Sam68 splicing regulation contributes to motor unit establishment in the postnatal skeletal muscle

Paola, Elisa De; Forcina, Laura; Pelosi, Laura; Pisu, Simona; Rosa, Piergiorgio La; Cesari, E.; Nicoletti, Carmine; Madaro, Luca; Neri, Margherita; Biamonte, Filippo; Nobili, Annalisa; D’Amelio, Marcello; Bardi, Marco De; Volpe, Elisabetta; Caporossi, Daniela; Sette, Claudio; Musarò, Antonio; Paronetto, Maria Paola

doi:10.26508/lsa.201900637

Cited by 7 publications

(1 citation statement)

References 77 publications

(116 reference statements)

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“…Src‐associated during mitosis, 68 kDa (Sam68/KHDRBS1) is one of the proteins for which more compelling evidence supporting a direct involvement in SMN2 exon 7 skipping has been presented (Pedrotti et al, 2010; Pagliarini et al, 2015; De Paola et al, 2020). Sam68 is the prototypical member of the STAR (Signal Transducer and Activator of RNA) subfamily of RNA‐binding proteins, which belongs in turn to the hnRNP K‐homology (KH) family (Valverde et al, 2008) (see Figure 1a for the domain organization of human Sam68, and Figure S2a for a sequence alignment with other STAR proteins).…”

Section: Introductionmentioning

confidence: 99%

Structure and function analysis of Sam68 and hnRNP A1 synergy in the exclusion of exon 7 from SMN2 transcripts

et al. 2023

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Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by the absence of a functional copy of the Survival of Motor Neuron 1 gene (SMN1). The nearly identical paralog, SMN2, cannot compensate for the loss of SMN1 because exon 7 is aberrantly skipped from most SMN2 transcripts, a process mediated by synergistic activities of Src‐associated during mitosis, 68 kDa (Sam68/KHDRBS1) and heterogeneous nuclear ribonucleoprotein (hnRNP) A1. This results in the production of a truncated, nonfunctional protein that is rapidly degraded. Here, we present several crystal structures of Sam68 RNA‐binding domain (RBD). Sam68‐RBD forms stable symmetric homodimers by antiparallel association of helices α3 from two monomers. However, the details of domain organization and the dimerization interface differ significantly from previously characterized homologs. We demonstrate that Sam68 and hnRNP A1 can simultaneously bind proximal motifs within the central region of SMN2 (ex7). Furthermore, we show that the RNA‐binding pockets of the two proteins are close to each other in their heterodimeric complex and identify contact residues using crosslinking‐mass spectrometry. We present a model of the ternary Sam68·SMN2 (ex7)·hnRNP A1 complex that reconciles all available information on SMN1/2 splicing. Our findings have important implications for the etiology of SMA and open new avenues for the design of novel therapeutics to treat splicing diseases.

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Section: Introductionmentioning

confidence: 99%

Structure and function analysis of Sam68 and hnRNP A1 synergy in the exclusion of exon 7 from SMN2 transcripts

et al. 2023

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Cytoplasmic HDAC4 regulates the membrane repair mechanism in Duchenne muscular dystrophy

Renzini

Marroncelli

Cavioli

et al. 2022

J cachexia sarcopenia muscle

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Background Histone deacetylase 4 (HDAC4) is a stress-responsive factor that mediates multiple cellular responses. As a member of class IIa HDACs, HDAC4 shuttles between the nucleus and the cytoplasm; however, HDAC4 cytoplasmic functions have never been fully investigated. Duchenne muscular dystrophy (DMD) is a genetic, progressive, incurable disorder, characterized by muscle wasting, which can be treated with the unspecific inhibition of HDACs, despite this approach being only partially effective. More efficient strategies may be proposed for DMD only after the different HDAC members will be characterized. Methods To fully understand HDAC4 functions, we generated dystrophic mice carrying a skeletal muscle-specific deletion of HDAC4 (mdx;KO mice). The progression of muscular dystrophy was characterized in mdx and age-matched mdx;KO mice by means of histological, molecular, and functional analyses. Satellite cells (SCs) from these mice were differentiated in vitro, to identify HDAC4 intrinsic functions influencing the myogenic potential of dystrophic SCs. Gain-of-function experiments revealed the cytoplasmic functions of HDAC4 in mdx;KO muscles. Results Histone deacetylase 4 increased in the skeletal muscles of mdx mice (~3-fold; P < 0.05) and of DMD patients (n = 3, males, mean age 13.3 ± 1.5 years), suggesting that HDAC4 has a role in DMD. Its deletion in skeletal muscles importantly worsens the pathological features of DMD, leading to greater muscle fragility and degeneration over time. Additionally, it impairs SC survival, myogenic potential, and muscle regeneration, ultimately compromising muscle function (P < 0.05-0.001). The impaired membrane repair mechanism in muscles and SCs accounts for the mdx;KO phenotype. Indeed, the ectopic expression of Trim72, a major player in the membrane repair mechanism, prevents SC death (~20%; P < 0.01) and increases myogenic fusion (~40%; P < 0.01) in vitro; in vivo it significantly reduces myofibre damage (~10%; P < 0.005) and improves mdx;KO muscle function (P < 0.05). The mdx;KO phenotype is also fully rescued by restoring cytoplasmic levels of HDAC4, both in vitro and in vivo. The protective role of HDAC4 in the cytoplasm of mdx;KO muscles is, in part, independent of its deacetylase activity. HDAC4 expression correlates with Trim72 mRNA levels; furthermore, Trim72 mRNA decays more rapidly (P < 0.01) in mdx;KO muscle cells, compared with mdx ones. Conclusions Histone deacetylase 4 performs crucial functions in the cytoplasm of dystrophic muscles, by mediating the muscle repair response to damage, an important role in ensuring muscle homeostasis, probably by stabilizing Trim72 mRNA. Consequently, the cytoplasmic functions of HDAC4 should be stimulated rather than inhibited in muscular dystrophy treatments, a fact to be considered in future therapeutic approaches.

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Dysregulation of alternative splicing underlies synaptic defects in familial amyotrophic lateral sclerosis

Verdile,

Palombo,

Ferrante

et al. 2023

Progress in Neurobiology

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Sam68 splicing regulation contributes to motor unit establishment in the postnatal skeletal muscle

Cited by 7 publications

References 77 publications

Structure and function analysis of Sam68 and hnRNP A1 synergy in the exclusion of exon 7 from SMN2 transcripts

Structure and function analysis of Sam68 and hnRNP A1 synergy in the exclusion of exon 7 from SMN2 transcripts

Cytoplasmic HDAC4 regulates the membrane repair mechanism in Duchenne muscular dystrophy

Dysregulation of alternative splicing underlies synaptic defects in familial amyotrophic lateral sclerosis

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