Nucleoporin POM121 signals TFEB-mediated autophagy via activation of SIGMAR1/sigma-1 receptor chaperone by pridopidine

Abstract

Macroautophagy/autophagy is an essential process for cellular survival and is implicated in many diseases. A critical step in autophagy is the transport of the transcription factor TFEB from the cytosol into the nucleus, through the nuclear pore (NP) by KPNB1/importinβ1. In the C9orf72 subtype of amyotrophic lateral sclerosis-frontotemporal lobar degeneration (ALS-FTD), the hexanucleotide (G4C2)RNA expansion (HRE) disrupts the nucleocytoplasmic transport of TFEB, compromising autophagy. Here we show that a molecular chaperone, the SIGMAR1/Sigma-1 receptor (sigma non-opioid intracellular receptor 1), facilitates TFEB transport into the nucleus by chaperoning the NP protein (i.e., nucleoporin) POM121 which recruits KPNB1. In NSC34 cells, HRE reduces TFEB transport by interfering with the association between SIGMAR1 and POM121, resulting in reduced nuclear levels of TFEB, KPNB1, and the autophagy marker LC3-II. Overexpression of SIGMAR1 or POM121, or treatment with the highly selective and potent SIGMAR1 agonist pridopidine, currently in phase 2/3 clinical trials for ALS and Huntington disease, rescues all of these deficits. Our results implicate nucleoporin POM121 not merely as a structural nucleoporin, but also as a chaperone-operated signaling molecule enabling TFEB-mediated autophagy. Our data suggest the use of SIGMAR1 agonists, such as pridopidine, for therapeutic development of diseases in which autophagy is impaired. Abbreviations : ALS-FTD, amyotrophic lateral sclerosis-frontotemporal dementiaC9ALS-FTD, C9orf72 subtype of amyotrophic lateral sclerosis-frontotemporal dementiaCS, citrate synthaseER, endoplasmic reticulumGSS, glutathione synthetaseHRE, hexanucleotide repeat expansionHSPA5/BiP, heat shock protein 5LAMP1, lysosomal-associated membrane protein 1MAM, mitochondria-associated endoplasmic reticulum membraneMAP1LC3/LC3, microtubule-associated protein 1 light chain 3NP, nuclear poreNSC34, mouse motor neuron-like hybrid cell lineNUPs, nucleoporinsPOM121, nuclear pore membrane protein 121SIGMAR1/Sigma-1R, sigma non-opioid intracellular receptor 1TFEB, transcription factor EBTMEM97/Sigma-2R, transmembrane protein 97

Sphingoid Bases Regulate the Sigma-1 Receptor—Sphingosine and N,N’-Dimethylsphingosine Are Endogenous Agonists

“…In the presence of S1R antagonists (e.g., haloperidol, BD1047), the oligomeric forms predominate, whereas in the presence of S1R agonists (e.g., pentazocine, PRE-084), smaller sizes predominate [ 3 , 4 , 76 ]. Recent studies have elegantly demonstrated that S1R agonists and antagonists could be distinguished through non-denaturing PAGE (also known as native gel) followed by S1R immunoblotting [ 17 , 76 , 77 , 78 ]. Of note, even a lower-affinity S1R antagonist such as progesterone exhibited a strong oligomer-stabilizing effect [ 76 ].…”

“…However, the oligomer-destabilizing effect of lower-affinity putative S1R agonists (e.g., DHEA) could not be readily discerned [ 76 ]. Moreover, S1R oligomers on blots typically appear as a broad “smeary” band [ 17 , 76 , 77 ]. It is, thus, impractical to distinguish an S1R-specfic signal from “false-positive” background or S1R homomers from S1R heteromers complexed with other proteins.…”

“…The S1R is located mainly in specialized intracellular endoplasmic reticulum (ER) membranes (mitochondrial-associated membranes (MAM)) [ 1 ], but also in the ER, lysosomal, golgi, nucleoplasmic reticulum [ 9 ], and plasma membranes [ 10 ]. The S1R is associated with a plethora of eukaryotic signaling pathways involved in peripheral [ 11 ] and CNS neuroprotection, neurogenesis [ 12 ], neuropathic pain [ 13 , 14 ], cellular oxidative stress [ 10 ], obesity [ 15 , 16 ], inflammation, autophagy [ 17 , 18 , 19 ], and retinal degeneration [ 20 ]. These cellular outcomes are underwritten, in part, by direct or indirect molecular associations of the S1R with various membrane-bound “client” proteins such as G-protein-coupled receptors (GPCRs); voltage-dependent sodium, potassium, chloride, and calcium channels; NMDA receptors [ 21 ]; dopamine transporters (DAT); transient potential activated (TRP) channels [ 22 ]; transcription factors [ 5 , 23 , 24 , 25 ].…”

Inhibition of MZF1/c-MYC Axis by Cantharidin Impairs Cell Proliferation in Glioblastoma

“…Nucleocytoplasmic transport has been reported to affect the translocation of MZF1 into the nucleus, inhibiting gene transcription in gliomas [ 4 ]. Approximately 30 nuclear nucleoporins (nuclear pore proteins) play an important role in nucleocytoplasmic transport [ 24 ]. Nevertheless, whether CTD inhibits nucleoporin expression to affect MZF1-regulated c-MYC transcription remains to be determined.…”

New developments and opportunities in drugs being trialed for amyotrophic lateral sclerosis from 2020 to 2022

“…Autophagy is enhanced as the activation of SIGMAR1/S1R by pridopidine can chaperone the NP protein POM121, which recruits KPNB1 to transport TFEB into the nucleus. Therefore, pridopidine may ameliorate the TFEB transport deficit in the C9orf72 subtype of amyotrophic lateral sclerosis-frontotemporal lobar degeneration (ALS-FTD), where the mutation damages the nucleocytoplasmic transport of TFEB ( Wang et al, 2022 ). It has been approved as an orphan drug for ALS in the US and Europe.…”