title: 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 N-myc 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 E-dependent 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.
authors.affiliation: Cell & Molecular Biology Section, Pediatric Oncology Branch, NCI, NIH, Bethesda, MD 20892, USA.
authors.forename: Chan-Wook
authors.initials: CW
authors.lastname: Woo
authors.forename: Enrico
authors.initials: E
authors.lastname: Lucarelli
authors.forename: Carol J
authors.initials: CJ
authors.lastname: Thiele
mesh_terms: D002227:Carbazoles / Q000494:pharmacology; D002452:Cell Count; D018797:Cell Cycle Proteins / Q000187:drug effects / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D019927:Cyclin E; D018844:Cyclin-Dependent Kinases / Q000187:drug effects / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D026121:Indole Alkaloids; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D020932:Nerve Growth Factor / Q000494:pharmacology*; D009447:Neuroblastoma; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D020917:Receptor, trkA / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D002227:Carbazoles; D018797:Cell Cycle Proteins; D019927:Cyclin E; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D004791:Enzyme Inhibitors; D026121:Indole Alkaloids; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; D020932:Nerve Growth Factor; C049985:staurosporine aglycone; D020917:Receptor, trkA; D018844:Cyclin-Dependent Kinases; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases; C482576:MAP3K1 protein, human