title: Receptor-interacting protein kinase 4 and interferon regulatory factor 6 function as a signaling axis to regulate keratinocyte differentiation.
abstract: Receptor-interacting protein kinase 4 (RIPK4) and interferon regulatory factor 6 (IRF6) are critical regulators of keratinocyte differentiation, and their mutation causes the related developmental epidermal disorders Bartsocas-Papas syndrome and popliteal pterygium syndrome, respectively. However, the signaling pathways in which RIPK4 and IRF6 operate to regulate keratinocyte differentiation are poorly defined. Here we identify and mechanistically define a direct functional relationship between RIPK4 and IRF6. Gene promoter reporter and in vitro kinase assays, coimmunoprecipitation experiments, and confocal microscopy demonstrated that RIPK4 directly regulates IRF6 trans-activator activity and nuclear translocation. Gene knockdown and overexpression studies indicated that the RIPK4-IRF6 signaling axis controls the expression of key transcriptional regulators of keratinocyte differentiation, including Grainyhead-like 3 and OVO-like 1. Additionally, we demonstrate that the p.Ile121Asn missense mutation in RIPK4, which has been identified recently in Bartsocas-Papas syndrome, inhibits its kinase activity, thereby preventing RIPK4-mediated IRF6 activation and nuclear translocation. We show, through mutagenesis-based experiments, that Ser-413 and Ser-424 in IRF6 are important for its activation by RIPK4. RIPK4 is also important for the regulation of IRF6 expression by the protein kinase C pathway. Therefore, our findings not only provide important mechanistic insights into the regulation of keratinocyte differentiation by RIPK4 and IRF6, but they also suggest one mechanism by which mutations in RIPK4 may cause epidermal disorders (e.g. Bartsocas-Papas syndrome), namely by the impaired activation of IRF6 by RIPK4.
authors.affiliation: From the Oral Health Cooperative Research Centre, Melbourne Dental School, and Bio21 Institute, and Department of Medicine, Royal Melbourne Hospital, The University of Melbourne, Melbourne, Victoria 3010, Australia and.
authors.forename: Mei Qi
authors.initials: MQ
authors.lastname: Kwa
authors.affiliation: From the Oral Health Cooperative Research Centre, Melbourne Dental School, and Bio21 Institute, and Department of Medicine, Royal Melbourne Hospital, The University of Melbourne, Melbourne, Victoria 3010, Australia and.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Huynh
authors.affiliation: From the Oral Health Cooperative Research Centre, Melbourne Dental School, and Bio21 Institute, and.
authors.forename: Jiamin
authors.initials: J
authors.lastname: Aw
authors.affiliation: From the Oral Health Cooperative Research Centre, Melbourne Dental School, and Bio21 Institute, and.
authors.forename: Lianyi
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Department of Medicine, Royal Melbourne Hospital, The University of Melbourne, Melbourne, Victoria 3010, Australia and.
authors.forename: Thao
authors.initials: T
authors.lastname: Nguyen
authors.affiliation: From the Oral Health Cooperative Research Centre, Melbourne Dental School, and Bio21 Institute, and.
authors.forename: Eric C
authors.initials: EC
authors.lastname: Reynolds
authors.affiliation: the Institute for Molecular Bioscience and Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Sweet
authors.affiliation: Department of Medicine, Royal Melbourne Hospital, The University of Melbourne, Melbourne, Victoria 3010, Australia and.
authors.forename: John A
authors.initials: JA
authors.lastname: Hamilton
authors.affiliation: From the Oral Health Cooperative Research Centre, Melbourne Dental School, and Bio21 Institute, and Department of Medicine, Royal Melbourne Hospital, The University of Melbourne, Melbourne, Victoria 3010, Australia and glenms@unimelb.edu.au.
authors.forename: Glen M
authors.initials: GM
authors.lastname: Scholz
mesh_terms: D002454:Cell Differentiation; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D004817:Epidermis / Q000378:metabolism; D020868:Gene Silencing; D005822:Genetic Vectors; D005982:Glutathione Transferase / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D050835:Interferon Regulatory Factors / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology*; D020125:Mutation, Missense; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; C473143:GRHL3 protein, human; C109803:IRF6 protein, human; D050835:Interferon Regulatory Factors; C490319:OVOL1 protein, human; D014157:Transcription Factors; D012694:Serine; D005982:Glutathione Transferase; C417187:RIPK4 protein, human; D017346:Protein Serine-Threonine Kinases; D011493:Protein Kinase C
keywords: Differentiation; Grainyhead-like 3; Interferon Regulatory Factor 6; Keratinocyte; OVO-like 1; Popliteal Pterygium; Protein Kinase C (PKC); Protein Phosphorylation; Receptor-interacting Protein Kinase 4; Transcription Factor