RESUMEN
Nuclear mRNA export via nuclear pore complexes is an essential step in eukaryotic gene expression. Although factors involved in mRNA transport have been characterized, a comprehensive mechanistic understanding of this process and its regulation is lacking. Here, we use single-RNA imaging in yeast to show that cells use mRNA retention to control mRNA export during stress. We demonstrate that, upon glucose withdrawal, the essential RNA-binding factor Nab2 forms RNA-dependent condensate-like structures in the nucleus. This coincides with a reduced abundance of the DEAD-box ATPase Dbp5 at the nuclear pore. Depleting Dbp5, and consequently blocking mRNA export, is necessary and sufficient to trigger Nab2 condensation. The state of Nab2 condensation influences the extent of nuclear mRNA accumulation and can be recapitulated in vitro, where Nab2 forms RNA-dependent liquid droplets. We hypothesize that cells use condensation to regulate mRNA export and control gene expression during stress.
Asunto(s)
Proteínas de Complejo Poro Nuclear , Proteínas de Saccharomyces cerevisiae , Transporte Activo de Núcleo Celular , Núcleo Celular/metabolismo , ARN Helicasas DEAD-box/metabolismo , Proteínas de Complejo Poro Nuclear/metabolismo , Proteínas de Transporte Nucleocitoplasmático/genética , Proteínas de Transporte Nucleocitoplasmático/metabolismo , ARN/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismoRESUMEN
Small molecule splicing modifiers have been previously described that target the general splicing machinery and thus have low specificity for individual genes. Several potent molecules correcting the splicing deficit of the SMN2 (survival of motor neuron 2) gene have been identified and these molecules are moving towards a potential therapy for spinal muscular atrophy (SMA). Here by using a combination of RNA splicing, transcription, and protein chemistry techniques, we show that these molecules directly bind to two distinct sites of the SMN2 pre-mRNA, thereby stabilizing a yet unidentified ribonucleoprotein (RNP) complex that is critical to the specificity of these small molecules for SMN2 over other genes. In addition to the therapeutic potential of these molecules for treatment of SMA, our work has wide-ranging implications in understanding how small molecules can interact with specific quaternary RNA structures.
Asunto(s)
Atrofia Muscular Espinal/tratamiento farmacológico , Piperazinas/farmacología , Precursores del ARN/metabolismo , Empalme del ARN/efectos de los fármacos , ARN Mensajero/metabolismo , Proteínas de Unión al ARN/metabolismo , Biflavonoides/farmacología , Sistema Libre de Células , Biología Computacional , Compuestos Epoxi/farmacología , Exones/genética , Fibroblastos , Células HEK293 , Células HeLa , Humanos , Ligandos , Macrólidos/farmacología , Atrofia Muscular Espinal/genética , Piperazinas/síntesis química , Unión Proteica , Estructura Cuaternaria de Proteína , Proteómica/métodos , Precursores del ARN/genética , ARN Mensajero/genética , Empalmosomas/efectos de los fármacos , Empalmosomas/metabolismo , Proteína 1 para la Supervivencia de la Neurona Motora/genética , Proteína 2 para la Supervivencia de la Neurona Motora/genéticaRESUMEN
New inhibitors of influenza viruses are needed to combat the potential emergence of novel human influenza viruses. We have identified a class of small molecules that inhibit replication of influenza virus at picomolar concentrations in plaque reduction assays. The compound also inhibits replication of vesicular stomatitis virus. Time of addition and dilution experiments with influenza virus indicated that an early time point of infection was blocked and that inhibitor 136 tightly bound to virions. Using fluorescently labeled influenza virus, inhibition of viral fusion to cellular membranes by blocked lipid mixing was established as the mechanism of action for this class of inhibitors. Stabilization of the neutral pH form of hemagglutinin (HA) was ruled out by trypsin digestion studies in vitro and with conformation specific HA antibodies within cells. Direct visualization of 136 treated influenza virions at pH 7.5 or acidified to pH 5.0 showed that virions remain intact and that glycoproteins become disorganized as expected when HA undergoes a conformational change. This suggests that exposure of the fusion peptide at low pH is not inhibited but lipid mixing is inhibited, a different mechanism than previously reported fusion inhibitors. We hypothesize that this new class of inhibitors intercalate into the virus envelope altering the structure of the viral envelope required for fusion to cellular membranes.
