title: Ursolic acid differentially modulates apoptosis in skin melanoma and retinal pigment epithelial cells exposed to UV-VIS broadband radiation.
abstract: The signaling pathways via mTOR (mammalian target of rapamycin) and AMPK (AMP-activated protein kinase) play key roles in transcription, translation and carcinogenesis, and may be activated by light exposure. These pathways can be modulated by naturally occurring compounds, such as the triterpenoid, ursolic acid (UA). Previously, the transcription factors p53 and NF-κB, which transactivate mitochondrial apoptosis-related genes, were shown to be differentially modulated by UA. UA-modulated apoptosis, following exposure to UV-VIS radiation (ultraviolet to visible light broadband radiation, hereafter abbreviated to UVR), is observed to correspond to differential levels of oxidative stress in retinal pigment epithelial (RPE) and skin melanoma (SM) cells. The cellular response to this phytochemical was characterized using western blot, flow cytometry, microscopy with reactive oxidative species probes MitoTracker and dihydroethidium, and membrane permeability assay. UA pretreatment potentiated cell cycle arrest and UVR-induced apoptosis selectively in SM cells while reducing photo-oxidative stress in the DNA of RPE cells presumably by antioxidant activity of UA. Mechanistically, the nuclear transportation of p65 and p53 was reduced by UA administration prior to UVR exposure while the levels of p65 and p53 nuclear transportation in SM cells were sustained at a substantially higher level. Finally, the mitochondrial functional assay showed that UVR induced the collapse of the mitochondrial membrane potential, and this effect was exacerbated by rapamycin or UA pretreatment in SM preferentially. These results were consistent with reduced proliferation observed in the clonogenic assay, indicating that UA treatment enhanced the phototoxicity of UVR, by modulating the activation of p53 and NF-κB and initiating a mitogenic response to optical radiation that triggered mitochondria-dependent apoptosis, particularly in skin melanoma cells. The study indicates that this compound has multiple actions with the potential for protecting normal cells while sensitizing skin melanoma cells to UV irradiation.
authors.affiliation: Department of Radiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.
authors.forename: Yuan-Hao
authors.initials: YH
authors.lastname: Lee
authors.forename: Exing
authors.initials: E
authors.lastname: Wang
authors.forename: Neeru
authors.initials: N
authors.lastname: Kumar
authors.forename: Randolph D
authors.initials: RD
authors.lastname: Glickman
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology* / Q000633:toxicity; D000975:Antioxidants / Q000494:pharmacology* / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D059447:Cell Cycle Checkpoints; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D008027:Light / Q000009:adverse effects*; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology; D008928:Mitochondria / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects; D020123:Sirolimus / Q000494:pharmacology; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology; D051996:Transcription Factor RelA / Q000378:metabolism; D014315:Triterpenes / Q000494:pharmacology* / Q000633:toxicity; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D014466:Ultraviolet Rays / Q000009:adverse effects; D000097245:Ursolic Acid; D000096142:Cutaneous Malignant Melanoma
chemical_list: D000903:Antibiotics, Antineoplastic; D000972:Antineoplastic Agents, Phytogenic; D000975:Antioxidants; D017382:Reactive Oxygen Species; D020123:Sirolimus; D051996:Transcription Factor RelA; D014315:Triterpenes; D016159:Tumor Suppressor Protein p53; D000097245:Ursolic Acid