Canonical WNT signaling in hematopoiesis and leukemia

SummaryCanonical Wnt signaling is crucial for embryonic development and the homeostasis of certain adult tissues such as the gut and the skin. The role of canonical Wnt signaling in hematopoiesis is still debated. The expression of a dominant-active β-catenin in hematopoietic stem cells (HSCs) enhances the self-renewal capacity of HSCs but is detrimental for long-term hematopoiesis. In contrast, loss of function experiments show that absence of β- and γ-catenin does not impair steady-state hematopoiesis. It has been argued that the inducible deletion of β-catenin using the IFN-responsive Mx promoter may somehow influence stem cell fate. Herein we used the constitutive deletion of β-catenin specifically in hematopoietic cells to show that the absence of β- catenin, as well as γ-catenin deletion, does not impair normal hematopoiesis and self-renewal capacity of HSCs.Dysregulation of canonical Wnt signaling is causal for several types of cancer, including colon carcinoma or breast cancer. Recently, it was found that Wnt signal transduction was upregulated in certain leukemias. Based on these data, we have investigated whether β- and γ-catenin play a role for the induction of leukemias by oncogenic BCR-ABL translocation product. We show that the induction of B-ALL (B cell acute lymphocytic leukemia) is strongly reduced in the absence of γ-catenin, while the induction of CML (chronic myeloid leukemia) occurs at a normal rate. In the combined absence of β- and γ-catenin the induction of both CML and B-ALL is essentially blocked. Consistent with these data others have found that β-catenin is essential for the induction of CML by BCR-ABL.Collectively, we find that β- and γ-catenin are dispensable for normal hematopoiesis but essential for the development of BCR-ABL induced leukemias. These findings suggest that the canonical Wnt pathway may represent a promising target for the therapy of leukemia.RésuméLa voie de signalisation canonique Wnt est essentielle pour le développement embryonnaire ainsi que l'homéostasie de certains tissus adultes, comme les intestins et la peau. Le rôle de la voie canonique Wnt pour l'hématopoïèse est encore incertain. D'un coté l'expression d'une forme active de β-catenine dans les cellules souches de la moelle augmente leur potentiel d'auto- renouvellement mais est préjudiciable pour l'hématopoïèse à long terme. Par contre, l'absence de β- et γ-catenine n'empêche pas le déroulement normal de l'hématopoïèse. La façon dont est supprimée β-catenine, en utilisant le promoteur IFN-inductible Mx, pourrait influencer le sort des cellules souches. Ici nous détruisons β-catenine spécifiquement dans les cellules hématopoïétiques de manière constitutive et montrons que, en combinaison avec l'absence de γ-catenine, l'absence de β-catenine n'affecte pas le déroulement normal de l'hématopoïèse et la capacité des cellules souches de la moelle à se renouveler.Plusieurs sortes de cancers, comme celui du colon ou du sein, sont parfois dus à une dérégulation de la voie canonique Wnt. Récemment, certaines leucémies ont présenté une activation du signal Wnt. A partir de ces données, nous avons examiné si β- et γ-catenine jouent un rôle dans l'induction des leucémies causées par le produit de translocation BCR-ABL. Nous avons montré que l'induction de la leucémie aiguë lymphoïde de cellules Β (LAL-B) est grandement diminuée en l'absence de γ-catenin, alors que l'induction de la leucémie myéloïde chronique (LMC) n'est pas affectée. En l'absence des deux catenines, l'induction des deux leucémies LAL-B et LMC est presque complètement bloquée. En confirmation de nos données, un autre groupe a montré que β-catenine est essentielle pour le développement de la LMC. Ensemble, ces données nous montrent que β- et γ-catenine ne sont pas nécessaires pour l'hématopoïèse normale, mais essentielle pour le développement des leucémies induites par BCR-ABL. Cela suggère que la voie de signalisation canonique Wnt est une cible prometteuse pour de futures thérapies.

Behavior of nuclear matrix proteins during camptothecin-induced apoptosis in HL-60 human leukemia cells.

