Akihiro Tomita

c-Myb acetylation at the carboxyl-terminal conserved domain by transcriptional co-activator p300

Transcription factor c-Myb plays important roles in cell survival and differentiation in immature hematopoietic cells. Here we demonstrate that c-Myb is acetylated at the carboxyl-terminal conserved domain by histone acetyltransferase p300 both in vitro and in vivo. The acetylation sites in vivo have been located at the lysine residues of the conserved domain (K471, K480, K485) by the use of the mutant Myb (Myb-KAmut), in which all three lysine residues are substituted into alanine. Electrophoretic mobility shift assay reveals that Myb-KAmut shows higher DNA binding activity than wild type c-Myb and that acetylation of c-Myb in vitro by p300 causes dramatic increase in DNA binding activity. Accordingly, transactivation activity of both mim-1 and CD34 promoters by Myb-KAmut is higher than that driven by wild type c-Myb. Furthermore, the bromodomain of p300, in addition to the histone acetyltransferase (HAT) domain, is required for effective acetylation of c-Myb, and hGCN5 is revealed to be a factor acetyltransferase for c-Myb in vitro. We present a new manner of post-translational modification of the c-Myb protein and the potential significance of the acetylation in c-Myb.

Functional regulation of GATA-2 by acetylation

The transcription factor GATA‐2 is expressed in hematopoietic stem and progenitor cells and is functionally implicated in their survival and proliferation. In the present study, we show that GATA‐2 exists as an acetylated protein in immature precursor cells, KG1. GATA‐2 was acetylated in vitro by p300 and GCN5. We have identified multiple acetylation sites by p300 on GATA‐2, which include sites outside the zinc finger domain. We confirmed that GATA‐2 acetylation occurred in transiently transfected 293T cells at sites similar to those induced by p300 in vitro. We have successfully shown that acetylation of GATA‐2 in vitro increased its DNA‐binding activity. In addition, GATA‐2 displayed a transcriptional synergism with p300 that was impaired by mutation of each acetylation site. More importantly, each mutation in the acetylation sites of GATA‐2 abolished its growth inhibitory effect on an interleukin‐3‐dependent progenitor, 32D. We conclude that acetylation provides multiple control points for the regulation of GATA‐2 function.

Mechanisms of action and resistance to all-trans retinoic acid (ATRA) and arsenic trioxide (As2O3) in acute promyelocytic leukemia

Since the introduction of all-trans retinoic acid (ATRA) and arsenic trioxide (As2O3) for the treatment of acute promyelocytic leukemia (APL), the overall survival rate has improved dramatically. However, relapse/refractory patients showing resistance to ATRA and/or As2O3 are recognized as a clinically significant problem. Genetic mutations resulting in amino acid substitution in the retinoic acid receptor alpha (RARα) ligand binding domain (LBD) and the PML-B2 domain of PML-RARα, respectively, have been reported as molecular mechanisms underlying resistance to ATRA and As2O3. In the LBD mutation, ATRA binding with LBD is generally impaired, and ligand-dependent co-repressor dissociation and degradation of PML-RARα by the proteasome pathway, leading to cell differentiation, are inhibited. The PML-B2 mutation interferes with the direct binding of As2O3 with PML-B2, and PML-RARα SUMOylation with As2O3 followed by multimerization and degradation is impaired. To overcome ATRA resistance, utilization of As2O3 provides a preferable outcome, and recently, a synthetic retinoid Am80, which has a higher binding affinity with PML-RARα than ATRA, has been tested in the clinical setting. However, no strategy attempted to date has been successful in overcoming As2O3 resistance. Detailed genomic analyses using patient samples harvested repeatedly may help in predicting the prognosis, selecting the effective targeting drugs, and designing new sophisticated strategies for the treatment of APL.

Monitoring of Hepatitis B Virus (HBV) DNA and Risk of HBV Reactivation in B-Cell Lymphoma: A Prospective Observational Study

