A genetic disorder reveals a hematopoietic stem cell regulatory network co-opted in leukemia.

The molecular regulation of human hematopoietic stem cell (HSC) maintenance is therapeutically important, but limitations in experimental systems and interspecies variation have constrained our knowledge of this process. Here, we have studied a rare genetic disorder due to MECOM haploinsufficiency, characterized by an early-onset absence of HSCs in vivo. By generating a faithful model of this disorder in primary human HSCs and coupling functional studies with integrative single-cell genomic analyses, we uncover a key transcriptional network involving hundreds of genes that is required for HSC maintenance. Through our analyses, we nominate cooperating transcriptional regulators and identify how MECOM prevents the CTCF-dependent genome reorganization that occurs as HSCs differentiate. We show that this transcriptional network is co-opted in high-risk leukemias, thereby enabling these cancers to acquire stem cell properties. Collectively, we illuminate a regulatory network necessary for HSC self-renewal through the study of a rare experiment of nature.

Ribosome Levels Selectively Regulate Translation and Lineage Commitment in Human Hematopoiesis.

Blood cell formation is classically thought to occur through a hierarchical differentiation process, although recent studies have shown that lineage commitment may occur earlier in hematopoietic stem and progenitor cells (HSPCs). The relevance to human blood diseases and the underlying regulation of these refined models remain poorly understood. By studying a genetic blood disorder, Diamond-Blackfan anemia (DBA), where the majority of mutations affect ribosomal proteins and the erythroid lineage is selectively perturbed, we are able to gain mechanistic insight into how lineage commitment is programmed normally and disrupted in disease. We show that in DBA, the pool of available ribosomes is limited, while ribosome composition remains constant. Surprisingly, this global reduction in ribosome levels more profoundly alters translation of a select subset of transcripts. We show how the reduced translation of select transcripts in HSPCs can impair erythroid lineage commitment, illuminating a regulatory role for ribosome levels in cellular differentiation.

Outcomes of hematopoietic stem cell gene therapy for Wiskott-Aldrich syndrome.

Wiskott-Aldrich syndrome (WAS) is a rare X-linked disorder characterized by combined immunodeficiency, eczema, microthrombocytopenia, autoimmunity, and lymphoid malignancies. Gene therapy (GT) to modify autologous CD34+ cells is an emerging alternative treatment with advantages over standard allogeneic hematopoietic stem cell transplantation for patients who lack well-matched donors, avoiding graft-versus-host-disease. We report the outcomes of a phase 1/2 clinical trial in which 5 patients with severe WAS underwent GT using a self-inactivating lentiviral vector expressing the human WAS complementary DNA under the control of a 1.6-kB fragment of the autologous promoter after busulfan and fludarabine conditioning. All patients were alive and well with sustained multilineage vector gene marking (median follow-up: 7.6 years). Clinical improvement of eczema, infections, and bleeding diathesis was universal. Immune function was consistently improved despite subphysiologic levels of transgenic WAS protein expression. Improvements in platelet count and cytoskeletal function in myeloid cells were most prominent in patients with high vector copy number in the transduced product. Two patients with a history of autoimmunity had flares of autoimmunity after GT, despite similar percentages of WAS protein-expressing cells and gene marking to those without autoimmunity. Patients with flares of autoimmunity demonstrated poor numerical recovery of T cells and regulatory T cells (Tregs), interleukin-10-producing regulatory B cells (Bregs), and transitional B cells. Thus, recovery of the Breg compartment, along with Tregs appears to be protective against development of autoimmunity after GT. These results indicate that clinical and laboratory manifestations of WAS are improved with GT with an acceptable safety profile. This trial is registered at clinicaltrials.gov as #NCT01410825.

Congenital anemia reveals distinct targeting mechanisms for master transcription factor GATA1.

