Title: Methylmercury decreases NGF-induced TrkA autophosphorylation and neurite outgrowth in PC12 cells.

Authors: Parran, Damani K; Barone Jr, Stanley; Mundy, William R

Published In Brain Res Dev Brain Res, (2003 Mar 14)

Abstract: Neurotrophin signaling through Trk receptors is important for differentiation and survival in the developing nervous system. The present study examined the effects of CH(3)Hg on (125)I-nerve growth factor (NGF) binding to the TrkA receptor, NGF-induced activation of the TrkA receptor, and neurite outgrowth in an in vitro model of differentiation using PC12 cells. Whole-cell binding assays using (125)I-NGF revealed a single binding site with a K(d) of approximately 1 nM. Methylmercury (CH(3)Hg) at 30 nM (EC(50) for neurite outgrowth inhibition) did not affect NGF binding to TrkA. TrkA autophosphorylation was measured by immunoblotting with a phospho-specific antibody. TrkA autophosphorylation peaked between 2.5 and 5 min of exposure and then decreased but was still detectable at 60 min. Concurrent exposure to CH(3)Hg and NGF for 2.5 min resulted in a concentration-dependent decrease in TrkA autophosphorylation, which was significant at 100 nM CH(3)Hg. To determine whether the observed inhibition of TrkA was sufficient to alter cell differentiation, NGF-stimulated neurite outgrowth was examined in PC12 cells after exposure to 30 nM CH(3)Hg, a concentration that inhibited TrkA autophosphorylation by approximately 50%. For comparison, a separate group of PC12 cells were exposed to a concentration of the selective Trk inhibitor K252a (30 nM), which had been shown to produce significant inhibition of TrkA autophosphorylation. Twenty-four hour exposure to either CH(3)Hg or K252a reduced neurite outgrowth to a similar degree. Our results suggest that CH(3)Hg may inhibit differentiation of PC12 cells by interfering with NGF-stimulated TrkA autophosphorylation.

PubMed ID: 12644250

MeSH Terms: Animals; Binding Sites/drug effects; Binding Sites/physiology; Binding, Competitive/drug effects; Binding, Competitive/physiology; Carrier Proteins/drug effects*; Carrier Proteins/metabolism; Cell Differentiation/drug effects*; Cell Differentiation/physiology; Central Nervous System/abnormalities; Central Nervous System/drug effects*; Central Nervous System/pathology; Dose-Response Relationship, Drug; Down-Regulation/drug effects; Down-Regulation/physiology; Enzyme Inhibitors/pharmacology; Female; Membrane Proteins/drug effects*; Membrane Proteins/metabolism; Mercury Poisoning, Nervous System/enzymology*; Mercury Poisoning, Nervous System/pathology; Mercury Poisoning, Nervous System/physiopathology; Methylmercury Compounds/toxicity*; Nerve Growth Factor/antagonists & inhibitors*; Nerve Growth Factor/metabolism; Neurites/drug effects*; Neurites/enzymology; Neurites/pathology; PC12 Cells; Phosphorylation/drug effects; Pregnancy; Prenatal Exposure Delayed Effects*; Rats; Receptor, trkA*