Dissecting the transcriptional phenotype of ribosomal protein deficiency: implications for Diamond-Blackfan Anemia.

Defects in genes encoding ribosomal proteins cause Diamond Blackfan Anemia (DBA), a red cell aplasia often associated with physical abnormalities. Other bone marrow failure syndromes have been attributed to defects in ribosomal components but the link between erythropoiesis and the ribosome remains to be fully defined. Several lines of evidence suggest that defects in ribosome synthesis lead to "ribosomal stress" with p53 activation and either cell cycle arrest or induction of apoptosis. Pathways independent of p53 have also been proposed to play a role in DBA pathogenesis. We took an unbiased approach to identify p53-independent pathways activated by defects in ribosome synthesis by analyzing global gene expression in various cellular models of DBA. Ranking-Principal Component Analysis (Ranking-PCA) was applied to the identified datasets to determine whether there are common sets of genes whose expression is altered in these different cellular models. We observed consistent changes in the expression of genes involved in cellular amino acid metabolic process, negative regulation of cell proliferation and cell redox homeostasis. These data indicate that cells respond to defects in ribosome synthesis by changing the level of expression of a limited subset of genes involved in critical cellular processes. Moreover, our data support a role for p53-independent pathways in the pathophysiology of DBA.

Loss of GATA-1 full length as a cause of Diamond-Blackfan anemia phenotype.

Mutations in the hematopoietic transcription factor GATA-1 alter the proliferation/differentiation of hemopoietic progenitors. Mutations in exon 2 interfere with the synthesis of the full-length isoform of GATA-1 and lead to the production of a shortened isoform, GATA-1s. These mutations have been found in patients with Diamond-Blackfan anemia (DBA), a congenital erythroid aplasia typically caused by mutations in genes encoding ribosomal proteins. We sequenced GATA-1 in 23 patients that were negative for mutations in the most frequently mutated DBA genes. One patient showed a c.2T > C mutation in the initiation codon leading to the loss of the full-length GATA-1 isoform.

Differential proteomic analysis in human cells subjected to ribosomal stress.

The biochemical phenotype of cells affected by ribosomal stress has not yet been studied in detail. Here we report a comparative proteomic analysis of cell lines silenced for the RPS19 gene versus cell lines transfected with scramble shRNA cells performed using the DIGE technology integrated to bioinformatics tools. Importantly, to achieve the broadest possible understanding of the outcome, we carried out two independent DIGE experiments using two different pH ranges, thus, allowing the identification of 106 proteins. Our data revealed the deregulation of proteins involved in cytoskeleton reorganization, PTMs, and translation process. A subset (26.9%) of these proteins is translated from transcripts that include internal ribosome entry site motifs. This supports the hypothesis that during ribosomal stress translation of specific messenger RNAs is altered.

Compound heterozygosity for two new TERT mutations in a patient with aplastic anemia.

Dyskeratosis congenita (DC) is a genetically heterogeneous syndrome characterized by reticular skin pigmentation, nail dystrophy, mucosal leukoplakia, short telomeres, and a predisposition to bone marrow failure and malignancy. Patients carrying mutations in TERT show a wide clinical spectrum of abnormalities, including classical DC, isolated bone marrow failure and lung fibrosis. Here, we report the clinical description and biological analysis of a patient with compound heterozygosity for two new missense mutations in TERT (V96L and V119L). Both mutations segregate with a short telomere phenotype, though only V96L segregates with clinical signs of DC.

Analysis of telomeres in peripheral blood cells from patients with bone marrow failure.

BACKGROUND: The determination of telomere length is useful for the characterization of dyskeratosis congenita (DC) and of aplastic anemias (AA) as well as hematological malignancies. Short telomeres result from a specific defect of telomere maintenance in DC and likely from higher cellular turnover in AA and hematological malignancies. Data are not conclusive for Diamond-Blackfan anemia (DBA), a pure erythroid aplasia due to defects of ribosomal proteins. Our aim was to evaluate the utility of a qPCR method for telomere length assessment to evaluate the diagnostic contribution of telomere measurement in bone marrow failure syndromes (BMFS). PROCEDURE: Telomere length was evaluated by qPCR in peripheral blood cells from 95 normal individuals and 62 patients with BMFS, including 45 patients with DBA. RESULTS: Results obtained with qPCR are comparable with other quantitative methods, such as flow-FISH and Southern blotting. Our data show that only one DBA patient and a minority of other BMFS patients have very short telomeres, defined as less than the 1st percentile of controls. CONCLUSIONS: The qPCR method for telomere length evaluation is an easy alternative to other methods and may thus be valuable in a clinical hematological laboratory setting. Telomere maintenance does not seem to be involved in the pathogenesis of DBA unlike in other BMFSs.

NOLA1 gene mutations in acquired aplastic anemia.

BACKGROUND: Telomerase complex genes mutations (DKC1, TERC, TERT, and NOP10) lead to premature telomere shortening and are responsible for different forms of dyskeratosis congenita. TERC and TERT mutations were also found in patients with aplastic anemia. The aim of this work is to analyze the possible involvement of the telomerase complex gene NOLA1, in a population of Italian AA patients. PROCEDURE: DNA of 108 AA patients and 170 normal controls was amplified by PCR and analyzed by DHPLC. For each abnormal elution profile PCR products was directly sequenced using ABI prism 3100 Genetic Analyzer. RESULTS: We identified, in two patients and two control, the new c.390A > T variation, which is not reported in GenBank, and leads to p.H28L amino acidic change. Telomere analysis shows that the subjects carrying the change have a telomere length comparable to that of healthy controls thus suggesting that this variation has no effect on telomerase complex activity. CONCLUSIONS: We did not find any clear disruptive mutation in NOLA1 gene. The non-conservative variation identified in our sample has no effect on telomeres length. This result suggests that heterozygous point mutations in NOLA1 gene are not responsible for AA in our patients at least acting via telomere. However, in our experience, molecular analysis of other telomerase complex gene (TERC, TERT) is important for AA patients and family members in order to set up an adequate therapeutic or surveillance program and identify carriers or exclude them as potential bone marrow donors.