title: Activation of c-Raf kinase by ultraviolet light. Regulation by retinoids.
abstract: The present study highlights retinoids as modulators of c-Raf kinase activation by UV light. Whereas a number of retinoids, including retinol, 14-hydroxyretroretinol, anhydroretinol (AR), and retinoic acid bound the c-Raf cysteine-rich domain (CRD) with equal affinity in vitro as well as in vivo, they displayed different, even opposing, effects on UV-mediated kinase activation; retinol and 14-hydroxyretroretinol augmented responses, whereas retinoic acid and AR were inhibitory. Oxidation of thiol groups of cysteines by reactive oxygen, generated during UV irradiation, was the primary event in c-Raf activation, causing the release of zinc ions and, by inference, a change in CRD structure. Retinoids modulated these oxidation events directly: retinol enhanced, whereas AR suppressed, zinc release, precisely mirroring the retinoid effects on c-Raf kinase activation. Oxidation of c-Raf was not sufficient for kinase activation, productive interaction with Ras being mandatory. Further, canonical tyrosine phosphorylation and the action of phosphatase were essential for optimal c-Raf kinase competence. Thus, retinoids bound c-Raf with high affinity, priming the molecule for UV/reactive oxygen species-mediated changes of the CRD that set off GTP-Ras interaction and, in context with an appropriate phosphorylation pattern, lead to full phosphotransferase capacity.
authors.affiliation: Immunology Program, Memorial Sloan-Kettering Cancer Center, New York 10021, USA.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Hoyos
authors.forename: Asiya
authors.initials: A
authors.lastname: Imam
authors.forename: Irina
authors.initials: I
authors.lastname: Korichneva
authors.forename: Ester
authors.initials: E
authors.lastname: Levi
authors.forename: Ramon
authors.initials: R
authors.lastname: Chua
authors.forename: Ulrich
authors.initials: U
authors.lastname: Hammerling
mesh_terms: D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D010084:Oxidation-Reduction; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D017382:Reactive Oxygen Species; D012176:Retinoids / Q000494:pharmacology*; D014466:Ultraviolet Rays; D015032:Zinc / Q000378:metabolism; D018631:ras Proteins / Q000737:chemistry
chemical_list: D017382:Reactive Oxygen Species; D012176:Retinoids; D019908:Proto-Oncogene Proteins c-raf; D018631:ras Proteins; D015032:Zinc