutants were also found to promote 3T3 cell survival, and their oncogenic activity was sensitive to rapamycin. Our data thus show that mTOR acquires transforming activity through genetic changes in cancer, and they suggest that such tumors may be candidates for molecularly targeted therapy with mTOR inhibitors.