BACKGROUND There is no standard management of reactivation of hepatitis B virus (HBV) infection in HBV-resolved patients without hepatitis B surface antigen (HBsAg), but with antibodies against hepatitis B core antigen and/or antibodies against HBsAg (anti-HBs). METHODS We conducted a prospective observational study to evaluate the occurrence of HBV reactivation by serial monthly monitoring of HBV DNA and to establish preemptive therapy guided by this monitoring in B-cell non-Hodgkin lymphoma (B-NHL) treated with rituximab plus corticosteroid-containing chemotherapy (R-steroid-chemo). The primary endpoint was the incidence of HBV reactivation defined as quantifiable HBV DNA levels of ≥ 11 IU/mL. RESULTS With a median HBV DNA follow-up of 562 days, HBV reactivation was observed in 21 of the 269 analyzed patients. The incidence of HBV reactivation at 1.5 years was 8.3% (95% confidence interval, 5.5-12.4). No hepatitis due to HBV reactivation was observed in patients who received antiviral treatment when HBV DNA levels were between 11 and 432 IU/mL. An anti-HBs titer of <10 mIU/mL and detectable HBV DNA remaining below the level of quantification at baseline were independent risk factors for HBV reactivation (hazard ratio, 20.6 and 56.2, respectively; P < .001). Even in 6 patients with a rapid increase of HBV due to mutations, the monthly HBV DNA monitoring was effective at preventing HBV-related hepatitis. CONCLUSIONS Monthly monitoring of HBV DNA is useful for preventing HBV reactivation-related hepatitis among B-NHL patients with resolved HBV infection following R-steroid-chemo (UMIN000001299).

Target Antigen Density Governs the Efficacy of Anti–CD20-CD28-CD3 ζ Chimeric Antigen Receptor–Modified Effector CD8+ T Cells

The effectiveness of chimeric Ag receptor (CAR)–transduced T (CAR-T) cells has been attributed to supraphysiological signaling through CARs. Second- and later-generation CARs simultaneously transmit costimulatory signals with CD3ζ signals upon ligation, but may lead to severe adverse effects owing to the recognition of minimal Ag expression outside the target tumor. Currently, the threshold target Ag density for CAR-T cell lysis and further activation, including cytokine production, has not yet been investigated in detail. Therefore, we determined the threshold target Ag density required to induce CAR-T cell responses using novel anti-CD20 CAR-T cells with a CD28 intracellular domain and a CD20-transduced CEM cell model. The newly developed CD20CAR–T cells demonstrated Ag-specific lysis and cytokine secretion, which was a reasonable level as a second-generation CAR. For lytic activity, the threshold Ag density was determined to be ∼200 molecules per target cell, whereas the Ag density required for cytokine production of CAR-T cells was ∼10-fold higher, at a few thousand per target cell. CD20CAR–T cells responded efficiently to CD20-downregulated lymphoma and leukemia targets, including rituximab- or ofatumumab-refractory primary chronic lymphocytic leukemia cells. Despite the potential influence of the structure, localization, and binding affinity of the CAR/Ag, the threshold determined may be used for target Ag selection. An Ag density below the threshold may not result in adverse effects, whereas that above the threshold may be sufficient for practical effectiveness. CD20CAR–T cells also demonstrated significant lytic activity against CD20-downregulated tumor cells and may exhibit effectiveness for CD20-positive lymphoid malignancies.

Epigenetic Regulation of CD20 Protein Expression in a Novel B-Cell Lymphoma Cell Line, RRBL1, Established from a Patient Treated Repeatedly with Rituximab-Containing Chemotherapy

Rituximab is a chimeric monoclonal antibody to the surface antigen CD20 and has provided better outcomes against CD20+ B-cell lymphomas than chemotherapy with conventional antitumor drugs alone. Treatment with rituximab poses a considerable problem, however, because of CD20- tumor transformation and subsequent disease progression. We have established a CD20- lymphoma cell line, RRBL1, from a diffuse large B-cell lymphoma with CD20- transformation from CD20+ follicular lymphoma after treatment with rituximab. RRBL1 was CD10+, CD19+, and CD20- by flow cytometry. CD20 expression was not detected by immunohistochemistry. Immunoblotting with whole RRBL1 cell lysate showed a very faint CD20 band only with longer exposures. The level of CD20 messenger RNA (mRNA) expression detected by quantitative reverse transcriptase-polymerase chain reaction analysis was almost 100 times lower than that in CD20+ lymphoma cells. When we treated RRBL1 cells with trichostatin A, an epigenetic drug that modulates histone-acetylation status, we detected dramatically increased CD20 mRNA and protein expression, suggesting that epigenetic mechanisms may explain the CD20- phenotype in RRBL1 cells. Thus, RRBL1 may be useful not only for analyses of mechanisms for the absence of CD20 expression in vitro but also for exploration of therapies against CD20- B-cell malignancies in vivo.

