Erythropoiesis in polycythemia vera is hyper-proliferative and has accelerated maturation

Novel therapeutic approaches in thalassemias, sickle cell disease, and other red cell disorders

ABSTRACT

In this last decade, a deeper understanding of the pathophysiology of hereditary red cell disorders and the development of novel classes of pharmacologic agents have provided novel therapeutic approaches to thalassemias, sickle cell disease (SCD), and other red cell disorders. Here, we analyze and discuss the novel therapeutic options according to their targets, taking into consideration the complex process of erythroid differentiation, maturation, and survival of erythrocytes in the peripheral circulation. We focus on active clinical exploratory and confirmatory trials on thalassemias, SCD, and other red cell disorders. Beside β-thalassemia and SCD, we found that the development of new therapeutic strategies has allowed for the design of clinic studies for hereditary red cell disorders still lacking valuable therapeutic alternative such as α-thalassemias, congenital dyserythropoietic anemia, or Diamond-Blackfan anemia. In addition, reduction of heme synthesis, which can be achieved by the repurposed antipsychotic drug bitopertin, might affect not only hematological disorders but multiorgan diseases such as erythropoietic protoporphyria. Finally, our review highlights the current state of therapeutic scenarios, in which multiple indications targeting different red cell disorders are being considered for a single agent. This is a welcome change that will hopefully expand therapeutic option for patients affected by thalassemias, SCD, and other red cell disorders.

Novel germline JAK2R715T mutation causing PV-like erythrocytosis in 3 generations. Amelioration by Ropeg-Interferon

Polycythemia vera (PV) is a clonal disorder arising from the acquired somatic mutations of the JAK2 gene, including JAK2V617F or several others in exon 12. A 38-year-old female had a stroke at age 32 and found to have elevated hemoglobin, normal leukocytes, normal platelets, and tested negative for JAK2V617F and exon 12 mutations. Next generation sequencing revealed a novel mutation: JAK2R715T in the pseudokinase domain (JH2) at 47.5%. Its presence in her nail DNA confirmed a germline origin. Her mother and her son similarly had erythrocytosis and a JAK2R715T mutation. Computer modeling indicated gain-of-function JAK2 activity. The propositus and her mother had polyclonal myelopoiesis, ruling out another somatic mutation-derived clonal hematopoiesis. Some erythroid progenitors of all three generations grew without erythropoietin, a hallmark of PV. The in vitro reporter assay confirmed increased activity of the JAK2R715T kinase. Similar to PV, the JAK2R715T native cells have increased STAT5 phosphorylation, augmented transcripts of prothrombotic and inflammatory genes, and decreased KLF2 transcripts. The propositus was not controlled by hydroxyurea, and JAK2 inhibitors were not tolerated; however, Ropeginterferon-alfa-2b (Ropeg-IFN-α) induced a remission. Ropeg-IFN-α treatment also reduced JAK2 activity in the propositus, her mother and JAK2V617F PV subjects. We report dominantly inherited erythrocytosis secondary to a novel germline JAK2R715T gain-of-function mutation with many but not all comparable molecular features to JAK2V617F PV. We also document a previously unreported inhibitory mechanism of JAK2 signaling by Ropeg-IFN-α.

Real-world, retrospective study evaluating thromboembolic events, associated risk factors, and health-care resource utilization in Japanese patients with polycythemia vera

In this retrospective, real-world study, we used medical claims data to evaluate the incidence of thromboembolic events (TEs), time to TE, associated risk factors, and health-care resource utilization (HRU) in Japanese patients with polycythemia vera (PV; N = 606) from April 1, 2008, to August 31, 2015. Baseline characteristics of interest included median age, 67.0 years; previous TEs, 11.6%; cardiovascular conditions (CVCs), 45.7%; and ≥ 3 risk factors, 17.8%. Overall, 100 patients experienced TEs (118 events) at a rate of 8.15/100 person-years [TE-free survival rate, 69.3% (2008-2015)]. The annual total health-care costs [mean (per person)] were significantly impacted by the presence of TEs (yes vs. no: ¥993,000 vs ¥459,000; P < 0.001). These results confirm that the presence of CVCs increases the risk of TEs in Japanese patients with PV; occurrence of TEs was associated with a higher HRU in these patients.