In this study we focused our attention on the behavior of four nuclear matrix proteins during the various stages of apoptosis in the HL-60 cell line exposed to the DNA topoisomerase I inhibitor, camptothecin. We have examined the following antigens by immunocytochemical techniques: (i) the 180-kDa nucleolar isoform of DNA topoisomerase II; (ii) a 126-kDa polypeptide of nuclear bodies; (iii) a 125-kDa protein; and (iv) a 160-kDa polypeptide which are known to be components of the matrix inner network. Indirect immunofluorescence experiments were performed to follow these nuclear matrix antigens during apoptosis. Moreover, the ultrastructural localization of both 125- and 160-kDa proteins was investigated by electron microscope immunocytochemistry with gold-conjugated secondary antibodies. While the antibody to the nucleolar isoform of DNA topoisomerase II gave a fluorescent pattern that was well-maintained until the late phases of apoptosis, the other three nuclear antigens showed marked modifications in their distribution. A common feature, particularly evident for 125- and 160-kDa proteins, was their absence from cap-shaped chromatin marginations, whereas they were present in the areas of remaining decondensed chromatin. The 126-kDa polypeptide concentrated progressively in an irregular mass at the opposite side of the crescentic caps and then broke up in fine spots. The 125- and 160-kDa proteins localized in the nucleolus and precisely within certain granules which are known to appear in the nucleolar area after camptothecin administration. These results show that, in addition to the well-known chromatin changes, nuclear organization undergoes other rearrangements during the apoptotic process.

Receptor activator for NF-κB ligand in acute myeloid leukemia: expression, function, and modulation of NK cell immunosurveillance.

The TNF family member receptor activator for NF-κB ligand (RANKL) and its receptors RANK and osteoprotegerin are key regulators of bone remodeling but also influence cellular functions of tumor and immune effector cells. In this work, we studied the involvement of RANK-RANKL interaction in NK cell-mediated immunosurveillance of acute myeloid leukemia (AML). Substantial levels of RANKL were found to be expressed on leukemia cells in 53 of 78 (68%) investigated patients. Signaling via RANKL into the leukemia cells stimulated their metabolic activity and induced the release of cytokines involved in AML pathophysiology. In addition, the immunomodulatory factors released by AML cells upon RANKL signaling impaired the anti-leukemia reactivity of NK cells and induced RANK expression, and NK cells of AML patients displayed significantly upregulated RANK expression compared with healthy controls. Treatment of AML cells with the clinically available RANKL Ab Denosumab resulted in enhanced NK cell anti-leukemia reactivity. This was due to both blockade of the release of NK-inhibitory factors by AML cells and prevention of RANK signaling into NK cells. The latter was found to directly impair NK anti-leukemia reactivity with a more pronounced effect on IFN-γ production compared with cytotoxicity. Together, our data unravel a previously unknown function of the RANK-RANKL molecule system in AML pathophysiology as well as NK cell function and suggest that neutralization of RANKL with therapeutic Abs may serve to reinforce NK cell reactivity in leukemia patients.

Targeting PI3KC2β Impairs Proliferation and Survival in Acute Leukemia, Brain Tumours and Neuroendocrine Tumours.

BACKGROUND: Eight human catalytic phosphoinositide 3-kinase (PI3K) isoforms exist which are subdivided into three classes. While class I isoforms have been well-studied in cancer, little is known about the functions of class II PI3Ks. MATERIALS AND METHODS: The expression pattern and functions of the class II PI3KC2β isoform were investigated in a panel of tumour samples and cell lines. RESULTS: Overexpression of PI3KC2β was found in subsets of tumours and cell lines from acute myeloid leukemia (AML), glioblastoma multiforme (GBM), medulloblastoma (MB), neuroblastoma (NB), and small cell lung cancer (SCLC). Specific pharmacological inhibitors of PI3KC2β or RNA interference impaired proliferation of a panel of human cancer cell lines and primary cultures. Inhibition of PI3KC2β also induced apoptosis and sensitised the cancer cells to chemotherapeutic agents. CONCLUSION: Together, these data show that PI3KC2β contributes to proliferation and survival in AML, brain tumours and neuroendocrine tumours, and may represent a novel target in these malignancies.

