Reduced Retinoic Acid-Sensitivities of Nuclear Receptor Corepressor Binding to PML- and PLZF-RARα Underlie Molecular Pathogenesis and Treatment of Acute Promyelocytic Leukemia

How retinoic acid and arsenic transformed acute promyelocytic leukemia therapy

Acute promyelocytic leukemia (APL) is associated with severe coagulopathy leading to rapid morbidity and mortality if left untreated. The definitive diagnosis of APL is made by identifying a balanced reciprocal translocation between chromosomes 15 and 17. This t(15;17) results in a fusion transcript of promyelocytic leukemia (PML) and retinoic acid receptor alpha (RARA) genes and the expression of a functional PML/RARA protein. Detection of a fused PML/RARA genomic DNA sequence using fluorescence in situ hybridization (FISH) or by detection of the PML/RARA fusion transcript via reverse transcriptase polymerase chain reaction (RT-PCR) has revolutionized the diagnosis and monitoring of APL. Once confirmed, APL is cured in over 90% of cases, making it the most curable subtype of acute leukemia today. Patients with low-risk APL are successfully treated using a chemotherapy-free combination of all-trans retinoic acid and arsenic trioxide (ATO). In this review, we explore the work that has gone into the modern-day diagnosis and highly successful treatment of this once devastating leukemia.

KDM5A suppresses PML-RARα target gene expression and APL differentiation through repressing H3K4me2

Epigenetic abnormalities are frequently involved in the initiation and progression of cancers, including acute myeloid leukemia (AML). A subtype of AML, acute promyelocytic leukemia (APL), is mainly driven by a specific oncogenic fusion event of promyelocytic leukemia-RA receptor fusion oncoprotein (PML-RARα). PML-RARα was reported as a transcription repressor through the interaction with nuclear receptor corepressor and histone deacetylase complexes leading to the mis-suppression of its target genes and differentiation blockage. Although previous studies were mainly focused on the connection of histone acetylation, it is still largely unknown whether alternative epigenetics mechanisms are involved in APL progression. KDM5A is a demethylase of histone H3 lysine 4 di- and tri-methylations (H3K4me2/3) and a transcription corepressor. Here, we found that the loss of KDM5A led to APL NB4 cell differentiation and retarded growth. Mechanistically, through epigenomics and transcriptomics analyses, KDM5A binding was detected in 1889 genes, with the majority of the binding events at promoter regions. KDM5A suppressed the expression of 621 genes, including 42 PML-RARα target genes, primarily by controlling the H3K4me2 in the promoters and 5' end intragenic regions. In addition, a recently reported pan-KDM5 inhibitor, CPI-455, on its own could phenocopy the differentiation effects as KDM5A loss in NB4 cells. CPI-455 treatment or KDM5A knockout could greatly sensitize NB4 cells to all-trans retinoic acid-induced differentiation. Our findings indicate that KDM5A contributed to the differentiation blockage in the APL cell line NB4, and inhibition of KDM5A could greatly potentiate NB4 differentiation.

Variant Acute Promyelocytic Leukemia Presenting Without Auer Rods Highlights the Need for Correlation with Cytogenetic Data in Leukemia Diagnosis

Variant acute promyelocytic leukemia (vAPL) is a rare leukemia characterized by rearrangement between RARα and a non-PML partner gene. This type of leukemia can be difficult to recognize by histomorphologic evaluation, particularly in patients with few or no Auer rods, and by flow cytometry, but it can be identified by distinct cytogenetic features. Herein, we report on a patient with vAPL with t(11;17)(q23;q21) who presented an initial diagnostic challenge. Detailed flow cytometry findings are presented for this rare entity. Our case study also presents novel treatment (chemotherapy in combination with venetoclax) chosen based on mechanistic data from preclinical studies.

Arsenic induced epigenetic changes and relevance to treatment of acute promyelocytic leukemia and beyond

Epigenetic alterations regulate gene expression without changes in the DNA sequence. It is well-demonstrated that aberrant epigenetic changes contribute to the leukemogenesis of acute promyelocytic leukemia (APL). Arsenic trioxide (ATO) is one of the most common drugs used in the frontline treatment of APL that act through targeting and destabilizing the PML/RARα oncofusion protein. ATO together with all-trans retinoic acid (ATRA) lead to durable remission of more than 90% non-high-risk APL patients, turning APL treatment into a paradigm of oncoprotein targeted cure. Although relapse and drug resistance in APL are yet to be resolved in the clinic, epigenetic machineries might hold the key to address this issue. Further, ATO also showed promising anticancer activities against a variety of malignancies, but its application is particularly restricted due to limited understanding of the mechanism. Thus, a thorough understanding of epigenetic mechanism behind anti-leukemic effects of ATO would benefit the development of ATO-based anticancer strategy. Role of ATRA on APL associated epigenetic alterations has been extensively studied and reviewed. Recently, accumulating evidence suggest that ATO also induces some epigenetic changes that might favor APL eradication. In this article, we comprehensively discuss arsenic induced epigenetic changes and its relevance in APL treatment and beyond, so as to provide novel insights into overcoming arsenic resistance in APL and promote application of this drug to other malignancies.

Expression of the PTEN/FOXO3a/PLZF signalling pathway in pancreatic cancer and its significance in tumourigenesis and progression

Pancreatic cancer (PC) is one of the most lethal gastrointestinal malignancies. The PTEN/AKT signalling pathway is closely related to the tumourigenesis and progression of PC. The downstream effectors, FOXO3a, PLZF and VEGF, are reported to be involved in angiogenesis, lymph node metastasis and poor survival in PC. By using tissue microarrays and immunohistochemistry, we found, that PTEN, FOXO3a and PLZF expression was significantly decreased in PC specimens compared with that in chronic pancreatitis (CP) specimens, while VEGF expression was significantly increased. Furthermore, the expression of PTEN was positively correlated with that of FOXO3a and PLZF but negatively correlated with that of VEGF. Our results suggest that the PTEN/FOXO3a/PLZF signalling pathway may negatively regulate VEGF expression in PC. Through clinical analysis of 69 PC patients, PTEN, FOXO3a and PLZF expression was found to be significantly decreased in specimens from PC patients with lymph node metastasis and poor prognosis, while VEGF expression was significantly increased. Taken together, these reaults suggest that the PTEN/FOXO3a/PLZF signalling pathway may be capable of inhibiting growth and metastasis in PC by regulating VEGF-mediated angiogenesis, which requires further in vivo and in vitro studies and can potentially be a therapeutic target for PC.

