The stem cell zinc finger 1 (SZF1)/ZNF589 protein has a human-specific evolutionary nucleotide DNA change and acts as a regulator of cell viability in the hematopoietic system

The stem cell zinc finger 1 (SZF1)/ZNF589 protein belongs to the large family of Krüppel-associated box domain-zinc finger (KRAB-ZNF) transcription factors, which are present only in higher vertebrates and epigenetically repress transcription by recruiting chromatin-modifying complexes to the promoter regions of their respective target genes. Although the distinct biological functions of most KRAB-ZNF proteins remain unknown, recent publications indicate their implication in fundamental processes, such as cell proliferation, apoptosis, differentiation, development, and tumorigenesis. SZF1/ZNF589 was first identified as a gene with SZF1-1 isoform specifically expressed in CD34(+) hematopoietic cells, strongly suggesting a role in epigenetic control of gene expression in hematopoietic stem/progenitor cells (HSPCs). However, the function of SZF1/ZNF589 in hematopoiesis has not yet been elucidated. Our study reveals SZF1/ZNF589 as a gene with a human-specific nucleotide DNA-change, conferring potential species-specific functional properties. Through shRNA-mediated loss-of-function experiments, we found that changes in expression of fundamental apoptosis-controlling genes are induced on SZF1/ZNF589 knockdown, resulting in inhibited growth of hematopoietic cell lines and decreased progenitor potential of primary human bone marrow CD34(+) cells. Moreover, we found that the SZF1/ZNF589 gene is differentially regulated during hypoxia in CD34(+) HSPCs in a cytokine-dependent manner, implicating its possible involvement in the maintenance of the hypoxic physiologic status of hematopoietic stem cells. Our results establish the role of SZF1/ZNF589 as a new functional regulator of the hematopoietic system.

BCL6--regulated by AhR/ARNT and wild-type MEF2B--drives expression of germinal center markers MYBL1 and LMO2

Genetic heterogeneity is widespread in tumors, but poorly documented in cell lines. According to immunoglobulin hypermutation analysis, the diffuse large B-cell lymphoma cell line U-2932 comprises two subpopulations faithfully representing original tumor subclones. We set out to identify molecular causes underlying subclone-specific expression affecting 221 genes including surface markers and the germinal center oncogenes BCL6 and MYC. Genomic copy number variations explained 58/221 genes differentially expressed in the two U-2932 clones. Subclone-specific expression of the aryl-hydrocarbon receptor (AhR) and the resulting activity of the AhR/ARNT complex underlaid differential regulation of 11 genes including MEF2B. Knock-down and inhibitor experiments confirmed that AhR/ARNT regulates MEF2B, a key transcription factor for BCL6. AhR, MEF2B and BCL6 levels correlated not only in the U-2932 subclones but in the majority of 23 cell lines tested, indicting overexpression of AhR as a novel mechanism behind BCL6 diffuse large B-cell lymphoma. Enforced modulation of BCL6 affected 48/221 signature genes. Although BCL6 is known as a transcriptional repressor, 28 genes were up-regulated, including LMO2 and MYBL1 which, like BCL6, signify germinal center diffuse large B-cell lymphoma. Supporting the notion that BCL6 can induce gene expression, BCL6 and the majority of potential targets were co-regulated in a series of B-cell lines. In conclusion, genomic copy number aberrations, activation of AhR/ARNT, and overexpression of BCL6 are collectively responsible for differential expression of more than 100 genes in subclones of the U-2932 cell line. It is particularly interesting that BCL6 - regulated by AhR/ARNT and wild-type MEF2B - may drive expression of germinal center markers in diffuse large B-cell lymphoma.