European guidelines for antifungal management in leukemia and hematopoietic stem cell transplant recipients: summary of the ECIL 3--2009 update.

In 2005, several groups, including the European Group for Blood and Marrow Transplantation, the European Organization for Treatment and Research of Cancer, the European Leukemia Net and the Immunocompromised Host Society created the European Conference on Infections in Leukemia (ECIL). The main goal of ECIL is to elaborate guidelines, or recommendations, for the management of infections in leukemia and stem cell transplant patients. The first sets of ECIL slides about the management of invasive fungal disease were made available on the web in 2006 and the papers were published in 2007. The third meeting of the group (ECIL 3) was held in September 2009 and the group updated its previous recommendations. The goal of this paper is to summarize the new proposals from ECIL 3, based on the results of studies published after the ECIL 2 meeting: (1) the prophylactic recommendations for hematopoietic stem cell transplant recipients were formulated differently, by splitting the neutropenic and the GVHD phases and taking into account recent data on voriconazole; (2) micafungin was introduced as an alternative drug for empirical antifungal therapy; (3) although several studies were published on preemptive antifungal approaches in neutropenic patients, the group decided not to propose any recommendation, as the only randomized study comparing an empirical versus a preemptive approach showed a significant excess of fungal disease in the preemptive group.

Molecular cloning of a novel human I-mfa domain-containing protein that differently regulates human T-cell leukemia virus type I and HIV-1 expression.

Regulation of viral genome expression is the result of complex cooperation between viral proteins and host cell factors. We report here the characterization of a novel cellular factor sharing homology with the specific cysteine-rich C-terminal domain of the basic helix-loop-helix repressor protein I-mfa. The synthesis of this new factor, called HIC for Human I-mfa domain-Containing protein, is controlled at the translational level by two different codons, an ATG and an upstream non-ATG translational initiator, allowing the production of two protein isoforms, p32 and p40, respectively. We show that the HIC protein isoforms present different subcellular localizations, p32 being mainly distributed throughout the cytoplasm, whereas p40 is targeted to the nucleolus. Moreover, in trying to understand the function of HIC, we have found that both isoforms stimulate in T-cells the expression of a luciferase reporter gene driven by the human T-cell leukemia virus type I-long terminal repeat in the presence of the viral transactivator Tax. We demonstrate by mutagenesis that the I-mfa-like domain of HIC is involved in this regulation. Finally, we also show that HIC is able to down-regulate the luciferase expression from the human immunodeficiency virus type 1-long terminal repeat induced by the viral transactivator Tat. From these results, we propose that HIC and I-mfa represent two members of a new family of proteins regulating gene expression and characterized by a particular cysteine-rich C-terminal domain.

In situ RHAMM protein expression in acute myeloid leukemia blasts suggests poor overall survival.

Treatment options for patients with high-risk acute myeloid leukemia (AML) include high-dose chemotherapy regimens in combination with allogeneic hematopoietic stem cell transplantation, which takes advantage of the donor T-cell-mediated graft-versus-leukemia effect. Together with beneficial responses observed in assays targeted at leukemia-associated antigens (LAA), this encouraged research on cancer vaccines and adoptive cellular therapies in AML. The receptor for hyaluronic acid-mediated motility (RHAMM, CD168) was identified as one of the most promising LAA in AML. Thus far, little is known about in situ expression in leukemic bone marrow blasts or the prognostic role of RHAMM and its interaction partners in AML. We immunohistochemically analyzed the expression and prognostic significance of RHAMM on trephine bone marrow biopsies from 71 AML cases that had been evaluated for cytogenetics and presence of FLT3-internal tandem duplications and NPM1 mutations. Fifty-five patients (77%) were treated with curative intent, while 16 (23%) received the most appropriate supportive care. Twenty of 71 (28%) AML cases were considered RHAMM+. Receiver operating characteristic curves showed significant discriminatory power considering overall survival (OS) in AML patients treated curatively for RHAMM (p = 0.015). Multivariable analysis revealed that expression of RHAMM in >5% of leukemic blasts identifies a subgroup of curatively treated cases with adverse OS independent of failures to achieve complete remission. RHAMM not only represents a promising LAA with specific T-cell responses in AML but, if assessed in situ on blasts, also a probable prognostic factor.

