The intracellular domain of \u03b2-dystroglycan mediates the nucleolar stress response by suppressing UBF transcriptional activity

Paulina Margarita Azuara-Medina,Griselda Vélez-Aguilera,Ivette Martínez-Vieyra,Arturo Ortega,Reynaldo Tiburcio-Félix,Ricardo Modragón-González,Guadalupe Elizabeth Jiménez-Gutiérrez,Jonathan Javier Magaña,Gernot Längst,Laura A Jacobs,Bulmaro Cisneros,Juan De Dios Gómez-López,Rocío Suárez-Sánchez,Sara L Morales-Lázaro,Steve J Winder,Rita De Cassia Ramos Perlingeiro,Ariana María Sandoval-Duarte

doi:10.1038/s41419-019-1454-z

Abstract

β-dystroglycan (β-DG) is a key component of multiprotein complexes in the plasma membrane and nuclear envelope. In addition, β-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 β-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, β-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 β-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 β-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.

Highlights

Regulated proteolysis of cell surface receptors that liberates biologically active proteins/peptides from the plasma membrane (PM) to the cytosol is a critical step in a variety of different signaling pathways that respond to external (DAPC), is transcribed from the DAG1 gene and translated as a single propeptide, which is proteolytically processed to generate the extracellular subunit α-dystroglycan (α-DG) and the transmembrane subunit β-dystroglycan (β-DG)5. α-DG binds to different extracellular matrix proteinsOfficial journal of the Cell Death Differentiation AssociationAzuara-Medina et al Cell Death and Disease (2019)10:196Page 2 of 17 196 including laminin, agrin, or perlecan[6], while β-DG connects actin through various cytolinker proteins including dystrophin or utrophin
The immunoreactive band corresponding to β-DG (~43 kDa), which was observed in primary fibroblast lysates from a healthy subject, was absent in Walker–Warburg syndrome primary fibroblast lysates (Supplementary Figure 1A, right panel)
Recent in vitro and in vivo evidence showed that β-DG undergoes two successive and possibly coordinate proteolytic cleavages that result in the liberation of the intracellular domain (ICD) into the cytosol; first matrix metalloproteinases, MMP-2 and MMP-9 cleave the extracellular domain of β-DG23 and create a membrane-tethered intermediate that is subsequently processed by γ-secretase, a PM-embedded protease complex, to render a final cleavage product that approximates the entire ICD21

Summary

Introduction

Regulated proteolysis of cell surface receptors that liberates biologically active proteins/peptides from the plasma membrane (PM) to the cytosol is a critical step in a variety of different signaling pathways that respond to external (DAPC), is transcribed from the DAG1 gene and translated as a single propeptide, which is proteolytically processed to generate the extracellular subunit α-dystroglycan (α-DG) and the transmembrane subunit β-dystroglycan (β-DG)5. α-DG binds to different extracellular matrix proteinsOfficial journal of the Cell Death Differentiation AssociationAzuara-Medina et al Cell Death and Disease (2019)10:196Page 2 of 17 196 including laminin, agrin, or perlecan[6], while β-DG connects actin through various cytolinker proteins including dystrophin or utrophin. Β-DG is assembled with nuclear envelope (NE) components, including emerin, and lamins A/C and B1, to preserve the nuclear structure/function[11,12] and where it can indirectly regulate gene expression[13]. This functional diversity of β-DG, acting as a platform for both PM- and NE-associated processes, is further expanded by proteolytic cleavage of the protein. Β-DG ICD appears to be a key contributor to the nucleolar stress response

Methods

Results

Conclusion