Fast-diffusing p75 ^NTR monomers support apoptosis and growth cone collapse by neurotrophin ligands

Abstract

SignificanceNeurotrophins (NTs) are homodimeric growth factors displaying fundamental roles in the nervous system. Their activity stems from binding and activation of 3 different receptor types in nervous cell membranes. The p75 NT receptor (p75NTR) was the first to be discovered in 1986; nevertheless, for the numerous structural and functional facets so far reported, its activation mechanisms have remained elusive. Here, we demonstrate that its pleiotropic functions are regulated by different redistributions of the receptors, which crucially depend on the available NT and on the involved subcellular compartment but are unrelated to its oligomerization state. Single-particle studies proved receptors to be monomers with a fast-diffusive behavior in the membrane with, at most, transient self-interactions on the millisecond time scale.

Fluorolabeling of the PPTase-Related Chemical Tags: Comparative Study of Different Membrane Receptors and Different Fluorophores in the Labeling Reactions

“…Here, we apply it to the case of chemical tags target of PPTase conjugations (Yin et al, 2005). Together with other works by our group and others (De Nadai et al, 2016;Di Matteo et al, 2017;Gobbo et al, 2018;Marchetti et al, 2019;Amodeo et al, 2020), we provide evidence for a good labeling performance of these tags both on purified proteins (Figure 4) and on membrane receptors of living cells (Figures 1-3). In the former case, we established, by means of experiments in living neurons, that the identity of the fluorophore does not affect biological function, provided that purification in vitro of the labeled protein is achieved.…”

“…From the chemical labeling perspective, their extracellular domains (ECDs) have different lengths, with p75NTR displaying the shortest and VEGFR2 the longest distance from cell surface. Cloning of the S6 tag sequence at the ECD of the three of them previously allowed for their labeling and imaging with SM resolution on the cell surface in living cells (Marchetti et al, 2019;Amodeo et al, 2020). Here, we compared how the same labeling reactions perform on these three moieties, considering also their different exposure from the cell membrane, which may be relevant for enzymatic recognition of the tag.…”

“…In the last years, our group has exploited the acyl and peptidyl carrier protein (ACP and PCP) derived chemical tags applied to the labeling of neurotrophins and their receptors, respectively, acting on the purified protein and in a living cell context (Callegari et al, 2012;Gobbo et al, 2018;Marchetti et al, 2019;Amodeo et al, 2020). A great advantage of this labeling technology is that these short peptides, once inserted in the protein of interest, have low steric footprint on its structure and function.…”

NTRK Fusions in Central Nervous System Tumors: A Rare, but Worthy Target

“…Neurotrophin-3 (NT-3) binds TRK-C, while TRK-B has a lower binding specificity since both brain-derived growth factor (BDNF) and neurotrophin-4 (NT-4) can be ligands of this receptor [30][31][32][33][34]. Furthermore, also p75NTR, a membrane receptor, member of the tumor necrosis factor (TNF) receptor family, binds all the spectrum of neurotrophins described above and plays a crucial role in balancing cell survival versus death during CNS development [35]. Indeed, these last ligand-receptor relationships should be considered of low affinity [36,37].…”

Contribution of Neurotrophins to the Immune System Regulation and Possible Connection to Alcohol Addiction

“…It was shown that pro-NGF simultaneously binds p75NTR and sortilin to initiate signaling [6]. It should be noted that the formation of this complex was not confirmed by structural biology methods, and the exact signaling mechanism therefore remains to be established [7]. Interestingly, TrkA-mediated NGF activation of ADP-ribosylation factor 6 (ARF6) was shown to be important for increasing the expression of the p75NTR receptor, highlighting the possibility of regulation of sympathetic neurons response to neurotrophins during development [8].…”