Recent insights into the pathogenesis of Diamond-Blackfan anaemia

DNA damage repair in megakaryopoiesis: molecular and clinical aspects

INTRODUCTION

Endogenous DNA damage is a significant factor in the damage of hematopoietic cells. Megakaryopoiesis is one of the pathways of hematopoiesis that ends with the production of platelets and plays the most crucial role in hemostasis. Despite the presence of efficient DNA repair mechanisms, some endogenous lesions can lead to mutagenic alterations, disruption of pathways of hematopoiesis including megakaryopoiesis and potentially result in human diseases.

AREAS COVERED

The complex regulation of DNA repair mechanisms plays a central role in maintaining genomic integrity during megakaryopoiesis and influences platelet production efficiency and quality. Moreover, anomalies in DNA repair processes are involved in several diseases associated with megakaryopoiesis, including myeloproliferative disorders and thrombocytopenia.

EXPERT OPINION

In the era of personalized medicine, diagnosing diseases related to megakaryopoiesis can only be made with a complete assessment of their molecular aspects to provide physicians with critical molecular data for patient management and to identify the subset of patients who could benefit from targeted therapy.

Downregulation of SATB1 by miRNAs Reduces Megakaryocyte/Erythroid Progenitor Expansion in pre-clinical models of Diamond Blackfan Anemia

Diamond Blackfan Anemia (DBA) is an inherited bone marrow failure syndrome that is associated with anemia, congenital anomalies, and cancer predisposition. It is categorized as a ribosomopathy, because over 80% or patients have haploinsufficiency of either a small or large subunit-associated ribosomal protein (RP). The erythroid pathology is predominantly due to a block and delay in early committed erythropoiesis with reduced Megakaryocyte/Erythroid Progenitors (MEPs). To understand the molecular pathways leading to pathogenesis of DBA, we performed RNA-seq on mRNA and miRNA from RPS19-deficient human hematopoietic stem and progenitor cells (HSPCs) and compared an existing database documenting transcript fluctuations across stages of early normal erythropoiesis. We determined the chromatin regulator, SATB1 was prematurely downregulated through the coordinated action of upregulated miR-34 and miR-30 during differentiation in ribosomal-insufficiency. Restoration of SATB1 rescued MEP expansion, leading to a modest improvement in erythroid and megakaryocyte expansion in RPS19-insufficiency. However, SATB1 expression did not impact expansion of committed erythroid progenitors, indicating ribosomal insufficiency impacts multiple stages during erythroid differentiation.

Regulation of ribosomal protein genes: An ordered anarchy

Ribosomal protein genes are among the most highly expressed genes in most cell types. Their products are generally essential for ribosome synthesis, which is the cornerstone for cell growth and proliferation. Many cellular resources are dedicated to producing ribosomal proteins and thus this process needs to be regulated in ways that carefully balance the supply of nascent ribosomal proteins with the demand for new ribosomes. Ribosomal protein genes have classically been viewed as a uniform interconnected regulon regulated in eukaryotic cells by target of rapamycin and protein kinase A pathway in response to changes in growth conditions and/or cellular status. However, recent literature depicts a more complex picture in which the amount of ribosomal proteins produced varies between genes in response to two overlapping regulatory circuits. The first includes the classical general ribosome‐producing program and the second is a gene‐specific feature responsible for fine‐tuning the amount of ribosomal proteins produced from each individual ribosomal gene. Unlike the general pathway that is mainly controlled at the level of transcription and translation, this specific regulation of ribosomal protein genes is largely achieved through changes in pre‐mRNA splicing efficiency and mRNA stability. By combining general and specific regulation, the cell can coordinate ribosome production, while allowing functional specialization and diversity. Here we review the many ways ribosomal protein genes are regulated, with special focus on the emerging role of posttranscriptional regulatory events in fine‐tuning the expression of ribosomal protein genes and its role in controlling the potential variation in ribosome functions.

This article is categorized under:

Translation > Ribosome Biogenesis

Translation > Ribosome Structure/Function

Translation > Translation Regulation

Diamond Blackfan anemia is mediated by hyperactive Nemo-like kinase

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome associated with ribosomal gene mutations that lead to ribosomal insufficiency. DBA is characterized by anemia, congenital anomalies, and cancer predisposition. Treatment for DBA is associated with significant morbidity. Here, we report the identification of Nemo-like kinase (NLK) as a potential target for DBA therapy. To identify new DBA targets, we screen for small molecules that increase erythroid expansion in mouse models of DBA. This screen identified a compound that inhibits NLK. Chemical and genetic inhibition of NLK increases erythroid expansion in mouse and human progenitors, including bone marrow cells from DBA patients. In DBA models and patient samples, aberrant NLK activation is initiated at the Megakaryocyte/Erythroid Progenitor (MEP) stage of differentiation and is not observed in non-erythroid hematopoietic lineages or healthy erythroblasts. We propose that NLK mediates aberrant erythropoiesis in DBA and is a potential target for therapy.

