Small heat-shock protein HSPB3 promotes myogenesis by regulating the lamin B receptor

Tatiana Tiago,Maria Giovanna Garone,Simon Alberti,Marco Cimino,Esti Yeger-Lotem,Roberta Costa,Valentina Basile,Ina Poser,Francesco Antoniani,G Cenacchi ,Federica Morelli ,Ritwick Sawarkar,Jonathan Vinet,Veronica Galli,Laura Mediani,Alessandro Rosa,Silvia Pomella,Vincent Mouly,Beatrice Silvestri,Matteo Cassandri,Rossella Rota,Barbara Hummel,Anat Ben‐Zvi ,Serena Carra

doi:10.1038/s41419-021-03737-1

Abstract

One of the critical events that regulates muscle cell differentiation is the replacement of the lamin B receptor (LBR)-tether with the lamin A/C (LMNA)-tether to remodel transcription and induce differentiation-specific genes. Here, we report that localization and activity of the LBR-tether are crucially dependent on the muscle-specific chaperone HSPB3 and that depletion of HSPB3 prevents muscle cell differentiation. We further show that HSPB3 binds to LBR in the nucleoplasm and maintains it in a dynamic state, thus promoting the transcription of myogenic genes, including the genes to remodel the extracellular matrix. Remarkably, HSPB3 overexpression alone is sufficient to induce the differentiation of two human muscle cell lines, LHCNM2 cells, and rhabdomyosarcoma cells. We also show that mutant R116P-HSPB3 from a myopathy patient with chromatin alterations and muscle fiber disorganization, forms nuclear aggregates that immobilize LBR. We find that R116P-HSPB3 is unable to induce myoblast differentiation and instead activates the unfolded protein response. We propose that HSPB3 is a specialized chaperone engaged in muscle cell differentiation and that dysfunctional HSPB3 causes neuromuscular disease by deregulating LBR.

Highlights

Myoblast differentiation is a multistep process regulated by muscle-specific-regulatory transcription factors (MRFs) such as MYOD and myogenin (MYOG)
ChIPseq data showed that MYOD is present on a regulatory region of the HSPB3 gene in human skeletal muscle proliferating myoblasts (HSMMs) and its recruitment is enhanced in differentiated myotubes (HSMMtubes); in addition, MYOD de novo appeared on a distal regulatory region of the gene in HSMMtubes and was associated with enhanced H3K27 acetylation (H3K27ac), indicating potential active transcription (Supplementary Fig. S1B and GSE50413 dataset)
HSPB3 was distributed in the cytoplasm and nucleoplasm, while in other cells HSPB3 was enriched at the nuclear envelope (NE) (Fig. 1A)

Summary

Introduction

Myoblast differentiation is a multistep process regulated by muscle-specific-regulatory transcription factors (MRFs) such as MYOD and myogenin (MYOG). MRFs cooperative action induces the expression of muscle-specific genes, leading to myoblast withdrawal from cell cycle and cell–cell fusion to form multinucleated myotubes[1]. Myoblast differentiation is characterized by remodeling of the nucleus, cytoskeleton, and extracellular matrix (ECM)[2,3,4]. The lamin B receptor (LBR), which binds to LMNB1 and heterochromatin protein 1 (HP1)[5], tethers peripheral heterochromatin to the NE, inhibiting muscle-specific gene expression[6]. LBR expression decreases, as well as its binding to the NE; in addition, the LBR-tether is partially replaced by the lamin

Methods

Results

Conclusion