title: Down-regulation of Rap1GAP via promoter hypermethylation promotes melanoma cell proliferation, survival, and migration.
abstract: Melanoma is the most serious, highly aggressive form of skin cancer with recent dramatic increases in incidence. Current therapies are relatively ineffective, highlighting the need for a better understanding of the molecular mechanisms contributing to the disease. We have previously shown that activation of Rap1 promotes melanoma cell proliferation and migration through the mitogen-activated protein kinase pathway and integrin activation. In the present study, we show that expression of Rap1GAP, a specific negative regulator of Rap1, is decreased in human melanoma tumors and cell lines. Overexpression of Rap1GAP in melanoma cells blocks Rap1 activation and extracellular signal-regulated kinase (ERK) phosphorylation and inhibits melanoma cell proliferation and survival. In addition, overexpression of Rap1GAP also inhibits focal adhesion formation and decreases melanoma cell migration. Rap1GAP down-regulation is due to its promoter methylation, a mechanism of gene silencing in tumors. Furthermore, treatment of melanoma cells with the demethylating agent 5-aza-2'-deoxycytidine reinduces Rap1GAP expression, followed by decreased Rap1 activity, ERK phosphorylation, and cell proliferation and survival-changes that are significantly blunted in cells transfected by small interfering RNA-mediated Rap1GAP knockdown. Taken together, our findings indicate that down-regulation of Rap1GAP via promoter hypermethylation promotes melanoma cell proliferation, survival, and migration.
authors.affiliation: Department of Internal Medicine, Division of Dermatology and Hematology, Washington University School of Medicine, St Louis, Missouri 63110, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Zheng
authors.forename: Ling
authors.initials: L
authors.lastname: Gao
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Feng
authors.forename: Liya
authors.initials: L
authors.lastname: Yuan
authors.forename: Haibo
authors.initials: H
authors.lastname: Zhao
authors.forename: Lynn A
authors.initials: LA
authors.lastname: Cornelius
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D048708:Cell Growth Processes / Q000235:genetics; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics; D002470:Cell Survival / Q000235:genetics; D019175:DNA Methylation; D000077209:Decitabine; D015536:Down-Regulation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D022001:Focal Adhesions / Q000235:genetics / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000096:biosynthesis* / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008545:Melanoma / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D014162:Transfection; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
chemical_list: D000964:Antimetabolites, Antineoplastic; D020690:GTPase-Activating Proteins; C484658:RAP1GAP protein, human; D000077209:Decitabine; D048049:Extracellular Signal-Regulated MAP Kinases; D020827:rap1 GTP-Binding Proteins; D001374:Azacitidine