Master regulators, such as the hematopoietic transcription factor (TF) GATA1, play an essential role in orchestrating lineage commitment and differentiation. However, the precise mechanisms by which such TFs regulate transcription through interactions with specific cis-regulatory elements remain incompletely understood. Here, we describe a form of congenital hemolytic anemia caused by missense mutations in an intrinsically disordered region of GATA1, with a poorly understood role in transcriptional regulation. Through integrative functional approaches, we demonstrate that these mutations perturb GATA1 transcriptional activity by partially impairing nuclear localization and selectively altering precise chromatin occupancy by GATA1. These alterations in chromatin occupancy and concordant chromatin accessibility changes alter faithful gene expression, with failure to both effectively silence and activate select genes necessary for effective terminal red cell production. We demonstrate how disease-causing mutations can reveal regulatory mechanisms that enable the faithful genomic targeting of master TFs during cellular differentiation.

The Genetic Landscape of Diamond-Blackfan Anemia.

Diamond-Blackfan anemia (DBA) is a rare bone marrow failure disorder that affects 7 out of 1,000,000 live births and has been associated with mutations in components of the ribosome. In order to characterize the genetic landscape of this heterogeneous disorder, we recruited a cohort of 472 individuals with a clinical diagnosis of DBA and performed whole-exome sequencing (WES). We identified relevant rare and predicted damaging mutations for 78% of individuals. The majority of mutations were singletons, absent from population databases, predicted to cause loss of function, and located in 1 of 19 previously reported ribosomal protein (RP)-encoding genes. Using exon coverage estimates, we identified and validated 31 deletions in RP genes. We also observed an enrichment for extended splice site mutations and validated their diverse effects using RNA sequencing in cell lines obtained from individuals with DBA. Leveraging the size of our cohort, we observed robust genotype-phenotype associations with congenital abnormalities and treatment outcomes. We further identified rare mutations in seven previously unreported RP genes that may cause DBA, as well as several distinct disorders that appear to phenocopy DBA, including nine individuals with biallelic CECR1 mutations that result in deficiency of ADA2. However, no new genes were identified at exome-wide significance, suggesting that there are no unidentified genes containing mutations readily identified by WES that explain >5% of DBA-affected case subjects. Overall, this report should inform not only clinical practice for DBA-affected individuals, but also the design and analysis of rare variant studies for heterogeneous Mendelian disorders.

Macrothrombocytopenia associated with a rare GFI1B missense variant confounding the presentation of immune thrombocytopenia.

Growth factor-independent 1B (GFI1B) variants are a rare cause of thrombocytopenia. We report on a male child who was initially diagnosed with immune thrombocytopenia. However, subtle clinical signs led to suspicion of a genetic cause of thrombocytopenia. Gene panel sequencing revealed a rare variant in GFI1B (C168F), which has recently been reported in several families with thrombocytopenia. We demonstrate that this variant significantly alters platelet parameters in population studies. This case highlights how diagnoses of exclusion, such as immune thrombocytopenia, can be confounded by genetic variation. Our understanding of blood disorders will undoubtedly evolve from an increased knowledge of human genetic variation.

Insight into GATA1 transcriptional activity through interrogation of cis elements disrupted in human erythroid disorders.

Whole-exome sequencing has been incredibly successful in identifying causal genetic variants and has revealed a number of novel genes associated with blood and other diseases. One limitation of this approach is that it overlooks mutations in noncoding regulatory elements. Furthermore, the mechanisms by which mutations in transcriptionalcis-regulatory elements result in disease remain poorly understood. Here we used CRISPR/Cas9 genome editing to interrogate three such elements harboring mutations in human erythroid disorders, which in all cases are predicted to disrupt a canonical binding motif for the hematopoietic transcription factor GATA1. Deletions of as few as two to four nucleotides resulted in a substantial decrease (>80%) in target gene expression. Isolated deletions of the canonical GATA1 binding motif completely abrogated binding of the cofactor TAL1, which binds to a separate motif. Having verified the functionality of these three GATA1 motifs, we demonstrate strong evolutionary conservation of GATA1 motifs in regulatory elements proximal to other genes implicated in erythroid disorders, and show that targeted disruption of such elements results in altered gene expression. By modeling transcription factor binding patterns, we show that multiple transcription factors are associated with erythroid gene expression, and have created predictive maps modeling putative disruptions of their binding sites at key regulatory elements. Our study provides insight into GATA1 transcriptional activity and may prove a useful resource for investigating the pathogenicity of noncoding variants in human erythroid disorders.