Expression of CD markers in JAK2V617F positive myeloproliferative neoplasms: Prognostic significance

Myeloproliferative neoplasms (MPNs) are clonal stem cell disorders characterized by the presence of JAK2^V617F mutation. Thrombohemorrhagic as well as autoimmune or inflammatory phenomena are common clinical outcomes of these disorders. Recent studies have shown that abnormality in frequency and function of blood cells manifested by an alteration in CD markers' expression patterns play a key role in these complications. So, there may be a relationship between CD markers' expressions and prognosis of JAK2^V617F positive MPNs. Therefore, in this review, we have focused on these abnormalities from the perspective of changing expressions of CD markers and assessment of the relationship between these changes with prognosis of JAK2^V617F positive MPNs. It can be stated that the abnormal expression of a large number of CD markers can be used as a prognostic biomarker for clinical outcomes including thrombohememorrhagic events, as well as autoimmune and leukemic transformation in JAK2^V617F positive MPNs. Considering the possible role of CD markers' expressions in JAK2^V617F MPNs prognosis, further studies are needed to confirm the relationship between the expression of CD markers with prognosis to be able to find an appropriate therapeutic approach via targeting CD markers.

Quantitative proteomics reveals that miR-222 inhibits erythroid differentiation by targeting BLVRA and CRKL

miR-222 plays an important role in erythroid differentiation, but the potential targets of miR-222 in the regulation of erythroid differentiation remain to be determined. The target genes of miR-222 were identified by proteomics combined with bioinformatics analysis in this study. Thirteen proteins were upregulated, and 13 were downregulated in K562 cells following transfection with miR-222 inhibitor for 24 and 48 hours. Among these proteins, BLVRA and CRKL were upregulated after transfection of miR-222 inhibitor in K562 cells and human CD34+ HPCs. Moreover, miR-222 mimics reduced and miR-222 inhibitor enhanced the mRNA and protein levels of both BLVRA and CRKL. Luciferase assay showed that miR-222 directly targeted 3'-UTR of BLVRA and CRKL. In addition, overexpression of either BLVRA or CRKL or both increased the erythroid differentiation of K562 cells, while silencing of either BLVRA or CRKL or both by siRNA significantly attenuated hemin-induced erythroid differentiation of K562 cells. Our results indicated that BLVRA and CRKL are targets of miR-222.

Transcriptomic and phospho-proteomic analyzes of erythroblasts expanded in vitro from normal donors and from patients with polycythemia vera

Erythropoiesis is a tightly regulated process which becomes decoupled from its normal differentiation program in patients with polycythemia vera (PV). Somatic mutations in JAK2 are commonly associated with this myeloid proliferative disorder. To gain insight into the molecular events that are required for abnormally developing erythroid cells to escape dependence on normal growth signals, we performed in vitro expansion of mature erythroblasts (ERY) from seven normal healthy donors and from seven polycythemic patients in the presence of IL3, EPO, SCF for 10, 11, or 13 days. Normal ERYs required exposure to the glucocorticoid dexamethasone (Dex) for expansion, while PV-derived ERYs expanded in the absence of dexamethasone. RNA expression profiling revealed enrichment of two known oncogenes, GPR56 and RAB4a, in PV-derived ERYs along with reduced expression levels of transcription factor TAL1 (ANOVA FDR < 0.05). While both normal and polycythemic-derived ERYs integrated signaling cascades for growth, they did so via different signaling pathways which are represented by their differential phospho-profiles. Our results show that normal ERYs displayed greater levels of phosphorylation of EGFR, PDGFRβ, TGFβ, and cKit, while PV-derived ERYs were characterized by increased phosphorylation of cytoplasmic kinases in the JAK/STAT, PI3K, and GATA1 pathways. Together these data suggest that PV erythroblast expansion and maturation may be maintained and enriched in the absence of dexamethasone through reduced TAL1 expression and by accessing additional signaling cascades. Members of this acquired repertoire may provide important insight into the pathogenesis of aberrant erythropoiesis in myeloproliferative neoplasms such as polycythemia vera.

JAK2-V617F-induced MAPK activity is regulated by PI3K and acts synergistically with PI3K on the proliferation of JAK2-V617F-positive cells

The identification of a constitutively active JAK2 mutant, namely JAK2-V617F, was a milestone in the understanding of Philadelphia chromosome-negative myeloproliferative neoplasms. The JAK2-V617F mutation confers cytokine hypersensitivity, constitutive activation of the JAK-STAT pathway, and cytokine-independent growth. In this study we investigated the mechanism of JAK2-V617F-dependent signaling with a special focus on the activation of the MAPK pathway. We observed JAK2-V617F-dependent deregulated activation of the multi-site docking protein Gab1 as indicated by constitutive, PI3K-dependent membrane localization and tyrosine phosphorylation of Gab1. Furthermore, we demonstrate that PI3K signaling regulates MAPK activation in JAK2-V617F-positve cells. This cross-regulation of the MAPK pathway by PI3K affects JAK2-V617F-specific target gene induction, erythroid colony formation, and regulates proliferation of JAK2-V617F-positive patient cells in a synergistically manner.