Acute myelogenous leukemia in adolescents and young adults

The incidence of acute myelogenous leukemia (AML) increases progressively with age. Favorable genetic mutations are most prevalent in children, and unfavorable profiles increase proportionately in adolescents and young adults (AYA) and into later adulthood. Survival rates of AYA have improved over recent decades to 50-60%, but their accrual to clinical trials remains poor. In contrast to AYA with acute lymphoblastic leukemia, the prognostic benefit for AYA with AML enrolled in pediatric compared with adult trials is minor and only seen when different protocols are used. The distinctive needs of AYA, including intensive psychological services, call for their treatment within specialized centers that offer complex supportive care.

Multi-omics profiling reveals a distinctive epigenome signature for high-risk acute promyelocytic leukemia

Epigenomic alterations have been associated with both pathogenesis and progression of cancer. Here, we analyzed the epigenome of two high-risk APL (hrAPL) patients and compared it to non-high-risk APL cases. Despite the lack of common genetic signatures, we found that human hrAPL blasts from patients with extremely poor prognosis display specific patterns of histone H3 acetylation, specifically hyperacetylation at a common set of enhancer regions. In addition, unique profiles of the repressive marks H3K27me3 and DNA methylation were exposed in high-risk APLs. Epigenetic comparison with low/intermediate-risk APLs and AMLs revealed hrAPL-specific patterns of histone acetylation and DNA methylation, suggesting these could be further developed into markers for clinical identification. The epigenetic drug MC2884, a newly generated general HAT/EZH2 inhibitor, induces apoptosis of high-risk APL blasts and reshapes their epigenomes by targeting both active and repressive marks. Together, our analysis uncovers distinctive epigenome signatures of hrAPL patients, and provides proof of concept for use of epigenome profiling coupled to epigenetic drugs to ‘personalize’ precision medicine.

The corepressor NCOR1 regulates the survival of single-positive thymocytes

Nuclear receptor corepressor 1 (NCOR1) is a transcriptional regulator bridging repressive chromatin modifying enzymes with transcription factors. NCOR1 regulates many biological processes, however its role in T cells is not known. Here we show that Cd4-Cre-mediated deletion of NCOR1 (NCOR1 cKO^Cd4) resulted in a reduction of peripheral T cell numbers due to a decrease in single-positive (SP) thymocytes. In contrast, double-positive (DP) thymocyte numbers were not affected in the absence of NCOR1. The reduction in SP cells was due to diminished survival of NCOR1-null postselection TCRβ^hiCD69⁺ and mature TCRβ^hiCD69^- thymocytes. NCOR1-null thymocytes expressed elevated levels of the pro-apoptotic factor BIM and showed a higher fraction of cleaved caspase 3-positive cells upon TCR stimulation ex vivo. However, staphylococcal enterotoxin B (SEB)-mediated deletion of Vβ8⁺ CD4SP thymocytes was normal, suggesting that negative selection is not altered in the absence of NCOR1. Finally, transgenic expression of the pro-survival protein BCL2 restored the population of CD69⁺ thymocytes in NCOR1 cKO^Cd4 mice to a similar percentage as observed in WT mice. Together, these data identify NCOR1 as a crucial regulator of the survival of SP thymocytes and revealed that NCOR1 is essential for the proper generation of the peripheral T cell pool.

Current first- and second-line treatment options in acute promyelocytic leukemia

Outcome of acute promyelocytic leukemia (APL) has remarkably improved during the last 30 years, especially after the identification of PML-RARA oncogene as a key in the pathogenesis of APL and all-trans retinoic acid as therapeutic agent. Arsenic trioxide has been recently demonstrated to be the most effective single antileukemic agent and it has also showed synergistic action when combined with all-trans retinoic acid, decreasing relapse rate especially in low/intermediate-risk settings. Therapeutic advances led to complete remission rates of more than 90%, modifying disease history. In relapse setting, arsenic trioxide-based regimens showed efficacy for the achievement of second molecular complete remission. The most challenging issue in APL management remains the significant early deaths rate, nowadays the principal reason for treatment failure.

Regulation of hematopoietic development by ZBTB transcription factors

Hematopoietic development is governed by the coordinated expression of lineage- and differentiation stage-specific genes. Transcription factors play major roles in this process and their perturbation may underlie hematologic and immunologic disorders. Nearly 1900 transcription factors are encoded in the human genome: of these, 49 BTB (for broad-complex, tram-track and bric à brac)-zinc finger transcription factors referred to as ZBTB or POK proteins have been identified. ZBTB proteins, including BCL6, PLZF, ThPOK and LRF, exhibit a broad spectrum of functions in normal and malignant hematopoiesis. This review summarizes developmental and molecular functions of ZBTB proteins relevant to hematology.

Acute Promyelocytic Leukemia: A Review and Discussion of Variant Translocations

The majority of patients with acute promyelocytic leukemia (APL) manifest the t(15;17)(q24.1;q21.2) translocation; however, a minor but significant proportion of patients with APL harbor complex, cryptic, or variant translocations, which typically involve RARA. With the exception of ZBTB16/RARA, these variants have similar morphologic and immunophenotypic features as classic APL. Study of the variant forms of APL not only gives insight into the pathogenesis of APL but also allows us to understand the mechanism of retinoid therapy. It is important to identify these cryptic and variant translocations because certain variants, including ZBTB16/RARA and STAT5B/RARA, are resistant to treatment with all-trans retinoic acid, arsenic trioxide, and anthracyclines.

Synergistic targeted therapy for acute promyelocytic leukaemia: a model of translational research in human cancer

Acute promyelocytic leukaemia (APL), the M3 subtype of acute myeloid leukaemia, was once a lethal disease, yet nowadays the majority of patients with APL can be successfully cured by molecularly targeted therapy. This dramatic improvement in the survival rate is an example of the advantage of modern medicine. APL is characterized by a balanced reciprocal chromosomal translocation fusing the promyelocytic leukaemia (PML) gene on chromosome 15 with the retinoic acid receptor α (RARα) gene on chromosome 17. It has been found that all-trans-retinoic acid (ATRA) or arsenic trioxide (ATO) alone exerts therapeutic effect on APL patients with the PML-RARα fusion gene, and the combination of both drugs can act synergistically to further enhance the cure rate of the patients. Here, we provide an insight into the pathogenesis of APL and the mechanisms underlying the respective roles of ATRA and ATO. In addition, treatments that lead to more effective differentiation and apoptosis of APL cells, including leukaemia-initiating cells, and more thorough eradication of the disease will be discussed. Moreover, as a model of translational research, the development of a cure for APL has followed a bidirectional approach of 'bench to bedside' and 'bedside to bench', which can serve as a valuable example for the diagnosis and treatment of other malignancies.

