title: Abrogation of nerve growth factor-induced terminal differentiation by ret oncogene involves perturbation of nuclear translocation of ERK.
abstract: Oncogenic variants of the receptor tyrosine kinase, Ret, cause formation of tumors of neuroendocrine derivation in the multiple endocrine neoplasia type 2 and, thus, likely interfere with antiproliferative and/or differentiative extracellular signals. Here we took advantage of two rat pheochromocytoma-derived cell lines (PC12/MEN2A and PC12/MEN2B) to investigate whether Ret-induced nerve growth factor (NGF) unresponsiveness might involve impairment of ERK signaling. In fact, these cells, stably transfected with distinct forms of the active ret oncogene, fail to block proliferation, even upon NGF stimulation. In these cells we show the presence of both chronic ERKs activity and high expression levels of MKP-3, an ERK-specific phosphatase. Despite the presence of MKP-3, ERK activity can be further stimulated by NGF, but it fails to translocate into the nucleus and consequently to induce immediate-early gene transcription. Because of the presence of MKP-3, our results suggest the existence of a negative regulatory feedback acting on ERKs as a mechanism responsible for the abrogation of NGF-induced terminal differentiation. Indeed, MKP-3 seems to be implicated in the persistence of ERKs in cell cytoplasm. This interpretation is further supported by the observation that in ret-transfected cells, forced expression of an active form of MEK-1 may overcome this block; it restores transcription from the c-fos promoter, induces translocation of ERKs into the nucleus, and inhibits cell proliferation.
authors.affiliation: Centro di Endocrinologia ed Oncologia Sperimentale del CNR "G. Salvatore," c/o Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università di Napoli Federico II, via S. Pansini 5, Naples, Italy.
authors.forename: G L
authors.initials: GL
authors.lastname: Colucci-D'Amato
authors.forename: A
authors.initials: A
authors.lastname: D'Alessio
authors.forename: D
authors.initials: D
authors.lastname: Califano
authors.forename: G
authors.initials: G
authors.lastname: Cali
authors.forename: C
authors.initials: C
authors.lastname: Rizzo
authors.forename: L
authors.initials: L
authors.lastname: Nitsch
authors.forename: G
authors.initials: G
authors.lastname: Santelli
authors.forename: V
authors.initials: V
authors.lastname: de Franciscis
mesh_terms: D000818:Animals; D001692:Biological Transport; D002454:Cell Differentiation / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism*; D029721:Drosophila Proteins; D005786:Gene Expression Regulation / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D020932:Nerve Growth Factor / Q000502:physiology*; D009857:Oncogenes; D016716:PC12 Cells; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D051096:Proto-Oncogene Proteins c-ret; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D029721:Drosophila Proteins; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D020932:Nerve Growth Factor; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; C495001:Ret protein, rat; D020928:Mitogen-Activated Protein Kinases