Developmentally-faithful and effective human erythropoiesis in immunodeficient and Kit mutant mice.

Immunodeficient mouse models have been valuable for studies of human hematopoiesis, but high-fidelity recapitulation of erythropoiesis in most xenograft recipients remains elusive. Recently developed immunodeficient and Kit mutant mice, however, have provided a suitable background to achieve higher-level human erythropoiesis after long-term hematopoietic engraftment. While there has been some characterization of human erythropoiesis in these models, a comprehensive analysis from various human developmental stages has not yet been reported. Here, we have utilized cell surface phenotypes, morphologic analyses, and molecular studies to fully characterize human erythropoiesis from multiple developmental stages in immunodeficient and Kit mutant mouse models following long-term hematopoietic stem and progenitor cell engraftment. We show that human erythropoiesis in such models demonstrates complete maturation and enucleation, as well as developmentally appropriate globin gene expression. These results provide a framework for future studies to utilize this model system for interrogating disorders affecting human erythropoiesis and for developing improved therapeutic approaches.

Onconase induces autophagy sensitizing pancreatic cancer cells to gemcitabine and activates Akt/mTOR pathway in a ROS-dependent manner.

Onconase® (ONC) is a member of the RNase super-family that is secreted in oocytes and early embryos of Rana pipiens. Over the last years, research interest about this small and basic frog RNase, also called ranpirnase, constantly increased because of its high cytotoxicity and anticancer properties. Onconase is currently used in clinical trials for cancer therapy; however, the precise mechanisms determining cytotoxicity in cancer cells have not yet been fully investigated. In the present manuscript, we evaluate the antitumoral property of onconase in pancreatic adenocarcinoma cells and in non-tumorigenic cells as a control. We demonstrate that ONC stimulates a strong antiproliferative and proapoptotic effect in cancer cells by reporting for the first time that ONC triggers Beclin1-mediated autophagic cancer cell death. In addition, ONC inhibits the expression of mitochondrial uncoupling protein 2 (UCP2) and of manganese-dependent superoxide dismutase (MnSOD) triggering mitochondrial superoxide ion production. ONC-induced reactive oxygen species (ROS) are responsible for Akt/mTOR pathway stimulation determining the sensitivity of cancer cells to mTOR inhibitors and lessening autophagic stimulation. This indicates ROS/Akt/mTOR axis as a strategy adopted by cancer cells to reduce ONC-mediated cytotoxic autophagy stimulation. In addition, we demonstrate that ONC can sensitize pancreatic cancer cells to the standard chemotherapeutic agent gemcitabine allowing a reduction of drug concentration when used in combination settings, thus suggesting a lowering of chemotherapy-related side effects. Altogether, our results shed more light on the mechanisms lying at the basis of ONC antiproliferative effect in cancer cells and support its potential use to develop new anticancer strategies.

Mutant p53 stimulates chemoresistance of pancreatic adenocarcinoma cells to gemcitabine.

Pancreatic adenocarcinoma (PDAC) is the fourth leading cause of cancer-related deaths worldwide; PDAC is characterized by poor prognosis, resistance to conventional chemotherapy and high mortality rate. TP53 tumor suppressor gene is frequently mutated in PDAC, resulting in the accumulation of mutated protein with potential gain-of-function (GOF) activities, such as genomic instability, hyperproliferation and chemoresistance. The purpose of this study was to assess the relevance of the p53 status on the PDAC cells response to the standard drug gemcitabine. We also examined the potential therapeutic effect of p53-reactivating molecules to restore the mutant p53 function in GEM treated PDAC cells. We showed that gemcitabine stabilized mutant p53 protein in the nuclei and induced chemoresistance, concurrent with the mutant p53-dependent expression of Cdk1 and CCNB1 genes, resulting in a hyperproliferation effect. Despite the adverse activation of mutant p53 by gemcitabine, simultaneous treatment of PDAC cells with gemcitabine and p53-reactivating molecules (CP-31398 and RITA) reduced growth rate and induced apoptosis. This synergistic effect was observed in both wild-type and mutant p53 cell lines and was absent in p53-null cells. The combination drug treatment induced p53 phosphorylation on Ser15, apoptosis and autophagosome formation. Furthermore, pharmacological inhibition of autophagy further increased apoptosis stimulated by gemcitabine/CP-31398 treatment. Together, our results show that gemcitabine aberrantly stimulates mutant p53 activity in PDAC cells identifying key processes with potential for therapeutic targeting. Our data also support an anti-tumoral strategy based on inhibition of autophagy combined with p53 activation and standard chemotherapy for both wild-type and mutant p53 expressing PDACs.