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome that is associated with anemia. Here, the authors examine the role of Nemo-like kinase (NLK) in erythroid cells in the pathogenesis of DBA and as a potential target for therapy.

The Ribosome Biogenesis-Cancer Connection

Multifaceted relations link ribosome biogenesis to cancer. Ribosome biogenesis takes place in the nucleolus. Clarifying the mechanisms involved in this nucleolar function and its relationship with cell proliferation: (1) allowed the understanding of the reasons for the nucleolar changes in cancer cells and their exploitation in tumor pathology, (2) defined the importance of the inhibition of ribosome biogenesis in cancer chemotherapy and (3) focused the attention on alterations of ribosome biogenesis in the pathogenesis of cancer. This review summarizes the research milestones regarding these relevant relationships between ribosome biogenesis and cancer. The structure and function of the nucleolus will also be briefly described.

A small molecule p53 activator attenuates Fanconi anemia leukemic stem cell proliferation

Although p53 mutations are common in solid tumors, such mutations are found at a lower frequency in hematologic malignancies. In the genetic disorder Fanconi anemia (FA), p53 has been proposed as an important pathophysiological factor for two important hematologic hallmarks of the disease: bone marrow failure and leukemogenesis. Here we show that low levels of the p53 protein enhance the capacity of leukemic stem cells from FA patients to repopulate immunodeficient mice. Furthermore, boosting p53 protein levels with the use of the small molecule Nutlin-3 reduced leukemia burden in recipient mice. These results demonstrate that the level of p53 protein plays a crucial role in FA leukemogenesis.

Identification of novel drug targets for diamond-blackfan anemia based on RPS19 gene mutation using protein-protein interaction network

BACKGROUND

Diamond-Blackfan anemia (DBA) is a congenital erythroid aplasia that usually presents in infancy. In order to explore the molecular mechanisms of wild and mutated samples from DBA patients were exposed to bioinformatics investigation. Biological network of differentially expressed genes was constructed. This study aimed to identify novel therapeutic signatures in DBA and uncovered their mechanisms. The gene expression dataset of GSE14335 was used, which consists of 6 normal and 4 diseased cases. The gene ontology (GO), as well as Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed, and then protein-protein interaction (PPI) network of the identified differentially expressed genes (DEGs) was constructed by Cytoscape software.

RESULTS

A total of 607 DEGs were identified in DBA, including 433 upregulated genes and 174 downregulated genes. GO analysis results showed that upregulated DEGs were significantly enriched in biological processes, negative regulation of transcription from RNA polymerase II promoter, chemotaxis, inflammatory response, immune response, positive regulation of cell proliferation, negative regulation of cell proliferation, response to mechanical stimulus, positive regulation of cell migration, response to lipopolysaccharide, and defence response. KEGG pathway analysis revealed the TNF signalling pathway, Osteoclast differentiation, Chemokine signalling pathway, Cytokine -cytokine receptor interaction, Rheumatoid arthritis, Biosynthesis of amino acids, Biosynthesis of antibiotics and Glycine, serine and threonine metabolism. The top 10 hub genes, AKT1, IL6, NFKB1, STAT3, STAT1, RAC1, EGR1, IL8, RELA, RAC3, mTOR and CCR2 were identified from the PPI network and sub-networks.

CONCLUSION

The present study flagged that the identified DEGs and hub genes enrich our understanding of the molecular mechanisms underlying the development of DBA, and might shine some lights on identifying molecular targets and diagnostic biomarkers for DBA.

Fungal Ribotoxins: A Review of Potential Biotechnological Applications

Fungi establish a complex network of biological interactions with other organisms in nature. In many cases, these involve the production of toxins for survival or colonization purposes. Among these toxins, ribotoxins stand out as promising candidates for their use in biotechnological applications. They constitute a group of highly specific extracellular ribonucleases that target a universally conserved sequence of RNA in the ribosome, the sarcin-ricin loop. The detailed molecular study of this family of toxic proteins over the past decades has highlighted their potential in applied research. Remarkable examples would be the recent studies in the field of cancer research with promising results involving ribotoxin-based immunotoxins. On the other hand, some ribotoxin-producer fungi have already been studied in the control of insect pests. The recent role of ribotoxins as insecticides could allow their employment in formulas and even as baculovirus-based biopesticides. Moreover, considering the important role of their target in the ribosome, they can be used as tools to study how ribosome biogenesis is regulated and, eventually, may contribute to a better understanding of some ribosomopathies.

Biological Databases for Hematology Research

With the advances of genome-wide sequencing technologies and bioinformatics approaches, a large number of datasets of normal and malignant erythropoiesis have been generated and made public to researchers around the world. Collection and integration of these datasets greatly facilitate basic research and clinical diagnosis and treatment of blood disorders. Here we provide a brief introduction of the most popular omics data resources of normal and malignant hematopoiesis, including some integrated web tools, to help users get better equipped to perform common analyses. We hope this review will promote the awareness and facilitate the usage of public database resources in the hematology research.

