Expression of FLIP(Long) and FLIP(Short) in bone marrow mononuclear and CD34+ cells in patients with myelodysplastic syndrome: correlation with apoptosis

Hypoplastic Myelodysplastic Syndromes: Just an Overlap Syndrome?

Simple Summary

Hypoplastic myelodysplastic syndromes (hMDS) represent a diagnostic conundrum. They share morphologic and clinical features of both MDS (dysplasia, genetic lesions and cytopenias) and aplastic anemia (AA; i.e., hypocellularity and autoimmunity) and are not comprised in the last WHO classification. In this review we recapitulate the main clinical, pathogenic and therapeutic aspects of hypo-MDS and discuss why they deserve to be distinguished from normo/hypercellular MDS and AA. We conclude that hMDS may present in two phenotypes: one more proinflammatory and autoimmune, more similar to AA, responding to immunosuppression; and one MDS-like dominated by genetic lesions, suppression of immune surveillance, and tumor escape, more prone to leukemic evolution.

Abstract

Myelodysplasias with hypocellular bone marrow (hMDS) represent about 10–15% of MDS and are defined by reduced bone marrow cellularity (i.e., <25% or an inappropriately reduced cellularity for their age in young patients). Their diagnosis is still an object of debate and has not been clearly established in the recent WHO classification. Clinical and morphological overlaps with both normo/hypercellular MDS and aplastic anemia include cytopenias, the presence of marrow hypocellularity and dysplasia, and cytogenetic and molecular alterations. Activation of the immune system against the hematopoietic precursors, typical of aplastic anemia, is reckoned even in hMDS and may account for the response to immunosuppressive treatment. Finally, the hMDS outcome seems more favorable than that of normo/hypercellular MDS patients. In this review, we analyze the available literature on hMDS, focusing on clinical, immunological, and molecular features. We show that hMDS pathogenesis and clinical presentation are peculiar, albeit in-between aplastic anemia (AA) and normo/hypercellular MDS. Two different hMDS phenotypes may be encountered: one featured by inflammation and immune activation, with increased cytotoxic T cells, increased T and B regulatory cells, and better response to immunosuppression; and the other, resembling MDS, where T and B regulatory/suppressor cells prevail, leading to genetic clonal selection and an increased risk of leukemic evolution. The identification of the prevailing hMDS phenotype might assist treatment choice, inform prognosis, and suggest personalized monitoring.

What are the most promising new agents in myelodysplastic syndromes?

PURPOSE OF REVIEW

Myelodysplastic syndromes (MDS) are a diverse group of clonal disorders of hematopoietic stem or progenitor cells that represent the most common class of acquired bone marrow failure syndromes in adults. Despite significant improvement in the pathologic insight into this group of disorders, therapeutic options remain limited and allogeneic hematopoietic stem-cell transplantation is the only treatment that can induce long-term remission in patients with MDS. The goals of therapy for MDS are based on disease prognostication, with a focus of minimizing transfusion dependence and preserving quality of life in low-risk groups and preventing progression of disease to acute myeloid leukemia in high-risk groups. Given the dearth of approved treatment options, there is a marked need for novel therapies across the board, and there are several novel agents currently in the pipeline.

RECENT FINDINGS

Among the promising agents with preclinical and early phase efficacy in higher risk MDS, apoptosis targeting with BCL-2 inhibitors have been a standout. There is also a keen interest in immunotherapy, and targeted agents (genetic, signaling pathways, bispecific antibodies, antibody-drug conjugates, and others described in this review).

SUMMARY

In this review, we will highlight some of the promising new agents currently under investigation for the management of MDS.

Unraveling the Pathogenesis of MDS: The NLRP3 Inflammasome and Pyroptosis Drive the MDS Phenotype

Myelodysplastic syndromes (MDS) are characterized by bone marrow cytological dysplasia and ineffective hematopoiesis in the setting of recurrent somatic gene mutations and chromosomal abnormalities. The underlying pathogenic mechanisms that drive a common clinical phenotype from a diverse array of genetic abnormalities have only recently begun to emerge. Accumulating evidence has highlighted the integral role of the innate immune system in upregulating inflammatory cytokines via NF-κB activation in the pathogenesis of MDS. Recent investigations implicate activation of the NLRP3 inflammasome in hematopoietic stem/progenitor cells as a critical convergence signal in MDS with consequent clonal expansion and pyroptotic cell death though caspase-1 maturation. Specifically, the alarmin S100A9 and/or founder gene mutations trigger pyroptosis through the generation of reactive oxygen species leading to assembly and activation of the redox-sensitive NLRP3 inflammasome and β–catenin, assuring propagation of the MDS clone. More importantly, targeted inhibition of varied steps in this pathway restore effective hematopoiesis. Together, delineation of the role of pyroptosis in the clinical phenotype of MDS patients has identified novel therapeutic strategies that offer significant promise in the treatment of MDS.

Role of microRNA-29b in myelodysplastic syndromes during transformation to overt leukaemia

Chromosome 7q32 is a frequently deleted region in myelodysplastic syndromes (MDSs) and encodes the microRNAs (miRNAs) miR-29a/miR-29b. Both miR-29s down-regulate the anti-apoptotic protein myeloid cell leukaemia 1 (MCL-1) in acute myeloid leukaemia. Thus, to investigate the role of miR-29s in the transformation of MDS to overt leukaemia (OL), we analysed the relationship between miR-29 expression and MCL-1 expression. MiR-29b expression was down-regulated in refractory anaemia and OL bone marrow as compared to that in control bone marrow. MCL-1 expression level in OL was significantly higher than that in refractory anaemia with excess blasts and a negative correlation was observed between miR-29b and MCL-1 messenger RNA expression levels in OL samples. Immunohistochemical analysis showed that the MCL-1 positive rate among MDS bone marrow CD34 positive cells significantly increased during transformation to OL. Additionally, MCL-1 positive cells were negative for cleaved caspase 3, which indicated that these cells avoided apoptosis. Reduced miR-29b expression in MDS bone marrow cells might trigger transformation to OL via overexpression of MCL-1 in blastic cells.