Post transcriptional control of the epigenetic stem cell regulator PLZF by sirtuin and HDAC deacetylases

BACKGROUND

The transcriptional repressor promyelocytic leukemia zinc finger protein (PLZF) is critical for the regulation of normal stem cells maintenance by establishing specific epigenetic landscape. We have previously shown that CBP/p300 acetyltransferase induces PLZF acetylation in order to increase its deoxynucleotidic acid (DNA) binding activity and to enhance its epigenetic function (repression of PLZF target genes). However, how PLZF is inactivated is not yet understood.

RESULTS

In this study, we demonstrate that PLZF is deacetylated by both histone deacetylase 3 and the NAD+ dependent deacetylase silent mating type information regulation 2 homolog 1 (SIRT1). Unlike other PLZF-interacting deacetylases, these two proteins interact with the zinc finger domain of PLZF, where the activating CBP/p300 acetylation site was previously described, inducing deacetylation of lysines 647/650/653. Overexpression of histone deacetylase 3 (HDAC3) and SIRT1 is associated with loss of PLZF DNA binding activity and decreases PLZF transcriptional repression. As a result, the chromatin status of the promoters of PLZF target genes, involved in oncogenesis, shift from a heterochromatin to an open euchromatin environment leading to gene expression even in the presence of PLZF.

CONCLUSIONS

Consequently, SIRT1 and HDAC3 mediated-PLZF deacetylation provides for rapid control and fine-tuning of PLZF activity through post-transcriptional modification to regulate gene expression and cellular homeostasis.

Role of Retinoic Acid-Metabolizing Cytochrome P450s, CYP26, in Inflammation and Cancer

Vitamin A (retinol) and its active metabolite, all-trans-retinoic acid (atRA), play critical roles in regulating the differentiation, growth, and migration of immune cells. Similarly, as critical signaling molecules in the regulation of the cell cycle, retinoids are important in cancers. Concentrations of atRA are tightly regulated in tissues, predominantly by the availability of retinol, synthesis of atRA by ALDH1A enzymes and metabolism and clearance of atRA by CYP26 enzymes. The ALDH1A and CYP26 enzymes are expressed in several cell types in the immune system and in cancer cells. In the immune system, the ALDH1A and CYP26 enzymes appear to modulate RA concentrations. Consequently, alterations in the activity of ALDH1A and CYP26 enzymes are expected to change disease outcomes in inflammation. There is increasing evidence from various disease models of intestinal and skin inflammation that treatment with atRA has a positive effect on disease markers. However, whether aberrant atRA concentrations or atRA synthesis and metabolism play a role in inflammatory disease development and progression is not well understood. In cancers, especially in acute promyelocytic leukemia and neuroblastoma, increasing intracellular concentrations of atRA appears to provide clinical benefit. Inhibition of the CYP26 enzymes to increase atRA concentrations and combat therapy resistance has been pursued as a drug target in these cancers. This chapter covers the current knowledge of how atRA and retinol regulate the immune system and inflammation, how retinol and atRA metabolism is altered in inflammation and cancer, and what roles atRA-metabolizing enzymes have in immune responses and cancers.

Belinostat, a potent HDACi, exerts antileukaemic effect in human acute promyelocytic leukaemia cells via chromatin remodelling

Epigenetic changes play a significant role in leukaemia pathogenesis, therefore histone deacetylases (HDACis) are widely accepted as an attractive strategy for acute promyelocytic leukaemia (APL) treatment. Belinostat (Bel, PXD101), a hydroxamate-type HDACi, has proved to be a promising cure in clinical trials for solid tumours and haematological malignancies. However, insight into molecular effects of Bel on APL, is still lacking. In this study, we investigated the effect of Bel alone and in combination with differentiation inducer retinoic acid (RA) on human promyelocytic leukaemia NB4 and HL-60 cells. We found that treatment with Bel, depending on the dosage used, inhibits cell proliferation, whereas in combination with RA enhances and accelerates granulocytic leukaemia cell differentiation. We also evaluated the effect of used treatments with Bel and RA on certain epigenetic modifiers (HDAC1, HDAC2, PCAF) as well as cell cycle regulators (p27) gene expression and protein level modulation. We showed that Bel in combination with RA up-regulates basal histone H4 hyperacetylation level more strongly compared to Bel or RA alone. Furthermore, chromatin immunoprecipitation assay indicated that Bel induces the accumulation of hyperacetylated histone H4 at the p27 promoter region. Mass spectrometry analysis revealed that in control NB4 cells, hyperacetylated histone H4 is mainly found in association with proteins involved in DNA replication and transcription, whereas after Bel treatment it is found with proteins implicated in pro-apoptotic processes, in defence against oxidative stress and tumour suppression. Summarizing, our study provides some novel insights into the molecular mechanisms of HDACi Bel action on APL cells.

The Potential of Vitamin D-Regulated Intracellular Signaling Pathways as Targets for Myeloid Leukemia Therapy

The current standard regimens for the treatment of acute myeloid leukemia (AML) are curative in less than half of patients; therefore, there is a great need for innovative new approaches to this problem. One approach is to target new treatments to the pathways that are instrumental to cell growth and survival with drugs that are less harmful to normal cells than to neoplastic cells. In this review, we focus on the MAPK family of signaling pathways and those that are known to, or potentially can, interact with MAPKs, such as PI3K/AKT/FOXO and JAK/STAT. We exemplify the recent studies in this field with specific relevance to vitamin D and its derivatives, since they have featured prominently in recent scientific literature as having anti-cancer properties. Since microRNAs also are known to be regulated by activated vitamin D, this is also briefly discussed here, as are the implications of the emerging acquisition of transcriptosome data and potentiation of the biological effects of vitamin D by other compounds. While there are ongoing clinical trials of various compounds that affect signaling pathways, more studies are needed to establish the clinical utility of vitamin D in the treatment of cancer.