RPS24 knockdown inhibits colorectal cancer cell migration and proliferation in vitro

Besides new proteins synthesis, ribosomal protein has a role in extra-ribosomal functions, which are related to many diseases, such as Diamond-Blackfan anemia, hypoplasia, and cell apoptosis. However, the importance of RPS24 in human colon cancer is largely unknown. In this study, RPS24 gene expression was significantly inhibited in human colon cancer HCT116 and HT-29 cells using a lentivirus shRNA approach. Knockdown of RPS24 expression significantly inhibited cell proliferation, colony formation, cell migration and arrested cell in S phase. The results demonstrated for the first time that RPS24 gene had a critical role in human colon cancer. Therefore, our findings indicated that RPS24 gene may be a promising biomarker for therapy in human colon cancer and may have a potential application in the diagnosis or treatment of human colon cancer.

Ribosomopathies: Global process, tissue specific defects

Disruptions in ribosomal biogenesis would be expected to have global and in fact lethal effects on a developing organism. However, mutations in ribosomal protein genes have been shown in to exhibit tissue specific defects. This seemingly contradictory finding - that globally expressed genes thought to play fundamental housekeeping functions can in fact exhibit tissue and cell type specific functions - provides new insight into roles for ribosomes, the protein translational machinery of the cell, in regulating normal development and disease. Furthermore it illustrates the surprisingly dynamic nature of processes regulating cell type specific protein translation. In this review, we discuss our current knowledge of a variety of ribosomal protein mutations associated with human disease, and models to better understand the molecular mechanisms associated with each. We use specific examples to emphasize both the similarities and differences between the effects of various human ribosomal protein mutations. Finally, we discuss areas of future study that are needed to further our understanding of the role of ribosome biogenesis in normal development, and possible approaches that can be used to treat debilitating ribosomopathy diseases.

Systematic transcriptome analysis of the zebrafish model of diamond-blackfan anemia induced by RPS24 deficiency

BACKGROUND

Diamond-Blackfan anemia (DBA) is a class of human diseases linked to defective ribosome biogenesis that results in clinical phenotypes. Genetic mutations in ribosome protein (RP) genes lead to DBA phenotypes, including hematopoietic defects and physical deformities. However, little is known about the global regulatory network as well as key miRNAs and gene pathways in the zebrafish model of DBA.

RESULTS

In this study, we establish the DBA model in zebrafish using an RPS24 morpholino and found that RPS24 is required for both primitive hematopoiesis and definitive hematopoiesis processes that are partially mediated by the p53 pathway. Several deregulated genes and miRNAs were found to be related to hematopoiesis, vascular development and apoptosis in RPS24-deficient zebrafish via RNA-seq and miRNA-seq data analysis, and a comprehensive regulatory network was first constructed to identify the mechanisms of key miRNAs and gene pathways in the model. Interestingly, we found that the central node genes in the network were almost all targeted by significantly deregulated miRNAs. Furthermore, the enforced expression of miR-142-3p, a uniquely expressed miRNA, causes a significant decrease in primitive erythrocyte progenitor cells and HSCs.

CONCLUSIONS

The present analyses demonstrate that the comprehensive regulatory network we constructed is useful for the functional prediction of new and important miRNAs in DBA and will provide insights into the pathogenesis of mutant rps24-mediated human DBA disease.

Differential transcript accumulation and subcellular localization of Arabidopsis ribosomal proteins

Arabidopsis cytoplasmic ribosomes are an assembly of four rRNAs and 81 ribosomal proteins (RPs). With only a single molecule of each RP incorporated into any given ribosome, an adequate level of each RP in the nucleolus is a prerequisite for efficient ribosome biogenesis. Using Genevestigator (microarray data analysis tool), we have studied transcript levels of 192 of the 254 Arabidopsis RP genes, as well as the sub-cellular localization of each of five two-member RP families, to identify the extent to which these two processes contribute to the nucleolar pool of RPs available for ribosome biogenesis. While transcript levels from different RP genes show up to a 300-fold difference across the RP population, this difference is drastically reduced to ∼8-fold when considering RP gene families. Under various stimuli, while the transcript level for most RP genes remains unchanged some show a significantly increased or decreased level. Subcellular localization studies in tobacco not only showed differential targeting of RPs to the cytoplasm, nucleus and nucleolus, but also differential nucleolar import rates. This degree of variation in gene regulation and subcellular localization of RPs hints at the possibility of extra-ribosomal functions for some RP isoforms.