[Management of myelodysplastic syndromes]

Myelodysplastic syndromes are heterogeneous diseases whose molecular characteristics have only been identified in recent years. Better identification of prognostic factors, larger access to allogeneic stem cell transplantation and the advent of new drugs notably hypomethylating agents (azacitidine, decitabine) and lenalidomide have improved patient outcome.

The inflammatory microenvironment in MDS

Myelodysplastic syndromes (MDS) are a collection of pre-malignancies characterized by impaired proliferation and differentiation of hematopoietic stem cells and a tendency to evolve into leukemia. Among MDS's pathogenic mechanisms are genetic, epigenetic, apoptotic, differentiation, and cytokine milieu abnormalities. Inflammatory changes are a prominent morphologic feature in some cases, with increased populations of plasma cells, mast cells, and lymphocytes in bone marrow aspirates. Accumulating evidence suggests that the bone marrow microenvironment contributes to MDS disease pathology, with microenvironment alterations and abnormality preceding, and facilitating clonal evolution in MDS patients. In this review, we focus on the inflammatory changes involved in the pathology of MDS, with an emphasis on immune dysfunction, stromal microenvironment, and cytokine imbalance in the microenvironment as well as activation of innate immune signaling in MDS patients. A better understanding of the mechanism of MDS pathophysiology will be beneficial to the development of molecular-targeted therapies in the future.

Over-expression of cancerous inhibitor of PP2A (CIP2A) in bone marrow cells from patients with a group of high-risk myelodysplastic syndromes

Cancerous inhibitor of PP2A (protein phosphatase 2A) (CIP2A) is an inhibitor of PP2A, a phosphatase and tumor suppressor that regulates cell proliferation, differentiation, and survival. The aim of this study was to investigate whether CIP2A plays a role in the progression of myelodysplastic syndromes (MDS). Immunohistochemical analysis revealed that a fraction patients having refractory anemia with excess blasts (RAEB)-1 (4 out of 12) and RAEB-2 (10 out of 14) exhibited significant expression of CIP2A in bone marrow hematopoietic cells, while all patients with refractory cytopenia with unilineage or multilineage dysplasia (RCUD/RCMD) (0 out of 18) and the control group (0 out of 17) were negative. CIP2A was mainly expressed by the MPO-positive myeloid series of cells and partly by the CD34-positive cells in association with the expression of phosphorylated c-MYC (p-c-MYC) protein and the cell cycle-related proteins Ki-67, MCM2, and geminin. The percentage of p-c-MYC-positive cells in the bone marrow of CIP2A-positive MDS cases was significantly higher than that in CIP2A-negative MDS cases (P < 0.01). The expression levels of mRNA for CIP2A and PP2A exhibited positive correlation in MDS/control bone marrow. These results suggest that up-regulated expression of CIP2A might play a role in the proliferation of blasts in the MDS bone marrow and in disease progression in at least some cases.

Predictive value of Sp1/Sp3/FLIP signature for prostate cancer recurrence

Prediction of prostate cancer prognosis is challenging and predictive biomarkers of recurrence remain elusive. Although prostate specific antigen (PSA) has high sensitivity (90%) at a PSA level of 4.0 ng/mL, its low specificity leads to many false positive results and considerable overtreatment of patients and its performance at lower ranges is poor. Given the histopathological and molecular heterogeneity of prostate cancer, we propose that a panel of markers will be a better tool than a single marker. We tested a panel of markers composed of the anti-apoptotic protein FLIP and its transcriptional regulators Sp1 and Sp3 using prostate tissues from 64 patients with recurrent and non-recurrent cancer who underwent radical prostatectomy as primary treatment for prostate cancer and were followed with PSA measurements for at least 5 years. Immunohistochemical staining for Sp1, Sp3, and FLIP was performed on these tissues and scored based on the proportion and intensity of staining. The predictive value of the FLIP/Sp1/Sp3 signature for clinical outcome (recurrence vs. non-recurrence) was explored with logistic regression, and combinations of FLIP/Sp1/Sp3 and Gleason score were analyzed with a stepwise (backward and forward) logistic model. The discrimination of the markers was identified by sensitivity-specificity analysis and the diagnostic value of FLIP/Sp1/Sp3 was determined using area under the curve (AUC) for receiver operator characteristic curves. The AUCs for FLIP, Sp1, Sp3, and Gleason score for predicting PSA failure and non-failure were 0.71, 0.66, 0.68, and 0.76, respectively. However, this increased to 0.93 when combined. Thus, the “biomarker signature” of FLIP/Sp1/Sp3 combined with Gleason score predicted disease recurrence and stratified patients who are likely to benefit from more aggressive treatment.

Mouse models of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are hematopoietic malignancies characterized by peripheral cytopenias in the face of normo- or hypercellular, dysplastic bone marrow that arise from mutations in the hematopoietic stem/progenitor cell (HSPC). The disease is characterized by multiple cytogenetic and molecular defects, which result in an extremely heterogeneous phenotype. Recently, significant efforts have been made to develop appropriate mouse models to study this complex disease. Because of the heterogeneity of MDS, no single model is able to capture the MDS phenotype in its entirety. In this review, we describe several MDS mouse models and discuss the advances made in our understanding of the different disease mechanisms within the malignant clone and the marrow microenvironment. In addition, we describe progress in xenotransplantation models of MDS and discuss questions that remain to be answered.

NF-κB as a potential therapeutic target in myelodysplastic syndromes and acute myeloid leukemia

IMPORTANCE OF THE FIELD

The inactive NF-κB-inhibitor of NF-κB (IκB) complex is activated by stimuli including pro-inflammatory cytokines, mitogens, growth factors and stress-inducing agents. The release of NF-κB facilitates its translocation to the nucleus, where it promotes cell survival by initiating transcription of genes encoding stress-response enzymes, cell-adhesion molecules, pro-inflammatory cytokines and anti-apoptotic proteins. NF-κB and associated regulatory factors (IκB kinase subunits and bcl-3) are implicated in hematological and solid tumour malignancies. NF-κB appears to be involved in cell proliferation control, apoptosis control, angiogenesis promotion and possibly regulation of diffusion of metastases. There are several reports that inhibition of NF-κB as a therapeutic target may have a role in tumour cell death or growth inhibition.

