title: Inhibition of interferon-gamma signaling by a mercurio-substituted dihydropsoralen in murine keratinocytes.
abstract: Psoralens and ultraviolet light A (PUVA) are used in the treatment of a variety of epidermal proliferative and inflammatory disorders. These compounds are known to intercalate and photo crosslink DNA. Specific receptor proteins for psoralens have also been identified. We describe a novel activity of a thiol reactive derivative, iodomercurio-4',5'-dihydrotrimethylpsoralen (iodomercurio-H2TMP) in keratinocytes. Without UVA, this psoralen was found to be an effective inhibitor of interferon-gamma (IFN-gamma)-signaling as measured by induction of nitric oxide biosynthesis (IC50 = 0.8 microM). This activity was increased (IC50 = 0.1 microM) when the cells were depleted of intracellular glutathione (GSH) with buthionine sulfoximine. In keratinocytes, IFN-gamma stimulates expression of inducible nitric oxide synthase (NOS2). Although iodomercurio-H2TMP did not alter NOS2 enzymatic activity, it blocked IFN-gamma-induced expression of NOS2 mRNA and protein, an effect that was enhanced in GSH-depleted cells. Iodomercurio-H2TMP was found to readily inhibit IFN-gamma signaling in transient transfection assays using NOS2 promoter/luciferase reporter constructs. NOS2 gene expression is known to require a variety of transcription factors including STAT-1, NF-kappaB and AP-1. Using mobility shift assays the psoralen, at concentrations that inhibit nitric oxide biosynthesis, had no effect on the DNA binding activity of STAT-1 or NF-kappaB. However, iodomercurio-H2TMP was found to suppress AP-1. These data indicate that iodomercurio-H2TMP acts at sulfhydryl-sensitive sites to inhibit NOS2. Moreover, this is dependent on early events in the IFN-gamma signal transduction pathway. Inhibition of AP-1 suggests that the psoralen functions by interfering with an important transcription factor that regulates expression of NOS2 in keratinocytes.
authors.affiliation: Department of Chemistry, Lehigh University, Bethlehem, PA 18015, USA.
authors.forename: Christine A
authors.initials: CA
authors.lastname: Martey
authors.forename: Anna M
authors.initials: AM
authors.lastname: Vetrano
authors.forename: Marilyn S
authors.initials: MS
authors.lastname: Whittemore
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Mariano
authors.forename: Diane E
authors.initials: DE
authors.lastname: Heck
authors.forename: Debra L
authors.initials: DL
authors.lastname: Laskin
authors.forename: Ned D
authors.initials: ND
authors.lastname: Heindel
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Laskin
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D011564:Furocoumarins / Q000494:pharmacology*; D007371:Interferon-gamma / Q000037:antagonists & inhibitors*; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors; D009941:Organomercury Compounds / Q000494:pharmacology*; D011701:PUVA Therapy; D050794:STAT1 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors; D014307:Trioxsalen / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D011564:Furocoumarins; D016328:NF-kappa B; D009941:Organomercury Compounds; D050794:STAT1 Transcription Factor; D018808:Transcription Factor AP-1; C506539:iodomercurio-4',5'-dihydrotrimethylpsoralen; D007371:Interferon-gamma; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D014307:Trioxsalen