Journal: Experimental hematology
Red cell production is primarily determined by the action of erythropoietin. Additional erythropoiesis-regulatory factors include molecules and cellular interactions occurring within the bone marrow (BM) microenvironment. Sotatercept (ACE-011) is an activin receptor ligand trap which binds several members of the TGF-β superfamily. Treatment with ACE-011 reverses bone loss and reduces the degree of osteoporosis. Surprisingly, this was accompanied by elevated hemoglobin and hematocrit levels. The mechanisms underlying the beneficial effects of ACE-011 on red cell production remain unknown. This study explores the means by which ACE-011 promotes erythropoiesis. We showed that ACE-011 does not directly affect erythroid differentiation of human CD34(+) cells in vitro. We next tested whether ACE-011 acts indirectly by affecting BM accessory cells. Conditioned media (CM) produced by BM stromal cells (SC) inhibited erythroid differentiation of CD34(+) cells while maintained their ability to proliferate. However, CM from SC treated with ACE-011 partially restored erythropoiesis coinciding with changes in the molecular and secretory profile of SC, including the expression and secretion of erythropoiesis-modulatory factors. We conclude that inhibitory factors produced by BM-SC in vitro might control erythropoiesis in vivo and that agents that reverse these microenvironmental signals may provide an approach to attenuate anemia in clinical conditions.
SHP-1, encoded by the PTPN6 gene, is a protein tyrosine phosphatase with two src-homology-2 (SH2) domains that is implicated as providing suppression of hematopoietic malignancies. A number of reports have shown protein-protein interactions between SHP-1 SH2 domains and tyrosine-phosphorylated proteins. However, despite its having three proline-rich, potential SH3-binding motifs, no reports of protein-protein interactions through src-homology-3 (SH3)-binding domains with SHP-1 have been described. Herein we show that the SH3 domain-containing CT10 regulator of kinase-like (CrkL) adaptor protein associates with SHP-1. We also provide results that suggest this association is due to CrkL binding to PxxP domains located at amino acid residues 158-161 within the SHP-1 C-terminal SH2 domain, and amino acid residues 363-366 within its phosphatase domain. This study is the first to identify and define an interaction between SHP-1 and an SH3 domain-containing protein. Our findings provide an alternative way that SHP-1 can be linked to potential substrates.
The genomic events responsible for the pathogenesis of relapsed adult B lymphoblastic leukemia (B-ALL) are not yet clear. We performed integrative analysis of whole genome, exome, custom capture, RNA-seq, and locus-specific genomic assays across nine time points from a patient with primary de novo B-ALL. Comprehensive genome and transcriptome characterization revealed a dramatic tumor evolution during progression, yielding a tumor with complex clonal architecture at second relapse. We observed and validated point mutations in EP300 and NF1, a highly expressed EP300-ZNF384 gene fusion, a microdeletion in IKZF1, a focal deletion affecting SETD2, and large deletions affecting RB1, PAX5, NF1, and ETV6. While the genome analysis revealed events of potential biological relevance, no clinically actionable treatment options were evident at the time of the second relapse. However, transcriptome analysis identified aberrant overexpression of the targetable protein kinase encoded by the FLT3 gene. Although the patient had refractory disease after salvage therapy for the second relapse, treatment with the FLT3 inhibitor sunitinib rapidly induced a near complete molecular response, permitting the patient to proceed to a matched unrelated donor stem cell transplant. The patient remains in complete remission more than 4 years later. Analysis of this patient’s relapse genome revealed an unexpected, actionable therapeutic target that led to a specific therapy associated with a rapid clinical response. For some patients with relapsed or refractory cancers, this approach may indicate novel therapeutic interventions that could alter patient outcomes.
The cellular diversity of the hematopoietic system has been extensively studied and a plethora of cell-surface markers have been used to discriminate and prospectively purify different blood cell types. However, even within phenotypically-identical fractions of hematopoietic stem and progenitor cells (HSPCs) or lineage-restricted progenitors, significant functional heterogeneity is observed when single cells are analyzed. To address these challenges, researchers are now utilizing techniques to follow single cells and their progeny in order to improve our understanding for the underlying functional heterogeneity. On November 19(th) 2015 Drs. David Kent and Leïla Perié, two emerging young group leaders, presented their recent efforts to dissect the functional properties of individual cells in a webinar series organized by the International Society for Experimental Hematology (ISEH). Here, we provide a summary of the presented methods for cell labeling and clonal tracking and discuss how these different techniques have been employed to study hematopoiesis.