Molecular interactions involved in the transactivation of the human T-cell leukemia virus type 1 promoter mediated by Tax and CREB-2 (ATF-4).

The human T-cell leukemia virus type 1 (HTLV-1) Tax protein activates viral transcription through three 21-bp repeats located in the U3 region of the HTLV-1 long terminal repeat and called Tax-responsive elements (TxREs). Each TxRE contains nucleotide sequences corresponding to imperfect cyclic AMP response elements (CRE). In this study, we demonstrate that the bZIP transcriptional factor CREB-2 is able to bind in vitro to the TxREs and that CREB-2 binding to each of the 21-bp motifs is enhanced by Tax. We also demonstrate that Tax can weakly interact with CREB-2 bound to a cellular palindromic CRE motif such as that found in the somatostatin promoter. Mutagenesis of Tax and CREB-2 demonstrates that both N- and C-terminal domains of Tax and the C-terminal region of CREB-2 are required for direct interaction between the two proteins. In addition, the Tax mutant M47, defective for HTLV-1 activation, is unable to form in vitro a ternary complex with CREB-2 and TxRE. In agreement with recent results suggesting that Tax can recruit the coactivator CREB-binding protein (CBP) on the HTLV-1 promoter, we provide evidence that Tax, CREB-2, and CBP are capable of cooperating to stimulate viral transcription. Taken together, our data highlight the major role played by CREB-2 in Tax-mediated transactivation.

The complementary strand of the human T-cell leukemia virus type 1 RNA genome encodes a bZIP transcription factor that down-regulates viral transcription.

The RNA genome of the human T-cell leukemia virus type 1 (HTLV-1) codes for proteins involved in infectivity, replication, and transformation. We report in this study the characterization of a novel viral protein encoded by the complementary strand of the HTLV-1 RNA genome. This protein, designated HBZ (for HTLV-1 bZIP factor), contains a N-terminal transcriptional activation domain and a leucine zipper motif in its C terminus. We show here that HBZ is able to interact with the bZIP transcription factor CREB-2 (also called ATF-4), known to activate the HTLV-1 transcription by recruiting the viral trans-activator Tax on the Tax-responsive elements (TxREs). However, we demonstrate that the HBZ/CREB-2 heterodimers are no more able to bind to the TxRE and cyclic AMP response element sites. Taking these findings together, the functional inactivation of CREB-2 by HBZ is suggested to contribute to regulation of the HTLV-1 transcription. Moreover, the characterization of a minus-strand gene protein encoded by HTLV-1 has never been reported until now.

Azacytidine for acute myeloid leukemia in elderly or frail patients: a phase II trial (SAKK 30/07).

Abstract This phase II trial treated elderly or frail patients with acute myeloid leukemia (AML) with single-agent subcutaneous azacytidine at 100 mg/m(2), on 5 of 28 days for up to six cycles. Treatment was stopped for lack of response, or continued to progression in responders. The primary endpoint was response within 6 months. A response rate ≥ 34% was considered a positive trial outcome. From September 2008 to April 2010, 45 patients from 10 centers (median age 74 [55-86] years) were accrued. Patients received four (1-21) cycles. Best response was complete response/complete response with incomplete recovery of neutrophils and/or platelets (CR/CRi) in eight (18%; 95% confidence interval [CI]: 8-32%.), 0 (0%) partial response (PR), seven (16%) hematologic improvement, 17 (38%) stable disease. Three non-responding patients stopped treatment after six cycles, 31 patients stopped early and 11 patients continued treatment for 8-21 cycles. Adverse events (grade ≥ III) were infections (n = 13), febrile neutropenia (n = 8), thrombocytopenia (n = 7), dyspnea (p = 6), bleeding (n = 5) and anemia (n = 4). Median overall survival was 6 months. Peripheral blood blast counts, grouped at 30%, had a borderline significant association with response (p = 0.07). This modified azacytidine schedule is feasible for elderly or frail patients with AML in an outpatient setting with moderate, mainly hematologic, toxicity and response in a proportion of patients, although the primary objective was not reached.