AREA COVERED IN THIS REVIEW

We review data about inhibition of NF-κB in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). We describe the molecular mechanisms underlying NF-κB deregulation in these haematological malignancies.

WHAT THE READER WILL GAIN

Constitutive activation of NF-κB in the nucleus has been reported in some varieties of MDS/AML. The in vitro and in vivo results of NF-κB inhibition in myeloid malignancies are highlighted.

TAKE HOME MESSAGE

NF-κB selective inhibitory drugs may be useful, either as single agents or associated with conventional chemotherapy.

Myelodysplastic syndromes: an update on molecular pathology

The myelodysplastic syndromes (MDS) are a heterogeneous group of myeloid disorders characterised by impaired peripheral blood cell production due to bone marrow dysplasia affecting one or more of the major myeloid cell lines. MDS are one of five major categories of myeloid neoplasms according to the World Health Organization (WHO) classification system for haematological cancers. Given their cytological and cytogenetic heterogeneity, these diseases probably constitute a group of molecularly distinct entities with variable degrees of ineffective haematopoiesis and susceptibility to leukaemic transformation. Recent studies provide some insights into the physiopathology of MDS. In the early stages, one mechanism contributing to hypercellular marrow and peripheral blood cytopenia is a significant increase in programmed cell death (apoptosis) in haematopoietic cells. Furthermore, altered responses in relation to cytokines, the immune system and bone marrow stroma also contribute to the disease phenotype. Deletions of chromosome 5q31-q32 are the most common recurring cytogenetic abnormalities detected in MDS. The 5q- syndrome is a new entity recognised in the WHO classification since 2001 and is associated with a good prognosis. Haploinsufficiency of multiple genes mapping to the common deleted region at 5q31-32 may contribute to the pathogenesis of 5q- syndrome and other MDS with 5q- deletion. Many studies have demonstrated that altered DNA methylation and histone acetylation can alter gene transcription. Abnormal methylation of transcription promoter sites is universal in patients with MDS, and the number of involved loci is increased in high-risk disease and secondary leukaemias. A better understanding of the pathogenesis of MDS can contribute to the development of new treatments such as hypomethylating drugs, immunomodulatory agents such as lenalidomide, and immunosuppressive drugs aimed at reversing the specific alteration that results in improvement in patients with MDS.

Immunosuppression for myelodysplastic syndrome: how bench to bedside to bench research led to success

Laboratory evidence and clinical evidence suggest that some patients with myelodysplastic syndrome (MDS) have immunologically mediated disease. This article describes the laboratory evidence supporting a role for the immune system in the marrow failure of MDS and clinical trials using IST in these patients.

Expression of Toll-like receptor 9 in bone marrow cells of myelodysplastic syndromes is down-regulated during transformation to overt leukemia

Toll-like receptors (TLRs) play a crucial role in the host defense against invading microorganisms by recognizing pathogen-associated molecular patterns. Recently, a number of endogenous molecules have been reported to be ligands of TLRs. Some of these molecules are known to be expressed in cancer tissue and activate intracellular signal pathways via TLRs during cancer progression. Thus, in the present study, we analyzed the expression dynamics of TLRs in the bone marrow of myelodysplastic syndromes (MDS) during the course of transformation to overt leukemia (OL) using real-time RT-PCR. MDS bone marrow cells at the time of initial diagnosis tended to express higher levels of TLR2, TLR4 and TLR9 than control bone marrow cells. Among these TLRs, TLR9 exhibited a significant decrease of expression at the time of transformation to OL. The expression of TLR9 and TNF-alpha showed significant correlation in bone marrow cells from patients with MDS and OL. Immunohistochemically, TLR2 was mostly localized to neutrophils of the control and MDS bone marrow. TLR4 was observed in a subset of neutrophils and a few mononuclear cells in control and MDS bone marrow. In addition, TLR4 was weakly expressed in nearly half of immature myeloid cells of MDS cases. TLR9 was mainly localized to neutrophils in the control and RA bone marrow and strongly expressed in the immature myeloid cells of RAEB cases, although the blastic cells of OL cases did not express TLR9. Bone marrow cells in MDS exhibit frequent apoptosis, while OL cells are prone to be immortal. Thus, TLR9 might be associated with regulation of apoptotic/proliferative signals via TNF-alpha in the MDS bone marrow.

Hypocellular myelodysplasia

Myelodysplasia must be considered in the differential diagnosis of patients who have bone marrow failure, but bone marrow cellularity per se may not substantially affect either response to therapy or prognosis. It is unclear whether the primary pathophysiologic defect differs between hyper- and hypoplastic patients who have myelodysplasia. Cellularity does not seem to affect response to immunosuppressive therapy significantly and does not seem to be the major factor affecting improvements in response to lenalidomide, stem cell transplantation, or hematopoietic growth factors.

Involvement of FLIP in 2-methoxyestradiol-induced tumor regression in transgenic adenocarcinoma of mouse prostate model

PURPOSE

The purpose of this study is to investigate whether Fas-associated death domain interleukin-1 converting enzyme like inhibitory protein (FLIP) inhibition is a therapeutic target associated with 2-methoxyestradiol (2-ME2)-mediated tumor regression.

EXPERIMENTAL DESIGN

Expression and levels of FLIP were analyzed using (a) real-time PCR and immunoblot analysis in androgen-independent PC-3 cells treated with the newly formulated 2-ME2 and (b) immunohistochemistry in different Gleason pattern human prostate tumors. Transient transfections and chromatin immunoprecipitation (ChIP) assays were used to identify the transcription factors that regulate FLIP. Involvement of FLIP in 2-ME2-induced tumor regression was evaluated in transgenic adenocarcinoma mouse prostate (TRAMP) mice.

RESULTS

High Gleason pattern (5+5) human prostate tumors exhibit significant increase in FLIP compared with low Gleason pattern 3+3 (P=or<0.04). 2-ME2 reduced the levels and promoter activity of FLIP (P=0.001) in PC-3 cells. Transient expression assays show sequences between -503/+242 being sufficient for 2-ME2-induced inhibition of FLIP promoter activity. Cotransfection experiments show that overexpression of Sp1 activated, whereas Sp3 inhibited, Sp1 transactivation of FLIP promoter activity (P=0.0001). 2-ME2 treatment reduced binding of Sp1 to the FLIP promoter as evidenced by ChIP. Further, levels of FLIP associated with Fas or FADD decreased, whereas cleavage of caspase-8, levels of Bid, and apoptosis increased in response to 2-ME2 treatment in PC-3 cells. Administration of 2-ME2 regressed established prostate tumors in TRAMP mice that were associated with reduced expression of FLIP and Sp1.

