RESUMO
RNA helicases constitute a large protein family implicated in cellular RNA homeostasis and disease development. Here, we show that the RNA helicase IGHMBP2, linked to the neuromuscular disorder spinal muscular atrophy with respiratory distress type 1 (SMARD1), associates with polysomes and impacts translation of mRNAs containing short, GC-rich, and structured 5' UTRs. The absence of IGHMBP2 causes ribosome stalling at the start codon of target mRNAs, leading to reduced translation efficiency. The main mRNA targets of IGHMBP2-mediated regulation encode for components of the THO complex (THOC), linking IGHMBP2 to mRNA production and nuclear export. Accordingly, failure of IGHMBP2 regulation of THOC causes perturbations of the transcriptome and its encoded proteome, and ablation of THOC subunits phenocopies these changes. Thus, IGHMBP2 is an upstream regulator of THOC. Of note, IGHMBP2-dependent regulation of THOC is also observed in astrocytes derived from patients with SMARD1 disease, suggesting that deregulated mRNA metabolism contributes to SMARD1 etiology and may enable alternative therapeutic avenues.
Assuntos
Atrofia Muscular Espinal , Síndrome do Desconforto Respiratório do Recém-Nascido , Humanos , RNA Mensageiro/genética , Atrofia Muscular Espinal/genética , Regiões 5' não Traduzidas , Homeostase , Proteínas de Ligação a DNA/genética , Fatores de Transcrição/genéticaRESUMO
Spliceosomal snRNPs are multicomponent particles that undergo a complex maturation pathway. Human Sm-class snRNAs are generated as 3'-end extended precursors, which are exported to the cytoplasm and assembled together with Sm proteins into core RNPs by the SMN complex. Here, we provide evidence that these pre-snRNA substrates contain compact, evolutionarily conserved secondary structures that overlap with the Sm binding site. These structural motifs in pre-snRNAs are predicted to interfere with Sm core assembly. We model structural rearrangements that lead to an open pre-snRNA conformation compatible with Sm protein interaction. The predicted rearrangement pathway is conserved in Metazoa and requires an external factor that initiates snRNA remodeling. We show that the essential helicase Gemin3, which is a component of the SMN complex, is crucial for snRNA structural rearrangements during snRNP maturation. The SMN complex thus facilitates ATP-driven structural changes in snRNAs that expose the Sm site and enable Sm protein binding.
Assuntos
Precursores de RNA , RNA Nuclear Pequeno , Humanos , RNA Nuclear Pequeno/metabolismo , Proteínas do Complexo SMN/metabolismo , Precursores de RNA/metabolismo , Células HeLa , Ribonucleoproteínas Nucleares Pequenas/metabolismo , Proteínas Centrais de snRNP/genéticaRESUMO
Specialized assembly factors facilitate the formation of many macromolecular complexes in vivo. The formation of Sm core structures of spliceosomal U-rich small nuclear ribonucleoprotein particles (UsnRNPs) requires assembly factors united in protein arginine methyltransferase 5 (PRMT5) and survival motor neuron (SMN) complexes. We demonstrate that perturbations of this assembly machinery trigger complex cellular responses that prevent aggregation of unassembled Sm proteins. Inactivation of the SMN complex results in the initial tailback of Sm proteins on the PRMT5 complex, followed by down-regulation of their encoding mRNAs. In contrast, reduction of pICln, a PRMT5 complex subunit, leads to the retention of newly synthesized Sm proteins on ribosomes and their subsequent lysosomal degradation. Overexpression of Sm proteins under these conditions results in a surplus of Sm proteins over pICln, promoting their aggregation. Our studies identify an elaborate safeguarding system that prevents individual Sm proteins from aggregating, contributing to cellular UsnRNP homeostasis.