HELLP syndrome (hemolysis, elevated liver enzymes, and low platelets) is a severe variant of preeclampsia whose pathogenesis remains unclear. Recent evidence and clinical similarities suggest a link to atypical hemolytic uremic syndrome (aHUS), a disease of excessive activation of the alternative complement pathway effectively treated with a complement inhibitor, eculizumab. Therefore, we utilized a functional complement assay, the modified Ham test, to test sera of women with classic or atypical HELLP syndrome, preeclampsia with severe features, normal pregnancies and healthy non-pregnant women. Sera were also evaluated using levels of the terminal product of complement activation (C5b-9). We tested the in vitro ability of eculizumab to inhibit complement activation in HELLP serum. Increased complement activation was found in participants with classic or atypical HELLP compared to normal pregnancy and non-pregnant controls. Mixing HELLP serum with eculizumab containing serum resulted in a significant decrease in cell killing compared to HELLP serum alone. In conclusion, HELLP syndrome is associated with increased complement activation demonstrated by the modified Ham test. This assay may aid in the diagnosis of HELLP syndrome and confirm its pathophysiology relates to aHUS.
Arginine methylation is an abundant covalent modification that regulates diverse cellular processes including transcription, translation, DNA repair, and RNA processing. The enzymes that catalyze these marks are known as the protein arginine methyltransferases (PRMTs), and they can generate asymmetric dimethyl arginine (Type I arginine methyltransferases), symmetric dimethylarginine (Type II arginine methyltransferases), or monomethyarginine (Type III arginine methyltransferases). The PRMTs are capable of modifying diverse substrates, from histone components to specific nuclear and cytoplasmic proteins. Additionally, the PRMTs can orchestrate chromatin remodeling by blocking the docking of other epigenetic modifying enzymes or by recruiting them to specific gene loci. In the hematopoietic system, PRMTs can regulate cell behavior, including the critical balance between stem cell self-renewal and differentiation in at least two critical ways, via: 1) The covalent modification of transcription factors, and 2) The regulation of histone modifications at promoters critical to cell fate determination. Given these important functions, it is not surprising that these processes are altered in hematopoietic malignancies, such as acute myeloid leukemia (AML), where they promote increased self-renewal and impair hematopoietic stem and progenitor cell (HSPC) differentiation.
In chronic myeloid leukaemia, (CML), cells from different stages of maturation may have differential expression of BCR-ABL at both mRNA and protein level. However, the significance of such differential expression to clinical disease behaviour is unknown. Using the CML-derived, BCR-ABL expressing cell line, K562, distinct plastic-adherent (K562/Adh) and non-adherent (K562/NonAdh) sub-populations were established then analysed both as single cells and as bulk cell populations. BCR-ABL mRNA was up-regulated in K562/Adh compared to K562/NonAdh cells in both single cell and bulk population analyses (p<0.0001). Similarly, phosphorylation of BCR protein was up-regulated in K562/Adh, compared to K562/NonAdh cells (63.42% vs 23.1%, p=0.007), and these two K562 sub-populations were found to express significantly different miRNA species. Furthermore, treatment with the BCR-ABL tyrosine kinase inhibitor, imatinib, reduced cell viability more rapidly in K562/NonAdh compared to K562/Adh cells (p<0.005) both at single and bulk cell levels. This discovery of an adherent sub-population of K562 cells with increased BCR-ABL mRNA, increased phosphorylated BCR protein expression, differential miRNA expression, and increased imatinib resistance, suggests a similar sub-population of cells may also mediate clinical resistance to imatinib during treatment of CML patients.