Implication of microRNAs in the pathogenesis of MDS

MicroRNAs (miRNAs) are significant regulators of human hematopoietic stem cells (HSC), and their deregulation contributes to hematological malignancies. Myelodysplastic syndromes (MDS) represent a spectrum of hematological disorders characterized by dysfunctional HSC, ineffective blood cell production, progressive marrow failure, and an increased risk of developing acute myeloid leukemia (AML). Although miRNAs have been primarily studied in AML, only recently have similar studies been performed on MDS. In this review, we describe the normal function and expression of miRNAs in human HSC, and describe mounting evidence that deregulation of miRNAs contributes to the pathogenesis of MDS.

Expression patterns of microRNAs associated with CML phases and their disease related targets

Background

MicroRNAs are important regulators of transcription in hematopoiesis. Their expression deregulations were described in association with pathogenesis of some hematological malignancies. This study provides integrated microRNA expression profiling at different phases of chronic myeloid leukemia (CML) with the aim to identify microRNAs associated with CML pathogenesis. The functions of in silico filtered targets are in this report annotated and discussed in relation to CML pathogenesis.

Results

Using microarrays we identified differential expression profiles of 49 miRNAs in CML patients at diagnosis, in hematological relapse, therapy failure, blast crisis and major molecular response. The expression deregulation of miR-150, miR-20a, miR-17, miR-19a, miR-103, miR-144, miR-155, miR-181a, miR-221 and miR-222 in CML was confirmed by real-time quantitative PCR. In silico analyses identified targeted genes of these miRNAs encoding proteins that are involved in cell cycle and growth regulation as well as several key signaling pathways such as of mitogen activated kinase-like protein (MAPK), epidermal growth factor receptor (EGFR, ERBB), transforming growth factor beta (TGFB1) and tumor protein p53 that are all related to CML. Decreased levels of miR-150 were detected in patients at diagnosis, in blast crisis and 67% of hematological relapses and showed significant negative correlation with miR-150 proved target MYB and with BCR-ABL transcript level.

Conclusions

This study uncovers microRNAs that are potentially involved in CML and the annotated functions of in silico filtered targets of selected miRNAs outline mechanisms whereby microRNAs may be involved in CML pathogenesis.

Phosphorylation of p27Kip1 by JAK2 directly links cytokine receptor signaling to cell cycle control

Janus kinase 2 (JAK2) couples ligand activation of cell surface cytokine receptors to the regulation of cellular functions including cell cycle progression, differentiation and apoptosis. It thereby coordinates biological programs such as development and hematopoiesis. Unscheduled activation of JAK2 by point mutations or chromosomal translocations can induce hyperproliferation and hematological malignancies. Typical signal transduction by the JAK2 tyrosine kinase comprises phosphorylation of STAT transcription factors. In this study, we describe the identification of the cyclin-dependent kinase (CDK) inhibitor p27(Kip1) as a novel JAK2 substrate. JAK2 can directly bind and phosphorylate p27(Kip1). Both, the JAK2 FERM domain and its kinase domain bind to p27(Kip1). JAK2 phosphorylates tyrosine residue 88 (Y88) of p27(Kip1). We previously reported that Y88 phosphorylation of p27(Kip1) by oncogenic tyrosine kinases impairs p27(Kip1)-mediated CDK inhibition, and initiates its ubiquitin-dependent proteasomal degradation. Consistently, we now find that active oncogenic JAK2V617F reduces p27(Kip1) stability and protein levels in patient-derived cell lines harboring the mutant JAK2V617F allele. Moreover, tyrosine phosphorylation of p27(Kip1) is impaired and p27(Kip1) expression is restored upon JAK2V617F inactivation by small hairpin RNA-mediated knockdown or by the pyridone-containing tetracycle JAK inhibitor-I, indicating that direct phosphorylation of p27(Kip1) can contribute to hyperproliferation of JAK2V617F-transformed cells. Activation of endogenous JAK2 by interleukin-3 (IL-3) induces Y88 phosphorylation of p27(Kip1), thus unveiling a novel link between cytokine signaling and cell cycle control in non-transformed cells. Oncogenic tyrosine kinases could use this novel pathway to promote hyperproliferation in tumor cells.

