Altered keratinocyte differentiation and a defective epidermal barrier are prominent contributors to multiple skin diseases including ichthyoses, inflammatory skin diseases, skin cancer and wound healing defects. While the cell biology of epidermal differentiation is well characterized, less is known about the gene-regulatory mechanisms, including epigenetic factors and higher order chromatin structure, governing the coordinated expression of differentiation genes. Our long term goal has been to understand transcriptional regulation of epidermal differentiation in health and disease. As part of this effot we discovered the Grainyhead transcription factor Get1/Grhl3, a key regulator with functions in epidermal differentiation and wound healing that are conserved from flies to mammals. In this application we propose to pursue the hypotheses that in adult skin, Grhl3's main role is to participate in the repair of epidermal injury;that it directly targets different batteries of gene to carry out its distinct roles in keratinocyte differentiation, migration and barrier repair;and tha it acts by recruiting histone methyltransferases of the Trithorax (trxG) group to target genes. We propose three Specific Aims: 1) To define Grhl3 gene-regulatory mechanisms during keratinocyte differentiation and migration. We found that Grhl3 knockdown affects different gene batteries in human keratinocyte differentiation and migration, leading us to hypothesize that differential recruitment of Grhl3 and/or enhancer-promoter interactions underlies Grhl3's condition-selective activity. In this aim we use advanced genomic techniques and bioinformatics to understand how Grhl3 regulates selective genes under the two functional states. 2) To understand the role of trxG in Grhl3-mediated gene activation and epidermal differentiation. We found that Grhl3 interacts with Wdr5, a core component of the trxG group, leading us to hypothesize that Grhl3 activates target genes by recruiting histone methyltransferases of the trxG complex.
This aim uses a combination of molecular biology and functional approaches to address the mechanisms whereby Grhl3 activates transcription after it has been recruited into permissive chromatin at appropriate target genes. 3) To understand the role of Grhl3 in adult epidermal injury repair. We found that while Grhl3 is largely dispensable for adult epidermal homeostasis, it is critical for the repair of barrier-disrupting injury, leading us to hypothesize hat, as in embryonic epidermal development, there is a critical need for Grhl3 under conditions of injury.
This aim uses mouse models to explore Grhl3's barrier repair function and tests whether the Grhl3 regulatory network is defective in psoriasis. This work is highly significant because it reveals fundamental mechanisms in gene regulation as a cell switches its functional state. Also, the prominent role of Grhl3 in adult epidermal barrier repair has clear significance for many human skin diseases;the findings may lead to new ideas about therapeutic approaches for diseases with defective keratinocyte differentiation and/or aberrant barrier function. The application is innovative because we use cutting edge technologies to discover new transcriptional mechanisms of epidermal differentiation, migration, and barrier repair.

Public Health Relevance

As cells of the epidermis move towards the surface, they stop proliferating and specialize to carry out their function of forming a barrier protecting the organism;this process requires coordinated regulation of multiple genes. This application focuses on this gene-regulatory mechanism and how it contributes and responds to skin diseases such as impaired wound healing, skin cancer, inflammatory skin diseases and barrier disruption diseases.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Research Project (R01)
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Special Emphasis Panel (ZRG1-MOSS-T (02))
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Baker, Carl
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University of California Irvine
Internal Medicine/Medicine
Schools of Medicine
United States
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Plikus, Maksim V; Andersen, Bogi (2018) Skin as a window to body-clock time. Proc Natl Acad Sci U S A 115:12095-12097
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