NGF Causes TrkA to Specifically Attract Microtubules to Lipid Rafts

Abstract

Membrane protein sorting is mediated by interactions between proteins and lipids. One mechanism that contributes to sorting involves patches of lipids, termed lipid rafts, which are different from their surroundings in lipid and protein composition. Although the nerve growth factor (NGF) receptors, TrkA and p75NTR collaborate with each other at the plasma membrane to bind NGF, these two receptors are endocytosed separately and activate different cellular responses. We hypothesized that receptor localization in membrane rafts may play a role in endocytic sorting. TrkA and p75NTR both reside in detergent-resistant membranes (DRMs), yet they responded differently to a variety of conditions. The ganglioside, GM1, caused increased association of NGF, TrkA, and microtubules with DRMs, but a decrease in p75NTR. When microtubules were induced to polymerize and attach to DRMs by in vitro reactions, TrkA, but not p75NTR, was bound to microtubules in DRMs and in a detergent-resistant endosomal fraction. NGF enhanced the interaction between TrkA and microtubules in DRMs, yet tyrosine phosphorylated TrkA was entirely absent in DRMs under conditions where activated TrkA was detected in detergent-sensitive membranes and endosomes. These data indicate that TrkA and p75NTR partition into membrane rafts by different mechanisms, and that the fraction of TrkA that associates with DRMs is internalized but does not directly form signaling endosomes. Rather, by attracting microtubules to lipid rafts, TrkA may mediate other processes such as axon guidance.

Lipid rafts, synaptic transmission and plasticity: Impact in age-related neurodegenerative diseases

“…TrkA and p75 NTR are membrane receptors for Nerve Growth Factor (NGF), which mediate antagonistic functions; TrkA mediate cell survival while p75 NTR usually induces programmed cell death. It has been shown that NGF enhances the interaction between TrkA and microtubules in lipid rafts, whereas p75 NTR is sorted out of the rafts (Pryor et al, 2012), suggesting that raft/ cytoskeleton interactions may be relevant for cell fate. Regarding adhesion, a mechanism involving cytoskeleton and raft endocytosis has been proposed, so that when cells detach from the matrix, rafts are internalized and targeted to recycling endosomes in an actin-and microtubule-dependent manner; on the contrary, upon a new adhesion event, lipid rafts return to the cell membrane, through microtubules (Balasubramanian et al, 2007).…”

Signaling Endosomes and Growth Cone Motility in Axon Regeneration

“…Reprinted with permission from the Proceedings of the National Academy of Sciences (Steketee et al, 2011). Pryor, McCaffrey, Young, & Grimes, 2012). Finally, Trk activation is linked to three main intracellular signaling cascades via a wide variety of adaptor proteins, including mitogen-activated kinase (MAPK) (Howe et al, 2001), phospholipase C-gamma (PLCg) (Ming et al, 1999), and phosphoinositol-3-kinase (Quinn & Wadsworth, 2008), further emphasizing the possibility that each signaling endosome, with varying numbers of neurotrophin cargoes and receptors, likely has a distinct molecular and signaling profile.…”

“…Studies suggest the endosomal lipid environment also regulates endosome signaling. Prior to endocytosis, Trk receptors are often found in sphingolipid-cholesterol lipid rafts (Kamiguchi, 2006;Simons & Gerl, 2010), and neurotrophin activation of Trk receptors may stimulate Trk receptors to move into lipid rafts (Pryor et al, 2012). Lipid rafts are dynamic microdomains in the plasma membrane (Dietrich, Yang, Fujiwara, Kusumi, & Jacobson, 2002;Kusumi, KoyamaHonda, & Suzuki, 2004) formed by the preferential association of cholesterol with saturated fatty acids and glycosphingolipids (Simons & Vaz, 2004).…”

“…Lipid rafts are dynamic microdomains in the plasma membrane (Dietrich, Yang, Fujiwara, Kusumi, & Jacobson, 2002;Kusumi, KoyamaHonda, & Suzuki, 2004) formed by the preferential association of cholesterol with saturated fatty acids and glycosphingolipids (Simons & Vaz, 2004). Lipid rafts are concentrated in growth cones and mediate chemotropic guidance (Guirland, Suzuki, Kojima, Lu, & Zheng, 2004;Ibanez, 2004;Kamiguchi, 2006), possibly by locally stabilizing dynamic microtubules (Pryor et al, 2012) and organizing signaling molecule complexes (Golub, Wacha, & Caroni, 2004;Helms & Zurzolo, 2004;Simons & Toomre, 2000) that can modulate the activity of cytoskeletal effectors downstream of activated Trk receptor signaling, like Akt (Grider, Park, Spencer, & Shine, 2009).…”

“…For instance, both in PC12 cells and in DRG neurons, NGF both increased TrkA in lipid rafts and locally stabilized microtubules in lipid rafts with activated Trk receptors. However, activated phospho-TrkA was undetectable in lipid-raft-associated endosomes, suggesting that activated TrkA was sorted into lipid rafts upon activation, dephosphorylated, and then endocytosed into nonsignaling endosomes by a microtubule-dependent mechanism (Pryor et al, 2012).…”