BCR-ABL affects STAT5A and STAT5B differentially

Signal transducers and activators of transcription (STATs) are latent cytoplasmic transcription factors linking extracellular signals to target gene transcription. Hematopoietic cells express two highly conserved STAT5-isoforms (STAT5A/STAT5B), and STAT5 is directly activated by JAK2 downstream of several cytokine receptors and the oncogenic BCR-ABL tyrosine kinase. Using an IL-3-dependent cell line with inducible BCR-ABL-expression we compared STAT5-activation by IL-3 and BCR-ABL in a STAT5-isoform specific manner. RNAi targeting of STAT5B strongly inhibits BCR-ABL-dependent cell proliferation, and STAT5B but not STAT5A is essential for BCL-X_L-expression in the presence of BCR-ABL. Although BCR-ABL induces STAT5-tyrosine phosphorylation independent of JAK2-kinase activity, BCR-ABL is less efficient in inducing active STAT5A:STAT5B-heterodimerization than IL-3, leaving constitutive STAT5A and STAT5B-homodimerization unaffected. In comparison to IL-3, nuclear accumulation of a STAT5A-eGFP fusion protein is reduced by BCR-ABL, and BCR-ABL tyrosine kinase activity induces STAT5A-eGFP translocation to the cell membrane and co-localization with the IL-3 receptor. Furthermore, BCR-ABL-dependent phosphorylation of Y682 in STAT5A was detected by mass-spectrometry. Finally, RNAi targeting STAT5B but not STAT5A sensitizes human BCR-ABL-positive cell lines to imatinib-treatment. These data demonstrate differences between IL-3 and BCR-ABL-mediated STAT5-activation and isoform-specific effects, indicating therapeutic options for isoform-specific STAT5-inhibition in BCR-ABL-positive leukemia.

Differential expression of miR-17~92 identifies BCL2 as a therapeutic target in BCR-ABL-positive B-lineage acute lymphoblastic leukemia

Despite advances in allogeneic stem cell transplantation, BCR-ABL-positive acute lymphoblastic leukaemia (ALL) remains a high-risk disease, necessitating the development of novel treatment strategies. As the known oncomir, miR-17~92, is regulated by BCR-ABL fusion in chronic myeloid leukaemia, we investigated its role in BCR-ABL translocated ALL. miR-17~92-encoded miRNAs were significantly less abundant in BCR-ABL-positive as compared to -negative ALL-cells and overexpression of miR-17~19b triggered apoptosis in a BCR-ABL-dependent manner. Stable isotope labelling of amino acids in culture (SILAC) followed by liquid chromatography and mass spectroscopy (LC-MS) identified several apoptosis-related proteins including Bcl2 as potential targets of miR-17~19b. We validated Bcl2 as a direct target of this miRNA cluster in mice and humans, and, similar to miR-17~19b overexpression, Bcl2-specific RNAi strongly induced apoptosis in BCR-ABL-positive cells. Furthermore, BCR-ABL-positive human ALL cell lines were more sensitive to pharmacological BCL2 inhibition than negative ones. Finally, in a xenograft model using patient-derived leukaemic blasts, real-time, in vivo imaging confirmed pharmacological inhibition of BCL2 as a new therapeutic strategy in BCR-ABL-positive ALL. These data demonstrate the role of miR-17~92 in regulation of apoptosis, and identify BCL2 as a therapeutic target of particular relevance in BCR-ABL-positive ALL.

Opposing roles of Akt and STAT3 in the protection of the maternal heart from peripartum stress

BACKGROUND

Peripartum cardiomyopathy (PPCM) is a pregnancy-associated cardiomyopathy in previously healthy women. Mice with a cardiomyocyte-restricted deletion of signal transducer and activator of transcription-3 (STAT3, CKO) develop PPCM. PI3K-Akt signalling is thought to promote cardiac hypertrophy and protection during pregnancy. We evaluated the role of activated Akt signalling in the maternal heart postpartum.

METHODS AND RESULTS

CKO mice were bred to mice harbouring an Akt transgene, specifically expressed in cardiomyocytes (CAkt(tg)) generating CKO; CAkt(tg), CAkt(tg), CKO, and wild-type sibling mice. CAkt(tg) and CKO;CAkt(tg) female mice developed PPCM with systolic dysfunction. Both genotypes displayed cardiac hypertrophy and lower capillary density, showed increased phosphorylation of p66 Src homology 2 domain containing protein and FoxO3A, and reduced expression of manganese superoxide dismutase as well as increased cathepsin D activity and increased miR-146a levels [indicative for generation of the anti-angiogenic 16 kDa prolactin (PRL)]. Cardiac inflammation and fibrosis was accelerated in CKO;CAkt(tg) and associated with high postpartum mortality. The PRL blocker, bromocriptine (BR), prevented heart failure and the decrease in capillary density in CKO;CAkt(tg) and CAkt(tg) mice. BR attenuated high mortality, up-regulation of CCL2, and cardiac inflammation as well as fibrosis in CKO;CAkt(tg). PRL infusion induced cardiac inflammation in CKO;CAkt(tg) independent of pregnancy. In neonatal rat cardiomyocytes, PRL and interferon γ (IFNγ) induced the expression of CCL2 via activation of Akt.

