title: Melanoma coordinates general and cell-specific mechanisms to promote methotrexate resistance.
abstract: Melanoma, the most aggressive form of skin cancer, is notoriously resistant to all current modalities of cancer therapy, including to the drug methotrexate. Melanosomal sequestration and cellular exportation of methotrexate have been proposed to be important melanoma-specific mechanisms that contribute to the resistance of melanoma to methotrexate. In addition, other mechanisms of resistance that are present in most epithelial cancer cells are also operative in melanoma. This report elucidates how melanoma orchestrates these mechanisms to become extremely resistant to methotrexate, where both E2F1 and checkpoint kinase 1 (Chk1), two molecules with dual roles in survival/apoptosis, play prominent roles. The results indicated that MTX induced the depletion of dihydrofolate in melanoma cells, which stimulated the transcriptional activity of E2F1. The elevate expression of dihydrofolate reductase and thymidylate synthase, two E2F1-target genes involved in folate metabolism and required for G(1) progression, favored dTTP accumulation, which promoted DNA single strand breaks and the subsequent activation of Chk1. Under these conditions, melanoma cells are protected from apoptosis by arresting their cell cycle in S phase. Excess of dTTP could also inhibit E2F1-mediated apoptosis in melanoma cells.
authors.affiliation: Department of Biochemistry and Molecular Biology A, School of Biology, University of Murcia, Murcia, Spain.
authors.forename: Magalí
authors.initials: M
authors.lastname: Sáez-Ayala
authors.forename: María Piedad
authors.initials: MP
authors.lastname: Fernández-Pérez
authors.forename: María F
authors.initials: MF
authors.lastname: Montenegro
authors.forename: Luis
authors.initials: L
authors.lastname: Sánchez-del-Campo
authors.forename: Soledad
authors.initials: S
authors.lastname: Chazarra
authors.forename: Antonio
authors.initials: A
authors.lastname: Piñero-Madrona
authors.forename: Juan
authors.initials: J
authors.lastname: Cabezas-Herrera
authors.forename: José Neptuno
authors.initials: JN
authors.lastname: Rodríguez-López
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects*; D000071877:Checkpoint Kinase 1; D019008:Drug Resistance, Neoplasm; D050687:E2F1 Transcription Factor / Q000737:chemistry / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005492:Folic Acid / Q000378:metabolism; D006801:Humans; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology; D008727:Methotrexate / Q000494:pharmacology*; D051379:Mice; D008969:Molecular Sequence Data; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D059807:S Phase Cell Cycle Checkpoints; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D013940:Thymidylate Synthase / Q000235:genetics / Q000378:metabolism; D013942:Thymine Nucleotides / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D000964:Antimetabolites, Antineoplastic; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D013942:Thymine Nucleotides; D005492:Folic Acid; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse; C024157:thymidine 5'-triphosphate; D008727:Methotrexate