G-CSF-induced remission in two cases of acute myeloid leukemia.

We report on two elderly patients with newly diagnosed acute myeloid leukemia (AML) who were treated in palliative intention because of comorbidities and intermediate or poor risk cytogenetics. Both received G-CSF to reduce the risk of infection related to neutropenia. Interestingly, one patient achieved a full hematological remission and the other a peripheral remission with dramatic reduction of the bone marrow blast count. Although a direct therapeutic effect of myeloid growth factors seems to be unusual in AML, the use of G-CSF or GM-CSF may be recommended in patients such as elderly patients who are not suited for intensive chemotherapy.

Targeted therapy against multi-resistant bacteria in leukemic and hematopoietic stem cell transplant recipients: guidelines of the 4th European Conference on Infections in Leukemia (ECIL-4, 2011).

The detection of multi-resistant bacterial pathogens, particularly those to carbapenemases, in leukemic and stem cell transplant patients forces the use of old or non-conventional agents as the only remaining treatment options. These include colistin/polymyxin B, tigecycline, fosfomycin and various anti-gram-positive agents. Data on the use of these agents in leukemic patients are scanty, with only linezolid subjected to formal trials. The Expert Group of the 4(th) European Conference on Infections in Leukemia has developed guidelines for their use in these patient populations. Targeted therapy should be based on (i) in vitro susceptibility data, (ii) knowledge of the best treatment option against the particular species or phenotype of bacteria, (iii) pharmacokinetic/pharmacodynamic data, and (iv) careful assessment of the risk-benefit balance. For infections due to resistant Gram-negative bacteria, these agents should be preferably used in combination with other agents that remain active in vitro, because of suboptimal efficacy (e.g., tigecycline) and the risk of emergent resistance (e.g., fosfomycin). The paucity of new antibacterial drugs in the near future should lead us to limit the use of these drugs to situations where no alternative exists.

Superiority of the Triple Combination of Bortezomib-Thalidomide-Dexamethasone Over the Dual Combination of Thalidomide-Dexamethasone in Patients With Multiple Myeloma Progressing or Relapsing After Autologous Transplantation: The MMVAR/IFM 2005-04 Randomized Phase III Trial From the Chronic Leukemia Working Party of the European Group for Blood and Marrow Transplantation.

PURPOSE This prospective multicenter phase III study compared the efficacy and safety of a triple combination (bortezomib-thalidomide-dexamethasone [VTD]) versus a dual combination (thalidomide-dexamethasone [TD]) in patients with multiple myeloma (MM) progressing or relapsing after autologous stem-cell transplantation (ASCT). PATIENTS AND METHODS Overall, 269 patients were randomly assigned to receive bortezomib (1.3 mg/m(2) intravenous bolus) or no bortezomib for 1 year, in combination with thalidomide (200 mg per day orally) and dexamethasone (40 mg orally once a day on 4 days once every 3 weeks). Bortezomib was administered on days 1, 4, 8, and 11 with a 10-day rest period (day 12 to day 21) for eight cycles (6 months), and then on days 1, 8, 15, and 22 with a 20-day rest period (day 23 to day 42) for four cycles (6 months). Results Median time to progression (primary end point) was significantly longer with VTD than TD (19.5 v 13.8 months; hazard ratio, 0.59; 95% CI, 0.44 to 0.80; P = .001), the complete response plus near-complete response rate was higher (45% v 25%; P = .001), and the median duration of response was longer (17.2 v 13.4 months; P = .03). The 24-month survival rate was in favor of VTD (71% v 65%; P = .093). Grade 3 peripheral neuropathy was more frequent with VTD (29% v 12%; P = .001) as were the rates of grades 3 and 4 infection and thrombocytopenia. CONCLUSION VTD was more effective than TD in the treatment of patients with MM with progressive or relapsing disease post-ASCT but was associated with a higher incidence of grade 3 neurotoxicity.