Fine-Tuning of mTOR mRNA and Nucleolin Complexes by SMN

Abstract

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.

The Proteome Signatures of Fibroblasts from Patients with Severe, Intermediate and Mild Spinal Muscular Atrophy Show Limited Overlap

“…None of the enriched canonical pathways identified were statistically significant across all of the three SMA datasets, but several were significantly enriched across two of three datasets, with at least one differentially expressed protein from the third having been associated, including mTOR signalling, regulation of eIF4 and p70S6K signalling, eIF2 signalling and protein ubiquitination. The association of these pathways with SMA is supported by findings in previous studies, where low levels of SMN have been implicated in mTOR signalling [ 51 , 55 , 56 ], regulation of eIF2 [ 57 ] and eIF4 signalling [ 39 ], protein ubiquitination [ 49 ], mitochondrial dysfunction [ 45 , 46 , 47 , 48 ], signalling by Rho family GTPases [ 58 , 59 ] and semaphorin signalling in neurons via increased cleavage of PlexinD1 in SMA [ 60 ]. Future targeted experiments will be required, however, to verify and understand the involvement of specific proteins and pathways in less severe forms of SMA.…”

Exploring Mitochondrial Localization of SARS-CoV-2 RNA by Padlock Assay: A Pilot Study in Human Placenta

“…We recently optimized a padlock assay to visualize the RNA of interest in fixed cells. This method uses padlock probes combined with the rolling circle amplification (RCA) strategy [3][4][5]. The padlock assay is highly selective and efficient in identifying transcripts in fixed specimens [6].…”

“…We aimed to evaluate the efficiency of our published padlock assay in visualizing SARS-CoV-2 RNA in formalin-fixed paraffin-embedded (FFPE) tissues. In fixed cells, padlock probes can target a selected RNA with near-single-molecule resolution [3][4][5][6]. This method provides intracellular localization maps of transcripts with high spatial resolution and sequence specificity.…”

Characteristic Hallmarks of Aging and the Impact on Carcinogenesis

“…The microenvironment plays a key role in aging and tumorigenesis. Aged people tend to have increased cellular senescence, exhausted stem cells, higher oxidative stress and stimulated insulin and mTOR signalings (indeed, the inhibition of these two seems to increase lifespan), while malignancies show increased cellular senescence only in premalignant tumors evolving in fully malignant cancers, in the presence of active cancer stem cells (CSCs), higher oxidative stress and stimulated insulin and mTOR signaling (inhibition of these two has antineoplastic effects) [8,137]. The CSCs are selfrenewing cancer cells responsible for the expansion of the malignant mass in a dynamic process shaping the tumor microenvironment, impeding host immune surveillance [138].…”