The dominant negative β isoform of the glucocorticoid receptor is uniquely expressed in erythroid cells expanded from polycythemia vera patients

Glucocorticoid receptor (GR) agonists increase erythropoiesis in vivo and in vitro. To clarify the effect of the dominant negative GRβ isoform (unable to bind STAT-5) on erythropoiesis, erythroblast (EB) expansion cultures of mononuclear cells from 18 healthy (nondiseased) donors (NDs) and 16 patients with polycythemia vera (PV) were studied. GRβ was expressed in all PV EBs but only in EBs from 1 ND. The A3669G polymorphism, which stabilizes GRβ mRNA, had greater frequency in PV (55%; n = 22; P = .0028) and myelofibrosis (35%; n = 20) patients than in NDs (9%; n = 22) or patients with essential thrombocythemia (6%; n = 15). Dexamethasone stimulation of ND cultures increased the number of immature EBs characterized by low GATA1 and β-globin expression, but PV cultures generated great numbers of immature EBs with low levels of GATA1 and β-globin irrespective of dexamethasone stimulation. In ND EBs, STAT-5 was not phosphorylated after dexamethasone and erythropoietin treatment and did not form transcriptionally active complexes with GRα, whereas in PV EBs, STAT-5 was constitutively phosphorylated, but the formation of GR/STAT-5 complexes was prevented by expression of GRβ. These data indicate that GRβ expression and the presence of A3669G likely contribute to development of erythrocytosis in PV and provide a potential target for identification of novel therapeutic agents.

Extent of hematopoietic involvement by TET2 mutations in JAK2V⁶¹⁷F polycythemia vera

TET2 mutations are found in polycythemia vera and it was initially reported that there is a greater TET2 mutational burden than JAK2(V617F) in polycythemia vera stem cells and that TET2 mutations precede JAK2(V617F). We quantified the proportion of TET2, JAK2(V617F) mutations and X-chromosome allelic usage in polycythemia vera cells, BFU-Es and in vitro expanded erythroid progenitors and found clonal reticulocytes, granulocytes, platelets and CD34(+) cells. We found that TET2 mutations may also follow rather than precede JAK2(V617F) as recently reported by others. Only a fraction of clonal early hematopoietic precursors and largely polyclonal T cells carry the TET2 mutation. We showed that in vitro the concomitant presence of JAK2(V617F) and TET2 mutations favors clonal polycythemia vera erythroid progenitors in contrast with non-TET2 mutated progenitors. We conclude that loss-of-function TET2 mutations are not the polycythemia vera initiating events and that the acquisition of TET2 somatic mutations may increase the aggressivity of the polycythemia vera clone.

miR-451 enhances erythroid differentiation in K562 cells

Erythropoiesis is a multistep process regulated at the molecular level by intrinsic and extrinsic factors including microRNAs (miRNAs). We previously identified aberrant expression of miR-451 and miR-150 in polycythemia vera (PV) erythroid differentiating cells. To address the functional relevance of these miRNAs in erythroid differentiation, we employed synthetic mimics and inhibitors of miR-451 and miR-150 in erythroid differentiating K562 cells. We observed that miR-451 up-regulation and miR-150 down-regulation are associated with progression of erythroid maturation in K562 cells. Further, enforced expression of miR-451 promoted erythroid differentiation. Inhibition of miR-150 reduced hemoglobinization of K562 cells. Microarray data suggested potential targets regulated by miR-451: UBE2H, ARPP-19; and by miR-150: MS4A3, AGA, PTPRR. Our results demonstrate that miR-451 is involved in the regulation of erythroid differentiation and functions as an enhancer of differentiation. These data support the concept that aberrant expression of miRNAs may contribute to abnormal erythropoiesis such as that of PV.

Isolation and characterization of microRNAs of human mature erythrocytes

Human mature erythrocytes are terminally differentiated cells that have lost their nuclei and organelles during development. Even though mature erythrocytes lack ribosomal and other large-sized RNAs, they still retain small-sized RNAs. We have recently shown that there are abundant and diverse species of microRNAs in mature erythrocytes through the use of several different techniques, including northern blot, miRNA microarray, and real-time PCR. Furthermore, fractionation and genomic analysis has revealed that erythrocyte microRNA expression is different from that of reticulocytes or leukocytes and that mature erythrocytes contribute the majority of microRNA expression in whole blood. Therefore, global analysis of microRNA expression in circulating erythrocytes has the potential to provide mechanistic insights into erythrocyte biology and erythrocyte-related disorders. Here, we have provided the detailed methods for isolating and characterizing the microRNAs from human mature erythrocytes to enable such researches into human diseases involving erythrocytes.