title: The guanine nucleotide exchange factor CNrasGEF regulates melanogenesis and cell survival in melanoma cells.
abstract: cAMP-dependent Ras activation has been demonstrated in numerous cell types, particularly of neuronal (including melanoma cells) and endocrine origin, but the Ras activator involved has not been identified. In B16 melanoma cells, cAMP activates the Ras/Erk pathway, leading initially to stimulation but subsequently to long term (>24-h) inhibition of melanogenesis (dendrite extension and melanin production). Here we identify CNrasGEF as the Ras guanine nucleotide exchange factor (GEF) involved. We demonstrate that CNrasGEF is expressed endogenously in B16 melanoma cells and that cAMP-mediated activation of Ras and Erk1/2 in these cells can be augmented by CNrasGEF overexpression and reduced by its knockdown by RNA interference. Moreover, we show that CNrasGEF participates in the regulation of melanogenesis. Knockdown of CNrasGEF leads to increased dendrite extension and melanin production observed approximately 50 h after forskolin/isobutylmethylxanthine treatment, suggesting that CNrasGEF inhibits melanogenesis in the long term. Independently, we find that overexpression of CNrasGEF leads to apoptosis, whereas its knockdown by RNAi enhances cell proliferation, independent of cAMP. Collectively, these results suggest that CNrasGEF regulates melanogenesis but that it also has a distinct role in regulating cell proliferation/apoptosis.
authors.affiliation: Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Amsen
authors.forename: Nam
authors.initials: N
authors.lastname: Pham
authors.forename: Youngshil
authors.initials: Y
authors.lastname: Pak
authors.forename: Daniela
authors.initials: D
authors.lastname: Rotin
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D045744:Cell Line, Tumor; D048430:Cell Shape; D002470:Cell Survival / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism; D003712:Dendrites / Q000502:physiology; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics* / Q000378:metabolism*; D008543:Melanins / Q000378:metabolism*; D008544:Melanocytes / Q000166:cytology / Q000502:physiology; D008545:Melanoma / Q000378:metabolism* / Q000503:physiopathology; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
chemical_list: C508086:CNrasGEF protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D008543:Melanins; D000242:Cyclic AMP; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D018631:ras Proteins