Retinoic acid signaling in cancer: The parable of acute promyelocytic leukemia

Inevitably fatal some 40 years, acute promyelocytic leukemia (APL) can now be cured in more than 95% of cases. This clinical success story is tightly linked to tremendous progress in our understanding of retinoic acid (RA) signaling. The discovery of retinoic acid receptor alpha (RARA) was followed by the cloning of the chromosomal translocations driving APL, all of which involve RARA. Since then, new findings on the biology of nuclear receptors have progressively enlightened the basis for the clinical efficacy of RA in APL. Reciprocally, the disease offered a range of angles to approach the cellular and molecular mechanisms of RA action. This virtuous circle contributed to make APL one of the best-understood cancers from both clinical and biological standpoints. Yet, some important questions remain unanswered including how lessons learnt from RA-triggered APL cure can help design new therapies for other malignancies.

Overview of therapy and strategies for optimizing outcomes in de novo pediatric acute myeloid leukemia

Although acute myelogenous leukemia (AML) accounts for <20 % of leukemia in children, it is responsible for over half of all pediatric leukemia deaths. Improvement in event-free survival rates, now over 50 %, are due largely to intensification of chemotherapy, aggressive supportive care, development of risk stratification based on cytogenetic and molecular markers, and improved salvage regimens. Despite this improvement over the past few decades, the survival rates have recently plateaued, and further improvement will need to take into account advances in molecular characterization of AML, development of novel agents, and better understanding of host factors influencing toxicity and response to chemotherapy. This article reviews the epidemiology and biology trends in diagnosis and treatment of pediatric acute myelogenous leukemia.

Interaction with RXR is necessary for NPM-RAR-induced myeloid differentiation blockade

The t(5;17)(q35;q21) APL variant results in expression of a fusion protein linking the N-terminus of nucleophosmin (NPM) to the C-terminus of the retinoic acid receptor alpha (RAR). We have previously shown that NPM-RAR is capable of binding to DNA either as a homodimer or heterodimer with RXR. To determine the biological significance of NPM-RAR/RXR interaction, we developed two mutants of NPM-RAR that showed markedly diminished ability to bind RXR. U937 subclones expressing the NPM-RAR mutants showed significantly less inhibition of vitamin D3/TGFbeta-induced differentiation, compared with NPM-RAR. These results support the hypothesis that RXR interaction is necessary for NPM-RAR-mediated myeloid maturation arrest.

RARα-PLZF oncogene inhibits C/EBPα function in myeloid cells

In acute promyelocytic leukemia, granulocytic differentiation is arrested at the promyelocyte stage. The variant t(11;17) translocation produces two fusion proteins, promyelocytic leukemia zinc finger-retinoic acid receptor α (PLZF-RARα) and RARα-PLZF, both of which participate in leukemia development. Here we provide evidence that the activity of CCAAT/enhancer binding protein α (C/EBPα), a master regulator of granulocytic differentiation, is severely impaired in leukemic promyelocytes with the t(11;17) translocation compared with those associated with the t(15;17) translocation. We show that RARα-PLZF inhibits myeloid cell differentiation through interactions with C/EBPα tethered to DNA, using ChIP and DNA capture assays. Furthermore, RARα-PLZF recruits HDAC1 and causes histone H3 deacetylation at C/EBPα target loci, thereby decreasing the expression of C/EBPα target genes. In line with these results, HDAC inhibitors restore in part C/EBPα target gene expression. These findings provide molecular evidence for a mechanism through which RARα-PLZF acts as a modifier oncogene that subverts differentiation in the granulocytic lineage by associating with C/EBPα and inhibiting its activity.

The epigenetic regulator PLZF represses L1 retrotransposition in germ and progenitor cells

Germ cells and adult stem cells maintain tissue homeostasis through a finely tuned program of responses to both physiological and stress-related signals. PLZF (Promyelocytic Leukemia Zinc Finger protein), a member of the POK family of transcription factors, acts as an epigenetic regulator of stem cell maintenance in germ cells and haematopoietic stem cells. We identified L1 retrotransposons as the primary targets of PLZF. PLZF-mediated DNA methylation induces silencing of the full-length L1 gene and inhibits L1 retrotransposition. Furthermore, PLZF causes the formation of barrier-type boundaries by acting on inserted truncated L1 sequences in protein coding genes. Cell stress releases PLZF-mediated repression, resulting in L1 activation/retrotransposition and impaired spermatogenesis and myelopoiesis. These results reveal a novel mechanism of action by which, PLZF represses retrotransposons, safeguarding normal progenitor homeostasis.

8-CPT-cAMP/all-trans retinoic acid targets t(11;17) acute promyelocytic leukemia through enhanced cell differentiation and PLZF/RARα degradation

The refractoriness of acute promyelocytic leukemia (APL) with t(11;17)(q23;q21) to all-trans retinoic acid (ATRA)-based therapy concerns clinicians and intrigues basic researchers. By using a murine leukemic model carrying both promyelocytic leukemia zinc finger/retinoic acid receptor-α (PLZF/RARα) and RARα/PLZF fusion genes, we discovered that 8-chlorophenylthio adenosine-3', 5'-cyclic monophosphate (8-CPT-cAMP) enhances cellular differentiation and improves gene trans-activation by ATRA in leukemic blasts. Mechanistically, in combination with ATRA, 8-CPT-cAMP activates PKA, causing phosphorylation of PLZF/RARα at Ser765 and resulting in increased dissociation of the silencing mediator for retinoic acid and thyroid hormone receptors/nuclear receptor corepressor from PLZF/RARα. This process results in changes of local chromatin and transcriptional reactivation of the retinoic acid pathway in leukemic cells. Meanwhile, 8-CPT-cAMP also potentiated ATRA-induced degradation of PLZF/RARα through its Ser765 phosphorylation. In vivo treatment of the t(11;17) APL mouse model demonstrated that 8-CPT-cAMP could significantly improve the therapeutic effect of ATRA by targeting a leukemia-initiating cell activity. This combined therapy, which induces enhanced differentiation and oncoprotein degradation, may benefit t(11;17) APL patients.