CONCLUSION

Targeting Sp1-mediated FLIP signaling pathway may provide a novel approach for prostate cancer management.

Stroma-dependent apoptosis in clonal hematopoietic precursors correlates with expression of PYCARD

The role of the marrow microenvironment in the pathophysiology of myelodysplastic syndromes (MDSs) remains controversial. Using stromal/hematopoietic cell cocultures, we investigated the effects of stroma-derived signals on apoptosis sensitivity in hematopoietic precursors. The leukemia-derived cell line KG1a is resistant to proapoptotic ligands. However, when cocultured with the human stromal cell line HS5 (derived from normal marrow) and exposed to tumor necrosis factor-alpha (TNF-alpha), KG1a cells showed caspase-3 activation and induction of apoptosis. Apoptosis was contact dependent. Identical results were obtained in coculture with primary stroma. Gene-expression profiling of KG1a cells identified coculture-induced up-regulation of various genes involved in apoptosis, including PYCARD. Suppression of PYCARD expression in KG1a by miRNA interfered with apoptosis. Knockdown of the TNF receptor 1 (TNFR1) or TNFR2 in HS5 cells had no effect. However, knockdown of R1 in KG1a cells prevented TNF-alpha-induced apoptosis, while apoptosis was still induced by TNF-alpha-related apoptosis-inducing ligand. Primary CD34(+) cells from MDS marrow, when cocultured with HS5 and TNF-alpha, also underwent apoptosis. In contrast, no apoptosis was observed in CD34(+) cells from the marrow of healthy donors. These data indicate that stroma may convey not only protective effects on hematopoietic cells, but, dependent upon the milieu, may also facilitate apoptosis.

Differential responses of FLIPLong and FLIPShort-overexpressing human myeloid leukemia cells to TNF-alpha and TRAIL-initiated apoptotic signals

OBJECTIVE

Clonal marrow cells from patients with early myelodysplastic syndrome (MDS) undergo apoptosis in response to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL). Cells from advanced MDS are resistant to TRAIL. Two isoforms of the Flice inhibitory protein (FLIP) short (FLIPS) and FLIP long (FLIPL), which modulate TRAIL signals, showed disease-stage-dependent differential regulation. Therefore, we aimed at characterizing potential differential effects of FLIPL and FLIPS, on TRAIL and TNF-alpha-induced apoptosis in model leukemic cell lines.

MATERIALS AND METHODS

Using lentiviral constructs, FLIPL and FLIPS, as well as a green fluorescent protein control were overexpressed in ML-1 cells, which constitutively express very low levels of FLIP and are highly sensitive to apoptosis induction. Cells were then exposed to TRAIL or TNF-alpha, and effects on the extrinsic and intrinsic pathways of apoptosis induction were assessed.

RESULTS

Overexpression of FLIP reduced TRAIL and TNF-alpha-induced apoptosis in ML-1 cells. However, while FLIPL completely abrogated apoptosis, FLIPS allowed for BID cleavage and caspase-3 activation. Concurrently, there was a decline of Bcl-xL and X-linked inhibitor of apoptosis protein (XIAP) in FLIPS cells followed by apoptosis. Further, inhibition of nuclear factor-kappaB (NF-kappaB) activation in TNF-alpha-treated cells resulted in profound apoptosis in FLIPS, but not in FLIPL-overexpressing cells, consistent with the observations in patients with early stage MDS. Inhibition of NF-kappaB had only minimal effects on TRAIL signaling.

CONCLUSION

Thus, FLIPL and FLIPS exerted differential effects in myeloid leukemic cell lines in response to TRAIL and TNF-alpha. It might be possible to therapeutically exploit those differences with effector molecules specific for the FLIP isoforms.

Human urine extract CDA-2 induces apoptosis of myelodysplastic syndrome-derived MUTZ-1 cells through the PI3K/Akt signaling pathway in a caspase-3-dependent manner

AIM

The aim of this study was to investigate the antitumoral activity of human urine extract against myelodysplastic syndrome (MDS)-derived MUTZ-1 cells in vitro and in vivo.

METHODS

The MDS-refractory anemia with excess of blasts (RAEB)-derived MUTZ-1 cell line was used to examine the effects of a human urine preparation, CDA-2, on the induction of growth arrest and apoptosis. Apoptotic proteins, including caspase family, Bcl-2 family, the inhibitor of apoptosis protein (IAP) family, and the FLICE-like inhibitory protein (FLIP), as well as cell cycle-associated proteins were studied. The phosphoinositide 3 kinase (PI3K)/Akt survival signaling pathway and the NF-kappaB pathway were also examined. The caspase-3 inhibitor Z-DEVD-fmk was used to examine the involvement of caspase-3 and poly (ADP-ribose) polymerase (PARP). PI3K inhibitor LY294002 was used to examine the involvement of the PI3K/Akt signaling pathway in this apoptosis-inducing effect. MUTZ-1 cell xenografted serious combined immunodeficiency disease mice were used for the in vivo study.

RESULTS

We found that CDA-2 could induce growth arrest and apoptosis of MUTZ-1 cells in vitro and in vivo. The main mechanisms were related to the inhibition of PI3Kp110alpha expression at the transcriptional level, which inactivated the phosphorylation of Akt involving the prevention NF-kappaB phosphorylation and nuclear translocation, the downregulation of the IAP family and FLIPL protein, and the dephosphorylation of the Bad protein, which then triggered the activation of the caspase cascades. This phenomenon could be inhibited by the PI3K inhibitor LY294002 and caspase-3 inhibitor Z-DEVD-fmk.

CONCLUSION

Our results demonstrate the presence of active components in the human urine extract that can induce the growth arrest and apoptosis of MDS-RAEB-derived MUTZ-1 cells and may involve the PI3K/Akt signaling pathway in a caspase-3-dependent manner. This may provide new insights for the treatment of high-risk MDS.

