title: Status of RASSF1A in uveal melanocytes and melanoma cells.
abstract: RASSF1A gene, found at the 3p21.3 locus, is a tumor suppressor gene frequently hypermethylated in human cancers. In this study, we report that compared with melanocytes in normal choroid, RASSF1A is downregulated in uveal melanoma samples and in uveal melanoma cell lines. LOH at 3p21.3 was detected in 50% of uveal melanoma. Moreover, methylation of the RASSF1A promoter was detected in 35 of 42 tumors (83%) and RASSF1A was also weakly expressed at the mRNA level. These data indicate that LOH at the RASSF1A locus or RASSF1A promoter methylation may partly account for the suppression of RASSF1A expression observed in uveal melanoma. Furthermore, following ectopic expression in three RASSF1A-deficient melanoma cell lines (OCM-1, Mel270, and 92.1), RASSF1A weakly reduces cell proliferation and anchorage-independent growth of uveal melanoma cells without effect on ERK1/2 activation, cyclin D1 and p27(Kip1) expression. This study explored biological functions and underlying mechanisms of RASSF1A in the ERK1/2 pathway in normal uveal melanocytes. We showed that siRNA-mediated depletion of RASSF1A increased ERK1/2 activation, cyclin D1 expression, and also decreased p27(Kip1) expression in normal uveal melanocytes. Moreover, that the depletion of RASSF1A induced senescence-associated β-galactosidase activity and increased p21(Cip1) expression suggests that RASSF1A plays a role in the escape of cellular senescence in normal uveal melanocytes. Interestingly, we found that RASSF1A was epigenetically inactivated in long-term culture of uveal melanocytes. Taken together, these data show that depletion of RASSF1A could be an early event observed during senescence of normal uveal melanocytes and that additional alterations are acquired during malignant transformation to uveal melanoma.
authors.affiliation: Service Universitaire d'Ophtalmologie, Universitede Caen Basse-Normandie, Universite Paris-Descartes, CEA, CNRS, Centre CYCERON, Bd Henri Becquerel, BP5229, 14074 Caen cedex, France. calipel@cyceron.fr
authors.forename: Armelle
authors.initials: A
authors.lastname: Calipel
authors.forename: Véronique
authors.initials: V
authors.lastname: Abonnet
authors.forename: Olivier
authors.initials: O
authors.lastname: Nicole
authors.forename: Frédéric
authors.initials: F
authors.lastname: Mascarelli
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Coupland
authors.forename: Bertil
authors.initials: B
authors.lastname: Damato
authors.forename: Frédéric
authors.initials: F
authors.lastname: Mouriaux
mesh_terms: D045744:Cell Line, Tumor; D049109:Cell Proliferation; D016922:Cellular Senescence; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D019656:Loss of Heterozygosity; D020935:MAP Kinase Signaling System; D008544:Melanocytes / Q000378:metabolism*; D008545:Melanoma / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism*; D014604:Uveal Neoplasms / Q000235:genetics* / Q000378:metabolism*; D000098943:Uveal Melanoma
chemical_list: C493956:CDKN1A protein, human; C436291:CDKN1B protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C411762:RASSF1 protein, human; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27