Nuclear hormone receptors enable macrophages and dendritic cells to sense their lipid environment and shape their immune response

A key issue in the immune system is to generate specific cell types, often with opposing activities. The mechanisms of differentiation and subtype specification of immune cells such as macrophages and dendritic cells are critical to understand the regulatory principles and logic of the immune system. In addition to cytokines and pathogens, it is increasingly appreciated that lipid signaling also has a key role in differentiation and subtype specification. In this review we explore how intracellular lipid signaling via a set of transcription factors regulates cellular differentiation, subtype specification, and immune as well as metabolic homeostasis. We introduce macrophages and dendritic cells and then we focus on a group of transcription factors, nuclear receptors, which regulate gene expression upon receiving lipid signals. The receptors we cover are the ones with a recognized physiological function in these cell types and ones which heterodimerize with the retinoid X receptor. These are as follows: the receptor for a metabolite of vitamin A, retinoic acid: retinoic acid receptor (RAR), the vitamin D receptor (VDR), the fatty acid receptor: peroxisome proliferator-activated receptor γ (PPARγ), the oxysterol receptor liver X receptor (LXR), and their obligate heterodimeric partner, the retinoid X receptor (RXR). We discuss how they can get activated and how ligand is generated and eliminated in these cell types. We also explore how activation of a particular target gene contributes to biological functions and how the regulation of individual target genes adds up to the coordination of gene networks. It appears that RXR heterodimeric nuclear receptors provide these cells with a coordinated and interrelated network of transcriptional regulators for interpreting the lipid milieu and the metabolic changes to bring about gene expression changes leading to subtype and functional specification. We also show that these networks are implicated in various immune diseases and are amenable to therapeutic exploitation.

An emerging role for retinoid X receptor α in malignant hematopoiesis

The retinoid X receptor alpha is the obligatory heterodimerization partner for a range of nuclear hormone receptors, and is required for signaling through the pathways mediated by those receptors. While RXR alpha has critical roles in embryonic development, it appears to be dispensable in adult hematopoiesis. Strikingly, recent evidence has indicated that proper functioning of RXR alpha is necessary for the pathogenesis of acute promyelocytic leukemia (APL), suggesting a novel avenue that can be exploited in the management and treatment of this disease. In this review we highlight recent studies that clarify the role of RXR alpha in normal and malignant hematopoiesis.

Curing all patients with acute promyelocytic leukemia: are we there yet?

The introduction of all-trans retinoic acid to anthracycline-based chemotherapy has revolutionized the prognosis of patients with acute promyelocytic leukemia (APL). The introduction of arsenic trioxide enabled the therapeutic approach of rationally targeted frontline protocols with minimal or no traditional cytotoxic chemotherapy and without compromise of previously established outstanding outcomes with anthracycline-based regimens. Although most of the current investigative efforts in APL are focused on developing potentially curative therapy without the exposure to toxicities and risks of DNA-disrupting agents, the cure rate can further be increased by implementing meticulous supportive care strategies that counter early coagulopathy-related deaths.

Aberrant corepressor interactions implicated in PML-RAR(alpha) and PLZF-RAR(alpha) leukemogenesis reflect an altered recruitment and release of specific NCoR and SMRT splice variants

Human acute promyelocytic leukemia is causally linked to chromosomal translocations that generate chimeric retinoic acid receptor-α proteins (x-RARα fusions). Wild-type RARα is a transcription factor that binds to the SMRT/NCoR family of corepressors in the absence of hormone but releases from corepressor and binds coactivators in response to retinoic acid. In contrast, the x-RARα fusions are impaired for corepressor release and operate in acute promyelocytic leukemia as dominant-negative inhibitors of wild-type RARα. We report that the two most common x-RARα fusions, PML-RARα and PLZF-RARα, have gained the ability to recognize specific splice variants of SMRT and NCoR that are poorly recognized by RARα. These differences in corepressor specificity between the normal and oncogenic receptors are further magnified in the presence of a retinoid X receptor heteromeric partner. The ability of retinoids to fully release corepressor from PML-RARα differs for the different splice variants, a phenomenon relevant to the requirement for supraphysiological levels of this hormone in differentiation therapy of leukemic cells. We propose that this shift in the specificity of the x-RARα fusions to a novel repertoire of corepressors contributes to the dominant-negative and oncogenic properties of these oncoproteins and helps explain previously paradoxical aspects of their behavior.

Gain of MYC underlies recurrent trisomy of the MYC chromosome in acute promyelocytic leukemia

The leukemogenic effects of Myc drive recurrent trisomy in a mouse model of acute myeloid leukemia.

Gain of chromosome 8 is the most common chromosomal gain in human acute myeloid leukemia (AML). It has been hypothesized that gain of the MYC protooncogene is of central importance in trisomy 8, but the experimental data to support this are limited and controversial. In a mouse model of promyelocytic leukemia in which the MRP8 promoter drives expression of the PML-RARA fusion gene in myeloid cells, a Myc allele is gained in approximately two-thirds of cases as a result of trisomy for mouse chromosome 15. We used this model to test the idea that MYC underlies acquisition of trisomy in AML. We used a retroviral vector to drive expression of wild-type, hypermorphic, or hypomorphic MYC in bone marrow that expressed the PML-RARA transgene. MYC retroviruses cooperated in myeloid leukemogenesis and suppressed gain of chromosome 15. When the PML-RARA transgene was expressed in a Myc haploinsufficient background, we observed selection for increased copies of the wild-type Myc allele concomitant with leukemic transformation. In addition, we found that human myeloid leukemias with trisomy 8 have increased MYC. These data show that gain of MYC can contribute to the pathogenic effect of the most common trisomy of human AML.

Utilization of molecular phenotypes to detect relapse and optimize the management of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by a unique genetic aberration, the t(15;17) chromosome translocation. Translocation breakpoints are located within the promyelocytic leukemia (PML) locus on chromosome 15 and the retinoic acid receptor alpha (RARA) locus on chromosome 17. In the past 2 decades, critical advances have been made in understanding the molecular pathogenesis of APL. APL represents a paradigm for molecularly targeted therapy in cancer and an extraordinary model for translational research in medicine. In fact, the release of differentiation block upon treatment of APL with all-trans-retinoic acid (ATRA) has represented the first example of targeted therapy in human cancer. More recently, the advent of arsenic trioxide (ATO) has allowed further progress in the management of this disease through improved outcomes in patients receiving this agent in combination with ATRA. Finally, optimization of therapy and minimization of toxicity is feasible in this disease through careful monitoring of residual disease using polymerase chain reaction-based approaches targeting the PML-RARA fusion gene.