Apoptosis and antiapoptotic mechanisms in the progression of myelodysplastic syndrome

Myelodysplastic syndrome (MDS), previously known as preleukemia, comprises a spectrum of heterogeneous, clonal disorders of hematopoiesis. A patient's life expectancy can range from a few months to more than a decade. Recent studies provide some insight into the pathophysiology of MDS. One mechanism contributing to the constellation of hypercellular marrow and peripheral blood cytopenia is a significant increase in programmed cell death (apoptosis) in hematopoietic cells. Tumor necrosis factor (TNF)-alpha, Fas ligand, TNF-related apoptosis-inducing ligand, and other proapoptotic cytokines are upregulated in early-stage/low-risk MDS, and neutralization of these signals can improve hematopoiesis. TNF-related apoptosis inducing ligand induces apoptosis preferentially in clonal cells, which can contribute to containment of the clone. In a proportion of patients, MDS will eventually evolve to acute leukemia. This progression has been correlated with upregulation of nuclear factor kappaB; altered expression of adaptor molecules, such as Flice inhibitory protein; and enhanced activity of antiapoptotic members of the Bcl-2 and inhibitors of apoptosis protein families. Also, the ratio of TNF receptors 1 and 2 changes in favor of receptor 2. The role of the microenvironment in the pathophysiology and progression of MDS has remained controversial, although there is evidence that stroma and matrix components, and their interactions with clonal cells, play an important role. Microarray gene-expression studies are consistent with dysregulation of apoptosis, but not all data are in agreement.

Differential effects of bexarotene on intrinsic and extrinsic pathways in TRAIL-induced apoptosis in two myeloid leukemia cell lines

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces programmed cell death (apoptosis) preferentially in tumor cells. However, not all cancer cells are sensitive to TRAIL. We determined whether ligation of the retinoid receptor, RXR, would sensitize cells to TRAIL-mediated apoptosis. The leukemic cell lines KG1a (apoptosis-resistant) and ML-1 (apoptosis-sensitive) were treated with the RXR-specific retinoid bexarotene, TRAIL, or both, and apoptosis was determined. In KG1a cells, bexarotene downregulated FLIP(Long) and activated caspase-8, thereby allowing for TRAIL-triggered apoptosis. Overexpression of FLIP(Long) in ML-1 cells abrogated apoptosis. In unmodified ML-1 cells bexarotene enhanced programmed cell death via truncation of Bid and release of cytochrome C. Blockade of caspase-8 prevented enhancement in both cell lines; blockade of caspase-9 had a significant effect only in ML-1 cells. Thus, the effect of bexarotene on TRAIL-mediated programmed cell death involved proximal events of the extrinsic pathway; however, downstream signals involved the intrinsic pathway in ML-1 but not in KG1a cells. These studies add further information to the regulation of programmed cell death in leukemic cells that have to be considered when designing therapeutic strategies.

Regulation of enterocyte apoptosis by acyl-CoA synthetase 5 splicing

BACKGROUND AND AIMS

The constant renewal of enterocytes along the crypt-villus axis (CVA) of human small intestine is due to cell-inherent changes resulting in the apoptotic cell death of senescent enterocytes. The aim of the present study was to examine underlying molecular mechanisms of the cell death at the villus tip.

METHODS

Characterization of human acyl-coenzyme A (CoA) synthetase 5 (ACSL5) was performed by cloning, recombinant protein expression, biochemical approaches, and several functional and in situ analyses.

RESULTS

Our data show that different amounts of acyl-CoA synthetase 5-full length (ACSL5-fl) and a so far unknown splice variant lacking exon 20 (ACSL5-Delta 20) are found in human enterocytes. In contrast with the splice variant ACSL5-Delta 20, recombinant and purified ACSL5-fl protein is active at a highly alkaline pH. Over expression of ACSL5-fl protein is associated with a decrease of the anti-apoptotic FLIP protein in a ceramide-dependent manner and an increased cell-surface expression of the death receptor TRAIL-R1. Expression analyses revealed that the ACSL5-fl/ACSL5-Delta 20 ratio increases along the CVA, thereby sensitizing ACSL5-fl-dominated cells at the villus tip to the death ligand TRAIL, which is corroborated by functional studies with human small intestinal mucosal samples and an immortalized human small intestinal cell line.

CONCLUSIONS

Our results suggest an ACSL5-dependent regulatory mechanism that contributes to the cellular renewal along the CVA in human small intestine. Deregulation of the ACSL5-fl/ACSL5-Delta 20 homeostasis in the maturation and shedding of cells along the CVA might also be of relevance for the development of intestinal neoplasia.

Critical role for Fas-associated death domain-like interleukin-1-converting enzyme-like inhibitory protein in anoikis resistance and distant tumor formation

BACKGROUND

Normal epithelial cells undergo anoikis, or apoptosis on loss of anchorage to the extracellular matrix, by initiating the death receptor pathway of caspase activation. However, malignant epithelial cells with metastatic potential resist anoikis and can survive in an anchorage-independent fashion. We hypothesized that c-Fas-associated death domain-like interleukin-1-converting enzyme-like inhibitory protein (FLIP), an endogenous inhibitor of death receptor signaling, may suppress anoikis.

METHODS

We assessed viability and apoptosis of PPC-1 prostate cancer cells cultured in adherent and suspension conditions using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt and Annexin V staining assays. Expression of the death receptor Fas and activation of caspase 8 were measured using flow cytometry. Expression of Fas ligand was measured by reverse transcription-polymerase chain reaction. FLIP protein expression was measured by immunoblotting. Small-molecule inhibitors of FLIP (including the death receptor sensitizer 5809354) and small-interfering (si) RNA directed against FLIP were used to assess the effects of FLIP inhibition on anoikis of prostate cancer cells in vitro and in vivo. All statistical tests were two-sided.

