SMN protein promotes membrane compartmentalization of ribosomal protein S6 transcript in human fibroblasts

Gabanella, Francesca; Onori, Annalisa; Ralli, Massimo; Greco, Antonio; Passananti, Claudio; Certo, Maria Grazia Di

doi:10.1038/s41598-020-76174-3

Cited by 18 publications

(48 citation statements)

References 62 publications

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“…We provide evidence that SMN fine-tunes the sophisticated interplay between nucleolin and mTOR, two master regulators of translation platforms (Figure 5F). In agreement with our previous work [20], we suggest that SMN-deficient cells might prevent aberrant translation events by reducing cytoplasmic availability of translation-related transcripts. This study highlights the wide complexity of the SMN role in translational control and points to SMN as a key determinant, able to regulate protein synthesis from near and far.…”

Section: Discussionsupporting

confidence: 93%

“…To identify SMN-deficient cells an immunostaining for SMN was performed in parallel. As reported in previous works [ 16 , 20 ], no fluorescence signals above background levels were detectable in approximately 80–85% of siSMN-transfected fibroblasts (data not shown). In control cells, nucleolin immunostaining exhibited a peculiar localization pattern, characterized by a strong fluorescent signal from nucleoli.…”

Section: Resultssupporting

confidence: 88%

“…Phosphorylation of the padlock probe and PlaLock assay were performed as previously described [ 20 ].…”

Section: Methodsmentioning

confidence: 99%

“…To note, converging evidence highlights a role of SMN in ribosome biogenesis. SMN was found to interact with RP-coding transcripts [ 18 , 19 , 20 ], whose translation rate appears dysregulated in a mouse model of SMN deficiency [ 21 ]. Accordingly, we showed that a reduced level of SMN protein affects both the subcellular distribution and translation efficiency of RPS6 mRNA [ 20 ].…”

Section: Introductionmentioning

confidence: 99%

“…SMN was found to interact with RP-coding transcripts [ 18 , 19 , 20 ], whose translation rate appears dysregulated in a mouse model of SMN deficiency [ 21 ]. Accordingly, we showed that a reduced level of SMN protein affects both the subcellular distribution and translation efficiency of RPS6 mRNA [ 20 ]. Based on these findings, we assumed that SMN might impact the translation pathway early, by selective composition/localization of ribosomes.…”

Section: Introductionmentioning

confidence: 99%

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Fine-Tuning of mTOR mRNA and Nucleolin Complexes by SMN

Gabanella

Barbato

Fiore

et al. 2021

Cells

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Increasing evidence points to the Survival Motor Neuron (SMN) protein as a key determinant of translation pathway. Besides its role in RNA processing and sorting, several works support a critical implication of SMN in ribosome biogenesis. We previously showed that SMN binds ribosomal proteins (RPs) as well as their encoding transcripts, ensuring an appropriate level of locally synthesized RPs. SMN impacts the translation machinery in both neural and non-neural cells, in agreement with the concept that SMN is an essential protein in all cell types. Here, we further assessed the relationship between SMN and translation-related factors in immortalized human fibroblasts. We focused on SMN-nucleolin interaction, keeping in mind that nucleolin is an RNA-binding protein, highly abundant within the nucleolus, that exhibits a central role in ribosomes production. Nucleolin may also affects translation network by binding the mammalian target of rapamycin (mTOR) mRNA and promoting its local synthesis. In this regard, for the first time we provided evidence that SMN protein itself associates with mTOR transcript. Collectively, we found that: (1) SMN coexists with nucleolin–mTOR mRNA complexes at subcellular level; (2) SMN deficiency impairs nucleolar compartmentalization of nucleolin, and (3) this event correlates with the nuclear retention of mTOR mRNA. These findings suggest that SMN may regulate not only structural components of translation machinery, but also their upstream regulating factors.

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Section: Discussionsupporting

confidence: 93%

Section: Resultssupporting

confidence: 88%

“…Phosphorylation of the padlock probe and PlaLock assay were performed as previously described [ 20 ].…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fine-Tuning of mTOR mRNA and Nucleolin Complexes by SMN

Gabanella

Barbato

Fiore

et al. 2021

Cells

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Diminished motor neuron activity driven by abnormal astrocytic EAAT1 glutamate transporter activity in spinal muscular atrophy is not fully restored after lentiviral SMN delivery

Welby

Ebert

2023

Glia

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Spinal muscular atrophy (SMA) is characterized by the loss of the lower spinal motor neurons due to survival motor neuron (SMN) deficiency. The motor neuron cell autonomous and non‐cell autonomous disease mechanisms driving early glutamatergic dysfunction, a therapeutically targetable phenotype prior to motor neuron cell loss, remain unclear. Using microelectrode array analysis, we demonstrate that the secretome and cell surface proteins needed for proper synaptic modulation are likely disrupted in human SMA astrocytes and lead to diminished motor neuron activity. While healthy astrocyte conditioned media did not improve SMA motor neuron activity, SMA motor neurons robustly responded to healthy astrocyte neuromodulation in direct contact cultures. This suggests an important role of astrocyte synaptic‐associated plasma membrane proteins and contact‐mediated cellular interactions for proper motor neuron function in SMA. Specifically, we identified a significant reduction of the glutamate Na+ dependent excitatory amino acid transporter EAAT1 within human SMA astrocytes and SMA lumbar spinal cord tissue. The selective inhibition of EAAT1 in healthy co‐cultures phenocopied the diminished neural activity observed in SMA astrocyte co‐cultures. Caveolin‐1, an SMN‐interacting protein previously associated with local translation at the plasma membrane, was abnormally elevated in human SMA astrocytes. Although lentiviral SMN delivery to SMA astrocytes partially rescued EAAT1 expression, limited activity of healthy motor neurons was still observed in SMN‐transduced SMA astrocyte co‐cultures. Together, these data highlight the detrimental impact of astrocyte‐mediated disease mechanisms on motor neuron function in SMA and that SMN delivery may be insufficient to fully restore astrocyte function at the synapse.

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