Inhibition of angiogenesis by the BTB domain of promyelocytic leukemia zinc finger protein

Promyelocytic leukemia zinc finger is a negative regulator of cell cycle progression. In this study, we showed that PLZF inhibits endothelial cell angiogenesis using a human umbilical vein endothelial cell system. We also focused on characterizing the specific function of the BTB domain of PLZF as a novel apoptotic and anti-angiogenic protein via deletion mapping analysis. The BTB domain directly inhibited tube formation, as well as the biological functions of angiostatic activity in vivo, and reduced the expression of p-Akt and p-eNOS, which play a significant role in angiogenesis when stimulated by VEGF. These results strongly suggest that the BTB domain could potentially modulate the apoptotic and anti-angiogenic effects of PLZF.

Nuclear receptor repression: regulatory mechanisms and physiological implications

The ability to associate with corepressors and to inhibit transcription is an intrinsic property of most members of the nuclear receptor (NR) superfamily. NRs induce transcriptional repression by recruiting multiprotein corepressor complexes. Nuclear receptor corepressor (NCoR) and silencing mediator of retinoic and thyroid receptors (SMRT) are the most well characterized corepressor complexes and mediate repression for virtually all NRs. In turn, corepressor complexes repress transcription because they either contain or associate with chromatin modifying enzymes. These include histone deacetylases, histone H3K4 demethylases, histone H3K9 or H3K27 methyltransferases, and ATP-dependent chromatin remodeling factors. Two types of NR-interacting corepressors exist. Ligand-independent corepressors, like NCoR/SMRT, bind to unliganded or antagonist-bound NRs, whereas ligand-dependent corepressors (LCoRs) associate with NRs in the presence of agonist. Therefore, LCoRs may serve to attenuate NR-mediated transcriptional activation. Somewhat unexpectedly, classical coactivators may also function as "corepressors" to mediate repression by agonist-bound NRs. In this chapter, we will discuss the various modes and mechanisms of repression by NRs as well as discuss the known physiological functions of NR-mediated repression.

Differentiation therapy of acute myeloid leukemia: past, present and future

PURPOSE OF REVIEW

Since the 1970s, the concept of differentiation therapy has been viewed as a promising and revolutionary approach for the treatment of acute myeloid leukemia (AML) and other cancers. However, the successful clinical application of differentiation therapy has only been realized since the late 1980s and only in one subtype of AML, acute promyelocytic leukemia (APL). The use of all-trans-retinoic acid (ATRA) and arsenic trioxide, both of which induce degradation of the progressive multifocal leukoencephalopathy/retinoic acid receptor alpha oncoprotein, in combination with chemotherapy is currently the accepted treatment of APL, presenting a potential paradigm for differentiation therapy in clinical oncology.

RECENT FINDINGS

We have begun to understand why ATRA fails to induce differentiation in AML. The underlying reasons identified thus far are associated with an inability to target the removal of leukemogenic fusion proteins, aberrant epigenetic regulation of genes involved in the ATRA signaling pathway and the presence of factors that interfere with proper retinoic acid receptor alpha function.

SUMMARY

Here, we examine the reasons why the exquisite sensitivity of APL to ATRA-based differentiation therapy has not been extended to other of AML subtypes. Current differentiation-based combinatorial approaches to target AML will also be analyzed. Finally, we will evaluate the potential of novel strategies, high-throughput screening, and functional genomics to uncover new differentiation-based therapies for AML.

Hematopoiesis and Retinoids: Development and Disease

Retinoids function as activating ligands for a class of nuclear receptors that control gene expression programs for a wide range of tissues and organs during embryogenesis and throughout life. Over the years, three sets of observations have spurred interest in the function of retinoids with respect to development and disease of hematopoietic cells. Since the 1920s, epidemiological studies indicated altered hematopoiesis in vitamin A-deficient (VAD) human populations. More recently, the ability of retinoids to affect various aspects of hematopoietic development has been demonstrated in vitro. Finally, it was discovered that the gene encoding a retinoid receptor is a key target for chromosomal translocations that cause acute promyelocytic leukemia (APL). More recent investigations using targeted gene disruptions, VAD animal models, and mouse models of leukemia have continued to shed light on the function of the retinoid pathway in blood cells. It is now clear that retinoids are required for normal hematopoiesis during both yolk sac and fetal liver stages of hematopoiesis, while the pathway has at least modulatory functions for bone marrow derived progenitors. Studies of normal development and APL have provided complementary insight into the molecular control of blood cell differentiation. Here we review the evidence for retinoid requirements in hematopoiesis and also summarize current ideas regarding how this pathway is subverted in leukemia.

A label-free quantitative proteomics strategy to identify E3 ubiquitin ligase substrates targeted to proteasome degradation

The ubiquitin-proteasome system is a central mechanism for controlled proteolysis that regulates numerous cellular processes in eukaryotes. As such, defects in this system can contribute to disease pathogenesis. In this pathway, E3 ubiquitin ligases provide platforms for binding specific substrates, thereby coordinating their ubiquitylation and subsequent degradation by the proteasome. Despite the identification of many E3 ubiquitin ligases, the identities of their specific substrates are still largely unresolved. The ankyrin repeat-containing protein with a suppressor of cytokine signaling box 2 (ASB2) gene that we initially identified as a retinoic acid-response gene in acute promyelocytic leukemia cells encodes the specificity subunit of an E3 ubiquitin ligase complex that is involved in hematopoietic cell differentiation. We have recently identified filamin A and filamin B as the first ASB2 targets and shown that ASB2 triggers ubiquitylation and proteasome-mediated degradation of these proteins. Here a global quantitative proteomics strategy is provided to identify substrates of E3 ubiquitin ligases targeted to proteasomal degradation. Indeed we used label-free methods for quantifying proteins identified by shotgun proteomics in extracts of cells expressing wild-type ASB2 or an E3 ubiquitin ligase-defective mutant of ASB2 under the control of an inducible promoter. Measurements of spectral count and mass spectrometric signal intensity demonstrated a drastic decrease of filamin A and filamin B in myeloid leukemia cells expressing wild-type ASB2 compared with cells expressing an E3 ubiquitin ligase-defective mutant of ASB2. Altogether we provide an original strategy that enables identification of E3 ubiquitin ligase substrates that have to be degraded.

Curing APL: differentiation or destruction?