Bovine seminal ribonuclease triggers Beclin1-mediated autophagic cell death in pancreatic cancer cells.

Among the large number of variants belonging to the pancreatic-type secretory ribonuclease (RNase) superfamily, bovine pancreatic ribonuclease (RNase A) is the proto-type and bovine seminal RNase (BS-RNase) represents the unique natively dimeric member. In the present manuscript, we evaluate the anti-tumoral property of these RNases in pancreatic adenocarcinoma cell lines and in nontumorigenic cells as normal control. We demonstrate that BS-RNase stimulates a strong anti-proliferative and pro-apoptotic effect in cancer cells, while RNase A is largely ineffective. Notably, we reveal for the first time that BS-RNase triggers Beclin1-mediated autophagic cancer cell death, providing evidences that high proliferation rate of cancer cells may render them more susceptible to autophagy by BS-RNase treatment. Notably, to improve the autophagic response of cancer cells to BS-RNase we used two different strategies: the more basic (as compared to WT enzyme) G38K mutant of BS-RNase, known to interact more strongly than wt with the acidic membrane of cancer cells, or BS-RNase oligomerization (tetramerization or formation of larger oligomers). Both mutant BS-RNase and BS-RNase oligomers potentiated autophagic cell death as compared to WT native dimer of BS-RNase, while the various RNase A oligomers remained completely ineffective. Altogether, our results shed more light on the mechanisms lying at the basis of BS-RNase antiproliferative effect in cancer cells, and support its potential use to develop new anti-cancer strategies.

UCP2, a mitochondrial protein regulated at multiple levels.

An ever-increasing number of studies highlight the role of uncoupling protein 2 (UCP2) in a broad range of physiological and pathological processes. The knowledge of the molecular mechanisms of UCP2 regulation is becoming fundamental in both the comprehension of UCP2-related physiological events and the identification of novel therapeutic strategies based on UCP2 modulation. The study of UCP2 regulation is a fast-moving field. Recently, several research groups have made a great effort to thoroughly understand the various molecular mechanisms at the basis of UCP2 regulation. In this review, we describe novel findings concerning events that can occur in a concerted manner at various levels: Ucp2 gene mutation (single nucleotide polymorphisms), UCP2 mRNA and protein expression (transcriptional, translational, and protein turn-over regulation), UCP2 proton conductance (ligands and post-transcriptional modifications), and nutritional and pharmacological regulation of UCP2.

UCP2 inhibition triggers ROS-dependent nuclear translocation of GAPDH and autophagic cell death in pancreatic adenocarcinoma cells.

Mitochondrial uncoupling protein 2 (UCP2) can moderate oxidative stress by favoring the influx of protons into the mitochondrial matrix, thus reducing electron leakage from respiratory chain and mitochondrial superoxide production. Here, we demonstrate that UCP2 inhibition by genipin or UCP2 siRNA strongly increases reactive oxygen species (ROS) production inhibiting pancreatic adenocarcinoma cell growth. We also show that UCP2 inhibition triggers ROS-dependent nuclear translocation of the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH), formation of autophagosomes, and the expression of the autophagy marker LC3-II. Consistently, UCP2 over-expression significantly reduces basal autophagy confirming the anti-autophagic role of UCP2. Furthermore, we demonstrate that autophagy induced by UCP2 inhibition determines a ROS-dependent cell death, as indicated by the apoptosis decrease in the presence of the autophagy inhibitors chloroquine (CQ) or 3-methyladenine (3-MA), or the radical scavenger NAC. Intriguingly, the autophagy induced by genipin is able to potentiate the autophagic cell death triggered by gemcitabine, the standard chemotherapeutic drug for pancreatic adenocarcinoma, supporting the development of an anti-cancer therapy based on UCP2 inhibition associated to standard chemotherapy. Our results demonstrate for the first time that UCP2 plays a role in autophagy regulation bringing new insights into mitochondrial uncoupling protein field.