CONCLUSION

Postpartum Akt activation is detrimental for the peripartum heart as it lowers anti-oxidative defence and in combination with low STAT3 conditions, accelerate cardiac inflammation and fibrosis. PRL and its cleaved 16 kDa form are central for Akt-induced PPCM as indicated by the protection from the disease by PRL blockade.

MicroRNA-146a is a therapeutic target and biomarker for peripartum cardiomyopathy

Peripartum cardiomyopathy (PPCM) is a life-threatening pregnancy-associated cardiomyopathy in previously healthy women. Although PPCM is driven in part by the 16-kDa N-terminal prolactin fragment (16K PRL), the underlying molecular mechanisms are poorly understood. We found that 16K PRL induced microRNA-146a (miR-146a) expression in ECs, which attenuated angiogenesis through downregulation of NRAS. 16K PRL stimulated the release of miR-146a-loaded exosomes from ECs. The exosomes were absorbed by cardiomyocytes, increasing miR-146a levels, which resulted in a subsequent decrease in metabolic activity and decreased expression of Erbb4, Notch1, and Irak1. Mice with cardiomyocyte-restricted Stat3 knockout (CKO mice) exhibited a PPCM-like phenotype and displayed increased cardiac miR-146a expression with coincident downregulation of Erbb4, Nras, Notch1, and Irak1. Blocking miR-146a with locked nucleic acids or antago-miRs attenuated PPCM in CKO mice without interrupting full-length prolactin signaling, as indicated by normal nursing activities. Finally, miR-146a was elevated in the plasma and hearts of PPCM patients, but not in patients with dilated cardiomyopathy. These results demonstrate that miR-146a is a downstream-mediator of 16K PRL that could potentially serve as a biomarker and therapeutic target for PPCM.

U-2932: two clones in one cell line, a tool for the study of clonal evolution

Genetic heterogeneity is common in tumors, explicable by the development of subclones with distinct genetic and epigenetic alterations. We describe an in vitro model for cancer heterogeneity, comprising the diffuse large B-cell lymphoma cell line U-2932 which expresses two sets of cell surface markers representing twin populations flow-sorted by CD20 vs CD38 expression. U-2932 populations were traced to subclones of the original tumor with clone-specific immunoglobulin IgVH4-39 hypermutation patterns. BCL6 was overexpressed in one subpopulation (R1), MYC in the other (R2), both clones overexpressed BCL2. According to the combined results of immunoglobulin hypermutation and cytogenetic analysis, R1 and R2 derive from a mother clone with genomic BCL2 amplification, which acquired secondary rearrangements leading to the overexpression of BCL6 (R1) or MYC (R2). Some 200 genes were differentially expressed in R1/R2 microarrays including transcriptional targets of the aberrantly expressed oncogenes. Other genes were regulated by epigenetic means as shown by DNA methylation analysis. Ectopic expression of BCL6 in R2 variously modulated new candidate target genes, confirming dual silencing and activating functions. In summary, stable retention of genetically distinct subclones in U-2932 models tumor heterogeneity in vitro permitting functional analysis of oncogenes against a syngenic background.