In a recent issue of Nature Medicine, Nasr et al. show that the effectiveness of all-trans retinoic acid and arsenic trioxide in acute promyelocytic leukemia is independent of their ability to cause differentiation. Targeted destruction of the PML-RARalpha oncoprotein appears key to eliminating the cells from which relapse can arise.

Acute promyelocytic leukemia: a paradigm for differentiation therapy

Acute promyelocytic leukemia(APL) is characterized by the t(15;17) chromosomal translocation leading to the formation of the PML-RARalpha oncoprotein. This leukemia has attracted considerable interest in recent years, being the first in which therapies that specifically target the underlying molecular lesion, i.e., all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), leading to induction of differentiation and apoptosis have been successfully used in clinical practice. The advent of ATRA therapy has transformed APL from being a disease with a poor outlook to one of the most prognostically favorable subsets of acute myeloid leukemia. Further improvements in outcome may be achieved with the use of ATO, which achieves high rates of remission in the relatively small proportion of patients now relapsing following standard first-line therapy with ATRA and anthracycline-based chemotherapy. Moreover, recent studies have suggested that ATO and ATRA, or even ATO alone, used as front-line treatment of PML-RARA- associated APL can induce long-term remissions. This raises the possibility that some patients can be cured using differentiation therapies alone, without the need for chemotherapy, thereby potentially reducing treatment-related toxicity. It is clear that the success of such an approach is critically dependent upon molecular diagnostics and monitoring for minimal residual disease (MRD) to distinguish those patients who can potentially be cured with differentiation therapy from those requiring additional myelosuppressive agents. This represents an exciting new phase in the treatment of acute leukemia, highlighting the potential of molecularly targeted and MRD-directed therapies to achieve an individualized approach to patient management.

Molecular basis of the anti-cancer effects of histone deacetylase inhibitors

Histone deacetylase inhibitors comprise a variety of natural and synthetic compounds, which have in common that they inhibit enzymes that mediate the removal of acetyl groups from a range of proteins, including nucleosomal histones. Histone deacetylase inhibitors have anti-cancer activities in vitro and in vivo and are used in the clinic for the treatment of advanced cutaneous T cell lymphoma. The molecular pathways targeted by these compounds are discussed with an emphasis on the effects of these compounds on retinoic acid signaling.

Retinoblastoma protein and the leukemia-associated PLZF transcription factor interact to repress target gene promoters

Translocations of the retinoic acid receptor-alpha (RARalpha) locus with the promyelocytic leukemia zinc-finger (PLZF) or PML genes lead to expression of oncogenic PLZF-RARalpha or PML-RARalpha fusion proteins, respectively. These fusion oncoproteins constitutively repress RARalpha target genes, in large part through aberrant recruitment of multiprotein co-repressor complexes. PML and PML-RARalpha have previously been shown to associate with the retinoblastoma (Rb) tumour suppressor protein in its hypophosphorylated state. Here, we demonstrate that PLZF also interacts with Rb in vitro and in vivo. The interaction between PLZF and Rb is mediated through the Rb pocket and the region of PLZF that lies between its transcriptional repression (poxvirus and zinc-finger, POZ) and DNA-binding (zinc-finger) domains. In addition, Rb can simultaneously interact with PLZF and the E2F1 S phase-inducing transcription factor, suggesting that these proteins can exist in the same multiprotein complex. In contrast to the interaction of Rb with PML or E2F1, the PLZF-Rb interaction is not dependent on hypophosphorylation of Rb. These data are supported by chromatin immunoprecipitation analysis, which indicates that PLZF associates with the promoter region of CDC6, a known E2F/Rb target gene. Co-expression of PLZF and Rb results in enhancement of transcriptional repression of PLZF and E2F/Rb target genes, indicating functional co-operation between the two proteins. Both PLZF and Rb have been shown to function in stem cells and taken together these data suggest that interactions between PLZF and Rb could be important in stem cell biology.

Auranofin promotes retinoic acid- or dihydroxyvitamin D3-mediated cell differentiation of promyelocytic leukaemia cells by increasing histone acetylation

BACKGROUND AND PURPOSE

To investigate the molecular mechanism for the effect of auranofin on the induction of cell differentiation, the cellular events associated with differentiation were analysed in acute promyelocytic leukaemia (APL) cells.

EXPERIMENTAL APPROACH

The APL blasts from leukaemia patients and NB4 cells were cotreated with auroanofin and all-trans-retinoic acid (ATRA) at suboptimal concentration. The HL-60 cells were treated with auroanofin and a subeffective dose of 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2 vit D3) in combination. The effect of auroanofin was investigated on histone acetylation at the promoter of differentiation-associated genes and expression of cell cycle regulators.

KEY RESULTS

Treatment with auroanofin and ATRA cooperatively induced granulocytic differentiation of fresh APL blasts isolated from patients and NB4 cells. The combined treatment also increased reorganization of nuclear PML bodies and histone acetylation at the promoter of the RARbeta2 gene. Auroanofin also promoted monocytic differentiation of the HL-60 cells triggered by subeffective concentration of 1,25(OH)2 vit D3. The combined treatment of auroanofin and 1,25(OH)2 vit D3 stimulated histone acetylation at p21 promoters and increased the accumulation of cells in the G0/G1 phase. Consistent with this, the expressions of p21, p27 and PTEN were increased and the levels of cyclin A, Cdk2 and Cdk4 were decreased. Furthermore, the hypophosphorylated form of pRb was markedly increased in cotreated cells.

CONCLUSIONS AND IMPLICATIONS

These findings indicate that auroanofin in combination with low doses of either ATRA or 1,25(OH)2 vit D3 promotes APL cell differentiation by enhancing histone acetylation and the expression of differentiation-associated genes.

Regulation of epithelial sodium transport by promyelocytic leukemia zinc finger protein

Aldosterone is the principal regulator of Na homeostasis, and thereby blood pressure. One of the main targets of aldosterone is the epithelial Na channel (ENaC) located in the apical membrane of target cells. Previous studies identified several genes involved in the regulation of ENaC such as SGK1; however, SGK1 knockout mice have only a mild salt-losing phenotype, indicating that further genes must be involved in the action of aldosterone. In our search for further aldosterone-regulated genes, we discovered that aldosterone, at physiological concentrations, induces the expression of the promyelocytic leukemia zinc finger protein (PLZF) in renal cortical collecting duct (CCD) cell lines that stably express mineralocorticoid receptors (MRs). This effect is rapid and does not require de novo protein synthesis, suggesting a direct action. Surprisingly, stable overexpression of human or mouse PLZF isoforms significantly decreased transepithelial Na transport in CCD cells while having no effect on the integrity of the monolayers. In parallel with the decline in Na transport, PLZF suppressed the mRNA levels of beta- and gamma-ENaC subunits. These observations suggest that PLZF is a negative regulator of ENaC in renal epithelial cells and might be part of a negative feedback loop that limits aldosterone's stimulatory effects on sodium reabsorption.