The retinoblastoma gene (RB1) has been implicated as a tumor suppressor in multiple myeloma (MM), yet its role remains unclear because in the majority of cases with 13q14 deletions, un-mutated RB1 remains expressed from the retained allele. To explore the role of Rb1 in MM, we examined the functional consequences of single- and double-copy Rb1 loss in germinal center B cells, the cells of origin of MM. We generated mice without Rb1 function in germinal center B cells by crossing Rb1(Flox/Flox) with C-γ-1-Cre (Cγ1) mice expressing the Cre recombinase in class-switched B cells in a p107(-/-) background to prevent p107 from compensating for Rb1 loss (Cγ1-Rb1(F/F)-p107(-/-)). All mice developed normally, but B cells with two copies of Rb1 deleted (Cγ1-Rb1(F/F)-p107(-/-)) exhibited increased proliferation and cell death compared with Cγ1-Rb1(+/+)-p107(-/-) controls ex vivo. In vivo, Cγ1-Rb1(F/F)-p107(-/-) mice had a lower percentage of splenic B220+ cells and reduced numbers of bone marrow antigen-specific secreting cells compared with control mice. Our data indicate that Rb1 loss induces both cell proliferation and death in germinal center B cells. Because no B-cell malignancies developed after 1 year of observation, our data also suggest that Rb1 loss is not sufficient to transform post-germinal center B cells and that additional, specific mutations are likely required to cooperate with Rb1 loss to induce malignant transformation.
The MOZ-TIF2 translocation, that fuses MOZ (Monocytic Leukemia Zinc finger protein) histone acetyltransferase (HAT) with the nuclear co-activator TIF2, is associated the development of Acute Myeloid Leukemia. We recently showed that in the absence of MOZ HAT activity, p16(INK4a) transcriptional levels are significantly increased, triggering an early entrance into replicative senescence. Since oncogenic fusion proteins must bypass cellular safeguard mechanisms, such as senescence or apoptosis in order to induce leukemia, we hypothesized that this repressive activity of MOZ over p16(INK4a) transcription could be preserved, or even reinforced, in MOZ leukemogenic fusion proteins, such as MOZ-TIF2. We demonstrate here that, indeed, MOZ-TIF2 silences the expression of the CDKN2A locus (p16(INK4a) and p19(ARF)), inhibits the triggering of senescence and enhances proliferation, providing conditions favourable to the development of leukemia. Furthermore, we show that abolishing the MOZ HAT activity of the fusion protein leads to a significant increase in the expression of the CDKN2A locus and the number of hematopoietic progenitors undergoing senescence. Finally, we demonstrate that inhibition of senescence by MOZ-TIF2 is associated with increased apoptosis, suggesting a role of the fusion protein in p53 apoptosis-versus-senescence balance. Our results underscore the importance of the HAT activity of MOZ, preserved in the fusion protein, for the repression of the CDKN2A locus transcription and the subsequent block of senescence, a necessary step for the survival of leukemic cells.
Over-expression of PRL-3 has been identified in about 50% of patients with acute myeloid leukemia (AML). The mechanism of regulation of PRL-3 remains obscure. Signal transducer and activator of transcription 3 (STAT3), a latent transcriptional factor, has also been often found to be activated in AML. We first identified consensus STAT3 binding sites in the promoter of PRL-3 genes. Then we experimentally validated the direct binding and transcriptional activation. shRNA-mediated knockdown and overexpression approaches were applied in STAT3(-/-) liver cells and leukemic cells to validate the functional regulation of PRL-3 by STAT3. A STAT3 core signature, derived through data mining from publicly available gene expression data, was employed to correlate PRL-3 expression in large AML patient samples. We discovered that STAT3 binds to the -201 to -210 region of PRL-3, which was conserved between human and mouse. Importantly, PRL-3 protein was significantly reduced in mouse STAT3 knockout liver cells compared to STAT3-WT counterparts and ectopic expression of STAT3 in these cells led to a pronounced increase in PRL-3 protein. We demonstrated that STAT3 functionally regulated PRL-3 and STAT3 core signature was enriched in AML with high PRL-3 expression. Targeting either STAT3 or PRL-3 reduced leukemic cell viability. Silencing PRL-3 impaired invasiveness and induced leukemic cell differentiation. In conclusion, PRL-3 was transcriptionally regulated by STAT3. The STAT3/PRL-3 regulatory loop contributes to the pathogenesis of AML and it might represent an attractive therapeutic target for antileukemic therapy.