Transcriptome analysis of the zebrafish model of Diamond-Blackfan anemia from RPS19 deficiency via p53-dependent and -independent pathways

Diamond-Blackfan anemia (DBA) is a rare inherited bone marrow failure syndrome that is characterized by pure red-cell aplasia and associated physical deformities. It has been proven that defects of ribosomal proteins can lead to this disease and that RPS19 is the most frequently mutated gene in DBA patients. Previous studies suggest that p53-dependent genes and pathways play important roles in RPS19-deficient embryos. However, whether there are other vital factors linked to DBA has not been fully clarified. In this study, we compared the whole genome RNA-Seq data of zebrafish embryos injected with RPS19 morpholino (RPS19 MO), RPS19 and p53 morpholino simultaneously (RPS19+p53 MO) and control morpholino (control). We found that genes enriched in the functions of hematological systems, nervous system development and skeletal and muscular disorders had significant differential expression in RPS19 MO embryos compared with controls. Co-inhibition of p53 partially alleviates the abnormalities for RPS19-deficient embryos. However, the hematopoietic genes, which were down-regulated significantly in RPS19 MO embryos, were not completely recovered by the co-inhibition of p53. Furthermore, we identified the genome-wide p53-dependent and -independent genes and pathways. These results indicate that not only p53 family members but also other factors have important impacts on RPS19-deficient embryos. The detection of potential pathogenic genes and pathways provides us a new paradigm for future research on DBA, which is a systematic and complex hereditary disease.

RPS19 and TYMS SNPs and Prevalent High Risk Human Papilloma Virus Infection in Nigerian Women

High risk HPV (hrHPV) infection is a necessary cause of cervical cancer but the host genetic determinants of infection are poorly understood. We enrolled 267 women who presented to our cervical cancer screening program in Abuja, Nigeria between April 2012 and August 2012. We collected information on demographic characteristics, risk factors of cervical cancer and obtained samples of blood and cervical exfoliated cells from all participants. We used Roche Linear Array HPV Genotyping Test® to characterize the prevalent HPV according to manufacturer's instruction; Sequenom Mass Array to test 21 SNPs in genes/regions previously associated with hrHPV and regression models to examine independent factors associated with HPV infection. We considered a p<0.05 as significant because this is a replication study. There were 65 women with and 202 women without hrHPV infection. Under the allelic model, we found significant association between two SNPs, rs2305809 on RPS19 and rs2342700 on TYMS, and prevalent hrHPV infection. Multivariate analysis of hrHPV risk adjusted for age, body mass index, smoking, age of menarche, age at sexual debut, lifetime total number of sexual partners and the total number of pregnancies as covariates, yielded a p-value of 0.071 and 0.010 for rs2305809 and rs2342700, respectively. Our findings in this unique population suggest that a number of genetic risk variants for hrHPV are shared with other population groups. Definitive studies with larger sample sizes and using genome wide approaches are needed to understand the genetic architecture of hrHPV risk in multiple populations.

A novel mutation of ribosomal protein S10 gene in a Japanese patient with diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is an inherited bone marrow disease. The condition is characterized by anemia that usually presents during infancy or early childhood and congenital malformation. Several reports show that DBA is associated with mutations in the ribosomal protein (RP) genes, RPS19, RPS24, RPS17, RPL35A, RPL5, RPL11, and RPS7. Recently, 5 and 12 patients with mutations in RPS10 and RPS26, respectively, were identified in a cohort of 117 DBA probands. Therefore, we screened the DBA patients who were negative for mutations in these DBA genes for mutations in RPS10 and RPS26. The present case report describes the identification of the first Japanese DBA patient with a novel mutation in RPS10.

Single nucleotide polymorphisms in the PRDX3 and RPS19 and risk of HPV persistence and cervical precancer/cancer

Background

Host genetic factors might affect the risk of progression from infection with carcinogenic human papillomavirus (HPV), the etiologic agent for cervical cancer, to persistent HPV infection, and hence to cervical precancer and cancer.

Methodology/Principal Findings

We assessed 18,310 tag single nucleotide polymorphisms (SNPs) from 1113 genes in 416 cervical intraepithelial neoplasia 3 (CIN3)/cancer cases, 356 women with persistent carcinogenic HPV infection (median persistence of 25 months) and 425 randomly selected women (non-cases and non-HPV persistent) from the 10,049 women from the Guanacaste, Costa Rica HPV natural history cohort. For gene and SNP associations, we computed age-adjusted odds ratio and p-trend. Three comparisons were made: 1) association with CIN3/cancer (compared CIN3/cancer cases to random controls), 2) association with persistence (compared HPV persistence to random controls), and 3) progression (compared CIN3/cancers with HPV-persistent group). Regions statistically significantly associated with CIN3/cancer included genes for peroxiredoxin 3 PRDX3, and ribosomal protein S19 RPS19. The single most significant SNPs from each gene associated with CIN3/cancer were PRDX3 rs7082598 (P_trend<0.0001), and RPS19 rs2305809 (P_trend=0.0007), respectively. Both SNPs were also associated with progression.

Conclusions/Significance

These data suggest involvement of two genes, RSP19 and PRDX3, or other SNPs in linkage disequilibrium, with cervical cancer risk. Further investigation showed that they may be involved in both the persistence and progression transition stages. Our results require replication but, if true, suggest a role for ribosomal dysfunction, mitochondrial processes, and/or oxidative stress, or other unknown function of these genes in cervical carcinogenesis.

