RESUMO
Diamond Blackfan anaemia (DBA) is a severe congenital failure of erythropoiesis. Despite mutations in one of several ribosome protein genes, including RPS19, the cause of the erythroid specificity is still a mystery. We hypothesized that, because the chromatin of late erythroid cells becomes condensed and transcriptionally inactive prior to enucleation, the rapidly proliferating immature cells require very high ribosome synthetic rates. RNA biogenesis was measured in primary mouse fetal liver erythroid progenitor cells; during the first 24 h, cell number increased three to fourfold while, remarkably, RNA content increased sixfold, suggesting an accumulation of an excess of ribosomes during early erythropoiesis. Retrovirus infected siRNA RPS19 knockdown cells showed reduced proliferation but normal differentiation, and cell cycle analysis showed a G1/S phase delay. p53 protein was increased in the knockdown cells, and the mRNA level for p21, a transcriptional target of p53, was increased. Furthermore, we show that RPS19 knockdown decreased MYB protein, and Kit mRNA was reduced, as was the amount of cell surface KIT protein. Thus, in this small hairpin RNA murine model of DBA, RPS19 insufficient erythroid cells may proliferate poorly because of p53-mediated cell cycle arrest, and also because of decreased expression of the key erythroid signalling protein KIT.
Assuntos
Anemia de Diamond-Blackfan/genética , Eritropoese/genética , Anemia de Diamond-Blackfan/patologia , Anemia de Diamond-Blackfan/fisiopatologia , Diferenciação Celular/genética , Proliferação de Células , Células Cultivadas , Fase G1/genética , Técnicas de Silenciamento de Genes , Genes myb , Humanos , Fígado/citologia , Fígado/embriologia , RNA/biossíntese , RNA Interferente Pequeno/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Proteínas Ribossômicas/genética , Proteína Supressora de Tumor p53/metabolismoRESUMO
Diamond-Blackfan anemia (DBA) is a rare congenital red-cell aplasia characterized by anemia, bone-marrow erythroblastopenia, and congenital anomalies and is associated with heterozygous mutations in the ribosomal protein (RP) S19 gene (RPS19) in approximately 25% of probands. We report identification of de novo nonsense and splice-site mutations in another RP, RPS24 (encoded by RPS24 [10q22-q23]) in approximately 2% of RPS19 mutation-negative probands. This finding strongly suggests that DBA is a disorder of ribosome synthesis and that mutations in other RP or associated genes that lead to disrupted ribosomal biogenesis and/or function may also cause DBA.