Signal Transduction Pathways through TRK-A and TRK-B Receptors in Human Neuroblastoma Cells

National Institute of Neuroscience, NationalCenter of Neurology and Psychiatry, 4-1-1 Ogawakawahigashi-cho, Kodaira, Tokyo 187-8502Little is known about the signal transduction pathways of TRK family receptors in neuroblastoma(NB) cells. In this study, an NB cell line, designated MP-N-TS, was established from an adrenaltumor taken from a 2-year-old boy. This cell line expressed both TRK-A and TRK-B receptors,which is rare in a single NB cell line. Therefore, the MP-N-TS cell line was used to determinewhether the signal transduction through these constitutive receptors is functional. Three neurotro-phins, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5), induced tyrosine phosphorylation of panTRK, and BDNF and NT-4/5 induced tyrosinephosphorylation of TRK-B. Tyrosine phosphorylation of panTRK and/or TRK-B by the neurotro-phins was inhibited in the presence of a tyrosine kinase inhibitor K252a. Tyrosine phosphorylationof Src homologous and collagen (Shc), extracellular signal-regulated kinase (ERK)-1 and ERK-2,and phospholipase C-γ1 (PLC-γ1) was increased by the three neurotrophins and the increase wasinhibited in the presence of K252a. Activation of Ras, detected as the GTP-bound form of Ras, wasinduced by the three neurotrophins. The neurotrophins did not modulate the expressions of TRK-A or TRK-B mRNA, but they did induce the expression of c-fos mRNA. Exogenous NGF inducedweak neurite outgrowth, whereas exogenous BDNF and NT-4/5 induced distinct neurite out-growth. Exogenous BDNF and NT-4/5 increased the number of viable cells, while NGF did not.Our results demonstrate that the signal transduction pathways through TRK-A and TRK-B inMP-N-TS cells are functional and similar, and the main downstream signaling pathways from thethree neurotrophins are mitogen-activated protein kinase (MAPK) cascades through Shc, activatedRas, ERK-1 and ERK-2, and the transduction pathway through PLC-γ1. Further, BDNF and NT-4/5 increased cell viability. The MP-N-TS cell line should be useful for clarifying the TRK-A andTRK-B signaling pathways responsible for the different prognoses in patients with NB.Key words: Signal transduction — Neuroblastoma — TRK-A — TRK-B — Neurotrophins