title: Endothelial nitric oxide synthase uncoupling as a key mediator of melanocyte malignant transformation associated with sustained stress conditions.
abstract: Melanoma cell lines and cells corresponding to premalignant melanocytes were established by our group after subjecting a nontumorigenic murine melanocyte lineage, melan-a, to sequential cycles of anchorage blockade. Previous results showed that in melan-a cells the superoxide level increases after such procedure. Superoxide production during melanocyte de-adhesion was inhibited by L-sepiapterin, the precursor of eNOS cofactor BH4, and increased by the inhibitor of BH4 synthesis, DAHP, hence indicating a partial uncoupling state of eNOS. The eNOS uncoupling seems to be maintained in cells derived from melan-a, because they present decreased nitric oxide and increased superoxide levels. The inhibition of superoxide production in Tm5 melanoma cells with L-sepiapterin reinforces their eNOS-uncoupled state. The maintenance of oxidative stress seems to be important in melanoma apoptosis resistance because Mn(III)TBAP, a superoxide scavenger, or L-sepiapterin renders Tm5 cells more sensitive to anoikis and chemotherapy. More importantly, eNOS uncoupling seems to play a pivotal role in melanocyte malignant transformation induced by sustained anchorage impediment, because no malignant transformation was observed when L-NAME-treated melanocytes were subjected to sequential cycles of de-adhesion. Our results show that uncoupled eNOS contributes to superoxide production during melanocyte anchorage impediment, contributing to anoikis resistance and malignant transformation.
authors.affiliation: Disciplina de Imunologia, Universidade Federal de São Paulo, 04023-900 São Paulo, SP, Brazil.
authors.forename: Fabiana H M
authors.initials: FH
authors.lastname: Melo
authors.forename: Fernanda
authors.initials: F
authors.lastname: Molognoni
authors.forename: Alice S
authors.initials: AS
authors.lastname: Morais
authors.forename: Mariana
authors.initials: M
authors.lastname: Toricelli
authors.forename: Margareth G
authors.initials: MG
authors.lastname: Mouro
authors.forename: Elisa M S
authors.initials: EM
authors.lastname: Higa
authors.forename: José D
authors.initials: JD
authors.lastname: Lopes
authors.forename: Miriam G
authors.initials: MG
authors.lastname: Jasiulionis
mesh_terms: D000818:Animals; D008544:Melanocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects; D013481:Superoxides / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D013481:Superoxides; D052250:Nitric Oxide Synthase Type III; D019331:NG-Nitroarginine Methyl Ester