RESUMO
A substantial number of individuals with bone marrow failure (BMF) present with one or more extra-hematopoietic abnormality. This suggests a constitutional or inherited basis, and yet many of them do not fit the diagnostic criteria of the known BMF syndromes. Through exome sequencing, we have now identified a subgroup of these individuals, defined by germline biallelic mutations in DNAJC21 (DNAJ homolog subfamily C member 21). They present with global BMF, and one individual developed a hematological cancer (acute myeloid leukemia) in childhood. We show that the encoded protein associates with rRNA and plays a highly conserved role in the maturation of the 60S ribosomal subunit. Lymphoblastoid cells obtained from an affected individual exhibit increased sensitivity to the transcriptional inhibitor actinomycin D and reduced amounts of rRNA. Characterization of mutations revealed impairment in interactions with cofactors (PA2G4, HSPA8, and ZNF622) involved in 60S maturation. DNAJC21 deficiency resulted in cytoplasmic accumulation of the 60S nuclear export factor PA2G4, aberrant ribosome profiles, and increased cell death. Collectively, these findings demonstrate that mutations in DNAJC21 cause a cancer-prone BMF syndrome due to corruption of early nuclear rRNA biogenesis and late cytoplasmic maturation of the 60S subunit.
Assuntos
Anemia Aplástica/complicações , Anemia Aplástica/genética , Doenças da Medula Óssea/complicações , Doenças da Medula Óssea/genética , Proteínas de Choque Térmico HSP40/genética , Hemoglobinúria Paroxística/complicações , Hemoglobinúria Paroxística/genética , Mutação/genética , Neoplasias/complicações , Neoplasias/genética , Subunidades Ribossômicas Maiores de Eucariotos/metabolismo , Subunidades Ribossômicas Maiores de Eucariotos/patologia , Sequência de Aminoácidos , Transtornos da Insuficiência da Medula Óssea , Proliferação de Células , Forma Celular , Criança , Pré-Escolar , Feminino , Proteínas de Choque Térmico HSP40/química , Humanos , Leucemia Mieloide Aguda/complicações , Leucemia Mieloide Aguda/genética , Masculino , Ligação Proteica , RNA Ribossômico/biossínteseRESUMO
Ribosomopathies are a class of diseases caused by mutations that affect the biosynthesis and/or functionality of the ribosome. Although they initially present as hypoproliferative disorders, such as anemia, patients have elevated risk of hyperproliferative disease (cancer) by midlife. Here, this paradox is explored using the rpL10-R98S (uL16-R98S) mutant yeast model of the most commonly identified ribosomal mutation in acute lymphoblastic T-cell leukemia. This mutation causes a late-stage 60S subunit maturation failure that targets mutant ribosomes for degradation. The resulting deficit in ribosomes causes the hypoproliferative phenotype. This 60S subunit shortage, in turn, exerts pressure on cells to select for suppressors of the ribosome biogenesis defect, allowing them to reestablish normal levels of ribosome production and cell proliferation. However, suppression at this step releases structurally and functionally defective ribosomes into the translationally active pool, and the translational fidelity defects of these mutants culminate in destabilization of selected mRNAs and shortened telomeres. We suggest that in exchange for resolving their short-term ribosome deficits through compensatory trans-acting suppressors, cells are penalized in the long term by changes in gene expression that ultimately undermine cellular homeostasis.
Assuntos
Carcinogênese/genética , Modelos Moleculares , Leucemia-Linfoma Linfoblástico de Células T Precursoras/genética , Proteínas Ribossômicas/genética , Subunidades Ribossômicas Maiores de Eucariotos/patologia , Ribossomos/genética , Ribossomos/fisiologia , Proteína Ribossômica L10 , Proteínas Ribossômicas/química , Ribossomos/química , Saccharomyces cerevisiaeRESUMO
Diamond Blackfan anemia (DBA) is a congenital disorder with erythroid (Ery) hypoplasia and tissue morphogenic abnormalities. Most DBA cases are caused by heterozygous null mutations in genes encoding ribosomal proteins. Understanding how haploinsufficiency of these ubiquitous proteins causes DBA is hampered by limited availability of tissues from affected patients. We generated induced pluripotent stem cells (iPSCs) from fibroblasts of DBA patients carrying mutations in RPS19 and RPL5. Compared with controls, DBA fibroblasts formed iPSCs inefficiently, although we obtained 1 stable clone from each fibroblast line. RPS19-mutated iPSCs exhibited defects in 40S (small) ribosomal subunit assembly and production of 18S ribosomal RNA (rRNA). Upon induced differentiation, the mutant clone exhibited globally impaired hematopoiesis, with the Ery lineage affected most profoundly. RPL5-mutated iPSCs exhibited defective 60S (large) ribosomal subunit assembly, accumulation of 12S pre-rRNA, and impaired erythropoiesis. In both mutant iPSC lines, genetic correction of ribosomal protein deficiency via complementary DNA transfer into the "safe harbor" AAVS1 locus alleviated abnormalities in ribosome biogenesis and hematopoiesis. Our studies show that pathological features of DBA are recapitulated by iPSCs, provide a renewable source of cells to model various tissue defects, and demonstrate proof of principle for genetic correction strategies in patient stem cells.
