Ribosomal proteins sustain morphology, function and phenotype in acute myeloid leukemia blasts

Characterization and targeting of malignant stem cells in patients with advanced myelodysplastic syndromes

Myelodysplastic syndrome (MDS) is a chronic hematologic disorder that frequently evolves to more aggressive stages and in some cases leads to acute myeloid leukemia (AML). MDS arises from mutations in hematopoietic stem cells (HSCs). Thus, to define optimal therapies, it is essential to understand molecular events driving HSC pathogenesis. In this study, we report that during evolution of MDS, malignant HSCs activate distinct cellular programs that render such cells susceptible to therapeutic intervention. Specifically, metabolic analyses of the MDS stem cell compartment show a profound activation of protein synthesis machinery and increased oxidative phosphorylation. Pharmacological targeting of protein synthesis and oxidative phosphorylation demonstrated potent and selective eradication of MDS stem cells in primary human patient specimens. Taken together, our findings indicate that MDS stem cells are reliant on specific metabolic events and that such properties can be targeted prior to the onset of clinically significant AML, during antecedent MDS.

Relationship of differential gene expression profiles in CD34+ myelodysplastic syndrome marrow cells to disease subtype and progression

Microarray analysis with 40 000 cDNA gene chip arrays determined differential gene expression profiles (GEPs) in CD34(+) marrow cells from myelodysplastic syndrome (MDS) patients compared with healthy persons. Using focused bioinformatics analyses, we found 1175 genes significantly differentially expressed by MDS versus normal, requiring a minimum of 39 genes to separately classify these patients. Major GEP differences were demonstrated between healthy and MDS patients and between several MDS subgroups: (1) those whose disease remained stable and those who subsequently transformed (tMDS) to acute myeloid leukemia; (2) between del(5q) and other MDS patients. A 6-gene "poor risk" signature was defined, which was associated with acute myeloid leukemia transformation and provided additive prognostic information for International Prognostic Scoring System Intermediate-1 patients. Overexpression of genes generating ribosomal proteins and for other signaling pathways was demonstrated in the tMDS patients. Comparison of del(5q) with the remaining MDS patients showed 1924 differentially expressed genes, with underexpression of 1014 genes, 11 of which were within the 5q31-32 commonly deleted region. These data demonstrated (1) GEPs distinguishing MDS patients from healthy and between those with differing clinical outcomes (tMDS vs those whose disease remained stable) and cytogenetics [eg, del(5q)]; and (2) molecular criteria refining prognostic categorization and associated biologic processes in MDS.

Bystin-like protein is upregulated in hepatocellular carcinoma and required for nucleologenesis in cancer cell proliferation

The bystin-like (BYSL) gene was previously characterized to encode an accessory protein for cell adhesion that participates in early embryo implantation. It is also involved in 40S ribosomal subunit biogenesis and is found to be expressed in rapidly growing embryo and cancer cell lines. In order to explore the role of BYSL in cancer cell proliferation and growth, we used hepatocellular carcinoma (HCC) as a model. Here, we report that BYSL is crucial for HCC cell growth both in vitro and in vivo. Expression levels of BYSL mRNA and protein in human HCC specimens were markedly increased compared with those seen in adjacent non-cancerous tissue. In vitro, inhibition of BYSL by short hairpin RNA decreased HCC cell proliferation, induced apoptosis and partially arrested the cell cycle in the G2/M phase. In vivo, HCC cells treated with BYSL siRNA failed to form tumors in nude mice after subcutaneous implantation. To determine the cellular basis for BYSL RNAi-induced cell growth arrest, BYSL subcellular localization in mitotic and interphase HepG2 cells was examined. BYSL was present at multiple stages during nucleologenesis, including in nucleolus-derived foci (NDF), perichromosomal regions and the prenucleolar body (PNB) during mitosis. BYSL depletion remarkably suppressed NDF and PNB formation, and disrupted nucleoli assembly after mitosis, resulting in increased apoptosis and reduced tolerance of HCC cells to serum starvation. Taken together, our studies indicate that upregulated BYSL expression plays a role in hepatocarcinogenesis.

MicroRNA-10a binds the 5'UTR of ribosomal protein mRNAs and enhances their translation

MicroRNAs (miRNAs) are small RNAs that function as posttranscriptional regulators of gene expression. miRNAs affect a variety of signaling pathways, and impaired miRNA regulation may contribute to the development of cancer and other diseases. Here we show that miRNA miR-10a interacts with the 5' untranslated region of mRNAs encoding ribosomal proteins to enhance their translation. miR-10a alleviates translational repression of the ribosomal protein mRNAs during amino acid starvation and is required for their translational induction following anisomycin treatment or overexpression of RAS. We show that miR-10a binds immediately downstream of the regulatory 5'TOP motif and that the 5'TOP regulatory complex and miR-10a are functionally interconnected. The results show that miR-10a may positively control global protein synthesis via the stimulation of ribosomal protein mRNA translation and ribosome biogenesis and hereby affect the ability of cells to undergo transformation.

