title: The effect of LXR activators on AP-1 proteins in keratinocytes.
abstract: Oxysterols, via activation of liver X receptor (LXR), regulate keratinocyte differentiation by stimulating transglutaminase cross-linking of several constituent proteins leading to the formation of the cornified envelope. We previously reported that oxysterols increase the expression of one of these cross-linked proteins, involucrin, and that this effect can be abolished by mutations of the distal activator protein (AP)-1 response element in the involucrin promoter. Furthermore, oxysterols increase AP-1 binding in an electrophoretic gel mobility shift assay and increase the expression of an AP-1 reporter. In this study, we describe the individual components of the AP-1 complex that are involved in the oxysterol-mediated AP-1 activation and stimulation of keratinocyte differentiation. We identified Fra-1 within the AP-1 DNA binding complex by supershift analysis of nuclear extracts from oxysterol-treated, cultured keratinocytes and confirmed that oxysterol treatment increased the levels of Fra-1 by western blot analysis. Additionally, on Western and Northern analysis, oxysterol treatment increased two other AP-1 proteins, Jun-D and c-Fos, whereas Fra-2, Jun-B, and c-Jun were not changed. Similar alterations in AP-1 proteins occurred when 25-OH-cholesterol or non-steroidal LXR agonists (GW3965, TO-901317) were used. These results indicate that oxysterols induce specific AP-1 proteins, thereby activating involucrin, one of the genes required for epidermal differentiation.
authors.affiliation: Department of Medicine, University of California, San Francisco, California, USA.
authors.forename: Matthias
authors.initials: M
authors.lastname: Schmuth
authors.forename: Peter M
authors.initials: PM
authors.lastname: Elias
authors.forename: Karen
authors.initials: K
authors.lastname: Hanley
authors.forename: Peggy
authors.initials: P
authors.lastname: Lau
authors.forename: A
authors.initials: A
authors.lastname: Moser
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Willson
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Bikle
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Feingold
mesh_terms: D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D000078404:Epidermal Cells; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D006888:Hydroxycholesterols / Q000494:pharmacology*; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D011498:Protein Precursors / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists* / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D000099169:Fos-Related Antigen 1
chemical_list: D004268:DNA-Binding Proteins; D006888:Hydroxycholesterols; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D011498:Protein Precursors; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D018808:Transcription Factor AP-1; D000099169:Fos-Related Antigen 1; C003585:22-hydroxycholesterol; C032253:involucrin; C007997:25-hydroxycholesterol