title: The role of p38 in UVA-induced cyclooxygenase-2 expression in the human keratinocyte cell line, HaCaT.
abstract: We examined the expression of cycloxygenase-2, the rate-limiting enzyme in the production of prostaglandins, in the UVA-irradiated human keratinocyte cell line, HaCaT. UVA induced a dose-dependent increase in COX-2 at the protein level at 2 and 4 h post-irradiation and at the mRNA level at 1 and 2 h post-irradiation. Experiments using semi-quantitative RT-PCR demonstrate that UVA increased the half-life of the COX-2 message by more than fourfold in the presence of Actinomycin D (with a half life between 4 and 8 h post-irradiation), suggesting that UVA induction of COX-2 is post-transcriptionally regulated. Through the use of the specific p38 inhibitor, SB202190, increases in COX-2 message and protein levels were abrogated in UVA-irradiated cells. In UVA-irradiated cells treated with SB202190, the half-life of the COX-2 message was decreased to basal levels (between 1 and 2 h post-irradiation), indicating that p38 was responsible for the stabilization of the message. Luciferase activity was increased in UVA-irradiated cells transfected with reporter constructs containing the 3' UTR of COX-2, a region containing AU-rich elements (AREs). These regulatory sequences of AUUUA have been proposed as one mechanism of post-transcriptional regulation. Increases observed in luciferase activity could be decreased using a p38 dominant-negative construct. We report for the first that UVA can induce COX-2 expression in the human keratinocyte cell line, HaCaT. Additionally, p38 appears to play a critical role in the UVA-induced expression of COX-2 in these keratinocytes and may serve as a potential drug target in the chemoprevention of skin cancer.
authors.affiliation: Department of Radiation Oncology, Arizona Cancer Center, The University of Arizona, 1515 North Campbell Avenue, Tucson 85724, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Bachelor
authors.forename: Amy L
authors.initials: AL
authors.lastname: Silvers
authors.forename: Gim T
authors.initials: GT
authors.lastname: Bowden
mesh_terms: D020413:3' Untranslated Regions / Q000502:physiology; D002460:Cell Line; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000627:therapeutic use; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007527:Isoenzymes / Q000096:biosynthesis* / Q000235:genetics; D015603:Keratinocytes / Q000201:enzymology / Q000528:radiation effects*; D008565:Membrane Proteins; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis* / Q000235:genetics; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D012878:Skin Neoplasms / Q000209:etiology / Q000517:prevention & control; D014466:Ultraviolet Rays; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D020413:3' Untranslated Regions; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D007093:Imidazoles; D007527:Isoenzymes; D008565:Membrane Proteins; D011725:Pyridines; D012333:RNA, Messenger; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C090942:4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)imidazole