Hypomorphic Janus kinase 3 mutations result in a spectrum of immune defects, including partial maternal T-cell engraftment.

BACKGROUND: Mutations in Janus kinase 3 (JAK3) are a cause of severe combined immunodeficiency, but hypomorphic JAK3 defects can result in a milder clinical phenotype, with residual development and function of autologous T cells. Maternal T-cell engraftment is a common finding in infants with severe combined immunodeficiency but is not typically observed in patients with residual T-cell development. OBJECTIVE: We sought to study in detail the molecular, cellular, and humoral immune phenotype and function of 3 patients with hypomorphic JAK3 mutations. METHODS: We analyzed the distribution and function of T and B lymphocytes in 3 patients and studied the in vitro and in vivo responses of maternal T lymphocytes in 1 patient with maternal T-cell engraftment and residual production of autologous T lymphocytes. RESULTS: B cells were present in normal numbers but with abnormal distribution of marginal zone-like and memory B cells. B-cell differentiation to plasmablasts in vitro in response to CD40 ligand and IL-21 was abolished. In 2 patients the T-cell repertoire was moderately restricted. Surprisingly, 1 patient showed coexistence of maternal and autologous T lymphocytes. By using an mAb recognizing the maternal noninherited HLA-A2 antigen, we found that autologous cells progressively accumulated in vivo but did not compete with maternal cells in vitro. CONCLUSION: The study of 3 patients with hypomorphic JAK3 mutations suggests that terminal B-cell maturation/differentiation requires intact JAK3 function, even if partially functioning T lymphocytes are present. Maternal T-cell engraftment can occur in patients with JAK3 mutations despite the presence of autologous T cells.

Role of mitochondrial uncoupling protein 2 in cancer cell resistance to gemcitabine.

Cancer cells exhibit an endogenous constitutive oxidative stress higher than that of normal cells, which renders tumours vulnerable to further reactive oxygen species (ROS) production. Mitochondrial uncoupling protein 2 (UCP2) can mitigate oxidative stress by increasing the influx of protons into the mitochondrial matrix and reducing electron leakage and mitochondrial superoxide generation. Here, we demonstrate that chemical uncouplers or UCP2 over-expression strongly decrease mitochondrial superoxide induction by the anticancer drug gemcitabine (GEM) and protect cancer cells from GEM-induced apoptosis. Moreover, we show that GEM IC(50) values well correlate with the endogenous level of UCP2 mRNA, suggesting a critical role for mitochondrial uncoupling in GEM resistance. Interestingly, GEM treatment stimulates UCP2 mRNA expression suggesting that mitochondrial uncoupling could have a role also in the acquired resistance to GEM. Conversely, UCP2 inhibition by genipin or UCP2 mRNA silencing strongly enhances GEM-induced mitochondrial superoxide generation and apoptosis, synergistically inhibiting cancer cell proliferation. These events are significantly reduced by the addition of the radical scavenger N-acetyl-l-cysteine or MnSOD over-expression, demonstrating a critical role of the oxidative stress. Normal primary fibroblasts are much less sensitive to GEM/genipin combination. Our results demonstrate for the first time that UCP2 has a role in cancer cell resistance to GEM supporting the development of an anti-cancer therapy based on UCP2 inhibition associated to GEM treatment.

Cardiomyogenesis in the aging and failing human heart.