Altered intracellular localization and mobility of SBDS protein upon mutation in Shwachman-Diamond syndrome

Shwachman-Diamond Syndrome (SDS) is a rare inherited disease caused by mutations in the SBDS gene. Hematopoietic defects, exocrine pancreas dysfunction and short stature are the most prominent clinical features. To gain understanding of the molecular properties of the ubiquitously expressed SBDS protein, we examined its intracellular localization and mobility by live cell imaging techniques. We observed that SBDS full-length protein was localized in both the nucleus and cytoplasm, whereas patient-related truncated SBDS protein isoforms localize predominantly to the nucleus. Also the nucleo-cytoplasmic trafficking of these patient-related SBDS proteins was disturbed. Further studies with a series of SBDS mutant proteins revealed that three distinct motifs determine the intracellular mobility of SBDS protein. A sumoylation motif in the C-terminal domain, that is lacking in patient SBDS proteins, was found to play a pivotal role in intracellular motility. Our structure-function analyses provide new insight into localization and motility of the SBDS protein, and show that patient-related mutant proteins are altered in their molecular properties, which may contribute to the clinical features observed in SDS patients.

Ectopic mineralization in the middle ear and chronic otitis media with effusion caused by RPL38 deficiency in the Tail-short (Ts) mouse

Inflammation of the middle ear cavity (otitis media) and the abnormal deposition of bone at the otic capsule are common causes of conductive hearing impairment in children and adults. Although a host of environmental factors can contribute to these conditions, a genetic predisposition has an important role as well. Here, we analyze the Tail-short (Ts) mouse, which harbors a spontaneous semi-dominant mutation that causes skeletal defects and hearing loss. By genetic means, we show that the Ts phenotypes arise from an 18-kb deletion/insertion of the Rpl38 gene, encoding a ribosomal protein of the large subunit. We show that Ts mutants exhibit significantly elevated auditory-brain stem response thresholds and reduced distortion-product otoacoustic emissions, in the presence of normal endocochlear potentials and typical inner ear histology suggestive of a conductive hearing impairment. We locate the cause of the hearing impairment to the middle ear, demonstrating over-ossification at the round window ridge, ectopic deposition of cholesterol crystals in the middle ear cavity, enlarged Eustachian tube, and chronic otitis media with effusion all beginning at around 3 weeks after birth. Using specific antisera, we demonstrate that Rpl38 is an ∼8-kDa protein that is predominantly expressed in mature erythrocytes. Finally, using an Rpl38 cDNA transgene, we rescue the Ts phenotypes. Together, these data present a previously uncharacterized combination of interrelated middle ear pathologies and suggest Rpl38 deficiency as a model to dissect the causative relationships between neo-ossification, cholesterol crystal deposition, and Eustachian tubes in the etiology of otitis media.

Outcomes after related and unrelated umbilical cord blood transplantation for hereditary bone marrow failure syndromes other than Fanconi anemia

BACKGROUND

Allogeneic stem cell transplantation is the only curative option for patients with hereditary bone marrow failure syndromes. Umbilical cord blood is an alternative source of stem cells for allogeneic transplantation.

DESIGN AND METHODS

This multicenter, retrospective study is based on data reported to the Eurocord Registry about patients with hereditary bone marrow failure syndrome who underwent umbilical cord blood transplantation.

RESULTS

Sixty-four patients with hereditary bone marrow failure syndromes were transplanted from related (n = 20) or unrelated donors (n = 44). Diagnoses were Diamond-Blackfan anemia (21 patients), congenital amegakaryocytic thrombocytopenia (16 patients), dyskeratosis congenita (8 patients), Shwachman-Diamond syndrome (2 patients), severe congenital neutropenia (16 patients) and unclassified (1 patient). In the group of patients who received grafts from related donors, all patients but one received an HLA-matched sibling transplant. The median number of total nucleated cells infused was 5 × 10⁷/kg. The cumulative incidence of neutrophil recovery at 60 days was 95%. Two patients had grade II-IV acute graft-versus-host disease, while the 2-year cumulative incidence of chronic graft-versus-host disease was 11%. The 3-year overall survival rate was 95%. In the group of patients who received grafts from unrelated donors, 86% had HLA-mismatched grafts and three received two umbilical cord blood units. The median number of total nucleated cells infused was 6.1 × 10⁷/kg. The cumulative incidence of neutrophil recovery at day 60 in this group was 55%. The 100-day cumulative incidence of grade II-IV acute graft-versus-host disease was 24%, while the 2-year cumulative incidence of chronic graft-versus-host disease was 53%. The 3-year overall survival rate was 61%; better overall survival was associated with age less than 5 years (P = 0.01) and 6.1 × 10⁷/kg or more total nucleated cells infused (P = 0.05).

CONCLUSIONS

In patients with hereditary bone marrow failure syndromes, related umbilical cord blood transplantation is associated with excellent outcomes while increasing cell dose and better HLA matching might provide better results in unrelated umbilical cord blood transplantation.