EWS/FLI mediates transcriptional repression via NKX2.2 during oncogenic transformation in Ewing's sarcoma

EWS/FLI is a master regulator of Ewing's sarcoma formation. Gene expression studies in A673 Ewing's sarcoma cells have demonstrated that EWS/FLI downregulates more genes than it upregulates, suggesting that EWS/FLI, and/or its targets, function as transcriptional repressors. One critical EWS/FLI target, NKX2.2, is a transcription factor that contains both transcriptional activation and transcriptional repression domains, raising the possibility that it mediates portions of the EWS/FLI transcriptional signature. We now report that microarray analysis demonstrated that the transcriptional profile of NKX2.2 consists solely of downregulated genes, and overlaps with the EWS/FLI downregulated signature, suggesting that NKX2.2 mediates oncogenic transformation via transcriptional repression. Structure-function analysis revealed that the DNA binding and repressor domains in NKX2.2 are required for oncogenesis in Ewing's sarcoma cells, while the transcriptional activation domain is completely dispensable. Furthermore, blockade of TLE or HDAC function, two protein families thought to mediate the repressive function of NKX2.2, inhibited the transformed phenotype and reversed the NKX2.2 transcriptional profile in Ewing's sarcoma cells. Whole genome localization studies (ChIP-chip) revealed that a significant portion of the NKX2.2-repressed gene expression signature was directly mediated by NKX2.2 binding. These data demonstrate that the transcriptional repressive function of NKX2.2 is necessary, and sufficient, for the oncogenic phenotype of Ewing's sarcoma, and suggest a therapeutic approach to this disease.

Liver-specific deletion of histone deacetylase 3 disrupts metabolic transcriptional networks

Histone deacetylase 3 (Hdac3) is an enzymatic component of transcriptional repression complexes recruited by the nuclear hormone receptors. Inactivation of Hdac3 in cancer cell lines triggered apoptosis, and removal of Hdac3 in the germ line of mice caused embryonic lethality. Therefore, we deleted Hdac3 in the postnatal mouse liver. These mice developed hepatomegaly, which was the result of hepatocyte hypertrophy, and these morphological changes coincided with significant imbalances between carbohydrate and lipid metabolism. Loss of Hdac3 triggered changes in gene expression consistent with inactivation of repression mediated by nuclear hormone receptors. Loss of Hdac3 also increased the levels of Ppar gamma2, and treatment of these mice with a Ppar gamma antagonist partially reversed the lipid accumulation in the liver. In addition, gene expression analysis identified mammalian target of rapamycin signalling as being activated after deletion of Hdac3, and inhibition by rapamycin affected the accumulation of neutral lipids in Hdac3-null livers. Thus, Hdac3 regulates metabolism through multiple signalling pathways in the liver, and deletion of Hdac3 disrupts normal metabolic homeostasis.

Membrane-anchored growth factors, the epidermal growth factor family: beyond receptor ligands

The epidermal growth factor (EGF) family and the EGF receptor (EGFR, ErbB) tyrosine kinase family have been spearheading the studies of signal transduction events that determine cell fate and behavior in vitro and in vivo. The EGFR family and their signaling pathways are giving us tremendous advantages in developing fascinating molecular target strategies for cancer therapy. Currently, two important types of EGFR inhibitors are in clinical use: neutralizing antibodies of EGFR or ErbB2, and synthetic small compounds of tyrosine kinase inhibitors designed for receptors. On the other hand, basic research of the EGF family ligands presents new challenges as membrane-anchored growth factors. All members of the EGF family have important roles in development and diseases and are shed from the plasma membrane by metalloproteases. The ectodomain shedding of the ligands has emerged as a critical component in the functional transactivation of EGFRs in interreceptor cross-talk in response to various shedding stimulants such as G-protein coupled receptor agonists, growth factors, cytokines, and various physicochemical stresses. Among the EGFR-ligands, heparin-binding EGF-like growth factor (HB-EGF) is a prominent ligand in our understanding of the pathophysiological roles of ectodomain shedding in cancer, wound healing, cardiac diseases, etc. Here we focus on ectodomain shedding of the EGF family ligands, especially HB-EGF by disintegrin and metalloproteases, which are not only key events of receptor cross talk, but also novel intercellular signaling by their carboxy-terminal fragments to regulate gene expression directly.

Sequential valproic acid/all-trans retinoic acid treatment reprograms differentiation in refractory and high-risk acute myeloid leukemia

Epigenetic alterations of chromatin due to aberrant histone deacetylase (HDAC) activity and transcriptional silencing of all-trans retinoic acid (ATRA) pathway are events linked to the pathogenesis of acute myeloid leukemia (AML) that can be targeted by specific treatments. A pilot study was carried out in eight refractory or high-risk AML patients not eligible for intensive therapy to assess the biological and therapeutic activities of the HDAC inhibitor valproic acid (VPA) used to remodel chromatin, followed by the addition of ATRA, to activate gene transcription and differentiation in leukemic cells. Hyperacetylation of histones H3 and H4 was detectable at therapeutic VPA serum levels (>or=50 microg/mL) in blood mononuclear cells from seven of eight patients. This correlated with myelomonocytic differentiation of leukemic cells as revealed by morphologic, cytochemical, immunophenotypic, and gene expression analyses. Differentiation of the leukemic clone was proven by fluorescence in situ hybridization analysis showing the cytogenetic lesion +8 or 7q- in differentiating cells. Hematologic improvement, according to established criteria for myelodysplastic syndromes, was observed in two cases. Stable disease and disease progression were observed in five and one cases, respectively. In conclusion, VPA-ATRA treatment is well tolerated and induces phenotypic changes of AML blasts through chromatin remodeling. Further studies are needed to evaluate whether VPA-ATRA treatment by reprogramming differentiation of the leukemic clone might improve the response to chemotherapy in leukemia patients.