Epigenetic activation of a subset of mRNAs by eIF4E explains its effects on cell proliferation

Background

Translation deregulation is an important mechanism that causes aberrant cell growth, proliferation and survival. eIF4E, the mRNA 5′ cap-binding protein, plays a major role in translational control. To understand how eIF4E affects cell proliferation and survival, we studied mRNA targets that are translationally responsive to eIF4E.

Methodology/Principal Findings

Microarray analysis of polysomal mRNA from an eIF4E-inducible NIH 3T3 cell line was performed. Inducible expression of eIF4E resulted in increased translation of defined sets of mRNAs. Many of the mRNAs are novel targets, including those that encode large- and small-subunit ribosomal proteins and cell growth-related factors. In addition, there was augmented translation of mRNAs encoding anti-apoptotic proteins, which conferred resistance to endoplasmic reticulum-mediated apoptosis.

Conclusions/Significance

Our results shed new light on the mechanisms by which eIF4E prevents apoptosis and transforms cells. Downregulation of eIF4E and its downstream targets is a potential therapeutic option for the development of novel anti-cancer drugs.

Nucleolar adaptation in human cancer

While the nucleolus was first observed over two hundred years ago, its role in human cancers is only now being appreciated. Long thought to be a static, ribosome-producing, subnuclear organelle, recent investigations have shown a more dynamic and adaptable side of the nucleolus. Containing not only proteins for the production of ribosomes but also newfound nucleolar oncogenes and tumor suppressors, mechanistic links between the nucleolus and cancer are now more evident. In this regard, much of the work from the past decade has focused on the ability of these proteins to promote and suppress tumorigenesis from the nucleolus. In this review, we will discuss how historical measurements of the nucleolus are being translated into contemporary studies of nucleolar dysfunction in human cancer.

Does the ribosome translate cancer?

Ribosome biogenesis and translation control are essential cellular processes that are governed at numerous levels. Several tumour suppressors and proto-oncogenes have been found either to affect the formation of the mature ribosome or to regulate the activity of proteins known as translation factors. Disruption in one or more of the steps that control protein biosynthesis has been associated with alterations in the cell cycle and regulation of cell growth. Therefore, certain tumour suppressors and proto-oncogenes might regulate malignant progression by altering the protein synthesis machinery. Although many studies have correlated deregulation of protein biosynthesis with cancer, it remains to be established whether this translates directly into an increase in cancer susceptibility, and under what circumstances.

Concurrent measurement of antigen- and antibody-dependent oxidative burst and phagocytosis in monocytes and neutrophils

The current study aims to review flow cytometric (FCM) parameters for the quantification of phagocytosis. A limitation of existing methods is their difficulty with accurate quantification of the phagocytic index, i.e., number of beads per phagocyte, in individual cell lines in mixed cell suspensions. We have quantified phagocytosis and the oxidative burst simultaneously using fluorescent beads coated with meningococcal outer membrane vesicles (OMV beads) by the conversion of dihydrorhodamine 123 (DHR-123) to rhodamine 123 (R-123). Both these processes depend on specific serum opsonins. After the incubation, staining with a fluorescent anti-CD14 monoclonal antibody succeeded in discriminating phagocytosing monocytes from neutrophils. The spectral overlaps between OMV beads, R-123, and anti-CD14 could be completely compensated. Percentage of phagocytosis and the phagocytic index were similar in monocytes and neutrophils, but the oxidative burst behaved differently. Two monocyte subpopulations were observed. Both subpopulations spontaneously converted some DHR-123 into R-123, whereas the reaction was triggered by phagocytosis in neutrophils. The total oxidative response increased with increasing phagocytic index in both cell types, but the oxidative burst in monocytes was about twice that of neutrophils. The oxidative ratio (mean R-123 fluorescence value divided by the phagocytic index) declined with time in monocytes, but increased in neutrophils. Our results demonstrate the need for careful attention to technical details. This single-laser, three-color FCM method facilitates the comparative research of phagocytosis and the oxidative burst in monocytes and neutrophils and provides a basis for a number of applications in hematology, infectious medicine, and immunology.

Extra-Ribosomal Functions of the Ribosomal Protein, RPS3 as Predicted by In Silico Analysis

Products of ribosomal protein (RP) genes have been found to play extra-ribosomal roles that range from DNA repair to RNA splicing. Their association with congenital disorders or cancers has also been widely documented. However, the relatively large number of different RPs, each with perhaps unique biological roles, has compounded the comprehensive elucidation of the physiological functions of each RPs. Experimental functional studies on the many and variegated RPs are labour intensive, time-consuming and costly. Moreover, experimental studies unguided by theoretically insights entail inaccurate results. Therefore, knowledge on the actual roles of these proteins remains largely undefined. A valid alternative is the use of bioinformatics resources to computationally predict functional roles of these biomolecules. Findings from such in silico studies of the RPS3 are reported herein. We reveal an array of possible extra-ribosomal functions that includes regulation of transcription (including via NF-κB-mediated, POK-induced and DNA-dependent), regulation of p53 activities and its stabilisation, inflammatory immune response, modulation of nNOS activities, and anti-oxidative capabilities. Our findings provide computational prediction of de novo extra-ribosomal functions of RPS3. These results will enhance the theoretical basis for designing future experimental studies on elucidating its definitive physiological roles.