CpG-ODN 2006 and human parvovirus B19 genome consensus sequences selectively inhibit growth and development of erythroid progenitor cells

Recent studies have shown that anemia is commonly observed after exposure to pathogens or pathogen-derived products, which are recognized via Toll-like receptor 9 (TLR9). In the current study, we demonstrate that CpG oligodeoxynucleotide-2006, a TLR9 ligand with phosphodiester (PO; 2006-PO) but not with the phosphorothioate backbone, selectively inhibits the erythroid growth derived from human CD34(+) cells. The 2006-PO was internalized by the erythroid progenitors within 30 minutes; however, expression of TLR9 mRNA was not detected in these cells. The 2006-PO directly inhibited burst-forming unit-erythroid growth, resulted in the accumulation of cells in S and G(2)/M phases, and increased cell size and frequency of apoptotic cells. These features were similar to those observed in erythroid progenitors infected with human parvovirus B19 that causes pure red cell aplasia. The consensus sequence of 2006-PO was defined as 5'-GTTTTGT-3', which was located in the P6-promoter region of B19 and inhibited erythroid growth in a sequence-specific manner and down-regulated expression of erythropoietin receptor (EPOR) mRNA and EPOR. B19 genome extracted from serum also inhibited erythroid growth and down-regulated expression of EPOR on glycophorin A(+) cells. These results provide a possible insight into our understanding of the mechanisms of human parvovirus B19-mediated inhibition of erythropoiesis.

The p53 tumor suppressor protein is a critical regulator of hematopoietic stem cell behavior

In response to diverse stresses, the tumor suppressor p53 differentially regulates its target genes, variably inducing cell-cycle arrest, apoptosis or senescence. Emerging evidence indicates that p53 plays an important role in regulating hematopoietic stem cell (HSC) quiescence, self-renewal, apoptosis and aging. The p53 pathway is activated by DNA damage, defects in ribosome biogenesis, oxidative stress and oncogene induced p19 ARF upregulation. We present an overview of the current state of knowledge about p53 (and its target genes) in regulating HSC behavior, with the hope that understanding the molecular mechanisms that control p53 activity in HSCs and how p53 mutations affect its role in these events may facilitate the development of therapeutic strategies for eliminating leukemia (and cancer) propagating cells.

Thrombocytopenia and anemia in infants and children

Thrombocytopenia and anemia are the two most common hematologic conditions seen in the pediatric emergency department. Providers of emergency pediatric care must have an understanding of the causes and therapies for the various conditions that result from thrombocytopenia and anemia. This article reviews the common causes of isolated thrombocytopenia and anemia in infancy and childhood.

Identification of mutations in the ribosomal protein L5 (RPL5) and ribosomal protein L11 (RPL11) genes in Czech patients with Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a congenital red blood cell aplasia that is usually diagnosed during early infancy. Apart from defects in red blood cell maturation, the disorder is also associated with various physical anomalies in 40% of patients. Mutations in the ribosomal protein (RP) S19 are found in 25% of patients, while mutations in other proteins of the small ribosomal subunit--RPS17 and RPS24--have been found in a fraction of patients. Recently, mutations in RPL5, RPL11, and RPL35a of the large ribosomal subunit have also been reported in several DBA patients. Here, we present the identification of mutations in the RPL5 and RPL11 genes in patients from the Czech DBA Registry. Mutations in RPL5 were identified in eight patients from 6 out of 28 families (21.4%), and mutations in RPL11 in two patients from 2 out of 28 families (7.1%). Interestingly, all 10 patients with either an RPL5 or RPL11 mutation exhibited one or more physical anomalies; specifically, thumb anomalies (flat thenar) were always present, while no such anomaly was observed in seven patients with an RPS19 mutation. Moreover, 9 out of 10 patients with either an RPL5 or RPL11 mutation were born small for gestational age (SGA) compared to 3 out of 7 patients from the RPS19-mutated group. These observations may suggest that mutations, at least in RPL5, seem to generally have more profound impact on fetal development than mutations in RPS19. Since RPL5 and RPL11, together with RPL23, are also involved in the MDM2-mediated p53 pathway regulation, we also screened the RPL23 gene for mutations; however, no mutations were identified.

p53-independent apoptosis limits DNA damage-induced aneuploidy

DNA damage or unprotected telomeres can trigger apoptosis via signaling pathways that directly sense abnormal DNA structures and activate the p53 transcription factor. We describe a p53-independent mechanism that acts in parallel to the canonical DNA damage response pathway in Drosophila to induce apoptosis after exposure to ionizing radiation. Following recovery from damage-induced cell cycle arrest, p53 mutant cells activate the JNK pathway and expression of the pro-apoptotic gene hid. Mutations in grp, a cell cycle checkpoint gene, and puc, a negative regulator of the JNK pathway, sensitize p53 mutant cells to ionizing radiation (IR)-induced apoptosis. Induction of chromosome aberrations by DNA damage generates cells with segmental aneuploidy and heterozygous for mutations in ribosomal protein genes. p53-independent apoptosis limits the formation of these aneuploid cells following DNA damage. We propose that reduced copy number of haploinsufficient genes following chromosome damage activates apoptosis and helps maintain genomic integrity.