Reduction of STAT3 expression induces mitochondrial dysfunction and autophagy in cardiac HL-1 cells

Signal transducer and activator of transcription 3 (STAT3) is an important mediator of cardiac survival pathways. Reduced levels of STAT3 in patients with end-stage heart failure suggest a clinical relevance of STAT3 deficiency for cardiac disease. The recent identification of STAT3 as a mitochondrial protein which is important for full activity of mitochondrial complex I has opened a new field for the investigation of how STAT3 functions in cardioprotection. The goal of this study was to establish a cell culture model with a reduced STAT3 expression, and to use this model for the investigation of mitochondrial and mitochondrial-associated functions under STAT3 deficiency. In the murine cardiomyogenic cell line HL-1, the expression of STAT3 was silenced by lentiviral transduction with anti-STAT3 shRNA (STAT3 KD cells). STAT3 mRNA and protein levels were significantly reduced in HL-1 STAT3 KD cells compared to HL-1 cells transduced with a control shRNA. Spectrophotometric and polarographic assays with mitochondrial enriched fractions and intact cells showed reduced activities of respiratory chain complexes I, II, III and IV in HL-1 STAT3 KD cells. At ultrastructural level, a severe damage of mitochondrial integrity was observed, combined with a significant increase in autophagolysosomes in STAT3-deficient HL-1 cells. Our results demonstrate that the HL-1 STAT3 KD cell line is a good model to study cellular consequences of STAT3 deficiency. Moreover, this is the first study to show that STAT3 deficiency leads to a disruption of mitochondrial ultrastructure and increased autophagy.

Erythropoietin preserves the endothelial differentiation capacity of cardiac progenitor cells and reduces heart failure during anticancer therapies

Anticancer therapies, such as targeting of STAT3 or the use of anthracyclins (doxorubicin), can induce cardiomyopathy. In mice prone to developing heart failure as a result of reduced cardiac STAT3 expression (cardiomyocyte-restricted deficiency of STAT3) or treatment with doxorubicin, we observed impaired endothelial differentiation capacity of Sca-1(+) cardiac progenitor cells (CPCs) in conjunction with attenuated CCL2/CCR2 activation. Mice in both models also displayed reduced erythropoietin (EPO) levels in the cardiac microenvironment. EPO binds to CPCs and seems to be responsible for maintaining an active CCL2/CCR2 system. Supplementation with the EPO derivative CERA in a hematocrit-inactive low dose was sufficient to upregulate CCL2, restore endothelial differentiation of CPCs, and preserve the cardiac microvasculature and cardiac function in both mouse models. Thus, low-dose EPO treatment could potentially be exploited as a therapeutic strategy to reduce the risk of heart failure in certain treatment regimens.

Interleukin-1 assembles a proangiogenic signaling module consisting of caveolin-1, tumor necrosis factor receptor-associated factor 6, p38-mitogen-activated protein kinase (MAPK), and MAPK-activated protein kinase 2 in endothelial cells

OBJECTIVE

Interleukin-1β (IL-1β) is a major cytokine linking inflammation and angiogenesis in pathological vascular processes, such as atherosclerosis and tumor neoangiogenesis. However, signaling pathways mediating IL-1β-induced proangiogenic processes in endothelial cells (ECs) have barely been elucidated yet. Therefore, the present study investigated IL-1β-induced proangiogenic signaling in ECs.

METHODS AND RESULTS

IL-1β potently induced tube formation and migration of ECs. This was associated with and dependent on activation of p38-mitogen-activated protein kinase (MAPK) and MAPK-activated protein kinase 2 (MK2) as determined by pharmacological inhibition and gene silencing. Furthermore, silencing of the adaptor protein tumor necrosis factor receptor-associated factor 6 (TRAF6) (lentiviral short hairpin RNA) inhibited these IL-1β-induced processes. Moreover, IL-1β promoted translocation of TRAF6 to insoluble cellular fractions (containing membrane rafts/caveolae) and interaction of TRAF6 with caveolin-1. Accordingly, cellular cholesterol depletion (cyclodextrin) and silencing of caveolin-1 (small interfering RNA) inhibited IL-1β-induced activation of p38-MAPK and MK2, as well as IL-1β-induced tube formation and migration. Finally, silencing of TRAF6 and MK2 deficiency inhibited IL-1β-induced microvessel outgrowth in murine aortic rings ex vivo, and deficiency of MK2 or caveolin-1 significantly reduced IL-1β-induced angiogenesis in mice in vivo (Matrigel plug assay).

