Lithium ion inhibits nerve growth factor-induced neurite outgrowth and phosphorylation of nerve growth factor-modulated microtubule-associated proteins.

Abstract

LiCI (2.5-20 mM) reversibly suppressed nerve growth factor (NGF)-induced neurite outgrowth by cultured rat PC12 pheochromocytoma cells. Similar concentrations of LiCI also reversibly blocked NGF-dependent regeneration of neurites by PC12 cells that had been primed by long-term pre-exposure to NGF and by cultured newborn mouse sympathetic neurons. In contrast, transcription-dependent responses of PC12 cells to NGF such as priming and induction of the NGF-inducible large external glycoprotein, occurred despite the presence of Li ÷. SDS PAGE analysis of total cellular phosphoproteins (labeled by 2-h exposure to 32p_ orthophosphate) from neurite-bearing primed PC12 ceils revealed that Li ÷ reversibly inhibited the phosphorylation of a band of Mr 64,000 that was barely detectable in NGF-untreated PC12 cells. However, Li ÷ did not appear to affect the labeling of other phosphoproteins in either NGF-primed or untreated PC12 cultures, nor did it affect the rapid increase in phosphorylation of several proteins that occurs when NGF is first added to unprimed cultures. Several criteria indicated that the NGF-inducible phosphoprotein of Mr 64,000 is a microtubule-associated protein (MAP). Of the NGF-inducible phosphorylated MAPs that have been detected in PC12 cells (Mr 64,000, 72,000, 80,000, and 320,000), several (Mr 64,000, 72,000, and 80,000) were found to be substantially less phosphorylated in the presence of Li ÷. Neither a phorbol ester tumor promotor nor permeant cAMP analogs reversed the inhibitory effects of Li ÷ on neurite outgrowth or on phosphorylation of the component of Mr 64,000. Microtubules are a major and required constituent of neurites, and MAPs may regulate the assembly and stability of neuritic microtubules. The observation that Li ÷ selectively inhibits NGF-induced neurite outgrowth and MAP phosphorylation suggests a possible causal relationship between these two events.

Wnt-3a and Dvl Induce Neurite Retraction by Activating Rho-Associated Kinase

“…LiCl is known to inhibit GSK-3 and to activate the canonical ␤-catenin pathway (15). LiCl has also been shown to inhibit NGF-dependent neurite outgrowth in PC12 cells, probably through inhibition of the phosphorylation of microtubule-associated proteins (10). As shown in Fig.…”

Glycogen Synthase Kinase 3- and Extracellular Signal-Regulated Kinase-Dependent Phosphorylation of Paxillin Regulates Cytoskeletal Rearrangement

“…ERK/GSK-3-mediated phosphorylation of paxillin is involved in NGF-induced PC12 cell neurite outgrowth. Both GSK-3 and ERK are required for NGF-induced neuronal cell neurite outgrowth (7,33). To assess the role of ERK/GSK-3-mediated paxillin phosphorylation in neurite extension, PC12 cells were transiently transfected with EGFP-paxillin or EGFPpaxillin S126A/S130A, and the NGF-induced neurite extension of these cells was examined after 36 h. Transfected cells were identified as green cells by fluorescence microscopy, and neurite extension was examined by phase-contrast microscopy (Fig.…”

Lithium Attenuates Nerve Growth Factor–Induced Activation of AP-1 DNA Binding Activity in PC12 Cells

“…Therefore, to obtain a large, reproducible inhibitory effect of lithium, a concentration of 5 mmol/L lithium was used in the majority of the experiments. Although it appears that this higher concentration of lithium was accentuating the response obtained with a therapeutic lithium concentration (1 mmol/L), the results must be interpreted cautiously since it is possible that the effects of 5 mmol/L lithium represent toxic, rather than therapeutic, responses to lithium (Burstein et al 1985). It is not known if toxic effects of lithium are due to greater magnitude of effects at the same sites modulated by therapeutic levels of lithium, or if they result from different sites of action.…”