Phase I/II study of decitabine in patients with myelodysplastic syndrome: A multi-center study in Japan

The management of myelodysplastic syndrome (MDS) remains challenging. We performed a phase I/II study to evaluate the safety and efficacy of decitabine in patients with MDS in Japan. Patients with MDS with red cell transfusion dependence or 5–30% blasts in marrow and with an International Prognostic Scoring System score of intermediate‐1 or higher were eligible. Patients received intravenous decitabine at 15 or 20 mg/m2 daily for 5 days every 4 weeks. A total of 37 patients were enrolled. Three patients received 15 mg/m2 and experienced no dose limiting toxicity during the first cycle. Thirty‐four patients received 20 mg/m2. Grade 3 or greater non‐hematologic toxicities included cerebral infarction (n = 1), subdural hematoma (n = 1), elevated blood glucose (n = 1), and pulmonary hypertension (n = 1). At 20 mg/m2, complete response, partial response, and hematologic improvement were observed in 7 (20.6%), 2 (5.9%), and 7 (20.6%) patients, respectively. Complete cytogenetic response was observed in 30% of evaluable 20 patients. The median number of cycles to clinical response was 4 (range 4–8), and duration of remission was 474+ days (range 294–598+). The 2‐year rate of acute myeloid leukemia‐free survival was 52%. Correlative studies revealed hypomethylation in multiple genes in peripheral blood cells after treatment. Hypomethylation was generally more profound in CD15 + peripheral blood cells, which reflects myeloid cells, than in peripheral blood mononuclear cells. In summary, decitabine was safe and demonstrated efficacy in Japanese patients with high‐risk MDS. This trial was registered at ClinicalTrials.gov (NCT00796003).

Phase I and II study of azacitidine in Japanese patients with myelodysplastic syndromes.

Azacitidine, an inhibitor of DNA methyltransferase, is reported to have antileukemic efficacy and is approved for the treatment of myelodysplastic syndromes in Western countries. We have conducted a Phase I/II study of azacitidine in Japanese patients with myelodysplastic syndromes to evaluate its pharmacokinetics, efficacy, and safety. In all, 53 patients received 75 mg/m2 azacitidine subcutaneously or intravenously once daily for seven consecutive days on a 28‐day cycle. The Cmax following intravenous administration was approximately 3.7‐fold higher than that following subcutaneous administration, whereas the area under the plasma concentration–time curve from time zero to infinity was comparable for subcutaneous and intravenous administration. The bioavailability of azacitidine following subcutaneous administration was 91.1%, indicating that azacitidine is nearly completely absorbed after subcutaneous administration. The hematologic improvement and hematologic response rates were 54.9% (28/51) and 28.3% (15/53), respectively, and there were no differences between the two routes of administration. Azacitidine was generally well tolerated and clinically manageable in Japanese patients with myelodysplastic syndromes. Adverse events occurred in ≥20% of patients included hematologic toxicity, gastrointestinal events, and general disorders, such as malaise. Grade 3/4 adverse events that occurred in ≥50% of patients were all due to hematologic toxicity. The safety profile of azacitidine was generally similar for both routes of administration, with the exception of injection site reactions observed following subcutaneous administration. These results indicate that azacitidine can be expected to be a useful therapeutic agent in Japanese patients with myelodysplastic syndromes. (Cancer Sci 2011; 102: 1680–1686)

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.

Prognostic significance of pleural or pericardial effusion and the implication of optimal treatment in primary mediastinal large B-cell lymphoma: a multicenter retrospective study in Japan.

The prognosis of patients with primary mediastinal large B-cell lymphoma has improved over recent years. However, the optimal treatment strategy including the role of radiotherapy remains unknown. We retrospectively analyzed the clinical outcomes of 345 patients with newly diagnosed primary mediastinal large B-cell lymphoma in Japan. With a median follow up of 48 months, the overall survival at four years for patients treated with R-CHOP (n=187), CHOP (n=44), DA-EPOCH-R (n=9), 2nd- or 3rd-generation regimens, and chemotherapy followed by autologous stem cell transplantation were 90%, 67%, 100%, 91% and 92%, respectively. Focusing on patients treated with R-CHOP, a higher International Prognostic Index score and the presence of pleural or pericardial effusion were identified as adverse prognostic factors for overall survival in patients treated with R-CHOP without consolidative radiotherapy (IPI: hazard ratio 4.23, 95% confidence interval 1.48–12.13, P=0.007; effusion: hazard ratio 4.93, 95% confidence interval 1.37–17.69, P=0.015). Combined with the International Prognostic Index score and the presence of pleural or pericardial effusion for the stratification of patients treated with R-CHOP without radiotherapy, patients with lower International Prognostic Index score and the absence of effusion comprised approximately one-half of these patients and could be identified as curable patients (95% overall survival at 4 years). The DA-EPOCH-R regimen might overcome the effect of these adverse prognostic factors. Our simple indicators of International Prognostic Index score and the presence of pleural or pericardial effusion could stratify patients with primary mediastinal large B-cell lymphoma and help guide selection of treatment.