title: Rapamycin inhibits proliferation of human neuroblastoma cells without suppression of MycN.
abstract: MYCN and insulin-like growth factor (IGF) system are important for the pathogenesis and development of neuroblastoma. We previously reported evidence of a direct linkage between MycN and the IGF system in KP-N-RT human neuroblastoma cells, where IGF-I induced both MycN expression at the RNA level and G1-S cell cycle progression through the IGF-I receptor (IGF-IR)/ MEK/ mitogen-activated protein kinase (MAPK) pathway (A. Misawa et al., Cancer Res, 2000; 60:64-9). Our data also showed the possibility of a potent IGF-IR downstream signal cascade that accelerates progression into the S-phase, other than the MAPK pathway. In this study, we further investigated the role of this alternative pathway in the growth of neuroblastoma cells. A phosphoinositide 3-kinase (PI3K) inhibitor wortmannin blocked IGF-I-mediated induction of MycN. Our data suggest that the inhibition of MycN by wortmannin was transmitted through the MAPK pathway. Progression of the cell cycle from G1 to S phase was inhibited up to 90% by wortmannin or rapamycin, an inhibitor of mTOR, which acts downstream of PI3K. Despite its effects on induction of MycN and on progression through S phase, wortmannin did not block proliferation of neuroblastoma cells. On the other hand, rapamycin inhibited both IGF-I-induced cell cycle progression and cell proliferation in complete medium, although it had no effect on IGF-I-mediated MycN induction. Our study indicates maintenance of cell proliferation requires mTOR function, which is independent of MycN induction in human neuroblastoma cells.
authors.affiliation: Department of Pediatrics, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto, Japan. amisawa@koto.kpu-m.ac.jp
authors.forename: Akiko
authors.initials: A
authors.lastname: Misawa
authors.forename: Hajime
authors.initials: H
authors.lastname: Hosoi
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Tsuchiya
authors.forename: Tohru
authors.initials: T
authors.lastname: Sugimoto
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D000071447:N-Myc Proto-Oncogene Protein; D009447:Neuroblastoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; C459801:MYCN protein, human; D000071447:N-Myc Proto-Oncogene Protein; D009687:Nuclear Proteins; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D020123:Sirolimus; D000077191:Wortmannin