Nerve Growth Factor (NGF) Loop 4 Dimeric Mimetics Activate ERK and AKT and Promote NGF-like Neurotrophic Effects

Abstract

Previous work indicating that nerve growth factor (NGF) protein loops 2 and 4 interact with TrkA receptors raise the possibility that small molecule mimetics corresponding to TrkA-interacting domains that have NGF agonist activity can be developed. We applied our previously developed strategy of dimeric peptidomimetics to address the hypothesis that loop 4 small molecule dimeric mimetics would activate TrkA-related signal transduction and mimic NGF neurotrophic effects in a structure-specific manner. A loop 4 cyclized peptide dimer demonstrated NGF-like neurotrophic activity, whereas peptides with scrambled sequence, added or substituted residues, or cyclized in monomeric form were inactive. Activity was blocked by the TrkA inhibitors K252a and AG879 but not by NGF p75 receptor blocking antibody. Dimeric, but not monomeric, peptides partially blocked NGF activity. This profile was consistent with that of a NGF partial agonist. ERK and AKT phosphorylation was stimulated only by biologically active peptides and was blocked by K252a. The ERK inhibitor U0126 blocked the neurite-but not the survival-promoting activity of both NGF and active peptide. These studies support the proof of concept that small molecule NGF loop 4 mimetics can activate NGF signaling pathways and can mimic death-preventing and neurite-promoting effects of NGF. This finding will guide the rational design of NGF single-domain mimetics and contribute to elucidating NGF signal transduction mechanisms.Nerve growth factor (NGF) 1 acts via TrkA and p75 receptors to regulate neuronal survival, promote neurite outgrowth, and up-regulate certain neuronal functions such as mediation of pain and inflammation (1-5). These actions suggest that NGF agonists or antagonists might be useful in regulating these processes (6 -8). Factors limiting therapeutic applications of the NGF protein include restricted penetration of the central nervous system and the poor medicinal properties characteristic of most proteins (9, 10). The development of small molecule mimetics with favorable chemical properties that function as agonists or antagonists that mimic or inhibit NGF functions in the appropriate biological context will be critical in advancing potential in vivo applications of NGF. Moreover, in settings in which NGF might contribute to neuronal death, pain, or inflammatory mechanisms, NGF antagonists may be particularly relevant. Creation of single domain NGF mimetics will also constitute a powerful approach for linking specific NGF domains with specific patterns of intracellular signal transduction.A NGF mimetic (agonist or antagonist) would be expected to contain structural determinants of one or more NGF active sites that interact with NGF receptors. Multiple techniques have been used to deduce which domains of the NGF protein interact with NGF receptors (11). A peptide mapping approach in which synthetic peptides with sequences corresponding to specific NGF regions were tested for their ability to inhibit NGF activity pointed to residues 29 -35 as a key active ...

A New Nerve Growth Factor-Mimetic Peptide Active on Neuropathic Pain in Rats

“…Cyclic and homodimeric cyclic peptides have been shown to function as a partial NGF agonist (Longo et al, 1997;Xie et al, 2000). Our data indicate that L1L4 exerts biological activity at concentrations much lower than those reported in the literature, suggesting that the presence of two distinct loops is another important structural requirement for proper receptor activation.…”

“…The first NGF loop domain peptides described to have neurotrophic activity were the loop 1 homodimer mimetics described by Longo et al (1997). Subsequent studies (Maliartchouk et al, 2000a,b;Xie et al, 2000) described loop 4 mimetics with agonist activity.…”

Selectivity of Cell Signaling in the Neuronal Response Based on NGF Mutations and Peptidomimetics in the Treatment of Alzheimers Disease

“…Thus, the dimeric peptide was able to induce an NGF-like signal, by binding to and activating TrkA. Modifications in the peptide sequence abolished the agonistic activity, suggesting specificity conferred by the amino acid sequence (Xie et al, 2000). On the other hand, dimerization of a peptidomimetic does not always behave as expected.…”

“…Other studies, however, reported that cyclized monomeric loop 4 peptide mimetics had to be presented as dimers of cyclized peptides to show agonistic activity (Xie et al, 2000). Their dimeric cyclized peptide, involving amino acids 92-96, showed NGF like activity and induced neurite outgrowth and Akt activation in a TrkA-and ERK-dependent manner.…”

Tyrphostin ErbB2 Inhibitors AG825 and AG879 Have Non-specific Suppressive Effects on gp130/ STAT3 Signaling

“…For example, the ability of one EGFR inhibitor to up-regulate the retinoic acid receptor was shown to be independent of its ability to inhibit EGFR (Grunt et al, 2007), and AG1478 is known to inhibit potassium channel activity in addition to inhibiting ErbB1 (Choi et al, 2002). It should also be noted that AG879 is commonly used as a TrkA inhibitor (Xie et al, 2000). Thus, it seems plausible that AG825 and AG879 might possibly inhibit a crucial protein kinase or phosphatase involved in the IL-6 signaling pathway.…”