Nucleolin regulates 14‐3‐3ζ mRNA and promotes cofilin phosphorylation to induce tunneling nanotube formation

Abstract

Tunneling nanotubes (TNTs) mediate intercellular communication between animal cells in health and disease, but the mechanisms of their biogenesis and function are poorly understood. Here we report that the RNA-binding protein (RBP) nucleolin, which interacts with the known TNT-inducing protein MSec, is essential for TNT formation in mammalian cells. Nucleolin, through its RNA-binding domains (RBDs), binds to and maintains the cytosolic levels of 14-3-3ζ mRNA, and is, therefore, required for TNT formation. A specific region of the 3′-untranslated region (UTR) of the 14-3-3ζ mRNA is likely to be involved in its regulation by nucleolin. Functional complementation experiments suggest that nucleolin and 14-3-3ζ form a linear signaling axis that promotes the phosphorylation and inactivation of the F-actin depolymerization factor cofilin to induce TNT formation. MSec also similarly inactivates cofilin, but potentiates TNT formation independent of the nucleolin-14-3-3ζ axis, despite biochemically interacting with both proteins. We show that 14-3-3ζ and nucleolin are required for the formation of TNTs between primary mouse neurons and astrocytes and in multiple other mammalian cell types. We also report that the Caenorhabditis elegans orthologs of 14-3-3ζ and MSec regulate the size and architecture of the TNT-like cellular protrusions of the distal tip cell (DTC), the germline stem cell niche in the gonad. Our study demonstrates a novel and potentially conserved mRNA-guided mechanism of TNT formation through the maintenance of cellular 14-3-3ζ mRNA levels by the RBP nucleolin.

Membrane interaction to intercellular spread of pathology in Alzheimer’s disease

“…Similarly the endocytosis of HIV (human immunodeficiency virus) and HSV (herpes simplex virus) viruses via PAK dependent route induces the biogenesis of TNTs (Van den Broeke et al, 2009;Mukerji et al, 2012;Jacob et al, 2015;Jansens et al, 2020). Furthermore, cofilin an actin-binding protein, a downstream signaling cascade of PAK1, modulates F-actin polymerization and biogenesis of TNTs (Dagar et al, 2021). In our recent study, we have observed that the Aβ induced membrane damage instigates PAK1 dependent endocytosis and coupled lysosomal exocytosis to repair the membrane.…”

“…Role of cofilin has recently been reported in the biogenesis of TNT. A recent study by Dagar et al (2021); suggests that, in addition to cofilin-regulated actin modulation, the exocyst complex protein, M-sec dependent recycling of membrane needs to function in a cohort, as a necessary step in the biogenesis of TNTs. RNA-binding protein nucleolin interacts with M-sec, while nucleolin regulates 14-3-3ζ mRNA, which is also required for the formation of TNT.…”

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“…Após a descoberta dos nanotubos de tunelamento, eles foram observados em vários tipos celulares (in vitro) como: células imunes (71,(74)(75)(76), células renais (69,77), células epiteliais (78,79), células tumorais (80)(81), neurônios e astrócitos (82)(83)(84). Em células T Jurkat, nanotubos são capazes de conectar cerca de 15% das células em condições normais de cultura, sendo então um ótimo modelo de estudo para estas estruturas (85).…”

Oxidative stress and Rho GTPases in the biogenesis of tunnelling nanotubes: implications in disease and therapy

“…The actin-binding ability of the protein is modulated by phosphorylation of βCamKII [ 117 ]. Inactivation of cofilin by the RNA-binding protein nucleolin induces TNT biogenesis [ 118 ]. In addition, the alphaherpesvirus-induced biogenesis of TNTs depends on the US3 protein kinase-mediated activation of p21-activated kinases (PAKs) apparently by activation of Cdc42/Rac1 and Rho signalling axis, within a poorly understood complex mechanism [ 32 ].…”

“…Altogether, these studies suggest a complex regulatory mechanism of Rho GTPases in TNT biogenesis. A further recent report [ 118 ], has also shown that M-sec regulated exocyst complex needs to function together with actin polymerization by inhibiting activity of cofilin in the biogenesis of TNTs in multiple mammalian cellular models. The study suggests that in addition to actin polymerization, M-Sec-dependent plasma membrane (PM) re-modelling is a necessary step in formation of TNTs.…”