title: RET/papillary thyroid carcinoma oncogenic signaling through the Rap1 small GTPase.
abstract: RET/papillary thyroid carcinoma (PTC) oncoproteins result from the in-frame fusion of the RET receptor tyrosine kinase with protein dimerization motifs encoded by heterologous genes. Here, we show that RET/PTC1 activates the Rap1 small GTPase. The activation of Rap1 was dependent on the phosphorylation of RET Tyr(1062). RET/PTC1 recruited a complex containing growth factor receptor binding protein 2-associated binding protein 1 (Gab1), CrkII (v-crk sarcoma virus CT10 oncogene homologue II), and C3G (Rap guanine nucleotide exchange factor 1). By using dominant-negative and small interfering duplex (small interfering RNA) oligonucleotides, we show that RET/PTC1-mediated Rap1 activation was dependent on CrkII, C3G, and Gab1. Activation of Rap1 was involved in the RET/PTC1-mediated stimulation of the BRAF kinase and the p42/p44 mitogen-activated protein kinases. Proliferation and stress fiber formation of RET/PTC1-expressing PC Cl 3 thyroid follicular cells were inhibited by the dominant-negative Rap1(N17) and by Rap1-specific GTPase-activating protein. Thus, Rap1 is a downstream effector of RET/PTC and may contribute to the transformed phenotype of RET/PTC-expressing thyrocytes.
authors.affiliation: Istituto di Endocrinologia ed Oncologia Sperimentale del CNR G. Salvatore, c/o Dipartimento di Biologia e Patologia Cellulare e Molecolare, Universita' Federico II, via Sergio Pansini 5, 8-131 Naples, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: De Falco
authors.forename: Maria Domenica
authors.initials: MD
authors.lastname: Castellone
authors.forename: Gabriella
authors.initials: G
authors.lastname: De Vita
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Cirafici
authors.forename: Jerome M
authors.initials: JM
authors.lastname: Hershman
authors.forename: Carmen
authors.initials: C
authors.lastname: Guerrero
authors.forename: Alfredo
authors.initials: A
authors.lastname: Fusco
authors.forename: Rosa Marina
authors.initials: RM
authors.lastname: Melillo
authors.forename: Massimo
authors.initials: M
authors.lastname: Santoro
mesh_terms: D000199:Actins / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D002291:Carcinoma, Papillary / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D006801:Humans; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D048493:Proto-Oncogene Proteins B-raf / Q000096:biosynthesis / Q000235:genetics; D050737:Proto-Oncogene Proteins c-crk / Q000378:metabolism; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D013964:Thyroid Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D014162:Transfection; D020827:rap1 GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; C098587:GAB1 protein, human; D050737:Proto-Oncogene Proteins c-crk; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D020559:Monomeric GTP-Binding Proteins; D020827:rap1 GTP-Binding Proteins