RESULTS

PPC-1 cells cultured in suspension resisted anoikis, despite increased expression of Fas (0 versus 8 hours, mean relative percent expression = 100% versus 135%, difference = 35%, 95% confidence interval [CI] = 10% to 61%; P = .02) and Fas L (0 versus 24 hours, mean relative percent expression = 100% versus 208%, difference = 108%, 95% CI = 18% to 197%; P = .02). Knockdown of FLIP expression by siRNA or treatment with 5809354 sensitized prostate cancer cells to anoikis (control siRNA versus FLIP siRNA at 10 nM, mean relative percent viability = 95% versus 51%, difference = 44%, 95% CI = 34% to 54%; P<.001; control versus 5809354 at 20 microM, mean relative percent viability = 96% versus 52%, difference = 44%, 95% CI = 13% to 75%; P = .015). Inhibition of FLIP expression specifically activated caspase 8 in PPC-1 cells grown in suspension but not adherent conditions and decreased the metastatic potential of circulating PPC-1 cells in vivo.

CONCLUSIONS

FLIP may be a suppressor of anoikis and therefore a possible target for antimetastatic therapeutic strategies.

Toll-like Receptor-4 Is Up-Regulated in Hematopoietic Progenitor Cells and Contributes to Increased Apoptosis in Myelodysplastic Syndromes

PURPOSE

To investigate the function and expression of Toll-like receptors (TLR) in bone marrow cells of myelodysplastic syndrome (MDS) patients and to examine their involvement in the apoptotic phenomenon characterizing MDS hematopoiesis.

EXPERIMENTAL DESIGN

TLR mRNA and protein expression was investigated in bone marrow cell populations of MDS patients and controls. TLR-4 ability to recognize lipopolysaccharide and up-regulate self mRNA and protein expression was examined. Tumor necrosis factor involvement in the constitutive and lipopolysaccharide (LPS)-induced TLR expression was also evaluated. Possible correlation between TLR-4 overexpression and apoptosis was investigated by simultaneous staining with Annexin V and TLR-4.

RESULTS

TLR-2 and TLR-4 are expressed in almost all bone marrow cell lineages including megakaryocytes, erythroid cells, myeloid precursors, monocytes, and B lymphocytes and are up-regulated in MDS patients compared with controls. In hematopoietic CD34(+) cells, TLR-4 is also expressed and significantly up-regulated at both the mRNA and protein levels. Treatment with an anti-tumor necrosis factor antibody reduces both constitutive and LPS-induced TLR-4 levels. Increased TLR-4 expression correlates with increased apoptosis as TLR-4 is almost exclusively found in apoptotic bone marrow mononuclear and CD34(+) cells. The addition of the TLR-4 ligand LPS further enhances the apoptosis of these cells.

CONCLUSIONS

TLR-4 and other TLRs are significantly up-regulated in MDS patients whereas TLR-4 is involved in promoting apoptosis, possibly contributing to MDS cytopenia.

Reduced expression of FLIP SHORT in bone marrow of low risk myelodysplastic syndrome

Apoptosis is dysregulated in patients with myelodysplastic syndrome (MDS) and acute myelogenous leukaemia (AML). FLIP (FLICE (FAS-associated death-domain-like IL-1 beta-converting enzyme)-inhibitory protein) has been described as an anti-apoptotic protein. Here, we characterize the expression level of FLIP(LONG) and FLIP(SHORT) mRNA in bone marrow aspirates from 61 patients diagnosed with MDS or AML. FLIP(SHORT) mRNA expression was significantly lower in low risk MDS, compared to high risk MDS, according to FAB classification (RA/RARS versus RAEB/RAEBt, P=0.0127) and IPSS (low risk/intermediate-1 versus intermediate-2/high risk, P=0.0345). Furthermore, FLIP(SHORT) mRNA expression was significantly lower in low risk MDS, compared to MDS-AML/AML de novo (P=0.0006), according to FAB classification. FLIP(LONG) expression did not differ between these groups. Increased levels of FLIP(SHORT) in RAEB and AML may be related to apoptosis resistance in these diseases and to MDS progression.

Mitochondria in hematopoiesis and hematological diseases

Mitochondria are involved in hematopoietic cell homeostasis through multiple ways such as oxidative phosphorylation, various metabolic processes and the release of cytochrome c in the cytosol to trigger caspase activation and cell death. In erythroid cells, the mitochondrial steps in heme synthesis, iron (Fe) metabolism and Fe-sulfur (Fe-S) cluster biogenesis are of particular importance. Mutations in the specific delta-aminolevulinic acid synthase (ALAS) 2 isoform that catalyses the first and rate-limiting step in heme synthesis pathway in the mitochondrial matrix, lead to ineffective erythropoiesis that characterizes X-linked sideroblastic anemia (XLSA), the most common inherited sideroblastic anemia. Mutations in the adenosine triphosphate-binding cassette protein ABCB7, identified in XLSA with ataxia (XLSA-A), disrupt the maturation of cytosolic (Fe-S) clusters, leading to mitochondrial Fe accumulation. In addition, large deletions in mitochondrial DNA, whose integrity depends on a specific DNA polymerase, are the hallmark of Pearson's syndrome, a rare congenital disorder with sideroblastic anemia. In acquired myelodysplastic syndromes at early stage, exacerbation of physiological pathways involving caspases and the mitochondria in erythroid differentiation leads to abnormal activation of a mitochondria-mediated apoptotic cell death pathway. In contrast, oncogenesis-associated changes at the mitochondrial level can alter the apoptotic response of transformed hematopoietic cells to chemotherapeutic agents. Recent findings in mitochondria metabolism and functions open new perspectives in treating hematopoietic cell diseases, for example various compounds currently developed to trigger tumor cell death by directly targeting the mitochondria could prove efficient as either cytotoxic drugs or chemosensitizing agents in treating hematological malignancies.

cFLIP expression correlates with tumour progression and patient outcome in non-Hodgkin lymphomas of low grade of malignancy

The present study investigated whether the expression of cellular Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE) inhibitory protein (cFLIP) conveys prognostic information in non-Hodgkin lymphomas (NHLs). cFLIP expression was quantified by immunohistochemistry and immunofluorescence in biopsy specimens from 86 NHL patients for whom clinical information was available. NHL malignancy was graded as high/intermediate or low according to the World Health Organization Classification of Lymphoid Neoplasms. cFLIP was positive in 23 of 45 high-/intermediate-grade NHLs and in 25 of 41 low-grade NHLs. Negative expression of cFLIP was associated with the presence of apoptotic cells in the tumour mass, regardless of the histotype and of the malignancy grade. In NHLs positive for cFLIP, 11 of 23 (48%) high-/intermediate-grade cases and 18 of 25 (72%) low-grade cases showed a bad outcome. In NHLs negative for cFLIP, only four of 22 (18%) high-/intermediate-grade patients and 12 of 16 (75%) low-grade patients achieved complete remission. All these correlations were statistically significant. The correlation of cFLIP expression with clinical outcome was independent of therapy, whether or not it included anti-CD20 antibody (Rituximab). The present findings strongly indicate that cFLIP is a reliable predictor of tumour progression and clinical prognosis in NHLs of low grade of malignancy.

