RESUMEN

ß-dystroglycan (ß-DG) is a key component of multiprotein complexes in the plasma membrane and nuclear envelope. In addition, ß-DG undergoes two successive proteolytic cleavages that result in the liberation of its intracellular domain (ICD) into the cytosol and nucleus. However, stimuli-inducing ICD cleavage and the physiological relevance of this proteolytic fragment are largely unknown. In this study we show for the first time that ß-DG ICD is targeted to the nucleolus where it interacts with the nuclear proteins B23 and UBF (central factor of Pol I-mediated rRNA gene transcription) and binds to rDNA promoter regions. Interestingly DG silencing results in reduced B23 and UBF levels and aberrant nucleolar morphology. Furthermore, ß-DG ICD cleavage is induced by different nucleolar stressors, including oxidative stress, acidosis, and UV irradiation, which implies its participation in the response to nucleolar stress. Consistent with this idea, overexpression of ß-DG elicited mislocalization and decreased levels of UBF and suppression of rRNA expression, which in turn provoked altered ribosome profiling and decreased cell growth. Collectively our data reveal that ß-DG ICD acts as negative regulator of rDNA transcription by impeding the transcriptional activity of UBF, as a part of the protective mechanism activated in response to nucleolar stress.

Asunto(s)

Nucléolo Celular/metabolismo , Distroglicanos/metabolismo , Proteínas del Complejo de Iniciación de Transcripción Pol1/metabolismo , ARN Ribosómico/biosíntesis , Animales , Proliferación Celular/genética , Citoplasma/metabolismo , ADN Ribosómico/genética , ADN Ribosómico/metabolismo , Distroglicanos/antagonistas & inhibidores , Distroglicanos/genética , Ratones , Mioblastos , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Nucleofosmina , Estrés Oxidativo , Proteínas del Complejo de Iniciación de Transcripción Pol1/genética , Dominios Proteicos/genética , ARN Ribosómico/genética , Ribosomas/metabolismo , Transcripción Genética , Regulación hacia Arriba/genética

RESUMEN

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

RESUMEN

ß-Dystroglycan (ß-DG) is a transmembrane protein with critical roles in cell adhesion, cytoskeleton remodeling and nuclear architecture. This functional diversity is attributed to the ability of ß-DG to target to, and conform specific protein assemblies at the plasma membrane (PM) and nuclear envelope (NE). Although a classical NLS and importin α/ß mediated nuclear import pathway has already been described for ß-DG, the intracellular trafficking route by which ß-DG reaches the nucleus is unknown. In this study, we demonstrated that ß-DG undergoes retrograde intracellular trafficking from the PM to the nucleus via the endosome-ER network. Furthermore, we provided evidence indicating that the translocon complex Sec61 mediates the release of ß-DG from the ER membrane, making it accessible for importins and nuclear import. Finally, we show that phosphorylation of ß-DG at Tyr890 is a key stimulus for ß-DG nuclear translocation. Collectively our data describe the retrograde intracellular trafficking route that ß-DG follows from PM to the nucleus. This dual role for a cell adhesion receptor permits the cell to functionally connect the PM with the nucleus and represents to our knowledge the first example of a cell adhesion receptor exhibiting retrograde nuclear trafficking and having dual roles in PM and NE.