RESUMEN
In mammalian somatic cells, the post-transcriptional control of cytokine or proto-oncogene expression is often achieved by factors binding to sequence elements in the 3' untranslated region (3'UTR). The most studied are the AU-rich elements (ARE) that have been divided into three classes. Here, we show that in mammalian cells, the presence of the class III c-jun ARE in the 3'UTR of a reporter mRNA enhanced reporter protein expression. In contrast, the presence of a class II ARE in the 3'UTR decreased reporter protein expression. CUG-BP1/CELF1 is able to bind c-jun ARE. Protein expression was enhanced similarly to what was observed for c-jun ARE when the reporter mRNA contained a synthetic CUG-BP1/CELF1-binding site, or when this protein was tethered to the 3'UTR of a reporter mRNA. These results reveal an unexpected complexity of ARE-mediated post-transcriptional regulations, and indicate a function for CUG-BP1/CELF1 in class III ARE directed regulations.
Asunto(s)
Regiones no Traducidas 3'/genética , Adenosina/genética , Expresión Génica , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Uridina/genética , Regiones no Traducidas 3'/clasificación , Animales , Línea Celular , Genes Reporteros/genética , Humanos , Ratones , Unión Proteica , Proto-Oncogenes Mas , Proteínas Proto-Oncogénicas c-jun/genética , Proteínas Proto-Oncogénicas c-jun/metabolismoRESUMEN
Poly (A) binding proteins are intimately implicated in controlling a number of events in mRNA metabolism from nuclear polyadenylation to cytoplasmic translation and stability. The known poly(A) binding proteins can be divided into three distinct structural groups (prototypes PABP1, PABPN1/PABP2 and Nab2p) and two functional families, showing that similar functions can be accomplished by differing structural units. This has prompted us to perform a screen for novel poly(A) binding proteins using Xenopus laevis. A novel poly(A) binding protein of 32 kDa (p32) was identified. Sequence analysis showed that p32 has about 50% identity to the known nuclear poly(A) binding proteins (PABPN1) but is more closely related to a group of mammalian proteins of unknown function. The expression of Xenopus laevis ePABP2 is restricted to early embryos. Accordingly, we propose that p32 is the founder member of a novel class of poly(A) binding proteins named ePABP2.
Asunto(s)
Proteínas de Unión a Poli(A)/genética , ARN Mensajero/metabolismo , Proteínas de Unión al ARN/genética , Proteínas de Xenopus/genética , Secuencia de Aminoácidos , Animales , Clonación Molecular , Datos de Secuencia Molecular , Filogenia , Proteínas de Unión a Poli(A)/metabolismo , ARN Mensajero/genética , Proteínas de Unión al ARN/metabolismo , Alineación de Secuencia , Proteínas de Xenopus/metabolismo , Xenopus laevisRESUMEN
CUG-BP is a human nuclear and cytoplasmic RNA-binding protein. A role in the control of alternative splicing has been reported, but to date no cytoplasmic function for this protein has been demonstrated. A close sequence homolog of CUG-BP is EDEN-BP that is required for the specific cytoplasmic poly(A) tail shortening of certain mRNAs after fertilization of Xenopus eggs. Here, we show that human CUG-BP and Xenopus EDEN-BP have very similar RNA-binding specificities. In addition, we use a deadenylation assay to show that CUG-BP is able to act as a deadenylation factor. In contrast, a mutant form of CUG-BP, though still able to bind to RNA with a specificity similar to that of wild-type CUG-BP, does not act as a deadenylation factor. It is suggested that the CUG expansion associated with Type 1 myotonic dystrophy can affect the function or the activity of CUG-BP, leading to a trans-dominant effect on normal RNA processing. The results presented here identify CUG-BP-dependent deadenylation as a potential cytoplasmic target for this trans-dominant effect.