GSE160027
HSPB3 promotes myogenic differentiation by targeting the lamin B receptor.
HSPB3 is a member of the HSPB family that is absent in cycling cells. HSPB3 expression is induced by the myogenic specific transcription factor MyoD in muscle cells, where HSPB3 localizes to the nucleus. Yet, whether HSPB3 participates to muscle cell differentiation is unknown. One of the early events of cell differentiation consists in the switch between the lamin B receptor (LBR) and the lamin A/C (LMNA) tethers, which modulates chromatin remodeling and transcription. Here, we identified LBR as a specialized substrate regulated by HSPB3. HSPB3 affected the expression and nuclear distribution of LBR mimicking the changes that occur during differentiation. HSPB3 upregulation promoted the differentiation of two human muscle cell types: LHCNM2 cells, derived from satellite cells and fusion-negative rhabdomyosarcoma cells, which fail to commit to terminal differentiation. Conversely, HSPB3 depletion stabilized the LBR tether and affected the myogenic transcriptional program.  Four mutations in the HSPB3 gene are linked to distal hereditary motor neuropathy and congenital myopathy with unknown mechanisms. We focused on R116P-HSPB3, which was discovered in a myopathy patient with chromatin alterations and muscle fiber disorganization. Upon overexpression in cells R116-HSPB3 formed nuclear aggregates that immobilized LBR-GFP. In LHCNM2 cells R116-HSPB3 deregulated the transcriptional program required for cytoskeleton and ECM remodeling, while activating the unfolded protein response. We propose that HSPB3 is a highly specialized chaperone that participates to muscle cell differentiation by targeting LBR. Our findings pave the way for a better understanding of HSPB3 implication in the physiology and pathology of the neuromuscular system. Overall design: Examination of transcriptional changes upon HSPB3 overexpression /  knock-down