NGF activation of TrkA decreases N-myc expression via MAPK path leading to a decrease in neuroblastoma cell number

Abstract

In neuroblastoma (NB), expression of the TrkA receptor is correlated with good prognosis while N-myc amplification is correlated with poor prognosis. Decreased N-myc levels are key to controlling growth and inducing differentiation in NB cells. In this report, we detail mechanisms by which nerve growth factor (NGF) decreases N-myc levels in TrkA-transfected NB cells and its effect on NB cell proliferation. NGF induced a decrease in N-myc mRNA within 1 h of treatment that occurred in the presence of cycloheximide. The stability of N-myc mRNA was not affected by NGF, indicating a transcriptional control of N-myc mRNA by NGF. NGF but not brain-derived neurotrophic factor (BDNF) decreased N-myc levels demonstrating that p75 alone was not involved. The NGF-induced decrease in N-myc expression was blocked by the Trk tyrosine kinase (TK) antagonist K252a indicating that signals transduced by Trk TK downstream targets were involved. Pharmacologic inhibitors implicated the mitogen-activated protein kinase (MAPK) path. This was supported by the finding that expression of a constitutively activated component of the MAPK path, MAPK kinase (MEK), decreased Nmyc levels. Alterations in the level of N-myc are known to alter NB cell cycle progression by affecting the levels of E2Fs and p27 kip1 . Consistent with these findings, NGF decreased NB cell number and decreased cyclin Edependent kinase activity via an increase in p27 kip1 . Thus, our results indicate that the MAP kinase is selectively involved in the NGF-induced N-myc downregulation through a transcriptional mechanism. Furthermore, NGF affects the time required for 15N TrkA cells to complete a replication cycle by decreasing N-myc, E2Fs, cyclin E kinase activity and increasing p27 kip1 binding to cyclin E kinase.

On the death Trk

“…Nonetheless, Lucarelli et al (1997) showed that TrkA-transfected clones of N15 neuroblastoma cells exhibited a significant reduction in proliferation in response to NGF, while treatment of TrkB-transfected clones with BDNF had no effect. A decrease in neuroblastoma cell number was reported in another study from the same group, due to a TrkA-mediated decrease in N-myc expression (Woo et al, 2004). More recently, Kaplan and coworkers showed that virally mediated expression of TrkA induces apoptosis in two neuroblastoma cell lines, via a mechanism dependent on p53 and caspases (Lavoie et al, 2005).…”

All-trans retinoic acid arrests neuroblastoma cells in a dormant state. Subsequent nerve growth factor/brain-derived neurotrophic factor treatment adds modest benefit

“…According to Eggert et al [21], expression of TrkA resulted in growth inhibition of the transfected cells compared to parental cells, whereas TrkB transfectants demonstrated an increased proliferation rate. Woo et al [8] detailed mechanisms by which NGF decreased N-myc mRNA levels in TrkA-transfected NB cells and reduced proliferation. Ho et al [22] provided in vitro evidence that the TrkB-BDNF pathway is associated with enhanced survival and resistance to chemotherapy in the NB cell line SH-SY5Y.…”

“…These pathways may provide attractive targets for the development of therapy aimed at inducing differentiation or programmed cell death in these tumors. There is evidence that retinoids [3][4][5], neurotrophins [6][7][8], and substances secreted by Schwann cells [9,10] are strong antiproliferative agents and play key roles for a good outcome in NB. However, experimental data about their relative performance to inhibit proliferation of NB cell lines as well as their possible additive effects and interactions are contradictory, with some works postulating synergistic [11], other antagonistic effects for the neurotrophin brain-derived neurotrophic factor (BDNF; Tebu-Bio/ Peprotech, Offenbach, Germany) and nerve growth factor (NGF; Tebu-Bio/Peprotech, Offenbach, Germany) [12].…”

Insulin-like growth factor-I induces the phosphorylation and nuclear exclusion of forkhead transcription factors in human neuroblastoma cells

“…The most studied growth factor in NBL is nerve growth factor (NGF) which has a negative effect on NBL cell survival and growth. 3,4 In contrast, brain derived growth factor (BDNF) protects NBL from drug-induced apoptosis in vitro 5,6 and is associated with poor prognosis in NBL patients. 7 We have recently shown that insulin-like growth factor-I (IGF-I) signaling through its receptor (type I IGF receptor, IGF-IR) is altered and IGF-IR expression levels are increased in tumorigenic NBL cells.…”