Targeting NF-κB in hematologic malignancies

The transcription factor nuclear factor kappa B (NF-kappaB) can intervene in oncogenesis by virtue of its capacity to regulate the expression of a plethora of genes that modulate apoptosis, and cell survival as well as proliferation, inflammation, tumor metastasis and angiogenesis. Different reports demonstrate the intrinsic activation of NF-kappaB in lymphoid and myeloid malignancies, including preneoplastic conditions such as myelodysplastic syndromes, underscoring its implication in malignant transformation. Targeting intrinsic NF-kappaB activation, as well as its upstream and downstream regulators, may hence constitute an additional approach to the oncologist's armamentarium. Several small inhibitors of the NF-kappaB-activatory kinase IkappaB kinase, of the proteasome, or of the DNA binding of NF-kappaB subunits are under intensive investigation. Currently used cytotoxic agents can induce NF-kappaB activation as an unwarranted side effect, which confers apoptosis suppression and hence resistance to these drugs. Thus, NF-kappaB inhibitory molecules may be clinically useful, either as single therapeutic agents or in combination with classical chemotherapeutic agents, for the treatment of hematological malignancies.

NF-kappaB and FLIP in arsenic trioxide (ATO)-induced apoptosis in myelodysplastic syndromes (MDSs)

Tumor necrosis factor (TNF)-alpha, a potent stimulus of nuclear factor-kappaB (NF-kappaB), is up-regulated in myelodysplastic syndrome (MDS). Here, we show that bone marrow mononuclear cells (BMMCs) and purified CD34+ cells from patients with low-grade/early-stage MDS (refractory anemia/refractory anemia with ring sideroblasts [RA/RARS]) have low levels of NF-kappaB activity in nuclear extracts comparable with normal marrow, while patients with RA with excess blasts (RAEB) show significantly increased levels of activity (P = .008). Exogenous TNF-alpha enhanced NF-kappaB nuclear translocation in MDS BMMCs above baseline levels. Treatment with arsenic trioxide (ATO; 2-200 microM) inhibited NF-kappaB activity in normal marrow, primary MDS, and ML1 cells, even in the presence of exogenous TNF-alpha (20 ng/mL), and down-regulated NF-kappaB-dependent antiapoptotic proteins, B-cell leukemia XL (Bcl-XL), Bcl-2, X-linked inhibitor of apoptosis (XIAP), and Fas-associated death domain (FADD)-like interleukin-1beta-converting enzyme (FLICE) inhibitory protein (FLIP), leading to apoptosis. However, overexpression of FLIP resulted in increased NF-kappaB activity and rendered ML1 cells resistant to ATO-induced apoptosis. These data are consistent with the observed up-regulation of FLIP and resistance to apoptosis with advanced MDS, where ATO as a single agent may show only limited efficacy. However, the data also suggest that combinations of ATO with agents that interfere with other pathways, such as FLIP autoamplification via NF-kappaB, may have considerable therapeutic activity.

Effector CD4+ T cells generate intermediate caspase activity and cleavage of caspase-8 substrates

Caspase-8 activation promotes cell apoptosis but is also essential for T cell activation. The extent of caspase activation and substrate cleavage in these divergent processes remains unclear. We show that murine effector CD4(+) T cells generated levels of caspase activity intermediate between unstimulated T cells and apoptotic populations. Both caspase-8 and caspase-3 were partially activated in effector T cells, which was reflected in cleavage of the caspase-8 substrates, c-FLIP(L), receptor interacting protein 1, and to a lesser extent Bid, but not the caspase-3 substrate inhibitor of caspase-activated DNase. Th2 effector CD4(+) T cells manifested more caspase activity than did Th1 effectors, and caspase blockade greatly decreased initiation of cell cycling. The current findings define the level of caspase activity and substrates during initiation of T cell cycling.

Rescue of early-stage myelodysplastic syndrome-deriving erythroid precursors by the ectopic expression of a dominant-negative form of FADD

Myelodysplastic syndromes (MDSs) are characterized by peripheral blood cytopenia including anemia. We have investigated the implication of the extrinsic pathway of apoptosis in MDS-ineffective erythropoiesis by in vitro expansion of erythroid precursors from early stage (low and intermediate-1 International Prognosis Scoring System [IPSS]) MDS, advanced stage (intermediate-2 IPSS) MDS, and control bone marrow samples. We have previously shown that Fas and its ligand were overexpressed in early stage MDS erythroid cells. Here, we show that caspase-8 activity is significantly increased, whereas the expression of death receptors other than Fas, including the type 1 receptor for tumor necrosis factor α (TNF-α) and the receptors for the TNF-related apoptosis-inducing ligand (TRAIL), DR4 and DR5, was normal. We also observed that the adapter Fas-associated death domain (FADD) was overexpressed in early stage MDS erythroid cells. Transduction of early stage MDS-derived CD34+ progenitors with a FADD-encoding construct increased apoptosis of erythroid cells and dramatically reduced erythroid burst-forming unit (BFU-E) growth. Transduction of a dominant-negative (dn) mutant of FADD inhibited caspase-8 activity and cell death and rescued BFU-E growth without abrogating erythroid differentiation. These results extend the observation that Fas-dependent activation of caspase-8 accounts for apoptosis of early stage MDS erythroid cells and demonstrate for the first time that FADD is a valuable target to correct ineffective erythropoiesis in these syndromes.