Ribosomal mutations cause p53-mediated dark skin and pleiotropic effects

Mutations in genes encoding ribosomal proteins cause the Minute phenotype in Drosophila and mice, and Diamond-Blackfan syndrome in humans. Here we report two mouse dark skin (Dsk) loci caused by mutations in Rps19 (ribosomal protein S19) and Rps20 (ribosomal protein S20). We identify a common pathophysiologic program in which p53 stabilization stimulates Kit ligand expression, and, consequently, epidermal melanocytosis via a paracrine mechanism. Accumulation of p53 also causes reduced body size and erythrocyte count. These results provide a mechanistic explanation for the diverse collection of phenotypes that accompany reduced dosage of genes encoding ribosomal proteins, and have implications for understanding normal human variation and human disease.

Ribosomal protein S17 gene (RPS17) is mutated in Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a congenital erythroid aplasia characterized as a normochromic macrocytic anemia with a selective deficiency in red blood cell precursors in otherwise normocellular bone marrow. In 40% of DBA patients, various physical anomalies are also present. Currently two genes are associated with the DBA phenotype--the ribosomal protein (RP) S19 mutated in 25% of DBA patients and RPS24 mutated in approximately 1.4% of DBA patients. Here we report the identification of a mutation in yet another ribosomal protein, RPS17. The mutation affects the translation initiation start codon, changing T to G (c.2T>G), thus eliminating the natural start of RPS17 protein biosynthesis. RNA analysis revealed that the mutated allele was expressed, and the next downstream start codon located at position +158 should give rise to a short peptide of only four amino acids (Met-Ser-Arg-Ile). The mutation arose de novo, since all healthy family members carry the wild-type alleles. The identification of a mutation in the third RP of the small ribosomal subunit in DBA patients further supports the theory that impaired translation may be the main cause of DBA pathogenesis.

Inherited aplastic anaemias/bone marrow failure syndromes

The inherited aplastic anaemias/bone marrow (BM) failure syndromes are a heterogeneous group of disorders characterized by BM failure usually in association with one or more somatic abnormality. The BM failure often presents in childhood but this may not be until adulthood in some cases highlighting the need for the adult haematologist to be aware of these disorders. Indeed some patients initially labelled as "idiopathic aplastic anaemia" are cryptic presentations of these genetic syndromes. Since 1992, when the first Fanconi anaemia (FA) gene was cloned there have been considerable advances in the genetics of these syndromes. These advances are beginning to provide a better understanding of normal haemopoiesis and how this might be disrupted in patients with BM failure. They have also provided important insights into some fundamental biological pathways: DNA repair-FA/BRCA pathway; telomere maintenance- dyskeratosis congenita related genes; ribosome biogenesis-Shwachman Diamond syndrome and Diamond-Blackfan anaemia genes. Additionally, as these disorders are usually associated with developmental abnormalities and an increased risk of cancer they are providing new insights into human development and the genesis of cancer. These advances have led to improved diagnosis of patients with these disorders. They may now also provide the platform for developing new treatments.

Roles of the negatively charged N-terminal extension of Saccharomyces cerevisiae ribosomal protein S5 revealed by characterization of a yeast strain containing human ribosomal protein S5

Ribosomal protein (rp) S5 belongs to a family of ribosomal proteins that includes bacterial rpS7. rpS5 forms part of the exit (E) site on the 40S ribosomal subunit and is essential for yeast viability. Human rpS5 is 67% identical and 79% similar to Saccharomyces cerevisiae rpS5 but lacks a negatively charged (pI approximately 3.27) 21 amino acid long N-terminal extension that is present in fungi. Here we report that replacement of yeast rpS5 with its human homolog yielded a viable yeast strain with a 20%-25% decrease in growth rate. This replacement also resulted in a moderate increase in the heavy polyribosomal components in the mutant strain, suggesting either translation elongation or termination defects, and in a reduction in the polyribosomal association of the elongation factors eEF3 and eEF1A. In addition, the mutant strain was characterized by moderate increases in +1 and -1 programmed frameshifting and hyperaccurate recognition of the UAA stop codon. The activities of the cricket paralysis virus (CrPV) IRES and two mammalian cellular IRESs (CAT-1 and SNAT-2) were also increased in the mutant strain. Consistently, the rpS5 replacement led to enhanced direct interaction between the CrPV IRES and the mutant yeast ribosomes. Taken together, these data indicate that rpS5 plays an important role in maintaining the accuracy of translation in eukaryotes and suggest that the negatively charged N-terminal extension of yeast rpS5 might affect the ribosomal recruitment of specific mRNAs.

