title: Overexpression of the S-phase kinase-associated protein 2 in thyroid cancer.
abstract: Loss of expression of the cyclin-dependent kinase inhibitor p27 through enhanced protein degradation frequently occurs in human cancer. Degradation of p27 requires ubiquitination by the S-phase kinase-associated protein 2 (Skp2), a member of the F-box family of Skp1-Cullin-F-box protein ubiquitin ligases. In the present study, we have investigated the role of Skp2 in human thyroid tumours. Immunohistochemistry analysis showed that Skp2 was overexpressed significantly in thyroid carcinomas (26 out of 51) compared with goitres (0 out of 12, P<0.001) or adenomas (1 out of 10, P<0.05), and that high Skp2 expression was detected more often in anaplastic thyroid (ATC; 83%, n=12) than follicular thyroid (FTC; 40%, n=20) or papillary thyroid (PTC; 42%, n=19) carcinomas (P<0.05). Thyroid cancer cell lines and tissues with high levels of Skp2 protein presented high p27 degradation activity and there was an inverse correlation between Skp2 and p27 expression in thyroid cancer tissues (n=68; P<0.05). In most cases, the observed overexpression of Skp2 protein was paralleled by an increase in the levels of Skp2 mRNA, and we observed Skp2 gene amplification at 5p13 in 2 out of 6 cell lines and in 9 out of 23 primary tumours (six out of eight ATCs, two out of nine PTCs and one out of six FTCs) using Q-PCR and/or fluorescence in situ hybridization analysis. Finally, in vitro experiments demonstrated that suppression of Skp2 expression drastically reduced proliferation of thyroid cancer cells and, conversely, forced expression of Skp2 circumvented serum dependency and contact inhibition in Skp2-negative cells by promoting p27 degradation. These findings indicate that Skp2 plays an important role for the development of thyroid cancer.
authors.affiliation: Laboratorio Oncologia Sperimentale III, Istituto Nazionale Tumori, via M. Semmola, 80131 Napoli, Italy.
authors.forename: Gennaro
authors.initials: G
authors.lastname: Chiappetta
authors.forename: Carmela
authors.initials: C
authors.lastname: De Marco
authors.forename: Alfina
authors.initials: A
authors.lastname: Quintiero
authors.forename: Daniela
authors.initials: D
authors.lastname: Califano
authors.forename: Simona
authors.initials: S
authors.lastname: Gherardi
authors.forename: Donatella
authors.initials: D
authors.lastname: Malanga
authors.forename: Marianna
authors.initials: M
authors.lastname: Scrima
authors.forename: Cristina
authors.initials: C
authors.lastname: Montero-Conde
authors.forename: Letizia
authors.initials: L
authors.lastname: Cito
authors.forename: Mario
authors.initials: M
authors.lastname: Monaco
authors.forename: Maria Letizia
authors.initials: ML
authors.lastname: Motti
authors.forename: Rosa
authors.initials: R
authors.lastname: Pasquinelli
authors.forename: Valter
authors.initials: V
authors.lastname: Agosti
authors.forename: Mercedes
authors.initials: M
authors.lastname: Robledo
authors.forename: Alfredo
authors.initials: A
authors.lastname: Fusco
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Viglietto
mesh_terms: D002277:Carcinoma / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000032:analysis / Q000378:metabolism; D005784:Gene Amplification; D006801:Humans; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology*
chemical_list: D012333:RNA, Messenger; D044786:S-Phase Kinase-Associated Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27