title: Conditional apoptosis induced by oncogenic ras in thyroid cells.
abstract: Mutations of ras are tumor-initiating events for many cell types, including thyrocytes. To explore early consequences after oncogenic Ras activation, we developed a doxycycline-inducible expression system in rat thyroid PCCL3 cells. Beginning 3-4 days after H-Ras(v12) expression, cells underwent apoptosis. The H-Ras(v12) effects on apoptosis were decreased by a mitogen-activated protein kinase kinase (MEK1) inhibitor and recapitulated by doxycycline-inducible expression of an activated MEK1 mutant (MEK1(S217E/S221E)). As reported elsewhere, acute expression of H-Ras(v12) also induces mitotic defects in PCCL3 cells through ERK (extracellular ligand-regulated kinase) activation, suggesting that apoptosis may be secondary to DNA damage. However, acute activation of SAPK/JNK (stress-activated protein kinase/Jun N-terminal kinase) through acute expression of Rac1(v12) also triggered apoptosis, without inducing large-scale genomic abnormalities. H-Ras(v12)-induced apoptosis was dependent on concomitant activation of cAMP by either TSH or forskolin, in a protein kinase A-independent manner. Thus, coactivation of cAMP-dependent pathways and ERK or JNK (either through H-Ras(v12), Rac1(v12), or MEK1(S217E/S221E)) is inconsistent with cell survival. The fate of thyrocytes within the first cell cycles after expression of oncogenic Ras is dependent on ambient TSH levels. If both cAMP and Ras signaling are simultaneously activated, most cells will die. Those that survive will eventually lose TSH responsiveness and/or inactivate the apoptotic cascade through secondary events, thus enabling clonal expansion.
authors.affiliation: Department of Medicine, University of Cincinnati College of Medicine, Ohio 45267-0547, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Shirokawa
authors.forename: R
authors.initials: R
authors.lastname: Elisei
authors.forename: J A
authors.initials: JA
authors.lastname: Knauf
authors.forename: T
authors.initials: T
authors.lastname: Hara
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: H I
authors.initials: HI
authors.lastname: Saavedra
authors.forename: J A
authors.initials: JA
authors.lastname: Fagin
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D004318:Doxycycline / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D011905:Genes, ras; D007093:Imidazoles / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction; D013961:Thyroid Gland / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D013972:Thyrotropin / Q000378:metabolism / Q000494:pharmacology; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; D011725:Pyridines; D013972:Thyrotropin; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D020830:rac1 GTP-Binding Protein; D004318:Doxycycline; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one