BACKGROUND: Two opposite views of cardiac growth are currently held; one views the heart as a static organ characterized by a large number of cardiomyocytes that are present at birth and live as long as the organism, and the other views the heart a highly plastic organ in which the myocyte compartment is restored several times during the course of life. METHODS AND RESULTS: The average age of cardiomyocytes, vascular endothelial cells (ECs), and fibroblasts and their turnover rates were measured by retrospective (14)C birth dating of cells in 19 normal hearts 2 to 78 years of age and in 17 explanted failing hearts 22 to 70 years of age. We report that the human heart is characterized by a significant turnover of ventricular myocytes, ECs, and fibroblasts, physiologically and pathologically. Myocyte, EC, and fibroblast renewal is very high shortly after birth, decreases during postnatal maturation, remains relatively constant in the adult organ, and increases dramatically with age. From 20 to 78 years of age, the adult human heart entirely replaces its myocyte, EC, and fibroblast compartment ≈8, ≈6, and ≈8 times, respectively. Myocyte, EC, and fibroblast regeneration is further enhanced with chronic heart failure. CONCLUSIONS: The human heart is a highly dynamic organ that retains a remarkable degree of plasticity throughout life and in the presence of chronic heart failure. However, the ability to regenerate cardiomyocytes, vascular ECs, and fibroblasts cannot prevent the manifestations of myocardial aging or oppose the negative effects of ischemic and idiopathic dilated cardiomyopathy.

Autophagy induced by p53-reactivating molecules protects pancreatic cancer cells from apoptosis.

TP53 mutations compromising p53 transcriptional function occur in more than 50 % of human cancers, including pancreatic adenocarcinoma, and render cancer cells more resistant to conventional therapy. In the last few years, many efforts have been addressed to identify p53-reactivating molecules able to restore the wild-type transcriptionally competent conformation of the mutated proteins. Here, we show that two of these compounds, CP-31398 and RITA, induce cell growth inhibition, apoptosis, and autophagy by activating p53/DNA binding and p53 phosphorylation (Ser15), without affecting the total p53 amount. These effects occur in both wild-type and mutant p53 pancreatic adenocarcinoma cell lines, whereas they are much less pronounced in normal human primary fibroblasts. Furthermore, CP-31398 and RITA regulate the axis SESN1-2/AMPK/mTOR by inducing AMPK phosphorylation on Thr172, which has a crucial role in the autophagic response. The protective role of autophagy in cell growth inhibition by CP-31398 and RITA is supported by the finding that the AMPK inhibitor compound C or the autophagy inhibitors chloroquine or 3-methyladenine sensitize both pancreatic adenocarcinoma cell lines to the apoptotic response induced by p53-reactivating molecules. Our results demonstrate for the first time a survival role for autophagy induced by p53-reactivating molecules, supporting the development of an anti-cancer therapy based on autophagy inhibition associated to p53 activation.

The ephrin A1-EphA2 system promotes cardiac stem cell migration after infarction.

RATIONALE: Understanding the mechanisms that regulate trafficking of human cardiac stem cells (hCSCs) may lead to development of new therapeutic approaches for the failing heart. OBJECTIVE: We tested whether the motility of hCSCs in immunosuppressed infarcted animals is controlled by the guidance system that involves the interaction of Eph receptors with ephrin ligands. METHODS AND RESULTS: Within the cardiac niches, cardiomyocytes expressed preferentially the ephrin A1 ligand, whereas hCSCs possessed the EphA2 receptor. Treatment of hCSCs with ephrin A1 resulted in the rapid internalization of the ephrin A1-EphA2 complex, posttranslational modifications of Src kinases, and morphological changes consistent with the acquisition of a motile cell phenotype. Ephrin A1 enhanced the motility of hCSCs in vitro, and their migration in vivo following acute myocardial infarction. At 2 weeks after infarction, the volume of the regenerated myocardium was 2-fold larger in animals injected with ephrin A1-activated hCSCs than in animals receiving control hCSCs; this difference was dictated by a greater number of newly formed cardiomyocytes and coronary vessels. The increased recovery in myocardial mass with ephrin A1-treated hCSCs was characterized by further restoration of cardiac function and by a reduction in arrhythmic events. CONCLUSIONS: Ephrin A1 promotes the motility of EphA2-positive hCSCs, facilitates their migration to the area of damage, and enhances cardiac repair. Thus, in situ stimulation of resident hCSCs with ephrin A1 or their ex vivo activation before myocardial delivery improves cell targeting to sites of injury, possibly providing a novel strategy for the management of the diseased heart.