Balanced production of ribosomal proteins

Eukaryotic ribosomes contain one molecule each of 79 different proteins. The genes encoding these proteins are usually at widely scattered loci and have distinctive promoters with certain common features. This minireview discusses the means by which cells manage to balance the production of ribosomal proteins so as to end up with equimolar quantities in the ribosome. Regulation at all levels of gene expression, from transcription to protein turnover, is considered.

Molecular basis of Diamond-Blackfan anemia: structure and function analysis of RPS19

Diamond–Blackfan anemia (DBA) is a rare congenital disease linked to mutations in the ribosomal protein genes rps19, rps24 and rps17. It belongs to the emerging class of ribosomal disorders. To understand the impact of DBA mutations on RPS19 function, we have solved the crystal structure of RPS19 from Pyrococcus abyssi. The protein forms a five α-helix bundle organized around a central amphipathic α-helix, which corresponds to the DBA mutation hot spot. From the structure, we classify DBA mutations relative to their respective impact on protein folding (class I) or on surface properties (class II). Class II mutations cluster into two conserved basic patches. In vivo analysis in yeast demonstrates an essential role for class II residues in the incorporation into pre-40S ribosomal particles. This data indicate that missense mutations in DBA primarily affect the capacity of the protein to be incorporated into pre-ribosomes, thus blocking maturation of the pre-40S particles.

Cells depleted for RPS19, a protein associated with Diamond Blackfan Anemia, show defects in 18S ribosomal RNA synthesis and small ribosomal subunit production

The gene encoding the small subunit ribosomal protein 19 (RPS19) is mutated in about 25% of cases of the bone marrow failure syndrome Diamond Blackfan Anemia (DBA), a childhood disease characterized by failure of red cell production. In these cases DBA is inherited as an autosomal dominant trait and RPS19 haploinsufficiency is thought to cause the disease. To study the molecular pathogenesis of DBA we used siRNA to decrease the level of RPS19 in two human cell lines, HeLa cells and U-2 OS osteosarcoma cells. Cells with reduced RPS19 levels showed a dramatic reduction in the amounts of small 40S ribosome subunits and mature 80S ribosomes and an excess of large 60S subunits. These cells were defective in 18S rRNA production and accumulated 21S and 20S nuclear pre-rRNA molecules, suggesting that RPS19 is required for specific steps in rRNA processing. RPS19 depletion produced a reduction in steady-state levels of RPS6 and RPS16 via a post-transcriptional mechanism while the levels of RPL7 and RPL26 were unaltered, indicating that levels of ribosomal proteins are determined by subunit assembly. This has interesting implications for the pathogenesis of DBA suggesting that deficiency of any of the RPS proteins might have a similar effect and thus may be responsible for causing DBA. Finally in cell lines from DBA patients with mutations we find increased levels of 21S rRNA precursors but no abnormality in the ribosome profile on sucrose gradients or in the steady-state levels of RPS19 suggesting that some cells can partially compensate for the loss of one allele of RPS19. We conclude that defects in ribosome biogenesis may underlie the pathology of Diamond Blackfan Anemia.

Ribosomal protein mutations in Diamond‐Blackfan anemia: might they operate upstream from protein synthesis?

The inherited bone marrow failure syndromes are clinically distinct but share some common features. Difficult to treat and typified by a poor prognosis, their pathogenesis is unknown. Recent findings that some patients with the erythroblastopenia Diamond-Blackfan anemia (DBA) have mutations in ribosomal proteins have led to the idea that this and perhaps other bone marrow failure disorders result from an inadequate supply of normally functioning ribosomes. According to this hypothesis, an insufficiency of the protein synthetic capacity limits the replicative potential of cells, with the DBA disease phenotype in particular arising from a block of one or more of the two to four critical, temporally compressed cell divisions in the differentiation program of the erythroid lineage in the fetal liver and the postnatal bone marrow. Here I propose an alternative (but not mutually exclusive) hypothesis centered on nucleoli: the specialized intranuclear domains within which ribosomes are assembled. It was recently discovered that the nucleoli contain cell cycle machinery in close proximity to nascent ribosomes. Although mutations in ribosomal proteins might be expected to negatively influence the cell's protein synthetic capacity, I suggest it is also possible that the DBA mutations directly affect the nucleolus to destabilize or otherwise deregulate the coresident cell cycle machinery. This hypothesis envisions that the ribosomal protein mutations discovered in DBA act upstream from ribosome assembly by interfering with the staging of cell cycle progression machinery in the nucleolus, in a pretranslational mode of pathogenesis.

Diamond-Blackfan anemia: erythropoiesis lost in translation

Diamond-Blackfan anemia (DBA) is a congenital erythroid aplasia that usually presents as macrocytic anemia during infancy. Linkage analysis suggests that at least 4 genes are associated with DBA of which 2 have been identified so far. The known DBA genes encode the ribosomal proteins S19 and S24 accounting for 25% and 2% of the patients, respectively. Herein, we review possible links between ribosomal proteins and erythropoiesis that might explain DBA pathogenesis. Recent studies and emerging findings suggest that a malfunctioning translational machinery may be a cause of anemia in patients with DBA.