CONCLUSIONS

IL-1β assembles a proangiogenic signaling module consisting of caveolin-1, TRAF6, p38-MAPK, and MK2 in ECs, representing a potential target to intervene into angiogenesis-dependent processes and diseases.

Dendritic cells derived from HOXB4-immortalized hematopoietic bone marrow cells

Dendritic cells (DCs) are essential for the generation and modulation of cell-mediated adaptive immunity against infections. DC-based vaccination involves transplantation of ex vivo-generated DCs loaded with antigen in vitro, but remains limited by the number of autologous or allogeneic cells. While in vitro expansion and differentiation of hematopoietic stem cells (HSCs) into DCs seems to be the most viable alternative to overcome this problem, the complexity of HSC expansion in vitro has posed significant limitations for clinical application. We immortalized lineage-depleted murine hematopoietic bone marrow (lin(-)BM) cells with HOXB4, and differentiated them into CD11c(+)MHCII(+) DCs. These cells showed the typical DC phenotype and upregulated surface expression of co-stimulatory molecules on stimulation with various toll-like receptor ligands. These DCs efficiently presented exogenous antigen to T-cells via major histocompatibility complex (MHC) I and II and viral antigen on infection. Finally, they showed migratory capacity and were able to generate antigen-specific primed T-cells in vivo. In summary, we provide evidence that HOXB4-transduced lin(-)BM cells can serve as a viable means of generating fully functional DCs for scientific and therapeutic applications.

Modulation of anthracycline-induced cytotoxicity by targeting the prenylated proteome in myeloid leukemia cells

Deregulation of Ras/ERK signaling in myeloid leukemias makes this pathway an interesting target for drug development. Myeloid leukemia cell lines were screened for idarubicin-induced apoptosis, cell-cycle progression, cell-cycle-dependent MAP kinase kinase (MEK-1/2) activation, and Top2 expression. Cell-cycle-dependent activation of MEK/ERK signaling was blocked using farnesyltransferase inhibitor (FTI) BMS-214,662 and dual prenyltransferase inhibitor (DPI) L-778,123 to disrupt Ras signaling. Idarubicin caused a G2/M cell-cycle arrest characterized by elevated diphosphorylated MEK-1/2 and Top2α expression levels. The FTI/DPIs elicited distinct effects on Ras signaling, protein prenylation, cell cycling and apoptosis. Combining these FTI/DPIs with idarubicin synergistically inhibited proliferation of leukemia cell lines, but the L-778,123+idarubicin combination exhibited synergistic growth inhibition over a greater range of drug concentrations. Interestingly, combined FTI/DPI treatment synergistically inhibited cell proliferation, induced apoptosis and nearly completely blocked protein prenylation. Inhibition of K-Ras expression by RNA interference or blockade of its post-translational prenylation led to increased BMS-214,662-induced apoptosis. Our results suggest that nearly complete inhibition of protein prenylation using an FTI + DPI combination is the most effective method to induce apoptosis and to block anthracycline-induced activation of ERK signaling.

Activation of Paired-homeobox gene PITX1 by del(5)(q31) in T-cell acute lymphoblastic leukemia

In T-cell acute lymphoblasic leukemia (T-ALL), neoplastic chromosomal rearrangements are known to deregulate members of the homeobox gene families NKL and HOXA. Here, analysis of T-ALL cell lines and primary cells identified aberrant expression of a third homeobox gene group, the Paired (PRD) class. LOUCY cells revealed chromosomal deletion at 5q31, which targets the downstream regulatory region of the PRD homeobox gene PITX1, removing a STAT1 binding site. STAT1 mediates repressive interleukin 2 (IL2)-STAT1 signaling, implicating IL2 pathway avoidance as a possible activation mechanism. Among primary T-ALL samples, 2/22 (9%) aberrantly expressed PITX1, highlighting the importance of this gene. Forced expression of PITX1 in JURKAT cells and subsequent target gene analysis prompted deregulation of genes involved in T-cell development including HES1, JUN, NKX3-1, RUNX1, RUNX2, and TRIB2. Taken together, our data show leukemic activation of PITX1, a novice PRD-class homeobox gene in a subset of early-staged T-ALL, which may promote leukemogenesis by inhibiting T-cell development.