title: Interleukin-4 Downregulation of Involucrin Expression in Human Epidermal Keratinocytes Involves Stat6 Sequestration of the Coactivator CREB-Binding Protein.
abstract: Skin barrier defects play an important role in atopic dermatitis (AD). Involucrin, an important barrier protein suppressed in human AD, is downregulated by interleukin-4 (IL-4). However, the molecular mechanism for IL-4 downregulation of involucrin has not been delineated, and especially how Stat6, a transcriptional activator, represses involucrin expression is unknown. Since Stats usually recruit p300/CBP in the general transcription machinery of their target genes and involucrin expression also involves p300/CBP, we hypothesize that Stat6 activated by IL-4 may sequestrate p300/CBP from the involucrin transcription complex, thus suppressing involucrin expression in keratinocytes. Using IL-4 transgenic mice, an AD mouse model, we find that involucrin expression is similarly downregulated as in human AD. In HaCat cells, the Jak inhibitor and dominant negative studies indicate that the Jaks-Stat6 pathway is involved in IL-4 downregulation of involucrin. Next, we transfected HaCat cells with an involucrin promoter-luciferase construct and then treated them with IL-4. IL-4 greatly suppresses the promoter activity, which is totally abolished by cotransfecting the CREB-binding protein (CBP) expression vector, indicating that IL-4 cannot downregulate involucrin in the presence of excess CBP. Finally, chromatin immunoprecipitation assay demonstrates that IL-4 decreases CBP binding to the involucrin transcription complex. For the first time, we defined a molecular mechanism for IL-4 downregulation of involucrin in keratinocytes, which may play an important role in the pathogenesis of AD.
authors.affiliation: 1 Department of Dermatology, University of Illinois at Chicago , Chicago, Illinois.
authors.forename: Lei
authors.initials: L
authors.lastname: Bao
authors.affiliation: 1 Department of Dermatology, University of Illinois at Chicago , Chicago, Illinois.
authors.forename: Jaime B
authors.initials: JB
authors.lastname: Alexander
authors.affiliation: 1 Department of Dermatology, University of Illinois at Chicago , Chicago, Illinois.
authors.forename: Huayi
authors.initials: H
authors.lastname: Zhang
authors.affiliation: 1 Department of Dermatology, University of Illinois at Chicago , Chicago, Illinois.
authors.forename: Kui
authors.initials: K
authors.lastname: Shen
authors.affiliation: 1 Department of Dermatology, University of Illinois at Chicago , Chicago, Illinois.|2 Department of Microbiology & Immunology, University of Illinois at Chicago , Chicago, Illinois.|3 Medical Service, Jesse Brown VA Med Center , Chicago, Illinois.
authors.forename: Lawrence S
authors.initials: LS
authors.lastname: Chan
mesh_terms: D000818:Animals; D050882:CREB-Binding Protein / Q000378:metabolism*; D002460:Cell Line; D003876:Dermatitis, Atopic / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D020405:Dermis / Q000378:metabolism*; D004195:Disease Models, Animal; D015536:Down-Regulation; D005786:Gene Expression Regulation; D006801:Humans; D015847:Interleukin-4 / Q000235:genetics / Q000378:metabolism*; D015603:Keratinocytes / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D046912:Multiprotein Complexes / Q000378:metabolism; D011485:Protein Binding; D011498:Protein Precursors / Q000235:genetics* / Q000378:metabolism; D050800:STAT6 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D046912:Multiprotein Complexes; D011498:Protein Precursors; D050800:STAT6 Transcription Factor; D015847:Interleukin-4; C032253:involucrin; D050882:CREB-Binding Protein