Flow cytometric evaluation of circulating CD34 + cell counts and apoptotic rate in children with acquired aplastic anemia and myelodysplasia

OBJECTIVE

Identification of a rapid and noninvasive test for the follow-up of aplastic anemia (AA) patients during immunosuppressive therapy (IST) to evaluate its functional effect on hematopoietic progenitors (HPC) and for early detection of progression to myelodysplasia or relapse.

MATERIALS AND METHODS

Absolute count and apoptotic rate (AR) of peripheral blood (PB) CD34+ cells were evaluated by three-color flow cytometry for CD45, CD34, and annexin V in cord blood (CB), normal children, and adults, as well as in pediatric patients with AA at diagnosis and during IST, Fanconi anemia (FA), chronic immune cytopenia, and refractory anemia with excess blasts (RAEB).

RESULTS

In normal subjects, the AR of PB CD34+ cells showed a progressive increase (p < 0.05), while their counts decreased (p < 0.05) from birth to adulthood. In very severe AA (vSAA) and severe AA (SAA) at diagnosis, the AR was 91.6% +/- 2.8%, higher than controls (p < 0.05), and PB CD34+ cell count was 2.6 +/- 2.4/microL. In FA patients, the PB CD34+ AR was again significantly increased (54.2% +/- 13.7%) with an absolute count of 3.7 +/- 1.2/microL. Conversely, in RAEB the AR was 11.7% +/- 3.5% and the absolute count 85.1 +/- 48.2/microL (p < 0.05). Chronic immune cytopenias did not significantly differ from controls.

CONCLUSIONS

Flow cytometry evaluation of PB CD34+ AR and counts is a noninvasive and feasible first-step method for the differentiation of AA and myelodysplasia (MDS), and it might be useful for monitoring AA during IST to secure the early detection of relapse or transformation to MDS.

Increased AF1q gene expression in high-risk myelodysplastic syndrome

The AF1q gene is expressed in normal haematopoietic progenitors, but less so in differentiated blood cells. In 47 patients with myelodysplastic syndrome (MDS), AF1q copy numbers were 0-6.8 x 10(6)/microg RNA compared with 1.5-2.4 x 10(5)/microg RNA in normal marrow. AF1q levels correlated with international prognostic scoring system (IPSS) scores (P = 0.004) and the risk of post-transplant relapse (P = 0.05). Among IPSS high-risk patients, survival correlated inversely with AF1q levels (P = 0.04). Thus, AF1q levels correlate with high-risk MDS and may provide a marker for risk stratification.

Fanconi anemia type C-deficient hematopoietic cells are resistant to TRAIL (TNF-related apoptosis-inducing ligand)-induced cleavage of pro-caspase-8

OBJECTIVE

The pathophysiology of bone marrow failure in Fanconi anemia (FA) patients is thought to involve excessive apoptosis involving signaling triggered by fas ligation and tumor necrosis factor (TNF)-alpha, or interferon (IFN)-gamma exposure. We investigated whether a new member of the TNF family, TRAIL (TNF-related apoptosis-inducing ligand), would similarly trigger preferential apoptotic cell death in FA phenotype cells.

MATERIAL AND METHODS

Hematopoietic cells from FANCC(-/-) transgenic mice and human FA-C lymphoblasts (HSC536N) as well as their phenotypically corrected counterparts (FANCC(+/+), HSC536/FA-Cneo) were compared for their response to apoptosis induction by TRAIL and fas ligation in the presence or absence of IFN-gamma. Cells were also studied for the protein and gene expression of TRAIL-receptors, caspase-8 and its inhibitory protein, FLIP.

RESULTS

TRAIL exposure by itself or in combination with IFN-gamma did not lead to preferential apoptosis induction in human and murine FA-C phenotype hematopoietic cells. This resistance was unrelated to the expression of TRAIL receptors or FLIP isoforms, but correlated with absent cleavage of pro-caspase-8. Results were validated by those from gene expression profiling of relevant genes in the two lymphoblast cell lines.

CONCLUSION

TRAIL, in contrast to fas ligation, does not induce preferential apoptosis in FA-C phenotype cells despite shared downstream signaling described in non-FA models. These data provide further insight into the complexity of FA-C-regulated apoptotic signaling.

Matrix metalloproteinase inhibitor reduces apoptosis induction of bone marrow cells in MDS-RA

BACKGROUND AND OBJECTIVES

We examined the involvement of apoptosis with myelodysplastic syndrome (MDS) accompanied by peripheral cytopenias despite normo-hypercellular bone marrow.

MATERIALS AND METHODS

Bone marrow smears from 31 patients with MDS-refractory anemia (RA) and five normal controls were stained using the in situ end labeling (ISEL) method. Next, the inhibitory effects of a caspase-3 inhibitor, matrix metalloproteinase inhibitor (MMPI), anti-tumor necrosis factor (TNF)-alpha or anti-Fas antibody upon the apoptosis induction in overnight cultures of bone marrow cells from the patients were examined. Further, TNF-alpha, transforming growth factor (TGF)-beta and soluble Fas ligand (sFasL) concentrations in culture supernatants of the cells were assessed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The incidence of ISEL-positive cells among MDS patients was significantly higher than in normal controls (50.8 +/- 14.0% vs. 11.3 +/- 2.4%; P < 0.0001). A caspase-3 inhibitor reduced significantly the ISEL-positive rates (32.6 +/- 15.2% vs. 50.2 +/- 16.5%; P < 0.0001). Anti-TNF-alpha or anti-Fas antibody reduced the ISEL-positive rates significantly (28.2 +/- 6.0%, 29.2 +/- 5.8%, vs. 44.2 +/- 3.4%, P < 0.001, P = 0.001, respectively). KB-R7785 also significantly decreased the ISEL-positive rates (18.0 +/- 9.3% vs. 43.6 +/- 14.0%; P < 0.0001). The concentration of TNF-alpha was significantly reduced by KB-R7785 (P < 0.05), whereas that of TGF-beta was not. Concentration of sFasL was under detectable level in the present assay system. The derivatives of KB-R7785 that can be administrated orally showed inhibitory effect on apoptosis induction as well.

CONCLUSIONS

These findings suggest that MMPIs inhibits the apoptosis induction of MDS bone marrow cells via the inhibition of TNF-alpha and probably sFasL secretion, and that MMPIs can be used to control the abnormal induction of apoptosis in MDS.